Aluminium vs steel contraction when frozen

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PRW   10 kW

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Aluminium vs steel contraction when frozen

Post by PRW » Apr 18 2019 4:57am

So, I have a bearing outer ring stuck in a aluminium frame (the swingarm). The bearing has broken, leaving only the outer ring wedged in.

If I put the the swing arm in a freezer - would the aluminium extra contraction make it easy to extract? How brittle would the aluminium become if frozen?

Thanks

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DogDipstick   1 kW

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Re: Aluminium vs steel contraction when frozen

Post by DogDipstick » Apr 18 2019 6:50am

Aluminum expands much more than steel, when heated. Freezing witll contract the aluminum only to hold the broken race tighter? Try a heat gun or a torch or an iron or something to heat the aluminum . The aluminum will expand (3X) whle the steel will less (2x) and the bearing should come out. Ice on the bearing while heat on the frame might help.
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Punx0r   100 GW

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Re: Aluminium vs steel contraction when frozen

Post by Punx0r » Apr 18 2019 7:44am

This^

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Re: Aluminium vs steel contraction when frozen

Post by PRW » Apr 18 2019 2:24pm

the above replies are exactly what I thought, logically - until my wife gave her opinion which confused the hell out of me....

Her view is that when metal expands, all the metal will get bigger - so the hole gets smaller. When the metal freezes, all the metal shrinks, so the hole gets bigger.

My mind now switches between the way I originally thought, when any freezing naturally will tighten the hole... and above.

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spinningmagnets   100 GW

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Re: Aluminium vs steel contraction when frozen

Post by spinningmagnets » Apr 18 2019 2:45pm

I've measured steel holes for an interference fit. when you heat up the part, the hole gets bigger.

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Re: Aluminium vs steel contraction when frozen

Post by PRW » Apr 18 2019 3:08pm

thanks SM!

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Re: Aluminium vs steel contraction when frozen

Post by Punx0r » Apr 18 2019 4:25pm

Honestly, it's well known brain-teaser as to whether the hole in a ring gets bigger or smaller when it's heated. The trick is to mentally uncoil the ring into a rod. When you heat a rod it obviously gets much longer than it does thicker and if re-bent into a ring it would have both a larger outside and inside diameter.

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Re: Aluminium vs steel contraction when frozen

Post by PRW » Apr 18 2019 4:34pm

Punx0r wrote:
Apr 18 2019 4:25pm
Honestly, it's well known brain-teaser as to whether the hole in a ring gets bigger or smaller when it's heated. The trick is to mentally uncoil the ring into a rod. When you heat a rod it obviously gets much longer than it does thicker and if re-bent into a ring it would have both a larger outside and inside diameter.
Good explanation, PunxOr, thanks - even my wife agrees! 😀

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Re: Aluminium vs steel contraction when frozen

Post by Hillhater » Apr 19 2019 2:37am

Yes, common practice is to heat the “aperture” , and chill the “insert” in order to create clearance.
And heating is much more effective since you can get a much greater temperature differential than simply freezing. ( though dry ice or liquid Nitrogen is also used for some applications !)
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