Replacing Pattern Molds in Repairs by the Thermit Process

Posted By Tom Feltham on 18 March 2015

Posted in The Vintage Machinery Almanac

This article was originally published in Electrochemical and Metallurgical Industry Publication of July 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.

The chief difficulty in doing general repair work by the thermit process has been to design the proper pattern for the mold, and to determine the correct amount of thermit to be used. This has usually necessitated dividing the work between the foundry and the forge shop, and has often been the cause of delay and trouble.

The Goldschmidt Thermit Company has now developed a system which obviates these difficulties and permits of the entire work being done without the aid of the pattern maker.

By this system yellow wax is used as a pattern or matrix for the casting, and the parts to be welded are simply laid together, and this yellow wax pattern shaped about them. After this is done the mold box is placed in position, and molding sand (consisting of a mixture of fire-clay and sand) tamped around the matrix in the usual manner, except that a small hole is left in the lowest part of the mold. The pattern for gate and riser may be easily constructed of wood in the usual manner.

After the mold box is completely filled, the gate and riser patterns are withdrawn, then a torch is applied through the riser to the wax matrix, which will melt and run out through the opening at the bottom. The heating should be continued until the metal is red hot and the mold thoroughly dry, after which the opening at the bottom should be closed with a sand core. The weight of wax should be multiplied by 32, to give the correct weight of thermit required for the weld. For welds requiring over 50 pounds of thermit 15% of punchings should be used, for smaller welds 10% of punchings. The pouring is performed in the regular way.


Figure 1. Set of Four Tube Mills

This system of wax patterns enables repairs to be made much more quickly, cheaply and accurately than heretofore, and is applicable to all kinds of thermit welds.

For the special problem of welding locomotive frames the Goldschmidt Thermit Company has recently perfected a mold made of fire-brick which can be obtained in standard sizes ready for use; this eliminates much of the preliminary work which was formerly necessary and allows of the repair being made quickly and accurately. The work can now be done in division shops and round-houses, as all tools necessary are part of equipment of such metalworking shops. Further details may be found in a pamphlet recently issued by the Goldschmidt Thermit Company on fire-brick molds for welding locomotive frames by the thermit process.

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