Electric Arc Welding
ELECTRIC ARC WELDING
BY E. WANAMAKER AND H. R. PENNINGTON; 1921
DOWNLOAD FREE BOOK: Electric Arc Welding
PREFACE
The authors of this work have not attempted to cover the electric welding art in its broadest sense. The book is confined almost exclusively to autogenous electric arc welding.
The phenomena of the welding arc, and the metallurgy of welding, are in such a state of development that the authors' in- formation has been limited to the research which has come under their observation. Many phases of these subjects have been left, therefore, to specialists more adequately equipped both as to electric and metallurgical data as well as laboratory apparatus. The effort has been made to present information that is most in demand for practical purposes.
The material is conveniently and logically arranged for ready reference. A large amount of practical information on many phases of the application of the art has- been incorporated; for instance, descriptions of welding systems and their installation, phenomena of the metallic and carbon welding arc, training of operators, sequence of metal disposition for various types of joints and building up operations, electrode materials used, weldability of various metals, weld composition, thermal disturbances of parts affected by the welding process, physical properties of completed welds, efficiency of welding equipments expressed in pounds of metal used or deposited per kilowatt hours, welding cost, etc.
It is desired to lay particular stress on the fact that a very small percentage of the possibilities and advantages of arc welding, from an industrial standpoint, are being made use of at the present time, and if this work will result in a broader application of the art, as well as further and more extensive research, the authors will feel well repaid for their humble efforts.
The book is based largely on an extensive series of articles by the authors which was published in The Railway Electrical Engineer. Such parts of these articles as are used here, however, have been thoroughly revised and brought up-to-date.
The phenomena of the welding arc, and the metallurgy of welding, are in such a state of development that the authors' in- formation has been limited to the research which has come under their observation. Many phases of these subjects have been left, therefore, to specialists more adequately equipped both as to electric and metallurgical data as well as laboratory apparatus. The effort has been made to present information that is most in demand for practical purposes.
The material is conveniently and logically arranged for ready reference. A large amount of practical information on many phases of the application of the art has- been incorporated; for instance, descriptions of welding systems and their installation, phenomena of the metallic and carbon welding arc, training of operators, sequence of metal disposition for various types of joints and building up operations, electrode materials used, weldability of various metals, weld composition, thermal disturbances of parts affected by the welding process, physical properties of completed welds, efficiency of welding equipments expressed in pounds of metal used or deposited per kilowatt hours, welding cost, etc.
It is desired to lay particular stress on the fact that a very small percentage of the possibilities and advantages of arc welding, from an industrial standpoint, are being made use of at the present time, and if this work will result in a broader application of the art, as well as further and more extensive research, the authors will feel well repaid for their humble efforts.
The book is based largely on an extensive series of articles by the authors which was published in The Railway Electrical Engineer. Such parts of these articles as are used here, however, have been thoroughly revised and brought up-to-date.
CONTENTS
SECTION I
History of the Evolution of Welding Processes Smith or Forge Welding, Resistance Welding, Thermit Welding, Ox-acetylene Welding, and Electric Arc Welding
SECTION II
Equipment for Electric Arc Welding Types Used, Operating Characteristics and Circuits
SECTION III
Installation of Arc Welding, Equipment, Welding Accessories, Portable and Stationary Equipment, Eye and Body Protection, Cleaning Devices,
SECTION IV
Electric Arc Welding Principles, Circuit Polarity, Arc Heat, Arc Temperature, Arc Current and Potential, Metal Transfer, etc
SECTION V
Training of Operators, Practice Exercises, Sequence of Metal Deposition, Fusion, Penetration, Expansion and Contraction
SECTION VI
Carbon Arc Welding, Metal Cutting by Electric Arc and by Oxidation
SECTION VII
Electrode Materials, Composition, Specifications,
SECTION VIII
Preparation of Work for Electric Arc Welding, Various Designs of Welds, Types of Joints
SECTION IX
Iron and Steel, and the Welding of Each, Non-ferrous Metals and
Their Weldability
SECTION X
Application of Arc Welding to Railroads and Structural Engineering
SECTION XI
Miscellaneous Notes and Arc Welding Data, Composition of Weld, Thermal Disturbances, Physical Qualities Cost, etc.
