OXYACETYLENE WELDING
AND CUTTING
ELECTRIC AND THERMIT WELDING
TvlANUY
Oxy-Acetylene Welding and Cutting
Electric, Forge and Thermit Welding
Together with Related Methods and Materials Used in Metal Working
And
The Oxygen Process for Removal of Carbon
By
HAROLD P. MANLY
Chief Engineer The American Bureau of Engineering
CHICAGO
FREDERICK J . DRAKE & CO. Publishers
Copyright 1916
By Frederick J. Drake & Co.
Chicago
PREFACE
In the preparation of this work, the object has been to cover not only the several processes of welding, but also those other processes which are so closely allied in method and results as to make them, a part of the whole subject of joining metal to metal with the aid of heat.
The workman who wishes to handle his trade from start to finish finds that it is necessary to become familiar with certain other operations which precede or follow the actual joining of the metal parts, the purpose of these operations being to add or retain certain desirable qualities in the materials being han- dled. For this reason the following subjects have been included : Annealing, tempering, hardening, heat treatment and the restoration of steel.
In order that the user may understand the under- lying principles and the materials employed in this work, much practical information is given on the uses and characteristics of the various metals ; on the production, handling and use of the gases and other materials which are a part of the equipment ; and on the tools and accessories for the production and han- dling of these materials.
An examination will show that the greatest useful- ness of this book lies in the fact that all necessary information and data has been included in one vol- ume, making it possible for the workman to use one source for securing a knowledge of both principle
343651
6 < PREFACE
and practice, preparation and finishing of the work, and both large and small repair work as well as manu- facturing methods used in metal working.
An effort has been made to eliminate all matter which is not of direct usefulness in practical work, while including all" that those engaged in this trade find necessary. To this end, the descriptions have been limited to those methods and accessories which are found in actual use today. For the. same reason, the work includes the application of the rules laid down by the insurance underwriters which govern this work as well as instructions for the proper care and handling of the generators, torches and materials found in the shop.
Special attention has been given to definite direc- tions for handling the different metals and alloys which must be handled. The instructions have been arranged to form rules which are placed in the order of their use during the work described and the work has been subdivided in such a wray that it will be found possible to secure information on any one point desired without the necessity of spending time in other fields.
The facts which the expert welder and metal- worker finds it most necessary to have readily avail- able have been secured and prepared especially for this work, and those of most general use have been combined with the chapter on welding practice to which they apply.
The size of this volume has been kept as small as possible, but an examination of the alphabetical index will show that the range of subjects and details cov- ered is complete in all respects. This has been accom- plished through careful classification of the contents
•PREFACE 7
and the elimination of all repetition and all theoret- ical, historical and similar matter that is not abso- lutely necessary.
Free use has been made of the information given by those manufacturers who are recognized as the leaders in their respective fields, thus insuring that the work is thoroughly practical and that it repre- sents present day methods and practice.
THE AUTHOR.
CONTENTS
CHAPTER I
PAGE
METALS AND ALLOYS — HEAT TREATMENT: — The Use and Characteristics of the Industrial Alloys and Metal Ele- ments— Annealing, Hardening, Tempering and Case Hard- ening of Steel 11
CHAPTER II
WELDING MATERIALS : — Production, Handling and Use of the Gases, Oxygen and Acetylene — Welding Eods — Fluxes — Supplies and Fixtures 33
CHAPTER III
ACETYLENE GENERATORS: — Generator Requirements and Types — Construction — Care and Operation of Generators. 60
CHAPTER IV
WELDING INSTRUMENTS: — Tank and Regulating Valves and Gauges — High, Low and Medium Pressure Torches — Cut- ting Torches — Acetylene-Air Torches 85
CHAPTER V
OXY-ACETYLENE WELDING PRACTICE: — Preparation of Work — Torch Practice — Control of the Flame — Welding Vari- ous Metals and Alloys — Tables of Information Required in Welding Operations 106
CHAPTER VI
ELECTRIC WELDING: — Resistance Method — Butt, Spot and Lap Welding — Troubles and Remedies — Electric Arc
Welding 142
9
10 CONTENTS
CHAPTER VII
PAGE
HAND FORGING AND WELDING: — Blacksmithing, Forging and Bending — Forge Welding Methods 170
CHAPTER VIII
SOLDERING, BRAZING AND THERMIT WELDING: — Soldering Materials and Practice — Brazing — Thermit Welding. .. .188
CHAPTER IX OXYGEN PROCESS FOR EEMOVAL OF CARBON 207
INDEX 211
OXY-ACETYLENE WELDING AND
CUTTING, ELECTRIC AND
THERMIT WELDING
CHAPTER I
METALS AND THEIR ALLOYS— HEAT TREATMENT THE METALS
Iron. — Iron, in its pure state, is a soft, white, easily worked metal. It is the most important of all the metallic elements, and is, next to aluminum, the com- monest metal found in the earth.
Mechanically speaking, we have three kinds of iron : wrought iron, cast iron and steel. Wrought iron is very nearly pure iron; cast iron contains carbon and silicon, also chemical impurities; and steel contains a definite proportion of carbon, but in smaller quanti- ties than cast iron.
Pure iron is never obtained commercially, the metal always being mixed with various proportions of car- bon, silicon, sulphur, phosphorus, and other elements, making it more or less suitable for different purposes. Iron is magnetic to the extent that it is attracted by magnets, but it does not retain magnetism itself, as does steel. Iron forms, with other elements, many important combinations, such as its alloys, oxides, and sulphates.
11
12 V/ELDING
Cast Iron. — Metallic iron is separated from iron ore in the blast furnace (Figure 1), and when allowed to run into moulds is called cast iron. This form is used for engine cylinders and pistons, for brackets, covers, housings and at any point where its brittle-
Figure 1. — Section Through a Blast Furnace
ness is not objectionable. Good cast iron breaks with a gray fracture, is free from blowholes or roughness, and is easily machined, drilled, etc. Cast iron is slightly lighter than steel, melts at about 2,400 de- grees in practice, is about one-eighth as good an elec- trical conductor as copper and has a tensile strength of 13,000 to 30,000 pounds per square inch. Its com-
METALS AND THEIR ALLOYS— HEAT TREATMENT 13
pressive strength, or resistance to crushing, is very great. It has excellent wearing qualities and is not easily warped and deformed by heat. Chilled iron is cast into a metal mould so that the outside is cooled quickly, making the surface very hard and difficult to cut and giving great resistance to wear. It is used for making cheap gear wheels and parts that must withstand surface friction.
Malleable Cast Iron. — This is often called simply malleable iron. It is a form of cast iron obtained by removing much of the carbon from cast iron, making it softer and less brittle. It has a tensile strength of 25,000 to 45,000 pounds per square inch, is easily machined, will stand a small amount of bending at a low red heat and is used chiefly in making brackets, fittings and supports where low cost is of considerable importance. It is often used in cheap constructions in place of steel forgings. The greatest strength of a malleable casting, like a steel forging, is in the sur- face, therefore but little machining should be done.
Wrought Iron. — This grade is made by treating the cast iron to remove almost all of the carbon, silicon, phosphorus, sulphur, manganese and other impuri- ties. This process leaves a small amount of the slag from the ore mixed with the wrought iron.
Wrought iron is used for making bars to be ma- chined into various parts. If drawn through the rolls at the mill once, while being made, it is called "muck bar;" if rolled twice, it is called "merchant bar" (the commonest kind), and a still better grade is made by rolling a third time. Wrought iron is being grad- ually replaced in use by mild rolled steels.
Wrought iron is slightly heavier than cast iron, is a much better electrical conductor than either cast
14 WELDING
iron or steel, has a tensile strength of 40,000 to 60,000 pounds per square inch and costs slightly more than steel. Unlike either steel or cast iron, wrought iron does not harden when cooled suddenly from a red heat.
Grades of Irons. — The mechanical properties of cast iron differ greatly according to the amount of other materials it contains. The most important of these contained elements is carbon, which is present to a degree varying from 2 to 5% per cent. When iron containing much carbon is quickly cooled and then broken, the fracture is nearly white in color and the metal is found to be hard and brittle. When the iron is slowly cooled and then broken the fracture is gray and the iron is more malleable and less brittle. If cast iron contains sulphur or phosphorus, it will show a white fracture regardless of the rapidity of cooling, being brittle and less desirable for general work.
Steel. — Steel is composed of extremely minute par- ticles of iron and carbon, forming a network of layers and bands. This carbon is a smaller proportion of the metal than found in cast iron, the percentage being from T3Q- to 2!/2 per cent.
Carbon steel is specified according to the number of "points" of carbon, a point being one one-hundredth of one per cent of the weight of the steel. Steel may contain anywhere from 30 to 250 points, which is equivalent to saying, anywhere from -f$ to 2^ per cent, as above. A 70-point steel would contain 70/100 of one per cent or TT0- of one per cent of carbon by weight. The percentage of carbon determines the hardness of the steel, also many other qualities, and its suitability for various kinds of work. The more carbon contained in the steel, the harder the metal will be, and, of course, its brittleness increases with
METALS AND THEIR ALLOYS— HEAT TREATMENT 15
the hardness. The smaller the grains or particles of iron which are separated by the carbon, the stronger the steel will be, and the control of the size of these particles is the object of the science of heat treatment.
In addition to the carbon, steel may contain the following : Silicon, which increases the hardness, brittleness,
strength and difficulty of working if from 2 to 3
per cent is present. Phosphorus, which hardens and weakens the metal
but makes it easier to cast. Three-tenths per cent
of phosphorus serves as a hardening agent and may
be present in good steel if the percentage of carbon
is low. More than this weakens the metal. Sulphur, which tends to make the metal hard and
filled with small holes. Manganese, which makes the steel so hard and tough
that it can with difficulty be cut with steel tools.
Its hardness is not lessened by annealing, and it has
great tensile strength.
Alloy steel has a varying but small percentage of other elements mixed with it to give certain desired qualities. Silicon steel and manganese steel are some- times classed as alloy steels. This subject is taken up in the latter part of this chapter under Alloys, where the various combinations and their characteristics are given consideration.
Steel has a tensile strength varying from 50,000 to 300,000 pounds per square inch, depending on the carbon percentage and the other alloys present, as well as upon the texture of the grain. Steel is heavier than cast iron and weighs about the same as wrought iron. It is about one-ninth as good a conductor of electricity as copper.
16
WELDING
Steel is made from cast iron by three principal processes: the crucible, Bessemer and open hearth.
Crucible steel is made by placing pieces of iron in a clay or graphite crucible, mixed with charcoal and a small amount of any desired alloy. The crucible is then heated with coal, oil or gas fires until the iron melts, and, by absorbing the desired elements and giv- ing up or changing its percentage of carbon, becomes
Figure 2. — A Bessemer Converter
steel. The molten steel is then poured from the cru- cible into moulds or bars for use. Crucible steel may also be made by placing crude steel in the crucibles in place of the iron. This last method gives the finest grade of metal and the crucible process in general gives the best grades of steel for mechanical use.
Bessemer steel is made by heating iron until all the undesirable elements are burned out by air blasts which furnish the necessary oxygen. The iron is placed in a large retort called a converter (Figure 2), being poured, while at a melting heat, directly
METALS AND THEIR ALLOYS— HEAT TREATMENT 17
from the blast furnace into the converter. While the iron in the converter is molten, blasts of air are forced through the liquid, making it still hotter and burning out the impurities together with the carbon and man- ganese. These two elements are then restored to the iron by adding spiegeleisen (an alloy of iron, carbon and manganese) . A converter holds from 5 to 25 tons of metal and requires about 20 minutes to finish a charge. This makes the cheapest steel.
Figure 3. — An Open Hearth Furnace
Open hearth steel is made by placing the molten iron in a receptacle while currents of air pass over it, this air having itself been highly heated by just pass- ing over white hot brick (Figure. 3). Open hearth steel is considered more uniform and reliable than Bessemer, and is used for springs, bar steel, tool steel, steel plates, etc.
Aluminum is one of the commonest industrial metals. It is used for gear cases, engine crank cases, covers, fittings, and wherever lightness and moderate strength are desirable.
Aluminum is about one-third the weight of iron
18 WELDING
and about the same weight as glass and porcelain ; it is a good electrical conductor (about one-half as good as copper) ; is fairly strong itself and gives great strength to other metals when alloyed with them. One of the greatest advantages of aluminum is that it will not rust or corrode under ordinary conditions. The granular formation of aluminum makes its strength very unreliable and it is too soft to resist wear.
Copper is one of the most important metals used in the trades, and the best commercial conductor of elec- tricity, being exceeded in this respect only by silver, which is but slightly better. Copper is very malleable and ductile when cold, and in this state may be easily worked under the hammer. Working in this way makes the copper stronger and harder, but less duc- tile. Copper is not affected by air, but acids cause the formation of a green deposit called verdigris.
Copper is one of the best conductors of heat, as well as electricity, being used for kettles, boilers, stills and wherever this quality is desirable. Copper is also used in alloys with other metals, forming an impor- tant part of brass, bronze, german silver, bell metal and gun metal. It is about one-eighth heavier than steel and has a tensile strength of about 25,000 to 50,000 pounds per square inch.
Lead. — The peculiar properties of lead, and espe- cially its quality of showing but little action or chem- ical change in the presence of other elements, makes it valuable under certain conditions of use. Its prin- cipal use is in pipes for water and gas, coverings for roofs and linings for vats and tanks. It is also used to coat sheet iron for similar uses and as an important part of ordinary solder.
Lead is the softest and weakest of all the commer-
METALS AND THEIR ALLOYS— HEAT TREATMENT 19
cial metals, being very pliable and inelastic. It should be remembered that lead and all its compounds are poisonous when received into the system. Lead is more than one-third heavier than steel, has a tensile strength of only about 2,000 pounds per square inch, and is only about one-tenth as good a conductor of electricity as copper.
Zinc. — This is a bluish-white metal of crystalline form. It is brittle at ordinary temperatures and be- comes malleable at about 250 to 300 degrees Fahren- heit, but beyond this point becomes even more brittle than at ordinary temperatures. Zinc is practically unaffected by air or moisture through becoming cov- ered with one of its own compounds which immedi- ately resists further action. Zinc melts at low tem- peratures, and when heated beyond the melting point gives off very poisonous fumes.
The principal use of zinc is as an alloy with other metals to form brass, bronze, german silver and bear- ing metals. It is also used to cover the surface of steel and iron plates, the plates being then called galvanized.
Zinc weighs slightly less than steel, has a tensile strength of 5,000 pounds per square inch, and is not quite half as good as copper in conducting electricity.
Tin resembles silver in color and luster. Tin is ductile and malleable and slightly crystalline in form, almost as heavy as steel, and has a tensile strength of 4,500 pounds per square inch.
The principal use of tin is for protective platings on household utensils and in wrappings of tin-foil. Tin forms an important part of many alloys such as babbitt, Britannia metal, bronze, gun metal and bear- ing metals.
20 WELDING
Nickel is important in mechanics because of its combinations with other metals as alloys. Pure nickel is grayish-white, malleable, ductile and tenacious. It weighs almost as much as steel and, next to man- ganese, is the hardest of metals. Nickel is one of the three magnetic metals, the others being iron and co- balt. The commonest alloy containing nickel is ger- man silver, although one of its most important alloys is found in nickel steel. Nickel is about ten per cent heavier -than steel, and has a tensile strength of 90,000 pounds per square inch.
Platinum. — This metal is valuable for two reasons: it is not affected by the air or moisture or any ordi- nary acid or salt, and in addition to this property it melts only at the highest temperatures. It is a fairly good electrical conductor, being better than iron or steel. It is nearly three times as heavy as steel and its tensile strength is 25,000 pounds per square inch.
ALLOYS
An alloy is formed by the union of a metal with some other material, either metal or non-metallic, this union being composed of two or more elements and usually brought about by heating the substances together until they melt and unite. Metals are al- loyed with materials which have been found to give to the metal certain characteristics which are desired according to the use the metal will be put to.
The alloys of metals are, almost without exception, more important from an industrial standpoint than the metals themselves. There are innumerable pos- sible combinations, the most useful of which are here classed under the head of the principal metal entering into their composition.
METALS AND THEIR ALLOYS— HEAT TREATMENT 21
Steel. — Steel may be alloyed with almost any of the metals or elements, the combinations that have proven valuable numbering more than a score. The principal ones are given in alphabetical order, as follows :
Aluminum is added to steel in very small amounts for the purpose of preventing blow holes in castings.
Boron increases the density and toughness of the metal.
Bronze, added by alloying copper, tin and iron, is used for gun metal.
Carbon has already been considered under the head of steel in the section devoted to the metals. Carbon, while increasing the strength and hardness, decreases the ease of forging and bending and decreases the magnetism and electrical conductivity. High carbon steel can be welded only with difficulty. When the percentage of carbon is low, the steel is called "low carbon" or "mild" steel. This is used for rods and shafts, and called " machine " steel. When the car- bon percentage is high, the steel is called "high carbon" steel, and it is used in the shop as tool steel. One-tenth per cent of carbon gives steel a tensile strength of 50,000 to 65,000 pounds per square inch ; two-tenths per cent gives from 60,000 to 80,000 ; four- tenths per cent gives 70,000 to 100,000, and six-tenths per cent gives 90,000 to 120,000.
Chromium forms chrome steel, and with the further addition of nickel is called chrome nickel steel. This increases the hardness to a high degree and adds strength without much decrease in ductility. Chrome steels are used for high-speed cutting tools, armor plate, files, springs, safes, dies, etc.
Manganese has been mentioned under Steel. Its alloy is much used for high-speed cutting tools, the
22 WELDING
steel hardening when cooled in the air and being called self-hardening.
Molybdenum is used to increase the hardness to a high degree and makes the steel suitable for high- speed cutting and gives it self-hardening properties.
Nickel, with which is often combined chromium, increases the strength, springiness and toughness and helps to prevent corrosion.
Silicon has already been described. It suits the metal for use in high-speed tools.
Silver added to steel has many of the properties of nickel.
Tungsten increases the hardness without making the steel brittle. This makes the steel well suited for gas engine valves as it resists corrosion and pitting. Chromium and manganese are often used in com- bination with tungsten when high-speed cutting tools are made.
Vanadium as an alloy increases the elastic limit, making the steel stronger, tougher and harder. It also makes the steel able to stand much bending and vibration.
Copper. — The principal copper alloys include brass, bronze, german silver and gun metal.
Brass is composed of approximately one-third zinc and two-thirds copper. It is used for bearings and bushings where the speeds are slow and the loads rather heavy for the bearing size. It also finds use in washers, collars and forms of brackets where the metal should be non-magnetic, also for many highly finished parts.
Brass is about one-third as good an electrical con- ductor as copper, is slightly heavier than steel and
METALS AND THEIR ALLOYS— HEAT TREATMENT 23
has a tensile strength of 15,000 pounds when cast and about 75,000 to 100,000 pounds when drawn into wire.
Bronze is composed of copper and tin in various proportions, according to the use to which it is to be put. There will always be from six-tenths to nine- tenths of copper in the mixture. Bronze is used for bearings, bushings, thrust washers, brackets and gear wheels. It is heavier than steel, about 1/15 as good an electrical conductor as pure copper and has a tensile strength of 30,000 to 60,000 pounds.
Aluminum bronze, composed of copper, zinc and • aluminum has high tensile strength combined with ductility and is used for parts requiring this com- bination.
