THERMIT WELDING

Dominion, Volume 30, Issue 189, 7 May 1937, Page 12

THERMIT WELDING

Continuous Tram Rails WORK IN BUNNY STREET Even since Wellington has had electric trams there has been a degree of trouble with rail-wear. This, under the conditions existing 30 years ago, was unavoidable. The chief point of wear in tram or railway rails is that at which two rails meet. On railways particularly, the junction of rails helps to make the rhythmical beat as the train passes along. If those rails could be made continuous, without a break from station to station, there would be something missing from the song of the steel highway. That improvement has now been made possible. The joining up of rails for any length is not new, for the actual process was discovered by Professor Goldschmidt in 1599. Professor Goldschmidt evolved the thermit process of welding, which is now being applied to the Wellington tramways in Bunny Street, and is to be gradually applied to the rails over the whole of the system. It is worth while new, because during recetn years practically the whole of the tracks in Wellington have been relaid and the thermit system of joining the rails is economic, since it is the most effective method of preventing wear. Where two rails meet there is always a slight gap. It is that little gap which causes the trouble. However small, it causes the wheels to bump, and the thousands of those bumps registered daily cause the rails to "cup,” or wear down, where they feel the impact. For that reason, in the past, rails have either had to be ground by strong emery wheels electrically applied to their surface, or the depressions have had to be made up by a welding process. 'The latest application of the thermit process has been introduced to Wellington by Mr. W. Gutche, representing It. Granowski, of Sydney. The plant includes enormously strong clamps, by which the rail-ends are brought exactly opposite and level with one another, yet kept a fraction over a quarter of an inch apart. When the railends are adjusted, two moulds of sand, each representing half a rail, are placed over the joint, and when all apertures are plugged with pug, heat is applied by means of a petrol vapour flare until the rails are cherry-red. When that is done a funnel is placed over the mould and loaded with about 12 pounds weight of oxide of iron and aluminium, x>f the texture of fine sand. When the heat is about 3000 deg. Fahr., a special match, with a head about 2-lin. in length is lit. As soon as it Is lit, it is thrust into the thermit (the iron oxide and aluminium) in the funnel. In about 10 seconds the whole of the mass becomes white hot and fluid; the stopper is knocked out of the bottom of the funnel and the fluid metal runs into the mould and sets to form a perfect collar round the joint. It h.as been mentioned that the railends are kept a quarter of an inch apart. That is for a purpose. Into that space a piece of shaped Swedish charcoal iron is placed, which, having a low carbon content, consist iu making the perfect weld. This piece of metal is essential to the process.

There are really two welds made in the one process. The insertion of the Swedish charcoal iron into the gap helps to form a butt weld at the head of the rails while the weld applied to the foot of the rails is merely a fuse weld.

Mr. Gutche said yesterday that _ a gang of three men could weld six joints in a day, but under conditions better than in Bunny Street, where the rails are rigidly laid in concrete and afford no space below, probably more thau that number could be made. On railway jobs in Victoria a gang ha& been known to make IS welds in a day. There jibe system followed is to weld rails until they have lengths of 200 ft., when they are levered on to the tracks and then welded on to other 200 ft. lengths. (Picture on page 9.)