Summary for hard anodized aluminum wire Discussion
hard anodized aluminum wire as heater coil support is not likely to survive the conditions described. Gerry Mills asked whether a preformed, hard-anodized aluminum wire could support a loose resistance-wire heater coil running as hot as 1400 °F, with 240 VAC, vibration, and thermal cycling, and whether it could still provide 1000-volt breakdown and 30,000 hours of service. The reply from Garner, North Carolina was strongly negative: at only about 80 to 100 °C, fine cracks begin forming in anodic aluminum oxide because the coating expands far less than the aluminum beneath it. The film also dehydrates and shrinks, which adds more cracking. The answer warns that the coating would be stressed by both heat and motion, and notes that 2024 aluminum is even worse. The practical takeaway is that anodized aluminum is not a reliable support or insulation choice for a heater coil at these temperatures.
Q. All,
I’m interested in using a preformed, hard anodized aluminum wire (.002+) to support a resistance wire heater coil, where the stretched coil is threaded over the aluminum wire, which is then mechanically held in place. Visualize the aluminum wire in the shape of a light bulb exterior, with the coil occupying the bulge portion. The coil would be at least twice the diameter of the wire, therefore loose on the aluminum.
A typical heater coil might run brown to red hot, at temperatures as high as 1400 °F degrees, and carry voltage of 240 VAC, referred to the mechanical attachment point. There will be some natural relative motion, coil to wire, due to moderate vibration and the effects of coil shrinkage and growth when cycling from cold to hot. In qualifying vibration, think of something automotive, say the trunk of a car.
Assuming the wireform is either electro-polished after forming and prior to anodizing, or is blemish free after forming, can I expect at least 1000 volt breakdown and 30,000 hours of normal operation?
Gerry Mills
– Arden, North Carolina
2005
2005
A. Wow! 1400 °F ! Fine cracks start forming at about 80 to 100 °C
(which is only 212 ° F). Cracking is caused by the low coefficient of expansion of the anodic film (Aluminum Oxide) which is approximately 0.2 times that of the underlying aluminuim metal. Additionally, the coating will dehydrate and also shrink. So you get cracking both way. And 2024 is worse.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. In addition to what Robert said, the melting point of pure aluminum is 1220 °F. Alloys will be higher, but it will not have the strength of a wet noodle at 1400 °F. Bad choice. Ceramic might work, but some of it is fragile and can be a pain to work with.
James Watts
– Navarre, Florida
2005