Bearing bronze is a variable material, its composi- tion and proportion depending on the maker and the use for which it is designed. It usually contains from 75 to 85 per cent of copper combined with one or more elements, such as tin, zinc, antimony and lead.
White metal is one form of bearing bronze con- taining over 80 per cent of zinc together with cop- per, tin, antimony and lead. Another form is made with nearly 90 per cent of tin combined with copper and antimony.
Gun metal bronze is made from 90 per cent copper with 10 per cent of tin and is used for heavy bear- ings, brackets and highly finished parts.
Phosphor bronze is used for very strong castings and bearings. It is similar to gun metal bronze, except that about l1/^ per cent of phosphorus has been added.
Manganese bronze contains about 1 per cent of
24 WELDING
manganese and is used for parts requiring great strength while being free from corrosion.
German silver is made from 60 per cent of copper with 20 per cent each of zinc and nickel. Its high electrical resistance makes it valuable for regulating devices and rheostats.
Tin is the principal part of babbitt and solder. A commonly used babbitt is composed of 89 per cent tin, 8 per cent antimony and 3 per cent of copper. A grade suitable for repairing is made from 80 per cent of lead and 20 per cent antimony. This last formula should not be used for particular work or heavy loads, being more suitable for spacers. In- numerable proportions of metals are marketed under the name of babbitt.
Solder is made from 50 per cent tin and 50 per cent lead, this grade being called "half-and-half." Hard solder is made from two-thirds tin and one-third lead.
Aluminum forms many different alloys, giving in- creased strength to whatever metal it unites with.
Aluminum brass is composed of approximately 65 per cent copper, 30 per cent zinc and 5 per cent alu- minum. It forms a metal with high tensile strength while being ductile and malleable.
Aluminum zinc is suitable for castings which must be stiff and hard.
Nickel aluminum has a tensile strength of 40,000 pounds per square inch.
Magnalium is a silver-white alloy of aluminum with from 5 to 20 per cent of magnesium, forming a 'metal even lighter than aluminum and strong enough to be used in making high-speed gasoline engines.
METALS AND THEIR ALLOYS— HEAT TREATMENT 25 HEAT TREATMENT OF STEEL
The processes of heat treatment are designed to suit the steel for various purposes by changing the size of the grain in the metal, therefore the strength ; and by altering the chemical composition of the al- loys in the metal to give it different physical prop- erties. Heat treatment, as applied in ordinary shop work, includes the three processes of annealing, hard- ening and tempering, each designed to accomplish a certain definite result.
All of these processes require that the metal treated be gradually brought to a certain predetermined degree of heat which shall be uniform throughout the piece being handled and, from this point, cooled ac- cording to certain rules, the selection of wrhich forms the difference in the three methods.
Annealing. — This is the process which relieves all internal strains and distortion in the metal and softens it so that it may more easily be cut, machined or bent to the required form. In some cases anneal- ing is used only to relieve the strains, this being the case after forging or welding operations have been performed. In other cases it is only desired to soften the metal sufficiently that it may be handled easily. In some cases both of these things must be accom- plished, as after a piece has been forged and must be machined. No matter what the object, the pro- cedure is the same.
The steel to be annealed must first be heated to a dull red. This heating should be done slowly so that all parts of the piece have time to reach the same temperature at very nearly the same time. The piece may be heated in the forge, but a much better way is
26 WELDING
to heat in an oven or furnace of some type where the work is protected against air currents, either hot or cold, and is also protected against the direct action of the fire.
Probably the simplest of all ovens for small tools is made by placing a piece of ordinary gas pipe in the fire (Figure 4), and heating until the inside of the pipe is bright red. Parts placed in this pipe, after one end has been closed, may be brought to the de-
Figure 4. — A Gaspipe Annealing Oven
sired heat without danger of cooling draughts or chemical change from the action of the fire. More elaborate ovens may be bought which use gas, fuel oils or coal to produce the heat and in which the work may be placed on trays so that the fire will not strike directly on the steel being treated.
If the work is not very important, it may be with- drawn from the fire or oven^, after heating to the desired point, and allowed to cool in the air until all traces of red have disappeared when held in a dark place. The work should be held where it is reason- ably free from cold air currents. If, upon touching a pine stick to the piece being annealed, the wood
METALS AND THEIR ALLOYS— HEAT TREATMENT 27
does not smoke, the work may then be cooled in water.
Better annealing is secured and harder metal may be annealed if the cooling is extended over a number of hours by placing the work in a bed of non-heat- conducting material, such as ashes, charred bone, asbestos fibre, lime, sand or fire clay. It should be well covered with the heat retaining material and allowed to remain until cool. Cooling may be accom- plished by allowing the fire in an oven or furnace to die down and go out, leaving the work inside the oven with all openings closed. The greater the time taken for gradual cooling from the red heat, the more perfect will be the results of the annealing.
While steel is annealed by slow cooling, copper or brass is annealed by bringing to a low red heat and quickly plunging into cold water.
Hardening. — Steel is hardened by bringing to a proper temperature, slowly and evenly as for an- nealing, and then cooling more or less quickly, ac- cording to the grade of steel being handled. The degree of hardening is determined by the kind of steel, the temperature from which the metal is cooled and the temperature and nature of the bath into which it is plunged for cooling.
Steel to be hardened is often heated in the fire until at some heat around 600 to 700 degrees is reached, then placed in a heating bath of molten lead, heated mercury, fused cyanate of potassium, etc., the heating bath itself being kept at the proper tempera- ture by fires acting on it. While these baths have the advantage of heating the metal evenly and to exactly the temperature desired throughout without any part becoming over or under heated, their dis-
28 WELDING
advantages consist of the fact that their materials and the fumes are poisonous in most all cases, and if not poisonous, are extremely disagreeable.
The degree of heat that a piece of steel must be brought to in order that it may be hardened depends on the percentage of carbon in the steel. The greater the percentage of carbon, the lower the heat neces- sary to harden.
To find the proper heat from which any steel must be cooled, a simple test may be carried out provided
Figure 5. — Cooling the Test Bar for Hardening
a sample of the steel, about six inches long can be secured. One end of this test bar should be heated almost to its melting point, and held at this heat until the other end just turns red. Now cool the piece in water by plunging it so that both ends enter at the same time (Figure 5), that is, hold it parallel with the surface of the water when plunged in. This serves the purpose of cooling each point along the bar from a different heat. When it has cooled in the water remove the piece and break it at short intervals, about y2 inch, along its length. The point along the test bar which was cooled from the
METALS AND THEIR ALLOYS— HEAT TREATMENT 29
best possible temperature will show a very fine smooth grain and the piece cannot be cut by a file at this point. It will be necessary to remember the exact color of that point when taken from the fire, making another test if necessary, and heat all pieces of this same steel to this heat. It will be necessary to have the cooling bath always at the same tempera- ture, or the results cannot be alike.
While steel to be hardened is usually cooled in water, many other liquids may be used. If cooled in strong brine, the heat will be extracted much quicker, and the degree of hardness will be greater. A still greater degree of hardness is secured by cool- ing in a bath of mercury. Care should be used with the mercury bath, as the fumes that arise are poi- sonous.
Should toughness be desired, without extreme hard- ness, the steel may be cooled in a bath of lard oil, neatsfoot oil or fish oil. To secure a result between water and oil, it is customary to place a thick layer of oil on top of water. In cooling, the piece will pass thrugh the oil first, thus avoiding the sudden shock of the cold water, yet producing a degree of hard- ness almost as great as if the oil were not used.
It will, of course, be necessary to make a separate test for each cooling medium used. If the fracture of the test piece shows a coarse grain, the steel was too hot at that point; if the fracture can be cut with a file, the metal was not hot enough at that point.
When hardening carbon tool steel its heat should be brought to a cherry red, the exact degree of heat depending on the amount of carbon and the test made, then plunged into water and held there until all hissing sound and vibration ceases. Brine may be
30 WELDING
used for this purpose; it is even better than plain water. As soon as the hissing stops, remove the work from the water or brine and plunge in oil for complete cooling.
In hardening high-speed tool steel, or air hardening steels, the tool should be handled as for carbon steel, except that after the body reaches a cherry red, the cutting point must be quickly brought to a white heat,
Figure 6. — Cooling the Tool for Tempering
almost melting, so that it seems ready for welding. Then cool in an oil bath or in a current of cool air.
Hardening of copper, brass and bronze is accom- plished by hammering or working them while cold.
Tempering is the process of making steel tough after it has been hardened, so that it will hold a cutting edge and resist cracking. Tempering makes the grain finer and the metal stronger. It does not affect the hardness, but increases the elastic limit and reduces the brittleness of the steel. In that tem- pering is usually performed immediately after har-
METALS AND THEIR ALLOYS— HEAT TREATMENT 31
dening, it might be considered as a continuation of the former process.
The work or tool to be tempered is slowly heated to a cherry red and the cutting end is then dipped into water to a depth of y% to % inch above the point (Figure 6). As soon as the point cools, still leaving the tool red above the part in water, remove the work from the bath and quickly rub the end with a fine emery cloth.
As the heat from the uncooled part gradually heats the point again, the color of the polished portion changes rapidly. When a certain color is reached, the tool should be completely immersed in the water until cold.
For lathe, planer, shaper and slotter tools, this color should be a light straw.
Reamers and taps should be cooled from an ordi- nary straw color.
Drills, punches and wood working tools should have a brown color.
Blue or light purple is right for cold chisels and screwdrivers.
Dark blue should be reached for springs and wood saws.
Darker colors than this, ranging through green and gray, denote that the piece has reached its ordinary temper, that is, it is partially annealed.
After properly hardening a spring by dipping in lard or fish oil. it should be held over a fire while still wet with the oil. The oil takes fire and burns off, properly tempering the spring.
Remember that self -hardening steels must never be dipped in water, and always remember for all work
32 WELDING
requiring degrees of heat, that the more carbon, the less heat.
Case Hardening. — This is a process for adding more carbon to the surface of a piece of steel, so that it will have good wear-resisting qualities, while being tough and strong on the inside. It has the effect of forming a very hard and durable skin on the surface of soft steel, leaving the inside unaffected.
The simplest way, although not the most efficient, is to heat the piece to be case hardened to a red heat and then sprinkle or rub the part of the surface to be hardened with potassium ferrocyanide. This material is a deadly poison and should be handled with care. Allow the cyanide to fuse on the surface of the metal and then plunge into water, brine or mercury. Eepeating the process makes the surface harder and the hard skin deeper each time.
Another method consists of placing the piece to be hardened in a bed of powdered bone (bone which has been burned and then powdered) and cover with more powdered bone, holding the whole in an iron tray. Now heat the tray and bone with the work in an oven to a bright red heat for 30 minutes to an hour and then plunge the work into water or brine.
CHAPTER II
OXY-ACETYLENE WELDING AND CUTTING MATERIALS
Welding. — Oxy-acetylene welding is an autogenous welding process, in which two parts of the same or different metals are joined by causing the edges to melt and unite while molten without the aid of hammering or compression. When cool, the parts form one piece of metal.
The oxy-acetylene flame is made by mixing oxygen and acetylene gases in a special welding torch or blowpipe, producing, when burned, a heat of 6,300 degrees, which is more than twice the melting tem- perature of the common metals. This flame, while being of intense heat, is of very small size.
Cutting. — The process of cutting metals with the flame produced from oxygen and acetylene depends on the fact that a jet of oxygen directed upon hot metal causes the metal itself to burn away with great rapidity, resulting in a narrow slot through the sec- tion cut. The action is so fast that metal is not in- jured on either side of the cut.
Carbon Removal. — This process depends on the fact that carbon will burn and almost completely vanish if the action is assisted with a supply of pure oxygen gas. After the combustion is started with any convenient flame, it continues as long as carbon remains in the path of the jet of oxygen.
Materials. — For the performance of the above oper- ations we require the two gases, oxygen and acetylene, to produce the flames; rods of metal which may be added to the joints while molten in order to give
33
34 WELDING
the weld sufficient strength and proper form, and va- rious chemical powders, called fluxes, which assist in the flow of metal and in doing away with many of the impurities and other objectionable features.
Instruments. — To control the combustion of the gases and add to the convenience of the operator a number of accessories are required.
The pressure of the gases in their usual containers is much too high for their proper use in the torch and we therefore need suitable valves which allow the gas to escape from the containers when wanted, and other specially designed valves which reduce the pressure. Hose, composed of rubber and fabric, to- gether with suitable connections, is used to carry the gas to the torch.
The torches for welding and cutting form a class of highly developed instruments of the greatest accuracy in manufacture, and must be thoroughly understood by the welder. Tables, stands and special supports are provided for holding the work while being welded, and in order to handle the various metals and allow for their peculiarities while heated use is made of ovens and torches for preheating. The operator re- quires the protection of goggles, masks, gloves and appliances which prevent undue radiation of the heat.
Torch Practice. — The actual work of welding and cutting requires preliminary preparation in the form of heat treatment for the metals, including preheat- ing, annealing and tempering. The surfaces to be joined must be properly prepared for the flame, and the operation of the torches for best results requires careful and correct regulation of the gases and the flame produced.
Finally, the different metals that are to be welded
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 35
require special treatment for each one, depending on the physical and chemical characteristics of the ma- terial.
It will thus be seen that the apparently simple operations of welding and cutting require special materials, instruments and preparation on the part of the operator and it is a proved fact that failures, which have been attributed to the method, are really due to lack of these necessary qualifications. OXYGEN
Oxygen, the gas which supports the rapid combus- tion of the acetylene in the torch flame, is one of the elements of the air. It is the cause and the active agent of all combustion that takes place in the at- mosphere. Oxygen was first discovered as a separate gas in 1774, when it was produced by heating red oxide of mercury and was given its present name by the famous chemist, Lavoisier.
Oxygen is prepared in the laboratory by various methods, these including the heating of chloride of lime and 'peroxide of cobalt mixed in a retort, the heating of chlorate of potash, and the separation of water into its elements, hydrogen and oxygen, by the passage of an electric current. While the last process is used on a large scale in commercial work, the others are not practical for work other than that of an experimental or temporary nature.
This gas is a colorless, odorless, tasteless element. It is sixteen times as heavy as the gas hydrogen when measured by volume under the same temperature and pressure. Under all ordinary conditions oxygen remains in a gaseous form, although it turns to a liquid when compressed to 4,400 pounds to the square inch and at a temperature of 220° below zero.
36 WELDING
Oxygen unites with almost every other element, this union often taking place with great heat and much light, producing flame. Steel and iron will burn rapidly when placed in this gas if the combus- tion is started with a flame of high heat playing on the metal. If the end of a wire is heated bright red and quickly plunged into a jar containing this gas, the wire will burn away with a dazzling light and be entirely consumed except for the molten drops that separate themselves. This property of oxygen is used in oxy-acetylene cutting of steel.
The combination of oxygen with other substances does not necessarily cause great heat, in fact the com- bination may be so slow and gradual that the change of temperature can not be noticed. An example of this slow combustion, or oxidation, is found in the' conversion of iron into rust as the metal combines with the active gas. The respiration of human beings and animals is a form of slow combustion and is the source of animal heat. It is a general rule that the process of oxidation takes place with increasing rapid- ity as the temperature of the body being acted upon rises. Iron and steel at a red heat oxidize rapidly with the formation of a scale and possible damage to the metal.
Air. — Atmospheric air is a mixture of oxygen and nitrogen with traces of carbonic acid gas and water vapor. Twenty-one per cent of the air, by volume, is oxygen and the remaining seventy-nine per cent is the inactive gas, nitrogen. But for the presence of the nitrogen, which deadens the action of the other gas, combustion would take place at a destructive rate and be beyond human control in almost all cases. These two gases exist simply as a mixture to form the
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 37
air and are not chemically combined. It is there- fore a comparatively simple matter to separate them with the processes now available.
Water. — Water is a combination of oxygen and hydrogen, being composed of exactly two volumes of hydrogen to one volume of oxygen. If these two gases
Figure 7. — Obtaining Oxygen by Electrolysis
be separated from each other and then allowed to mix in these, proportions they unite with explosive violence and form water. Water itself may be sepa- rated into the gases by any one of several means, one making use of a temperature of 2,200° to bring about this separation.
The easiest way to separate water into its two parts is by the process called electrolysis (Figure 7). Water,
38 WELDING
with which has been mixed a small quantity of acid, is placed in a vat through the walls of which enter the platinum tipped ends of two electrical conductors, one positive and the other negative.
Tubes are placed directly above these wire ter- minals in the vat, one tube being over each electrode and separated from each other by some distance. With the passage of an electric current from one wire terminal to the other, bubbles of gas rise from each and pass into the tubes. The gas that comes from the negative terminal is hydrogen and that from the positive pole is oxygen, both gases being almost pure if the work is properly conducted. This method produces electrolytic oxygen and electrolytic hydro- gen.
The Liquid Air Process. — While several of the foregoing methods of securing oxygen are success- ful as far as this result is concerned, they are not profitable from a financial standpoint. A process for separating oxygen from the nitrogen in the air has been brought to a high state of perfection and is now supplying a major part of this gas for oxy- acetylene welding. It is known as the Linde process and the gas is distributed by the Linde Air Products Company from its plants and warehouses located in /the large cities of the country.
The air is first liquefied by compression, after which the gases are separated and the oxygen collected. The air is purified and then compressed by successive stages in powerful machines designed for this pur- pose until it reaches a, pressure of about 3,000 pounds to the square inch. The large amount of heat pro- duced is absorbed by special coolers during the process of compression. The highly compressed air is
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 39
then dried and the temperature further reduced by other coolers.
The next point in the separation is that at which the air is introduced into an apparatus called an in- terchanger and is allowed to escape through a valve, causing it to turn to a liquid. This liquid air is sprayed onto plates and as it falls, the nitrogen re- turn to its gaseous state arid leaves the oxygen to run to the bottom of the container. This liquid oxygen is then allowed to return to a gas and is stored in large gasometers or tanks.
The oxygen gas is taken from the storage tanks and compressed to approximately 1,800 pounds to the square inch, under which pressure it is passed into steel cylinders and made ready for delivery to the customer. This oxygen is guaranteed to be ninety- seven per cent pure.
Another process, known as the Hildebrandt process, is coming into use in this country. It is a later process and is used in Germany to a much greater extent than the Linde process. The Superior Oxygen Co. has secured the American rights and has established sev- eral plants.
Oxygen Cylinders. — Two sizes of cylinders are in use, one containing 100 cubic feet of gas when it is at atmospheric pressure and the other containing 250 cubic feet under similar conditions. The cylinders are made from one piece of steel and are without seams. These containers are tested at double the pres- sure of the gas contained to insure safety while handling.
One hundred cubic feet of oxygen weighs nearly nine pounds (8.921), and therefore the cylinders will we:'""1"1 fVally nine pounds more when full
40 WELDING
than after emptying, if of the 100 cubic feet size. The large cylinders weigh about eighteen and one- quarter pounds more when full than when empty, making approximately 212 pounds empty and 230 pounds full.
The following table gives the number of cubic feet of oxygen remaining in the cylinders according to various gauge pressures from an initial pressure of 1,800 pounds. The amounts given are not exactly correct as this would necessitate lengthy calculations which would not make great enough difference to affect the practical usefulness of the table :
Cylinder of 100 Cu. Ft. Capacity at 68° Fahr.
