Metal finishing Q&As since 1989

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Air agitation

2002

I have a water tank used to cool aluminum parts that are around 700 degrees F. The parts are in the tank close to 20 seconds. The water temperature stays around 100 degrees F. The parts cool to around 200 degrees F after they are removed from the tank. Will air or mechanical agitation help cool the parts quicker? Also, which would work better air or mechanical agitation?

Thank you,

Bill Price
- Shelby, North Carolina

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This is a metal finishing site so we tend to work in terms of plating rather than heat treatment. Extrapolating plating experience to heat treating might be dangerous, but air agitation is much more effective than mechanical agitation.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

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2002

Hi Bill,

First off, ask yourself the question ... if I get perfect mechanical mixing versus perfect air mixing, won't the far colder (ambient one hopes) air cause the tank temperature to fall much faster, eh? But will that have an effect on the parts? Would an 'overcool' cause stresses?

Perhaps go to the archives & have a gander at # 93ll.

It's all a matter of distribution AND cooling. Not knowing the tank size and the part sizing, I'm loath to make any suggestions. Heck, 20 seconds is a pretty short time. Why spend $ to gain a few parsecs?

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Are you hardening the aluminum? If so, there is a rate of cooling that is important, IE: the starting temp of the water is in a given range. I suspect that you are ending up with hot water because you do not have enough (a big enough heat sink). I also do not have a understanding for your need for speed. It appears to be a question that is possibly only a facet of the overall process and possibly out of context.

James Watts
- Navarre, Florida
2002

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What alloy(s), what part(s) geometry, what fixturing, and what are you trying to accomplish? The 700 F suggests an annealing, in which case cooling rate is relatively unimportant, and you are trying to ease handling and increase throughput. Increasing tank volume, overflowing cold water, pumping and proper fixturing will improve cooling. Air agitation will help if no air pockets and will also lower the water temperature by increasing evaporation. Like the other respondents, I don't understand limiting the cooling time to 20 seconds.

If solutionizing wrought alloys, an initial temperature of 830-970 F (dependent upon alloy) and quenching in cold water is preferred (except for bulky/complex shapes subject to quenching stresses). The final temperature of 200 F is excessive, especially for 7xxx alloys, as some precipitation hardening will occur prematurely. If solutionizing castings, an initial temperature 950-1000 F is used, and the quenching is normally into 150-212 F water to minimize stresses. If precipitation hardening (‘aging³) any alloy, the 700 F is excessive. Information is from Alcoa Aluminum Handbook (1962), but I expect it is valid for newer alloys except possibly Al-Li types.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2002