heating to remove

Mike (WA)

Well-known Member
Cast-iron collar rusted onto a steel shaft- been putting Kroil, PB Blaster, etc. onto it for months, still hasn't freed up. Time for heat, methinks.

The question- do I heat the collar, or the shaft? I'm thinking the collar, to get it to expand. But don't want to make the problem worse.
 
Usually depending on your individual situation - I would heat the collar as hot aswas reasonable and let it cool then reheat .Do this a couple times then when hot attempt to remove it. The repeated heating & cooling helps break the rust bond.
 
Don't heat the Shaft! When it expands It could break the cast iron Collar. Cast iron can do just about anything it wants to when you heat it. Take it slow any easy Don't heat the collar in one spot, Heat it all around I would try to heat it one time only, Try to remove while it is still hot. But you may have to do as oldmisterbill says.
 
you can also swage the CI collar while it is hot with a drilling hammer.. a few perp blows will expand it. between heat and cool cycle with the penetrat as a quench, then anpother heat and swage. it should practically fall off unless the steel shaft beneath it is very rusted and bubly
 
What are we working with?

"Cast iron collar on a steel shaft" is NOT something most of us would see very often???
 
Well, common sense says you want to heat the thing on the outside, but that's not always possible. In your case I assume you can easily heat the collar without heating the shaft. But if you were trying to free up a bolt tapped into an engine block, it's nearly impossible to get the block hot enough to release the bolt. In these cases, heating the inner part (the bolt) works surprisingly well. Heat does more than just expand the parts; it also breaks up corrosion and changes the coefficient of friction between the seized parts.
 

My theory.
When metal is heated, it expands in all directions.
When a bolt is in something, and the bolt is heated, it can only expand length ways. When it cools it contracts back in from all directions. There fore it will loosen quicker if the bolt is heated, instead of what it is in.
 
Actually that situation is fairly common. Even the bearings on the old style hay rakes that have set for several years I have to do that on all the time. And collars to control end movement of the shafts.
 
i would heat the collar evenly. i've heard to let wax melt into it suggested before, but i haven't tried it yet myself.
 
Dusty, that's a good theory, but it doesn't jibe with what I've observed in the real world. I will heat a stuck fastener until it starts to turn red. At that point, it will easily unscrew from whatever it's threaded into. But as the fastener cools, the torque required to turn it will increase significantly and it's often necessary to reheat the fastener to complete its removal. Why? Because when you heat steel to over a thousand degrees fahrenheit, its properties change.

(A lot of folks insist you need to let a heated fastener cool before removing it, but that's simply not true.)
 
assuming the collar is accessible, i'd heat that.
keep in mind that rust is hydrated iron oxide, Fe2O3·nH2O which expands as it forms. so when you heat it sufficiently to break the chemical bonds and drive off the water, the remaining iron takes up much less space than the rust, loosening the joint. so in the case of the bolt stuck in an engine block, yes, heating the bolt will expand it making it tighter except that when the rust shrinks it will be looser.

whatever the theory, my experience is if the part is heated to cherry red-and sometimes it doesn't even need that hot- it comes apart easily.
 

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