238 



CEMENTS, LIMES, AND PLASTERS. 



Types of grinding machinery employed. In Chapter XXXV, where 

 the crushing and grinding machinery used in Portland-cement plants is 

 described in detail, a classification of these machines is introduced as 

 a guide to the descriptions of individual machines. As all but one 

 of the groups there distinguished are represented by one or more 

 machines used in natural-cement mills, the same grouping will be used 

 in the present chapter. It is as follows: 



Class 1. JAW CRUSHERS; material crushed between two jaws which approach 



and recede BLAKE CRUSHER. 



Class 2. CONE GRINDERS; material crushed by revolution of a toothed cone or 



spindle within a toothed cup GATES CRUSHER, CRACKERS. 



Class 3. ROLLS; material crushed between two or more plain, fluted, or 



toothed cylinders revolving in opposite directions. 

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



of which revolves. 



MILLSTONES, BUHRS, STURTEVANT EMERY MILL, CUMMINGS MILL. 

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



on a horizontal axis and gyrating about a vertical axis. 



EDGE-RUNNERS, DRY-PANS. 

 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, CYCLONE PULVERIZER. 



Jaw crushers. So far as known to the writer no jaw crushers of 

 the Blake type are at present used in natural-cement plants. At one 

 plant, and possibly at others, the Sturtevant roll-jaw crusher is in use 

 as a preliminary reducer on clinker. 



Cone grinders. Though the heavier crushers of this class, such as 

 the Gates crushers, are used at but few natural-cement plants, the group 

 includes a series of machines which have always been held in favor as 

 preliminary reducers on natural-cement clinker the so-called "crackers". 



The "crackers" so extensively used in the natural-cement indus- 