Gauge Volume Gauge Volume
Pressure Remaining Pressure Remaining
1800 100 700 39
1620 90 500 28
1440 80 300 17
1260 70 100 6
1080 60 18 1
900 50 9 %
Cylinder of 250 Cu. Ft. Capacity at 68° Fahr.
Gauge Volume Gauge Volume
Pressure Remaining Pressure Remaining
1800 250 700 9-7
1620 225 500 70
1440 200 300 42
1260 175 100 15
1080 150 18 8
900 125 9 1%
The temperature of the cylinder affects the pressure in a large degree, the pressure increasing with a rise in temperature and falling with a fall in temperature. The variation for a 100 cubic foot cylinder at various temperatures is given in the following tabulation :
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 41
At 150° Fahr 2090 pounds.
At 100° Fahr 1912 pounds.
At 80° Fahr 1844 pounds.
At 68° Fahr 1800 pounds.
At 50° Fahr 1736 pounds.
At 32° Fahr 1672 pounds.
At 0 Fahr 1558 pounds.
At — 10° Fahr 1522 pounds.
Chlorate of Potash Method. — In spite of its higher cost and the inferior gas produced, the chlorate of potash method of producing oxygen is used to a
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Figure 8. — Oxygen from Chlorate of Potash
limited extent when it is impossible to secure the gas in cylinders.
An iron retort (Figure 8) is arranged to receive about fifteen pounds of chlorate of potash mixed with three pounds of manganese dioxide, after which the cylinder is closed with a tight cap, clamped on. This retort is carried above a burner using fuel gas or other means of generating heat and this burner is lighted after the chemical charge is mixed and com- pressed in the tube.
The generation of gas commences and the oxygen is led through water baths which wash and cool it
42 WELDING
before storing in a tank connected with the plant. From this tank the gas is compressed into portable cylinders at a pressure of about 300 pounds to the square inch for use as required in welding operations.
Each pound of chlorate of potash liberates about three cubic feet of oxygen, and taking everything into consideration, the cost of gas produced in this way is several times that of the purer product secured by the liquid air process.
These chemical generators are oftentimes a source of great danger, especially when used with or near the acetylene gas generator, as is sometimes the case with cheap portable outfits. Their use should not be tolerated when any other method is available, as the danger from accident alone should prohibit the prac- tice except when properly installed and cared for away from other sources of combustible gases.
ACETYLENE
In 1862 a chemist, Woehler, announced the dis- covery of the preparation of acetylene gas from cal- cium carbide, which he had made by heating to a high temperature a mixture of charcoal with an alloy of zinc and calcium. His product would decompose water and yield the gas. For nearly thirty years these substances were neglected, with the result that acety- lene was practically unknown, and up to 1892 an acetylene flame was seen by very few persons and its possibilities were not dreamed of. "With the de- velopment of the modern electric furnace the possi- bility of calcium carbide as a commercial product became known.
In the above year, Thomas L. "Willson, an electrical engineer of Spray, North Carolina, was experiment-
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 43
ing in an attempt to prepare metallic calcium, for which purpose he employed an electric furnace oper- ating on a mixture of lime and coal tar with about ninety-five horse power. The result was a molten mass which became hard and brittle when cool. This apparently useless product was discarded and thrown in a nearby stream, when, to the astonisment of on- lookers, a large volume of gas was immediately lib- erated, which, when ignited, burned with a bright and smoky flame and gave off quantities of soot. The solid material proved to be calcium carbide and the gas acetylene.
Thus, through the incidental study of a by-product, and as the result of an accident, the possibilities in carbide were made known, and in the spring of 1895 the first factory in the world for the production of this substance was established by the Willson Alumi- num Company.
When water and calcium carbide are brought to- gether an action takes place which results in the for- mation of acetylene gas and slaked lime.
CARBIDE
Calcium carbide is a chemical combination of the elements carbon and calcium, being dark brown, black or gray with sometimes a blue or red tinge. It looks like stone and will only burn when heated with oxygen.
Calcium carbide may be preserved for any length of time if protected from the air, but the ordinary moisture in the atmosphere gradually affects it until nothing remains but slaked lime. It always possesses a penetrating odor, which is not due to the carbide itself but to the fact that it is being constantly af-
44 WELDING
fected by moisture and producing small quantities of acetylene gas.
This material is not readily dissolved by liquids, but if allowed to come in contact with water, a de- composition takes place with the evolution of large quantities of gas. Carbide is not affected by shock, jarring or age.
A pound of absolutely pure carbide will yield five and one-half cubic feet of acetylene. Absolute purity cannot be attained commercially, and in practice good carbide will produce from four and one-half to five cubic feet for each pound used.
Carbide is prepared by fusing lime and carbon in the electric furnace under a heat in excess of 6,000° Fahrenheit. These materials are among the most diffi- cult to melt that are known. Lime is so infusible that it is frequently employed for the materials of cruci- bles in which the highest melting metals are fused, and for the pencils in the calcium light because it will stand extremely high temperatures.
Carbon is the material employed in the manufac- ture of arc light electrodes and other electrical appli- ances that must stand extreme heat. Yet these two substances are forced into combination in the manu- facture of calcium carbide. It is the excessively high temperature attainable in the electric furnace that causes this combination and not any effect of the elec- tricity other than the heat produced.
A mixture of ground coke and lime is introduced into the furnace through which an electric arc has been drawn. The materials unite and form an ingot of very pure carbide surrounded by a crust of less purity. The poorer crust is rejected in breaking up the mass into lumps which are graded according to
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 45
their size. The largest size is 2 by 3y2 inches and is called "lump," a medium size is y2 by 2 inches and is called ' ' egg, ' ' an intermediate size for certain types of generators is % by 1^4 inches and called "nut," and the finely crushed pieces for use in still other types of generators are 1/12 by 14 inch in size and are called "quarter." Instructions as to the size best suited to different generators are furnished by the makers of those instruments.
These sizes are packed in air-tight sheet steel drums containing 100 pounds each. The Union Carbide Company of Chicago and New York, operating under patents, manufactures and distributes the supply of calcium carbide for the entire United States. Plants for this manufacture are established at Niagara Falls, New York, and Sault Ste. Marie, Michigan. This company maintains a system of warehouses in more than one hundred and ten cities, where large stocks of all sizes are carried.
The National Board of Fire Underwriters gives the following rules for the storage of carbide:
Calcium carbide in quantities not to exceed six hundred pounds may be stored, when contained in approved metal packages not, to exceed one hundred pounds each, inside insured property, provided that the place of storage be dry, waterproof and well ven- tilated and also provided that all but one of the packages in any one building shall be sealed and that seals shall not be broken so long as there is car- bide in excess of one pound in any other unsealed package in the building.
Calcium carbide in quantities in excess of six hun- dred pounds must be stored above ground in detached buildings, used exclusively for the storage of cal-
46 WELDING
cium carbide, in approved metal packages, and such buildings shall be constructed to be dry, waterproof and well ventilated.
Properties of Acetylene. — This gas is composed of twenty-four parts of carbon and two parts of hydro- .gen by weight and is classed with natural gas, petro- leum, etc., as one of the hydrocarbons. This gas con- tains the highest percentage of carbon known to exist in any combination of this form and it may there- fore be considered as gaseous carbon. Carbon is the fuel that is used in all forms of combustion and is present in all fuels from whatever source or in what- ever form. Acetylene is therefore the most power- ful of all fuel gases and is able to give to the torch flame in welding the highest temperature of any flame.
Acetylene is a colorless and tasteless gas, possessed of a peculiar and penetrating odor. The least trace in the air of a room is easily noticed, and if this odor is detected about an apparatus in operation, it is certain to indicate a leakage of gas through faulty piping, open valves, broken hose or otherwise. This leakage must be prevented before proceeding with the work to be done.
All gases which burn in air will, when mixed with air previous to ignition, produce more or less vio- lent explosions, if fired. To this rule acetylene is no exception. One measure of acetylene and twelve and one-half of air are required for complete combustion ; this is therefore the proportion for the most perfect explosion. This is not the only possible mixture that will explode, for all proportions from three to thirty per cent of acetylene in air will explode with more or less force if ignited.
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 47
The igniting point of acetylene is lower than that of coal gas, being about 900 degrees Fahrenheit as against eleven hundred degrees for coal gas. The gas issuing from a torch will ignite if allowed to play on the tip of a lighted cigar.
It is still further true that acetylene, at some pres- sures, greater than normal, has under most favorable conditions for the effect, been found to explode ; yet it may be stated with perfect confidence that under no circumstances has anyone ever secured an explosion in it when subjected to pressures not exceeding fif- teen pounds to the square inch.
Although not exploded by the application of high heat, acetylene is injured by such treatment. It is partly converted, by high heat, into other compounds, thus lessening the actual quantity of the gas, wasting it and polluting the rest by the introduction of sub- stances which do not belong there. These compounds remain in part with the gas, causing it to burn with a persistent smoky flame and with the deposit of objectionable tarry substances. Where the gas is gen- erated without undue rise of temperature these diffi- culties are avoided.
Purification of Acetylene. — Impurities in this gas are caused by impurities in the calcium carbide from which it is made or by improper methods and lack of care in generation. Impurities from the material will be considered first.
Impurities in the carbide may be further divided into two classes: those which exert no action on wrater and those which act with the water to throw off other gaseous products which remain in the acetylene. Those impurities which exert no action on the water consist of coke that has not been changed in the
48 WELDING
furnace and sand and some other substances which are harmless except that they increase the ash left after the acetylene has been generated.
An analysis of the gas coming from a typical gen- erator is as follows:
Per cent
Acetylene 99.36
Oxygen 08
Nitrogen 11
Hydrogen 06
Sulphuretted Hydrogen . 17
Phosphoretted Hydrogen 04
Ammonia 10
Silicon Hydride 03
Carbon Monoxide 01
Methane 04
The oxygen, nitrogen, hydrogen, methane and car- bon monoxide are either harmless or are present in such small quantities as to be neglected. The phos- phoretted hydrogen and silicon hydride are self- inflammable gases when exposed to the air, but their quantity is so very small that this possibility may be dismissed. The ammonia and sulphuretted hydrogen are almost entirely dissolved by the water used in the gas generator. The surest way to avoid impure gas is to use high-grade calcium carbide in the gener- ator and the carbide of American manufacture is now so pure that it never causes trouble.
The first and most important purification to which the gas is subjected is its passage through the body of water in the generator as it bubbles to the top. It is then filtered through felt to remove the solid
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 49
particles of lime dust and other impurities which float in the gas.
Further purification to remove the remaining am- monia, sulphuretted hydrogen and phosphorus con- taining compounds is accomplished by chemical means. If this is considered necessary it can be easily accomplished by readily available purifying appa- ratus which can be attached to any generator or in- serted between the generator and torch outlets. The following mixtures have been used.
"Heratol," a solution of chromic acid or sulphuric acid absorbed in porous earth.
"Acagine," a mixture of bleaching powder with fifteen per cent of lead chromate.
"Puratylene," a mixture of bleaching powder and hydroxide of lime, made very porous, and containing from eighteen to twenty per cent of active chlorine.
"FrQnkoline," a mixture of cuprous and ferric chlorides dissolved in strong hydrochloric acid ab- sorbed in infusorial earth.
A test for impure acetylene gas is made by placing a drop of ten per cent solution of silver nitrate on a white blotter and holding the paper in a stream of gas coming from the torch tip. Blackening of the paper in a short length of time indicates impurities.
Acetylene in Tanks. — Acetylene is soluble in water to a very limited extent, too limited to be of prac- tical use. There is only one liquid that possesses sufficient power of containing acetylene in solution to be of commercial value, this being the liquid ace- tone. Acetone is produced in various ways, often- times from the distillation of wood. It is a trans- parent, colorless liquid that flows with ease. It boils at 133° Fahrenheit, is inflammable and burns with
50 WELDING
a luminous flame. It has a peculiar but rather agree- able odor.
Acetone dissolves twenty-four times its own bulk of acetylene at ordinary atmospheric pressure. If this pressure is increased to two atmospheres, 14.7 pounds above ordinary pressure, it will dissolve just twice as much of the gas and for each atmosphere that the pressure is increased it will dissolve as much more.
If acetylene be compressed above fifteen pounds per square inch at ordinary temperature without first being dissolved in acetone a danger is present of self- ignition. This danger, while practically nothing at fifteen pounds, increases with the pressure until at forty atmospheres it is very explosive. Mixed with acetone, the gas loses this dangerous property and is safe for handling and transportation. As acetylene is dissolved in the liquid the acetone increases its vol- ume slightly so that when the gas has been drawn out of a closed tank a space is left full of free acetylene.
This last difficulty is removed by first filling the cylinder or tank with some porous material, such as asbestos, wrood charcoal, infusorial earth, etc. As- bestos is used in practice and by a system of packing and supporting the absorbent material no space is left for the free gas, even when the acetylene has. been completely withdrawn.
The acetylene is generated in the usual way and is washed, purified and dried. Great care is used to make the gas as free as possible from all impurities and from air. The gas is forced into containers filled with acetone as described and is compressed to one hundred and fifty pounds to the square inch. From these tanks it is transferred to the smaller port- able cvlinders for consumers ' use.
OXY-ACETYLBNE WELDING AND CUTTING MATERIALS 51
The exact volume of gas remaining in a cylinder at atmospheric temperature may be calculated if the weight of the cylinder empty is known. One pound of the gas occupies 13.6 cubic feet, so that if the difference in weight between the empty cylinder and the one considered be multiplied by 13.6, the result will be the number of cubic feet of gas contained.
The cylinders contain from 100 to 500 cubic feet of acetylene under pressure. They cannot be filled with the ordinary type of generator as they require special purifying and compressing apparatus, which should never be installed in any building where other work is being carried on, or near other buildings which are occupied, because of the danger of ex- plosion.
Dissolved acetylene is manufactured by the Prest- 0-Lite Company, the Commercial Acetylene Com-, pany and the Searchlight Gas Company and is dis- tributed from warehouses in various cities.
These tanks should not be discharged at a rate per hour greater than one-seventh of their total capacity, that is, from a tank of 100 cubic feet capacity, the discharge should not be more than fourteen cubic feet per hour. If discharge is carried on at an ex- cessive rate the acetone is drawn out with the and reduces the heat of the welding flame.
For this reason welding should not be attempted with cylinders designed for automobile and boat lighting. When the work demands a greater delivery than one of the larger tanks will give, two or more tanks may be connected with a special coupler such as may be secured from the makers and distributers of the gas. These couplers may be arranged for two, three, four or five tanks in one battery by removing
52 WELDING
the plugs on the body of the coupler and attaching additional connecting pipes. The coupler body car- ries a pressure gauge and the valve for controlling the pressure of the gas as it flows to the welding torches. The following capacities should be provided for:
Acetylene Consumption Combined Capacity of
of Torches per Hour Cylinders in Use
Up to 15 feet 100 cubic feet
16 to 30 feet 200 cubic feet
31 to 45 feet 300 cubic feet
46 to 60 feet 400 cubic feet
61 to 75 feet 500 cubic feet
WELDING RODS
The best welding cannot be done without using the best grade of materials, and the added cost of these materials over less desirable forms is so slight when compared to the quality of work performed and the waste of gases with inferior supplies, that it is very unprofitable to take any chances in this respect. The makers of welding equipment carry an assortment of supplies that have been standardized and that may be relied upon to produce the desired result when properly used. The safest plan is to secure this class of material from the makers.
"Welding rods, or welding sticks, are used to supply the additional metal required in the body of the weld to replace that broken or cut away and also to add to the joint whenever possible so that the work may have the same or greater strength than that found in the original piece. A rod of the same material as
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 53
that being welded is used when both parts of the work are the same. When dissimilar metals are to be joined x rods of a composition suited to the work are em- ployed.
These filling rods are required in all work except steel of less than 16 gauge. Alloy iron rods are usedV for cast iron. These rods have a high silicon content, the silicon reacting with the carbon in the iron to produce a softer and more easily machined weld than would otherwise be the case. These rods are often made so that they melt at a slightly lower point than cast iron. This is done for the reason that when the part being welded has been brought to the fusing heat by the torch, the filling material can be instantly melted in without allowing the parts to cool. The metal can be added faster and more easily controlled.
Rods or wires of Jforwyron are used for steel
^
welding in almost all cases. The purity of this grade 1 of iron gives a homogeneous, soft weld of even texture, great ductility and exceptionally good machining qualities. For welding heavy steel castings, a rod of rolled carbon steel is employed. For working on high carbon steel, a rod of the steel being welded must be employed and for alloy steels, such as nickel, man- ganese, vanadium, etc., special rods of suitable alloy composition are preferable.
Aluminum welding rods are made from this metal
alloyed to give the even flowing that is essential.
< Aluminum is one of the most difficult of all the metals
to handle in this work and the selection of the proper
rod is of great importance.
Brass is filled with brass wire when in small cast- ings and sheets. For general work with brass castings, manganese bronze or Tobin bronze may be used.
54 WELDING
Bronze is welded with manganese bronze or Tobin bronze, while copper is filled with copper wire.
These welding rods should always be used to fill the weld when the thickness of material makes their employment necessary, and additional metal should always be added at the weld when possible as the joint cannot have the same strength as the original piece if made or dressed off flush with the surfaces around the weld. This is true because the metal welded into the joint is a casting and will never have more strength than a casting of the material used for filling.
Great care should be exercised when adding metal from welding rods to make sure that no metal is added at a point that is not itself melted and molten when the addition is made. When molten metal is placed upon cooler siirfaces the result is not a weld but merely a sticking together of the two parts with- out any strength in the joint.
FLUXES
Difficulty would be experienced in welding with only the metal and rod to work with because of the scale that forms on many materials under heat, the oxides of other metals and the impurities found in almost all metals. These things tend to prevent a perfect joining of the metals and some means are necessary to prevent their action.
Various chemicals, usually in powder form, are used to accomplish the result of cleaning the weld and making the work of the operator less difficult. They are called fluxes.
^ A flux is used to float off physical impurities from the molten metal; to furnish a protecting coating
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 55
around the weld ; to assist in the removal of any ob- jectionable oxide of the metals being handled ; to lower the temperature at which the materials flow ; to make a cleaner weld and to produce a better quality of metal in the finished work.
The flux must be of such composition that it will accomplish the desired result without introducing new difficulties. They may be prepared by the oper- ator in many cases or may be secured from the mak- ers of welding apparatus, the same remarks applying to their quality as were made regarding the welding rods, that is, only the best should be considered. 4-The flux used for cast iron should have a softening effect and should prevent burning of the metal. In many cases it is possible and even preferable to weld cast iron without the use of a flux, and in any event the smaller the quantity used the better the result should be. Flux should not be added just before the completion of the work because the heat will not have time to drive the added elements out of the metal or to incorporate them with the metal properly.
/Aluminum should never be welded without using a flux because of the oxide formed. This oxide, called alumina, does not melt until a heat of 5,000° Fahren- heit is reached, four times the heat needed to melt the aluminum itself. It is necessary that this oxide be broken down or dissolved so that the aluminum may have a chance to flow together. Copper is another metal that requires a flux because of its rapid, oxida- tion under heat.
