Hardening, tempering, annealing and forging of steel; a treatise on the practical treatment and working of high and low grade steel .. . ual expansion. By keeping the surface of the lead covered with broken char-coal, drops will be prevented from forming. After the heatinghas been concluded empty the crucible. Io8 HARDENING, TEMPERING AND ANNEALING. To get good results when hardening by heating in lead, stirthe liquid occasionally so as to equalize the heat, as the bottom,will always be hotter than the top. When tools or parts withfine projections or teeth are heated, take a stiff brush and cl
Hardening, tempering, annealing and forging of steel; a treatise on the practical treatment and working of high and low grade steel .. . ual expansion. By keeping the surface of the lead covered with broken char-coal, drops will be prevented from forming. After the heatinghas been concluded empty the crucible. Io8 HARDENING, TEMPERING AND ANNEALING. To get good results when hardening by heating in lead, stirthe liquid occasionally so as to equalize the heat, as the bottom,will always be hotter than the top. When tools or parts withfine projections or teeth are heated, take a stiff brush and cleanoff any particles of lead which may stick in them before quench-ing. This is necessary as steel will not harden when lead hasstuck to it, as the spots do not come in contact with the bath. Hardening Metal harden metal saws or articles of a similar nature, providea pair of flat cast-iron plates and oil the faces well with a heavyoil. Heat the saws in a box or some other arrangement whichwill prevent the fire from coming in contact with them (a flatplate will do) and prevent the article from warping during the ^^T^i. I^IG. 72,.—METAL SAW. heating process. When heated to a bright red remove the articleand place it on the lower oiled plate and drop the other plate onit quickly, and hold it down until the article is cold. If a pairof hinged plates are used one man can do the job; if not, twowill be required. Mixture to Prevent Lead from formula here given is taken from the report of the Chiefof Ordnance of the United States War Department, and is usedwhen hardening files, and has also given good results when hard-ening small taps, milling cutters, reamers, broaches, rotary filesand similar tools having fine teeth. The following is a copy o£the report: THE HARDENING OF STEEL. IO9 Before hardening-, the files are treated with a mixture of salt?and carbonaceous materials to protect the teeth from decarboniza-tion and oxidation. The kinds and proportions o
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