CANE SUGAR. 



Draw the positions of the rollers to scale, Fig. 118 ; join OB and OC\ 

 draw XT parallel to OC; draw JO 7 " perpendicular to XT, cutting 00 at N-, 

 with JVas centre and NK as radius draw an arc JOf ; then -Of is very close 

 to the original logarithmic spiral. 



J. N. S. Williams 4 gives the following data regarding a nine-roller mill 

 at Puunene, in the Hawaiian Islands : 



Pressure on top roller, tons 



Distance of trash plate from top roller . . 



Opening of top and front rollers . . 



Opening of top and back rollers . . 



Distance between trash plate and 1: 



Speed of rollers, feet per minute . . 



Engine : 60 in. X 30 in. Working pressure at boilers 83 Ib. per square 

 inch. Average horse-power developed, 317*86. Revolutions per minute, 48. 

 Tons of cane per hour, 50 '28 short tons. 



FIG. 118. 



In Java, a distance between trash turner and top roller, measured along 

 the vertical line through the centre of the latter of about 55 mm. (2-45 

 inches) for mills 30 in. X 60 in. (crushing about 600 tons in 24 hours) has 

 been found very satisfactory; for every 1000 piculs (60 tons) increase in cane 

 milled per 24 hours, the distance between trash turner and top roller is 

 increased 3mm. ($ inch) or so. 



Proportions of Mill Rollers. A very general proportion for the 

 size of rollers is that the length be twice the diameter. Increasing the 

 diameter of the roller calls for greater power to drive, and at the same time 

 increases the tendency to fracture, due to torsional strains ; at the same time 

 the gudgeons can be made larger, and whereas the torsional strain only 

 increases directly with the diameter, the strength of the gudgeon increases 

 proportionately to the square of the diameter. Another objection to rollers of 

 large diameter is that the trash turner also becomes larger, and the friction 



188 