While the flux is often thrown or sprinkled along the break while welding, much better results will be obtained by dipping the hot end of the welding rod into the flux whenever the work needs it. Suffi-
56 WELDING
cient powder will stick on the end of the rod for all ) purposes, and with some fluxes too much will adhere. Care should always be used to avoid the application of excessive flux, as this is usually worse than using too little.
SUPPLIES AND FIXTURES
Goggles. — The oxy-acetylene torch should not be used without the protection to the eyes afforded by goggles. These not only relieve unnecessary strain, but make it much easier to watch the exact progress of the work with the molten metal The difficulty of protecting the sight while welding is even greater than when cutting metal with the torch.
Acetylene gives a light which is nearest to sunlight of any artificial illuminant. But for the fact that this gas light gives a little more green and less blue in its composition, it would be the same in quality and practically the same in intensity. This light from the gas is almost abseqt during welding, being lost with the addition of the) extra oxygen needed to produce the welding heat. * The light that is dan- gerous comes from the molten metal which flows under the torch at a bright white heat.
Goggles for protection against this light and the heat that goes with it may be secured in various tints, the darker glass being for welding and the lighter for cutting. Those having frames in which the metal parts do not touch the flesh directly are most desirable because of the high temperature reached by these parts.
Gloves. — While not as necessary as are the goggles, gloves are a convenience in many cases. Those in which leather touches the hands directly are really
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 57
of little value as the heat that protection is desired against makes the leather so hot that nothing is gained in comfort. Gloves are made with asbestos cloth, which are not open to this objection in so great a degree.
Figure 9. — Frame for Welding Stand
Tables and Stands. — Tables for holding work while being welded (Figure 9) are usually made from lengths of angle steel welded together. The top should be rectangular, about two feet wide and two and one- half feet long. The legs should support the working surface at a height of thirty-two to thirty-six inches from the floor. Metal lattice work may be fastened or laid in the top framework and used to support a layer of firebrick bound together with a mixture of one-third cement and two-thirds fireclay. The piece being welded is braced and supported on this table with pieces of firebrick so that it will remain station- ary during the operation.
58 WELDING
Holders for supporting the tanks of gas may be made or purchased in forms that rest directly on the floor or that are mounted on wheels. These holders are quite useful where the floor or ground is very uneven.
Hose. — All permanent lines from tanks and gener- ators to the torches are made with piping rigidly sup- ported, but the short distance from the end of the pipe line to the torch itself is completed with a flexi- ble hose so that the operator may be free in his move- ments while welding. An accident through which the gases mix in the hose and are ignited will burst this part of the equipment, with more or less painful re- sults to the person handling it. For that reason it is well to use hose with great enough strength to with- stand excessive pressure.
A poor grade of hose will also break down inside and clog the flow of gas, both through itself and through the parts of the torch. To avoid outside dam- age and cuts this hose is sometimes encased with coiled sheet metal. Hose may be secured with a burst- ing strength of more than 1,000 pounds to the square inch. Many operators prefer to distinguish between the oxygen and acetylene lines by their color and to allow this, red is used for the oxygen, and bla£k_Jor acetylene.
Other Materials. — Sheet asbestos and asbestos fibre in flakes are used to cover parts of the work while pre- paring them for welding and during the operation kself. The flakes and small pieces that become de- tached from the large sheets are thrown into a bin where the completed small work is placed to allow slow and even cooling while protected by the asbestos.
Asbestos fibre and also ordinary fireclay are often
OXY-ACETYLENE WELDING AND CUTTING MATERIALS 59
used to make a backing or mould into a form that may be placed behind aluminum and some other metals that flow at a low heat and which are accord- ingly difficult to handle under ordinary methods. This forms a solid mould into which the metal is prac- tically cast as melted by the torch so that the desired shape is secured without danger of the walls of metal breaking through and flowing away.
Carbon blocks and rods are made in various shapes and sizes so that they may be -used to fill threaded holes and other places that it is desired to protect during welding. These may be secured in rods of various diameters up to one inch and in blocks of several different dimensions.
CHAPTER III ACETYLENE GENERATORS
Acetylene generators used for producing the gas from the action of water on calcium carbide are di- vided into three principal classes according to the pressure under which they operate.
Low pressure generators are designed to operate at one pound or less per square inch. Medium pressure systems deliver the gas at not to exceed fifteen pounds to the square inch while high pressure types furnish gas above fifteen pounds per square inch. High pressure systems are almost unknown in this country, the medium pressure type being often referred to as "high pressure."
Another important distinction is formed by the method of bringing the carbide and water together. The majority of those now in use operate by drop- ping small quantities of carbide into a large volume of water, allowing the generated gas to bubble up through the water before being collected above the surface. This type is known as the "carbide to water " generator.
A less used type brings a measured and small quan- tity of water to a comparatively large body of the carbide, the gas being formed and collected from the chamber in which the action takes place. This is called the "water to carbide77 type. Another way of expressing the difference in feed is that of desig- nating the two types as "carbide feed'7 for the former and "water feed77 for the latter.
60
ACETYLENE GENERATORS 61
A further division of the carbide to water ma- chines is made by mentioning the exact method of feeding the carbide One type, called "gravity feed" operates by allowing the carbide to escape and fall by the action of its own weight, or gravity; the other type, called "forced feed," includes a separate mech- anism driven by power This mechanism feeds defi- nite amounts of the carbide to the water as required by the demands on the generator. The action of either feed is controlled by the withdrawal of gas from the generator, the aim being to supply suffi- cient carbide to maintain a nearly constant supply.
Generator Requirements. — The qualities of a good generator are outlined as follows :*
It must allow no possibility of the existence of an explosive mixture in any of its parts at any time. It is not enough to argue that a mixture, even if it exists, cannot be exploded unless kindled. It is necessary to demand that a dangerous mixture can at no time be formed, even if the machine is tampered with by an ignorant person. The perfect machine must be so constructed that it shall be impossible at any time, under any circumstances, to blow it up.
It must insure cool generation. Since this is a rela- tive term, all machines being heated somewhat dur- ing the generation of gas, this amounts to saying that a machine must heat but little. A pound of carbide decomposed by water develops the same amount of heat under all circumstances, but that heat can be allowed to increase locally to a high point, or it can be equalized by water so that no part of the material becomes heated enough to do damage.
r See Pond's "Calcium Carbide and Acetylene."
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It must be well constructed. A good generator does not need, perhaps, to be ' ' built like a watch, ' ' but it should be solid, substantial and of good material. It should be built for service, to last and not simply to sell; anything short of this is to be avoided as unsafe and unreliable.
It must be simple. The more complicated the ma- chine the sooner it will get out of order. Understand your generator. Know what is inside of it and be- ware of an apparatus, however attractive its exterior, whose interior is filled with pipes and tubes, valves and diaphragms whose functions you do not per- fectly understand.
It should be capable of being cleaned and re- charged and of receiving all other necessary atten- tion without loss of gas, both for economy 's sake, and more particularly to avoid danger of fire.
It should require little attention. All machines have to be emptied and recharged periodically; but the more this process is simplified and the more quickly this can be accomplished, the better.
It should be provided with a suitable indicator to designate how low the charge is in order that the refilling may be done in good season.
It should completely use up the carbide, generat- ing the maximum amount of gas.
Overheating. — A large amount of heat is liberated when acetylene gas is formed from the union of cal- cium carbide and water. Overheating during this process, that is to say, an intense local heat rather than a large amount of heat well distributed, brings about the phenomenon of polymerization, converting the gas, or part of it, into oily matters, which can do nothing but harm. This tarry mass coming through
ACETYLENE GENERATORS 63
the small openings in the torches causes them to be- come partly closed and alters the proportions of the gases to the detriment of the welding flame. The only remedy for this trouble is to avoid its cause and secure cool generation.
Overheating can be detected by the appearance of the sludge remaining after the gas has been made. Discoloration, yellow or brown, shows that there has been trouble in this direction and the resultant effects at the torches may be looked for. The abundance of water in the carbide to water machines effects this cooling naturally and is a characteristic of well de- signed machines of this class. It has been found best and has practically become a fundamental rule of generation that a gallon of water must be provided for each pound of carbide placed in the generator. With this ratio and a generator large enough for the number of torches to be supplied, little trouble need be looked for with overheating.
Water to Carbide Generators. — It is, of course, much easier to obtain a measured and regular flow of water than to obtain such a flow of any solid sub- stance, especially when the solid substance is in the form of lumps, as is carbide This fact led to the use of a great many water-feed generators for all classes of work, and this type is still in common use for the small portable machines, such, for instance, as those used on motor cars for the lamps. The water-feed machine is not, however, favored for welding plants, as is the carbide feed, in spite of the greater difficul- ties attending the handling of the solid material.
A water-feed generator is made up of the gas pro- ducing part and a holder for the acetylene after it is made. The carbide is held in a tray formed of a
64 WELDING
number of small compartments so that the charge in each compartment is nearly equal to that in each of the others. The water is allowed to flow into one of these compartments in a volume sufficient to pro- duce the desired amount of gas and the carbide is completely used from this one division. The water then floods the first compartment and finally over- flows into the next one, where the same process is repeated. After using the carbide in this division, it is flooded in turn and the water passing on to those next in order, uses the entire charge of the whole tray.
These generators are charged with the larger sizes of carbide and are easily taken care of. The residue is removed in the tray and emptied, making the gen- erator ready for a fresh supply of carbide.
Carbide to Water Generators. — This type also is made up of two principal parts, the generating cham- ber and a gas holder, the holder being part of the generating chamber or a separate device. The gen- erator (Figure 10) contains a hopper to receive the charge of carbide and is fitted with the feeding mech- anism to drop the proper amount of carbide into the water as required by the demands of the torches. The charge of carbide is of one of the smaller sizes, usually "nut" or "quarter."
Feed Mechanisms. — The device for dropping the carbide into the water is the only part of the machine that is at all complicated. This complication is brought about by the necessity of controlling the mass of carbide so that it can never be discharged into the water at an excessive rate, feeding it at a regular rate and in definite amounts, feeding it posi- tively whenever required and shutting off the feed
ACETYLENE GENERATORS
65
just as positively when the supply of gas in the holder is enough for the immediate needs.
The charge of carbide is unavoidably acted upon by the water vapor in the generator and will in time
til
n «••••* O
become more or less pasty and sticky. This is more noticeable if the generator stands idle for a consider- able length of time This condition imposes another duty on the feeding mechanism ; that is, the necessity of self-cleaning so that the carbide, no matter in what
66 WELDING
condition, cannot prevent the positive action of this part of the device, especially so that it cannot prevent the supply from being stopped at the proper time.
The gas holder is usually made in the bell form so that the upper portion rises and falls with the addition to or withdrawal from the supply of gas in the holder. The rise and fall of this bell is often used to control the feed mechanism because this movement indicates positively whether enough gas has been made or that more is required. As the bell lowers it sets the feed mechanism 'in motion, and when the gas passing into the holder has raised the bell a sufficient distance, the movement causes the feed mechanism to stop the fall of carbide into the water. In practice, the movement of this part of the holder is held within very narrow limits.
Gas Holders. — No matter how1 close the adjustment of the feeding device, there will always be a slight amount of gas made after the fall of carbide is stopped, this being caused by the evolution of gas from the carbide with which water is already in con- tact. This action is called " after generation" and the gas holder in any type of generator must provide sufficient capacity to accommodate this excess gas. As a general rule the water -to carbide generator requires a larger gas holder than the carbide to water type because of the greater amount of carbide being acted upon by the water at any one time, also be- cause the surface of carbide presented to the moist air within the generating chamber is greater with this type.
Freezing. — Because of the rather large body of water contained in any type of generator, there is always danger of its freezing and rendering the
ACETYLENE GENERATORS 67
device inoperative unless placed in a temperature above the freezing point of the water. It is, of course, dangerous and against the insurarce rules to place a generator in the same room with a fire of any kind, but the room may be heated by steam or hot water coils from a furnace in another building or in another part of the same building.
When the generator is housed in a separate struc- ture the walls should be made of materials or con- struction that prevents the passage of heat or cold through them to any great extent. This may be accomplished by the use of hollow tile or concrete blocks or by any other form of double wall providing air spaces between the outer and inner facings. The space between the parts of the wall may be filled with materials that further retard the loss of heat if this is necessary under the conditions prevailing.
Residue From Generators. — The sludge remaining in the carbide to water generator may be drawn off into the sewer if the piping is run at a slant great enough to give a fall that carries the whole quantity, both water and ash, away without allowing settling and consequent clogging. Generators are provided with agitators which are operated to stir the ash up with the water so that the whole mass is carried off when the drain cock is opened.
If sewer connections cannot be made in such a way that the ash is entirely carried away, it is best to run the liquid mass into a settling basin outside of the building. This should be in the form of a shallow pit which will allow the water to pass off by soaking into the ground and by evaporation, leaving the comparatively dry ash in the pit. This ash which remains is essentially slaked lime and can often be
68 WELDING
disposed of to more or less advantage to be used in mortar, whitewash, marking paths and any other use for which slaked lime is suited. The disposition of the ash depends entirely on local conditions. An average analysis of this ash is as follows :
Sand 1.10 per cent.
Carbon 2.72
Oxide of iron and alumina. . 2.77
Lime 64.06
Water and carbonic acid. . . 29.35 "
Toooo
GENERATOR CONSTRUCTION
The water for generating purposes is carried in the large tank-like compartment directly below the car- bide chamber. See Figure 11. This water compart- ment is filled through a pipe of such a height that the water level cannot be brought above the proper point or else the water compartment is provided with a drain connection which accomplishes this same re- sult by allowing an excess to flow away.
The quantity of water depends on the capacity of the generator inasmuch as there must be one gallon for each pound of carbide required. The generator should be of sufficient capacity to furnish gas under working conditions from one charge of carbide to all torches installed for at least five hours continuous use.
After calculating the withdrawal of the whole number of torches according to the work they are to do for this period of five hours the proper gen-
ACETYLENE GENERATORS 69
erator capacity may be found on the basis of one cubic foot of gas per hour for each pound of carbide. Thus if the torches were to use sixty cubic feet of gas per hour, five hours would call for three hundred cubic feet and a three hundred pound generator should be installed. Generators are rated according to their carbide capacity in pounds.
Charging. — The carbide capacity of the generator should be great enough to furnish a continuous sup- ply of gas for the maximum operating time, basing the quantity of gas generated on four and one-half cubic feet from each pound of lump carbide and on four cubic feet from each pound of quarter, inter- mediate sizes being in proportion.
Generators are built in such a way that it is impos- sible for the- acetylene to escape from the gas holding: compartment during the recharging process. This is accomplished (1) by connecting the water inlet pipe opening with a shut off valve in such a way that the inlet cannot be uncovered or opened without first closing the shut off valve with the same move- ment of the operator; (2) by incorporating an auto- matic or hydraulic one-way valve so that this valve closes and acts as a check when the gas attempts to flow from the holder back to the generating chamber, or by any other means that will positively accomplish this result.
In generators having no separate gas holding chamber but carrying the supply in the same com- partment in which it is generated, the gas contained under pressure is allowed to escape through vent pipes into the outside air before recharging with carbide. As in the former case, the parts are so interlocked that it is impossible to introduce carbide
70 WELDING
or water without first allowing the escape of the gas in the generator.
It is required by the insurance rules that the entire change of carbide while in the generator be held in such a way that it may be entirely removed without difficulty in case the necessity should arise.
Generators should be cleaned and recharged at regular stated intervals. This work should be done during daylight hours only and likewise all repairs should be made at such a time that artificial light is not needed. Where it is absolutely necessary to use artificial light it should be provided only by incandescent electric lamps enclosed in gas tight globes.
In charging generating chambers the old ash and all residue must first be cleaned out and the operator should be sure that no drain or other pipe has become clogged. The generator should then be filled with the required amount of water. In charging carbide feed machines be careful not to place less than a gallon of water in the water compartment for each pound of carbide to be used and the water must be brought to, but not above, the proper level as indi- cated by the mark or the maker's instructions. The generating chamber must be filled with the proper amount of water before any attempt is made to place the carbide in its holder. This rule must always be followed. It is also necessary that all automatic water seals and valves, as well as any other water tanks, be filled with clean water at this time.
Never recharge with carbide without first cleaning the generating chamber and completely refilling with clean water. Never test the generator or piping for leaks with any flame, and never apply flame to any
ACETYLENE GENERATORS 71
open pipe or at any point other than the torch, and only to the torch after it has a welding or cutting nozzle attached. Never use a lighted match, lamp, candle, lantern, cigar or any open flame near a gen- erator. Failure to observe these precautions is liable to endanger life and property.
Operation and Care of Generators. — The following instructions apply especially to the Davis Bournon- ville pressure generator, illustrated in Figure 11. The motor feed mechanism is illustrated in Figure 12.
Before filling the machine,, the cover should be removed and the hopper taken out and examined to see that the feeding disc revolves freely; that no chains have been displaced or broken, and that the carbide displacer itself hangs barely free^of the feed- ing disc when it is revolved. After replacing the cover, replace the bolts and tighten them equally, a little at a time all around the circumference of the cover — not screwing tight in one place only. Do not screw the cover down any more than is necessary to make a tight fit.
To charge the generator, proceed as follows : Open the vent valve by turning the handle which extends over the filling tube until it stands at a right angle with the generator. Open the valve in the water filling pipe, and through this fill with water until it runs out of the overflow pipe of the drainage cham- ber ; then close the valve in the water filling pipe and vent valve. Remove the carbide filling plugs and fill the hopper with li/4"x%" carbide ("nut" size). Then replace the plugs and the safety-locking lever chains. Now rewind the motor weight. Run the pressure up to about five pounds by raising the con- trolling diaphragm valve lever by hand (Figure 12,
72
WELDING
lever marked E). Then raise the blow-off lever, allowing the gas to blow off until the gauge shows about two pounds; this to clear the generator of air mixture. Then run the pressure up to about eight
Figure 11. — Pressure Generator (Davis Bournonville). A, Feed motor weight; B, Carbide feed motor; C, Motor control diaphragm; D, Carbide hopper ; E, Carbide feed disc ; F, Overflow pipe ; G, Over- flow pipe seal ; H, Overflow pipe valve ; J, Filling funnel ; K, Hydraulic valve ; L, Expansion chamber ; M , Escape pipe ; N, Feed pipe ; O, Agitator for residuum ; P3 Residuum valve ; Q, Water level
ACETYLENE GENERATORS 73
pounds by raising the controlling valve lever E, or until this controlling lever rests against the upper wing of the fan governor, and prevents operation of the feed motor. After this is done, ,the motor will operate automatically as the gas is consumed.
Should the pressure rise much above the blow-off point, the safety controlling diaphragm valve will operate and throw the safety clutch in interference
Figure 12. — Feed Mechanism of Pressure Generator
and thus stop the motor. This interference clutch will then have to be returned to its former position before the motor will operate, but cannot be replaced before the pressure has been reduced below the blow- off point.
The parts of the feed mechanism illustrated in Figure 12 are as follows : A, motor drum for weight cable. B, carbide filling plugs. C, chains for con- necting safety locking lever of motor to pins on the- top of the carbide plugs. D, interference clutch of motor. E, lever on feed controlling diaphragm valve.
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F, lever of interference controlling diaphragm valve that operates interference clutch. G, feed controlling diaphragm valve. H, diaphragm valve controlling operation of interference clutch. I, interference pin to engage emergency clutch. J, main shaft driving carbide feeding disc. Y, safety locking lever.
