Pressure is the relevant parameter to describe the mechanics of crushing cane. This calculator uses a near proxy, namely, force per adjusted roller length. The adjusted roller length is obtained by subtracting 3 inches from the real roller length. This adjustment accounts for “unused” roller on either end and was obtained by rounding downward an extrapolation of Goldens’ recommendations for their No. 2-4 series for force (obtained by assuming 100% efficiency of input horsepower, their recommended rpms, hence torque, hence force) vs. real roller length. This adjustment is also in reasonable agreement with the relative sizes of the feedboxes and rollers.

Force to crush stalks of cane was determined empirically at Don and Carol Dean’s Thirteen Oaks Farm by an unseemly crew. The raw data were typical, minimum, and maximum forces to crush three stalks that were fed simultaneously into the mill so that there was no or minimum lateral overlap on the discharge side. Four cultivars were tested (C.P. 36-111, C.P. 52-48, C.P. 67-500, and ribbon). Extraction was nominally 45-55%.

As expected, C.P. 52-48 and C.P. 67-500 required the most force to crush the cane. The maximum force was expressed on a per stalk basis. This value was converted to torque, then to force on the roller. Finally, total force was divided by 3”, the approximate width of a crushed stalk of average C.P. 67-500. This final value is force per inch of adjusted roller length.

For the mill of the most interest to me, viz. Goldens’ No. 2, the output of this calculator is 1272 ft-lbs. In a separate exercise, recommended torques of Goldens’ No. 1-4 and of Goldens’ No. 22x-44x were calculated from their recommended horsepowers for converted mills assuming 100% mechanical efficiency. Inexplicably, Goldens' values did not agree well with each other. Nevertheless, a fifth-order equation that favored the recommendations for the No. 1-4 for short rollers and favored recommendations for No. 22x-44x for long rollers was developed. For a Goldens' No. 2, the solution for this equation was 1460 ft-lbs, which is in good agreement with this calculator’s return.

The torque return of this calculator exceeds the mechanization design of one of my Goldens' No. 2s by an estimated 40%. This mill easily crushes one line of C.P. 67-500 at 60% extraction and has a juice output with this cane of 30-35 gallons per hour at 6.3 rpm (or ~45 gallons per hour at the optimum rpm). This mechanization design is not sufficient for two lines of this cane, although the mill itself is. These "field" observations might be taken into account in use of the "Minimum Torque Requirement," which is the output of this calculator, to establish a torque requirement for a specific application. (Obviously, a mill has a lower extraction rate with some canes, e.g. Hybrid No. 14, and a several-fold higher rate with Home Green, a large-bore, succulent cane).

Of course, torque requirements are very specific to the conditions. If the cane is harder, if cane is fed with lateral overlap, if the extraction percentage is higher . . ., the required torque will obviously be increased. For these reasons and because no margin of error has been built in, the output of this calculator has been specified as "Minimum Torque Requirement." This output nomenclature does not imply desirability of maximizing torque, which damages mills when they are overloaded. In my opinion, the torque should be just sufficient to crush the cane, but not damage the mill. Again, the output of this calculator is intended to aid in setting the design torque for a particular application.