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Full text of "Metallurgy Of Cast Iron"

TAPPlNG-OUT AND STOPPING-UP FURNACES,   ETC.        91
the hearth or crucible is not mtich over four inches below the level of the notch, but continual running and < fast driving- " of a furnace soon cut out the bottom lining, so that it is no uncommon result for metal to burn the bottom down two to three feet below the level of a notch, as indicated by the  dotted line S in Fig. 18. Furnacemen claim it is not until a bottom is cut down for a foot  or two that the best output and quality of product can be obtained, and also that a deep bed is very desirable to help maintain a uniform product. Often has a furnace cut the bottom out to such a depth as to force  an opening for metal to pass  downward through the ground or  outward  through  the   sides, about as is indicated by the lines N, M, and H, Fig. 18. The havoc such an escaping body of metal can make, if bursting out,  as it often does, into a reservoir of water, which is always more or less deep around the hearth of a furnace at N, can be but partly conceived. The mass of liquid metal in the bed of a furnace often   weighs   50 to   100   tons.    This   often  solidifies and  lies   in   a furnace  until  it  is  torn down,   or the hearth portion removed to permit its being broken by dynamite.    It has happened that, through a furnace ' i getting off'' or working badly, the bed of metal has solidified above the level of the notch, so that to tap the metal out of the  furnace it  would  have  to  be drawn off at the flushing or slag-hole at A, Fig.   18. Some furnaces have run   for a  week or two in this manner before they were able to  get  the  solidified mass melted down, so as to again draw metal from the notch-hole.    A  furnace   in  this   condition   must   be tapped much oftener than when it can be tapped at the regular notch.    It is often surprising how rapidly, as about 75 per cent of the heat generated from the solid fuel is utilized. This is attained where one ton of coke will produce one ton of iron; and Sir........................    2,720     "