Bearing Design Standard
Bearing Design Standard
(OP)
Is there a recognized design standard for bearings that provides a factor on a static load for normal service?
Alternatively is there a recommended factor that should be used with a reliable reference?
Efunda gives factors but the source is not given.
Alternatively is there a recommended factor that should be used with a reliable reference?
Efunda gives factors but the source is not given.
corus





RE: Bearing Design Standard
fs = Co/Po
where Co = Basic Static Load Rating
Po = Equivalent Static Bearing Load
The value of Co is computed based on the total rolling element and raceway deformation equaling .01% of the rolling element diameter on the most heavily loaded rolling element. This is a somewhat arbitrary criterion, and as will be seen below, it may often be exceeded without disastrous consequences.
The above reference quotes the following acceptable values for fs, the logic of which I do not profess to fully comprehend :
Occasional rotation : fs = 1
Less deformation acceptable (50% of standard) : fs = 1.5
Larger slewing, no shock : fs = 0.6 balls, 0.7 rollers
Shock loads or small oscillation angles : fs = 0.7 balls, 0.75 rollers
Spherical roller thrusts : fs = 4 (because of unfavorable lip loading)
I don't know if this is what you are after. I have frequently used safety factors of 2 or 3, because the real loading conditions are often unknown. It all depends on how accurately you can predict the loading. Of course, bear in mind that with static load ratings, if you only exceed the rating one time - you will permanently brinell the bearing some definite amount. On the other hand, nothing noticeable will necessarily occur immediately – possibly just some extra noise.
RE: Bearing Design Standard
RE: Bearing Design Standard
Just a couple of points come to mind:-
Firstly I think that in the latest ISO76 they have slightly changed the way they define the rating. It was 0.01% indent depth, now they say the Co correspondes to a max contact stress at the most heavily loaded element of approximately 4000 N/mm2(depending on brg). I've no idea why they made this change, I just cant see that it really helps anyone (other than perhaps makes the standards people feel useful!)
Secondly, regarding the brinelling and noise creation, I think the concern here applies only really to situations where the brg is stationary, or virtually so, when an extreme load is applied to it. The loads, in this situation, will create indents that will be detectable by vibration/noise measurement when the brg is subsequently run at speed under a much lighter 'normal' load.
However, if the duration of the shockload and movement of the brg is sufficient, the indents/brinels will tend to elongate and overlap. Since the rolling elements wont then bump in and out of 'ruts', vibration/noise doesn't become an issue at subsequent light-load running.
Gerry'
RE: Bearing Design Standard
RE: Bearing Design Standard
corus
RE: Bearing Design Standard
RE: Bearing Design Standard
RE: Bearing Design Standard
dynamic capacities are almost always
lower than the static capacities.
Earthquake loads imposed severe limits
on many bearings. Catastophic failure
can be as high as 3 to 5 times the static
capacity depending on the shape and size
of the bearing and its support structure.
I would be surprised if this value does
not also correlate to some Rockwell C
value for the steel surfaces if they have
adopted it as a standard. Subsurface
shear stresses are still limiting the
capacities and these have been based on
material hardness below the Rockwell C case
for bearings and their rolling elements.
I will have to review the standard and see
what else is new. Thanks for the posting.