Terry_Cowan (16K)

Tips & Tricks From the Pros

This column is available for professionals in the metalshaping community to share some of their knowledge.

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Our first contributor is

Ron Covell

Questions on annealing:

"Can aluminum be annealed more than once? Can you 'over' anneal aluminum?"

I don't believe there is a limit to the number of times you can anneal a piece of aluminum. After aluminum is annealed, it starts to harden as it is worked, and sometimes after a good deal of working, taking the time to soften the panel again can save time if the part needs to be stretched (or shrunk) a great deal.

Some alloys, like 2024, need to be heated and cooled under very highly controlled conditions, otherwise they are prone to cracking while being worked. For this reason, this alloy should only be annealed in a heat-treating facility.

The "friendly" alloys of aluminum, like 1100 and 3003, can be easily annealed in the shop, just by heating to their critical temperature, which is near 800 degrees Fahrenheit.

This temperature can be easily monitored by coating the metal with a LIGHT coating of soot from a pure acetylene flame, then heating the metal gently with a neutral flame until the soot film just burns off.

One of Ron's students works annealed aluminum into a sandbag, rough forming a motorcycle gas tank side.

You can also buy temperature-indicating crayons at welding supply stores to more closely monitor the temperature of the metal as you heat it.

Go carefully here, since the melting temperature of these alloys is around 1200 degrees Fahrenheit, so you must be vigilant about keeping the flame moving evenly across the panel, otherwise you may inadvertently overheat areas. If this happens, even slightly, you will get 'chalky' areas on the surface of the metal. In this case you should probably start over with a new panel, since you have changed the 'wrought' (rolled) sheet into cast metal, which doesn't have much workability.

Ron displays a partially finished gas tank.

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