Failure & Consequences, bit O.T.

Exciting morning in the office.

400HP/1800RPM/480VAC/TEFC/NEMA B Torque/1.15 S.F. failed at customer site in NJ, I am in WI. Motor broke its 4.5" OD shaft, Soft starter and PLC kept motor going. Destroyed ductile iron sheave, and v-belts, drive guard damaged. Motor has about 1000 hours of operation and is <1 year old.

Had to search for all replacements, now we will airfreight overnight replacement motor from TX to NJ, and other parts from WI to NJ.

Could use a motion detector to verify driven sheave is turning. But would not prevent the motor failure.

Customer is down, we have to get them up and running again. No one hurt, and our driven machine intact.

Regards,

AB

Wow.

What is the driven load? What brand of motor? Around here we don't break motor shafts. Please let me know how this pans out. Knowledge is power.

Here's a couple of links for rotational speed monitors
Turck
red lion
And here's a link for a torque limiter!
Autogard

My 2 cents!

Some of this stuff reminds me of the soooo little importance mechanics sometimes put into the shear-pins selection.

I'm not saying that this IS the problem but I've seen it before.

Cannot mention brands at this time. Machine is used for material size reduction. Drive is via 8 * 8V belts, used to transmit power and isolate motor from shocks. Drive and driven sheave are about 1:2 diameter ratio, about 8 feet on center. No shear pins.

If the driven machine stalls (not a common situation), the motor might trip on overload or it might keep turning and "smoke" the v-belts. At the site, there are 2 of these machines side by side, so I am wondering when the other motor will fail!

Thanks for the interest in the failure.

AB

I may be stating the obvious here but this sounds like an overhung load issue to me. I know, the bearings should have failed first if this was the case. But with all the belts the shaft force due to tension must be pretty high. To fit all the belts the sheave must be pretty long. I wonder if the combination of belt tension and impulse loading down the belt from the machine fatigued the shaft.

Keith

I agree with Pierre on the shear pins. We have a hogger system similar to what AB describes that chews up logs, bark, butts, rocks, mud, and anything else that gets in to be burned for electric co-generation as long as it's not metal. We have shear pins (mechanical version of a fuse) that break at the anvil if and when metal gets to it (we have a detector). Our prox switch at the shear pins shuts it down and indicates that this has happened. Sounds like AB should be shopping for something similar.

Here is a link to see what we have:

http://www.cbi-inc.com/sawmills.html