224 



CHAPTER XI 



3 X 2000 



62-25 X I '35 



and that of the juice is 



3-66 X 2000 



71-39 c. ft.. 



= 110-88. 



62-25 X 1-07 



In all, the total volume of residue passed out is 182-27 c. ft. per hour, or 

 3 • 038 c. ft. per minute, and this must be equal to the escribed volume. 



At two revolutions per minute the area developed in one minute by a 

 line on the roller equal to its length and parallel to its axes is7rX2X2-5X5 

 = 78-56 sq. ft. Then if x be the opening necessary 



78-56 X = 3-038, whence x = 0-0387 ft. = ^ inch. 

 This calculation assumes that the rollers are smooth ; actually not only 



M are they grooved, but 

 ]| II also the cavities in the 



metal occupy an ap- 

 preciable volume. Hence 

 a setting closer than this 

 will be adopted. It also 

 follows that the setting 

 will not increase in direct 

 proportion to the quan- 

 tity of material to be 

 passed, but will partake 

 of the relation a : b = 

 K + di'. K + d2 where 

 a and b are the quan- 

 tities of material passed, 

 d^ and ^2 ^^^ the open- 

 ings, and K is the con- 

 stant volume of the 

 groovings and cavitieSg 



In rigid mills, after 

 the setting has once 

 been made, in order to 

 obtain uniform results, 

 the quantity of fibre 

 passing in unit time 

 should be unvariable. If the quantity of fibre offered to the mill increases, 

 the rollers must be operated at a higher surface speed, in order that the 

 necessary escribed volume be developed. If the bagasse is to remain of 

 unchanged composition, the increase in speed must be directly proportional 

 to the increase in fibre. This statement resolves itself into increased engine 

 speed and increased consumption of power in direct proportion to the fibre 

 operated on. If, however, the surface speed of the rollers remain unchanged, 

 there must still be an increase in the power developed to reduce the greater 

 quantity of material to the constant volume, and this power will be obtained 

 by increase in the mean effective pressure on the piston. In this case, however, 

 with the escribed volume constant and increased volume of fibre, there will 

 remain a less volume for the juice to occupy, and there will be a less quantity 

 of juice in the bagasse. Accepting the apphcability of the experimental 

 results discussed earlier in this chapter, this condition would only be obtained 



Fig. 



130 



