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We have a Buffalo Forge motor-belt driven blower (Ty E, Size 6) used to provide ambient air for ventilation. The unit was recently refurbished (new shaft, balanced, aligned, new bearings) and running very smooth.
While taking vibration data (very smooth), I noticed both pillow block bearings very hot to the touch. These are Fafnir RSAO type supporting fan shaft, mounted with offset cam, running at 3550 RPM and, according to the installation notes, not normally needing periodic greasing. Took temp readings and the outside block temperatures were as high as 207 deg F. In comparison, another identical blower's bearings measured almost ambient ~ 93 deg F.
I contacted Fafnir and they stated that this temp would not degrade the bearing but could offer no advice on why it was hot in the first place. Based on this information, we decided to continue operation and monitor the temperatures.
Today, after 1 day of operation, the highest temp dropped from 207 to 179 deg F.
My question is whether other maintenance personnel have seen similar temp swings as this? One concern I still have is that the bearings have been in storage for over 10 years. Discussions with Fafnir tech's indicate that the rust preservative shelf life is typcially 6 years.
Is it possible that some oil/base seperation or lose of preventative is a root cause here? If so, why is temp dropping?
In any case, would appreciate any comments on similar observations and possible explanations. I will continue to monitor the trend of these temps.

Jim P

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Just some thoughts.
Could the bearing have had some pre-load added during installation?

Setting for 10 years but vibration is very smooth kind of cancels that idea out.

How long has the other fan you referenced been operating?

Are belts over tightened? Typically belts will stretch after some run time and at 24 hours you may be seeing that?

What are your g's readings?
What are your HFD numbers? gSE-Peakvue etc.?
The other fan has been running for over two years since it was overhauled.
I dont think the belts were overtightened. We've set up a good procedure for belt tensioning, alignment, runout, etc. Do you have past experience of overtightening belts causing excessive heating of the bearings?? I've nev er read about that before.
Right now I'm on vacation in OBX so I dont have actual readings to provide off top of my head...I can say that the baseline readings (velocity) were very normal...but will post when I get back. I will also have more information regarding a week and half of temperature trend data to provide

Wally - The bearings were simply installed as-is from the warehouse. Since they were ordered and stocked 10 years ago, that is where my focus is on now. I plan take one from stock and open the shields to see what the grease looks like.
Thanks for the comments - more to come

I have seen the overtigtening of v-belts create excessive bearing temperature. Vibration was smooth but later the bearing failed. High frequency, gSE started to climb then the failure mode continued. Think of the amount of pressure/stress being applied to the bearings if the belts are overtightened. Bearing training classes have mentioned this too. To tight of belts can really create heat and then add with that maybe overgreasing and you could have a great deal of heat.

I'll see if I can find the information about belt overtightening and post the link.

Here is a link to one article I found.

Back in the day when I would work on my car, changing the v-belt, I actually overtightened the generator v-belt and took out the generator bearing. For those of you that remember that automobiles use to have generators. Wink
Last edited by Registered Member
Thanks for the link.
Just as the authors stated in the article, our mechanics also tightened the belts using a belt tensioning device using Fn measurement. This device is still a fairly new unit for us and was not there that day to oversee the procedure.

A thermograph was used to identify the "hot" DE bearing but most of the article dealt with L10 calculations rather than efect on temperaure (or did I miss something?). The article also showed only the DE bearing having high temperature vs. our case where BOTH DE and NDE bearings as being hot. "Assuming" that overtension is the root cause, I can only image this affecting both bearings if there is a strong cantilever effect on the NDE bearing (which is also the hottest).

I will post an update on this case once I return to work next week. Either the temps will have stabilized to some temperature I feel a little more easy with or, if still high, I will have the belts re-checked or simply loosened to see the effect.

Thanks again to eveyone with their comments

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