Letter 40111

Zinc Barrel Plating Current Density

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I have a question regarding zinc barrel plating
the barrel can hold 15,000 pcs of object which surface area of each object is 0.16 dm^2
the barrel are designed to pass through current of max 300A
I wish to plating 0.8 um of zinc

what is the current density and plating time required?

thanks,

Alan
electronic mfgr - Hong Kong

Per Faraday's Law, at 100% efficiency it would take 96,484 Amp-seconds (a Faraday) to deposit one gram molecular weight of zinc (that is the atomic weight of zinc divided by its oxidation number), which is 65.38/2 or 37.69 grams of zinc.

Since the density of zinc is about 7.14 g/mL, one Faraday will deposit 5.28 mL of zinc. If you have a surface area of 15,000 x 0.16 = 2400 dm^2, that's 240,000 cm^2. So one Faraday will deposit a thickness of 5.28/240000 or cm, that is 0.000022 cm or .22 micron. So for 0.8 micron thickness you would need 0.8/0.22 or 3.64 Faradays or 350,850 Amp-seconds. At 300 A, this would take 1170 seconds or 19.5 minutes. But efficiency is not 100 percent; it might be 50 percent for cyanide and 75 percent for acid zinc. So the plating time would be 30 to 40 minutes.

Alan, your question remained unanswered for a very long time, despite having been seen by hundreds of zinc platers. I apologize for this reticence on our readers' part but it usually indicates that they didn't like the question :-)

I think people didn't like being asked to do the math for you as part of their answer; so please try to phrase future questions in a way that doesn't require others to do all the caluclations for you :-)

Good luck.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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