Torque Capacities for screw conveyors

Although a given conveyor may be adequate insofar as material conveying capacity is concerned, the horsepower available to operate the system may exceed the torque capacities of standard components during overloaded or stalled conditions.

To insure adequate torque capacities without undue additional cost, means are provided in the Industrial standard series of conveyor components for more than one maximum allowable horsepower value. This is accomplished by not only a choice of power-transmitting component sizes but also of the materials of construction.

Analysis of a specific conveyor system with regard to component torque adequacy may be conveniently and quickly made by use of the two following nomographs.

Carbon Steel Conveyors

The first nomograph covers carbon and high-tensile steel coupling bolts and shafts (drive and coupling) and conveyor pipe (in Schedule 40 and for high capacity, Schedule 80).

These components are listed according to their associated standard conveyor shaft diameters.

The following table lists actual nominal pipe diameters corresponding to the standard conveyor shaft diameter.

Shaft Diameter	1	1-1/2	2	2-7/16	3	3-7/16
Nominal Pipe Size	1-1/4	2	2-1/2	3	3-1/2	4

Stainless Steel Conveyors

The second nomograph covers stainless steel coupling bolts, shafts and conveyor pipe. Coupling bolts are listed by the corresponding standard conveyor shaft diameter with which they are used.

Conveyor pipes are listed in both Schedule 40s and 80s by their nominal pipe sizes.

The pipe size selected should correspond to the standards listed for carbon steel pipe. Deviations from this standard are sometimes possible, in sectional conveyors, by the use of smaller pipe sizes (for economy) when the torque rating is adequate. This procedure requires reaming of the pipe bore for shaft insertion rather than the use of a bushing. It is recommended that requirements for such conveyors be referred to Kase’s Engineering Department.

Note: High starting torque motors must not be used without design verification by Kase’s Engineering Department.

Example: A 12-inch carbon steel conveyor has been selected with a required shaft horsepower of 8.9 and a speed of 64 RPM. The drive to be used has an efficiency of 85%, thus requiring a drive input of 10.46 horsepower. Therefore, a 15 horsepower motor must be used. This total motor horsepower could be transmitted to the conveyor components if overloaded or stalled.

Three standard shaft sizes are available for 12-inch conveyors. They are 2″, 2-7/16″ and 3″.

A straight edge is placed from 15 horsepower on the left scale to 64 RPM on the center scale. Project the straight line to the left vertical line of the chart at the right. A horizontal line from this point will pass through component groups suitable for the torque.

For the conveyor under consideration, it is found that standard components will be adequate, with the exception of coupling bolts which must be high tensile.