Screw Feeders - Circumferential and Linear Speeds

There is an entire industry devoted to manufacturing powder feeders. Instead of attempting to reinvent the wheel, I recommend contacting one and testing with their equipment. It will cost you nothing more than the price of shipping test material. Additionally should something go awry with the production equipment, the manufacturer will warrant their feeder configuration and be responsible for any required screw or other changes to meet your feedrate.

While every feeder manufacturer has their own closely-guarded screw specifications, I estimate your application could be handled on a 35 mm diameter screw @ 80 RPM. Remember with higher RPM, the effect of pulsing will be less, so will have a more accurate second-second feedrate. If you are looking to "convey" as opposed to "feed" you can slow the screw but will have to enlarge the diameter.

The rule of thumb for trough sizing is to allow three material diameters clearance from the screw.

The big challenge with your application is hoppering the material and promoting flow into the relatively small screw. Some form of flow activation will be required (vibration, agitation, stirring, etc) so testing will be critical to select the proper feeder.

The manufacturers of auger parts publish excellent application information in their catalogs. These easy to understand equations and look up tables take into account material density, abrasiveness, flow rate, auger length, etc. I have sized several screw feeders with the Martin Material Handling Products Catalog, then bought the hardware from them with the help of a distributor. I am sure other manufacturers work the same way.

The things that usually limit the auger rotational speed in my experience has been the allowable torque thru the auger shaft and shaft "whip".