Electric welding - Viall

Few fields afford a greater opportunity for study to the mechanic, the student, or the engineer, than that of electric welding. Arc welding, with its practical, every-day, shop applications for repair and manufacture, is in some respects crowding closely into the field in which the gas-torch has seemed supreme. With the development of mechanical devices for the control of the arc, the range of application to production work has greatly increased.

Resistance welding presents in its various branches some of the most interesting scientific and mechanical problems to be found anywhere. Spot-welding - butt-welding - line-welding - all occupy a particular place in our manufacturing plants today, and new uses are being constantly found.

In the gathering and arranging of the material used in this book, particular care has been taken to classify and place various subjects together as far as possible. This is not only convenient for reference purposes, but enables the reader to easily compare different makes and types of apparatus. In most cases, the name of the maker of each piece of apparatus is mentioned in the description in order to save the time of those seeking information.

No time or pains have been spared in the endeavor to make this the most comprehensive book on electric welding equipment and practice, ever published. Every possible source of information known to the long-experienced editor has been drawn upon and properly credited.

It is hoped that this book will prove a permanent record of electric welding as it is today, and also be an inspiration and source of information for those engaged in practice, research or development.

Electric Arc Welding is the transformation of electrical energy into heat through the medium of an arc for the purpose of melting and fusing together two metals, allowing them to melt, unite, and then cool. The fusion is accomplished entirely without pressure. The heat is produced by the passage of an electric current from one conductor to another through air which is a poor conductor of electricity, and offers a high resistance to its passage. The heat of the arc is the hottest flame that is obtainable, having a temperature estimated to be between 3,500 and 4,000 deg. C. (6,332 to 7,232 deg. F.).

The metal to be welded is made one terminal of the circuit, the other terminal being the electrode. By bringing the electrode into contact with the metal and instantly withdrawing it a short distance, an arc is established between the two. Through the medium of the heat thus produced, metal may be entirely melted away or cut, added to or built up, or fused to another piece of metal as desired. A particularly advantageous feature of the electric arc weld is afforded through the concentration of this intense heat in a small area, enabling it to be applied just where it is needed. Direct-current is now more generally used for arc welding than alternating-current. When using direct-current, the metal to be welded is made the positive terminal of the circuit, and the electrode is made the negative terminal.

Regarding alternating-current it is obvious that an equal amount of heat will be developed at the work and at the electrode, while with direct-current welding we have considerably more heat developed at the positive terminal. Also in arc welding the negative electrode determines the character of the arc, which permits of making additions to the weld in a way that is not possible with alternating-current. Inasmuch as the work always has considerably greater heat-absorbing capacity than the electrode, it would seem only reasonable that the direct-current arc is inherently better suited for this work.

Two systems of electric arc welding, based on the type of electrode employed, are in general use, known as the carbon (or graphite) and the metallic electrode processes. The latter process is also sub-divided into those using the bare and the covered metallic electrodes.

The Carbon Electrode Process - In this process, the negative terminal or electrode is a carbon pencil from 6 to 12 in. in length and from 1/4 to 1/2 in. in diameter. This was the original process devised by Bernardos and has been in more or less general use for more than thirty years. The metal is made the positive terminal as in the metallic electrode process in order that the greater heat developed in this terminal may be applied just where it is needed. Also, if the carbon were positive, the tendency would be for the carbon particles to flow into the weld and thereby make it hard and more difficult to machine.

The current used in this process is usually between 300 and
450A For some special applications as high as from 600 to 800 may be required, especially if considerable speed is desired. The arc supplies the heat and the filler metal must be fed into the weld by hand from a metallic bar.

The class of work to which the carbon process may be applied includes cutting or melting of metals, repairing broken parts and building up materials, but it is not especially adapted to work where strength is of prime importance unless the operator is trained in the use of the carbon electrode. It is not practical to weld with it overhead or on a vertical surface but there are many classes of work which can be profitably done by this process. It can be used very advantageously for improving the finished surface of welds made by metal electrodes. The carbon electrode process is very often useful for cutting cast iron and non-ferrous metals, and for filling up blowholes.

The Metallic Electrode Process - In the metallic electrode process, a metal rod or pencil is made the negative terminal, and the metal to be welded becomes the positive terminal. When the arc is drawn, the metal rod melts at the end and is automatically deposited in a molten state in the hottest portion of the weld surface. Since the filler is carried directly to the weld, this process is particularly well adapted to work on vertical surfaces and to overhead work.

