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No coverage of the part in decorative chrome plating

July 24, 2008

Hello everyone,

I am facing two problems,

1) After bright nickel plating(MS sheet) pitting comes onto the surface. Operating conditions are,
Bright nickel plating
Temperature: 40-45 centigrade
Ph: 4
Density: 19 baumé
Voltage: 6 Volts
Surface area: 300 square inches of mild steel sheet
process Time: 1 hr, but pitting comes too earlier
Cleaning: electrolytic cleaning at 40-45 °C for 15 seconds
Acid dip time: 15 seconds
Part: Motor bike fuel tank of MS sheet.

2) After nickel plating small pieces having surface area 200 square inches( MS sheet) chrome plate well but when the surface area of the same piece is exceeded to 100 square inches more, no chrome deposits at all, which is surprising although all conditions are kept same.

Operating conditions are,

Temperature: 35-40 °C
Density: 19
Voltage: 20 volts (1000 amperes rectifier)
Time: 1 minute
Part: Motor bike fuel tank of the same MS sheet.

Please suggest the solution

Thanks

Majid

Majid Habib
Plating shop - Lahore, Pakistan

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July , 2008

Hi, Majid. For the first problem, look at the pits under low power magnification. If they are hemispherical and bright they are gas pits (hydrogen bubbles growing at that spot). The first defense is checking the surface tension of your nickel plating bath and adding wetter as required, and improving the agitation. If that doesn't do it, you need to look at your cleaning cycle; sometimes little areas of contaminants can serve as seeds for hydrogen generation.

Regarding the second problem, had you omitted to tell us the chrome amperage, I would say the answer is simple: chrome doesn't plate at all if the current density is too low. This isn't a "problem", it's just the way it is. But according to your figures you are successfully plating at 5 amps/ square inch, and unsuccessful at 3.3 amps / square inch. These are very high numbers and I think you need to recheck your calculations.

But your bath temperatures are much too low: for the nickel you should be at 60 deg C, not 40-45; similarly, for the chrome you should be at 43-44 deg C, not 35-40. After you fix the temperatue, the other problems may go away. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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Dear sir,
You are operating the nickel bath at very lower temparature.Generally nickel bath works at 55-60 degrees temparature.And pitting occurs when the cleaning process is improper,less boric acid concentration and the pH Is very low or higher.
The chrome bath also you are operating at lower temparature.Operate at 45-50 degrees temparature.When the bath contains high sulphate content it reduces the coverage,reduce the sulphate content with barium carbonate and try. Good luck

Shoban Kesarapu
plating chemicals supplier - Secunderabad, A.P., India
September 5, 2008