Maintenance Plan for Bearing Servicing/Replacement
2

Question

Maintenance Plan for Bearing Servicing/Replacement

Finglas (Mechanical)

(OP)

23 Feb 19 17:04

I'm in the process of putting together a maintenance plan for the maintenance section of an operating manual for a machine build. So far I've been going trough manufacturers documentation and taking data from this or referring the customer to the document. i'd like to be able to give more accurate data for bearing replacement. This is not proving easy however. we have purchased most of our OTS parts from Misumi (a great supplier by the way) but I cannot find any info on their webite in terms of the expected lifetimes of these bearings.

Bearing w/Housing, BGMW6902ZZ-50 is one such part that uses an NSK 6902 bearing. Unfortunately I an't find any info on the lifetime of this bearing online. Could anyone post a link to where I can find bearing reliability data/lifetimes? This is about as close as I can get to finding out more. Note that the zoomed in image is not the bearing I'm referring to, that's a linear bearing which I'm also trying to figure out maintenance info for.

Thanks.

romke (Automotive) · Answer 1 · 2019-02-26 14:17:04

Based on the load of the bearing and the manufacturers info you should be able to calculate the statistical bearing life of the bearing. However - that bearing life is statistical, meaning that some bearings will fail earlier and quite a lot will last a lot longer....One of the things that is assumed in this kind of "calculation" is the fact that the bearing will be correctly lubricated at all times....another not exactly defined condition. Assuming that the bearing is not overloaded and correctly lubricated there are various ways to calculate the actual service life depending on things like positioning (horizontal/vertical), whether the bearing is subjected to vibration, moisture, air, pollutants etc - where each factor will lead to a certain shortening of the expected life of the bearing. That shortening of the bearing life needs then to be calculated with correction factors - that unfortunately not come as constants but as various ranges depending on the amount of vibration, amount of moisture etc.....One constant is there in the formula - the formula is based on the use of a NLGI2 grease on the basis of a lithium thickener and a mineral oil. That in effect is the level of grease quality from the early seventies in the previous age, modern lithium complex greases will perform much better. T o sum it all up: you can calculate whatever you want, but it will only reach the level of a educated guess - as SKF puts it: "the calculation is for information purposes only. the real maintenance schedule should be based on actual practice and the result may differ quite a lot from the calculated outcome..." In other words: do not worry too much, check whether a sufficient size of bearing is used and fill it up with the right amount of grease as collected by the bearing manufacturer with a modern ,lithium based complex grease or when used in a food manufacturing plant with a aluminium complex grease.

Finglas (Mechanical) · Answer 2 · 2019-03-01 18:52:39

Got a good help page here: http://www.jp.nsk.com/app02/BearingGuide/html/bear...

geesamand (Mechanical) · Answer 3 · 2019-03-06 17:39:08

In reality, bearing life varies wildly depending on load, speed, misalignment, shock loads, lubrication. There is also the fact that rolling bearings do not fail at a consistent lifetime (they're not like tires where all four can reach end of life around the same time). This all pertains to predicting fatigue life.

Fatigue life is just one mode of failure - contamination, loss of lubricant, overheating, etc, are different failure modes that are often more common than fatigue.
Predicting life without any past history is a funky kind of guessing. I recommend you consider giving your customer sensible inspection points and guidelines when replacement is necessary.

Finglas (Mechanical) · Answer 4 · 2019-03-07 21:36:32

That makes a lot of sense geesamand and. Thanks for the feedback.

Finglas (Mechanical) · Answer 5 · 2019-04-16 16:54:53

I don't suppose someone could point me in the right direction for calculating radial and axial loads?

Michael-Lu (Mining) · Answer 6 · 2019-09-23 06:50:47

I recommend you consider giving your customer sensible inspection points and guidelines when replacement is necessary.

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Maintenance Plan for Bearing Servicing/Replacement
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