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topic 520

Processing parts though black chromate tank on production basis


(1996)

Does anyone have any ideas as to the best way to process zinc and black chromate parts through a return type automatic machine? The machine will process both black chromated and clear chromated zinc plated parts. In order to leave parts in the black chromate for the standard two minutes, the machine would have to be slowed by one-half. Is it possible to heat or make a more concentrated black chromate in order to cut the time down and still get a consistent quality finish? Any ideas as to maintaining quality control on a high production return type zinc automatic line would be greatly appreciated.

Regards,

Keith Rosenblum
plating shop - St. Paul, Minnesota


(1996)

Try using Missouri Electrochem's Black Chromate. It deposits in 45 seconds and is jet black. Add a little acetic acid and you get a brilliant non-rainbowing gold. Great stuff.

Good Luck,
Dave

Dave Kinghorn
Dave Kinghorn
Chemical Engineer
SUNNYvale, California



(2001)

Sir,

The automatic return-type plant can be programmed to have both the types of chromate passivation processes. Movement graphs for the transporters can help in adjustment of the dwell time in the black passivation station or, the pH value may be lowered to speedup the black passivation so that the dwell time can be reduced. But I feel the rinse tanks for black passivation line should be dedicated and not common. The black passivation solution should be monitored for temp, hex.chromium content and pH. The color of the black passivated zinc should not be brownish with or without iridescence. Movement of the transporters should be such as to avoid any contamination of the blue passivation by drips from the black passivation or the rinses.

Regards,

Subramanian Ramajaaym
- Bangalore, Karnataka, India


(2001)

Good advice on the process, Mr. Ramajaaym, thanks. But I believe that the plating machine Mr. Rosenblum is describing is not a programmed hoist/crane/transporter line. Rather, in the U.S. the phrase 'return type automatic machine' indicates either a "split rail machine" or a "side arm machine" as illustrated in the Metal Finishing Guidebook or the book Electroplated Plastics by ASEP.

And indeed, by definition, it is impossible to get an immersion in a single-station process tank that is longer than the basic dwell time. Shorter times are achievable with a delayed-set-down or advance-pick-up accessory, but longer times can only be achieved by making the chromate cell a two-station tank.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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