440 CEMENTS, LIMES, AND PLASTERS. 



hour, ground to pass 93 per cent through a 100-mesh sieve. For grind- 

 ing clinker to a fineness of 90 or 92 per cent on 100-mesh, the Hunting- 

 don mill has given good satisfaction, but for the greater fineness now 

 required by many specifications, it is probable that the finishing work 

 can be done more economically with the tube mill. The rate of grind- 

 ing clinker, quoted above, is equivalent to an expenditure of 5 H.P. 

 hours per barrel of cement, which is about the same as the work done 

 by the Griffin mill under similar conditions. 



Griffin mill. If we disregard the enormous Atlas plants, the Griffin 

 mill is by far the most extensively used of the class of centrifugal grind- 

 ers. It is shown in section in Fig. 94. 



On reference to this figure it will be seen that the power is received 

 by a pulley (17) running horizontally. From this pulley is suspended 

 the shaft (1) by means of a universal joint (9), and to the lower ex- 

 tremity of this shaft is rigidly secured the crushing roll (31), which is 

 thus free to swing in any direction within the case. This case consists 

 of the base, or pan (24), containing the ring, or die (70), against which 

 the roll (31) works, and upon the inner vertical surface of which the 

 pulverizing is done. 



In dry pulverizing, this pan, or base (24), has a number of openings 

 through it downward, outside of the ring, or die, which lead into a pit, 

 or receptacle, from which it is delivered by a conveyor. 



Upon this base is secured the screen frame (44), which is surrounded 

 with a sheet-iron cover (45) (in the wet mill this cover is not used), 

 and to the top of which is fastened a conical shield (25), open at the 

 apex, through which the shaft works. 



The cut shows the pulverizing roll attached to the lower end- of the 

 shaft (1), and just above the roll is the fan (7), which is used in the 

 dry mill, but not in the wet. On the under side of the roll are shown 

 shoes, or plows (5), which are used in both, and varied in shape accord- 

 ing to the nature of the work to be done. 



The pulley (17) revolves upon the tapered and adjustable bearing 

 (20), which is supported by the frame composed of the standards (23). 

 Two of these standards (23a) are extended above the pulley to carry 

 the arms (22), in which is secured the hollow journal pin (12). 



Within the pulley is the universal joint from which the shaft (1) 

 is suspended. This joint is composed of the ball, or sphere (9), with 

 trunnions attached thereto. These trunnions work in half boxes (11) 

 which slide up and down recesses in the pulley-head casting (16). 



The joint in the pulley is enclosed by means of the cover (13), thus 

 keeping the working parts away from all dust and grit. 



