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Metal finishing Q&As since 1989

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Coating or Finish for ADC12 for Sliding Wear Resistance

Q. Hello,
I work at a company that deals with a lot of small mechanisms. I have an aluminium die cast part that is gripped by Nylon (PA66) to create a sliding mechanism that holds a weight. The trick is that it needs to slide but when it stops, it also needs to stick (stay in place), so it can't be lubricated. The problem is that it squeaks and jams after about 800 movement cycles and it can't be serviced by the end user. Ideally it could last up to 10k cycles. We have tried various different plastics: POM (too lubricious), PBT, PA66 (lubricant impregnated) and all with and without glass fibre). We have also tried numerous finishes, both mechanical and additive. Mechanical finishes include; vibration finishing with various media, blasting with various media and grits, linishing and other wheel finishing with various grits. We have also tried electroless nickel, anodising, satin chrome, e-coat and passivation processes. So far the only coating that has worked is ceramic coating (like the 'enamel' coating found on cast iron or aluminium pots - the samples were actually coated at a pot factory), however this was too expensive. The e-coat was the second best, performing the function but has a cosmetic issue - the e-coat wears off at around 2000 cycles.
Does anyone have any suggestions for a suitable finish that can resist wear on an aluminium die cast part?
We are producing the part in China, so brand names are less likely to be helpful.
Many thanks in advance!

Mitch Mountain
- Melbourne, Australia
September 13, 2022