430 CEMENTS, LIMES, AND PLASTERS. 



Class 4. MILLSTONES; material crushed between two flat or grooved discs, 



one of which revolves. 



MILLSTONES, BUHRS, STURTEVANT EMERY MILLS, CUMMINGS MILL. 

 Class 5. EDGE-RUNNERS; material crushed in a pan, under a cylinder turning 



on a horizontal axis and gyrating about a vertical axis. 



EDGE-RUNNERS, DRY-PAN. 

 Class 6. CENTRIFUGAL GRINDERS; material crushed between rollers and an 



annular die, against which the rollers are pressed by centrifugal 



force. 



HUNTINGDON MILL, GRIFFIN MILL, NAROD MILL, CLARK PULVERIZER. 

 Class 7. BALL GRINDERS; material crushed by balls or pebbles rolling freely 



in a revolving horizontal cylinder. 



KOMINUTER, BALL MILL, TUBE MILL. 



Class 8. IMPACT PULVERIZERS; material crushed by a blow in space delivered 

 by revolving hammers, bars, cups, or cages. 



WILLIAMS MILL, RAYMOND PULVERIZER, STURTEVANT DISINTE- 

 GRATOR, STEDMAN DISINTEGRATOR, CYCLONE PULVERIZER. 



Class i. Jaw Crushers. 



In this familiar type of coarse crushing machines, of which the Blake 

 crusher is both the oldest and best-known representative, the material 

 is fed between two powerful jaws, and crushed by their near approach 

 to each other. The principle upon which these machines work is well 

 adapted for breaking stone, but is not serviceable for finer reduction. 

 The Blake crusher in its various forms, and the Dodge and other de- 

 vices of the movable- jaw type, are therefore machines suitable for 

 first reduction only. 



For detailed descriptions of the Blake crusher, and of the modifi- 

 cations in which the same principle has appeared, reference should be 

 made to the valuable paper cited below.* 



In mining and metallurgical practices jaw crushers are commonly 

 used, but in the cement industry they have almost entirely given place 

 to the gyratory crushers described in the next section. 



Class 2. Cone Grinders; Gyratory Crushers. 



Under this heading are grouped the crushing machines in which 

 the material is crushed between a toothed or grooved cone or spindle 

 and the grooved cup within which it revolves. The Gates crusher, 

 the Mosser crusher, and the McEntee and other "crackers" are here 



* Blake, W. P. The Blake stone and ore-breaker: its invention, forms, and 

 modifications, and its importance in engineering industries. Trans. Amer. Inst. 

 Mining Engineers, 1903, pp. 988-1031. 



