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Curran919

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Reply with quote  #16 
Quote:
Originally Posted by RustyCas
From a geometry standpoint, if the bearing is uniformly overheated, shouldn’t it return to normal shape when cooled? If the balls dimple the race due to taking out the clearance, shouldn’t ball pass frequencies show up on both races?


I'm just approaching this logically, not from experience:
If the entire bearing is heated? Or just the inner race? If it is all heated (e.g. in a full oil bath), then the clearance should shrink minimally, I think. Either way... it should return to its normal shape. If you overheat the inner race, yes the force on your inner and outer races is the same, but you have a lower (sharper) 'contact area' on your inner race, which increases the pressure minorly. Furthermore, the overheated material is now softer and will yield before the outer race does. However, as the dimple (contact area) on the inner race grows and the pressure decreases, the outer race will probably start to dimple as well, just later.


Danny Harvey

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Reply with quote  #17 
Curran,

I think what you are saying is logical given uniform heating.

In Pete's case, I think that in addition to overheating, it was non-uniform leaving a portion of the inner race distorted to a different degree than the rest.
Curran919

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Reply with quote  #18 
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Originally Posted by Danny Harvey

In Pete's case, I think that in addition to overheating, it was non-uniform leaving a portion of the inner race distorted to a different degree than the rest.


Is the problem in Pete's case really nonuniform heating? My understanding of this problem is the main failure mode here is softening of the material and dimpling of the bearing surface. Sure you will have some geometric hysteresis (permanent deformation) when you heat up and cool down, though Rusty's question is valid, I'm not sure how severe this is?

I also can't imagine the bearing being worse off if only a portion of the bearing has this deformation vs. the whole thing. In what way would it deform to 'cancel out' deformation from the other side of the bearing?
John from PA

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Reply with quote  #19 
Quote:
Originally Posted by RustyCas
From a geometry standpoint, if the bearing is uniformly overheated, shouldn’t it return to normal shape when cooled? If the balls dimple the race due to taking out the clearance, shouldn’t ball pass frequencies show up on both races?


That's a big "if".
RustyCas

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Reply with quote  #20 
When I said "uniformly overheated" I was thinking oil bath, or even a rose bud wielded by someone with experience, but perhaps faulty temperature indication.  I'm not familiar with induction heaters, but wouldn't that be somewhat non-uniform, by default?  I have little experience with heating bearings - the only bearings I am routinely involved with are tapered sleeve. 
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Danny Harvey

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Reply with quote  #21 
I'm assuming that the heating wasn't uniform because the discoloration is not.  The idea that it may not return to it's original position was more of a question than a statement. There was some mechanism that excited bpfi and I wonder if that could be it.
MarkL

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Reply with quote  #22 
Induction heaters tend to heat uniformly as the current inducing the reaction(heat) passes through the body uniformly, this was one of main advantages over the practice of heating with a torch or dropping in hot oil (can't believe people actually do the torch thing but hey!!!!)

Danny Harvey

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Reply with quote  #23 
Am I seeing things or does it appear from the discoloration to have been uneven? The appearance of uneven heating may have been due to torch heating during removal. 
John from PA

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Reply with quote  #24 
Quote:
Originally Posted by Danny Harvey
Am I seeing things or does it appear from the discoloration to have been uneven? The appearance of uneven heating may have been due to torch heating during removal. 


Danny, you need to at least glance at the previous entries in the thread.  Much of the discussion has been around uneven heating since about 9 days ago!
Danny Harvey

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Reply with quote  #25 
Very sorry John.

I reread it when I get the opportunity.

Maybe when I'm retired I'll have time.[smile]
electricpete

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Reply with quote  #26 
Danny you're right the discoloration is not uniform in the bore of the inner ring, but it's fairly uniform in both faces.we don't really expect the bore or the hidden face against the shaft shoulder to get darkened by torch during removal, but I didn't jump to any conclusions myself. When I initially talkrd to the craftsmen who installed the bearing, I showed him the bearing and started with that exact question: did this heating occur during removal. He said: nope, it was that way when they installed it. He blamed it on the malfunctioning temperature gun. They were surprised to see the bearing turning colors, but they figured it was ok and installed it anyway. I went back later after you guys reminded me about emissivity and asked some more. It definitely was a temperature gun used for that first bearing and then they used a contact probe for the second bearing on that motor.

I got a message from our mechanics that the bearing is finally cut apart...but I'm out on vacation. So l won't be able to report what the inside of the bearing looks like until I get back Monday 7/23
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