Annealing Copper

[Shopgeezer]

I have read all the threads I can find on annealing the copper end plates of small boilers before hammering them over a form. You Tube videos show the fellow heating the endplate up to cherry red and dropping it into water. The main thread I could find on this forum had an entry saying you can air cool the endplate or drop it in water, it will be the same softness either way.

So is this a characteristic of Copper? I fear the wrath of my old shop instructor who laboured hard to make us understand how to anneal steel to whatever hardness is required for the job. Dropping a piece of steel into water after heating would harden it immediately.

 

[Picko]

I have read all the threads I can find on annealing the copper end plates of small boilers before hammering them over a form. You Tube videos show the fellow heating the endplate up to cherry red and dropping it into water. The main thread I could find on this forum had an entry saying you can air cool the endplate or drop it in water, it will be the same softness either way.

So is this a characteristic of Copper? I fear the wrath of my old shop instructor who laboured hard to make us understand how to anneal steel to whatever hardness is required for the job. Dropping a piece of steel into water after heating would harden it immediately.

What you have found is correct. It doesn't matter how you cool copper for annealing.

 

[R Degen]

You just have to watch you don't get get it to hot i turn out the lights in the room so you can see the color better than quench in water . Randy

 

[retailer]

The copper will work harden so you may need to anneal it several times until you have the desired bends/shape.

 

[Shopgeezer]

So other than work hardening does copper return to a hardened state with time? I am wondering about strength if the end plate was annealed for final shaping but still soft when used in the boiler. I guess this begs the question about silver soldering. If you get the copper hot enough to flow the solder does this anneal the work piece? Does the copper return to normal hardness after it sits at room temperature for a day?

 

[tornitore45]

You can buy soft copper tubing that sat on the shelf for month and is still soft. My conclusion is that soft copper stay soft until worked.

Since silver soldering bring the part to a red color, I would say the copper is soft when done.

 

[werowance]

in my very limited experience here what I do is much the same as I do with sheet aluminum. soot it with my oxy accetaline torch. then adjust mixture for a cleaner flame and then heat the piece by swiping flame back and fourth over the whole piece just until the soot burns off. when the soot is gone then I stop and I'm ready to work it and repeat the soot burn off again if need be.

I cant say if it returns to full normal hardness after a day but it does seem to harden up a bit after a while.

 

[fcheslop]

Heat to dull red in subdued light and either air cool or quench
For boiler end plates or any copper that is going to be hammered I always quench in a pickle made from citric acid
If you dont use a pickle you may find the dirt and scale from softening gets into the surface when you hammer it around the former and makes soldering for more of a problem
It will take several goes at softening to make the flange as the copper quickly work hardens I also make the former about 15 thou too large then the finished cap canbe machined to fit the shell
Im just making a simple pot hedge hog boiler at the moment although the copper bashing is done
regards
frazer

 

[tornitore45]

Aluminum age hardens but copper does not.

 

[Cogsy]

The pressure changes of the boiler will likely work harden the copper pretty quickly. I know soft water pipes in houses harden up rapidly.

 

[Ken I]

I once accidentally left some copper strips in a charcoal fire - only retrieving it the next morning - stone cold - so it had cooled very slowly.
It was ridiculously soft - best described as "limp" - but it work hardened rapidly - so much so that if you bent it with your fingers you could actually feel it stiffening up as you bent it.
Regards, Ken

 

[fcheslop]

When pressure testing the finished boiler. You take it upto the required pressure in stages returning to zero each time
So a little hardening should occur
In the UK first hydro test is twice working pressure for a new boiler
cheers

 

[Andy Munns]

Softening carbon steel depends on speed of cooling through S curves (because they are "S" shaped). Copper does not have S curves so quenching is convenient but not necessary. Work hardening of say copper steam pipes required delagging every 5 odd years and a quick anneal to remove effects of work hardening. WH due to pressure and flexing but had to be plastic deformation as relatively large grains (metal crystals) developed dislocations within each grain and also became smaller. Heating to red allows firstly a relaxation of dislocations and stressed grains. Prolonged heating (like overnight) allows for grain growth as well. Sometimes objects to be totally softened would be heated up close to the end of a day (or week) and the furnace turned off