The Boy's Book of New Inventions

by Harry E. Maule

Finally the mould is broken down and the weld is found complete, with big extensions of the steel extending from the weld, in just the shape of the pouring gate "riser" and heating aperture.

The molten thermit steel rushing in at the bottom of the mould has risen between the heated broken ends, and all around them, in just the shape left by the wax pattern. As the scientists say, the thermit steel has united the broken sternframe and formed a homogeneous mass with it. In other words the terrific heat of the thermit rushing on the heated ends has resulted in the two parts becoming one with the added thermit steel.

After the mould is broken down the oxygen-gas torch comes into use again to cut away the ends of steel sticking up where they had cooled in the pouring gate, "riser" and heating aperture. After this the weld looks like a great swelling upon the sternframe, and if the swelling is where it will not interfere with the working of the rudder or steamer propellers, nothing more need be done. On the other hand, if the swelling is in the way, it can be reduced to the size of the frame, and squared off with machines built for the purpose.

Thus the ship is repaired and is ready to be taken out of drydock for her next trip, as good as new.

About the same plan is followed out on all kinds of welding except pipes and rails. Locomotives can be repaired without taking the complicated machinery apart just by working around until the crucible can be so hung, and the pouring gate so arranged that the metal can be poured into the place designed for it. The chief difference lies in the size of the weld to be made and the consequent amount of thermit to be used. Welds have been made where as much as 2,000 pounds of thermit—enough to make 1,000 pounds of steel—have been run into a mould. In these very big welds a certain percentage of steel "punchings," or small pieces of steel, and a little pure manganese are used to give the additional hardness to the weld.

Without going into details as to the manner in which the principle of the thermit process is applied on rails or pipes, it will be enough to say that in welding rails three different systems are used. The first is done by building the mould around the ends of the two rails to be welded together and letting the thermit steel run in and completely surround the rails and the space between them. This gives one continuous rail just as far as the welding is carried on, and one through which the electric current of an electric road can pass without any trouble at all. It is plain, then, why this system is used so much on third rails of electric roads. The trouble with it is that the swelling on the top and inside of the rails must be machined down to present a smooth running surface to the wheels.

The next system, which is now almost out of date, is one in which two moulds are used so that the thermit does not come up over the running surface of the rails. This relieves the engineers of the necessity of machining the welded joints.

The third system is a mixture of the joining by plates and the thermit process. This is called the "Clark joint," after the name of Chief Engineer Charles H. Clark of the Cleveland, (Ohio) Electric Company, who formulated the plan. The rails are joined with plates and bolted, or riveted together in the old way, but a thermit weld is made at the base of the rail, welding the bases of the two rails together and to the plate.

The method of welding steel pipes is an exact reversal of the principle of welding together solid pieces of steel or iron. After the pipes are cut off clean, the mould, which is made of cast iron, is placed around them with specially constructed clamps to force the two ends closer together after the thermit has been poured in. The thermit is then set off in a flat-bottomed crucible like a long-handled ladle, and poured into the mould by hand as if from a ladle. As the slag rises to the top it goes into the mould first and coats the pipes. The thermit steel does not touch the pipes, but merely supplies the heat to weld them perfectly, so that they are as strong as the piping itself. Just after the pour has been made, the clamps are tightened up and the white-hot pipe ends forced together. They are thus held until cold, when the mould is broken away. The slag coats the outside of the pipes and this is chipped away, leaving a perfect weld.

Another interesting use of thermit is in the great foundries where cauldrons of metal have to be kept at a very high temperature. To help keep the mass in a liquid state thermit can be introduced in it either by throwing it into the cauldrons in bags, with a little ignition powder so fixed that it will be touched off by the heat of the boiling metal, or by putting it in especially designed cans affixed to the ends of long rods. By these rods the thermit can be plunged to the bottom of the cauldron before it "burns." The reaction of the thermit, with the intense heat caused by it, helps to keep the mass at the proper temperature.