Spot and arc welding

Front matter

BY

FRANKLIN INSTITUTE LIBRARY

PHILADELPHIA Class . .($. . ./T./. . Book. .//. . -Z S^. Accession 7^.^.3 S i-

Preface

Although electric welding has been used for many years for repair work, there exists to-day a hesitancy in applying it to new construction, especially to the joining of heavy steel parts. It is the purpose of this book to endeavor to dispel this apprehension. The data of tests made in the spot welding of heavy steel plates by the Emergency Fleet Corporation is furnished in full with the expectation that in making this information available to shipbuilders and others, they will be able to adopt this process to their own manufacturing advantage. In like manner the underlying question of arc-welding processes is fully discussed with the intent of reassuring any one who may doubt the ability of these methods to supersede the rivet.

The author wishes to acknowledge the courtesies extended to him both by those who have contributed to the text and those who have permitted the reprinting of valuable published material.

Minerva, N. Y. H. A. HoRNOR.

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Contents

CHAPTER PAGE

I. Materials 1

II. Electric-Welding Systems 14

Chapter I

The essential consideration for those who practice the art of electric welding is the character of the materials to be joined. As a matter of fact, this principle has been the basis of all successful engineering achievement and a lack of it the cause for many vital failures. The wide range of processes combined with ingenious designs permits the broad statement of probability that all the metals and their alloys may in varying degrees be held together by electric methods. This provides a varied and interesting fi^ld for the engineer although, like untilled ground, there will be found many obstacles in the way of cultivation. The success of the harvest will be in direct proportion to the thought bestowed upon the actions of the metals when under the treatment required for their jointure.

It is not proposed to consider here the welding of the soft metals such as gold, silver, copper, tin, zinc, aluminum, etc. It is sufficient to affirm that in small articles processes of electric welding have been devised that satisfactorily accomplish such joints as are needed for special industries. The processes employed are fully described in many published articles/ As metal is added to the objects joined the method is referred to as soldering rather than welding. On the other hand, nickel, copper,

' " Electric Welding," by D. T. Hamilton and Erik Oberg, 1918. 1 1 and aluminum wires of small diameter are joined by means of a condenser spark, the process being called percussion welding. Interesting as these apphcations are, only this brief mention can be made in order to allow a full opportunity for the discussion of the welding of heavy steel pieces.

Definition. — Doctor Howe gives this definition of steel in its specific sense: " A compound of iron possessing, or capable of possessing, decided hardness simultaneously with a valuable degree of toughness when hot or when cold, or both. It includes primarily compounds of iron combined with from, say, 0.30 to 2 per cent, of carbon, which can be rendered decidedly soft and tough or intensely hard by slow and rapid cooling respectively, and secondarily, compounds of iron with chromium, tungsten, manganese, titanium, and other elements, compounds which like carbon possess intense hardness with decided toughness.^ " The reasons underlying the behavior of this material when subjected to temperature changes must be sought for in the researches made by eminent metallurgists. This is the broad subject of the heat treatment of steel with which the practical welding engineer should have some knowledge in order to escape the error of applying electric welding to the detriment of the original materials.

Production of Iron. — Iron ore when taken from the earth may contain many and various minerals. The ore is treated in a blast furnace for the purpose of removing the oxygen which had a persistent affinity for the pure iron. The product* of the blast furnace is not chemically

'"Metallurgy of Steel," by H. M. Howe, vol. i, chap, i, p. 1, ^nd Ed., 1891.

pure, consisting usually of iron, carbon, silicon, manganese, sulphur, phosphorus, and oxygen. Pure iron may be obtained by careful preparation in the laboratory but not for commercial purposes. This molten metal from the furnace is cast into a form called " pig iron." When pig iron is remelted in a crucible and cast into some commercial form it is called cast iron."

