26 



BULLETIN 343, IT. S. DEPARTMENT OF AGRICULTURE.. 



of the stone. Stronger pulp is obtained, however, at conditions of 

 low speed and high pressure than is obtained at conditions of high 

 speed and low pressure. It is believed, however, that the pressure is 

 more responsible here than the speed. Figure 19 shows that the 

 strength of paper, when the same amount of power is applied, is much 

 less when the power is utilized at high speed and low pressure than 

 at high pressure and low speed. 



TEMPERATURE OF GRINDING. 



There has always been more or less discussion about the effect of 

 grinding hot or cold. Throughout the experimental work discussed 

 little influence has been noted in grinding under conditions of varying 

 temperature. It is true that the production in 24 hours is less when 



220 



200 



180 



160 



140 







































































































































































































































































































































































AFI 



> 6 



HO 



UR 



S 





















































































































































































































































bl 































































































































































































































































































































































































































































































































































































































































































30 40 SO 



STEAMING PRESSURE - POUNDS 



60 



70 



60 



Fig. 16. — Effect of steaming pressure on speed — horsepower to grinder constant. 



inclusive.) 



(Spruce runs 233 to 242, 



grinding cold than when the hot process is used, but the variation of 

 the temperature from 125° to 190° F. does not materially influence 

 the rate of production. The pulp is somewhat finer when ground cold, 

 but there is not as much difference between pulps manufactured by 

 the cold and hot processes as is generally believed. 



OTHER FACTORS. 



Among the other factors which influence the power consumption, 

 production in 24 hours, and the quality and yield of pulp are the 

 amount of seasoning the wood has undergone before grinding, the 

 dry weight per cubic foot, the size of bolts, and the rate of growth. 



It is easier to grind green wood and secure a satisfactory pulp than 

 it is to grind seasoned wood. Seasoned wood almost invariably 



