Screw Feeders - How to Calculate Horsepower

Contact your local screw feeder dealer, and ask him for an engineering manual. Here in the US they are readily available, and standard for all makes. The one I happen to have on my desk at the moment is the Thomas company out of Burleson, TX - home of several screw conveyor manufacturers (they are all spin-offs of each other and compete happily together in a shared sandbox).

These engineering manuals will have about 110 to 120 pages on how to size the conveyor, pick the components, and all the calculations, tables, and information required to do so. It looks like a daunting task up front, but it only takes an hour or so to do the first one, and less time after you have done it a few times.

They will tell you proper trough loading for your product, as well as delivery rates for sizes of trough, etc. that you use to decide where to start, then all the calculations for coming up with the combined horsepower to do the job. Follow every step as you go through the process, and you will come up with the right number. Always round up on the HP's and you will not get into trouble. Running at the hairy edge is usually like shooting yourself in the foot... However, I have found that you can usually do much better on delivery rates than the tables show, so you can usually push that number to the limit without worry of falling short. Do not EVER think that a screw running at steeper than a 30 degree angle is a good idea - it is NOT - despite what the catalogs and salesmen tell you.

Some things that affect horsepower:

Unexpectedly wet product

Poor Maintenance

Back-ups from downstream

Avoid these and the calculations should be pretty good if carried out completely. You don't need to worry about intermediate bearings at only 5 feet, and everything is pretty straight forward, so I don't anticipate that your calculations will be anything difficult. If you are going to buy a new conveyor, the salesman should be able to do the sizing for you as well, if you give him the right input information, but it would not hurt to go through the exercise yourself to see if he is over-selling you. Unless ZnO is a lot different than everything I have handled, I would be shocked if the motor needs to be anything over 2 HP, and could probably be done with a 1 HP motor.