442 



CEMENTS, LIMES, AND PLASTERS. 



When a quantity of the material to be reduced has been fed into 

 the mill sufficient to fill the pan as high as the shoes, or plows, on the 

 lower side of the roll, they work in it, stir it up, and throw it against 

 the ring, so that it is acted upon by the roll; and when fairly in oper- 

 ation the whole body of loose material whirls around rapidly within 

 the pan, and, being brought between the roll and die, is crushed, and 

 all that is sufficiently fine passes at once through the screen above the 

 die, the coarser portion falling down to be acted upon again. 



The universal joint, by which the shaft is connected with the pulley, 

 allows perfect freedom of movement to the roll, so that it can safely 

 pass over pieces of iron, steel, etc., such as are usually found in all 

 rock to be pulverized, without damage to the mill. 



The fan attached to the shaft above the roll draws air in at the top 

 of the cone, forcing it through the screens and out into the discharge, 

 thus effectually keeping all dust within the mill. 



In working dry the screen which surrounds the pulverizing chamber 

 is of much coarser mesh than the delivered product; for instance, a 

 16-mesh screen delivers a product over 90 per cent of which will pass 

 a 60-mesh screen. Two sizes of the Griffin mill are made: 



TABLE 178. 

 SIZES, POWER, ETC., OP GRIFFIN MILL. 



When running on clinker which has been previously crushed to about 

 ^-inch size the Griffin mill will handle from 5 to 10 barrels per hour, 

 using 25 to 30 H.P. For clinker-grinding the mill is usually equipped 

 with 30- or 32-mesh screens, giving a product of about 95 per cent 

 through a 100-mesh, and 70 to 80 per cent through a 200-mesh. 



In grinding raw materials, 24- or 28-mesh screens are used, which, 