Cast iron takes two forms, depending upon its treatment when poured. If the molten metal is cast in sand it is a grey iron casting, if it is cast in metal moulds (chilled) it is a white iron casting. The point to observe here is the difference caused by the slow and rapid cooling of the molten metal. The names given to these castings are taken from the appearance of the fracture caused by the large amount of free carbon in a case of grey cast iron and the small amount of free carbon in the case of white cast iron.

Annealing is effected by slow cooling from a high temperature. If then white iron castings, which are brittle as compared to grey iron castings, are annealed so as to free the carbon which is in a combined state, malleable castings will result. Malleable iron is free iron with which is mixed carbon in a free state in the form of graphite. The effect of annealing does not penetrate the mass of metal and annealed castings seldom show any effect much further than an inch below the surface.

When pig iron is melted in a puddling furnace at a point where the pure iron appears to separate from the mass of impurities it is removed and the slag that it tenaciously carries with it is squeezed out by means of rolls. The rolls naturally form the mass of metal into the shape of bars. This mechanical treatment of the iron tends to produce purity and its efficiency is in direct ratio to the quality of the resultant wrought iron. From the mechanical treatment it receives it derives the name of wrought iron. The purity also bears a direct relation to the ore, and for this reason imported iron (Norway and Swedish) is well known for this quality. Wrought iron because of its purity is used in the manufacture of highgrade crucible steel.

Steel Processes, — The essential difference between the manufacture of steel by the open-hearth or crucible processes is disclosed by their names. In the latter case, iron of like or unlike carbon percentage is melted in crucibles usually totally enclosed, the molten mass is held in these crucibles (either graphite or clay), so that it may absorb silicon from the crucible walls, and then the liquid metal poured into castings or ingot forms. The open-hearth process melts the pig iron in a cupola, transfers it to an apparatus whereby the impurities are removed after which desired elements may be added to obtain various properties in the finished steel. The process is referred to by steel makers as basic or acid in accord with the chemical nature of the lining of the vessel used for removing the impurities. Crucible steel is of high grade, more expensive of manufacture and more costly. It is used for cutting tools, springs, firearms, etc. The added elements in the open-hearth process may be varied in many ways, thus producing many steel alloys useful to the industries. For ordinary plates and shapes the controlling elements are carbon and manganese. Both these elements hold high favor due to their ability to add greatly to the tensile strength and ductility of steel.

From the steel furnace by either process the metal is cast either into moulds for steel castings or ingot moulds for rolling into plates or shapes or into billets for forging. It should be carefully noted that plates, with which the electric-welding engineer is much concerned, are really steel castings which have received additional temperature and mechanical treatment in proceeding through the rolling mill. In applying the processes of spot and arc welding to new steel construction it will be such material that will require successful joining. As heat is the prerequisite for the welding of the metals in any case it becomes necessary to give close attention to the theories of the heat treatment of steel, the metallurgy of steel. This subject will be taken up in a later chapter.

Chemical Constituents of Steel. — Without proceeding into a maze of theoretical argument it may be well to consider briefly a few opinions regarding the effects of the various elements added to steel and following that their composite action on the weldability of steel.

" As the carbon increases, the tensile strength, elastic limit, elastic ratio, and compressive strength increase within limits; the fusibility, hardness, and hardening power increase perhaps without limit; while the malleableness and ductility, both hot and cold, and the welding power diminish apparently without limit. The modulus of elasticity appears nearly independent of the percentage of carbon, at least within the limits of carbon zero to carbon two per cent." ^

Silicon is considered by some authorities to cause brittleness and redshortness, and by others to be in many

" Metallurgy of Steel," by H. M. Howe, vol. i, chap, ii, p. 13, 2nd Ed., 1891.

cases harmless, sometimes even increasing the ductihty and in the presence of manganese " to counteract its tendency to cause redshortness." ^

Phosphorus is an undesirable element. It is well known to cause " coldshort " or brittleness. The steel manufacturer takes every care to remove as much of this element as possible so that only a small percentage is found in good commercial grades of steel. It is negligible as far as welding problems are concerned.

