When designing a shaftless screw for use in various types of equipment i.e. (shaftless screw conveyor, shaftless screw feeder, grit classifier…) the most common assumption is the thickest part of the screw profile, should be the out-side peripheral edge of the screw, (in contact with the liner), because this is where the maximum stress is (commonly used flight profiles 1” 3/4 x 1/2” inner and 2” 1/4 x 3/4” outer for a 11” 1/2 OD screw).
After researching the best profiles for shaftless screws by manufacturing different profiles and then performing destructive testing (in both pulling and pushing modes), it turns out that the maximum amount of stress imposed on the screw, is in fact imposed by the gear drive along the inside center axis of the screw, justifying the fact that a thicker inside profile would allow for greater resistance over time.
Two solutions seem to be better suited to get the maximum out of your shaftless screw equipment, extending the life of the screw, reducing the cost of operation and maintenance downtimes:
- Go with a shaftless screw with a thicker inner section and thinner outer section (for example 3” x 3/4” inner and 1” 1/4 x 1/2” outer for a 11” 1/2 OD screw)
- Ask for a supplier that can manufacture your screws in one section only (4” x 3/4” for the same 11” 1/2 OD screw).