Hi I'm designing an avionic system. Sometimes, when part contour is complicated (like big heatsink), I'm using black (for example) hard anodize per MIL-A-8625. Rest of the parts are been painted (epoxy or polyurithane based paint per spec). Now, I ask my self, why don't I do all parts using this hard anodize coating, and save the painting costs? What are the pros and cons for coating vs painting??? I can give one issue: when coating, masking process is needed (in electrical contact areas), while when painting, the whole assembly can be painted so masking contact areas is not needed Please give ideas
The hard anodising has one drawback and that is in the fact that is a hard surface and is created by a controlled "corrosion" of the material. In parts of an airframe that are load bearing and subject to fatigue loads, the hard anodised part is more likely to have a shorter fatigue life due to its coating process than a painted part. Hard anodizing is normally only used on parts that need a hard outer skin due to running against a bearing surface or similar. An additional factor is part size. The anodising process requires the part to be completely immersed in a chemical tank. There are limits to the size of tanks available and products are normally designed with this constraint in mind. I would expect that the hard anodising cost is higher than the painting price, but in the case of heatsinks etc, the paint also acts as an insulator.
