Electric welding
ELECTRIC WELDING
MACHINERY'S REFERENCE BOOK NO. 127
PUBLISHED BY MACHINERY, NEW YORK, 1914
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CONTENTS
- Electric Welding Processes
- Electric Resistance Process of Welding
- Point and Ridge Method of Electric Welding
- Electric Arc Welding
- Electric Soldering
CHAPTER I - ELECTRIC WELDING PROCESSES
Although the electric welding process passed out of the experimental into the practical stage some years ago, electric welding is still a rather vague subject to most mechanics. Electric welding, however, plays an important part nowadays in the manufacture of a great many articles, and several companies have been formed which devote their entire attention to the manufacture of articles in which electric welding is an integral part of the manufacturing process. Without the process of electric welding, many of these products would have to be manufactured in an entirely different way, and in many cases at a greatly increased cost.
There are at least five distinct processes of electric welding in use at the present time. These processes are commonly known as the Zerener, the Benardos, the Strohmenger-Slaughter, the La Grange-Hoho, and the Thomson processes.
The Zerener Process
In the first process mentioned above, the Zerener process, perhaps more commonly known as the electric blow-pipe method, an electric arc is drawn between two carbon electrodes. This arc is then caused to impinge upon the metal surfaces to be welded by means of an electro-magnet. This welding system was introduced by Dr. Zerener of Berlin, Germany, some twenty years ago. No current passes through the work in this case.
The Zerener system, as well as all arc-welding systems, is based upon the fact that when two rods of carbon, connected by suitable means to the poles of a dynamo or to the terminals of current supply cables, are brought into contact, a flame is caused to play between them, this flame being known as an arc. Variations in the gap or distance between the carbon electrodes, or the interposition of resistances of varying intensity, increase or decrease, as the case may be, the amount of current passing through the electrodes, and thus alter the size of tire flame or arc.
In an improvement on this method, known as the Voltex process, the carbons contain a small percentage of metallic oxides oxide of iron, for instance which is converted by the heat generated into its metallic form and then vaporized. The vapor tends to increase the size of the arc and minimizes or prevents the carbonization of the work by the carbon of the electrodes at the welding point.
The various systems of electric arc welding are especially valuable when the parts to be welded must, after welding, retain their original positions or relationship with reference to each other. A crack in a machine part illustrates such a case. These methods are also applicable when making an abrupt joint between two plates, filling up holes in castings and generally for any work in which it is necessary to add metal to form the joint.
In arc welding the temperature of the arc is practically impossible of control; to avoid melting, then, even in cases where melting is unnecessary, which not often is the case, it would be compulsory to remove the work or arc at the very instant welding heat was attained, a point not readily determined, having regard to the intense light at the arc necessitating the use of almost opaque spectacles, which not only obscure the vision, but result in severe eye-strain. The heat generated is so intense that it is necessary also to guard the hands and face to avoid burning.
In the case of the iron alloys, the arc method is often open to the objection that it demands infallibility on the part of the operator. While a good weld is almost as good as original continuity, the fact that this is only possible when the pieces are heated to a definite temperature, renders the method less satisfactory than the Thomson process yet to be described. From the point of view of perfection of product, the process is lacking, for the reason that the temperature of the arc between 5000 and 7000 degrees P. is far in excess of the melting-point of the iron alloys, and is extremely difficult to control.
The Benardos Process
The Benardos process is also based upon the use of the electric arc, the characteristic principle of this process being that the electric arc is drawn directly between the metal to be welded, which itself forms one electrode for the electric current, and the carbon electrode, which forms the other terminal of the circuit. In this process, the pieces of metal to be welded are melted on their faces together with a small iron rod which acts as a kind of solder and flows in between the two surfaces to be joined together by the welding process. This system, if properly adapted to the work to be done, and with a plant well designed for generating, distributing and regulating the current, is practical, simple and effective. The quantity of current used depends on the thickness to be welded and may, in ordinary practice, range from 200 to 500 amperes. The arrangement of using the metal to be welded as one electrode for the electric circuit makes it possible to obtain a great amount of heat in the weld.
