What is your opinion on pillow block bearing cleaning and complete grease replacement, say, every 1-2 years ? In particular on those bearings operating at temperatures of
180F -190F and dusty environment.

Thanks,
David

A few questions.

How critical is this equipment?
Are vibration readings being taken, including HFD or gSE readings?
Is a good PM program in place that grease is added on schedule?
What kind of seals and how dusty?

Don,

I understand where you are getting to. I guess you imply that grease contamination can be captured with HFD, gSE, PeakVue, ultrasound, etc. Yes, it can be and is in fact being detected in my case.

But the fact is that due to hard dust particles contamination, grease decradation due to heat, grease becomes over time a hardened chunk of cake filling up the space around the bearing. Replenishment has to be done in this case (based on above measurements ) more frequently. It may take 1 or 2 years but sooner or later this caked mass has to be removed. So why not do it, say every 2 years ( interval established by experience ) on all identical machines at once during annual shut down? Is it a common practice ?

One of our clients (grain industry) repacks their fan pillow block bearings every couple of years or so. Most of the time there is a lot of excess grease that needs to be removed. Seems to be a good old school practice (they've been doing it since they can remember)

Regards,

Good comments.

There was a lot of discussion of this question here:
http://maintenanceforums.com/e...19103451/m/869100432

It was mentioned SKF recommends periodic repack. It's hard to argue against an OEM recommendation. However we don't do it periodically on any motors and that is pretty standard among utilities. (For example see the linked article regarding EPRI practices - now periodic repack). If I were going to do it I would pick the few high D*N which gives us problems with grease degradation. Maybe it is a similar situation for your machines (what is speed and beairng size by the way?).

I'm not that familiar with pillow block beairngs. If grease were repacked on a pillow block, would it be done in place or the pillow block removed to the shop?

• If done in place, considering the dusty environment you mentioned, there may be quite a potential for contamination.
  
• If the whole pillow block is removed I think it will require careful re-alignment upon reinstallation which increases the work even further. If you're going to all that trouble, perhaps makes more sense to just replace the bearings on condition-based basis while you're at it as long as there has been good warning on these in the past.

May be I missed it, but I did find about repacking in EPRI material.

For the pillow block bearings repacking is done normally in place, as far as know. In my case it is a 1800 RPM, D = 5 inch bearing.

I think repacking makes a good sense. After awhile old degraded ( most often a caked mass )grease fills up the cavity blocking heat exhange and affecting replenished grease action. The situation gets aggrevated when it gets mixed up with the ingressed particles.

One has to find a resonable interval for repacking. I am curious as to how many people are doing it ( I refer in this case only pillow block bearings, not motors').

quote:

Originally posted by David_G:
May be I missed it, but I did find about repacking in EPRI material.

Precisely. Their entire electric motor regreasing program does not include repacking.

quote:

For the pillow block bearings repacking is done normally in place, as far as know

Thatg makes sense. I'm not sure even how one would go about removing the pillow block without very major work. But wouldn't you have concerns about contamination when repacking in a dusty environment?

We don't have many pillow block machines. I know of a few fans that have them and I'm pretty sure they get periodic relub, no repack. I tend to see grease coming out of the side of them just about always which makes me think we just keep adding grease.

I'm not sure what's different about pillow blocks than a small motor.

• Do pillow blocks have much of a cavity inside?
  
• I imagine it may be a little easier to access the cavity than to remove the endbell of a motor... especially inboard endbell which may require uncoupling and removing the coupling hub.

You said 5" bearing. Let's say that is the bore (is it?). That would be around 125mm (something like) 6325. At 1800rpm that is D*N=225,000. Similar to my 6313 at 3600rpm. We have a fair amount of problem with those machines. Periodically we get symptoms of lubrication problems (often seems to be 2*BSF/harmonics with cage sidebands and general raised noise floor) and often the lub is discolored (not quite as bad as our 6316 but we still have this problem on the 6313's). I can see the motivation to do something about it by going after the grease before it ages out. If it is other than a ball bearing the grease life is even lower than for ball bearings of similar D*N. Heat and load can also accelerate aging. But just based on the D*N alone I would tend to think the relatively high D*N could be aging your grease. I don't have experience wit a dusty evnironment, especially varisous kinds of product dust that can have different characteristics. But I have a hard time imagining outside dust is aging your grease... the outside dust shouldn't be getting inside the cavity, right? If it is that seems like a big problem in itself.

