206 



CHAPTER XI 



direction of the radius vector in order that it should easily and without 

 excessive friction pass over the trash turner. When c = o, m also = o, and 

 a = 90. It then follows 



r = c - 1 = R or r = R = constant. 



In this case the trash turner is a circle of radius r = R = — + s, where D is 



2 



the diameter of the roller cjdinder. In practice such a condition never 



Fig. 106 



Fig. 107 



occurs, due to the pressure between the top cylinder and the trash turner 

 following on the elasticity of the crushed cane. This is why c must always 

 be greater than i. If c becomes too great, then the cylinder 3 cannot take 

 the feed and will cause a stoppage. The velocity c must be such that the 

 angle A is somewhat less than 90°. 



The trash turner curve following this argument of Bergmans can be found 

 graphically wHh close approximation as follows : — 



Draw the positions of the rollers to scale. Fig. 106 ; join OB and OC ; 

 draw KT parallel to OC ; draw KN perpendicular to KT, cutting OC Sit N ; 

 with N as centre and NK as radius draw an arc KM ; then KM is very close 

 to the original logarithmic spiral. 



Fig. 108 



The trash turner itself consists of two parts : the bar, which is a permanent 

 feature of the plant, and the knife or plate, which is renewable. The knife, 

 a, is attached securely to the bar, b, as indicated in two forms in Fig. 107. 



The bar runs parallel to the rollers from housing to housing upon which 

 it is supported. As the bar may be treated as a beam supported at both 

 ends and uniformly loaded, its longitudinal section should be a parabola, 

 as shown in Fig. 108. Vertical stiffening ribs are also generally included. 