In the Benardos process, the direction of flow of the electric cur- rent may be in either direction, but, as a rule, the work or metal electrode is the positive and the carbon electrode the negative pole. In case the flow is reversed, the arc will be shorter and the carbon from the electrode is more liable to enter the weld, thereby hardening the material and rendering it brittle. In commencing the weld, the carbon electrode is brought into contact with the work, thus causing an electric current to flow, but is quickly withdrawn, introducing a resistance which produces an arc of high temperature.
In all arc-welding systems, it is difficult to absolutely prevent the introduction of carbon into the work. An improvement, known as the Slavianoff system, in which a very small arc is used, and which, for that reason, is much slower, prevents, to a large extent, the introduction of carbon into the work, and is therefore preferred, particularly for small work. In this process the electrode is of the same metal as the work.
When a number of welding machines working according to the Benardos system are employed, it is necessary that the current be supplied in such a manner that one machine will not affect the arc of another. This is effected very simply by generating in a compound wound dynamo of ample capacity, and the machine should be slightly over, rather than under, compounded. By this arrangement an in-crease of load does not lower the voltage. In a well-designed machine the voltage scarcely varies, provided the engine driving it is efficient to maintain its speed. The arcs are arranged in parallel, and each arc is provided with a regulator to adjust the current to the work to be done. The rod of carbon forming the negative electrode is fastened in an insulated holder of light construction. The workman holds this in his hand, strikes the arc by placing the carbon in contact with the work, and manipulates it so as to spread the arc and heat the work at and near the point to be welded with what is described as a soaking heat. When the welding heat is attained, the work is hammered or not according to circumstances. Screens with colored glass windows are used to protect the eyes and skin of the workman from the effect of violet rays.
The Strohmenger-Slaughter System
The Strohmenger-Slaughter system, also an arc-welding system, may be worked with either direct or alternating current. It is generally assumed that the alternating current is preferable for this purpose. The voltage need not be very high and the amount of the current within limits is not important. Successful welding has been carried out with 85 volts used with direct current and 220 volts with alternating current. The quantity of the current depends upon the nature of the work. The parts to be welded are placed in the required position and an electrode is laid upon and along the welding line. This electrode consists of a soft iron rod covered all over except at the extreme ends with a flux suitable for the metal to be welded. Then the work and one end of the electrode are brought into contact, causing, by a series of arcs along the welding line, the electrode to melt and to coat the weld with the flux, thereby preventing oxidation. The flux will flake off when the metal cools. It is claimed that this system is .used successfully in the welding of rails and in other repairs by building up worn places, but it' is not as generally known as the other systems.
The La Grangre-Hoho Process
The La Grange-Hoho system, commonly known as the "water pail" forge, is distinctly different from all other processes in principle as well as in its practical application, and is, properly speaking, only a heating process replacing the blacksmith's fire. A wooden tank is filled with a bath containing a solution of borax and potassium carbonate in water. In this bath, the positive electrode of the electric circuit is placed. The negative electrode is connected to the metal to be forged or welded, which is then also immersed in the fluid in the tank. The metal is then permitted to remain in the fluid until it has reached the welding temperature. The object to be welded is then removed and the actual forging or welding process is carried out in the usual manner on the anvil under a hammer. Strictly speaking, therefore, this is not an electric welding process, but merely an electric heating process for bringing the metal to a welding heat.