The same remarks apply to sulphur. Howe states: " Sulphur has the specific effect of making iron exceedingly brittle at a red heat and of destroying its welding power." ^

The effect of manganese on steel is still in the regions of dispute. One of the best authorities states: The net effects of manganese on tensile strength and ductility are slight." Manganese seems to promote continuity and in this manner aids the ductility of steel. This is an important characteristic of this element which may throw light upon its use in the composition of electrodes for arc welding.

Chromium gives hardness to hardened steel probably increasing the tensile strength and elastic limit. The weldability of steel is reduced by chromium.

The addition of tungsten tends to produce great hardness in the steel alloy. This characteristic which it retains at high temperature makes it useful for the manufacture of high-speed cutting tools. Tungsten

''"Metallurgy of Steel," by H. M. Howe, vol. i, chap, iii, p. 40, 9nd Ed., 1891.

^ " Metallurgy of Steel," by H. M. Howe, vol. i, chap, iii, p. 52, 2nd Ed., 1891.

steel is brittle and is difficult to forge even at relatively high temperatures. Doctor Howe doubts if it can be truly welded by ordinary methods.

Nickel steel surpasses the best carbon steel in its superior tensile strength combined with elongation. Upon its first introduction it was found difficult to machine, but this disadvantage has been overcome by improvements in machine tools. This alloy is also less liable to corrosion than steel.

Vanadium influences steel in much the same manner as nickel. Its first introduction was heralded by claims which soon disappeared in the presence of tungsten steel.

Copper and iron act curiously in combination. A little copper with iron or a little iron with copper are said to unite into a homogeneous mass, but if the proportions approach equality they seem to split up into alloys. The effect of copper is like that of sulphur, causing redshortness, brittleness, and an opposition to welding. This tendency of the metals must be carefully held in mind by those who seek to improve the non-corrodibility of an arc-welded seam by the introduction of copper into the composition of the electrode material.

Many other metals, such as zinc, tin, lead, titanium, arsenic, cobalt, aluminum, may occur in iron but disappear in the manufacture of steel. Those that have been treated in brief detail above are to be found in commercial steel and must be investigated by those who are desirous of making a successful application of the practical processes of electric welding. For those who wish to investigate and experiment with steel compositions for the betterment of any special welding process there remains the action of the alkaline earths and the combination of iron with the noble metals. This latter field attracted the attention of some of the older and illustrious scientists without material success, but the sign of their failures may by modern methods be turned to a mark of attainment.

Weldability of Steel. — The important consideration for the welding engineer is the degree of weldability of the metals placed before him to join. Not only is this knowledge of great concern prior to the performance of the work, but also is necessary for the investigation of immediate and subsequent failures. Commercial steel castings upon analysis show a general chemical composition as follows :

Of these five chemical elements the proportion of phosphorus and sulphur are so slight as to make them negligible. Among technicians there is argument regarding sulphur. The extreme is that 0.02 per cent, sulphur opposes welding, the other extreme that successful welds can be made with sulphur as high as 0.07 per cent. Sulphur as high as 0.15 per cent, is considered quite unweldable." There remains the three principal constituents, carbon, silicon, and manganese, of which many scholars give carbon the leading place in lessening the weldability of the alloy. This opinion is largely borne out in practice. The whole subject resolves itself into one needing at the present time much earnest study and careful research, especially when con-

Carbon

Silicon

Manganese Phosphorus Sulphur . .

sidered with the comphcations introduced by the arewelding process.

As regards manganese and sihcon so Httle of their reactions are known that no trustworthy statements can be made other than those quoted and referred to above. • Doctor Howe says of sihcon: The good welding power of crucible steel, usually rich in silicon, goes to show that silicon is not especially injurious in this respect." For the benefit of the practitioner and the art as a whole it would be well for some of our colleges to engage in this industrially useful field of research.

