Thermit Process

This process of welding metals is effected by pouring superheated thermit steel around the parts to be united. Thermit is a mixture of finely divided aluminium and iron oxide. This mixture is placed in a crucible and the steel is produced by igniting the thermit in one spot by means of a special powder, which generates the intense heat necessary to start the chemical reaction. When the reaction is once started it continues throughout the entire mass, the oxygen of the iron being taken up by the aluminum (which has a strong affinity for it), producing aluminum oxide (or slag) and superheated thermit steel, ordinarily, the reaction requires from 35 seconds to one minute, depending upon the amount of thermit used. As soon as it ceases, the steel sinks to the bottom of the crucible and is tapped into a mold surrounding the parts to be welded. As the temperature of the steel is about 5400 degrees F., it fuses and amalgamates with the broken sections, thus forming a homogeneous weld.

It is necessary to pre-heat the sections to be welded before pouring, to prevent chilling the steel. The principal steps of the welding operation are, to clean the sections to be welded, remove enough metal at the fracture to provide for a free flow of thermit steel, align the broken members and surround them with a mold to retain the steel, pre-heat by means of a gasoline torch to prevent chilling the steel,...