The authoritative public forum
  for Metal Finishing since 1989
-----

Which phosphating is best suited for automobile components?

 

Which phosphating is best for piston rings? Please give reasons.

Ganesanponnusamy
engineers & electroplaters - Chennai, Tamilnadu

---

Speaking generically (which is the only way we like to speak on these technical pages), manganese phosphate is best because it is heavy, soft, and oil-absorbing.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

Phosphating is not an accepted finish for internal engine components. The only automotive acceptable finish is hot black oxide.

Dan Brewer
chemical process supplier - Gurnee, Illinois

---

Dan, don't make me stop this car! I know that aluminum pistons have been tin plated, liners nickel-silicon plated, and upper piston rings chrome plated. I've seen "oil-scraper" piston rings that certainly weren't black; I thought they were phosphated-- although that's a while ago admittedly. It would be nice to hear from an automotive engineer what is standard these days.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

Hard chromium plating is applied to the outer diameter of some rings and the surface is lapped or in some cases back etched. To combat top ring scuffing some applications use molybdenum sprayed into a groove machined into the outside surface of the ring. The ring is then ground back to size. The porous nature of the molybdenum retains oil and the moly itself gives added wear protection.

Graham Dodd
- Melbourne, Australia

---

I have adverts for manganese phosphate for use on valve stems in engines. This is in the UK!

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England
 

---

I understand that the manganese phosphate coating helps especially during the break-in, when the lubricity of the coating is all important as the parts make their first go around, to reduce the chance of seizing.

  
Tom Pullizzi
Falls Township, Pennsylvania