KWS Manufacturing

Screw Conveyor Torque

Torque is defined as the twisting force exerted by the drive unit on the conveyor screw. Torque is transmitted through the drive shaft of the drive unit to the screw and converted to force to convey the bulk material. Properly selecting screw conveyor components is important to minimizing downtime and maintenance.

Full Motor Torque is the maximum torque generated by the drive unit. The equation for Full Motor Torque is shown below:

Full Motor Torque Equation

HP = Nameplate Horsepower of the motor on the screw conveyor
S = Conveyor Speed

Torque is measured in inch-lbs. for screw conveyor components. The torque rating of the drive shaft, coupling shafts, coupling bolts and conveyor screw must be able to withstand Full Motor Torque without failing. Every KWS screw conveyor is designed to this criteria with a minimum safety factor of 5 to 1. The motor on the screw conveyor will stall out before there is a mechanical failure of a screw conveyor component.

Maximum torque ratings for each screw conveyor component are shown in the Torque Tables. Maximum torque ratings are based on a safe stress value for the specific material of construction. The screw conveyor components will have an infinite life under normal operating conditions.

Screw Conveyor Coupling Bolts, Pipe and Shaft
Standard Screw Construction (by Shaft Size)
Shaft Diameter (in.)11-1/222-7/1633-7/163-15/164-7/16
Nominal Pipe Size1-1/422-1/233-1/2456
Coupling Bolt Dia. (in.)3/81/25/85/83/47/81-1/81-1/4

Torque Table – Carbon Steel

Shaft Dia.Carbon Steel Torque Values
ShaftCoupling Bolts (2-Bolt)Pipe – Schedule 40
C-1045Grade 5A-53
TorsionBolts in ShearPipe in ShearPipe in Bearing
Safe StressTorque RatingSafe StressTorque RatingSafe StressTorque RatingSafe StressTorque Rating
PSIIn-LbsPSIIn-LbsPSIIn-LbsPSIIn-Lbs
18,7501,00015,5003,4006,7003,1006,7002,200
1-1/28,7503,80015,5009,1006,7007,6006,7005,600
28,7509,50015,50019,0006,70014,2006,7008,900
2-7/168,75018,70015,50023,0006,70023,0006,70013,200
38,75035,40015,50041,0006,70031,9006,70017.500
3-7/168,75053,00015,50064,0006,70042,7006,70024,700
3-15/168,75076,40015,500121,3006,70072,6006,70058,200
4-7/168,750110,20015,500168,8006,700112,9006,700101,300
Screw Conveyor Torque Diagram

Torque On Shaft, Coupling Bolts and Pipe

Torque Table – Stainless Steel

Shaft Dia.Stainless Steel Torque Values
ShaftCoupling Bolts (2-Bolt)Pipe – Schedule 40
304 & 31618-8A-312
TorsionBolts in ShearPipe in ShearPipe in Bearing
Safe StressTorque RatingSafe StressTorque RatingSafe StressTorque RatingSafe StressTorque Rating
PSIIn-LbsPSIIn-LbsPSIIn-LbsPSIIn-Lbs
16,0007006,0001,3006,0002,8006,0001,900
1-1/26,0002,6006,0003,5006,0006,8006,0005,000
26,0006,5006,0007,3006,00012,7006,0007,900
2-7/166,00012,8006,0008,9006,00020,6006,00011,800
36,00024,3006,00015,9006,00028,6006,00015,700
3-7/166,00036,4006,00024,8006,00038,3006,00022,100
3-15/166,00052,4006,00046,9006,00065,0006,00052,100
4-7/166,00075,6006,00065,3006,000101,1006,00090,700

A Statement From KWS Concerning COVID-19