It has been found that there are no changes in the composition or temper of the steel in the rail and it is left just as it was, except that the ends are melted together up to, and generally a little above the bottom of the tread of the rail, and that a slight longitudinal expan sion has taken place.
The so-called third rail is also welded by this means.
Steel girders for construction work can, of course, be welded in the same way as rails. Practically the same process is used in butt welding pipe up to six inches diameter. In making marine and other large repairs thermit welding has proved invaluable, the mold being made and the work done in place, without re moval to a foundry. In this way the broken crank shafts or rudder and stern posts of great steamships have been welded in a few hours.
Among the pure metals produced by the alumino-genetic reaction may be mentioned in the first instance chromium free of carbon. It is used in. the manufacture of particular quali ties of chromium steel with a limited percentage of carbon, and nowadays hardly an high-speed tool steel is made without it. Pure manganese also produced by this process finds employment in copper and nickel manufacture, and, further more, in the production of particular sorts of manganese steel of great strength and great elasticity with 12 to 14 per cent manganese, used particularly for bolts of machinery ex posed to great strains. Pure molybdenum and ferro-vanadium have also lately been put on the market. Ferro-titanium has been in use with a number of steel works for quite a considerable time, to deoxidize the steel and remove nitrogen. It also gathers sulphur and phosphorus, and imparts density, toughness and strength. In addition to the pure metals several
of their alloys are produced in exceptionally pure form by the alumino-thermic processes.
In foundry practice the thermit is plunged to the bottom of the molten metal in the pour ing ladle or thrown upon the surface of metal in the riser. In making small castings required quickly the thermit is ignited in a flat-bottom crucible and in 30 seconds can be poured into the mold. Where more than 10 pounds of thermit is used it is necessary to add 10 per cent of clean steel punchings or rivets to the thermit to modify the intensity of the reaction. A further addition of 1 per cent of metallic manganese and 1 per cent of nickel thermit will improve the quality of the casting. In the replacing of parts broken off the desired form is modeled on to the work with yellow wax and the molding loam packed around it. The wax melts away when the work is heated preparatory to the pouring of the thermit steel.
In the use of thermit for locally softening armor plate and other hardened steel the powder is heaped within a confining ring and ignited. The heat generated is sufficient to affect the metal to a depth of two inches. From 30 to 40 pounds of thermit are required to the square foot.
Analyses of thermit steel show an average of carbon, .05 to .1 per cent; manganese, .08 to .1 per cent; silicon, .09 to .2 per cent; sul phur, .03 to .04 per cent; phosphorus, .04 to .05 per cent.; aluminum, .07 to .18 per cent.
The quarterly magazine Reactions is de voted to the alumino-thermic industry. Con siderable work of this kind has already been done in Germany.