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.

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.

There are many different factors to consider when designing a screw conveyor. The purpose of this example is to provide a step-by-step process that a Macwell Engitech would follow when designing a screw conveyor. It is important for the person designing the screw conveyor to understand how each factor affects the final screw conveyor design.The following information will be used for the example –

•      Bulk Material: Corn Meal

•      Capacity: 25,600 lbs/hr

•      Screw Conveyor Length: 16-feet, 0-inches from centerline of inlet to centerline of discharge

•      Screw Conveyor Degree of Incline: 0° Horizontal

 The screw conveyor for the example is control fed at the inlet by another screw conveyor.

The Selection Capacity will be used to select the proper screw conveyor diameter and speed from the Capacity Table. Using the Recommended Trough % loading and calculated Selection Capacity, select the proper conveyor diameter. The Selection Capacity must be less than the maximum capacity given in the Capacity Table. Fill in the blanks below based on your previous calculations:

Conveyor Diameter:    12”   Capacity at Max RPM: 1,161 Capacity at 1 RPM: 12.9