The carbon content has received more careful and substantial investigation with the result that more harmony of opinion exists. The same authority states: " It was formerly thought that the presence of a little carbon was indispensable or at least very favorable to welding; but this, I think, is no longer believed. Certain it is that in general the difficulty of welding increases with the proportion of carbon, and the welding power probably practically disappears when the carbon rises above 1.3 per cent. The larger the proportion of other elements present, probably the lower, in general, is the welding power for given percentage of carbon. Thus the welding of apparently common Bessemer steel is said to be hardly possible with 0.20 to 0.35 per cent, of carbon, and impracticable with 0.35 to 0.50 per cent.; while to the practiced worker the welding of the relatively pure crucible steel is said to be easy with 0.87 per cent., and possible, using the greatest care, with 1.25 per cent, of carbon. Though the difference is probably much less

" Metallurgy of Steel," by H. M. Howe, vol. i, chap, xiv, p. 2nd Ed., 1891.

than this rather loose wording implies, and though there are welds and welds, it appears to be very marked.

" A reason why rising carbon lowers the welding power is that it lowers the point to which we can heat the metal without danger of burning, but does not lower correspondingly the temperature at which plasticity sets in; indeed, it seems to diminish the plasticity and adhesiveness for given temperatures." ^

Doctor Howe is here treating purely of the weldability of steel in general and his statements, although in a large degi-ee apply, must not be construed as referring to the electric weldability of steel. To indicate his agreement with others and subjecting the question to a specific reference to electric welding the following opinion is also quoted: " Little is known at the present time regarding the effect of the weldability produced by the presence of most of the impurities given above, where the electric arc-welding process is used. No data has been published on the subject. It is known, however, that steel containing 0.5 per cent, or more carbon is subject to " burning " at much lower temperatures than low-carbon steels. This fact can readily be observed in arc-welding practice, i.e., the tendency being towards " burnt " metal in the weld. The observations which have been made up to the present time seem to indicate that the tendency toward " burning " shown in steel of comparative high-carbon content, is the only considerable effect which is produced on the weldability by the presence of any of the impurities in their usual amounts."

Physical Characteristics. — The foregoing opinions

^ " Metallurgy of Steel," by H. M. Howe, vol. i, chap, xiv, p. 251, 2nd Ed., 1891.

deal with the chemical nature of steel and are given concretely with the hope that the practitioner may find them convenient in his daily application of electric welding. Of an equal degree of importance are the physical changes that take place in steel when subjected to high and low temperature, sudden and slow changes of temperature. Here is to be considered not the composition nor the changes of composition of the material, but simply its physical properties.

Steel is hardened by rapid cooling from a high temperature. This is practically attained by quickly immersing the heated steel in a bath of water or oil. The kind of liquid used to quench the steel develops a greater degree of tensile strength and different methods must be pursued for difference in carbon content. Thus it is stated that to give the highest tensile strength to low carbon steel it should be quenched in water from a high temperature; for mild carbon steel (0.40 per cent.) it should be quenched in oil with a " rather high quenching temperature; " ^ and for steel with large percentage of carbon (1.25 per cent.) it should cool slowly from a low temperature and immersed in oil. In general the hardening of steel brings about the desirable physical characteristics of better elastic limit, greater firmness, and better tensile strength. The ductility tends to diminish as well as the specific gravity. Steel may be quenched in other media such as tallow, coal tar, and even lead, but tensile strength is not bettered by these methods over the use of oil.

The tempering of steel is employed to modify to some extent the previous effects of hardening. This re-

Metallurgy of Steel," by H. M. Howe, vol. i, chap, li, p. 19, ^nd Ed., 1891.

quires the reheating but to a lower temperature and then in general cooling quickly and in some cases slowly. As hardened steel is brittle tempering increases its ductility and makes it much tougher. It does this without decreasing the tensile strength and, in fact, it has been stated to increase the tensile strength. Though the ductility is bettered by tempering over that of the hardening process it is still not as ductile as annealed steel. The advantage of tempering which apparently is an unnecessary second operation lies in the better control of temperature with the result that hardness and tensile strength are not impaired but to them is restored the ductility lost in the hardening operation.