EVOLUTION OF WELDING PROCESSES
There are several methods of joining metals other than by means of mechanical fastenings, such as bolts, clamps, rivets, hinges, etc. The first form of jointure known to man, other than the above-mentioned, was fire or forge welding performed by a smith, the operation consisting essentially of heating the parts to be welded to the proper temperature and perfecting a union by applying pressure by means of hammer and anvil.
As pressure welding was limited in its application man endeavored to find some other way to join metals, or to make additions of metal to other metal, without the use of pressure. He was eventually successful in this endeavor and welding without pressure came to be known as autogenous welding, so called because of its self- or auto-generation; i. e., it is self-produced by the application of intense heat without any physical process of compression or hammering.
We, therefore, have two general forms of welding one requiring external application of pressure to complete the weld, and one in which the weld is completed without the external application of pressure. In the first form the union is secured by using a comparatively low heat and high pressure. In the second the union is secured by a relatively high temperature without the aid of any external pressure. It will be seen, in view of the fact that welding requires actual fusion of the metals joined or added, that the process differs inherently from those methods of joining metals known as brazing or soldering, in which cold surfaces are united by the interposition of a fused metallic cementing material, which is an example of adhesion rather than cohesion.
Electric Arc Welding. Electric arc welding is commercially the most recent and newest process of any form of welding. Benardos and Slavianoff are generally credited with the discovery of the possibilities of the carbon arc and metallic arc, respectively, for the welding of metals. The carbon arc process was the first one to be used for welding metals, and was first used, on a small scale, 30 years ago. This form of arc welding is sometimes called the Benardos process. Not long after the carbon arc process was demonstrated by Benardos, Slavianoff demonstrated the possibilities of the metallic arc process, but it was not until comparatively recent years that either was used to any appreciable commercial extent.
After the first discovery of the more or less vague possibilities of electric arc welding the progress in the development of the art was extremely slow, due to the fact that it was only with great difficulty that the work of development could be carried on. There were several reasons for the existence of such a condition, most important of which was the fact that the men who first conceived and worked to develop and improve the welding art were apparently versed only in one branch or phase of that science.
It must be borne in mind that to develop this art it was necessary to make an extensive investigation into the phenomena existing in the arc, both carbon and metallic, when using it for the fusion of metals. No matter how well versed a man may be in electrical science it does not necessarily follow that he may understand the behavior of an electric arc when used for welding metals. On the other hand, although a man may be well trained in metallurgy it does not necessarily follow that he can under- stand the behavior of the metals when subjected to the temperature of the electric arc. In other words, the electrical men did not understand, nor were they thoroughly acquainted with the peculiarities manifested by the electric arc when used in conjunction with molten metal during the welding process. And the metallurgical men were not conversant with the behavior of metals under the action of the arc stream with its attendant high temperature variations.
In view of these existing conditions it was necessary that much time be spent in research work by both electrical and metallurgical men. Indeed, it was not until the electrical phenomena and metallurgical phenomena were coordinated that a real beginning was made in the development of the art of arc welding. And not until then did the metal using industries begin to see the possibilities of its use and to lend their financial assistance to its development.
The Electric Arc. If two carbons which are connected to a sufficiently powerful electric source are brought together and then slowly separated the current will not cease to flow, provided they are not too widely separated. Instead an arc will be formed and the current will continue to flow, since the vapor formed between the two carbons serves as a conductor for the passage of the current across the intervening space. The temperature of the positive electrode of a carbon arc has been estimated at about 7,500 deg. Fahr. If an arc is formed between two metallic electrodes the temperature will be somewhat lower. The temperature of any arc will be at least equal to the vaporization point of the materials forming the electrodes. In electric welding the heat is communicated to the metal by an electric arc. In one method the arc is deflected from the space between the carbon electrodes by a magnetic field. In this case the metal takes no part in the conduction of the current; the heat is communicated by the gases of the arc, and to a small extent by the radiation from the hot carbon electrodes between which the arc is formed. This particular method was inherently not a commercial success, as is evidenced by the mechanical impracticability of applying the arc to the work. Also, minute particles of carbon in the arc stream produced by the consumption of the electrodes were deposited in the weld, thereby leaving the finished weld exceedingly hard.