Recharging Generator. — Turn the agitator handle rapidly for several revolutions, and then open the residuum valve, having five or six pounds gas pres- sure on the machine. If the carbide charge has been exhausted and the motor has stopped, there is gen- erally enough carbide remaining in the feeding disc that can be shaken off, and fed by running the motor to obtain some pressure in the generator. The desir- ability of discharging the residuum with some gas pressure is because the pressure facilitates the dis- charge and at the same time keeps the generator full of gas, preventing air mixture to a great extent. As soon as the pressure is relieved by the withdrawal of the residuum, the vent valve should be opened, as if the pressure is maintained until all of the residuum is discharged gas would escape through the discharge valve.
Having opened the vent pipe valve and relieved the pressure, open the valve in the water filling tube. Close the residuum valve, then run in several gallons of water and revolve the agitator, after which draw out the remaining . residuum ; then again close the residuum valve and pour in water until it discharges from the overflow pipe of the drainage chamber. It is desirable in filling the generator to pour the wTater in rapidly enough to keep the filling pipe full of water, so that air will not pass in at the same time.
After the generator is cleaned and filled with
ACETYLENE GENERATORS 75
water, fill with carbide and proceed in the same man- ner as when first charging.
Carbide Feed Mechanism. — Any form of carbide to water machine should be so designed that the car- bide never falls directly from its - holder into the water, but so that it must take a more or less cir- cuitous path. This should be true, no matter what position the mechanism is in. One of the commonest types of forced feed machine carries the carbide in a hopper with slanting sides, this hopper having a large opening in the bottom through which the car- bide passes to a revolving circular plate. As the pieces of carbide work out toward the edge of the plate under the influence of the mass behind them, they are thrown off into the water by small stationary fins or plows which are in such a position that they catch the pieces nearest the edges and force them off as the plate revolves. This arrangement, while allowing a free passage for the carbide, prevents an excess from falling should the machine stop in any position.
When, as is usually the case, the feed mechanism is actuated by the rise or fall of pressure in the generator or of the level of some part of the gas holder, it must be built in such a way that the feed- ing remains inoperative as long as the filling opening on the carbide holder remains open.
The feed of carbide should always be shut off and controlled so that under no condition can more gas be generated than could be cared for by the relief valve provided. It is necessary also to have the feed mechanism at least ten inches above the surface of the water so that the parts will never become clogged with damp lime dust.
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Motor Feed. — The feed mechanism itself is usually operated by power secured from a slowly falling weight which, through a cable, revolves a drum. To this drum is attached suitable gearing for moving the feed parts with sufficient power and in the way desired. This part, called the motor, is controlled by two levers, one releasing a brake and allowing the motor to operate the feed, the other locking the gear- ing so that no more carbide will be dropped into the water. These levers are moved either by the quantity of gas in the holder or by the pressure of the gas, depending on the type of machine.
With a separate gas holder, such as used with low pressure systems, the levers are operated by the rise and fall of the bell of the holder or gasometer, alter- nately starting and stopping the motor as the bell falls and rises again. Medium pressure generators are provided with a diaphragm to control the feed motor.
This diaphragm is carried so that the pressure within the generator acts on one side while a spring, whose tension is under the control of the operator, acts on the other side. The diaphragm is connected to the brake and locking device on the motor in such a way that increasing the tension on the spring presses the diaphragm and moves a rod that releases the brake and starts the feed. The gas pressure, increasing with the continuation of carbide feed, acts on the other side and finally overcomes the pressure of the spring tension, moving the control rod the other way and stopping the motor and carbide feed. This spring tension is adjusted and checked with the help of a pressure gauge attached to the generating chamber.
Gravity Feed. — This type of feed differs from the
ACETYLENE GENERATORS 77
foregoing in that the carbide is simply released and is allowed to fall into the water without being forced to do so. Any form of valve that is sufficiently powerful in action to close with the carbide passing through is used and is operated by the power secured from the rise and fall of the gas holder bell. When this valve is first opened the carbide runs into the water until sufficient pressure and volume of gas is generated to raise the bell. This movement operates the arm attached to the carbide shut off valve and slowly closes it. A fall of the bell occasioned by gas being withdrawn again opens the valve and more gas is generated.
Mechanical Feed. — The previously described meth- ods of feeding carbide to the water have all been automatic in action and do not depend on the oper- ator for their proper action.
Some types of large generating plants have a power-driven feed, the power usually being from some kind of motor other than one operated by a weight, such as a water motor, for instance This motor is started and stopped by the operator when, in his judgment, more gas is wanted or enough has been generated. This type of machine, often called a "non-automatic generator," is suitable for large installations and is attached to a gas holder of suffi- cient size to hold a day's supply of acetylene. The generator can then be operated until a quantity of gas has been made that will fill the large holder, or gasometer, and then allowed to remain idle for some time.
Gas Holders. — The commonest type of gas con- tainer is that known as a gasometer. This consists of a circular tank partly filled with water, into which
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is lowered another circular tank, inverted, which is made enough smaller in 'diameter than the first one so that three-quarters of an inch is left between them. This upper and inverted portion, called the bell, receives the gas from the generator and rises or falls in the bath of water provided in the lower tank as a greater or less amount of gas is contained in it.
These holders are made large enough so that they will provide a means of caring for any after genera- tion and so that they maintain a steady and even flow. The generator, however, must be of a capacity great enough so that the gas holder will not be drawn on for part of the supply with all torches in opera- tion. That is, the holder must not be depended on for a reserve supply.
The bell of the holder is made so that when full of gas its lower edge is still under a depth of at least nine inches of water in the lower tank. Any further rise beyond this point should always release the gas, or at least part of it, to the escape pipe so that the gas will under no circumstances be forced into the room from between the bell and tank. The bell is guided in its rise and fall by vertical rods so that it will not wedge at any point in its travel.
A condensing chamber to receive the water which condenses from the acetylene gas in the holder is usually placed under this part and is provided with a drain so that this water of condensation may be easily removed.
Filtering. — A small chamber containing some closely packed but porous material such as felt is placed in the pipe leading to the torch lines. As the acetylene gas passes through this filter the parti- cles of lime dust and other impurities are extracted
ACETYLENE GENERATORS
79
from it so that danger of clogging the torch openings is avoided a's much as possible.
The gas is also filtered to a large extent by its passage through the water in the generating chamber, this filtering or "scrubbing" often being facilitated by the form of piping through which the gas must pass from the generating chamber into the holder. If the gas passes out of a number of small openings when going into the holder the small bubbles give a better washing than large ones would.
Piping. — Connections from generators to service pipes should preferably be made with right and left couplings or long thread nipples with lock nuts. If unions are used, they should be of a type. that does not require gaskets. The piping should be carried and supported so that any moisture condensing in the lines will drain back toward the generator and where low points occur they should be drained through tees leading into drip cups which are per- manently closed with screw caps or plugs. No pet cocks should be used for this purpose.
For the feed pipes to the torch lines the following pipe sizes are recommended. % inch pipe. 26 feet long. 3/2 inch pipe. 30 feet long. % inch pipe. 50 feet long.
1 inch pipe. 70 feet long. 1% inch pipe. 100 feet long. iy2 inch pipe. 150 feet long.
2 inch pipe. 200 feet long. 125 cubic feet per hour. 2y2 inch pipe. 300 feet long. 190 cubic feet per hour.
3 inch pipe. 450 feet long. 335 cubic feet per hour. When drainage is possible into a sewer, the gen- erator should not be connected directly into the sewer
2 cubic feet per hour.
4 cubic feet per hour. 15 cubic feet per hour. 27 cubic feet per hour. 50 cubic feet per hour. 65 cubic feet per hour.
80 WELDING
but should first discharge into an open receptacle, which may in turn be connected to the sewer.
No valves or pet cocks should open into the gen- erator room or any other room when it would be possible, by opening them for draining purposes, to allow any escape of gas. Any condensation must be removed without the use of valves or other work- ing parts, being drained into closed receptacles. It should be needless to say that all the piping for gas must be perfectly tight at every point in its length.
Safety Devices. — Good generators are built in such a way that the operator must follow the proper order of operation in charging and cleaning as well as in all other necessary care. It has been mentioned that the gas pressure is released or shut off before it is possible to fill the water compartment, and this same idea is carried further in making the generator inop- erative and free from gas pressure before opening the residue drain of the carbide filling opening on top of the hopper. Some machines are made so that they automatically cease to generate should there be a sudden and abnormal withdrawal of gas such as would be caused by a bad leak. This method of adding safety by automatic means and interlocking parts may be carried to any extent that seems desir- able or necessary to the maker.
All 'generators should be provided with escape or relief pipes of large size which lead to the open air. These pipes are carried so that condensation will drain back toward the generator and after being led out of the building to a point at least twelve feet above ground, they end in a protecting hood so that no rain or solid matter can find its way into them. Any escape of gas which might ordinarily pass into
ACETYLENE GENERATORS 81
the generator room is led into these escape pipes, all parts of the system being connected with the pipe so that the gas will find this way out.
Safety blow off valves are provided so that any excess gas which cannot be contained by the gas holder may be allowed to escape without causing an undue rise in pressure. This valve also allows the escape of pressure above that for which the generator was designed. Gas released in this way passes into the escape pipe just described.
Inasmuch as the pressure of the oxygen is much greater than that of the acetylene when used in the torch, it will be seen that anything that caused the torch outlet to become closed would allow the oxygen to force the acetylene back into the generator and the oxygen would follow it, making a very explosive mixture. This return of the gas is prevented by a hydraulic safety valve or back pressure valve, as it is often called.
Mechanical check valves have been found unsuit- able for this use and those which employ water as a seal are now required by the insurance rules. The valve itself (Figure 13) consists of a large cylinder containing water to a certain depth, which is indi- cated on the valve body. Two pipes come into the upper end of this cylinder and lead down into the water, one being longer than the other. The shorter pipe leads to the escape pipe mentioned above, while the longer one comes from the generator. The upper end of the cylinder has an opening to which is at- tached the pipe leading to the torches.
The gas coming from the generator through the longer pipe passes out of the lower end of the pipe which is under water and bubbles up through the
WELDING
Figure 13. — Hydraulic B a c k- Pressure Valve. A, Acetylene sup- ply line; B, Vent pipe; C, Water filling plug; D, Acetylene service cock; E, Plug to gaa^e height of water ; F, Gas openings under water ; G, Return pipe for sealing water ; H, Tube to carry gas be- low water line ; /,, Tube to carry gas to escape pipe ; J ' , Gas cham- ber ; K, Plug in upper gas cham- ber ; L, Hish water level ; M, Opening through which water re- turns ; O, Bottom clean out cast- ing
ACETYLENE GENERATORS 83
water to the space in the top of the cylinder. From there the gas goes to the pipe leading to the torches. The shorter pipe is closed by the depth of water so that the gas does not escape to the relief pipe. As long as the gas flows in the normal direction as de- scribed there will be no escape to the air. Should the gas in the torch line return into the hydraulic valve its pressure will lower the level of water in the cylinder by forcing some of the liquid up into the two pipes. As the level of the water lowers, the shorter pipe will be uncovered first, and as this is the pipe leading to the open air the gas will be allowed to escape, while the pipe leading back to the generator is still closed by the water seal. As soon as this reverse flow ceases, the water will again resume its level and the action will continue. Because of the small amount of water blown out of the escape pipe each time the valve is called upon to perform this duty, it is necessary to see that the correct water level is always maintained.
AVhile there are modifications of this construction, the same principle is used in all types. The pressure escape valve is often attached to this hydraulic valve body.
Construction Details. — Flexible tubing (except at torches), swring pipe joints, springs, mechanical check valves, chains, pulleys and lead or fusible piping should never be used on acetylene apparatus except where the failure of those parts will not affect the safety of the machine or permit, either directly or indirectly, the escape of gas into a room. Floats should not be used except where failure will only render the machine inoperative.
It should be said that the National Board of Fire
84. WELDING
Underwriters have established an inspection service for acetylene generators and any apparatus which bears their label, stating that that particular model and type has been passed, is safe to use. This service is for the best interests of all concerned and looks toward the prevention of accidents. Such inspection is a very important and desirable feature of any outfit and should be insisted upon.
Location of Generators. — Generators should pref- erably be placed outside of insured buildings and in properly constructed generator houses. The oper- ating mechanism should have ample room to work in and there should be room enough for the attendant to reach the various parts and perform the required duties without hindrance or the need of artificial light. They should also be protected from tampering by unauthorized persons.
Generator houses should not be within five feet of any opening into, nor have any opening toward, any adjacent building, and should be kept under lock and key. The size of the house should be no greater than called for by the requirements mentioned above and it should be well ventilated.
The foundation for the generator itself should be of brick, stone, concrete or iron, if possible. If of wood, they should be extra heavy, located in a dry- place and open to circulation of air. A board plat- form is not satisfactory, but the foundation should be of heavy planking or timber to make a firm base and so that the air can circulate around the wood.
The generator should stand level and no strain should be placed on any of the pipes or connections or any parts of the generator proper.
CHAPTER IV
WELDING INSTRUMENTS
VALVES
Tank Valves. — The acetylene tank valve is of the needle type, fitted with suitable stuffing box nuts and ending1 in an exposed square shank to which the special wrench may be fitted when the valve is to be opened or closed.
The valve used on Linde oxygen cylinders is also a needle type, but of slightly more complex construc- tion. The body of the valve, which screws into the top of the cylinder, has an opening below through which the gas comes from the cylinder, and another opening on the side through which it issues to the torch line. A needle screws down from above to close this lower opening. The needle which closes the valve is not connected directly to the threaded member, but fits loosely into it. The threaded part is turned, by a small hand wheel attached to the upper end. "When this hand wheel is turned to the left, or up, as far as it will go, opening the valve, a rubber disc is compressed inside of the valve body and this disc serves to prevent leakage of the gas around the spindle.
The oxygen valve also includes a safety nut having a small hole through it closed by a fusible metal which melts at 250° Fahrenheit. Melting of this plug allows the gas to exert its pressure against a thin copper diaphragm, this diaphragm bursting under the gas pressure and allowing the oxygen to escape into the air.
85
86
WELDING
The hand wheel and upper end of the valve mech- anism are protected during shipment by a large steel cap which covers them when screwed on to the end of the cylinder. This cap should always be in place when tanks are received from the makers or returned to them.
>*IGH PRESSURE GAUGE CON-
CONNECTION TO OXYGEN CYLINOCR
Figure 14. — Regulating Valve
Regulating Valves. — While the pressure in the gas containers may be anything from zero to 1,800 pounds, and will vary as the gas is withdrawn, the pressure of the gas admitted to the torch must be held steady and at a definite point. This is accom- plished .by various forms of automatic regulating valves, which, while they differ somewhat in details of construction, all operate on the same principle.
The regulator body (Figure 14) carries a union which attaches to the side outlet on the oxygen tank valve. The gas passes through this union, following
WELDING INSTRUMENTS 87
an opening which leads to a large gauge which regis- ters the pressure on the oxygen remaining in the tank and also to a very small opening in the end of a tube. The gas passes through this opening and into the interior of the regulator body. Inside of the body is a metal or rubber diaphragm placed so that the pressure of the incoming gas causes it to bulge slightly. Attached to the diaphragm is a sleeve or an arm tipped writh a small piece of fibre, the fibre being placed so that it is directly opposite the small hole through which the gas entered the diaphragm chamber. The slight movement of the diaphragm draws the fibre tightly over the small opening through which the gas is entering, with the result that further flow is prevented.
Against the opposite side of the diaphragm is the end of a plunger. This plunger is pressed against the diaphragm by a coiled spring. The tension on the coiled spring is controlled by the operator through a threaded spindle ending in a wing or milled nut on the outside of the regulator body. Screwing in on the nut causes the tension on the spring to increase, with a consequent increase of pressure on the side of the diaphragm opposite to that on which the gas acts. Inasmuch as the gas pressure acted to close the small gas opening and the spring pressure acts in the oppo- site direction from the gas, it will be seen that the spring pressure tends to keep the valve open.
When the nut is turned way out there is, of course, no pressure on the spring side of the diaphragm and the first gas coming through automatically closes the opening through which it entered. If now the ten- sion on the spring be slightly increased, the valve will again open and admit gas until the pressure of
88 WELDINa
gas within the regulator is just sufficient to overcome the spring pressure and again close the opening. There will then be a pressure of gas within the regu- lator that corresponds to the pressure placed on the spring by the operator. An opening leads from the regulator interior to the torch lines so that all gas going to the torches is drawn from the diaphragm chamber.
Any withdrawal of gas will, of course, lower the pressure of that remaining inside the regulator. The spring tension, remaining at the point determined by the operator, will overcome this lessened pressure of the gas, and the valve will again open and admit enough more gas to bring the pressure back to the starting point. This action continues as long as the spring tension remains at this point and as long as any gas is taken from the regulator. Increasing the spring tension will require a greater gas pressure to close the valve and the pressure of that in the regu- lator will be correspondingly higher.
When the regulator is not "being used, the hand nut should be unscrewed until no tension remains on the spring, thus closing the valve. After the oxygen tank valve is open, the regulator hand nut is slowly screwed in until the spring tension is sufficient to give the required pressure in the torch lines. Another gauge is attached to the regulator so that it com- municates with the interior of the diaphragm cham- ber, this gauge showing the gas pressure going to the torch. It is customary to incorporate a safety valve in the regulator which will blow off at a dangerous pressure.
In regulating valves and tank valves, as well as all other parts with which the oxygen comes in con-
WELDING INSTRUMENTS
89
tact, it is not permissible to use any form of oil or grease because of danger of ignition and explosion. The mechanism of a regulator is too delicate to be handled in the ordinary shop and should any trouble or leakage develop in this part of the equipment it should be sent to a company familiar with this class of work for the necessary repairs. Gas must never be admitted to a regulator until the hand nut is all
Figure 15. — High and Low Pressure Gauges with Regulator
the way out, because of danger to the regulator itself and to the operator as well. A regulator can only be properly adjusted when the tank valve and torch valves are fully opened.
Acetylene regulators are used in connection with tanks of compressed gas. They are built on exactly the same lines as the oxygen regulating valve and operate in a similar way. One gauge only, the low pressure indicator, is used for acetylene regulators, although both high and low pressure may be used if desired. (See Figure 15.)
90 WELDING
TORCHES
Flame is always produced by the combustion of a gas with oxygen and in no other way. When we burn oil or candles or anything else, the material of the fuel is first turned to a gas by the heat and is then burned by combining with the oxygen of the air. If more than a normal supply of air is forced into the flame, a greater heat and more active burning follows. If the amount of air, and consequently oxy- gen, is reduced, the flame becomes smaller and weaker and the combustion is less rapid. A flame may be easily extinguished by shutting off all of its air supply.
The oxygen of the combustion only forms one-fifth of the total volume of air; therefore, if we were to supply pure oxygen in place of air, and in equal volume, the action would be several times as intense. If the oxygen is mixed with the fuel gas in the pro- portion that burns to the very best advantage, the flame is still further strengthened and still more heat is developed because of the perfect combustion. The greater the amount of fuel gas that can be burned in a certain space and within a certain time, the more heat will be developed from that fuel.'
