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Thread: Steel Part Seized in Aluminum

  1. #1

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    Steel Part Seized in Aluminum

    I am doing a CLA on a Sinar Norma following Philip Morgan's excellent directions and Video and have run into a problem. I can't remove the fine focus assembly from the monorail sleeve. This is a steel part in a snug aluminum hole and I assume that after 50 years it has seized and won't budge. I have been soaking it in PB Blaster for 24 hours, and have tried heating it with a butane torch. I have also liberally applied swearing—all to no avail. Before I resort to explosives is there anything else I can try?

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    lenser's Avatar
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    Re: Steel Part Seized in Aluminum

    Knowing nothing about the relative expansion and shrinkage of metals, I'm admittedly going way out on a limb here, but two ideas come to mind.

    First, try putting it in a freezer for a few hours in case they shrink at different rates which may allow them to free up. Secondly, instead of just a localized heating with a blow torch, if the assembly is in an all metal unit that won't be harmed or warped by heating, try the entire unit in your kitchen oven at a moderate heat level. It may be that just the local heating isn't working because the expansion is being limited by the larger surrounding mass of the outer unit not being heated on an wide enough front.
    "One of the greatest necessities in America is to discover creative solitude." Carl Sandburg

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    Re: Steel Part Seized in Aluminum

    Aluminium expands roughly twice as much as steel for a given increase of temperature. That means if it is a steel shaft in an aluminium housing, heat is your friend. For, say, an aluminium plug in a steel part, you want to cool it. If it has corroded or galled, you may have a problem. Let it soak as long as you can. Gentle warming and cooling will help to draw the penetrant in, possibly loosening the parts. Be patient - almost everything will come apart if you are patient and don't hammer on it.
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  4. #4

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    Re: Steel Part Seized in Aluminum

    Yes, aluminum would also expand more than steel, so if the shaft is steel, and the collar (i.e. hole) is aluminum, heating should work. But if it is corroded, well, that's like saying that it is chemically glued onto the shaft.

    Maybe try thermally cycling the parts.

    Maybe when the parts are hot, try tapping the sleeve.

    Maybe make another part with a hole that butts up against the collar/sleeve to aid with tapping.

    Good luck

  5. #5
    Scott Walker's Avatar
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    Re: Steel Part Seized in Aluminum

    Put it in liquid propane for a few minutes. Once you remove it from the propane you should be able to tap the center out after a few minutes as the aluminum warms up and expands at a much greater rate than the steel.

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    Re: Steel Part Seized in Aluminum

    Interesting—where do I get liquid propane? Propane torch cylinder maybe?

    Quote Originally Posted by Scott Walker View Post
    Put it in liquid propane for a few minutes. Once you remove it from the propane you should be able to tap the center out after a few minutes as the aluminum warms up and expands at a much greater rate than the steel.

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    Re: Steel Part Seized in Aluminum

    Quote Originally Posted by Richard Wasserman View Post
    I am doing a CLA on a Sinar Norma following Philip Morgan's excellent directions and Video and have run into a problem. I can't remove the fine focus assembly from the monorail sleeve. This is a steel part in a snug aluminum hole and I assume that after 50 years it has seized and won't budge. I have been soaking it in PB Blaster for 24 hours, and have tried heating it with a butane torch. I have also liberally applied swearing—all to no avail. Before I resort to explosives is there anything else I can try?
    In the case of a steel part in an aluminum hole the TCE (Thermal Expansion Coefficient) difference goes the wrong way for heating. Aluminum is typically 20 to 24X10^-6 whereas iron/steel may be down around 7 to 14X10^-6 about a factor of three different. Since the aluminum expands greater per degree C one would normally try to cool the combination hoping the aluminum hole would open up slightly while the steel expands less slightly. So a freezer might work but a liquid nitrogen dunk (I think about 77 K) would be better. This assumes that the joining was originally just a press fit (poor design for dis-similar materials. If an adhesive was originally used the cooling might actually rupture the bond, even if very sturdy epoxy, so the release can be made.

    Nate Potter, Austin TX.

    Yes the hole gets smaller so heat is needed. Ignore my stupidity.
    Last edited by Nathan Potter; 26-Jun-2012 at 10:55. Reason: Wrong way - need coffee

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    Re: Steel Part Seized in Aluminum

    Quote Originally Posted by Richard Wasserman View Post
    Interesting—where do I get liquid propane? Propane torch cylinder maybe?
    Your freezer and boiling water will work just fine.
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    Scott Walker's Avatar
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    Re: Steel Part Seized in Aluminum

    Quote Originally Posted by Richard Wasserman View Post
    Interesting—where do I get liquid propane? Propane torch cylinder maybe?
    It depends on your laws, the old propane tanks had no tip protection so they would release the liquid by turning them upside down and opening the valve and literally pouring the liquid into a plastic pail.
    It is more complicated to get liquid out with the new tanks but still doable, and certainly with the small torch tanks.
    I keep an old 20 lb bbq tank for such purposes and know someone that will refill it, as it is not really legal to fill the old ones here.

    I would recomend doing this outdoors, and remember propane gas is heavy and can linger for many hours in the right conditions.

  10. #10

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    Re: Steel Part Seized in Aluminum

    The steel part is supposed to be a slip fit held in place by a set-screw—no press fit or adhesive which I suppose is in my favor. Where am I supposed to find things like liquid propane and nitrogen? I don't think my neighborhood hardware store is going to have them...


    Quote Originally Posted by Nathan Potter View Post
    In the case of a steel part in an aluminum hole the TCE (Thermal Expansion Coefficient) difference goes the wrong way for heating. Aluminum is typically 20 to 24X10^-6 whereas iron/steel may be down around 7 to 14X10^-6 about a factor of three different. Since the aluminum expands greater per degree C one would normally try to cool the combination hoping the aluminum hole would open up slightly while the steel expands less slightly. So a freezer might work but a liquid nitrogen dunk (I think about 77 K) would be better. This assumes that the joining was originally just a press fit (poor design for dis-similar materials. If an adhesive was originally used the cooling might actually rupture the bond, even if very sturdy epoxy, so the release can be made.

    Nate Potter, Austin TX.

    Yes the hole gets smaller so heat is needed. Ignore my stupidity.

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