WELDING TRAM-RAILS.

Star (Christchurch), Issue 8779, 16 November 1906, Page 3

WELDING TRAM-RAILS.

THE THERMIT PROCESS

Up to the persent, the Christchuroli Tramway Board has used, to joint t : Jie rails of the tramways fish-plates for the meohanioal part or tho joint, and copper tape for the electrical connection. This morning a trial was made of the new "thermit " process of bonding the rails by welding the ends of the metals together. Tho process, quite a new one, is being rapidly adopted in many parts of the world, and by its simplicity, cheapness and efficiency, commends itself strongly to tramway engineers.

The trial was made at the corner of Stanmore Road and "Worcester Street, where a new line is being laid, and the process will bo adopted by the Board for future use. The spectators included Mi W. Eeece, chairman, Messrs F. Richardson. C. M. Gray, M.H.R., and D.f Sykes, members of the Board, F. Chamberlain, its engineer, Scott Symington, its electrical engineer, H. Macandrew, District Railway Engineer, and E. Cuthbert, engineer to the Drainage Board. The- work was in charge of a workman-expert. The ends of the rails rhaving been cleaned up, they were fixed in a heavy clamp ©o that they could be pulled forcibly together. A mould-box, with a clay r mouldi enclosed, was then clamped round the two ends of the rails, which were put close together, and, tlio top of the mil being protected by plastering it, all was ready for the heating process. This is carried out by pouring round the ends a quantity of molten steel, made very quickly by the use of " thermit." This is a patented mixture of powdered aluminium and steel, whose efficiency depends upon the affinity or" aluminium for oxygen under favourable circumstances. Once the combination of aluminium and oxygen is commenced by heat, eo much is engendered in the process that not only is the combination facilitated, but there is enough to bring the steel to melting point. The thermit com- 1 pound, which is not in ths least dangerous itself, is a fine grey powder, and is poured into a small crucible standing on a tripod directly ov.er the rail. A little igniting power of special composition is placed on top, and lit with a match. A sheet-iron cover is popped over all, and then a little powder* od manganese-steel, to act as a flux, is poured through a hole in the cover. The process is rapidity itself. In about ten seconds the chemical action is complete throughout the mass. The action is, like all chemical heat-productive actions, extremely violent. "White fumes rush out of the top of the crucible, the metal roars, there is . a glow that searches the eyes, and sparks, and glow and fumes make a very fine show of fireworks. The uproar dies away, and, after a few seconds waiting for tho mass to settle, the bottom of the crucible is tapped, and a golden stream of melted steel and slag ru»s into the mould. In twenty secor.ds from that time the rails have been raised to a welding heat, and the clamps drag the ends together, each r ail being shortened by the pressure up eigiu-n of an inch. When the joint is cool, the mould and clamps are taken off, and tho rail is found perfectly welded, with a knob of steel cast round the sides and bottom. The cast steel acts as a fish-plate, not that one is in any way necessary, for the weld«>d joint has been found to be actually the strongest part of the rail. The rails are bulged a little at the weld, and the projecting part is chipped off witn chisels, and the bond is complete. The thermit bond costs about half-a-crown per joint, more than the fish-plated and copper-taped Ijpnd. But its saving in the life of the rail is estimated to L« about £3 per joint. Of course, the process makes one* long rail of several, and the electrical efficiency of the rails as return conductors is higher. Provision has to be made for expansion and contraction of the rails, and so eravy 150 yards an expansion joint is made in tii© ordinary way. Thermit is not the only rail-welding process. Others in use include the ordinary ".caet-weld/' but this necessitates carrying a com- J plete melting furnace ; and. the eleetri- i cal welding process, which also needs some bulky and expensive property. The thermit jH'ocess is characterised by the extreme portability of the appliances needed.

All those present at the trial to-day were well pleased at its results.