The annealing of steel is to completely undo the effects of hardening and bring the steel to a very soft and tough state. " It increases the ductility and specific gravity and it generally lowers the elastic limits." ^ Besides restoring the tensile strength of violently hardened steel annealing also restores the tensile strength caused by cold working and internal stresses in steel castings. Much of the advantage gained by annealing resides in the cooling temperature and the medium used for the cooling process. It may be stated broadly that slow cooling brings about the softer and tougher qualities desired, but for many purposes both cold-worked low-carbon steel and steel castings the cooling may be interrupted at a certain point and the material quenched. This procedure will not give results equal to full slow cooling, but often will serve the purposes required.

It is thus seen that iron and steel in many shapes and with a great variety of physical properties will be laid

""Metallurgy of Steel," by H. M. Howe, vol. i, chap, ii, p. 24, 2hd Ed., 1891.

before the electric- welding engineer, and it will depend more or less upon his familiarity with this wide range of conditions how he will meet and solve the problems. This brief resume from the mining of the iron ore to its fabrication for use in the mechanic arts is a necessary preliminary to the study and practice of the joining of steel by electric power. To materials that have already been subjected to modifications in their chemical constituents, to changes in their physical properties by the application of different temperatures, and to internal mutations of their own making — to these materials are applied chemical reactions, and physicaLeff ects of like nature to obtain a connection which will either approach or exceed the advantageous characteristics of the original metal. It is mainly upon this point that objectors to electric welding rest their argument : that no joint can be equal to the original material. It is upon the same point that those who are favorable toward and well acquainted with electric welding uphold their belief in the process because the e^ddence has accumulated to a degree which permits the statement: that electric- welded joints can be made which will be stronger than the metals joined.

Summary. — This plainly places before the engineer a new problem, namely, whether he wishes his jointures to be more or less lasting than the materials which he is using for a given purpose. On the other hand, with this new ability to secure a more favorable joint will he not economically and safely reduce the amount of materials to secure the same result? These engineering problems are closely knit with a study of the metallurgy of steel and the modern applications of electricity to the welding of steel.

Chapter II

Fundamental principles separate electric-welding processes into two distinct groups: resistance methods and arc methods. As its name implies, resistance welding is accomplished by the phenomenon of the transformation of electric energy into heat energy by opposition to the flow of current. The arc method follows the behavior of the electric circuit whenever it is suddenly opened, namely, the production of a spark which if the distance between the terminals is maintained will preserve an arc. It was this characteristic of electricity that produced the first electric-lighting unit, the arc lamp; and the former, or resistance characteristic, that furnished the incandescent lamp.

Many processes of welding have been devised from these two primary groups but, as will be seen, the differences rest entirely on details generally associated with special applications. The following diagram gives the sub-divisions of each group :

Resistance Processes

Arc Processes

1. Butt welding

3. Seam welding

1. Carbon arc welding

2. Metallic arc welding a. Bare electrode 6. Covered electrode

1. Gas flux

2. Liquid flux

Butt Welding. — This process consists of bringing two pieces of metal into contact end on end and then clamping these ends between two jaws of high conductive material supphed with high current at low voltage from the secondary of a transformer. With pressure applied forcing the two pieces together and the current turned on, a localized welding temperature is provided which, as the operation is visible at all times, may be held on until proper fusion results. It is usual practice to maintain the pressure for a short time after the current is turned off. Due to the end pressure a burr will form at the juncture of the pieces aiding the observer to make a satisfactory weld. As the outer surface of the metals tends to conduct heat away from the point of contact of the clamping jaws so advantageously, the interior metal offering the greater resistance will arrive at a welding heat before the exterior. This feature protects the process from any doubt as to the soundness of the finished weld. In blacksmith welding the reverse is true and the finished weld exteriorly may look sound but in reality cover poor fusion. There is a large field in the industries for the application of butt welding, especially for the welding of tool shanks, rods, etc.

