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:
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.
| 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 |
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 |
