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topic 7575

Coated Aluminum Tubing to Replace Copper Tubing


(2001)

Q. We are a manufacturer of consumer and light duty industrial air compressors. On many of the air compressor outfits the customer requests copper tubing believing it to be superior to aluminum. Nothing supports this belief but it is industry wide.

I am searching for a coated aluminum tube that is visually similar to copper, that could replace the copper tube. Ideally this coated tube would then be able to handle forming on a CNC tube bender. The tube would also see temperatures of 400 °F during the operation of the air compressor. What type of coating/finish can handle this application?

John B
-Jackson, Tennessee, USA


Air Compressor

(2001)

A. I disagree very strongly that "nothing supports this belief", John.

Aluminum is not a noble metal like copper; rather it is a very active metal that "rusts" almost instantly. In some benign environments, like a home or office, aluminum will build an oxide coating that it fairly tight and impervious, so that the aluminum does not corrode excessively. That is, it pretty much seals itself up underneath that oxide coating. It can be a wonderful material of construction for a lot of things.

But in many industrial environments, for example in the average plating shop where there may be some amount of acid vapors in the air, those aluminum oxidation products act like steel corrosion products--that is, they are porous and do not retard further corrosion at all. Aluminum corrodes faster than steel in an environment that has acid vapors, and it is a miserable material for such applications! Whereas copper is resistant to mild mineral acid vapors.

Many industrial facilities do plating, or they may do painting/powder coating that uses acid immersions before the painting processes. Other industrial shops have wastewater treatment systems that use acids. And others use deionized water systems that require acid and may therefore have acid fumes in the air. Aluminum will not hold up in the presence of acid fumes. Please visit some plating shops before you decide that aluminum tubing will be satisfactory, and certainly do so before making the mistake of trying to disguise aluminum as copper to try to fool people who know they need to purchase copper into believing that that is what you are selling.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2001)

A. I represent a company that has for several years been supplying coated aluminum for the automotive industry both in North America and Europe. To meet corrosion resistance criteria we coat the aluminum with a thin PA12 layer which gives the tube very high resistance to impact, general corrosion and a variety of chemicals. Since the coating is plastic you can choose any color you like but it also limits the max service temperature to approx. 300 °F, but can for short periods of time peak higher. The tube can be bent in CNC bender and easily adapts to existing tooling.

Flemming Christiansen
- Cape Canaveral, Florida



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