NEW WELDING PROCESS.
ADOPTED BY THE TRAMWAY BOARD. The Christchurch Tramway Board is at present adopting the thermit welding process, and will make a trial tomorrow morning. The process is entirely up-to-date, and Christchurch is the first place to adopt it in New Zealand. The thermit used for welding is in the .form of a powder, and consists of oxide of ironand aluminium, mixed in proper proportions. It is not explosive, and can be handled in safety. A heat, however, equal to melting steel is required to start the thermit, and this is done by placing a small quantity of igniting powder, which consists of powdered aluminium (bavium-superoxide) on the thermit, which ha 6 been placed in crucibles made from manganese ore. The igniting powder is set alight by a common match. The process is extreely simple. The ends and sides and top and bottom surfaces of the rails are properly cleaned. An. especially constructed clamp is attached to the rail, and so built as to pull the rail ends "close butted ;" the mould is then placed around the joint and well packed with moist sand, putty being used to protect the grooves from filling with thermit. The required quantity of thermit is then placed in the crucible and ignited by means of the bariumsuperoxide powder. In a few seconds the reaction is complete. The crucible will then contain at the bottom the molten steel covered with a lay«r of three times its volume, but equal weight of molten aluminium slag (corundum). This mass is po-ured into the mould. The corundum 6lag flows out before the steel touches the rails, depositing a layer around it and protecting the rail from contact with the molten thermit 6teel that follows. The thermit steel and corundum now surrounding the rails bring its butted joint to a welding heatwithin about twentyfive seconds. As soon as this takes place the clamps are drawn together, forcing the rails together, after which the welding heat gradually decreases and the weld is complete. A small amount of filing and cutting with cold setts is then necessary.
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