Spot Welding. — This process is so called because the materials are not joined together continuously, but spaced as in riveting. Plates are lapped and then brought to a machine and placed as in butt welding between two high conducting points. Spot welding for this reason is frequently referred to as " point " welding. Pressure is brought to bear upon these points, current of high value is turned on, the materials at the points are thus raised to a welding temperature, current is then removed, the pressure released, and the weld completed. The intensity of the current produces a very rapid rise of temperature which with the pressure tend to prevent the ill effects of entrapping oxygen in the weld. This characteristic assists in practice to blow out the slag which may form on the surfaces of the plates. It is natural to see an analogy between smith welding and resistance welding, for just as the smith heats his materials in a forge and then applies pressure with his hammer, so the spot-welding machine raises the material to welding heat and then applies pressure. It would be reasonable to believe that the differences in the application of pressure would have a marked effect upon the results in a relative degree to the time difference in the raising of the temperature, but this particular interesting side of spot welding has never been fully investigated or at least reported. Spot welding of light materials, steel up to inch, has had a remarkable development in this country for some years. Heavy spot welding, steel up to 1 inch, was experimented with in the last few years. In the manufacture of automobile bodies, metal furniture, and bicycle parts, it has established itself firmly. It is especially fitted for shop work, and for new construction, but has not been developed nor used for repair work. The decided advantages of resistance welding over arc welding rest upon the fact that a weld can be made independently of the operator, that the work can be done rapidly and in the open, and that it permits of practical inspection. As will be seen later these points of advantage give a confidence in results not accorded to any of the practical processes of arc welding. It is for this reason that those who are responsible for new construction work are less conservative to the introduction of spot welding on a large scale.

Seam Welding. — A minor application of resistance welding is employed on very thin sheets for making a continuous seam. Instead of clamping jaws, or points, the current is led to the work on rollers under pressure. It is possible that this method may be capable of extension to heavier materials but it has not been shown by any large commercial use. The seam welded successfully in this way would undoubtedly provide a ready means for obtaining fluid-tight work and its point of economy would then rest upon the speed with which good welding could be accomplished. When considering fluid-tight work one point of vital difference must be borne in mind, namely, the simple retaining of the liquid in the vessel as against the hquid under pressure.^ It may be stated as a general precaution that all electric-welding processes should be carefully investigated before applying them to work involving danger to human life. Doubtless future research will permit this work to be done, but the applications not involving such risks are plentiful.

Carbon Arc Welding. — In this process an arc is held between the metals to be joined and a pencil or rod of carbon. In all arc welding the rod used for maintaining the arc and manipulated by the operator is called the electrode. The carbon electrode is connected to the negative side of a low potential circuit (60 to 75 volts) and the work to the positive side. A very intense heat is produced by the carbon arc which draws from the electric supply 300 to 600 amperes. Flanged or butted edges of thin tank steel (1/16 inch and 3/32 inch thick) are satisfactorily fused together by the carbon electrode

^ This refers also to gases under pressure.

without added metal,^ but steel of greater thickness requires a melt rod of proper composition to supply the filling. The process under these conditions bears a similarity to soldering. Where there is a great quantity of shop repetition work with thin materials, automatic machines equipped with carbon electrodes are feasible and economical. The process is specially valuable in the heating of large areas and the filling of large holes. It is a good tool for heavy repair work. It is also possible to cut metals with the carbon arc, but few operators are able to follow a sharp line and thus the uncontrolled arc leaves a very poor working edge. It is stated that the carbon arc is economical for the rough cutting of scrap materials and the demohtion of steel buildings. Undoubtedly there is a future for this process not only in special lines, but for extensive application to new construction when methods have been devised for the better control of the arc and ease in manipulation.