222 



CHAPTER XI 



experiment corresponds to 100,000 lbs. of cane, with 12 per cent, fibre, 

 milled in a 78-inch mill at a surface L,peed of 25 ft. per minute. For pressures 

 of 1,000 lbs. per sq. in. and upwards it was found roughly that HP^^g-^, 



Immediately above, H has been given in terms of the roller radius, 

 the opening, and the distance from line of nearest approach of the rollers. 



The pressure exerted on the rollers can then be calculated for any distance 

 from the line of nearest approach, and the results expressed as a curve. 

 As an experimental datum, the writer observed that under conditions such 

 that H^ P =9-5, the top roller lifted 0-25 inch if the top and back rolls 

 were set metal to metal. 



The curve in Fig. 128 is tnc graph of H^ P =9-5, as calculated for 



30-inch and 44-inch diameter 

 rollers, the opening, k, being 

 taken as 0-25 inch. This 

 curve is only an approxi- 

 mate representation of what 

 happens, for the constancy 

 of H^ P only begins to be 

 apparent when P approaches 

 a value of i,oco lbs. per sq. 

 in. In Fig. 129 is given the 

 graph as obtained from the 

 actually observed values 

 quoted on page 189. 



The conditions between 

 the top and the front rollers 

 are less easy to represent. 

 Supposing that at rest the 

 front opening was 0-5 inch, 

 the working opening with a 

 lift in the top roll of o • 25 will 

 be nearly 0-75 inch. The 

 pressure corresponding to a 

 height of 0-71 inch was 

 found (see table on page 189) 

 to be 162 lbs. per sq. in., 

 whence it follows that the 

 pressure between the top 

 and front rollers is many 

 times less than that be- 

 tween the top and back 

 rollers. How much less is very hard to say, but in such mill settings as 

 the writer has seen he believes that it is thirty to fifty times less. 



The section immediately above discussed the resolution of the forces 

 acting in a three-roller mill, in which p was the pressure between the front 

 and top rollers, and np was the pressure between top and back rollers. 

 If the writer's experimentally derived conclusions are correct, the resultant 

 of the forces p and np is only very little deflected from the line joining the 

 centres of the top and back rollers, cis can easily be calculated or obtained 

 graphically, by giving to n the value of 30. In addition, the value of the side 

 thrust becomes very great ; thus with m = 30 and a vertical angle of 80° 



Fig. 12S 



