The method of welding steel is as follows; but before proceeding to get the heat make a point of having a shallow tin on the forge large enough to hold a sufficient quantity of the flux, so that it will cover the scarfed end when being dipped in same. Have a clean fire and plenty of firing on the hearth, so that the heat can be well covered. Start with gentle blast until the heat is nearly up to burning point. If necessary, stop the blast and let the heat soak for a few seconds so as to ensure a uniform heat. Gradually force the blast, and keep withdrawing the “heats” and roll them well in the flux, and so continue until it is thought that the heat is plastic enough to unite. Place the scarfs in position, give a few light blows until the parts stick together, then hammer well home and move smartly so as to ensure the proper joining together whilst in a plastic state. When welded, do not continue the hammering or tooling at too low a heat; but if further hammering is necessary, re-heat the work.
These hints are not applicable to every make of steel. With the special steels manufacturers issue particular instructions.
A flux for welding cast steel consists of 2 oz. each of powdered chalk, soda and burnt borax, mixed with 1 lb. of silver sand.
A firm of steel manufacturers recommend a mixture of 21 oz. of sand and 7 oz. of salt, moistened; the steel is to be treated in a fire of sulphurless coal.
=How to Make a Bench Gas Blowpipe.=--The blowpipe illustrated by Fig. 67 gives a powerful flame. It can be clamped to the edge of the workbench by means of a winged nut, a hole being made near the edge of the bench to accommodate the bolt. A piece of hard wood A, 5 in. by 2 in. by 1 in. thick, has a strong iron bolt B passed through at one end. A 2-in. cube C, which should also be of good hard wood, is screwed firmly to the other end of A, the combined block being perforated through the centre to take a length of gas tube D, which carries a gas-bracket with flange, elbow joint, and tap E. The flange should be screwed down to the top of the block. The elbow joint allows the direction of the flame to be adjusted within a wide range movement. The arm of the bracket is removed, and a shorter tube F, 3 in. long, is substituted. This carries a 1/2-in. iron [T]-piece G. The tube H, which is 3 in. long, should be of brass, threaded at one end to fit into the [T].