The Thomson Process
In the Thomson process, also known as the incandescent or resistance process, the metals to be welded are brought into intimate con- tact, being usually held closely together by metal clamps actuated by springs so as to permit a permanent pressure on the parts even when the metal at the welding surfaces commences to melt. By this contact, the parts to be welded complete an electric circuit, and the resistance at the points of contact between the metals produces a welding temperature in a very few seconds, at the same time as the two metals are, by the spring-actuated clamps, forced together automatically, and welded. A distinct feature of this electric welding process is that the interior is raised to a welding temperature before the surface reaches that heat. When heated in the forge for welding, the opposite conditions take place. In the process of electric welding, if the exterior surfaces weld, the operator is sure that the interior is also welded, since it must, by necessity, be of a somewhat higher heat. With ordinary forge welding the surfaces may present a perfect weld and still cover an imperfect joint inside.
A few years ago it was thought that electric welding would be practical only for very small objects, on account of the high amperage required, but since that time the process has been developed so that it is now possible to electrically weld parts of considerable size. The process is particularly suited for the manufacture of automobile and bicycle parts, carriage hardware, and mechanics' tools of various descriptions.
When, as mentioned above, the two parts to be welded have been placed against each other, in the electric circuit, which heats the metal at the juncture to a molten state, the separate parts will be united into one piece in such a manner that the joint is practically imperceptible, but at first a burr or upset is produced around the welded surface, composed of the expelled oxidized and otherwise inferior metal. This oxidation is, of course, removed, and then a perfect joint is the result.
One very important question in regard to electric welding, and for that matter any other process for joining metallic parts, is whether the joint is sound. Experiments and tests, as well as use of electrically welded joints, have unquestionably demonstrated its reliability. In the case of electric welding, the great variety of parts so joined has shown, beyond doubt, that the joint is practically as sound as the solid sections in the parts so joined. Very commonly the parts which are welded by the electric process are subjected to abuse and rough handling, or to heavy stresses. Especially is this so in automobile work. The results obtained have been so satisfactory as to place the art among the most useful of the applications of electricity.
In this connection, it may be well to mention that the Thomson process, while originally an American invention, has also received considerable attention in England. A writer in the London Times some time ago, called attention to the fact that the system has caused a complete revolution in existing methods of manufacture in many industries, and that electric welding had created some entirely new manufactures. As to the reliability of these joints, this writer also mentioned that tests had been carried on regarding the comparative strength of electric and ordinary forged welds, and that these tests show that while the ordinary forge weld of iron bars shows an average strength of 89,3 per cent, as compared with the strength of the solid, electrically welded joints show a strength of 91,9 per cent.
In giving a summary of the advantages which can, with propriety, be claimed for the electric welding process, the following may be stated as being the most important: Finished or nearly finished work may be welded and repaired without damage; the welding operation can be closely watched as it proceeds, and faulty welds prevented; the process is carried out with great rapidity, occupying only a few seconds, and in small work it is performed almost instantaneously; and, finally, impurities are expelled from the joint, and a perfectly homogeneous weld is obtained. The cost for the generation of heat, generally speaking, is probably the same for forge and electric welding, but with the electric process the cost of labor is greatly reduced.
In the following chapters the more important of these welding processes will be dealt with in detail, the methods connected with each being explained and the advantages pointed out.
Welding Machines
The electric current transformer, the clamping device and the pressure device are the three necessary elements in an electric welding machine. Although it is possible to give the transformer a different location from that of the two mechanical elements, it is rarely done, the commercial welding machine employing all three elements in the same structure. There are, of course, many special departures from this general form. The mechanical and electrical controls may be operated by hand, by foot, or may be automatic and operated by power. For small work, like welding wire, spring pressure in forming the weld is usually employed, and clamping is done either by hand or by power; for metals like copper and brass a weight pressure is usually best; for rounds and like sections up to % inch, hand pressures are usually employed; for larger sections, hydraulic pressure or pressure obtained through self-contained oil jacks is used.
Electric welding machines are necessarily more or less special in the construction of their clamps and electrodes, no one machine being suitable for a great variety of sizes or forms of work, and some are entirely special and suitable only for the work for which they are built. Some are called semi-automatic, as when the operator's duty is only the putting in and taking out of the pieces, while other machines are entirely automatic, as regards clamping, exerting pressure for welding, and controlling the current.
