THE EXTRACTION OF THE JUICE BY MILLS 



223 





the side thrust becomes "^ — . = V =0-784 V, where V is the 



31 V I + cos 80 

 hydrauHc load. 



The discussion in this and the preceding section lea^'es out of 

 consideration : — 



1. The reaction between the bagasse and the top roller. 



2. The volume occupied by cavities in the mill rollers, as affecting the 

 value taken for the working openings. 



It assumes : — 



1. That the pressure of the expanding bagasse on the deliver}^ side of 

 a roller is nugatory. 



2. That the pressure exerted by 

 the bagasse acts along the hne join- 

 ing the centres of the rollers, a con- 

 dition which will not obtain if the 

 assumption in (i) is correct. 



3. That fluid expressed from 

 the bagasse is able to escape freely. 



On account of these and other ^ 



reasons, the writer's conclusions t 



have been quite reasonably criticised ^ 



by Bolk^ in Java, particularly in ^ 



regard to the value deduced for n \ 



in the discussion above. >^ 



The Setting oi Mills. — In order ^ 

 that the residue of fibre and juice ^ 

 may pass out from the mill, a certain • 

 opening must be left between the § 

 top and back roller. The product ^ 

 of this opening into the area length ^ 

 of roller x surface speed of roller 

 gives a volume which for lack of a 

 better expression may be called the 

 escribed, volume. Evidently the vol- 

 ume escribed in unit time is corre- 

 lated with the quantity of material 

 emergent from the top roller and 

 the back roller. This material con- 

 sists of a solid residue, fibre, and a 



fluid residue, dihde juice. The solid material is unalterable as regards its abso- 

 lute volume ; and hence the volume of the fluid residue must be that 

 of the escribed volume less, that of the fibre. This reasoning gives a 

 preliminary basis upon which the necessary opening in rigid mills may 

 be determined. For example, let there be a rigid mill, 30-in. x 6o-in., 

 making two revolutions per minute, and let it be desired to mill 30 tons of 

 cane containing 10 per cent, of fibre per hour. The emergent bagasse is to con- 

 tain 45 per cent, of fibre and 56 per cent, of juice, the densities of those 

 materials being taken as 1-35 and i • o respectively. The volume of fibre 

 passing per hour is : — 



Fig. 129 



