Bearing Storage

[NaikD]

All,

We have an instrument that uses two angular contact bearings. These bearings are separated by porous polymide material that serves as lubricant retainer. The lubricant for the bearings is Apiezon C.

This instrument will be kept in storage for 7 years.
In view of this following things come to my mind.

1. Lubricant loss due to evaporation
2. Lubricant deterioration during this time
3. Lubricant deprivation between bearing races and balls

Do you have similar experience or can suggest any other thing that can go wrong?

Thanks in advance.

- Dipak

 

[diamondjim]

What is the thickness and od of these
bearings? Are they wrapped in heavy
coated waxed paper?

 

[unclesyd]

Apiezon C (now Invoil C) is a diffusion pump oil so it's not going to evaporate unless it's in outer space, its good to 10^-7 Torr.
The oil and its vapors are considered non-corrosive.
It is not a film former so it will drain off the bearings very readily.
It has such a high boiling point I wouldn’t suspect oxidation to be problem with the oil. The bearings if alloy steel, 52100, M2 etc, need to be protected.


Are the bearings in equipment or on the shelf?
It the bearings are static will they sense any vibration from their enviroment?
Are they to be used in a high vacuum enviroment when activated?

 

[NaikD]

Diamonjim and unclesyd,

Thanks for your prompt reply. I appreciate it.

Here are the details:
Bearings are from BARDON, however I do not know the product number as specified in the catalogue.
Bearing OD: 1.2598"
Bearing Width: 0.5000"
Bearing ID: 0.5118

The bearings are already installed in a science instrument and hence will see static load. Since the instrument will be in storage for 7 years, we need to come up with a test plan so that instrument motor will run smoothly when started.

Right now the storage testing plan calls out test every one year. i.e. running the instrument every year. However we need to check if we can do that for every 1 1/2 or 2 years. I am still trying to get information on number of balls etc. Then I will assume the bearing outer race, inner race and balls as planetary gear train to come up with (hypothetically) how many revolutions (assuming balls will not skid) are needed to run the instrument in the storage tests. Let me know if this approach is not correct.

The science instrument is for weather prediction so it will see high vacuum (space) environment.

The parts surrounding the bearings are coated with3M #FC725 anti migration coating.

I will check whether there will be any damage to shaft or bearing, since the load will be localized due to storage. I am not sure about vibration. The instrument has gone through sine burst, sine and random vibration acceptance tests. Other than earthquakes which are normal in California the Instrument (bearings) will not see any other vibrations.

We have spare bearings that are lubricated with the same lubricant and kept ready. But I need to check the details for those.

Thanks again for very informative response.

Regards,

- Dipak

 

[diamondjim]

You probably do not want to hear this,
but I would check the bearings before
running the test unless Bardon tells
you differently. Do not know the temperature
diffences that the bearings see in storage
or how good the 3m barrier is. If you
are going to do this 14 times before the
full assemly is put in the actual application,
that may give you the answer you need.
7 years is a long time in storage.

 

[Skogsgurra]

Spare motors for paper and steel mills stay on their shelves for many years before they are needed (if needed at all). Same is valid for gear boxes, pumps etcetera.

Some mills have routines in effect to rotate the outgoing shaft once or twice every year. This is to avoid marks due to stationary contact, which - due to always present micro-vibrations - gets worse over time.

But I also know of many mills where this is not being done. And I have not heard about any problems. I will be attending a conference with a panel discussion about bearings and maintenance the next few days. I will bring this subject up.

 

[NaikD]

skogsura,

Thanks for very relevant and practical information. I will look forward to hearing from you on this subject once the conference is over.

Regards,

- Dipak

 

[NaikD]

unclesyd,

The bearings are for space (vacuum) application. Are there any other limitations like lubricant evaporation due to exposure to high temperatures during storage?

Thanks for your help.

- Dipak

 

[unclesyd]

I don’t have a Vapor Pressure Curve for this oil. As you see below the BP at 1 Torr is 225°C. You should be able to get a technical data sheet from the manufacturer. Also they should tell you of their experiences if any with this oil in space applications as this is one shot application.

I would also check with NASA to see what they say about this particular oil in space applications.