The form of carbon arc welding generally referred to, is one in which .the work, or part on which metal is to be added, forms the positive pole of a direct current circuit, and an arc is drawn between this and a carbon rod to which a handle is attached for manipulating. At the point of arc contact on the work the metal becomes molten. The metal, which it is necessary to add to the weld, is supplied by melting a filler rod in the arc, the minute globules of molten metal commingling and fusing with the molten metal of the parts to be welded. In this method the bad effects of deposited carbon are largely eliminated by making the work positive, in which case the current flows from the metal to the carbon instead of from the carbon to the metal, as was the original and former practice.
A constant potential source of current supply, together with a choking resistance in series with the heating arc so arranged as to permit an adjustment of current strength, has long been used, and is yet to a considerable extent. Sufficient potential is always required (approximately 70 volts) to maintain steadily an arc of proper length. The current required will range from 50 amperes to 600 amperes, and even higher in some instances, depending upon the character of the work.
The carbon arc process has been limited in its scope of application by its practical confinement to down-hand welding; to the tendency to oxidation resulting in brittleness; to the large area heated, resulting in the bad effects of excessive expansion and contraction, loss of energy or heat radiated by the large arc area, and conduction by the metal being welded; and the necessity of heavy currents with the cumbersome equipment required.
During the past two years much has been contributed to the electric welding art. Most of the development has been along the lines of metallic arc welding, consisting of improvements in equipments, electrodes and weld protection, which has in turn led to a more intelligent application of the process, and the resultant greater extension of its use.
Metallic arc welding consists of drawing an arc between the part to be welded and a metallic electrode. The electrode is in the form of a wire, or small rod. It may or may not be of similar composition to the metal which is to be welded. The arc is established by striking the wire electrode to be fused to the work with a dragging touch and withdrawing it a slight distance, approximately 1/8 in., forming what is commonly called the metallic arc. This form of arc welding differs from the carbon arc in the fact that the filler rod or wire forms one terminal of the arc, which is melted and is conveyed in liquid form across the arc and deposited in the crater on the work piece, which forms the other terminal of the arc.
Due to the fact that it is possible to project metal horizontally and vertically upward, it is possible to do welding on a wall or overhead with this form of arc welding, something which is not commercially possible with the carbon arc. This feature has been a contributory factor toward making the metallic arc welding process to all intents and purposes universal, and gives it an extremely wide field of application.
After many years of research it has been conclusively demonstrated that the metallic arc welding process demands a certain close coordination of the equipment and the arc characteristic, if the best results are to be obtained. Great strides have been made in the perfection of welding equipments and electrode materials for various services.
It is the intention of the authors to cover the requirements, design, and installation of electric welding equipments, together with a complete treatise to date on the subject of electric arc welding, carefully treating each phase of the subject in turn, and concluding with examples of detailed application to the various actual operations which have come under their personal observation.
EQUIPMENT FOR ELECTRIC ARC WELDING
Due to the well-known characteristics of the electric arc that its resistance decreases with increases in current, and vice-versa to overcome the inherent instability, welding arcs must be connected in a circuit having a drooping volt-ampere characteristic so that the tendency for current to rise or fall will be immediately countered and checked by reduction or increase of voltage respectively. In other words, variations in the arc current should cause the arc voltage to vary in the opposite sense. Furthermore, each arc circuit must include its own independent means of producing the drooping volt-ampere characteristic, the properties of the arc above mentioned absolutely preventing the operation of two or more arcs in parallel in a single branch circuit.
When electric arc welding was first originated, direct current power circuits were used to a greater extent than they are now. The first arc welding was done by inserting a resistance in the supply line having a potential of 125 or 250 volts. Water or grid rheostats were used as resistance. These served to adjust the voltage to approximately the proper value for welding. In this scheme the power wasted was considerable, being dissipated in as much as that consumed by the arc, when a metallic electrode was used. In certain cases of welding such as electric railway work where the power is taken from a trolley wire through a resistance, approximately 95 per cent of the total power used power, the saving effected in making repairs in many industries by electric welding is so great compared to former methods, that the waste is more than offset. This form of equipment is commonly known as a constant voltage system.