This message has been edited. Last edited by: electricpete,

Yes, the dust should not be getting inside the cavity, but with the OEM's labirinth seal, it does. Better seals would not hurt, of course. May be in the future they will get replaced with a better type. 120F ambient temperature also helps to cake the grease. So these are, I guess, more significant factors then D*N. Pillow blocks have relatively larger cavity then motor end bell housings, I believe.

Do BPF with cage SBs go away after greasing?

I agree there are other factors besides D*N and I had mentioned few. (I wasn't sure about dust but I'll take your word for it.) Most of the recommendations for lubricant selection or relubrication intergval or aging predictions start with D*N and then make corrections if there are unusual load, temperautre, etc. My general impression talking to peopls at our plant is that most of them intuitively understand that high ambient temperature, high temperature due to process, high load etc have a big impact but they are oblivious to the role of speed and size (D*N) upon lubricant aging.

We have in the past sometimes seen regreasing these motors (with high D*N that show symptoms) temporarily reduces the symptoms but usually within a few months they are back.

My question about pillow block mounted bearings was just trying to figure out if and why they would have a different strategy. If it's not that pillow blocks have smaller caviety, then maybe it's just the difficulty removing endbell of a motor (especially the inboard end). I'll be interested ot hear others' further comments on repack strategies for pillow block bearings.

This message has been edited. Last edited by: electricpete,

David,
I just needed more information before responding.

I work in several types of plants. Electrical generation, steam, chilled water and waste water. The repacking procedure for pillow block bearings you are talking about is standard based on equipment experience. Most are repacked during yearly overhaul schedules. Again experience and criticality of equipment plays in the decision. Repacking is completed in place, even in dusty areas. Special care is taken in those areas to prevent dust contamination.

Glad to here you are using the HFD type of readings. Most useful for lubrication conditions.

At one site we worked with a bearing company and changed lubrication from grease to an oil bath. At that time we installed highly rated breathers and bearing isolator seals. Gross contamination became a thing of the past for that equipment but yearly maintenance checks and flushing was completed and seemed to take less time.

Don

There are several points to consider here.
I realise that I may be pointing out the obvious, but too often in my experience the obvious has been overlooked!
Are the "Pillow block bearings" you refer to;-
1) Split, shell type.
a) May be self-lubricating
b) Pressed steel with lube groove running through it.
2) Self contained roller/ball bearing with greasing nipples. If so contamination should not be an issue if basic cleaning of contact areas between the gun and nipple is observed. When applying grese through an applicator the medium will always find the easiest path, it's difficult bt you have to try and apply a restriction to the initial outlet, being careful not to blow out the seals.
3) Self contained roller/ball bearing with NO obvious grease application points. This type are to be replaced as a unit at specific intervals according to the manufacturers periodics... Or when they get hot and burn/sieze up!


You should be able to find out what you need through the bearing manufacturers website, of course bearing in mind they want to flog you something.

Rick

In my case these are split pillow blocks. The grease fitting is positioned so that grease is added to the cavity.

Although we lubricate using ultrasound technology, in some cases bearing temperature goes up ( 20-30F above normal) and adding more grease does not help. In this case we repack and this brings temperature down.

In general, it is obvious that over time the old soap gets accumulated, grease - contaminated/degrades, etc. Therefore one day the bearing has to be repacked if you do not want a failure to occur. Just some bearings will need it every year, while others - every 5 years. As I hear it, many people do it, but as many - do not. All of the above pertains to motors as well, but I did hear that repacking is done on a big motor bearing. I could be wrong here...

David

Sys_fan3_OB_hot.doc (60 KB, 15 downloads)

David

First question is what type of lubricant are you using(i.e. mineral or synthetic) and are the bearings ball or roller? With synthetic lubricants you can utilize longer relube intervals base on oxidation life of the grease. We routinely relube our split pillow block bearing ever 2 years and change out the grease every 4 years, while monitoring vibration and temperature.