I would be hard pressed to use anything in a Space application without an in-depth knowledge of the material and some accredited approval.

http://www.emsdiasum.com/microscopy/products/microscope/grease.aspx?mm=18

 

[NaikD]

unclesyd,

Thanks for the information. I have already emailed the manufacturer for the vapor pressure curve for this oil.

Regards,

- Dipak

 

[Skogsgurra]

I am back from that conference. We were 56 maintenance people and trouble-shooters for paper and steel works. Twelve people said that they were aware of the need to move the shaft of motors and gear boxes once or twice a year. But only one company actually did it.

There was some concensus that a motor that had rested for a long time should be re-greased before putting into service. There was some concern about over-greasing.

A couple of works had done some vibration monitoring to make sure that the levels were not too hogh. One company had moved the spare motors from a store close to the rail-way to a less shaky location.

 

[Tmoose]

We could never get a lubricant manufacturer to "sign up" for grease service life more than 3 or 4 years in OEM sealed containers. One limit, but not the only limit, was oil separation that could be corrected to some degree by stirring the can.

Storing the device on rubber pads with at least 1/4 inch deflection can provide pretty effective isolation

 

[unclesyd]

Out of the box.

If the bearing isn’t that expensive you might want to have a dummy setup where the bearing sees the same load and conditions as the installed bearing. Remove and check it periodically.

If there is any doubt about storage you might look at testing the bearings with the following device. The bearing should be checked prior to installation. There are several pages of information.

http://www.dynaroll.com/catalog4/pag01.htm

This is a good small bearing information site.

 

[NaikD]

skogsgurra,

Thanks for the information. Looks like even though majority of the companies did not rotate the shaft, in the end there was no problem.

Tmoose,

The bearing lubricant that we are using is Apiezon C oil. I talked to the manufacture and according to them the shelf life of this lubricant, if container is unopened is 10 years. Since the lubricant is already in the bearing, I have requested them to check if the oil would change chemically if in use for approximately 12 years (7 years in storage and 5 years orbital life). Thanks for the information.

unclesyd,

I, finally managed to get the vapor pressure curve from the manufacturer. I also found information on the life test that was carried out by NASA on the same bearing. Only 12% of lubricant was lost in 6 years of accelerated life test in vaccum.

Thanks for the information.

All,

I really learnt a lot from all you. I appreciate your help in this project.

Regards,

- Dipak

 

[electricpete]

I think in our plant if a critical piece of equipment had been sitting on the shelf 7 years with no maintenance we would consider disassembling and replacing lubricant before installation as mentioned by diamondjim.

I am not clear if this is grease or oil. If oil you might consider sampling.

In addition to the bearings, bending of the shaft may be an issue of long-slending shafts are not rotated periodically.

In the end, part of the issue is the pain associated with failure after installation. If you are pulling it off the shelf and installing into non-critical application, it is just as easy to see if it fails in-service and rebuild it then as it is to disassemble and inspect before installation. If it is going into outer space I imagine it would be much more painful to address a failure in-service.

There is no right answer and each opinion is valid.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[brgguy22]

http://www.bardenbearings.com/

All Barden bearings are ABEC 7 (at least and can be quite expensive). I would double check with them on the long term storage issue. They are a great company and really know their stuff, aerospace and all. Ambient vibration will be an issue and I concur on running the unit periodically.

 

[NaikD]

electricpete,

Thanks for the response. I am getting good information and ideas from all of you.

I think it would be a good idea to have an experimental setup (since we have spare bearings) and shaft (I do not know whether we have a spare) next to the instrument in storage and study the effects of lubricant deterioration, lubricant loss, shaft bending and microbrinnels etc., without having to touch the actual instrument.

Thanks again!

brgguy22,

Yes, I will check with Barden on this issue. I wonder how I would attack the problem of long term loading of a shaft analytically. However, I have not thought about it yet. May be I should look at it from the point of view of creep. I was able to calculate the lubricant loss due to vapor pressure.

Thanks,

- Dipak

 

[diamondjim]

I worked with Vickas Naik in Canton Ohio
back in the 60s. Do not know if you are
related or not. Naik is probably like
Smith in this culture.

 

[NaikD]

diamondjim,

No. You are right, Naik is like Smith...and Dipak sometimes spelled Deepak is like John....a common name here.

Regards,

- Dipak