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Zinc Plating Problem

We are having a problem with black streaks in low current density area on our finished Zinc plated product. Have tried carbon treating, dummy plating and permanganate treatment. Even when adding extra brighteners the problem still exists. We are using an alkaline zinc bath with zinc metal at 1.00 and caustic level at 13.00. Any suggestions? Thanks

Mike Capps
electroplating business - Bon Aqua, Tennessee, USA
2005

Have you discussed this with your brightener supplier? Usually they can analyze a solution sample to determine what impurities are plating out in the low current density areas. It does sound like an impurity in the plate.

Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee

HI!
Analyse your bath on amount of Cr(6+). When it is present even in very small quantities, the result of plating is similar as described in your post.

Dimitrij Us
- Kranj, Slovenija (EU)

Firstly, is the bath within the parameters from your supplier? What does your supplier have to say? How did you dummy? How did you permanganate treat? How did you carbon treat? If these were not done right they can not be used to rule out certain problems. Are you doing rack or barrel work? What is your average current density? Does the streaking show immediately after plating or after chromating?

Basically, a lot more information is needed for a reasonable response. The above questions are those which your supplier should be asking you when you call with a problem. Also a sample should be sent to your supplier if you do not have facilities to do a Hull Cell test, also so that your supplier can check for metallic contaminants such as copper and cadmium.

Gene Packman
process supplier - Great Neck, New York

Sounds like metallic contamination, possibly copper. Try a small addition of "purifier" which your chemical supplier should have available. If he doesn't, then locate a source for sodium polysulfide, try adding 50 ppm at a time.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

Mike,
You have not given much details about your bath such as:
Barrel/vat plating
How old your bath is
what type of job you plate etc.
Please furnish more details. But some tips:-
Metal to caustic ratio 1:10 is ideal. You are maintaining less metal. For Barrel, maintain the same ratio but keep 10% higher. Supply houses usually supplies apart from Brightener, an additive to take care of Low current density areas and another additive to take care of impurities.
I would suggest you immediately call your supplier and try to get more information about the chemistry.
Regards,

T.K. Mohan
plating process supplier - Mumbai, India

Mike
Please check your metal and maintain 10gm/lit and caustic 100 gm/lit. give zinc dust [on eBay or Amazon] treatment. Don't add tooooo much brightener. Maintain as per the manufacturer recommendation.

P. Gurumoorthi
electroplating process chemicals - Chennai, Tamilnadu, India
2005

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