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Manganese phosphating procedure to get pitch black color

We are having part which is made by Metal Injection Molding Process with S7 material. which is having dimn. of 0.018 micron tolerance. parts are heat treated and the hardness is 50-55HRC. The required finish condition is Manganese phosphating with Pinch block color. but we are getting dimn. variation (undersize) and graysh color after Manganese phosphating.

how we get that finish as well as maintain the dimn.

with regards

K.A. ANBARASU
- Bangalore, INDIA
August 14, 2009

I will take an educated guess that there is some step that is out of tolerance including the prep steps. Manganese phosphate is normally very nearly a jet black. Since you are not getting a desired build up, the tank chemistry is off, probably your free acid /total acid ratio, or your tank is loosing temp due to a large cold load or you are not staying in the tank long enough.

Get your chemical vendor involved. If they will not provide the required on site help, find a different vendor. Normally, the possibility of loosing a customer will get their undivided attention.

James Watts
- Navarre, Florida
August 17, 2009

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