Electrochemical and metallurgical industry . thick, and stands off about inch from the inner wall of themold. It is constructed so as to overlap like a flange the upperpart of the lower mold box without touching its edge. Thering must be well covered with graphite and the inner surfacewell smeared with clay and dried. It must tightly fit onto theroll, and, where necessary, spaces must be stopped with clay must not exude onto the inner face, as moisture onthe welding surface is bad. The flange-like rim of the ring is made to overlap the edgeof the mold and protect it from any drops of
Electrochemical and metallurgical industry . thick, and stands off about inch from the inner wall of themold. It is constructed so as to overlap like a flange the upperpart of the lower mold box without touching its edge. Thering must be well covered with graphite and the inner surfacewell smeared with clay and dried. It must tightly fit onto theroll, and, where necessary, spaces must be stopped with clay must not exude onto the inner face, as moisture onthe welding surface is bad. The flange-like rim of the ring is made to overlap the edgeof the mold and protect it from any drops of liquid iron whichmay splash up during the reaction and pouring of the metal. About 30 pounds of thermit are required to the superficialfoot of cast-iron surface. This quantity will soften the metalto the depth of about 2 inches. For steel rolls, 10 per cent to20 per cent more thermit is required than for cast iron. It isnot necessary to make the roll red-hot; a basketful of cokeplaced inside the mold until the iron cannot be touched by hand. FIG. -THEKMIT WELDING OF BROKENROLL. is sufficient. A few sand pits surrounding the roll, and filledwith a few hundred-weight of cast iron, will do as well, evenwith very large rolls. After firmly imbedding the ring in the mold box, a thin layerof cast iron and steel, say y, inch, is poured into it, which mustcompletely cover the welding surface. A thin layer of pow-dered charcoal can be used instead, but has the objection ofproducing a spray of sparks. The whole of the thermit, accurately calculated and weighed,is then quickly added and ignited in the usual way, viz.: a thim-bleful of ignition powder is placed upon it in a small heap andlighted with a hot iron or a fuse. Immediately after ignition,the mold should be covered with an iron or wood lid, coveredwith clay on its under side; the wood will char, but not burn. The reaction, even with large quantities of thermit up toiy> cwt. at a time, is finished in half a minute, and the l
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectmetallurgy
