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To remove add heat

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Brian

02-15-2001 18:31:22




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Why does heating a seized nut on bolt usually allow the nut to be removed? Does the heat shrink the metal? Just curious. Thanks.




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T_Bone

02-15-2001 19:59:32




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 Re: To remove add heat in reply to Brian, 02-15-2001 18:31:22  
Hi Brian, If you took the nut off while hot, then it would be explanded slightly alowing the nut to become loose. If heated then let cool to it's original temp, no expansion would occur.

Take a piece of rusted metal and heat it with a torch and see what happens to the rust?
The rust pops off in small chunks and thats what loosens the nut when rusted to the bolt.

Why?, rust is iron oxide that has a small crystal structure on the surface composed of millions of particles, where clean steel has a flim layer of oxide that is that are smaller crystals and more flat and smooth to the surface, so the rust will less attached to the oxide layer.

T_Bone

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Al English

02-15-2001 19:03:01




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 Re: To remove add heat in reply to Brian, 02-15-2001 18:31:22  
Hi Brian, I think two things happen when a seized nut is heated. First, heat causes the diameter of the bolt to increase, which fractures the solid layer of rust that has "welded" the nut to the bolt. Second, the increase in diameter caused by heating makes the nut a looser fit on the bolt, allowing it to be removed. The evidence of this is that when the nut is hot enough it can be moved, but if allowed to cool, it will often become immovable again. Part of the reason a rusted bolt freezes in place is that rust is bigger than the metal it comes from. So, the small amount of clearance that exists between the threads is filled with a "wedge" of rust. The other part of this is that the rust "grows into the surface of the both the bolt and nut, acting like a low strength glue or weld. Hope I answered your question without getting too carried away...Al English

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Brian

02-16-2001 06:38:50




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 Re: Re: To remove add heat in reply to Al English, 02-15-2001 19:03:01  
Not at all Al; your explanation and that of T_Bone satisfied my curiosity quite well. My Dad always wanted me to understand why and how things worked.



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