The great amount of heat contained in acetylene gas, greater than that found in any other gaseous fuel, is used by leadfing this gas to the oxy-acetylene torch and there combining it with just the right amount of oxygen to make a flame of the greatest power and heat than can possibly be produced by any form of combustion of fuels of this kind. The heat developed by the flame is about 6300° Fahrenheit and easily melts all the metals, as well as other solids.
WELDING INSTRUMENTS 91
Other gases have been and are now being used in the torch. None of them, however, produce the heat that acetylene does, and therefore the oxy-acetylene process has proved the most useful of all. Hydrogen was used for many years before acetylene was intro- duced in this field. The oxy-hydrogen flame develops a heat far below that of oxy-acetylene, namely 4500'° Fahrenheit. Coal gas, benzine gas, blaugas and others have also been used in successful applications, but for the present we will deal exclusively with the acetylene fuel.
It was only with great difficulty that the obstacles in the way of successfully using acetylene were over- come by the development of practicable controlling devices and torches, as well as generators. At pres.- ent the oxy-acetylene process is the most universally adaptable, and probably finds the most widely ex- tended field of usefulness of any welding process.
The theoretical proportion of the gases for perfect combustion is two and one-half volumes of oxygen to one of acetylene. In practice this proportion is one and one-eighth or one* and one-quarter volumes of oxygen to one volume of acetylene, so that the cost is considerably reduced below what it would be if the theoretical quantity were really necessary, as oxygen costs much more than acetylene in all cases.
While the heat is so intense as to fuse anything brought into the path of the flame, it is localized in the small "welding cone" at the torch tip so that the torch is not at all difficult to handle without special protection except for the eyes, as already noted. The art of successful welding may be ac- quired by any operator of average intelligence within a reasonable time and with some practice. One
92 WELDING
trouble met with in the adoption of this process has been that the operation looks so simple and so easy of performance that unskilled and unprepared per- sons have been tempted to try welding, with results that often caused condemnation of the process, when the real fault lay entirely with the operator.
The form of torch usually employed is from twelve to twenty-four inches long and is composed of a handle at one end with tubes leading from this handle to the "welding head '^ or torch proper. At or near one end of the handle are adjustable cocks or valves for allowing the gases to flow into the tojrch or to prevent them from doing so. These cocks are often used for regulating the pressure and amount of gas flowing to the welding head, but are not always con- structed for this purpose and should not be so used when it is possible to secure pressure adjustment at the regulators (Figure 16).
Figure 16 shows three different sizes of torches. The number 5 torch is designed especially for jew- elers ' work and thin sheet steel welding. It is eleven inches in length and weighs nineteen ounces. The tips for the number 10 torch are interchangeable with the number 5. The number 10 torch is adapted for general use on light and medium heavy work. It has six tips and its length is sixteen inches, with a weight of twenty-three ounces.
The number 15 torch is designed for heavy work, being twenty-five inches in length, permitting the operator to stand away from the heat of the metal being worked. These heavy tips are in two parts, the oxygen check being renewable.
Figures 17 and 18 show two- sizes of another weld- ing torch. Still another type is shown in Figure 19
WELDING INSTRUMENTS
93
g
(-* O5
H tr
!
94
WELDING
with four interchangeable tips, the function of each being as fol]ows:
No. 1. For heavy castings.
No. 2. Light castings and heavy sheet metal.
No. 3. Light sheet metal.
No. 4. Very light sheet metal and wire.
4 3 3 t
Figure 17. — Cox Welding Torch (No. 1)
Figure 18. — Cox Welding Torch (No. 2)
Figure 19. — Monarch Welding Torch
At the side of the shut off cock away from the torch handle the gas tubes end in standard forms of hose
WELDING INSTRUMENTS 95
nozzles, to which the rubber hose from the gas supply tanks or generators can be attached. The tubes from the handle to the head may be entirely separate from each other, or one may be contained within the other. As a general rule the upper one of two separate tubes carries the oxygen, while this gas is carried in the inside tube when they are concentric with each other.
In the welding head is the mixing chamber de- signed to produce an intimate mixture of the two gases before they issue from the nozzle to the flame. The nozzle, or welding tip, of a suitable size and design for the work to be handled and the pressure of gases being used, is attached to the welding head, and consists essentially of the passage at the outer end of which the flame appears.
The torch body and tubes are usually made of brass, although copper is sometimes used. The joints must be very strong, and are usually threaded and soldered with silver solder. The nozzle proper is made from copper, because it withstands the heat of the flame better than other less suitable metals. The torch must be built in such a way that it is not at all liable to come apart under the influence of high temperatures.
All torches are constructed in such a way that it is impossible for the gases to mix by any possible chance before they reach the head, and the amount of gas contained in the head and tip after being mixed is made as small as possible. In order to prevent the return of the flame through the acetylene tube under the influence of the high pressure oxygen, some form of back flash preventer is usually incor- porated in the torch at or near the point at which the acetylene enters. This preventer takes the form
96 WELDING
of some porous and heat absorbing material, such as aluminum shavings, contained in a small cavity through which the gas passes on its way to the head. High Pressure Torches. — Torches are divided into the same classes as are the generators; that is, high pressure, medium pressure and low pressure. As mentioned before, the medium pressure is usually called the high pressure, because there are very few true high pressure systems in use, and comparatively
Figure 20. — High Pressure Torch Head
speaking the medium pressure type is one of high pressure.
With a true high pressure torch (Figure 20) the gases are used at very nearly equal heads so that the mixing before ignition is a simple matter. This type admits the oxygen at the inner end of a straight passage leading to the tip of the nozzle. The acety- lene comes into this same passage from openings at one side and near the inner end. The difference in direction of the two gases as they enter the passage assists in making a homogeneous mixture. The con- struction of this nozzle is perfectly simple and is easily understood. The true high pressure torch
WELDING INSTRUMENTS
97
nozzle is only suited for use with compressed and dissolved acetylene, no other gas being at a sufficient pressure to make the action necessary in mixing the gases.
Medium Pressure Torches. — The medium pressure (usually called high pressure) torch (Figure 21) uses acetylene from a medium pressure generator or from tanks of compressed gas, but will not take the acetylene from low pressure generators.
Figure 21. — Medium Pressure Torch Head
The construction of the mixing chamber and nozzle is very similar to that of the high pressure torch, the gases entering in the same way and from the same positions of openings. The pressure of the acetylene is but little lower than that of the oxygen, and the two gases, meeting at right angles, form a very inti- mate mixture at this point of juncture. The mixture in its proportions of gases depends entirely on the sizes of the oxygen and acetylene openings into the mixing chamber and on the pressures at which the gases are admitted. There is a very slight injector action as the fast moving stream of oxygen tends to draw the acetylene from the side openings into the
98
WELDING
chamber, but the operation of the torch does not depend on this action to any extent.
Low Pressure Torches. — The low pressure torch (Figure 22) will use gas from low pressure gener- ators, from medium pressure machines or from tanks in which it has been compressed and dissolved. This type depends for a perfect mixture of gas upon the principle of the injector just as it is applied in steam boiler practice.
Figure 22. — Low Pressure Torch with Separate Injector Nozzle
The oxygen enters the head at considerable pres- sure and passes through its tube to a small jet within the head. The opening of this jet is directly opposite the end of the opening through the nozzle which forms the mixing chamber and the path of the gases to the flame. A small distance remains between the opening from which the oxygen issues and the inner opening into the mixing passage. The stream of oxygen rushes across this space and enters the mixing chamber, being driven by its own pressure.
The acetylene enters the head in an annular space surrounding the oxygen tube. The space between oxygen jet and mixing chamber opening is at one
WELDING INSTRUMENTS 99
end of this acetylene space and the stream of oxygen seizes the acetylene and under the injector action draws it into the mixing chamber, it being necessary only to have a sufficient supply of acetylene flowing into the head to allow the oxygen to draw the re- quired proportion for a proper mixture.
The volume of gas drawn into the mixing chamber depends on the size of the injector openings and the pressure of the oxygen. In practice the oxygen pressure is not altered to produce different sized flames, but a new nozzle is substituted which is designed to give the required flame. Each nozzle carries its own injector, so that the design is always suited to the conditions. While torches are made having the injector as a permanent part of the torch body, the replaceable nozzle is more commonly used, because it makes the one torch suitable for a large range of work and a large number of different sized flames. "With the replaceable head a definite pressure of oxygen is required for the size being used, this pressure being the one for which the injector and corresponding mixing chamber were designed in pro- ducing the correct mixture.
Adjustable Injectors. — Another form of low pres- sure torch operates on the injector principle, but the injector itself is a permanent part of the torch, the nozzle only being changed for different sizes of work and flame. The injector is placed in or near the handle and its opening is the largest required by any work that can be handled by this particular torch. The opening through the tip of the injector through which the oxygen issues on its way to the mixing chamber may be wholly or partly closed by a needle valve which may be screwed into the opening or
100 WELDING
withdrawn from it, according to the operator's judg- ment. The needle valve ends in a milled nut outside the torch handle, this being the adjustment provided for the different nozzles.
Torch Construction. — A well designed torch is so designed that the weight distribution is best for hold- ing it in the proper position for welding. When a torch is grasped by its handle with the gas hose attached, it should balance so that it does not feel appreciably heavier on one end than on the other.
The head and nozzle may be placed so that the flame issues in a line at right angles with the torch body, or they may be attached at an angle convenient for the work to be done. The head set at an angle of from 120 to 170 degrees with the body is usually preferred for general work in welding, while the cutting torch usually has its head at right angles to the body.
Removable nozzles have various size openings through them and the different sizes are designated by numbers from 1 up. The same number does not always indicate the same size opening in torches of different makes, nor does it indicate a nozzle of the same capacity.
The design of the nozzle, the mixing chamber, the injector, when one is used, and the size of the gas openings must be such that all these things are suited to each other if a proper mixture of gas is to be secured. Parts that are not made to work together are unsafe if used because of the danger of a flash back of the flame into the mixing chamber and gas tubes. It is well known that flame travels through any inflammable gas at a certain definite rate of speed, depending on the degree of inflammability of
WELDING INSTRUMJEjS^g? \J >>, \ ] A 101
the gas. The easier and quicker the gas burns, the faster will the flame travel through it.
If the gas in the nozzle and mixing chamber stood still, the flame would immediately travel back into these parts and produce an explosion of more or less violence. The speed with which the gases issue from the nozzle prevent this from happening because the flame travels back through the gas at the same speed at which the gas issues from the torch tip. Should the velocity of the gas be greater than the speed of flame propagation through it, it will be impossible to keep the flame at the tip, the tendency being for a space of unburned gas to appear between tip and flame. On the other hand, should the speed of the flame exceed the velocity with which the gas comes from the torch there will result a flash back and explosion.
Care of Torches. — An oxy-acetylene torch is a very delicate and sensitive device, much more so than appears on the surface. It must be given equally as good care and attention as any other high-priced piece of machinery if it is to be maintained in good condition for use.
It requires cleaning of the nozzles at regular inter- vals if used regularly. This cleaning is accomplished with a piece of copper or brass wire run through the opening, and never with any metal such as steel or, iron that is harder than the nozzle itself, because of the danger of changing the size of the openings. -The torch head and nozzle can often be cleaned by allow- ing the oxygen to blow through at high pressure without the use of any tools.
In using a torch a deposit of carbon will gradually form inside of the head, and this deposit will be more
102 *' c * < WELDING
rapid if the operator lights the stream of acetylene before turning any oxygen into the torch. This deposit may be removed by running kerosene through the nozzle while it is removed from the torch, setting fire to the kerosene and allowing oxygen to flow through while the oil is burning.
Should a torch become clogged in the head or tubes, it may usually be cleaned by removing the oxygen hose from the handle end, closing the acety- lene cock on the torch, placing the end of the oxygen hose over the opening in the nozzle and turning on the oxygen under pressure to blow the obstruction back through the passage that it has entered. By opening the acetylene cock and closing the oxygen cock at the handle, the acetylene passages may then be cleaned in the same way. Under no conditions' should a torch be taken apart any more than to remove the changeable nozzle, except in the hands of those experienced in this work.
Nozzle Sizes. — The size of opening through the nozzle is determined according to the thickness and kind of metal being handled. The following sizes are recommended for steel :
Davis-Bournonville. O x w e 1 d Low
Thickness of Metal (Medium Pressure.) Pressure
1/32 Tip No. 1 Head No. 2
1/16 2
5/64 3
3/32 3 4
1/8 4 5
3/16 5 6
1/4 6 7
5/16 7
3/8 8 8
1/2 9 10
5/8 10 12
3/4 11 15
Very heavy 12 15
WELDING INSTRUMENTS 103
Cutting Torches. — Steel may be cut with a jet of oxygen at a rate of speed greater than in any other practicable way under usual conditions. The action consists of burning away a thin section of the metal by allowing a stream of oxygen to flow onto it while the gas is at high pressure and the metal at a white heat.
The cutting torch (Figure 23) has the same char- acteristics as the welding torch, but has an additional nozzle or means for temporarily using the welding
Figure 23. — Cutting Torch
opening for the high pressure oxygen. The oxygen issues from the opening while cutting at a pressure of from ten to 100 pounds to the square inch.
The work is first heated to a white heat by adjust- ing the torch for a welding flame. As soon as the metal reaches this temperature, the high pressure oxygen is turned on to the white-hot portion of the steel. When the jet of gas strikes the metal it cuts straight through, leaving a very narrow slot and removing but little metal. Thicknesses of steel up to ten inches can be economically handled in this way.
The oxygen nozzle is usually arranged so that it is surrounded by a number of small jets for the heating flame. It will be seen that this arrangement
104 WELDING
makes the heating flame always precede the oxygen jet, no matter in which direction the torch is moved.
The torch is held firmly, either by hand or with the help of special mechanism for guiding it in the desired path, and is steadily advanced in the direc- tion it is desired to extend the cut, the rate of advance being from three inches to two feet per minute through metal from nine inches down to one- quarter of an inch in thickness.
The following data on cutting is given by the Davis-Bournonville Company :
•3 5 |
2 a * $$ *
S -8 2s & s
° 5 * °* ft ?s
O O ~° * - 00
j s I !! A » *
II I !i I! I !l
1/4 lOlbs. 41bs. .40 .086 24 $ .013
1/2 20 4 .91 .150 15 .029
3/4 30 4 1.16 .150 15 .036
1 30 4 1.45 .172 12 .045 11/2 30 5 2.40 .380 12 .076
2 40 5 2.96 .380 12 .093 4 50 5 9.70 .800 7 .299 6 70 6 21.09 1.50 4 .648 9 100 6 43.20 2.00 3 1.311
Acetylene-Air Torch. — A form of torch which burns the acetylene after mixing it with atmospheric air at normal pressure rather than with the oxygen under higher pressures has been found useful in certain pre-heating, brazing and similar operations. This torch (Figure 24) is attached by a rubber gas hose to any compressed acetylene tank and is regu- lated as to flame size and temperature by opening or closing the tank valve more or less.
WELDING INSTRUMENTS 105
After attaching the torch to the tank, the gas is turned on very slowly and is lighted at the torch tip. The adjustment should cause the presence of a green- ish-white cone of flame surrounded by a larger body of burning gas, the cone starting at the mouth of the torch.
By opening the tank valve more, a longer and hotter flame is produced, the length being regulated
Figure 24. — Acetylene-Air Torch
.
by the tank valve also. This torch will give sufficient heat to melt steel, although not under conditions suited to welding. Because of the excess of acetylene always present there is no danger of oxidizing the metal being heated.
The only care required by this torch is to keep the small air passages at the nozzle clean and free from carbon deposits. The flame should be extinguished when not in use rather than turned low, because this low flame rapidly deposits large quantities of soot in the burner.
CHAPTER V
OXY-ACETYLENE WELDING PEACTICE PREPARATION OF WORK
Preheating. — The practice of heating the metal around the weld before applying the torch flame is a desirable one for two reasons. First, it makes the whole process more economical; second, it avoids the danger of breakage through expansion and contrac- tion of the work as it is heated and as it cools.
When it is desired to join two surfaces by welding them, it is, of course, necessary to raise the metal from the temperature of the surrounding air to its melting point, involving an increase in temperature of from one thousand to nearly three thousand de-' grees. To obtain this entire increase of temperature with the torch flame is very wasteful of fuel and of the operator's time. The total amount of heat nec- essary to put into metal is increased by the con- ductivity of that metal because the heat applied at the weld is carried to other parts of the piece being handled until the whole mass is considerably raised in temperature. To secure this widely distributed increase the various methods of preheating are adopted.
As to the second reason for preliminary heating. It is understood that the metal added to the joint is molten at the time it flows into place. All the metals used in welding contract as they cool and occupy a much smaller space than when molten. If addi- tional metal is run between two adjoining surfaces which are parts of a surrounding body of cool metal,
106
OXY-ACETYLENE WELDING PRACTICE 107
this added metal will cool while the surfaces them- selves are held stationary in the position they Grig-* in ally occupied. The inevitable result is that the metal added will crack under the strain, or, if the weld is exceptionally strong, the main body of the work will be broken by the force of contraction. To overcome these difficulties is the second and most important reason for preheating and also for slow cooling following the completion of the weld.
There are many ways of securing this preheating. The work may be brought to a red heat in the forge if it is cast iron or steel ; it may be heated in special ovens built for the purpose; it may be placed in a bed of charcoal while . suitably supported; it may be heated by gas or gasoline preheating torches, and with very small Work the outer flame of the welding torch automatically provides means to this end.
The temperature of the parts heated should be gradually raised in all cases, giving the entire mass of metal a chance to expand equally arid to adjust itself to the strains imposed by the preheating. After the region around the weld has been brought to a proper temperature the opening to be filled is ex- posed so that the torch flame can reach it, while the remaining surfaces are still protected from cold air currents and from cooling through natural radiation.
One of the commonest methods and one of the best for handling work of rather large size is to place the piece to be welded on a bed of fire brick and build a loose wall around it with other fire brick placed in rows, one on top of the other, with air spaces left between adjacent bricks in each row. The space between the brick retaining wall and the work is filled with charcoal, which is lighted . from below.
108
The top opening of the temporary oven is then cov- ered with asbestos and the fire kept up until the work has been uniformly raised in temperature to the desired point.
When much work of the same general character and size is to be handled, a permanent oven may be constructed of fire brick, leaving a large opening through the top and also through one side. Charcoal may be used in this form of oven as with the tem- porary arrangement, or the heat may be secured from any form of burner or torch giving a large volume of flame. In any method employing flame to do the heating, the work itself must be protected from the direct blast of the fire. Baffles of brick or metal should be placed between the mouth of the torch and the nearest surface of the work so that the flame will be deflected to either side and around the piece being heated.
The heat should be applied to bring the point of welding to the highest temperature desired and, ex- cept in the smallest work, the heat should gradually shade off from this point to the other parts of the piece. In the case of cast iron and steel the tem- perature at the point to be welded should be great enough to produce a dull red heat. This will make the whole operation much easier, because there will be no surrounding cool metal to reduce the tempera- ture of the molten material from the welding rod below the point at which it will join the work. From this red heat the mass of metal should grow cooler as the distance from the weld becomes greater, so that no great strain is placed upon any one part. With work of a very irregular shape it is always best to heat the entire piece so that the strains will
OXY-ACETYLENE WELDING PRACTICE 109
be so evenly distributed that they can cause no dis- tortion or breakage under any conditions.