Power machines for spot welding are built with heating time-adjustments and regulation so that the machine can be set for the right speed and the correct time of heating required for varying thicknesses and conditions of stock. They can be operated continuously or intermittently as necessary, so that the greatest amount of work which the operator can handle will be taken care of by the machine.
There are at least five distinct processes of electric welding in use at the present time. These processes are commonly known as the Zerener, the Benardos, the Strohmenger-Slaughter, the La Grange-Hoho, and the Thomson processes.
The Zerener Process
In the first process mentioned above, the Zerener process, perhaps more commonly known as the electric blow-pipe method, an electric arc is drawn between two carbon electrodes. This arc is then caused to impinge upon the metal surfaces to be welded by means of an electro-magnet. This welding system was introduced by Dr. Zerener of Berlin, Germany, some twenty years ago. No current passes through the work in this case.
The Zerener system, as well as all arc-welding systems, is based upon the fact that when two rods of carbon, connected by suitable means to the poles of a dynamo or to the terminals of current supply cables, are brought into contact, a flame is caused to play between them, this flame being known as an arc. Variations in the gap or distance between the carbon electrodes, or the interposition of resistances of varying intensity, increase or decrease, as the case may be, the amount of current passing through the electrodes, and thus alter the size of tire flame or arc.
In an improvement on this method, known as the Voltex process, the carbons contain a small percentage of metallic oxides oxide of iron, for instance which is converted by the heat generated into its metallic form and then vaporized. The vapor tends to increase the size of the arc and minimizes or prevents the carbonization of the work by the carbon of the electrodes at the welding point.
The various systems of electric arc welding are especially valuable when the parts to be welded must, after welding, retain their original positions or relationship with reference to each other. A crack in a machine part illustrates such a case. These methods are also applicable when making an abrupt joint between two plates, filling up holes in castings and generally for any work in which it is necessary to add metal to form the joint.
In arc welding the temperature of the arc is practically impossible of control; to avoid melting, then, even in cases where melting is unnecessary, which not often is the case, it would be compulsory to remove the work or arc at the very instant welding heat was attained, a point not readily determined, having regard to the intense light at the arc necessitating the use of almost opaque spectacles, which not only obscure the vision, but result in severe eye-strain. The heat generated is so intense that it is necessary also to guard the hands and face to avoid burning.
In the case of the iron alloys, the arc method is often open to the objection that it demands infallibility on the part of the operator. While a good weld is almost as good as original continuity, the fact that this is only possible when the pieces are heated to a definite temperature, renders the method less satisfactory than the Thomson process yet to be described. From the point of view of perfection of product, the process is lacking, for the reason that the temperature of the arc between 5000 and 7000 degrees P. is far in excess of the melting-point of the iron alloys, and is extremely difficult to control.
The Benardos Process
The Benardos process is also based upon the use of the electric arc, the characteristic principle of this process being that the electric arc is drawn directly between the metal to be welded, which itself forms one electrode for the electric current, and the carbon electrode, which forms the other terminal of the circuit. In this process, the pieces of metal to be welded are melted on their faces together with a small iron rod which acts as a kind of solder and flows in between the two surfaces to be joined together by the welding process. This system, if properly adapted to the work to be done, and with a plant well designed for generating, distributing and regulating the current, is practical, simple and effective. The quantity of current used depends on the thickness to be welded and may, in ordinary practice, range from 200 to 500 amperes. The arrangement of using the metal to be welded as one electrode for the electric circuit makes it possible to obtain a great amount of heat in the weld.
