CANE SUGAR. 



contact, its width should be as small as possible. The width of the trash 

 turner is determined by what may be called the vertical angle of the mill, i.e., 

 the apex of the triangle formed by joining the centre of the rollers; the 

 larger this angle, the wider the trash turner. In actual practice, vertical 

 angles lying between 75 and 90 are met with, a very general angle being 

 about 82- 84. In addition to a small vertical angle diminishing the width 

 of the trash turner, the component of the downward pressure exerted 

 vertically on the top roller, on the line joining the centres of two rollers, is 

 greater. There is a limit, however, to decrease in the vertical angle since, as 

 this narrows, the space available for the shaft of the lower rollers becomes 

 less. By the employment of the best material, mills with small shafts of 

 sufficient strength and narrow trash turners can be made. 



A very large number of curves has been suggested for the trash turner, 

 in all of which the personal equation of their originators appears very largely. 

 On certain mathematical grounds it can be shown that the correct curve is a 

 logarithmic spiral, the construction to obtain which is given below. The 

 method which appeals most to the writer is one of trial and error : indicating 

 the engine with different settings, and adopting that setting which is 

 found to absorb least power. Another essentially practical method is to adopt 

 that curve into which an old trash plate has been worn. It must be borne in 

 mind, however, that the proper curve and setting is dependent amongst other 

 things on the nature of the canes ground, particularly on the amount of fibre 

 and on its mechanical structure and resistance to compression, so that a 

 setting satisfactory with one lot of canes may be the reverse with another ; 

 continual watchfulness on the part of the engineer is called for here. 



The efforts of engineers have been directed largely in late years towards 

 diminishing the width of the trash turner, and towards obtaining at the same 

 time a small apex to the mill ; all the departures from conventionality 

 instanced above have had this point in view. 



Bergmans' Theory of the Trash Turner 3 . The following 

 mathematical treatment of the trash turner was published in 1889, by 

 R. F. Bergmans and is here reproduced : 



The duty of the trash turner in sugar mills is to direct the crushed cane 

 from the first cylinder pair (one and two) to the second (two and three). 

 The crushed cane must be so guided that cylinder 3 can take the feed 

 without stopping the working of the plant. 



Let T! represent the speed with which the crushed cane leaves the 

 first cylinder pair and T 2 that of the bagasse leaving the second cylinder pair 

 (see Ftg. 114) > then must always 7\ = T 2 and it hence follows that the 

 passage of the bagasse over the trash turner must be uniform. 



184 