As pressure welding was limited in its application man endeavored to find some other way to join metals, or to make additions of metal to other metal, without the use of pressure. He was eventually successful in this endeavor and welding without pressure came to be known as autogenous welding, so called because of its self- or auto-generation; i. e., it is self-produced by the application of intense heat without any physical process of compression or hammering.
We, therefore, have two general forms of welding one requiring external application of pressure to complete the weld, and one in which the weld is completed without the external application of pressure. In the first form the union is secured by using a comparatively low heat and high pressure. In the second the union is secured by a relatively high temperature without the aid of any external pressure. It will be seen, in view of the fact that welding requires actual fusion of the metals joined or added, that the process differs inherently from those methods of joining metals known as brazing or soldering, in which cold surfaces are united by the interposition of a fused metallic cementing material, which is an example of adhesion rather than cohesion.
Electric Arc Welding. Electric arc welding is commercially the most recent and newest process of any form of welding. Benardos and Slavianoff are generally credited with the discovery of the possibilities of the carbon arc and metallic arc, respectively, for the welding of metals. The carbon arc process was the first one to be used for welding metals, and was first used, on a small scale, 30 years ago. This form of arc welding is sometimes called the Benardos process. Not long after the carbon arc process was demonstrated by Benardos, Slavianoff demonstrated the possibilities of the metallic arc process, but it was not until comparatively recent years that either was used to any appreciable commercial extent.
After the first discovery of the more or less vague possibilities of electric arc welding the progress in the development of the art was extremely slow, due to the fact that it was only with great difficulty that the work of development could be carried on. There were several reasons for the existence of such a condition, most important of which was the fact that the men who first conceived and worked to develop and improve the welding art were apparently versed only in one branch or phase of that science.
It must be borne in mind that to develop this art it was necessary to make an extensive investigation into the phenomena existing in the arc, both carbon and metallic, when using it for the fusion of metals. No matter how well versed a man may be in electrical science it does not necessarily follow that he may understand the behavior of an electric arc when used for welding metals. On the other hand, although a man may be well trained in metallurgy it does not necessarily follow that he can under- stand the behavior of the metals when subjected to the temperature of the electric arc. In other words, the electrical men did not understand, nor were they thoroughly acquainted with the peculiarities manifested by the electric arc when used in conjunction with molten metal during the welding process. And the metallurgical men were not conversant with the behavior of metals under the action of the arc stream with its attendant high temperature variations.
In view of these existing conditions it was necessary that much time be spent in research work by both electrical and metallurgical men. Indeed, it was not until the electrical phenomena and metallurgical phenomena were coordinated that a real beginning was made in the development of the art of arc welding. And not until then did the metal using industries begin to see the possibilities of its use and to lend their financial assistance to its development.
The Electric Arc. If two carbons which are connected to a sufficiently powerful electric source are brought together and then slowly separated the current will not cease to flow, provided they are not too widely separated. Instead an arc will be formed and the current will continue to flow, since the vapor formed between the two carbons serves as a conductor for the passage of the current across the intervening space. The temperature of the positive electrode of a carbon arc has been estimated at about 7,500 deg. Fahr. If an arc is formed between two metallic electrodes the temperature will be somewhat lower. The temperature of any arc will be at least equal to the vaporization point of the materials forming the electrodes. In electric welding the heat is communicated to the metal by an electric arc. In one method the arc is deflected from the space between the carbon electrodes by a magnetic field. In this case the metal takes no part in the conduction of the current; the heat is communicated by the gases of the arc, and to a small extent by the radiation from the hot carbon electrodes between which the arc is formed. This particular method was inherently not a commercial success, as is evidenced by the mechanical impracticability of applying the arc to the work. Also, minute particles of carbon in the arc stream produced by the consumption of the electrodes were deposited in the weld, thereby leaving the finished weld exceedingly hard.
