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Alkaline zinc plating: parts burning

adv.
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Quickstart:
     The term 'burning' in electroplating refers to the parts getting a coarse, granular look, generally in high current density areas like edges and corners. It occurs when the current is too high for the situation, which causes excessive separation of the water in the plating solution into hydrogen and hydroxide and/or the plated deposit to occur so fat that it cannot form the correct crystal development.

Q. Parts came out from alkaline zinc tank burned at high current density areas, and the burn looks like white powder. The temp. in the tank is 85 deg F and the zinc metal concentration is 1.2 oz/gal and the caustic potash concentration is 20.0 oz/gal. We are using brightener and starter(refine rack). All parts are burning on the rack but the bottom and side parts are burning more. The current density we are plating at is 19 to 26 amps/sq. ft.

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A. Dear Mr PP,

You need to up the Metal conc. to 2 oz/gal and also ensure that the NaOH does not exceed what you currently have. Maintain a metal:OH ratio of 1:10 and you will regain control.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

Thanks very much for the knowledgable and confident response, KV.

Regards,