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Do an online search for EPRI NP-7502, which is a public domain document. Appendix B has a curve for grease quantity versus Shaft diameter (bearing bore). At one time, I had scanned the curve and developed a curve-fit equation. I could dig that out if you want it.

This document was developed for Electric Motors, and provides guidance on intervals based upon speed, power, ambient temperature, and operation (continuous / standby).
RM
quote:
Originally posted by Steve Ciesla:
Do an online search for EPRI NP-7502, which is a public domain document. Appendix B has a curve for grease quantity versus Shaft diameter (bearing bore). At one time, I had scanned the curve and developed a curve-fit equation. I could dig that out if you want it.

This document was developed for Electric Motors, and provides guidance on intervals based upon speed, power, ambient temperature, and operation (continuous / standby).


I would propose that there are much better resources relative to grease quantity than the B-1 chart from the referenced document.

http://www.skf.com/group/produ...brication/index.html

http://www.klueber.com/ecomaXL..._tips_and_advice.pdf
page 11

http://www.machinerylubricatio...e-quantity-frequency

Should you use automatic lubrication devices there is even a smartphone app at http://www.skf.com/group/produ...f-dialset/index.html
RM
The grease quantities and the intervals should be coordinated with each other.

The EPRI NP7502 approach tends to add larger quantity of grease at longer intervals, as compared to most bearing manufacture's recommendations. The longer interval saves manpower required for relubrication activities. The larger quantity is an attempt to compensate somewhat for the longer interval. Small quantities at short intervals are clearly best in terms of lubrication conditions alone (without regard for manpower expended to lubricate).

So, these are different approaches representing a tradeoff.

With regard to the calculation of volume, which has a form that suggests more accuracy?
* The SKF formula for volume is directly proportional to the product of D*B (even though bearing volume would be more closely proportional to D^2*B).
* The EPRI curve provides a non-linear function of d which is approximately the required d^2, but does not account for B which varies.
* Neither one accounts for changing ration d/D for example 62xx vs 63xx
* Based on above, Neither one gives a result which is proportional to volume exactly. And greasing is not an exact science. I'm not inclined to think one form is better than the other.
* Comparing ease of use of the two forms: I can find d knowing part number alone (without consulting product tables) but not D or B. Not having to consult product tables is an advantage for the EPRI approach which is counteracted by the fact that I have to consult a curve for EPRI approach. Net result, neither one is much easier than the other.
RM
Last edited by Registered Member

The SKF formulas to determine volume and a chart to determine replenishment intervals we were capable of developing a good starting point for our lubrication program. We have now instituted an online vibration program that allows us to collect real time data. What we have discovered is that the replenish intervals are about double what the chart recommends and the volume of lubrication is about half of the SKF results.

 

RM

Along the same lines as this question.  I've calculated a whole bunch of grease quantities and ideal intervals for our electric motors in a plant environment.  To manage the work load we've fixed our routes to 60 days.

 

This is where my question comes in -

 

I'm not concerned about adjusting the grease quantity down when the calculation tells me to less often.  Example  - calculation tells me to add 100 grams of grease every 120 days and set our program at 50 grams every 60 days.

 

Where I get concerned is when I have to adjust the 60 day quantity up.  Example - calculation tells me to add 50 grams every 30 days so we set the program at 100 grams every 60 days.

 

I realize that Ultrasonic is the way to do this properly but I'd like to hear some feedback on this case where we have to double our grease addition because the interval is twice what the calculators tell us. 

 

Thanks!

RM

Troy- the adjustment for going from 30 to 60 days is not optimum.  The equation to calculate volume is the volume to apply at each calculated regrease interval. The volume that is calculated is the estimated amount of grease that it takes to replace the grease in the open spaces of the bearing itself, not including housing space. The equation to calculate regrease interval is actually calculating the estimated L1 life of the grease...meaning that 99% of the time, when you go out to regrease that bearing, the grease will still be good.  Having said that...if you are doubling the regrease interval, such as you are when going from 30-60 days, you do NOT double the amount of grease you are adding. You're just wasting grease at this point. I'd encourage you to have a separate 30-day task route. The motors that require that frequent of an interval are likely just a few so having the optimum route for these shouldn't disrupt the schedules too much.

RM
Reliability posted:

I suggest you download and read the Acoustic Lubrication Guidelines created by a special AMP vSIG (virtual Special Insterest Group).   It is a great document and will assist you in regreasing.

 

https://www.maintenance.org/cli...stic-lubrication-pdf 

I would also suggest this. Acoustic lubrication provides more precision in the correct application of grease to bearings that use it than calculators and equations can. All maintenance is conditional and when you have the opportunity to use technology that tells you the condition, take it!

Best Regards,

Michael Meehan, CMRP, CRL

RM

We have a mature ultrasound program where I work and it works great for identifying bearing failures very early.  I'm a huge proponent of the technology.  We don't however use it as the sole decision maker for greasing.  Keep in mid that the basis for using ultrasound to grease bearing is only ball bearing at greater than 300 RPM.  IMO, it also doesn't work well on small bearings and leads over-greasing anything less than ~1.5" diameter.

RM

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