thermal expansion slide bearing 1

[gerdjan]

I am trying to calculate a thermal expansion, but i am not sure if i do this the right way . Can someone with knowledge about this take a look at this, and tell me if i am doing it right?. It is a really simple calculation, but i've never done this before, and i am doubting myself (it looks I think too simple)

See the attached pdf for details

Thanks,

 

[desertfox]

Hi gerdjan

What you have calculated is the expansion if the sleeve and bearing were free to expand which I hasten to add there not.
Firstly delta T is the temperature difference between say the liquid your pumping and the surroundings, if your pumped fluid is at 200 degrees centigrade then that is not the temperature difference, the difference would be say 200-30 where 30 is the ambient temperature of the room where the pump is situated for example, now putting 170 as delta T in your calculation would leave the sleeve free.
However your problem is more complex than that firstly the bearing is fitted into a bearing cover which shows a size and size fit which in my opinion should be an interference fit to prevent the bearing coming loose when everything expands, having an intereference fit at this point would slightly close the bearing bore down and reduce the clearence between it and the sleeve. The intereference between housing and bearing should take account of the temperature rise and loading it will see in service without slipping occurring between the mating faces.
In order to get your sleeve clearence correct you need to do a transient heat transfer analysis as I doubt that all the components will heat up uniformly, which may well end up with your sliding sleeve seizing as you suggest.
You need to also to look at how the housing expands with temperature as well as that as a much larger area to dissipate heat when compared to the other components.
Basically because the components are not free to expand but restrained by other components stresses will be induced in each all which are subject to the temperature rise, I suggest you look in any mechanics book for temperature stresses it may give you a better understanding of whats happening.

 

[gerdjan]

Thanks for your reply,
The bearing is indeed fitted with an interference fit, so the bearing size as shown in the drawing is not correct, and is a little bit larger.
The bearing is situated in the pumped liquid, and is lubricated whit this liquid. so the temperature rise is for all components the same i think.
The strange thing is, that we heated up the bearinghousing, and when we measured the inside diameter, it seems to get smaller... so to sugested formula is not correct.

I also tried to run a solidworks cosmos analysis on this problem, but i don't have enough knowledge on this part to get a proper result, i don't even know if it is possible to do this in cosmos
I don't know if you familiar whit this, but do you know if it is possible to do a transient heat transfer analysis in solidworks cosmos??

 

[desertfox]

Hi gerdjan

How was the bearing housing heated ie was it restrained in anyway?
I can only think the bore would become smaller if the housing was restrained from expanding,but that would indicate fairly high stresses occuring, one other possible answer might be if the housing was stress relieving itself
during your test, although 200 degrees centigrade is a low temperature for that process.
I cannot help with your analysis in solidworks/cosmos as I have no experience of that software.
However if you can give the actual intereference fit of the bearing/housing and the wall thickness of the bearing housing that surrounds the bearing itself I may be able to help further.
Can you also confirm the temperature rise and not just the temperature of the pumped fluid.

Regards
desertfox

 

[gerdjan]

Hello desertfox

I don't have the exact diameters from the parts right now, I will give them to you tomorrow, it would be great if you could help me whit this, I'm doing a traineeship, so if you are able to help, it would be great if you can show me how to do this. is only the wall thickness that surounds the bearing importent? and not the total mate (239 mm) as shown in the pdf?

greetings Gerdjan

 

[desertfox]

hi Gerdjan

The wall thickness of the bearing housing is important from the point of view of the intereference fit with the bearing.
I need you to confirm the temperature rise or difference between the pumped liquid and its surroundings also.
If your a trainee is there no person there you can turn to for help?

regards

desertfox