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Tech Question

Post by Guest on Thu 23 Jul 2015, 7:07 pm

Imagine say, a washer. Fairly big one like this:


Now, lets say the washer is heated. What does the inside and outside diameters do? Similar question for cooling?

Anyone know for sure? I'm in doubt, my guess is that when heated the outside expands, thus outside diameter becomes larger and inside diameter becomes smaller because of said expansion. The opposite for cooling... I may be wrong. scratch

If what I think is true than getting a bearing out will be easier when the thing is cold! Or not??
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jerryfudd
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Re: Tech Question

Post by jerryfudd on Thu 23 Jul 2015, 7:18 pm

lol headstock or wheel bearing? ......which is giving you grief?

btw I believe the answer is as you say heat to expand and cold to contract
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ashcroc
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Re: Tech Question

Post by ashcroc on Thu 23 Jul 2015, 7:38 pm

Bearings are easier to be put in if they have been stored in the freezer overnight so it stands to reason they should come out easier when cold too.
The problem comes with the expansion/contraction rates between the differing metals of the bearing & housing.
Something like pipe freezing spray may work but it could just be easier to apply heat to the mount to get the desired size difference. Or are you considering using both heat & cold to make things easier still?

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Re: Tech Question

Post by Guest on Thu 23 Jul 2015, 7:41 pm

Not really based on a practical problem as such. I'd just like to know for sure what that inner diameter does under said heating/cooling... still baffles me today!

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Re: Tech Question

Post by Guest on Thu 23 Jul 2015, 7:43 pm

@ ashcroc

I agree on the effects of heating/cooling on the outside diameter of things. Hot = expand (bigger) and Cold = contract (smaller), but what about the inside diameter??
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ashcroc
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Re: Tech Question

Post by ashcroc on Thu 23 Jul 2015, 7:57 pm

Been a while since I did any theory in the area but iirc the inside diameter actually gets larger with heat & smaller with cold just like the outside.in short, a ring acts in the same way as a solid disc. It should be easy enough to find out with a set of vernier callipers, a freezer & a blow torch.
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Re: Tech Question

Post by jerryfudd on Thu 23 Jul 2015, 7:59 pm

I found this discussion amusing when I was trying to remove the bearng cups from the frame.

http://www.bikechatforums.com/viewtopic.php?t=251795

puts across that a massive increase in heat and then the cooler ambient temperatue will make something contract in an interesting term.
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ashcroc
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Re: Tech Question

Post by ashcroc on Thu 23 Jul 2015, 8:03 pm

@jerryfudd wrote:I found this discussion amusing when I was trying to remove the bearng cups from the frame.

http://www.bikechatforums.com/viewtopic.php?t=251795

puts across that a massive increase in heat and then the cooler ambient temperatue will make something contract in an interesting term.
Post 7 is truely inspired. affraid

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Re: Tech Question

Post by Guest on Thu 23 Jul 2015, 8:08 pm

Found it!

So heat expands both outer and inner diameters and cold contracts them. Heat = bigger inner diameter and cold = smaller inner diameter... must be true as the video below shows. But I swear for a long time I believed it to be not so tongue

https://www.youtube.com/watch?v=3pnj4ytORQw
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jimbobs63
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Re: Tech Question

Post by jimbobs63 on Fri 24 Jul 2015, 12:40 pm

Hi,

It is counter-intuitive but you have found the right answer!

The simplest way to think about the inner edge is like this:

When the washer heats up, just like all objects it expands, so ALL surface dimensions get bigger.  That of course includes the inner circumference getting longer, therefore the hole gets bigger!

Jim
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steady Eddy
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Re: Tech Question

Post by steady Eddy on Fri 24 Jul 2015, 12:45 pm

very interesting thread, you could easily be forgiven for thinking the hole would get smaller.

Spose its like inflating an inner tube.
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Re: Tech Question

Post by alvamiga on Sun 26 Jul 2015, 9:06 am

I think the confusion is that the thinking is that the WASHER expands, so both edges move away from the perceived body of the washer.

In reality, any part of the washer expands equally in all directions, so the radius has to increase. If you want to get really petty, it gets thicker, too! Smile

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