If the proper length of arc is uniformly maintained on clean work, the voltage across the arc will never greatly exceed 22 volts for bare electrodes and 35 volts for coated electrodes. The arc length will vary to a certain degree however, owing to the physical impossibility of an operator being able to hold the electrode at an absolutely uniform distance from the metal throughout the time required to make the weld. It is very essential that the surfaces be absolutely clean and free from oxides and dirt, as any foreign matter present will materially affect the success of the weld. When using a metallic electrode, the arc which is formed by withdrawing it from the work, consists of a highly luminous central core of iron vapor surrounded by a flame composed largely of oxide vapors. At the temperature prevailing in the arc stream and at the electrode terminals, chemical combinations occur instantaneously between the vaporized metals and the atmospheric gases. These reactions continue until a flame of incandescent gaseous compounds is formed which completely envelopes the arc core. However, drafts created by the high temperature of the vapors and by local air currents tend to remove this protecting screen as fast as it is formed, making it necessary for the welder to manipulate the electrode so that the maximum protective flame for both arc stream and electrode deposit is continuously secured. This can be obtained automatically by the maintenance of a short arc and the proper inclination of the electrode towards the work in order to compensate for draft currents.

Selection of Electrodes - The use of a metallic electrode for arc welding has proved more satisfactory than the use of a carbon or graphite electrode which necessitates feeding the new metal or filler into the arc by means of a rod or wire. The chief reason for this is that, when the metallic electrode process is used, the end of the electrode is melted and the molten metal is carried through the arc to be deposited on the material being welded at the point where the material is in a molten state produced by the heat of the arc. Thus a perfect union or fusion is produced with the newly deposited metal.

Wire for metallic arc welding must be of uniform, homogeneous structure, free from segregation, oxides, pipes, seams, etc. The commercial weldability of electrodes should be determined by means of tests performed by an experienced operator, who can ascertain whether the wire flows smoothly and evenly through the arc without any detrimental phenomena.

A coated electrode is one which has had a coating of some kind applied to its surface for the purpose of totally or partially excluding the atmosphere from the metal while in a molten state when passing through the arc and after it has been deposited.

Electrode holders should be simple, mechanically strong, and so designed as to hold the electrode firmly. It should be practically impossible to burn or damage the holder by accidental contact so that it will not work. Small, flimsy or light projecting parts are almost sure to be broken off or bent. Fig. 15 shows one of these holders that answers the requirements. However, any of the companies selling arc welding apparatus will be able to supply dependable holders.

A holder made by the Arc Welding Machine Co., New York, is shown in Fig. 16 and in detail in Fig. 17. The metal rod is clamped in by means of an eccentric segment operated by a thumb lever. If the rod should freeze to the work it will not pull out of the holder, but will be gripped all the tighter. The welding current enters at the rear end of the composition shank, passes along the shank to the head of the tool, and from there directly into the electrode. It will be noted that there are no joints in this tool except where the cable is soldered into the shank. There is a relatively large contact surface between the electrode and the holding head, which precludes any possible heating at this point. The trigger is intended for remote control employed with the closed circuit system. Whenever this holder is used on other systems, the trigger is omitted.

Cable - For arc welding service the cables leading to the electrode holder should be very flexible in order to allow the operator full control of the arc.

The following sizes of cable have been found by the General Electric Co. suitable for this service, due account being taken of the intermittent character of the work. It is extra flexible stranded dynamo cable, insulated for 75-v. circuit, with varnished cambric insulation, covered with weather proof braid. Conditions under which the welders work, and their personal preferences, largely dictate which type is to be used. However, no welder should ever attempt arc welding without a protecting screen fitted with the right kind of glass. Cheap glass is dear at any price, for the light rays thrown off from the arc are very dangerous to the eyesight. The guard should be so made as to not only protect the eyes from dangerous light rays, but should also protect the face and neck from flying sparks of metal.

A very good face mask made by Julius King Optical Co., New York, is shown in Fig. 18. Those masks are made of fiber and provision is made for a free circulation of air between the front and the face, not only keeping the operator cool, but preventing the tendency of the lenses to fog. The  masks are supported by bands over the head and it is said that weight is not apparent and that they are as comfortable to wear as a cap. Two styles are made - with and without side screens. The one without screens may be had with combination lenses tinted for acetylene or electric welding or with any other tint. for specific work. The one with side screens, providing side vision, is fitted either with combination lenses or with clear Saniglass lenses. A hand shield is shown in Fig. 19.

In arc welding in the open, other workmen or onlookers are liable to injury as well as the welders, so screens should be placed around the work to conceal the light rays from the view of others besides the welder. Such an arrangement is shown in Fig. 20.

Where repetition work is to be done, it is well to provide individual stalls or booths, somewhat similar to the one shown in Fig. 21. These were designed for use in the welding schools under the supervision of the Lincoln Electric Co. For actual shop work, curtains or screens should be provided back of the welders. It must be remembered also, that owing to the presence of ultra-violet rays, severe flesh bums may result with some people if proper gloves and clothing are not worn - especially when using the carbon arc.

