Hi Dimitri,

A conventional screw conveyor has a shaft with end bearings. That means the power to drive the empty screw is only a factor at bearing friction.

In a shaftless application the dead weight of the screw must be included in the friction calculation - which could vary between metal to metal friction, and metal to product.

In both cases the gland packing at the shaft exit can generate extra frictional resistance. The extra resistance due to this and other incidental factors is not easy to estimate. Usually an assessment is made based on past experience with operating screw equipment. Such fudge factors are not easy to come by. Many consultants treat them as a trade secret.

Regards - John.Rz

Conveyor Calculation http://www.cospire.com/browse.aspx?id=4317 ■

It is worth pointing out that the weight of shaftless flights are generally heavier than normal screw flights because they have to transmit the torque. The capacity is also very marginally less because of the flight thickness, but otherwise normal screw calculations apply with the extra friction indicated by John. ■