Max RPM for step pulleys

S

Saul Kokkinos

Joined
Sep 4, 2015
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14
I am trying to figure out the drive system for my new belt grinder, and i'm having an issue trying to find any information on the RPM limits of cast aluminium step pulleys.

I'm after a belt speed range of around 1000 SFM to 7000 SFM. The plan is to have a 4 groove (2", 3", 4" and 5") step pulley on the 2800 RPM motor, and another 4 groove (2.5", 3.5", 4.5" and 5.5") step pulley on the axle that runs the 5" drive wheel for my abrasive belts. This should result in belt speeds from 1332 SFM to 7330 SFM.

When i'm running this at top speed though, the second step pulley will be spinning at about 5600 RPM, so my question is, is this too fast for a cast aluminium step pulley? Is it going to explode?

Any help is much appreciated!

Here is a link to the pulleys i am looking at, just to show what they look like.
http://www.ebay.com./itm/182360698273?_trksid=p2055119.m1438.l2649&var=484913310803&ssPageName=STRK%3AMEBIDX%3AIT
 
Two things:
1) Is it cast aluminum or cast zinc? Most of the lower cost pulleys are zinc.
2) Is it machined or just cast? Machined pulleys made from cast steel or cast aluminum, are the best. They are properly balanced and run smoother.

Machined cast aluminum pulleys should easily run up to 10,000 RPM, and even the lower quality cast only pulleys should run at 5600RPM. I would think the Zinc pulleys would hold up at 5600 RPM, too. Machined cast steel pulleys would be super smooth running and safe at double your speed. Caution - You do not want to run a cast iron pulley at high speed, they can explode.

It is when a pulley is damaged by a blow or other bend that they can come apart. Properly aligned and in good condition, they are quite safe. The most common cause of failure is improper mounting or balance. Use all the set screws the pulley has and properly tighten them evenly. A loose fit on the shaft is asking for trouble. A bent or worn shaft is asking for trouble, too. Test spin a new pulley with no load. Run it for five or ten minutes at full speed and feel for vibration. If there is any, either fix the problem or return the pulley.
 
Saul, Considering the cost and hassle of setting up multiple pulleys wouldn't you rather spend that money on a variable frequency drive (VFD) instead? You could dial your speed at your fingertips and eliminate all those pulleys and pulley changes. Once you use variable speed on your grinder you will never go back to pulleys. Not just my opinion. Larry

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