Bearing Life Calculation
Bearing Life Calculation
(OP)
Has anybody any advise on calculating bearing life combining static load (crushing) and dynamic load (wear). The static load is high relative to the dynamic loads 6 x 1.
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RE: Bearing Life Calculation
My feeble understanding when you say dynamic loading is much less than static loading... that means that the load is lower when the unit is rotating then when it is stationary?
If such were the case I would think life calculations should be based solely on the dynamic loading and dynamic rating. If the static rating is ever exceeded (while stationary or rotating) then damage may occur but it is right away, not a cuumulative fatigue lifetime issue.
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RE: Bearing Life Calculation
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RE: Bearing Life Calculation
Certainly static rating is vitally important and cannot be exceeded, preferably not even approached.
An important note comparing static vs. dynamic however is that when more than one brg is used, say two brgs. for example: the staic rating for the brg. combination is double that for a single brg. But dyanimic rating is 2^7/9.
If you are able to incorporate three brgs. then the static rating is triple that for a single brg. while dynamic is 3^7/9 etc.
Again, the best approach is to contact a reputable brg. manufacturer, tell them what you are dealing with, and let them help you reach a succussful solution.
RE: Bearing Life Calculation
RE: Bearing Life Calculation
It is my understanding that Dynamic loading should never exceed the Static load rating. If rotation is occurring the load would probably be considered dynamic unless it is rotating very slowly.
I would be interested in seeing some reference from manufacturers stating that the Static load rating may be exceeded whether Static or Dynamic.
Thanks.
RE: Bearing Life Calculation
And although the dynamic load may be larger than the static load rating. The load must continue to be dynamic, and if it stops rotating then the actual load that used to be dynamic must not exceed the static load rating.
Clear as mud.
RE: Bearing Life Calculation
RE: Bearing Life Calculation
Thanks, I read the thread listed above. It sure sounds like you and the other posters know what you are talking about.
Thanks for the insight.
RE: Bearing Life Calculation
load limitation is based on rolling
element diameter squared, plus many
other factors and the dynamic load
limitation is based on the diameter
cubed, plus many other factors.
Have always wondered about this.
For slow moving slewing bearings
is .01 rpm, the static capacity is
often used. Even this limit might
have a safety factor or 2 or more
before the bearing explodes or
ruptures. If the loads are dynamic
and fast rpm is involvled the limits
are much lower. Dynamic life might
be defined as .0001 x the rolling diameter
as being the allowable deformation of the
raceways. This is an arbitrary value
and the bearing might see another
20 percent more life before it siezes
up. Static bearing loads may result in
.0003 times the rolling diameter in the
raceways and still not fail.
It really is dependent on the application
whether static or dynamic values should
apply and what defines the useful life
of a particular bearing application.
time
raceway
RE: Bearing Life Calculation
If the lube is dirty or thin, or the rpm are low, then the balls and races will touch and scuff, and life will be more like wear, and the L10 calculation would probably apply.
As others said, the static load is limited by deformation.
Precision bearings (machine tool spindles) are usually limited to about 1/3 the "static load," as even slightly dented races will create crummy finishes (and probably even initiate fatigue failures at much lower stress levels when the spindle revs up later).
A low speed bearing would really benefit from keeping loads well below the static capacity, and using lube with oil thick enough for a good kappa at a few rpm. Oil that thick oil will probably reduce the upper speed limit.