Bearing ID increases or decreases w.r.t. temperature

[kamal11]

Hi all,
This is a general question.

When we heat a cylindrical bar, it expands in Length, Outer diameter and Inner diameter.

Now i have two queries.

1) We press fit a sleeve bearing made of steel with a tin babit coating on to an aluminum endshield. When this assembly is heated
will the ID of the bearing increase or decrease. Our vendor has sent us data with Id of the diameter to be decreasing when the assembly is heated.

2) If all the dimensions are increasing, where is the extra volume coming from?

 

[electricpete]

Just a thought? Since the bearing OD is press-fit into an endshield that doesn't increase in temperature, that endshield may tend to limit outward expansion of bearing od which would lessenoutward expansion of bearing id or possibly in extreme case make bearing id grow inward?

I'll be interested to hear other responses to your question.

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[kamal11]

Co-effcient of expansion of aluminum is more than steel.

 

[electricpete]

Bbut the steel heats far more then the aluminum.

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[kamal11]

We have put the whole e/s assembly overnight in a hot chamber so that whole assembly is at the same temperature

 

[Skogsgurra]

So, if you press the bearing into (Or do you really mean "onto"? Difficult to visulize that) the endbell, the Al expands and the hole gets larger. Your steel will also expand and that hole also gets larger.

Gunnar Englund

http://www.gke.org

 

[electricpete]

"We have put the whole e/s assembly overnight in a hot chamber so that whole assembly is at the same temperature"

ok, that is different than operating conditions but an interesting experiment. Just to clarify, there was a reduction in bearing I.D. measured during this experiement with the oven?

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[kamal11]

We got the Id of the bearing measured at two operators.
There is a max variation of +/-.002" between the operators.
But at different temperatures we are seeing a shift of -.003~.004" decrease in diameter with increase in temperature. Since the values i am talking about is very small should we attribute it to noise in the system.
Temperature difference is 9 C.
Diameter of the bearing 12.714
Co-efficient of expan of steel 1.17e-05
Co-efficent of expansion of Tin ~2e-05
Co-efficeient of expansion of Aluminum 2.3e-05
Change in daimeter for steel is of the order of .001"
and aluminum& tin is of the order .003" as per calculations.
I expect the diameters to increase. But i am seeing the diameters to decrease. Not sure weather i need to attribute it no noise or my vendor is giving me manipulated the data or some different phenomena is going on.

 

[Skogsgurra]

Hi,

Was the temperature of your measuring equipment the same at the two occasions? What did you use? A CMM, a bore caliper, a bore gauge or what?

Gunnar Englund

http://www.gke.org

 

[desertfox]

Hi kamal1

Reading your post I assume that the steel is press fitted into the aluminium endshield.
What we also need to know is what the interference is between the bearing and the endshield, when these parts are pressed together then you have created stresses that need to be taken into account ie:- the steel bearing will be under compression and the aluminium under tension.
That said when the assembly is heated and reached a final temperature I would have thought the bearing would have been loose in the endshield assuming that the aluminium was free to expand fully, however if the aluminium is restrained in any way it might explain why the steel bearing is decreasing in diameter.
If it is possible can you provide the temperature your heating the assembly too and inner and outer bearing diameters, inner and outer diameters of endshield as well as the intereference between them and I will try to help yoou further.

regards
desertfox

 

[kamal11]

Endshield OD 23.114 mm
Enshiled ID 15.857 mm

Bearing OD 15.913 mm
Bearing ID 12.714 mm

Interference is between Endshield ID and bearing OD.
We are heating the assembly by 10 C.

Regards
Kamalakar

 

[desertfox]

Hi kamal11

Thanks for the info, but please tell me what temperature your heating the assembly too ie:- 40C, 100C and not just how much your raising the temperature by.

regards
desertfox

 

[desertfox]

Hi kamal11

I have done some calculations and according to them when you press fit the bearing into the endshield the bearing bore will reduce by about 0.02mm.
If the bearing was free to expand (which it isen't) you would have to heat it by much more than 10C in order for it to achieve its original dimension.
I think therefore your reduction of bore size is due to the mechanical fit of the bearing into the endshield.

regards desertfox

 

[kamal11]

Actually room temperature out side is 35C.
and in air conditioned room of 25 C, the readings are taken again.
So i am treating the assembly to be heated from 25 to 35 C.

 

[desertfox]

Hi kamal11

Read my last post I think that your reduction in bore diameter is due to your mechanical press fit.
It is unlikely that with a 10C rise that you would notice
any significant change in bore diameter.
My calculations ignored the coating on the bearing as no thickness was given however I assumed that this would be very small.

regards

desertfox