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Aging / Heat treat of copper

Q. We are currently building from scratch a reproduction of the Allison powered P-51A Mustang from the original prints. The prints called for type N copper (no one was ever able to tell me what type N copper was) or equivalent replacement radiator tubes. (approx. 4000 per radiator) I had 40,000 tubes made from c12000 light annealed 12 inches long X .230 OD X .006 wall and am now working on the tool to swage the end and center into a .260 hex and all is going well. The question is that I fear that the tubes may be too soft when compared with a few originals I have from Mustang oil coolers. What is the aging process, if any, and what might I expect as an outcome?

Thanks,

Gerald Beck
aviation - Wahpeton, North Dakota
2003

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First, regarding Type N copper: Judging from the current classes, Type K (high-pressure), Type L (medium pressure) and Type M (low pressure), possibly Type N was the next lower pressure class. Since the wall thickness decrease in order of contained pressure, I estimate a wall thickness of 0.015 inch for your tube diameter. For tubing sizes, see https://www.copper.org/tubehdbk/tables/homepage.htm For a more definitive answer, contact the Copper Development Association by email: questions@cda.copper.org [There is a BS 1306:1975 specification for an N copper tubing, but with much greater wall thickness, suitable for pipe threads.]

Second, regarding heat treatment: Alloy C12000 is 99.90% Cu (includes Ag), with 0.008%P. It cannot be strengthened by heat treatment; it can be only be annealed at 700-1200 °F or 375-650 °C to remove any work hardening effects.

What are the original tubing dimensions, and do you know the operating pressure and temperature of the oil cooler?

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.
2003

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