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Cyanide zinc plating problems

Sir,

We have commissioned our own Cyanide zinc electroplating plant (Rack type).
We are doing plating on Sheet metal component that are ranging from 0.30 mm to 0.70 mm in thickness all CRC Material.

Since then I have encountered the following listed problems.

1. Black spots on the material after sending to the customer.
2. Concentration of Zinc metal at anode on the material being plated.

Please provide concentration percentage of all the three chemical i.e Cyanide, Zinc oxide & Caustic. The PH of water is around 12.75 gms/ltr
We use the following procedure.
First dip in HCl for cleaning - water rinse - sometimes material is being cleaned in diluted sulfuric acid.
Then the material is kept in mild cyanide solution - material hanged in the process tank through physical means - plating starts at room temp. the solution contains Cyanide, Zinc oxide & Caustic. Zinc 99.999% at anode. The voltage at rectifier is kept at 6 volts.
The material is then dipped in mild cyanide solution again.
Then in Chromating solution - again in mild chromating solution - water rinse - caustic solution for White colur - water rinse - water rinse - water rinse - hot water dip.
Please help very urgently as I have borne a loss for lakhs of rupees. the material getting returned is creating a mental tension too.

Tarun Gupta
Businessman - Delhi, India
September 8, 2010

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September 10, 2010

MR GUPTA BEST ZINC PLATING FOR SHEET METAL COMPONENTS IS ALKALINE CYANIDE FREE.
WHY YOU ARE LEACHING AFTER PASSIVATION.
VERY GOOD TRIVALENT PASSIVATIONS ARE THERE + SEALERS.
CONTACT A REPUTED CHEMICAL SUPPLIER IN YOUR AREA.
THEY CAN SOLVE THE PROBLEM.

Ajay Raina
Ludhiana, Punjab, India