In the Benardos process, the direction of flow of the electric cur- rent may be in either direction, but, as a rule, the work or metal electrode is the positive and the carbon electrode the negative pole. In case the flow is reversed, the arc will be shorter and the carbon from the electrode is more liable to enter the weld, thereby hardening the material and rendering it brittle. In commencing the weld, the carbon electrode is brought into contact with the work, thus causing an electric current to flow, but is quickly withdrawn, introducing a resistance which produces an arc of high temperature.
In all arc-welding systems, it is difficult to absolutely prevent the introduction of carbon into the work. An improvement, known as the Slavianoff system, in which a very small arc is used, and which, for that reason, is much slower, prevents, to a large extent, the introduction of carbon into the work, and is therefore preferred, particularly for small work. In this process the electrode is of the same metal as the work.
When a number of welding machines working according to the Benardos system are employed, it is necessary that the current be supplied in such a manner that one machine will not affect the arc of another. This is effected very simply by generating in a compound wound dynamo of ample capacity, and the machine should be slightly over, rather than under, compounded. By this arrangement an in-crease of load does not lower the voltage. In a well-designed machine the voltage scarcely varies, provided the engine driving it is efficient to maintain its speed. The arcs are arranged in parallel, and each arc is provided with a regulator to adjust the current to the work to be done. The rod of carbon forming the negative electrode is fastened in an insulated holder of light construction. The workman holds this in his hand, strikes the arc by placing the carbon in contact with the work, and manipulates it so as to spread the arc and heat the work at and near the point to be welded with what is described as a soaking heat. When the welding heat is attained, the work is hammered or not according to circumstances. Screens with colored glass windows are used to protect the eyes and skin of the workman from the effect of violet rays.
The Strohmenger-Slaughter System
The Strohmenger-Slaughter system, also an arc-welding system, may be worked with either direct or alternating current. It is generally assumed that the alternating current is preferable for this purpose. The voltage need not be very high and the amount of the current within limits is not important. Successful welding has been carried out with 85 volts used with direct current and 220 volts with alternating current. The quantity of the current depends upon the nature of the work. The parts to be welded are placed in the required position and an electrode is laid upon and along the welding line. This electrode consists of a soft iron rod covered all over except at the extreme ends with a flux suitable for the metal to be welded. Then the work and one end of the electrode are brought into contact, causing, by a series of arcs along the welding line, the electrode to melt and to coat the weld with the flux, thereby preventing oxidation. The flux will flake off when the metal cools. It is claimed that this system is .used successfully in the welding of rails and in other repairs by building up worn places, but it' is not as generally known as the other systems.
The La Grangre-Hoho Process
The La Grange-Hoho system, commonly known as the "water pail" forge, is distinctly different from all other processes in principle as well as in its practical application, and is, properly speaking, only a heating process replacing the blacksmith's fire. A wooden tank is filled with a bath containing a solution of borax and potassium carbonate in water. In this bath, the positive electrode of the electric circuit is placed. The negative electrode is connected to the metal to be forged or welded, which is then also immersed in the fluid in the tank. The metal is then permitted to remain in the fluid until it has reached the welding temperature. The object to be welded is then removed and the actual forging or welding process is carried out in the usual manner on the anvil under a hammer. Strictly speaking, therefore, this is not an electric welding process, but merely an electric heating process for bringing the metal to a welding heat.
The Thomson Process
In the Thomson process, also known as the incandescent or resistance process, the metals to be welded are brought into intimate con- tact, being usually held closely together by metal clamps actuated by springs so as to permit a permanent pressure on the parts even when the metal at the welding surfaces commences to melt. By this contact, the parts to be welded complete an electric circuit, and the resistance at the points of contact between the metals produces a welding temperature in a very few seconds, at the same time as the two metals are, by the spring-actuated clamps, forced together automatically, and welded. A distinct feature of this electric welding process is that the interior is raised to a welding temperature before the surface reaches that heat. When heated in the forge for welding, the opposite conditions take place. In the process of electric welding, if the exterior surfaces weld, the operator is sure that the interior is also welded, since it must, by necessity, be of a somewhat higher heat. With ordinary forge welding the surfaces may present a perfect weld and still cover an imperfect joint inside.
