CANE SUGAK. 



accumulator is b the pressure required to move the ram is -y- where x is the 

 sum total of the weights c c. When this system was first brought out the 

 pressure applied was generally three tons per linear inch of roller, so that a 

 roller sixty inches long had a pressure on the journals of 180 tons; to obtain 

 this pressure the weights co would be about two tons, but now pressures of 

 four, five, and even six tons per linear inch are not unusual. 



In MacDonald's design (and this is the form usually adopted by United 

 States engineering firms) the hydraulic is arranged beneath the mill, as shown 

 diagrammatically in Fig. 125. The pot of the hydraulic is seen at a bearing 

 directly on the sole plate of the mill ; the oil chamber is seen at c and the ram 

 at b ; the holding down bolts are united by a yoke seen at d. The action of 

 the two types is practically identical, a direct push in one case being replaced 

 by a pull. 



FIG. 126. 



In the MacDonald type of hydraulic the tension is transmitted through the 

 holding down bolts which may be as much as eight ft. long; any inaccuracy 

 there is then magnified in the adjustment of the top cap, and in addition the 

 unequal strains in the mill have a tendency to force the top cap out of the 

 plumb, so that it may jamb against the side of the mill and prevent the hydraulic 

 regulator acting ; on the other hand, the design is readily accessible, and burst 

 leathers can be replaced in a few minutes. 



A source of trouble in all types of hydraulic is the unequal pressure on 

 either side of the mill due to the thrust of the pinions ; this may in part be 

 compensated by making the area of the rams of different size, but in this case 

 the allowance once made is fixed. A more elegant scheme entails the use of 

 twin accumulators which may be loaded independently, and an equal travel on 

 both sides of the mill obtained by trial and error. 



The location of the hydraulic varies in practice ; it is found applied to the 

 top and to the back roll; in the former case it acts as a safety appliance 

 equally to the front roller, and this is the more rational method to follow, as is 

 also indicated by the following argument. 



196 



