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Indiana University Studies 



coarse crushing, and following these the material is fed to fine 

 crushers and rolls in succession before mixing. The crushers 

 most commonly used are crushers of the Gates gyratory type 

 which reduce the material to about 2-inch size. Fine crushers 

 follow these and are usually of the Gates and Gardiner types. 

 The material usually needs drying before it is mixed, and this is 

 accomplished by conducting it thru a smaller kiln into which the 

 waste gases from the calcining kilns are conducted. The tube 

 mills used consist of horizontal iron tubes about 16 feet long by 

 4 to 6 feet in diameter, which rotate on a shaft at the rate of 

 about 25 times per minute. The tube is about half full of quartz 

 pebbles about the size of hens' eggs and these produce a grinding 

 action as the tube rotates. These pebbles are retained in the tube 

 by the screens at the outlet end thru which the ground clinker 

 passes. The clinker is fed to the mill by means of belt conveyors, 

 and a new supply of pebbles is charged in the tube as fast as the 

 old ones wear out. The rapidity of rotation and the rate of the 

 feed determine the fineness of the product. 



This fine grinding is often done by a Griffin mill. This con- 

 sists of a heavy steel roll revolving on a vertical shaft with a 

 gyratory motion, and pressing by centrifugal force against a 

 steel-inclosing ring. These mills have a great capacity and will 

 grind very fine, but the cost of upkeep is much greater than with 

 the tube mill. 



The power required in the manufacture of cement is given 

 by Professor Bleininger, Geological Survey of Illinois, Bulletin 

 No. 17 (p. 57), as 1.5 horse-power per barrel of output, that is, 

 a 1,000-barrel plant would require 1,500 horse-power. This is 

 rather high for larger plants where one horse-power per barrel 

 of output has been realized. One 5,000-barrel plant is now 

 operating on 4,500 horse-power. 



The fact that the deposits of material for the manufacture 

 of cement are located near coal mines does not insure a cheap 

 supply of fuel under present conditions where powdered coal is 

 to be used as a fuel. Many coals are not suited for the burning 

 of cement since the ash from the coal mixes with the cement 

 in the kiln, and with a coal of high sulphur content or high per- 

 centage of ash these impurities will spoil the cement made. 

 Coals must have a high heating value since the temperature of 

 the kiln should be kept up to about 2,500 degree Fahrenheit. To 

 cause even heating thruout the entire length of the kiln the coal 

 should contain a large amount of volatile matter. These con- 



