Copper to brass. Copper to wrought iron. Copper to German silver. Copper to gold. Copper to silver. Brass to wrought iron. Brass to cast iron. Tin to zinc. Tin to brass. Brass to German silver. Brass to tin. Brass to mild steel. Wrought iron to cast iron. Wrought iron to cast steel. Wrought iron to mild steel.
Wrought iron to tool steel. Gold to German silver. Gold to silver. Gold to platinum. Silver to platinum. Wrought iron to
Mushet steel. Wrought iron to
Stubs steel. Wrought iron to crescent steel. Wrought iron to cast brass. Wrought iron to
German silver. Wrought iron to nickel. Tin to lead.
But Prof. Thomson was not satisfied with his progress made above ordinary welding; he early recognised the importance of a machine in which all conditions for successful operations are mechanically controlled to produce uniform results, work rapidly, and require little or no attendance.
Such machines, now known as automatic welding machines, have proved to be of special importance in connection with easily fusible metals, enabling the successful welding of aluminium, silicon, and aluminium-bronze, which require, even with the electric process, considerable skill.
Before entering into a detailed description of the automatic welder, a few general data on welding will be in order.
The Thomson process of electric welding can be and has been worked by means of continuous or alternating currents; secondary batteries or unipolar machines may be and have been used. There are such conditions as transportability, absence of motive power, situation in continuous distribution district, etc, which may make it advisable to use the continuous current. The alternating currents, however, have so far been found the best adapted to be economically produced of large volume at low E.M.F. They are easily and economically controlled, and allow of being distributed at high pressure with small conductors, and of being reduced to working pressure wherever needed. They have, however, another beneficial effect, which is of importance in all welds of large sections.
It is a well-known fact among manufacturers of incandescent lamp filaments of large section that the inner portion in a filament is apt to be overheated. In treating filaments as used in the commercial series lamp, in hydro-carbon atmosphere, the writer once thought of producing a specially good quality of carbon by starting with an extremely thin base '004 in. thick, and obtaining a filament 90-95 per cent, of which consisted of hard, grey, lustrous carbon. His idea was also to extend this process to the manufacture of arc light carbons, and even produce pencils of about \ in. diameter. What was his surprise, however, to find that although the lustrous surface presented at all times a dense grey structure, the core lost this character after a certain thickness of carbon had been deposited. In fact, a number of concentric layers would be discovered, from the inmost graphite to the dense grey, semi-crystalline nt the outside.
This action can in my mind only be attributed to the over-heating of the carbon particles in the inside. Alimilar action takes place in a bar of iron if heated by an electric, current. The surface exposed to radiation will be at a loner temperature than the core. It ii true that the heating of the metal will increase its resistance and thus lend to equalise the temperature, but not enough in all cases. By the use of alternating currents we gain, however, an assistance in the self-induction. The effect of the latter is especially marked, and has a tendency to concentrate the heat on the surface.
If there is any place that receives more current than another, the effect of the self-induction is emphasised by the (act that the surrounding part is cool, and its permeability is greater than the part traversed by the surplus of current. With very large and especially wide metal pieces the uueven-ness of distribution may be remedied by approaching iron masses to create at a given spot a greater self-induction or counter E.M.F., thus diverging the current from that section. Prof. Thomson has early recognised the importance of, and has patented, a device to prevent the heating of the metal at a given spot by creating locally increased self-indue tion or magnetic effects. .
In view of this, it is interesting to note the paper controversy between parties disputing the priority of a device that is to produce exactly the opposite result, with, however, the same
Two methods of distribution axe in uae: the direct and the indirect In the former an alternating current dynamo is used, having two windings on the armature, one of which furnishes currents rendered continuous by a commutator to excite the field magnets, and is controlled by switch and rheostat; the other consisting of a single turn of heavy copper cable furnishes the welding current, which is led through collector and brushes to movable copper clamps suitabla to receive and guide the welding specimens during the
In some other forma the field-magnet is the movable part, in which case no heavy currents hare to be carried through collector and brushes. No direct welders are built nt present for currents larger than 4000 ampere's.