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WELDING A BEARING

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Nicholas Farr12/03/2021 11:41:23
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Posted by noel shelley on 12/03/2021 11:12:13:

By the time I had put the electrode holder down, opened the vice and inverted the casting it just fell out ! It was in no way cold. To be honest I could not believe what had happened, I had 6 to do and they all behaved in this way. A job I had thought might take all afternoon was done in 15 mins. Noel

Hi Noel, It does depend on how tight the fit is and also the size, obviously you can get a lot of heat into a small bearing very quickly, but many of the bearings I was used too, the outer race was in the order of 6" to 8" and an odd one or two even bigger and the width could be 3" or more, and some of them were a press fit into the housing on vibration screens, and you could often just heat them up with an oxt/act. and let them cool.

Regards Nick.

Hopper12/03/2021 11:42:50
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Posted by Nicholas Wheeler 1 on 12/03/2021 11:13:37:
Posted by Hopper on 12/03/2021 10:44:21:
Posted by Nicholas Wheeler 1 on 12/03/2021 09:54:41:

Posted by Hopper on 12/03/2021 08:03:54:

Salted ice will get down to maybe minus 5 degrees. But it acts so slowly, compared with nitrogen or oxy/propane torch, that the temp differential between the bearing race and the surrounding metal will be minimal. Same with installing bearings. You can heat the housing, especially aluminium motorcycle crankcases etc, with a propane torch to 400F and bearings will fall in and out almost by themselves. But freezing a bearing overnight in the fridge make no noticeable difference to the fit. There just is not enough temperature difference.

I'm glad you didn't tell me that before I tried it! I've done several rear wheel bearings on Vauxhall Omegas and can tell you that if you place the bearing after a night in the freezer it goes about 2/3 of the way in(they're 47mm thick) with a single blow from a large hammer. After that it won't move without a press or forcing tool and a lot of effort.

Glad it worked for you. It has never once worked for me. Maybe it was a very light press fit. Lowering the temp of steel by 30 degrees C in the freezer compared with raising an aluminium or even cast iron housing by 200 C is chalk and cheese. Could do the sums but its too late at night here. But even in steel/iron you will get about 6 times the thermal expansion with the torch as you will by freezing according to those temp changes.. Then there is the greater coefficient of expansion of aluminium to add to it.

But hey if it works, do it!

 

The effect is small, but obvious. It's very short lived, which I suspect is due to the small temperature difference. But then I doubt that dunking a double row bearing in liquid nitrogen will do it any good....

Dry ice or a -85 degree freezer would be the go for roller bearings. Liquid nitrogen more for valve seat inserts and valve guides. etc. Nice stuff if you have it.  I am limited to a propane torch in the shed and a fridge inside for the beer!

Edited By Hopper on 12/03/2021 12:07:55

Hopper12/03/2021 12:13:16
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You only have to weld two flat plates together without clamping them down to find out how much welds shrink and/or contract within seconds of becoming non-molten. What started out flat on the bench will almost instantly look like a butterfly as the weld cools and pulls the two plate edges together. Right pain when trying to weld things up nice and flat and straight and square if you don't clamp and/or tack weld all over first.

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