Seized pedals help?!

[Yellow Saddle]

The spindle will expand quicker than the alloy crank, which is why alloy makes a good heat sink. However warming the crank/spindle then allowing to cool may help.

Take it too a shop before you do any more damage with a poor quality spanner, would be my advice.

Aluminium has a linear thermal expansion coefficient of 22 and steel 12. The units are not relevant, just the relative coefficients.
This means that for a given rise in temperature, aluminium will expand linearly, about twice as much as steel. This is the opposite of what you stated above.
Further, allowing it to cool will bring it to the same state as before, which also doesn't help.
The speed of the expansion is also not relevant, nor is the thermal conductivity.

All of this can be prevented by using copper compound on those joints and not over torque the pedals in the first place.

 

[screenman]

Getting the alloy up to heat is the problem.

 

[Yellow Saddle]

Getting the alloy up to heat is the problem.

Why? You just apply heat. And which alloy are you talking about? Steel is an alloy and the aluminium they use in cranks is alloyed.

 

[screenman]

Why? You just apply heat. And which alloy are you talking about? Steel is an alloy and the aluminium they use in cranks is alloyed.

I used to do a few alloy wheel repairs for dealers, hold the heat gun close to the wheel for 5 minutes and it is still cool. From this I designed a heat sink which is sold for cooling down windscreens prior to repairing them.

I am not saying you cannot heat aluminium, just that if there is some steel close by that will get up to temperature before the sky, at least that is my experience.

 

[Yellow Saddle]

I used to do a few alloy wheel repairs for dealers, hold the heat gun close to the wheel for 5 minutes and it is still cool. From this I designed a heat sink which is sold for cooling down windscreens prior to repairing them.

I am not saying you cannot heat aluminium, just that if there is some steel close by that will get up to temperature before the sky, at least that is my experience.

Oh I see what you mean. Yes, aluminium is such a good conductor of heat that locally applied heat will heat up the entire workpiece, whereas a poor conductor like stainless steel will heat up locally, quite easily. Conversely, stainless makes a very poor heatsink and alu or copper excellent ones.

 

[raleighnut]

I worked for many years in non-ferrous foundries and can tell you from experience that a splash of molten Brass or Bronze on your body or clothing will simply roll off still liquid whereas Aluminium cools down so fast that any splashes cool down and solidify so burning into you like hell.
Mind you any Brass/Bronze that does hit your bare arm rolls down it OK (without burning) snag is it stands a very good chance of ending up inside your gauntlet and you cannot just let go of a double ended ladle (2 person) with over 200lbs of molten metal in it to whip yer glove off and as for down yer boots good job proper foundry boots have a QR buckle. (and incidently an inch thick wooden sole for when you find yourself stood in a pool of molten metal due to a casting box leaking from where the 2 halves have been joined or a pot/crucible cracks.