A few years ago it was thought that electric welding would be practical only for very small objects, on account of the high amperage required, but since that time the process has been developed so that it is now possible to electrically weld parts of considerable size. The process is particularly suited for the manufacture of automobile and bicycle parts, carriage hardware, and mechanics' tools of various descriptions.
When, as mentioned above, the two parts to be welded have been placed against each other, in the electric circuit, which heats the metal at the juncture to a molten state, the separate parts will be united into one piece in such a manner that the joint is practically imperceptible, but at first a burr or upset is produced around the welded surface, composed of the expelled oxidized and otherwise inferior metal. This oxidation is, of course, removed, and then a perfect joint is the result.
One very important question in regard to electric welding, and for that matter any other process for joining metallic parts, is whether the joint is sound. Experiments and tests, as well as use of electrically welded joints, have unquestionably demonstrated its reliability. In the case of electric welding, the great variety of parts so joined has shown, beyond doubt, that the joint is practically as sound as the solid sections in the parts so joined. Very commonly the parts which are welded by the electric process are subjected to abuse and rough handling, or to heavy stresses. Especially is this so in automobile work. The results obtained have been so satisfactory as to place the art among the most useful of the applications of electricity.
In this connection, it may be well to mention that the Thomson process, while originally an American invention, has also received considerable attention in England. A writer in the London Times some time ago, called attention to the fact that the system has caused a complete revolution in existing methods of manufacture in many industries, and that electric welding had created some entirely new manufactures. As to the reliability of these joints, this writer also mentioned that tests had been carried on regarding the comparative strength of electric and ordinary forged welds, and that these tests show that while the ordinary forge weld of iron bars shows an average strength of 89,3 per cent, as compared with the strength of the solid, electrically welded joints show a strength of 91,9 per cent.
In giving a summary of the advantages which can, with propriety, be claimed for the electric welding process, the following may be stated as being the most important: Finished or nearly finished work may be welded and repaired without damage; the welding operation can be closely watched as it proceeds, and faulty welds prevented; the process is carried out with great rapidity, occupying only a few seconds, and in small work it is performed almost instantaneously; and, finally, impurities are expelled from the joint, and a perfectly homogeneous weld is obtained. The cost for the generation of heat, generally speaking, is probably the same for forge and electric welding, but with the electric process the cost of labor is greatly reduced.
In the following chapters the more important of these welding processes will be dealt with in detail, the methods connected with each being explained and the advantages pointed out.
Welding Machines
The electric current transformer, the clamping device and the pressure device are the three necessary elements in an electric welding machine. Although it is possible to give the transformer a different location from that of the two mechanical elements, it is rarely done, the commercial welding machine employing all three elements in the same structure. There are, of course, many special departures from this general form. The mechanical and electrical controls may be operated by hand, by foot, or may be automatic and operated by power. For small work, like welding wire, spring pressure in forming the weld is usually employed, and clamping is done either by hand or by power; for metals like copper and brass a weight pressure is usually best; for rounds and like sections up to % inch, hand pressures are usually employed; for larger sections, hydraulic pressure or pressure obtained through self-contained oil jacks is used.
Electric welding machines are necessarily more or less special in the construction of their clamps and electrodes, no one machine being suitable for a great variety of sizes or forms of work, and some are entirely special and suitable only for the work for which they are built. Some are called semi-automatic, as when the operator's duty is only the putting in and taking out of the pieces, while other machines are entirely automatic, as regards clamping, exerting pressure for welding, and controlling the current.
Power machines for spot welding are built with heating time-adjustments and regulation so that the machine can be set for the right speed and the correct time of heating required for varying thicknesses and conditions of stock. They can be operated continuously or intermittently as necessary, so that the greatest amount of work which the operator can handle will be taken care of by the machine.
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