The melting point of the work which is being pre- heated should be kept in mind and care exercised not to approach it too closely. Special care is necessary with aluminum in this respect, because of its low melting temperature and the sudden weakening and flowing without warning. Workmen have carelessly overheated aluminum castings and, upon uncovering the piece to make the weld, have been astonished to find that it had disappeared. Six hundred degrees is about the safe limit for this metal. It is possible to gauge the exact temperature of the work with a pyrometer, but when this instrument cannot be pro- cured, it might be well to secure a number of "tem- perature cones" from a chemical or laboratory sup- ply house. These cones are made from material that will soften at a certain heat and in form they are long and pointed. Placed in position on the part being heated, the point may be watched, and when it bends over it is sure that the metal itself has reached a temperature considerably in excess of the temperature at which that particular cone was de- signed to soften.
The object in preheating the metal around the weld is to cause it to expand sufficiently to open the crack a distance equal to the contraction when cool- ing from the melting point. In the case of a crack running from the edge of a piece into the body or of a crack wholly within the body, it is usually satis- factory to heat the metal at each end of the opening. This will cause the whole length of the crack to open sufficiently to receive the molten material from the rod.
110
WELDING
The judgment of the operator will be called upon to decide just where a piece of metal should be heated to open the weld properly. It is often possible to apply the preheating flame to a point some distance from the point of work if the parts are so connected
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Figure 25. — Preheating at A While Welding at B. C also May Be Heated
that the expansion of the heated part will serve to draw the edges of the weld apart. Whatever part of the work is heated to cause expansion and separa- tion, this part must remain hot during the entire time of welding and must then cool slowly at the same time as the metal in the weld cools.
An example of heating points away from the crack might be found in welding a lattice work with one
OXY-ACETYLENE WELDING PRACTICE 111
of the bars cracked through (Figure 25). If the strips parallel and near to the broken bar are heated gradually, the work will be so expanded that the edges of the break are drawn apart and the weld can be successfully made. In this case, the parallel bars next to the broken one would be heated highest, the next row not quite so hot and so on for some distance away. If only the one row were heated, the
Figure 26. — Cutting Through the Rim of a Wheel (Cut Shown at A)
strains set up in the next ones would be sufficient to cause a new break to appear.
If welding is to be done near the central portion of a large piece, the strains will be brought to bear on the parts farthest away from the center. Should a fly wheel spoke be broken and made ready to weld, the greatest strain will come on the rim of the wheel. In cases like this it is often desirable to cut through at the point of greatest strain with a saw or cutting torch, allowing free movement while the weld is made at the original break (Figure 26). After the
112 WELDING
inside weld is completed, the cut may be welded without danger, for the reason that it will always be at some point at which severe strains cannot be set up by the contraction of the cooling metal.
In materials that will spring to some extent with- out breakage, that is, in parts that are not brittle, it may be possible to force the work out of shape with jacks or wedges (Figure 27) in the same way that it would be distorted by heating and expanding some portion of it as described. A careful examination will show whether this method can be followed in such a way as to force the edges of the break to
Figure 27. — Using a Wedge While Welding
separate. If the plan seems feasible, the wedges may be put in place and allowed to remain while the weld is completed. As soon as the work is finished the wedges should be removed so that the natural contraction can take place without damage.
It should always be remembered that it is not so much the expansion of the work when heated as it is the contraction caused by cooling that will do the damage. A weld may be made that, to all appear- ances, is perfect and it may be perfect when com- pleted; but if provision has not been made to allow for the contraction that is certain to follow, there will be a breakage at some point. It is not possible to weld the simplest shapes, other than straight bars, without considering this difficulty and making pro- vision to take care of it.
OXY-ACETYLENE WELDING PRACTICE 113
The exact method to employ in preheating will always call for good judgment on the part of the workman, and he should remember that the success or failure of his work will depend fully as much on proper preparation as on correct handling of the wreld itself. It should be remembered that the outer flame of the oxy-acetylene torch may be depended on for a certain amount of preheating, as this flame gives a very large volume of heat, but a heat that is not so intense nor so localized as the welding flame itself. The heat of this part of the flame should be fully utilized during the operation of melting the metal and it should be so directed, when possible, that it will bring the parts next to be joined to as high a temperature as possible.
When the work has been brought to the desired temperature, all parts except the break and the sur- face immediately surrounding it on both sides should be covered with heavy sheet asbestos. This protect- ing cover should remain in place throughout the operation and should only be moved a distance suffi- cient to allow the torch flame to travel in the path of the weld. The use of asbestos in this way serves a twofold purpose. It retains the heat in the work and prevents the breakage that would follow if a draught of air were to strike the heated metal, and it also prevents such a radiation of heat through the surrounding air as would make it almost impos- sible for the operator to perform his work, especially in the case of large and heavy castings when the amount of heat utilized is large.
Cleaning and, Champ fering. — A perfect weld can never be made unless the surfaces to be joined have been properly prepared to receive the new metal.
114 WELDING
All spoiled, burned, corroded and rough particles must positively be removed with .chisel and hammer and with a free application of emery cloth and wire brush. The metal exposed to the welding flame should be perfectly clean and bright all over, or else the additional material will not unite, but will only stick at best.
Following the cleaning it is always necessary to bevel, or champfer, the edges except in the thinnest
Figure 28. — Tapering the Opening Formed by a Break
sheet metal. To make a weld that will hold, the metal must be made into one piece, without holes or unfilled portions at any point, and must be solid from inside to outside. This can only be accom- plished by starting the addition of metal at one point and gradually building it up until the outside, or top, is reached. With comparatively thin plates the molten metal may be started from the side far- thest from the operator and brought through, but with thicker sections the addition is started in the middle and brought flush with one side and then with the other.
It will readily be seen that the molten material
OXY-ACETYLENE WELDING PRACTICE 115
cannot be depended upon to flow between the tightly closed surfaces of a crack in a way that can be at all sure to make a true weld. It will be necessary for the operator to reach to the farthest side with the flame and welding rod, and to start the new surfaces there. To allow this, the edges that are to be joined are beveled from one side to the other (Figure 28), so that when placed together in approximately the position they are to occupy they will leave a grooved channel between them with its sides at an angle with
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Figure 29. — Beveling for Thin Work
Figure 30. — Beveling for Thick Work
each other sufficient in size to allow access to every point of each surface.
With work less than one-fourth inch thick, this angle should be forty-five degrees on each piece (Figure 29), so that when they are placed together the extreme edges will meet at the bottom of a groove whose sides are square, or at right angles, to each other. This beveling should be done so that only a thin edge is left where the two parts come together, just enough points in contact to make the alignment easy to hold. With work of a thickness greater than a quarter of an inch, the angle of bevel on each piece may be sixty degrees (Figure 30), so that when placed together the angle included be-
116
WELDING
tween the sloping sides will also be sixty degrees. If the plate is less than one-eighth of an inch thick the beveling is not necessary, as the edges may be melted all the way through without danger of leaving blowholes at any point.
This beveling may be done in any convenient way. A chisel is usually most satisfactory and also quick- est. Small sections may be handled by filing, while metal that is too hard to cut in either of these wavs
Figure 31. — Beveling Both Sides of a Thick Piece
Figure 32. — Beveling the End of a Pipe
may be shaped on the emery wheel. It is not nec- essary that the edges be perfectly finished and abso- lutely smooth, but they should be of regular outline and should always taper off to a thin edge so that when the flame is first applied it can be seen issuing from the far side of the crack. If the work is quite thick and is of a shape that will allow it to be turned over, the bevel may be brought from both sides (Figure 31), so that there will be two grooves, one on each surface of the work. After completing the weld on one side, the piece is reversed and finished on the other side. Figure 32 shows the proper bevel-
OXY-ACETYLENE WELDING PRACTICE 117
ing for welding pipe. Figure 33 shows how sheet metal may be flanged for welding.
Welding should not be attempted with the edges separated in place of beveled, because it will be found impossible to build up a solid web of new metal from one side clear through to the other by this method. The flame cannot reach the surfaces to make them molten while receiving new material from the rod, and if the flame does not reach them it will only serve to cause a few drops of the metal to join and will surely cause a weak and defective weld.
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Figure 33. — Flanging Sheet Metal for Welding
Supporting Work. — During the operation of weld- ing it is necessary that the work be well supported in the position it should occupy. This may be done with fire brick placed under the pieces in the correct position, or, better still, with some form of clamp. The edges of the crack should touch each other at the point where welding is to start and from there should gradually separate at the rate of about one- fourth inch to the foot. This is done so that the cooling of the molten metal as it is added will draw the edges together by its contraction.
Care must be used to see that the work is sup- ported so that it will maintain the same relative position between the parts as must be present when the work is finished. In this connection it must be
118
WELDING
remembered that the expansion of the metal when heated may be great enough to cause serious dis- tortion and to provide against this is one of the difficulties to be overcome.
Perfect alignment should be secured between the separate parts that are to be joined and the two edges must be held up so that they will be in the same plane while welding is carried out. If, by any chance, one drops below the other while molten metal
Figure 34. — Rotary Movement of Torch in Welding
is being added, the whole job may have to be undone and done over again. One precaution that is nec- essary is that of making sure that the clamping or supporting does not in itself pull the work out of shape while melted.
TORCH PRACTICE
The weld is made by bringing the tip of the weld- ing flame to the edges of the metals to be. joined. The torch should be held in the right hand and moved slowly along the crack with a rotating motion, traveling in small circles (Figure 34), so that the
OXY-ACETYLENE WELDING PRACTICE 119
welding flame touches first on one side of the crack and then on the other. On large work the motion may be simply back and forth across the crack, advancing regularly as the metal unites. It is usually best to weld toward the operator rather than from him, although this rule is governed by circum- stances. The head of the torch should be inclined at an angle of about %60 degrees to the surface of the work. The torch handle should extend in the same line with the break (Figure 35) and not across it, except when welding very light plates.
Figure 35. — Torch Held in Line with the Break
If the metal is 1/16 inch or less in thickness it is only necessary to circle along the crack, the metal itself furnishing enough material to complete the weld without additions. Heat both sides evenly until they flow together.
Material thicker than the above requires the addi- tion of more metal of the same or different kind from the welding rod, this rod being held by the left hand. The proper size rod for cast iron is one having a diameter equal to the thickness of metal being welded up to a one-half inch rod, which is the largest used. For steel the rod should be one-half the thickness of the metal being joined up to one-fourth inch rod.
120
WELDING
As a general rule, better results will be obtained by the use of smaller rods, the very small sizes being twisted together to furnish enough material while retaining the free melting qualities.
The tip of the rod must at all times be held in contact with the pieces being welded and the flame
Figure 36. — The Welding Rod Should Be Held in the Molten Metal
must be so directed that the two sides of the crack and the end of the rod are melted at the same time (Figure 36). Before anything is added from the rod, the sides of the crack are melted down suffi- ciently to fill the bottom of the groove and join the
Figure 37. — Welding Pieces of Unequal Thickness
two sides. Afterward, as metal comes from the rod in filling the crack, the flame is circled along the joint being made, the rod always following the flame.
Figure 37 illustrates the welding of pieces of unequal thickness.
OXY-ACETYLENE WELDING PRACTICE 121
Figure 38 illustrates welding at an angle.
The molten metal may be directed as to where it should go by the tip of the welding flame, which has considerable force, but care must be taken not to blow melted metal on to cooler surfaces which it cannot join. If, while welding, a spot appears which does not unite with the weld, it may be handled by heating all around it to a white heat and then imme- diately welding the bad place.
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Figure 38. — Welding at an Angle
Never stop in the middle of a weld, as it is ex- tremely difficult to continue smoothly when resuming work.
The Flame. — The welding flame must have exactly the right proportions of each gas. If there is too much oxygen, the metal will be burned or oxidized; the presence of too much acetylene carbonizes the metal; that is to say, it adds carbon and makes the work harder. Just the right mixture will neither burn nor carbonize and is said to be a "neutral" flame. The neutral flame, if of the correct size for the work, reduces the metal to a melted condition, not too fluid, and for a width about the same as the thickness of the metal being welded.
"When ready to light the torch, after attaching the
122 WELDING
right tip or head as directed in accordance with the thickness of metal to be handled, it will be necessary to regulate the pressure of gases to secure the neutral flame.
The oxygen will have a pressure of from 2 to 20 pounds, according to the nozzle used. The acetylene will have much less. Even with the compressed gas, the pressure should never exceed 10 pounds for the largest work, and it will usually be from 4 to 6. In low pressure systems, the acetylene will be re- ceived at generator pressure. It should first be seen that the hand-screws on the regulators are turned way out so that the springs are free from any ten- sion. It will do no harm if these screws are turned back until they come out of the threads. This must be done with both oxygen and acetylene regulators.
Next, open the valve from the generator, or on the acetylene tank, and carefully note whether there is any odor of escaping gas. Any leakage of this gas must be stopped before going on with the work.
The hand wheel controlling the oxygen cylinder valve should now be turned very slowly to the left as far as it will go, which opens the valve, and it should be borne in mind the pressure that is being released. Turn in the hand screw on the oxygen regulator until the small pressure gauge shows a reading according to the requirements of the noz- zle being used. This oxygen regulator adjustment should be made with the cock on the torch open, and after the regulator is thus adjusted the torch cock may be closed.
Open the acetylene cock on the torch and screw in on the acetylene regulator hand-screw until gas commences to come through the torch. Light this
OXY-ACETYLENE WELDING PRACTICE 123
flow of acetylene and adjust the regulator screw to the pressure desired, or, if there is no gauge, so that there is a good full flame. With the pressure of acetylene controlled by the type of generator it will only be necessary to open the torch cock.
With the acetylene burning, slowly open the oxy- gen cock on the torch and allow this gas to join the flame. The flame will turn intensely bright and then blue white. There will be an outer flame from four to eight inches long and from one to three inches thick. Inside of this flame will be two more rather distinctly defined flames. The inner one at the torch tip is very small, and the intermediate one is long and pointed. The oxygen should be turned on until the two inner flames unite into one blue-white cone from one-fourth to one-half inch long and one-eighth to one-fourth inch in diameter. If this single, clearly defined cone does not appear when the oxygen torch cock has been fully opened, turn off some of the acetylene until it does appear.
If too much oxygen is added to the flame, there will still be the central blue-white cone, but it will be smaller and more or less ragged around the edges (Figure 39). When there is just enough oxygen to make the single cone, and when, by turning on more acetylene or by turning off oxygen, two cones are caused to appear, the flame is neutral (Figure 40), and the small blue-white cone is called the welding flame.
While welding, test the correctness of the flame adjustment occasionally by turning on more acety- lene or by turning off some oxygen until two flames or cones appear. Then regulate as before to secure the single distinct cone. Too much oxygen is not
124 WELDING
usually so harmful as too much acetylene, except with aluminum. (See Figure 41.) An excessive amount of sparks coming from the weld denotes that
Figure 39. — Oxidizing Flame — Too Much Oxygen
Figure 40. — Neutral Flame
Figure 41. — Reducing Flame — Showing an Excess of Acetylene
OXY-ACETYLENE WELDING PRACTICE 125
there is too much oxygen in the flame. Should the opening in the tip become partly clogged, it will be difficult to secure a neutral flame and the tip should be cleaned with a brass or copper wire — never with iron or steel tools or wire of any kind. While the torch is doing its work, the tip may become exces- sively hot due to the heat radiated from the molten metal. The tip may be cooled by turning off the acetylene and dipping in water with a slight flow of oxygen through the nozzle to prevent water find- ing its way into the mixing chamber.
The regulators for cutting are similar to those for welding, except that higher pressures may be han- dled, and they are fitted with gauges reading up to 200 or 250 pounds pressure.
In welding metals which conduct the heat very rapidly it is necessary to use a much larger nozzle and flame than for metals which have not this prop- erty. This peculiarity is found to the greatest extent in copper, aluminum and brass.
Should a hole be blown through the work, it may be closed by withdrawing the flame for a few sec- onds and then commencing to build additional metal around the edges, working all the way around and finally closing the small opening left at the center with a drop or two from the welding rod.
WELDING VARIOUS METALS
Because of the varying melting points, rates of expansion and contraction, and other peculiarities of different metals, it is necessary to give detailed consideration to the most important ones.
Characteristics of Metals. — The welder should thor- oughly understand the peculiarities of the various
126 WELDING
metals with which he has to deal. The metals and their alloys are described under this heading in the first chapter of this book and a tabulated list of the most important points relating to each metal will be found at the end of the present chapter. All this information should be noted by the operator of a welding installation before commencing actual work.
Because of the nature of welding, the melting point of a metal is of great importance. A metal melting at a low temperature should have more care- ful treatment to avoid undesired flow than one which melts at a temperature which is relatively high. When two dissimilar metals are to be joined, the one which melts at the higher temperature must be acted upon by the flame first and when it is in a molten condition the heat contained in it will in many cases be sufficient to cause fusion of the lower melting metal and allow them to unite without play- ing the flame on the lower metal to any great extent.
The heat conductivity bears a very important relation to welding, inasmuch as a metal with a high rate of conductance requires more protection from cooling air currents and heat radiation than one not having this quality to such a marked extent. A metal which conducts heat rapidly will require a larger volume of flame, a larger nozzle, than other- wise, this being necessary to supply the additional heat taken away from the welding point by this conductance.
The relative rates of expansion of the various metals under heat should be understood in order that parts made from such material may have proper* preparation to compensate for this expansion and contraction. Parts made from metals having widely
OXY-ACETYLENE WELDING PRACTICE 127
varying rates of expansion must have special treat- ment to allow for this quality, otherwise breakage is sure to occur.
Cast Iron. — All spoiled metal should be cut away and if the work is more than one-eighth inch in thickness the sides of the crack should be beveled to a 45 degree angle, leaving a number of points touching at the bottom of the bevel so that the work may be joined in its original relation.
The entire piece should be preheated in a bricked-up oven or with charcoal placed on the forge, when size does not warrant building a temporary oven. The entire piece should be slowly heated and the portion immediately surrounding the weld should be brought to a dull red. Care should be used that the heat does not warp the metal through application to one part more than the others. After welding, the work should be slowly cooled by covering with ashes, slaked lime, asbestos fibre or some other non-con- ductor of heat. These precautions are absolutely essential in the case of cast iron.
A neutral flame, from a nozzle proportioned to the thickness of the work, should be held with the point of the blue-white cone about one-eighth inch from the surface of the iron.
A cast iron rod of correct diameter, usually made with an excess of silicon, is used by keeping its end in contact with the molten metal and flowing it into the puddle formed at the point of fusion. Metal should be added so that the weld stands about one- eighth inch above the surrounding surface of the work.
Various forms of flux may be used and they are applied by dipping the end of the welding rod into
128 WELDING
the powder at intervals. These powders may con- tain borax or salt, and to prevent a hard, brittle weld, graphite or ferro-silicon may be added. Flux should be added only after the iron is molten and as little as possible should be used. No flux should be used just before completion of the work.
The welding flame should be played on the work around the crack and gradually brought to bear on the work. The bottom of the bevel should be joined first and it will be noted that the cast iron tends to run toward the flame, but does not stick together easily. A hard and porous weld should be carefully guarded against, as described above, and upon com- pletion of the work the welded surface should be scraped with a file, while still red hot, in order to remove the surface scale.
