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

Phosphate coating surface affect on seal life

I am wondering what iron phosphate coatings do to the surface of steel and how this would affect an o-ring seal. This is used on a hydraulic cylinder where we wash the base and then paint the outside but leave an iron phosphate coating on the inside. We have noticed a rougher "feel" but cannot detect with a profilometer.

Thanks,

Tom Waterworth
- Cottage Grove, WI
2002

---

2002

Hi Tom,

What exactly do you mean by "affect an O-ring?" An iron phosphate coating is part of a broader class of coatings called conversion coatings. As the name implies, the top surface of the metal is chemically converted into the coating. In the case of an iron phosphate coating, we are talking about phosphates and oxides of iron.

The surface looks roughened because it is. One of the reasons the conversion coating improves paint adhesion as compared to a bare surface is that the phosphated surface has a greater surface area.

George Gorecki
- Naperville, Illinois