Screw Conveyors

[albresco]

Does anyone know of a formula to calculate the loading on the thrust bearing of a screw conveyor?

 

[GCPeters]

Are you referring to a power screw used for axial movement?

Need more info please

 

[albresco]

Yes this conveyor is a simple power screw used for axial movement of wood pulp in a paper mill.
Mark's Handbook has a calculation for the power requirement but I can't find a formula for the thrust bearing load.
Thanks,
Doug

 

[GCPeters]

I still dont fully understand the problem. Are you designing a new system, or are you replacing the thrust bearing with something larger. Are you able to determine the load that the power screw is moving. I have formulas that can help if you know the screw torque,lead angle, diameter, surface area and type of thrust bearing (solid/rolling element)and also the friction coefficient.

Cheers

 

[albresco]

This is a new conveyor. We have been told the required delivery, (106 m^3/hr) the screw diameter (20" dia 3/4 pitch) and the length of 21 feet. We must make an assumption about the coefficient of friction but we have been told that the wet pulp has a density of 60lbs/ft^3. Operating time is 24 hr/day 350 days per year.
We have also been told that the screw must be 3/8" SS flights on a 6"eh SS pipe. Our understanding is that the mill has an existing conveyor of this capacity that has problems with the thrust bearing that they are looking to fix with the new conveyor.
Doug

 

[gbent]

You could size the bearing based on the mass lifted, and the force which must be applied. However, I would want to look at the existing installation as a benchmark. If it's thrust bearing is failing, yours should be sized accordingly.

Another probability is water contamination of the bearing. Make sure you can keep it dry. A problem can be a bearing gets hot while running in a wet environment. Due to some other problem, the machine is shut off for a short time. (even a fraction of a minute) The bearing cools, and water is drawn past seals which are in good condition. The bearing fails months later, but nobody remembers the brief shutdown.

You say the flighting is 3/4 pitch. Is this 3/4 foot or 3/4 of the OD? The usual pitch of flighting is between 1/2 and 1 times the OD of the flighting.