Malleable Iron. — This material should be beveled in the same way that cast iron is handled, and pre- heating and slow cooling are equally desirable. The flame used is the same as for cast iron and so is the flux. The welding rod may be of cast iron, although better results are secured with Norway iron wire or else a mild steel wire wrapped with a coil of copper wire.
It will be understood that malleable iron turns to ordinary cast iron when melted and cooled. Welds in malleable iron are usually far from satisfactory and a better joint is secured by brazing the edges together with bronze. The edges to be joined are brought to a heat just a little below the point at which they will flow and the opening is then quickly filled from a rod of Tobin bronze or manganese bronze, a brass or bronze flux being used in this work.
OXY-ACETYLENE WELDING PRACTICE 129
Wrought Iron or Semi-Steel. — This metal should be beveled and heated in the same way as described for cast iron. The flame should be neutral, of the same size as for steel, and used with the tip of the blue-white cone just touching the work. The welding rod should be of mild steel, or, if wrought iron is to be welded to steel, a cast iron rod may be used. A cast iron flux is well suited for this work. It should be noted that wrought iron turns to ordinary cast iron if kept heated for any length of time.
Steel. — Steel should be beveled if more than one- eighth inch in thickness. It requires only a local preheating around the point to be welded. The welding flame should be absolutely neutral, without excess of either gas. If the metal is one-sixteenth inch or less in thickness, the tip of the blue-white cone must be held a short distance from the surface of the work; in all other cases the tip of this cone is touched to the metal being welded.
The welding rod may be of mild, low carbon steel or of Norway iron. Nickel steel rods may be used for parts requiring great strength, but vanadium alloys are very difficult to handle. A very satis- factory rod is made by twisting together two wires of the required material. The rod must be kept constantly in contact with the work and should not be added until the edges are thoroughly melted. The flux may or may not be used. If one is wanted, it may be made from three parts iron filings, six parts borax and one part sal ammoniac.
It will be noticed that the steel runs from the flame, but tends to hold together. Should foaming commence in the molten metal, it shows an excess of oxygen and that the metal is being burned.
130 WELDING
High carbon steels are very difficult to handle. It is claimed that a drop or two of copper added to the weld will assist the flow, but will also harden the work. An excess of oxygen reduces the amount of carbon and softens the steel, while an excess of acety- lene increases the proportion of carbon and hardens the metal. High speed steels may sometimes be welded if first coated with semi-steel before welding.
Aluminum. — This is the most difficult of the com- monly found metals to weld. This is caused by its high rate' of expansion and contraction and its lia- bility to melt and fall away from under the flame. The aluminum seems to melt on the inside first, and, without previous warning, a portion of the work will simply vanish from in front of the operator's eyes. The metal tends to run from the flame and separate at the same time. To keep the metal in shape and free from oxide, it is worked or puddled while in a plastic condition by an iron rod which has been flat- tened at one end. Several of these rods should be at hand and may be kept in a jar of salt water while not being used. These rods must not become coated with aluminum and they must not get red hot while in the weld.
The surfaces to be joined, together with the adja- cent parts, should be cleaned thoroughly and then washed with a 25 per cent solution of nitric acid in hot water, used on a swab. The parts should then be rinsed in clean water and dried with sawdust. It is also well to make temporary fire clay moulds back of the parts to be heated, so that the metal may be flowed into place and allowed to cool without danger of breakage.
Aluminum must invariably be preheated to about
OXY-ACETYLENE WELDING PRACTICE 131
600 degrees, and the whole piece being handled should be well covered with sheet asbestos to prevent, excessive heat radiation.
The flame is formed with an excess of acetylene such that the second cone extends about an inch, or slightly more, beyond the small blue-white point. The torch should be held so that the end of this second cone is in contact with the work, the small cone ordinarily used being kept an inch or an inch and a half from the surface of the work.
Welding rods of special aluminum are used and must be handled with their end submerged in the molten metal of the weld at all times.
When aluminum is melted it forms alumina, an oxide of the metal. This alumina surrounds small masses of the metal, and as it does not melt at tem- peratures below 5000 degrees (while aluminum melts at about 1200), it prevents a weld from being made. The formation of this oxide is retarded and the oxide itself is dissolved by a suitable flux, which usually contains phosphorus to break down the alumina.
Copper. — The whole piece should be preheated and kept well covered while welding. The flame must be much larger than for the same thickness of steel and neutral in character. A slight excess of acety- lene would be preferable to an excess of oxygen, and in all cases the molten metal should be kept envel- oped with the flame. The welding rod is of copper which contains phosphorus; and a flux, also contain- ing phosphorus, should be spread for about an inch each side of the joint. These assist in preventing oxidation, which is sure to occur with heated copper.
Copper breaks very easily at a heat slightly under
132 WELDING
the welding temperature and after cooling it is sim- ply cast copper in all cases.
Brass and Bronze. — It is necessary to preheat these metals, although not to a very high temperature. They must be kept well covered at all times to pre~ vent undue radiation. The flame should be produced with a nozzle one size larger than for the same thickness of steel and the small blue-white cone should be held from one-fourth to one-half inch above the surface of the work. The flame should be neutral in character.
A rod or wire of soft brass containing a large per- centage of zinc is suitable for adding to brass, while copper requires the use of copper or manganese bronze rods. Special flux or borax may be used to assist the flow.
The emission of white smoke indicates that the zinc contained in these alloys is being burned away and the heat should immediately be turned away or reduced. The fumes from brass and bronze welding are very poison,ous and should not be breathed.
RESTORATION OF STEEL
The result of the high heat to which the steel has been subjected is that it is weakened and of a dif- ferent character than before welding. The operator may avoid this as much as possible by first playing the outer flame of the torch all over the surfaces of the work just completed until these faces are all of uniform color, after which the metal should be well covered with asbestos and allowed to cool with- out being disturbed. If a temporary heating oven has been employed, the work and oven should be allowed to cool together while protected with the
OXY-ACETYLENE WELDING PRACTICE 133
sheet asbestos. If the outside air strikes tlie freshly welded work, even for a moment, the result will be breakage.
A weld in steel will always leave the metal with a coarse grain and with all the characteristics of rather low grade cast steel. As previously men- tioned in another chapter, the larger the grain size in steel the weaker the metal will be, and it is the purpose of the good workman to avoid, as far as possible, this weakening.
The structure of the metal in one piece of steel will differ according to the heat that it has under- gone. The parts of the work that have been at the melting point will, therefore, have the largest grain size and the least strength. Those parts that have not suffered any great rise in temperature will be practically unaffected, and all the parts between these two extremes will be weaker or stronger accord- ing to their distance from the weld itself. To restore the steel so that it will have the best grain size, the operator may resort to either of two methods: (1) The grain may be improved by forging. That means that the metal added to the weld and the surfaces that have been at the welding heat are hammered, much as a blacksmith would hammer his finished work to give it greater strength. The hammering should continue from the time the metal first starts to cool until it has reached the temperature at which the grain size is best for strength. This temperature will vary somewhat with the composition of the metal being handled, but in a general way, it may be stated that the hammering should continue without inter- mission from the time the flame is removed from the weld until the steel just begins to show attraction
134 WELDING
for a magnet presented to it. This temperature of magnetic attraction will always be low enough and the hammering should be immediately discontinued at this point. (2) A method that is more satisfac- tory, although harder to apply, is that of reheating the steel to a certain temperature throughout its whole mass where the heat has had any effect, and then allowing slow and even cooling from this tem- perature. The grain size is affected by the tempera- ture at which the reheating is stopped and not by the cooling, yet the cooling should be slow enough to avoid strains caused by uneven contraction.
After the weld has been completed the steel must be allowed to cool until below 1200° Fahrenheit. The next step is to heat the work slowly until all those parts to be restored have reached a temperature at which the magnet just ceases to be attracted. While the very best temperature will vary according to the nature and hardness of the steel being handled, it will be safe to carry the heating to .the point indi- cated by the magnet in the absence of suitable means of measuring accurately these high temperatures. In using a magnet for testing, it will be most satisfac- tory if it is an electromagnet and not of the perma- nent type. The electric current may be secured from any small battery and will be the means of making sure of the test. The permanent magnet will quickly lose its power of attraction under the com- bined action of the heat and the jarring to which it will be subjected.
In reheating the work it is necessary to make sure that no part reaches a temperature above that desired for best grain size and also to see that all parts are brought to this temperature. Here enters the great-
OXY-ACETYLENB WELDING PRACTICE 135
est difficulty in restoring the metal. The heating may be done so slowly that no part of the work on the outside reaches too high a temperature and then keeps the outside at this heat until the entire mass is at the same temperature. A less desirable way is to heat the outside higher than this temperature and allow the conductivity of the metal to distribute the excess to the inside.
The most satisfactory method, where it can be employed, is to make use of a bath of some molten metal or some chemical mixture that can be kept at the exact heat necessary by means of gas fires that admit of close regulation. The temperature of these baths may be maintained at a constant point by watching a pyrometer, and the finished work may be allowed to remain in the bath until all parts have reached the desired temperature.
WELDING INFORMATION
The following tables include much of the informa- tion that the operator must use continually to handle the various metals successfully. The temperature scales are given for convenience only. The composi- tion of various alloys will give an idea of the diffi- culties to be contended with by consulting the infor- mation on welding various metals. The remaining tables are of self-evident value in this work.
136
WELDING
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OXY-ACETYLENE WELDING PRACTICE 137
METAL ALLOYS
(Society of Automobile Engineers)
Babbitt- Tin 84.00%
Antimony 9.00%
Copper 7.00%
Brass, "White —
Copper 3.00% to 6.00%
Tin (minimum) 65.00%
Zinc : .• 28.00% to 30.00%
Brass, Red Cast —
Copper 85.00%
Tin 5.00%
Lead 5.00%
Zinc 5.00%
Brass, Yellow —
Copper 62.00% to 65.00%
Lead 2.00% to 4.00%
Zinc 36.00% to 31.00%
Bronze, Hard —
Copper 87.00% to 88.00%
Tin 9.50% to 10.50%
Zinc 1.50% to 2.50%
Bronze, Phosphor —
Copper 80.00%
Tin 10.00%
Lead 10.00%
Phosphorus 50% to .25%
Bronze, Manganese —
Copper (approximate) , 60.00%
Zinc (approximate) 40.00%
Manganese (variable) small
Bronze, Gear —
Copper 88.00% to 89.00%
Tin 11.00% to 12.00%
Phosphorus 15% to .30%
138
WELDING
Copper Zinc 8.5-7.0% 2.0-3.0% 15% 35.0%
Manganese Not over 0.40%
Aluminum Alloys —
Aluminum
No. 1.. 90.00%
No. 2.. 80.00%
No. 3.. 65.00%
Cast Iron —
Gray Iron Malleable
Total carbon 3.0 to 3.5%
Combined carbon ...0.4 to 0.7%
Manganese 0.4 to 0.7% 0.3 to 0.7%
Phosphorus 0.6 to 1.0% Not over 0.2%
Sulphur Not over 0.1% Not over 0.6%
Silicon 1.75 to 2.25% Not over 1.0%
Carbon Steel (10 Point) —
Carbon 05% to .15%
Manganese 30% to .60%
Phosphorus (maximum) .045%
Sulphur (maximum) .05%
(20 Point) —
Carbon 15% to .25%
Manganese 30% to .60%
Phosphorus (maximum) .045%
Sulphur (maximum) .05%
(35 Point) —
Manganese 50% to .80%
Carbon 30% to .40%
Phosphorus (maximum) .05%
Sulphur (maximum) .05%
(95 Point) —
Carbon 90% to 1.05%
Manganese 25% to .50%
Phosphorus (maximum) .04%
Sulphur ' (maximum) .05%
OXY-ACETYLENE WELDING PRACTICE 139
HEATING POWER OP FUEL GASES
(In B. T. U. per Cubic Foot.)
Acetylene 1498.99 Ethylene 1562.95
Hydrogen 291.96 Methane 953.62
Alcohol 1501.76
MELTING POINTS OF METALS
Platinum 3200°
Iron, wrought 2900°
malleable 2500°
cast 2400°
pure 2760°
Steel, mild 2700°
medium 2600°
hard 2500°
Copper 1950°
Brass 1800°
Silver 1750°
Bronze ....1700°
Aluminum , 1175°
Antimony 1150°
Zinc 800°
Lead 620°
Babbitt 500-700°
Solder 500-575°
Tin 450°
NOTE. — These melting points are for average com- positions and conditions. The exact proportion of elements entering into the metals affects their melting points one way or the other in practice.
140 WELDING
TENSILE STRENGTH OF METALS
Alloy steels can be made with tensile strengths as high as 300,000 pounds per square inch. Some car- bon steels are given below according to "points":
- Pounds per Square Inch
Steel, 10 point 50,000 to 65,000
20 point 60,000 to 80,000
40 point 70,000 to 100,000
60 point 90,000 to 120,000
Iron, Cast 13,000 to 30,000
Wrought 40,000 to 60,000
Malleable 25,000 to 45,000
Copper 24,000 to 50,000
Bronze 30,000 to 60,000
Brass, Cast 12,000 to 18,000
Boiled 30,000 to 40,000
Wire 60,000 to 75,000
Aluminum 12,000 to 23,000
Zinc 5,000 to 15,000
Tin ; 3,000 to 5,000
Lead 1,500 to 2,500
CONDUCTIVITY OF METALS
(Based on the Value of Silver as 100)
Heat Electricity
Silver 100 100
Copper 74 99
Aluminum 38 63
Brass 23 22
Zinc 19 29
Tin 14 15
OXY-ACETYLENE WELDING PRACTICE 141
Heat Electricity
Wrought Iron 12 16
Steel 11.5 12
Cast Iron 11 12
Bronze 9 7
Lead 8 9
WEIGHT OF METALS
(Per Cubic Inch)
Pounds Pounds
Lead 410 Wrought Iron 278
Copper 320 Tin 263
Bronze 313 Cast Iron 260
Brass , . .300 Zinc 258
Steel 283 Aluminum 093
EXPANSION OF METALS
(Measured in Thousandths of an Inch per Foot of
Length When Raised 1000 Degrees
in Temperature)
Inch Inch
Lead 188 Brass 115
Zinc 168 Copper 106
Aluminum 148 Steel .' 083
Silver 129 Wrought Iron 078
Bronze .118 Cast Iron.. .068
CHAPTER VI ELECTEIC WELDING RESISTANCE METHOD
Two distinct forms of electric welding apparatus are in use, one producing heat by the resistance of the metal being treated to the passage of electric cur- rent, the other using the heat of the electric arc.
The resistance process is of the greatest use in manufacturing lines where there is a large quantity of one kind of work to do, many thousand pieces of one kind, for instance. The arc method may be ap- plied in practically any case where any other form of weld may be made. The resistance process will be described first.
It is a well known fact that a poor conductor of electricity will offer so much resistance to the flow of electricity that it will heat. Copper is a good con- ductor, and a bar of iron, a comparatively poor con- ductor, wh^n placed between heavy copper conductors of a welder, becomes heated in attempting to carry the large volume of current. The degree of heat depends on the amount of current and the resistance of the conductor.
In an electric circuit the ends of two pieces of metal brought together form the point of greatest resistance in the ' electric circuit, and the abutting ends instantly begin to heat. The hotter this metal becomes, the greater the resistance to the flow of cur- rent; consequently, as the edges of the abutting ends heat, the current is forced into the adjacent cooler
142
ELECTRIC WELDING
143
parts, until there is a uniform heat throughout the entire mass. The heat is first developed in the inte- rior of the metal so that it is welded there as perfectly as at the surface.
Figure 42. — Spot Welding Machine
The electric welder (Figure .42) is built to hold the parts to be joined between two heavy copper dies or contacts. A current of three to five volts, but of very great volume (amperage), is allowed to pass across these dies, and in going through the metal to be welded, heats the edges to a welding temperature. It may be explained that the voltage of an electric
144 WELDING
current measures the pressure or force with which it is being sent through the circuit and has nothing to do with the quantity or volume passing. Amperes measure the rate at which the current is passing through the circuit and consequently give a measure of the quantity which passes in any given time. Volts correspond to water pressure measured by pounds to the square inch ; amperes represent the flow in gallons per minute. The low voltage used avoids all danger to the operator, this pressure not being sufficient to be felt even with the hands resting on the copper contacts.
Current is supplied to the welding machine at a higher voltage and lower amperage than is actually used between the dies, the low voltage and high am- perage being produced by a transformer incorporated in the machine itself. By means of windings of suit- able size wire, the outside current may be received at voltages ranging from 110 to 550 and converted to the low pressure needed.
The source of current for the resistance welder must be alternating, that is, the current must first be negative in value and then positive, passing from one extreme to the other at rates varying from 25 to 133 times a second. This form is known as alternating current, as opposed to direct current, in which there is no changing of positive and negative.
The current must also be what is known as single phase, that is, a current which rises from zero in value to the highest point as a positive current and then recedes to zero before rising to the highest point of negative value. Two-phase of three-phase currents would give two or three positive impulses during this time.
ELECTRIC WELDING 145
As long as the current is single phase alternating, the voltage and cycles (number of alternations per second) may be anything convenient. Various volt- ages and cycles are taken care of by specifying all these points when designing the transformer which is to handle the current.
Direct current is not used because there is no way of reducing the voltage conveniently without placing resistance wires in the circuit and this uses power without producing useful work. Direct current may be changed to alternating by having a direct current motor running an alternating current dynamo, or the change may be made by a rotary converter, al- though this last method is not so satisfactory as the first.
The voltage used in welding being so low to start with, it is absolutely necessary that it be maintained at the correct point. If the source of current supply is not of ample capacity for the welder being used, it will be very hard to avoid a fall of voltage when the current is forced to pass through the high resistance of the weld. The current voltage for various work is calculated accurately, and the efficiency of the outfit depends to a great extent on the voltage being con- stant.
A simple test for fall of voltage is made by con- necting an incandescent electric lamp across the sup- ply lines at some point near the welder. The lamp should burn with the same brilliancy when the weld is being made as at any other time. If the lamp burns dim at any time, it indicates a drop in voltage, and this condition should be corrected.
The dynamo furnishing the alternating current may be in the same building with the welder and
146 WELDING
operated from a direct current motor, as mentioned above, or operated from any convenient shafting or source of power. When the dynamo is a part of the welding plant it should be placed as close to the welding machine as possible, because the length of the wire used affects the voltage appreciably.
In order to hold the voltage constant, the Toledo Electric Welder Company has devised connections which include a rheostat to insert a variable resist- ance in the field windings of the dynamo so that the voltage may be increased by cutting this resistance out at the proper time. An auxiliary switch is con- nected to the welder switch so that both switches act together. When the welder switch is closed in mak- ing a weld, that portion of the rheostat resistance between two arms determining the voltage is short circuited. This lowers the resistance and the field magnets of the dynamo are made stronger so that additional voltage is provided to care for the re- sistance in the metal being heated.
A typical machine is shown in the accompanying cut (Figure 43). On top of the welder are two jaws for holding the ends of the pieces to be welded. The lower part of the jaws is rigid while the top is brought down on top of the work, acting as a clamp. These jaws carry the copper dies through which the current enters the work being handled. After the work is clamped between the jaws, the upper set is forced closer to the lower set by a long com- pression lever. The current being turned on with the surfaces of the work in contact, they immedi- ately heat to the welding point when added pressure on the lever forces them together and completes the weld.
ELECTRIC WELDING
147
148 WELDING
The