Can anybody recommend a suitable acid that will remove fine scale and discolouration after annealing a copper gasket ? I appreciate that I could use a fine wire wool but I have found that it is not particularly effective.
Citric acid works well and can be disposed of easily.
Soaking copper coins in Coca Cola brings them up like new but don’t know how a gasket would fare.
Hi the best way to do it safely is to use a scotch brite pad as you don`t have to use any chemicals at all so safer for everyone, I just done some on my BSA RGS and that was Recommended by the company who made them and I must admit that it worked out great so hope that helps.
I believe that the active ingredient in Coca-Cola is phosphoric acid, but very-very weak.
The cinder will disapear if you chill it immediateley after annealing. (please apologize my bad english)
Fritz. If you quench the freshly annealed copper washer in cold water you are un-doing the annealing process. Quenching annealed copper effectively re-hardens the the copper in a similar way to to hardening high carbon steels such as chisels. Any metal being annealed needs to be allowed to cool slowly, preferably by burying in sand or wrapping it in a heat/fire-proof blanket.
The best way to descale copper is to either soak it in a mild acid as already mentioned or cleaning with an abrasive like wire wool or 'scotch-brite' .
Copper does not quench, a plunge into cold water after heating to cherry red does not affect the anneal, it is still fully soft. Fritz is correct, the water stops the scale from bonding to the copper,
John Sunderland, your information is incorrect so please be careful what you write on forums that may be viewed for many years to come.
Copper doesn't care whether it is cooled slowly or quenched when annealing, the critical factor is the temperature that is reached which should be between 400 & 600 degrees centigrade or visually - a dull cherry red.
In this way you can use a blowlamp to anneal a head gasket in that the whole of the gasket doesn't need to be a dull red across its entirety - so long as every single part of the gasket has reached that temperature it will be annealed and as said above, quenching then removes the most of the scale/oxides.
The problem comes from calling the cold water plunge a quench, it is not a quench as quenching is part of moderating a heat treatment.
In materials science, quenching is the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, from occurring.
With copper the plunge into cold water does not change the heat treatment of heating the copper cherry red. No change in properties means it is not a quench, air cooling from cherry red results in the same end property of fully soft.
Although not practical for the home mechanic, and just for interest re. materials science, when I worked for a copper products company we used a "bright annealing" process to minimise scale during annealing. This involved heating the copper in a steel container in which the air was evacuated prior to the heating process. This resulted in perfectly scale free components, fully annealed. And agreed, my experience is that water quenching from cherry red still produces fully annealed copper and a quick rub with an abrasive of choice is all that's needed to remove any scale. We sometimes over engineer our issues, me included.
As some have said heat to dull red and drop in water, parts come out very soft and clean, worked for me for last 50 years
I agree with the above comments regarding sudden immersion not undoing the annealing process with copper , however it is important to always drop the gasket into the water (or oil ) on edge, not flat wise - this will allow both surfaces to cool at the same time . To do otherwise will risk warpage and disformation.
Much information on the internet is incorrect about "annealing" copper. Ask a proper scientist! It needs to be heated evenly to about 400Deg C and can be allowed to cool naturally. The cooling rate isn't critical. This will normalise any work-hardening that may have happened and soften the copper, which should be the aim for gaskets. You don't want them hardened, although quenching in water will not do that anyway. That can occur with high carbon steels, depending on the temperature it is raised to.
Quench in water if you need to use it straight away, but this isn't a necessary part of the annealing process.