Selecting a Welding Outfit - Welding outfits may be of the stationary or the portable type. These may also be divided into motor-generator sets and the “transformer” types. Both DC and AC current may be used primarily, depending on the apparatus employed and the source of current available. Regarding the selection of any particular outfit J. M. Ham, writing in the General Electric Review for December, 1918, says:

Few things electrical have in so short a period of time created such wide-spread interest as that of arc welding. Engineers having to do with steel products, in whatever form produced or in whatever way employed, have investigated its uses not only as a building agent when applied to new material but as a reclaiming agent for worn or broken parts. In both - cases its possibilities as a means of greatly increasing output and in saving otherwise useless parts at a small fraction of their original or replacement value has proved astounding. Out of these investigations have grown several systems of arc welding. To exploit these is the duty of the sales department and the measure of its success depends upon the quality of service rendered.

The difficulties of giving service are perhaps not fully appreciated. Where so many systems have been called for and where so many individual ideas have to be met, the problems of the manufacturer become multiplied.

During a period of freight congestion when locomotives were in unprecendented demand, an engine was run into the repair shop with slid flat spots on each of the eight driving wheels, and orders were issued to return it ready for service in record time. In three hours repairs had been completed by means of the electric arc (to have put on new tires would have required three to four days) and the locomotive was out on the road. Many other achievements as remarkable as these have been obtained.

The arc-welding set must pay its way. It must earn dividends and conserve materials, and when properly selected and applied does both of these things to a degree quite gratifying. To the discriminating purchaser it is not sufficient merely to know that an outfit will make a weld, he wants to know if it is the best weld that can be made, if it can be made in the shortest possible time, and whether the ratio between cost of the entire system to the savings affected is the lowest obtainable.


EYE PROTECTION IN WELDING OPERATIONS

Radiation from an intensely heated solid or vapor may be divided under the three headings:

(1) Invisible infra-red rays
(2) Visible light rays
(3) Invisible ultra-violet rays.

There is no clear line of demarcation between these divisions, as they melt gradually one into the other like the colors of the visible spectrum. When the heated matter is solid, such as the filament of an incandescent lamp, the visible spectrum is usually continuous, that is, without lines or bands; but when it is in the form of a gas or vapor, as in the iron arc used for welding operations, the spectrum is divided up into bands or is crossed by lines which are characteristic of the element heated.

The radiations under the foregoing three headings, although of common origin, produce very diverse effects upon our senses. Thus, the infra-red rays produce the sensation of heat when they fall on our unprotected skin, but they are invisible to our eyes. The visible light rays enable us to see; but we have no sense that perceives the ultra-violet rays, so that we know of them only by their effects. The intense glare emitted in the process of arc welding consists of a combination of all these rays, and special safety devices are required to protect the operator from their harmful effects. For welding with acetylene and for light electric welding, it may be necessary only to protect the eyes with goggles fitted with suitable colored glasses.

A hand shield, made of light wood, and which has a safety colored glass window in the center is also sometimes used. This device is used for medium weight electric welding done with one hand. The shield serves the double purpose of protecting the eyes of the operator and also shielding his face from the heat ra3rs and the ultra-violet radiation, which might otherwise cause a severe sunburn effect.

For heavy electric welding, which requires the use of both hands, it is common practice for the operator to protect his eyes and neck with a helmet fitted with a round or rectangular window of safety glass. These helmets are usually made of some strong light material such as vulcanized fiber and are designed so that they can be slipped on and off easily, the weight resting on the shoulders of the operator.

There are a great many different kinds of special safety glasses on the market, and many combinations of ordinary colored glass are also in common use, so a brief discussion of this very important subject is in order.

It is well known that the normal human eye shows considerable chromatic aberration towards the red and blue-violet ends of the spectrum and that this defect is completely corrected in regard to the middle colors. It, therefore, naturally follows that a much clearer definition of an object is obtained by combinations of yellow-green light than by red alone, or especially by blue or violet light alone. The eye is also more sensitive to the yellow and green rays than it is to the red and blue rays; or in other words, yellow-green light has the highest luminous efficiency. This may easily be verified by looking at a sunlit landscape or fleecy clouds in a blue sky through plates of different colored glass. A glass of a light amber color or amber slightly tinted with green will clearly bring out details that are hardly observable without the glass, and which will be obscured entirely by a blue or violet glass. It is therefore obvious that in order to obtain the clearest definition or visibility with the least amount of glare, the selection of the color tint in safety glasses should properly be decided by an expert; but the depth of tint or, in other words, the amount of obscuration may be determined best by the operator himself, owing to the individual difference in visual acuity which will permit one man to see clearly through a glass that would be too dark for another man.

In selecting colored glasses, great care should be taken to discard all samples that show streaks or spots, as these defects are liable to produce eye-strain. The glass should be uniform in color and thickness throughout, and the colored plate should be protected from outside injury by a thin piece of clear glass that can easily be renewed.

When operating with a source of light that is known to be rich in ultra-violet rays, such as the iron arc in welding operations, it is not sufficient to guard the eyes with ordinary spectacles because these invisible rays are capable of reflection, just the same as visible light, and injury may easily ensue from slanting reflections reaching the eye behind the spectacle lenses. Goggles that fit closely around the eyes are the only sure protection in such cases. Also, when using a hand shield it should be held close against the face and not several inches away from it.