Screw Conveyor Speed for a Target Capacity
The inverse of the screw-conveyor tile: the auger speed needed to hit a target volumetric capacity, rpm = target_ft3_hr / (flight_area x (pitch/12) x 60 x loading) (CEMA Book No. 350). A 9 in screw with a 2.5 in shaft, 9 in pitch, at 30% loading needs 40 RPM for 220 ft^3/hr; double the target and it needs 80 RPM (capacity is linear in speed). Divide a mass rate by the bulk density for the volumetric target first. A flagged high RPM means step up a screw size. CEMA and the manufacturer govern.
Formula and source
rpm = target_ft3_hr / ((pi/4)(D^2 - d^2) x (pitch/12) x 60 x loading), all lengths in feet. The inverse of Q = (pi/4)(D^2-d^2) x pitch x RPM x loading x 60.
CEMA Screw Conveyor standard (Book No. 350) capacity method solved for speed, by name.
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