Re: Cast iron in zinc
My 2 cents. It sounds like your current density was way too high. Even with the right current for the part area calculated, if the anodes are 1/2 in. from the part the current density in that vicinity will be much higher.
Really high current density will do a few things: The zinc plated will be 'burnt', dull, grainy, dark, etc. Zinc can't dissolve fast enough from the anodes so some oxygen is formed instead, it will oxidize the brightener chemicals resulting in some unwanted organics in the bath. The pH of the bath will change, you may need to adjust it back into the right range.
You may be able to save the bath if you carbon treat and then adjust pH back to normal. Caswell tech supp will know best.
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