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topic 17451

Standards for iron phosphatizing


Hello friend,

We have a very old iron phosphating line in 3 steps(for buses and trucks ). First step is degreasing, and 2nd step is rinsing, and the final step is degreasing+iron phosphate . All steps are in a spray line. We have a problem in the final step . Could you please give us some information and standards about surface of iron phosphating as a basis for painting over?

Nader Bayrami Tarouni
- Tehran, Tehran, Iran


Hi there,

A 3 stage process (often called cleaner-coater) consists of Degrease phosphate, cold water rinse, final (hot optional) water rinse containing special rinse additives. If you are using the cleaner-coater in the final stage the paint finish on your buses will fall apart rapidly in service!
Stage 1 2-4 minutes at 35-45 °C iron phosphate plus efficient detergent additive, 4-7 pts strength.
Stage 2 60 secs mains water rinse,overflowed to keep clean
Stage 3 1-2 mins cold or hot water rinse containing a paint compatible rust inhibitor or a performance boosting additive. Water quality of the final rinse is crucial to paint performance.

Roger Bridger
- Croydon, UK


Dear Mr. Roger Bridger ,

At first I want to thank you for your response . But we could not have a uniform iron phosphating in our body ,and as you see ,we have problem in paint over that . We use epoxy polyamid base resin primer on iron phosphating . First of all I want to know have this primer problem with iron phosphating?

Nader Bayrami Tarouni
- Tehran, Tehran, Iran



I assume by a non uniform phosphate you mean the appearance is streaky and patchy. Primers do not normally cause a problem over phosphate altho' once at Iran National I did see a black wet paint for vehicle seating that had poor adhesion on iron phosphate. What is the actual problem you are experiencing with the finish? What are the chemicals you are using? Is this a normal spray plant or are you applying via a high pressure lance? Times, temperatures and concentrations of chemicals used in each stage would be useful.

Roger Bridger
- Croydon, UK

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