Coating/plating for mild steel part that will survive 50 dishwasher cycles

A. Hi Anthony. I may be missing something, but I think the component should be made of 18/0 stainless steel. This is magnetic and is the material that less expensive flatware is made of, so it will certainly be reasonably satisfactory for cleaning in a dishwasher. Good luck.

Regards,

A. I thought that flatware was 18/8, not 18/0.

A. Hi Jim. Both 18/0 and 18/8 have been widely used for a long time. Because of the high cost of nickel, and the desire of some people for nickel-free stainless, the 18/0 is increasingly popular especially at the low end. Oneida for example switched many of their traditional 18/8 patterns to 18/0 (www.oneida.com/buying-guides/flatware-buying-guide).

Regards,

A. Hi Anthony. You are probably limited to RoHS-compatible trivalent chromating on the zinc plating. The severity of this duty cycle probably hinges upon which dishwasher detergent is used, as both lemon detergent and alkalis (some are stronger than others) attack zinc plating.

The thickness of the zinc plating across the surface of the part tends to vary widely, so you probably need to specify the minimum thickness rather than the average. It is usual to specify the minimum for any area that can be touched by a 3/4 inch diameter ball, but I'm not sure whether that would be a good spec for your particular part.

Unless cost is critical, I would probably specify a minimum thickness of 0.0004" touchable by the ball. This is not based on knowledge of what thickness would actually survive for 50 cycles (I don't know), but simply to make sure your parts are not handled as "commercial zinc finish" -- not a real spec, but a common industry synonym for "cheap", with a thickness of 0.00015" - 0.0002" and sometimes priced by the pound and produced with no real expectation of durability.

There are many available specs for zinc plating; probably ASTM B633 is the most common. Good luck.

Regards,

Hi Ted,

Just to close off. We tried increasing the Zinc thickness as proposed and yes it delays the time to white rust. Probably good enough for our application but marginal. We also tried Nickel plating and this worked much better, however Nickel is hard to glue to the ABS substrate. In the end we have used SUS 441, it offers enough magnetic coupling for our purpose and of course is more robust in the dishwasher.

A. What about color anodizing? 400-series color well. It will survive dishwasher cycles, since it survives high pressure sterilization of color-coded medical instruments.