Stupid Question?

[MercianScribe]

Maybe my basic physics is lacking... Dry heat works for separating sections and barrels and all kinds of other movements you may want to do. How does it work?

 

If I apply heat to the join of a section and barrel, surely the section expands with the heat too, as well as the barrel threads if there are any, so why doesn't it become harder to get out of the barrel?

[Retro-user]

I'm not a physicist, but two thoughts: (a) if there is any adhesive on the joints, heat may loosen it or ( the expansion of the different parts may not occur at the same rate, and so the very act of disturbing one part may be enough to loosen it.

Edited October 4, 2017 by Retro-user

[praxim]

I'm not a physicist, but two thoughts: (a) if there is any adhesive on the joints, heat may loosen it or (b ) the expansion of the different parts may not occur at the same rate, and so the very act of disturbing one part may be enough to loosen it.

Yes and potentially yes to (a) (soften) and (b ) (provided the coefficient of thermal expansion for the inner part is not greater). Where the parts are of the same material, consider that there will be a very small gap between them. However small this gap, for it not to increase with heat would imply that the inner part expands more than the outer to maintain the same physical gap, rather than the gap being proportionately greater. If they are the same material, that makes no sense.

 

I can work an example if that is not yet clear.

Edited October 4, 2017 by praxim

[Freddy]

Maybe my basic physics is lacking... Dry heat works for separating sections and barrels and all kinds of other movements you may want to do. How does it work?

 

If I apply heat to the join of a section and barrel, surely the section expands with the heat too, as well as the barrel threads if there are any, so why doesn't it become harder to get out of the barrel?

 

Mat:

 

For your reading pleasure: Pen Repair Don'ts..by David Nishimura.

Scroll down to Opening A Pen:..then to Heating:

https://www.vintagepens.com/pen_repair_donts.htm

 

Fred

 

...read..think..speak..and write...

[eachan]

The full physics of it is beyond my ability to explain - but would be interesting if anyone else is around who knows the stuff. Using heat to loosen a barrel so that the section will come out more easily: the barrel is the outer part and gets more of the short application of heat and so expands more. The slight softening is enough to prevent cracking.

[praxim]

There may indeed be an advantageous effect that you are heating the outer section more. However, the basic physics (last I knew it) means the gap expands proportionally with the expansion of the outer and inner sections, i.e. it expands in the same proportion they do, and there is a tiny gap between them in the first place, else you could not separate them at all. Look up types of fit on the interwebz or in Machinery's Handbook.

 

Softening of any binding agent deals with a lot of the problem, maybe most.

[eachan]

Binding agents are rare in friction fit sections. A few Watermans and some pens repaired by people who don't know better. That's about it.

[Astronymus]

Same effect as a heated shrink chuck.

[praxim]

Binding agents are rare in friction fit sections. A few Watermans and some pens repaired by people who don't know better. That's about it.

 

True. I was thinking of excess ink while trying to cover all the bases.

Edited October 5, 2017 by praxim

[eachan]

Good point!