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.) 1 1-1/2 2 2-7/16 3 3-7/16 3-15/16 4-7/16
Nominal Pipe Size 1-1/4 2 2-1/2 3 3-1/2 4 5 6
Coupling Bolt Dia. (in.) 3/8 1/2 5/8 5/8 3/4 7/8 1-1/8 1-1/4

Torque Table – Carbon Steel

Shaft Dia. Carbon Steel Torque Values
Shaft Coupling Bolts (2-Bolt) Pipe – Schedule 40
C-1045 Grade 5 A-53
Torsion Bolts in Shear Pipe in Shear Pipe in Bearing
Safe Stress Torque Rating Safe Stress Torque Rating Safe Stress Torque Rating Safe Stress Torque Rating
PSI In-Lbs PSI In-Lbs PSI In-Lbs PSI In-Lbs
1 8,750 1,000 15,500 3,400 6,700 3,100 6,700 2,200
1-1/2 8,750 3,800 15,500 9,100 6,700 7,600 6,700 5,600
2 8,750 9,500 15,500 19,000 6,700 14,200 6,700 8,900
2-7/16 8,750 18,700 15,500 23,000 6,700 23,000 6,700 13,200
3 8,750 35,400 15,500 41,000 6,700 31,900 6,700 17.500
3-7/16 8,750 53,000 15,500 64,000 6,700 42,700 6,700 24,700
3-15/16 8,750 76,400 15,500 121,300 6,700 72,600 6,700 58,200
4-7/16 8,750 110,200 15,500 168,800 6,700 112,900 6,700 101,300
Screw Conveyor Torque Diagram

Torque On Shaft, Coupling Bolts and Pipe

Torque Table – Stainless Steel

Shaft Dia. Stainless Steel Torque Values
Shaft Coupling Bolts (2-Bolt) Pipe – Schedule 40
304 & 316 18-8 A-312
Torsion Bolts in Shear Pipe in Shear Pipe in Bearing
Safe Stress Torque Rating Safe Stress Torque Rating Safe Stress Torque Rating Safe Stress Torque Rating
PSI In-Lbs PSI In-Lbs PSI In-Lbs PSI In-Lbs
1 6,000 700 6,000 1,300 6,000 2,800 6,000 1,900
1-1/2 6,000 2,600 6,000 3,500 6,000 6,800 6,000 5,000
2 6,000 6,500 6,000 7,300 6,000 12,700 6,000 7,900
2-7/16 6,000 12,800 6,000 8,900 6,000 20,600 6,000 11,800
3 6,000 24,300 6,000 15,900 6,000 28,600 6,000 15,700
3-7/16 6,000 36,400 6,000 24,800 6,000 38,300 6,000 22,100
3-15/16 6,000 52,400 6,000 46,900 6,000 65,000 6,000 52,100
4-7/16 6,000 75,600 6,000 65,300 6,000 101,100 6,000 90,700