ELECTRIC WELDING DEVELOPMENT. 283 



In pipe bending and coiling, as in nniting ordinary lengtlis of 

 pipe into very long leiigths without screw joints, the electric weld 

 has a special adaptability. Hundreds of miles of street-railway rails 

 have been welded into continuous lengths and now exist in many 

 cities. Where rails are bonded only the electric welder assists in the 

 production of brazed or welded l)on(ls. It is a wide range between 

 buckles, typewriter bars, and umbrella rods to the local annealing 

 of armor plates on warships, but the electric welder covers that 

 range. It is no wider, however, than that from fine wires of a 

 diameter of one-fiftieth of an inch up to heavy steel wii-e for the 

 armor of submarine ca!)les, and again up to street-railway rail joints. 



In recent years elaborate machinery for the actual production on 

 a large scale of steel tubing from flat stock or skelp by the progres- 

 sive welding of a longitudinal seam has been put into operation. 

 The long strip, or skelp, is rolled up so that its edges meet. In this 

 condition it enters between tlie welding rolls, which pass the heating 

 current locally across the edges to weld them, and the operation is 

 [)rogressive from one end of the pipe to the other as it is fed into 

 the machine. The result is a pipe of which the walls are of even 

 thickness and the diameter uniform. This pipe can be afterwards 

 drawn, if needed, to the exact size desired. Very thin pipe can be 

 made of steel, the longitudinal seam or weld in which is a delicate 

 bead along the length — a beautiful product, for the extreme localiza- 

 tion of the heat has allowed preservation of surface and finisli of the 

 metal outside the joint. Taper tul>es, such as are used for bicycle 

 front forks and the like, are easily made. 



A similar machine for large work has lately been constructed, and 

 by its use large diameter tubes or shells, up to IG inclies in diameter, 

 are produced from sheet steel or iron. The illustration shows such a 

 nuicliine ready for operation. The Avelding transformer is at the toj) 

 of the machine, and the secondary circuit has for its terminals two 

 copper rolls inclined to each other on two nearly horizontal shafts 

 adjustable in position over the work. Below are the guide rolls, one 

 on each side on vertical shafts, and between these the shell to be 

 welded passes with its meeting edges uppermost and in contact with 

 the copper contact rolls. As the metal shell passes along under these 

 rolls the joint is progressively heated by the welding current crossing- 

 it, and the weld is finished by the side pressure of the guiding rolls. 

 The process, as well as the resulting welded product, is unicjue. 



For a considerable time past welding machines have been applicnl 

 to the production of bands or tires from stock of varying width, thick- 

 ness, and sectional form. More recently the practice of welding plain 

 bands or cylindrical rings, and afterwards rolling them with the form 

 of section desired, has been largely adopted; such as, for exami)le, in 



