3. End pressure applied to force the abutting ends into each other at welding heat.
5. Interruption of current at proper
1. The projection of the abutted pieces varies with the diameter. It has been found that for copper, a projection of twice the diameter for each clamp gives the most economical results. With steel and iron, the most economical projection equals the diameter, and is for brass 1 1/2 times the latter.
The projections sensibly affect the energy required, and the moat economical one depends upon the hent-con-ducting properties and specific resistance of the specimens. Accordingly high conducting bodies require longer projections, highly resistant ones short projections. Conductors of larger and smaller diameters may be welded by giving to each its respective projection. In the same manner may wires of different material be joined to each other.
It is easily understood that since unequal projections on different sized conductor) produce the proper heating of both at their junction, equal projection of equal sized conductors will be required. All other conditions neglected, it is important to keep the projection for a given size and material constant.
2. The E.M.F. required depends upon the projection and the resistance of the material to be welded. For larger material and the resistance of copper conductors. The E.M.F. required for iron and steel is nearly double that for capper, and would be 4 times if equal projection were used for both.
Cross section, the specific self-induction plays an important role, and indirectly the shape of the specimen.
Another factor affecting the E.M.F.
A certain drop of E.M.F. will be found from the clamps to the specimens. This drop is rather low on material having naturally bright surfaces, as, for instance, copper, brass, German silver, tin, or even cold-rolled iron and steel. For a large class of work, however, especially in carriage hardware, the surfaces to ha used for contacts have a light scale left after passing through the rolls, which hsa either to be removed by grinding or filing, or to be overcome by the E.M.F. of the current. In a good many cases, the introduction of a special process of cleaning is deemed to be more eipensive than to use a little extra power to work through the
3. For uniformity of result the end pressure required to press the abutting specimens into each other at welding heat is of more importance than any of the former agencies: this is, in fact, the one which controls and rectifies any inaccuracies in the former conditions. If the pressure necessary for a given size and material is used, the weld cannot be performed until the metal has acquired the necessary plasticity to yield to the pressure. If, for one reason or another, the E M.F. and, consequently, the current should have been too strong, the time necessary for welding alone is affected, and in this case shortened. The bars will, however, be nnited at the same temperature and with the same force, whatever the time may hate been used to bring about the plasticity necessary. The pressure will in some respects influence the heat by forcing higher or lower temperature, and by so doing cause the action to be interrupted at an earlier or later period, as may be
The pressure required varies with the material, and is approximately 1800 lb. per sq. in. for steel, 1200 per sq. in. of iron, 600 lb. per sq. in. of copper. It varies also with the area of cross section, as indicated by its being eipressed a function with the surface as one of the
4. The interruption of the current as soon as the we'd is completed is important for all easibly fusible metals. When two copper wires are welded together, the welded portion being increased In cross section owing to the end pressure, if the current is not interrupted a large portion of the conductor on either side of the weld, including the latter, becomes heated, and hill melt and be torn asunder before any pressure device could follow and over-bridge the gap.
The current should, therefore, ha interrupted as soon as the weld is completed. It is also sometimes required that the parts to be welded should be of a certain predetermined length, In which case the interruption of the current as soon as the allowable distance has been reached is essentinl.
All these conditions are maintained constant in the automatic welder before us, which is the first commercial type of its kind. This welder is not entirely automatic in the strict sense of the word. The degree of Automatic action has to be considered for each individual object separately. This machine contains, however, the leading features as covered by Prof. Thomson's patent, with a few improvement! in mechanical construction. The capacity of the machine is nominally copper wire No. 6 to No. 17 AG. It will, however, weld larger and smaller sizes. It weighs 1301b. complete; the secondary is one solid copper casting of a cross section resembling a hollow square box with one of the sides removed.
This casting is firmlyscrewed to an iron table. A saw-cut at right angles to the plane of loop creates the two poles, one insulated from the table, and the other constituting a V-shaped bearing suitable to receive a sliding clamping device.