Letter 39012

What wear plating is best for hard S7 steel and corrosion resistant to bleach? [Nevada] 

January 11, 2006

I have several cam-type parts used in a clinical laboratory instrument. Originally the parts were made from 440C stainless and hardened. The parts include some small, close tolerance features that are difficult to machine from 440C. Our Mfg group prefers to machine the part from S7 tool steel instead. However, the parts are subject to wash down with a high concentration bleach solution, so corrosion resistance is required.

What plating should I use that will stand up to bleach and also have good wear characteristics in a metal-to-metal cam assembly?

Can the contacting cam parts have the same finish & hardness? Should one be softer than the other?

Tom Barresi
- Reno, NV, USA

Chrome is very good in sliding applications but I have my doubts about it resisting bleach. Consider electroless nickel, either alone or (better but more expensive) with dispersed particles of Molybdenum Disulphide or Teflon.

Guillermo Marrufo
Monterrey, NL, Mexico

Hard chrome will stand up to bleach but does not stand up to that type of friction it will crack I would use the tool steel or a stainless steel that is harder than 72 rockwell because that is how hard the chrome would be.

Nick Johnson
- Seattle, Washington

Thanks, Nick. But there is more to wear than just hardness, and chrome is used for countless metal-on-metal wear situations where tool steel or stainless steel would not do.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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