Concerning the form of the pieces which can be dealt with in the electric welder, there nre but few limitations. Of course, the welding of uniform sections of wires or bars presents the least difficulty. These sections may be round, square, polygonal, or irregular, provided the holding clamps are adapted to grasp them and hold them securely. Flat strips like band saws may be operated upon similarly, and even teeth may be welded into saws where they have been broken out. The edges of sheets of considerable width may likewise be united. The welding of pipe sections of large or small diameter is performed with facility. In such work, as also is the case of solid-bar welding, in many instances, the weld is per fected by hammering, the blows of a light hammer, rapidly delivered at the weld while the metal is heated, being preferred. For such purposes, both mechanical and rapid pneumatic hammers which can readily be applied to the work are in use. Pipe welding in the lighter work may require a mandrel introduced into the interior of the pipe, daring the hammering, though this is not a necessity in the case of pipe with heavy walls. ocess finds appli cation in the welding of iron pipe sections into continuous long lengths for coiling. It is readily applied to the joining of lead-pipe sections without solder, and without any enlarge ment at the joint. The diameter and thickness of the pipe is preserved, while the metal becomes a continuous piece. When applied to the welding of tires or rings, the conditions are such that it might be expected at first that the electric current, if applied by contacts or clamps at each side of a break or proposed joint in a ring, would be liable to short-circuit itself through the complete portion. Some current does pass around such a ring, but it is slight as compared with that which passes at the proposed weld or joint. This is owing to the greater resistance to the current given by the length of metal in the path formed by the metal of the ring outside the clamps, as compared with the short length between the closely approximated clamps where the joint is to be made. Moreover, with alternating currents the path around the ring has a much higher self-induction, which acts as an opposing influ ence, and so acts to check current in that path. Further, if desired, the insertion of a magnetizable body of iron in the interior of the ring, such body being made of it bundle of iron wires or plates, will give an opposing effect, or self-induction so greatly increased that in most cases very little current will pass around the ring as compared with that which passes at the joint, and which heats and welds the same. It will be evident, without fur ther explanation, that pieces of special or irregular outline may be operated upon or welded to others by simply providing the necessary and suitable clamps and contacts for passing into the pieces the proper current, and for pressing the metal together at the joint, provided, of course, that the requisite projection of parts and meeting of pieces between the clamps is permitted.
While in most cases the operation of electric welding by the Thomson process is effected by butt welding, or joining the pieces in a plane substantially transverse to the line joining die pieces, it is equally applicable to making lap welds ; but practically the butt welds made electrically are equal to lap welds as ordinarily made, and often supplant the latter with great advantage. it is customary to dress off orlammer down the burr or expansion left in the butt welding of the pieces, due to their being pressed together while in a plastic state, but in many cases the presence of the burr is not objectionable, while it is consider ably conducive to strength, as it makes the weld in most eases the strongest part of the structure. In other cases the burr may, by suitable dies. be finished into a uniform bead which is ornamental in character. (See Fig. 2.) In regard to the preparation which is given
to the ends of the pieces before welding, it is noticeable that for moderate-sized wires the ends may be simply cut off in wire cutters, and abutted thereafter for passage of current and welding. In larger work, such as large bars of iron, the ends are somewhat rounded or convex, and the heating and welding therefore begins in the center, or near the axis of the bar. As the metal heats, softens, and yields. the weld continues to spread laterally until it includes the whole of the section. It has been proved possible to weld bars without producing any expansion or burr at the joint by first preparing the ends suitably—i.e..
by first removing from the ends of the pieces just that portion of metal which during the welding would have gone to form the expansion. However. this operation requires skill and judgment, and is not generally practised. The de gree of heat to which a bar may be brought in the electric welder is only limited by the fusing point of the metal, unless the losses by conduction and radiation from pieces too large for the machine, limit it. The fact that most metals when heated possess less conductivity for current is important, for it lessens the volume or flow of current required to be passed. Other wise the current would need to be increased as the section welded was increased during the operation. This, however, is not requisite, for in the case of iron, as an example, the specific resistance of the metal at the welding heat may be ten to twelve times what it is at ordinary temperatures. This fact has also another important bearing on the operation of electric welding. for it leads to a uniform distribution of the heating effect in the different parts of the weld, assuming that no disturbing effect which otherwise prevents such uniformity exists. The action is briefly that if in a weld one portion of the meeting surfaces is comparatively cooler than another, its resistance will be less, more current will therefore be diverted to such cooler portions, and a conse quent increased heat production will ensue thereat which rapidly brings the metal to a temperature nearly uniform with the rest.
The development of the Thomson eleetrie-welding process has shown that instead of a few only of the metals and alloys being the weldable ones, there are few if any exceptions among the metals so far as their weldability by electricity is concerned. It has appeared also that in many eases metals are united with great ease which before were regarded as non weldable. Doubtless the reason for this is that the perfect control of temperature and pres sure obtained enables the operator to work within so much narrower limits of fusibility and plasticity as would be impossible with the ordinary methods. The metals which have been found to weld with facility include wrought-iron, cast-iron, steels of various grades, steel castings, Bessemer metal, copper, lead, tin, zine, nickel. cobalt, silver, gold, platinum, anti mony, bismuth, magnesium, aluminum. manganese, cadmium, and such alloys as cast and rolled brass, bronze, gun metal, aluminum brass, aluminum bronze, phosphor bronze, silicon bronze, coin silver, gold of varying fineness, typo metal, pot metal, pewter, solder, German silver, fuse aluminum iron, etc. The process permits the combination of differciA metals and alloys to be effected without solder, such as copper to brass. copper to soft iron, copper to German silver, copper to gold, copper to silver, brass to soft iron, brass to east-iron, tin to zinc, tin to brass, brass to German silver, brass to tin. brass to mild steel. wrought to cast-iron. wrought_iron to east-steel and to mild, steel,.gold to German silver, gold to silver, gold to platinum, silver to platinum, soft iron to cast brass, iron to German silver, iron to nickel, tin to lead, etc.