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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing 1989-2024
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Plating Is Thinner at Same Amp-Hours than Historically. Current Leak to Ground?
Q. Hi.
I've been evaluating bright acid tin plating. For my parameters, I've been using constant current of 100A with voltage of 4.9V ~ 5.1V. This parameters gives me good thickness. When I resumed my evaluation after 4 months, when I use 100A of constant current, I noticed that my voltage goes up to 6.5V ~ 7V, and my thickness becomes very low. I changed my solution since it very turbid as well as cleaning all contacts for any resistance and anode bags were replaced, but still the voltage is 6.5V ~ 7V. I tried measuring actual voltage using a multi meter and the voltage is the same with the display of voltage in the machine. One observation that bugs me is that when my negative probe of multi meter is tap in the negative terminal of busbar, and the positive probe is tap in body/frame of the machine, there is a voltage registered in multi meter, around ~ 6.1V. Is there any chance that my machine is shorted? Thanks.
- Abrantes Portugal
July 6, 2024
A. Hi Jose.
Although neither anode nor cathode should be grounded, such voltmeter readings often doesn't mean much because if no current is flowing and we're talking only "static" readings, they can vary quite a bit. A current leak is more likely if that voltage reading is consistent than if it bounces around.
Faraday's Law doesn't lie. If you're applying the same current to the same surface area for the same amount of time, you should be getting the same thickness. I'd like to see you looking around for an uninsulated heating or coiling coil, or a contact saddle with bad insulation on the bolts, hot joints in the bus bar, etc.
Hull Cell testing can probably tell you if there is a problem with the plating solution, as well as giving you the efficiency of the plating so that you can confirm what thickness you should be getting.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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