208 



CHAPTER XI 



the lever which engages with the projection on the bar is elongated to 

 afford a vertical adjustment by means of shims or packing strips. 



The Trash Turner and the Fibre Volume. The writer attempted to obtain 

 some analysis of the trash turner, based on the results obtained from the 

 behaviour of cane fibre on compression. His treatment was as follows. 2 



Under pressures up to 60 Ibs. per sq. in. he found that the volume of 

 bagasse varied as the 2 5th root of the pressure. In the experiment of which 

 the results are given on page 189, 0-221 Ib. bagasse with 32-6 per cent, fibre 

 was compressed on a base of 8-43 sq. ins. This quantity corresponds to 

 100,000 Ibs. of cane with 12 per cent, fibre per hour, ground in a 78-in. mill 

 at a surface speed of 25 ft. per min. The average value of HP"-*, where 

 // is the height of the column of bagasse in inches, and P is the pressure 

 in Ibs. per sq. in., was 4-8, whence H 2 - 5 P may be rounded off at 50. 



Let the projected area of the trash plate be a square inches, and let the 

 mean height of the column of bagasse be H inches : then solving # 2 ' 5 P = 50 



FIG. no 



gives the average pressure per sq. in. on the projected area of the trash 

 plate, whence the total pressure on the trash plate is aP Ibs. 



With settings such as are found in practice, it is sufficient to take H as 

 the vertical distance from the lowest point of the top roller to the trash 

 plate. With a mill of this size at rest, H is seldom found less than I inch 

 or 1-25 inches, allowing a lift of 0-25 inch when grinding at the normal 

 rate. With H = 1-25, P is found to be 28-6 Ibs. per sq. in. The projected 

 area of the trash plate with this drop in a 78-inch mill will be from 1,100 

 to 1,300 sq. ins., depending on the vertical angle, so that the total pressure 

 on the bar will be 31,000 to 37,000 Ibs. 



Now let the trash turner be lowered until the drop at rest is 1-50 inches, 

 corresponding to a drop, when working, of 1-75 inches. P now becomes 

 12 '3 Ibs. per sq. in. If the distance of the trash plate from the back roller 

 be kept constant, lowering the trash plate will reduce the projected area, 

 which will now be 1,000 to 1,200 sq. in., so that the total pressure is com- 

 puted to be 12,300 to 14,800 Ibs. 



If the fibre in the cane increase, or if the quantity of cane milled increase, 

 the pressure on the trash plate may be maintained constant by increasing 

 the speed of the mills in proportion to the increase in the fibre passing in a 