The form of carbon arc welding generally referred to, is one in which .the work, or part on which metal is to be added, forms the positive pole of a direct current circuit, and an arc is drawn between this and a carbon rod to which a handle is attached for manipulating. At the point of arc contact on the work the metal becomes molten. The metal, which it is necessary to add to the weld, is supplied by melting a filler rod in the arc, the minute globules of molten metal commingling and fusing with the molten metal of the parts to be welded. In this method the bad effects of deposited carbon are largely eliminated by making the work positive, in which case the current flows from the metal to the carbon instead of from the carbon to the metal, as was the original and former practice.
A constant potential source of current supply, together with a choking resistance in series with the heating arc so arranged as to permit an adjustment of current strength, has long been used, and is yet to a considerable extent. Sufficient potential is always required (approximately 70 volts) to maintain steadily an arc of proper length. The current required will range from 50 amperes to 600 amperes, and even higher in some instances, depending upon the character of the work.
The carbon arc process has been limited in its scope of application by its practical confinement to down-hand welding; to the tendency to oxidation resulting in brittleness; to the large area heated, resulting in the bad effects of excessive expansion and contraction, loss of energy or heat radiated by the large arc area, and conduction by the metal being welded; and the necessity of heavy currents with the cumbersome equipment required.
During the past two years much has been contributed to the electric welding art. Most of the development has been along the lines of metallic arc welding, consisting of improvements in equipments, electrodes and weld protection, which has in turn led to a more intelligent application of the process, and the resultant greater extension of its use.
Metallic arc welding consists of drawing an arc between the part to be welded and a metallic electrode. The electrode is in the form of a wire, or small rod. It may or may not be of similar composition to the metal which is to be welded. The arc is established by striking the wire electrode to be fused to the work with a dragging touch and withdrawing it a slight distance, approximately 1/8 in., forming what is commonly called the metallic arc. This form of arc welding differs from the carbon arc in the fact that the filler rod or wire forms one terminal of the arc, which is melted and is conveyed in liquid form across the arc and deposited in the crater on the work piece, which forms the other terminal of the arc.
Due to the fact that it is possible to project metal horizontally and vertically upward, it is possible to do welding on a wall or overhead with this form of arc welding, something which is not commercially possible with the carbon arc. This feature has been a contributory factor toward making the metallic arc welding process to all intents and purposes universal, and gives it an extremely wide field of application.
After many years of research it has been conclusively demonstrated that the metallic arc welding process demands a certain close coordination of the equipment and the arc characteristic, if the best results are to be obtained. Great strides have been made in the perfection of welding equipments and electrode materials for various services.
It is the intention of the authors to cover the requirements, design, and installation of electric welding equipments, together with a complete treatise to date on the subject of electric arc welding, carefully treating each phase of the subject in turn, and concluding with examples of detailed application to the various actual operations which have come under their personal observation.
EQUIPMENT FOR ELECTRIC ARC WELDING
Due to the well-known characteristics of the electric arc that its resistance decreases with increases in current, and vice-versa to overcome the inherent instability, welding arcs must be connected in a circuit having a drooping volt-ampere characteristic so that the tendency for current to rise or fall will be immediately countered and checked by reduction or increase of voltage respectively. In other words, variations in the arc current should cause the arc voltage to vary in the opposite sense. Furthermore, each arc circuit must include its own independent means of producing the drooping volt-ampere characteristic, the properties of the arc above mentioned absolutely preventing the operation of two or more arcs in parallel in a single branch circuit.
When electric arc welding was first originated, direct current power circuits were used to a greater extent than they are now. The first arc welding was done by inserting a resistance in the supply line having a potential of 125 or 250 volts. Water or grid rheostats were used as resistance. These served to adjust the voltage to approximately the proper value for welding. In this scheme the power wasted was considerable, being dissipated in as much as that consumed by the arc, when a metallic electrode was used. In certain cases of welding such as electric railway work where the power is taken from a trolley wire through a resistance, approximately 95 per cent of the total power used power, the saving effected in making repairs in many industries by electric welding is so great compared to former methods, that the waste is more than offset. This form of equipment is commonly known as a constant voltage system.
DOWNLOAD FREE BOOK: Electric Arc Welding
