fr-o/r? /jr 



-f nearest approach ft*- a 



*"&-/tc<y/ axis A cfrsf&rrcf /?-0frr//fre 



THE EXTRACTION OF THE JUICE BY MILLS 223 



the side thrust becomes 29 , I V =0-784 V, where V is the 



31 v i 4- cos 80 



hydraulic load. 



The discussion in this and the preceding section leaves 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 delivery side of 

 a roller is nugatory. 



2. That the pressure exerted by 

 the bagasse acts along the line 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 

 have been quite reasonably criticised 

 by Bolk 3 in Java, particularly in 

 xegard to the value deduced for n 

 in the discussion above. 



The Setting of 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, dilute 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, 3O-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 



