Cup and cone bearings and temperature

[MikeF]

https://www.physics.purdue.edu/demos/di ... item=3A-02

[Mick F]

Never ever considered it.

Same bike with cup and cone bearings, been everywhere.
Hot countries and cold ones, and never ever bothered with adjusting or checking.

Set them up, and forget them.

[pwa]

I'd never seen this as a science demonstration. I've just watched a few videos.

Of course they show the inner diameter of the ring expanding on heating, which is the part that might be counterintuitive.

But I haven't found one that shows what you're describing... the ball not fitting through the ring but then doing so when both are heated together...

Yes, I did a quick look and couldn't find it, but that is what happened when the experiment was conducted at my school in the late 1970s. The ball and hoop were obviously matched so that the ball would nearly go through at room temperature and only required moderate heating of both to prove the point. An explanation followed but I don't remember it. Clearly the ball also expanded but not as much as the hole in the hoop. It must be to do with the particular way a hoop expands. Done in reverse, with cooling rather than heating, there could be a theoretical danger of a bearing getting tight. But then you would expect some increased friction which would generate heat......

Thanks

I don't understand why that effect would occur if their temperatures increased identically. But most ways of heating would make the ring hotter faster than the ball...

Jonathan

I have a vague recollection that it has something to do with the way the molecules in a ring are lined up, concentrating its expansion along its length rather than to the sides. A ball can only expand outwards. Both metal objects will expand by the same amount, but the ring sees expansion on the inner surface of the ring more than offset by expansion along its length. Imagine a metre long length of wire with a thickness of 1mm at room temperature. Heating would increase the width a tiny bit but the length would increase visibly. It is a classic experiment precisely because the outcome is not obvious, even when you know heating will bring about expansion.

But back to the main subject, I would anticipate that a significantly tightened bearing, brought about by the race shrinking more than the balls within, might generate its own heat and thus limit the cooling. By that point, though, it will be behaving inefficiently and it will be potentially doing damage to itself.

I'm half tempted to rummage around the garage to find an old hub and do up the bearings to a point where, at room temperature, they are as tight as they can be and still run easily. Then wait for a frosty night, or stick the hub in the freezer, to see if it runs less easily when really cold. But I wonder if the effect might be so small as to leave me wondering whether I am imagining it.

[Mike_Ayling]

I thought metal expanded on heating?
a warm assembly going stiff in cold doesn’t add up does it?

Do you remember the classic experiment that has a steel ball resting on a steel ring that is a tiny bit too small to let the ball through. The ball and the ring are both heated, so both expand, but the hole in the ring grows more than the ball, so the ball falls through. If you did it the other way, a bearing race would contract more than the balls within.

Never heard or seen that experiment but thank you for the insight. That’s like magic

Would have been 65 years ago but I still remember it!

[francovendee]

I never really got my head around holes and their expansion when heated.
It seems counter-intuitive that a hole in a piece of metal gets bigger with heating. In my poor logic the metal expands in all directions so the hole should be smaller.
In my years in engineering I stopped questioning it and just used it when needed.

[Jdsk]

Do you remember the classic experiment that has a steel ball resting on a steel ring that is a tiny bit too small to let the ball through. The ball and the ring are both heated, so both expand, but the hole in the ring grows more than the ball, so the ball falls through. If you did it the other way, a bearing race would contract more than the balls within.

Never heard or seen that experiment but thank you for the insight. That’s like magic

Would have been 65 years ago but I still remember it!

I don't think that's what happens when both are heated equally...

Jonathan

[Jdsk]

I never really got my head around holes and their expansion when heated.
It seems counter-intuitive that a hole in a piece of metal gets bigger with heating. In my poor logic the metal expands in all directions so the hole should be smaller.
In my years in engineering I stopped questioning it and just used it when needed.

Yes. That is the part that some find counter-intuitive, and that's why the demonstration is so helpful.

But for an explanation: how about the thought experiment that the outer face of the ball and the inner face of the ring are part of a single object. Then that region where they join would be expected to expand as part of the bulk expansion. Now... why it should be any different if that single object is considered as two perfectly-fitting objects?

Jonathan

PS: There's a similar thought experiment showing that the period of a pendulum is independent of its mass. It needs a fine silk thread...

[Greystoke]

I'm with Mick f, the only thing I need to do is regrease after water ingress. I think I've fixed this with some foam with a hole in to pass the crank thru and grease either side....so far so good

[KM2]

Isn’t it that the ball has higher mass and therefore takes longer to heat up. The ring is smaller and grows in temperature quicker. The inner circumference of the ring must grow, if it got smaller, that’s contraction. So the ball drops through

[Jdsk]

Isn’t it that the ball has higher mass and therefore takes longer to heat up. The ring is smaller and grows in temperature quicker. The inner circumference of the ring must grow, if it got smaller, that’s contraction. So the ball drops through

Yes, that could happen, and is likely to with real world heating.

Jonathan

[Mike Sales]

Imagine a flat plate. Heat it. It will expand in all directions and dimensions..
Now cut a hole in the plate and reheat it.
The hole will expand with the rest of the plate.

[Jdsk]

Imagine a flat plate. Heat it. It will expand in all directions and dimensions..
Now cut a hole in the plate and reheat it.
The hole will expand with the rest of the plate.

Yes. That's similar to the thought experiment that I was trying to describe above. But not quite because the absence of the central disc in the second run might affect the result. With the one object/ two object model that doesn't happen.

Jonathan

[Paulatic]

Imagine a flat plate. Heat it. It will expand in all directions and dimensions..
Now cut a hole in the plate and reheat it.
The hole will expand with the rest of the plate.

But if as you say it will expand in all directions then the inner edge of the plate ( outer of hole) expands and makes the hole smaller?

[Mike Sales]

Imagine a flat plate. Heat it. It will expand in all directions and dimensions..
Now cut a hole in the plate and reheat it.
The hole will expand with the rest of the plate.

But if as you say it will expand in all directions then the inner edge of the plate ( outer of hole) expands and makes the hole smaller?

But in the intact plate such expansion ought to produce a buckling of the plate.
Does not the circumference of the hole expand or lengthen too?

[Jdsk]

On what happens to the edge of the circle in the plate after the disc has been removed... bulk expansion on heating is a property of objects. That edge isn't an object, it's a sort of human construct. And to illustrate that if anyone disagrees... what's the mass of the edge? : - )

Jonathan