Letter 34052

Manganese phosphate coating on steel for finishing steel objects [Netherlands] 

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I would like to get a recipe for a manganese phosphate coating for steel. If someone perhaps can explain me the actual chemical actions taking place on the surface.

I've learned that there are many applications such as: 1 high wear resistant and 2 better resistant against corrosion and a nice finish 3 as a pre-treatment for painting etc. Is there a big difference in the recipe and chemicals ? The one I'm most interested in is protection against corrosion and finish.

Thanks

Jan Van Velde
hobbyist - Kesteren, Netherlands

You can use next solution:
25 gm phosphoric acid
1,5 gm manganese dioxide
1 lit water
Boil your objects 2-4 hours.
you must oil,lacquer or wax it!
(according to Angier:Bluing and Browning of Firearms)

Goran Budija
- Zagreb, Croatia

Jan Van Velde

Manganese phosphating formulations contains basically a manganese salt, phosphoric acid and an accelerator. Deposition of manganese phosphate coating is normally performed at very high temperatures of the order of 95 deg.C for a period of 30-60 minutes.

It is a conversion coating process and involves the dissolution of the base metal which subsequently forms part of the coating. In manganese phosphate coating the species that deposits on steel is manganese iron phosphate and hence requires a large amount of metal dissolution so that the formation of manganese iron phosphate is possible. This is the reason for the requirement of high operating temperature and higher processing time.

Manganese phosphate coating offers good wear resistance. It can retain oil and lubricants and improves the scuffing resistance. Manganese phosphate coating with higher coating weight offers good corrosion resistance. Impregnation with oil further improves the corrosion resistance.

Zinc phosphate coating is mainly recommended as pretreatment coating for painting.

T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India

My company conducts manganese phosphate coating to carbon steel pipe. We use heating element to heat the bath where the pipe coating carried out. The problem is after the coating maybe for a week the heating element covered by sludge. The workers usually remove the sludge from the heating element by hammer ( mechanical). It doesn't only remove sludge but also cause damage to the heating element ( made from stainless steel ). So...How to remove the sludge without causing damage to the heating element ?

Dodi Syafardi
- Cilegon, Banten, Indonesia

Ed. note: Letters 11465 and 5142 address this issue in some depth, Dodi. Patient use of our search engine will uncover still more tips on this subject. Good luck.

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