dynamic load and static load

[assot]

Good evening, I haven't been writing in the forum for a long time, but I need help on something that isn't very clear to me, I've done a lot of internet research, but nothing useful to me.
looking at skf ,ina bearing catalogs, fag... I noticed that ball bearings, but also other bearings have the largest dynamic load of static load, but this seems very strange to me.
Also in the wohler diagrams (curve s-n) the static limit is larger than the dynamic limit, as you see in this video of you tube.

thanks await your clarification thanks

 

[TETRASTORE]

in bearings where the risk of "brinellation" is greater, generally the static load is lower than the dynamic one.
further information can be found in this discussion: bearings with high static load (from post n°8 onwards).

 

[assot]

thanks for the answer, but I'm not so clear a thing, I have seen the old discussion, but we do an example , we take a 6309 bearing with static load 31500 and dynamic load 52700, if I load it with 31500n from anchor the load makes a mark on the bearing and it is not exceeded the static test, if instead the load with 31500n and goes to a certain speed ' the bearing according to the dynamic test 4,
So it seems that by turning, the bearing is less and harder than that?
I thought it was more logical a situation where the static load is larger than the dynamic load and there was a fatigue diagram (s/n)
as in the photo attached
thanks for the help

 

[meccanicamg]

I normally use basic other bearings....that is to two adjustable roller crowns. making steel industry machines have the highest values for static than for dynamics.
if you have bearings with dot contact and single element you have little static load capacity. if you have two rows of....rulli....spheres etc. increase the contact area and then statically hertz pressure decreases and you have greater static load resistance.

 

[assot]

Thank you, I understand that.
but what I do not understand, how does a static load have different durations if a static or dynamic test is made?
from all these discussions I think that when wheel doesn't ruin the bearing as long as it's still.

 

[meccanicamg]

Thank you, I understand that.
but what I do not understand, how does a static load have different durations if a static or dynamic test is made?
from all these discussions I think that when wheel doesn't ruin the bearing as long as it's still.

a ball bearing held under load by firm imprint the track and ovaluates the ball. If he does one round, he'll turn around. I remember that by static it means below 10rpm.
It is quite normal that dynamically, with fat that floats the balls, not breaking the film to lubricate, is able to endure higher load.

 

[assot]

Thank you, that was clear to me, but why in the photo and video attached to me make a 'analogy with the s/n diagram and put as a maximum limit the static load? Maybe it's like that in the fatigue calculation of a tree? But for a bearing it's different?
Thank you very much

 

[meccanicamg]

Thank you, that was clear to me, but why in the photo and video attached to me make a 'analogy with the s/n diagram and put as a maximum limit the static load? Maybe it's like that in the fatigue calculation of a tree? But for a bearing it's different?
Thank you very much

fatigue calculation is equal for all. whöeler diagram works the same.
the balls or rollers continue to be compressed and released by the compression load.

 

[assot]

Okay, but the maximum limit, so it's not the static load as in the right photo?

 

[TETRASTORE]

Thank you, that was clear to me, but why in the photo and video attached to me make a 'analogy with the s/n diagram and put as a maximum limit the static load? Maybe it's like that in the fatigue calculation of a tree? But for a bearing it's different?

the calculation of the bearings follows special norms dedicated to them: see skf in: choice of size according to static load.
if you want to deepen the theory of hertz applied to bearings you can consult This university document on page 5 and on page 15, par. 2.4.