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Ideal Surface Prior to Phosphating
Q. This company makes steel parts which go through a vibratory bowl for deburring prior to cleaning and phosphating. We currently use ceramic tumbling media but are thinking of switching to steel media for a variety of reasons. The steel media tends to "burnish" up the parts a bit more than the ceramic, and I wonder if this will have a negative effect on the phosphating process. Is there a general rule of thumb when it comes to surface finishes prior to Phosphating? Are rougher surfaces better, or does it matter since phosphating happens on a molecular level?
Trey EllingtonStamping - Epping, NH, USA
2005
A. You are correct in saying phosphating occurs at the molecular level. To get a good coating, the surface should be in an equipotential state; that is, the surface should be electrochemically uniform. This means there should be as little surface contamination as possible and definitely no rust! Furthermore, if possible the surface should be uniform in composition, so if possible there should be no work hardening done to the substrate, or if it is done, it should be all over the surface. So, the ideal surface should be as chemically clean and uniform as possible with as little surface engineering as possible.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005
Q. Thanks for the information. You were very helpful. I wonder if anyone else has actually used steel tumbling media on steel stampings before going into a phosphate line. If so, what was your experience? Did you have any problems with the phosphating?
Trey Ellington- Epping, NH, USA
2005
Q. We have a phosphating plant in the manufacture of railway bearings. Post grinding it is required that we wipe the surfaces of the bearings manually before adding them to the KOD tank. If we do not do this, it results in marks on the phosphated pieces. We are currently in need of an automated process to substitute for the wiping operation. I have also heard from people around that using detergent before the KOD plant might help. Or using a degreasing-> rinsing-> surface activation system instead of manual wiping. What do you suggest. Thank You
Ranjan NayyarEngineer - Jaipur, Rajasthan, India
August 31, 2013
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