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topic 4376

Zinc plating high resistance black



We have a customer who specifies a zinc plate 0.0002 minimum, with a "HC black finish". They also require 240 hours to white and 400 hours to red rust in salt spray. Does anyone out there know what this process is? Your help would be greatly appreciated.


Mike Adams
- Rockford, il.

First of two simultaneous responses-- (2000)

Dear Mr. Adams:

The salt spray may vary from process to process even if the basic chemistry is the same. Our process is cyanide zinc with a black chromate that has achieved 500 to white rust. The bath requires a 300 - 500 ppm of silver, but we constantly run between 100 -200 ppm of silver. This is the only thing that is done differently from the data sheet. It may or may not be the answer to why we achieve such good results. You have to be careful though because the low silver tends to turn green in the field. Give this a try if it doesn't work I can let you know what we use.


Ken Hutchinson
- Minneapolis, MN, USA

Second of two simultaneous responses-- (2000)

Hi Mike,

The term HC Black is specific to one of my customers.That is why you don't recognize the name.

The high corrosion protection Black Chromate can be done in barrels or baskets. 240 hours to white is normal, but in all honesty I don't know who started saying 400 to red. After you reach white corrosion, all that's left is the zinc before you come to the red.

Mike McDonald
mack products - Jefferson, Wisconsin

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