Iron phosphate solutions react with the steel surface to form a very thin, glassy iron phosphate layer, typically around 30 to 80 milligrams per square foot. Many systems clean and phosphate in one stage, so iron phosphate fits short three-stage washers. It gives good adhesion and modest corrosion help, enough for most indoor products and some outdoor ones when paired with a good seal.
Iron phos is down to 4 points, so dose it before second shift or the coating weight drops off.
Iron phosphate coating weight drops quietly when the bath runs weak, so the parts look normal and fail salt spray weeks later.
Also heard as
- iron phos
- iron phosphating
Do not mix it up with
- Zinc phosphate: Zinc phosphate forms a heavier, crystalline coating that gives much better corrosion resistance but costs more to run.
Related terms
Zinc phosphate
A heavy crystalline phosphate conversion coating that gives steel top-tier corrosion resistance under powder.
Conversion coating
A thin layer formed by chemically reacting the metal surface, which improves adhesion and slows corrosion under powder.
Points
The titration reading for a washer bath, given in milliliters of titrant and used to judge bath strength.
Five-stage
Shop name for a spray washer with five tanks: clean, rinse, conversion coat, rinse and final seal or DI rinse.