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Smoky/Milky Surface Observed in HCD Areas after Plating with Blue Passivation

September 30, 2008

We are the manufacturers of Barrel closures and Levers which are used in locking of drums
we have a fully automated Acid Zn Plating process with a capacity of 15 Ton/day.We have been running this plant from past 4 years without any major problem.
Recently we have introduced Automatic dosing of additive(M) and brightener(R).M & R is mixed with the ratio of 1:1 and for every 1000Ah 900ml is dosed automatically.Plating bath PH is maintained between 4.8 to 5.2.
Electrolyte conc. Zn metal 28 gms/ltr. Total chloride 130 gms/ltr,Boric acid -30 gms/ltr
Temp maintained within 35deg.
After 3 months running we are getting Milky surface on HCD and dullness in LCD areas.
Please suggest us what is the exact problem.

SATHISH KUMAR
Employee - Bangalore,Karnataka, India

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First of three simultaneous responses --

Assuming that manual operation of your process has been OK in the past, the key to your problem is probably the comment "Recently we have introduced Automatic dosing...".

It is a commonly held belief that using autodosing will solve a very problem; this is not true. The key to successful autodosing is to have it set up properly. If it is not, the bath will gradually run out of specification and get progressively worse. Autodosing eliminates human error and allows for more consistent bath compositions, but only if it is set up correctly - if it isn't, it will cause havoc with your systems.

I would recommend that you do a complete and thorough bath analysis and rectify the bath composition manually.

I would also do quick tests to see the effects of over and underdosing the bath with your autodosed additives. You will then know what the effects of overdosing and underdosing are and this will be a good reference for the future

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
October 2, 2008

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Second of three simultaneous responses --

Contact your brightener supplier. I would guess that you do not have the correct ratio of brightener components in your bath.

Gene Packman
process supplier - Great Neck, New York
October 2, 2008

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Third of three simultaneous responses --

Hi Satish,
Your brightener dosage is very higher side.For 1000AH generally takes 150-200 ml M& R brightener. Excess brightener leads to same problem. And you are doing blue passivation for this you very much concentrate on brightener dosage. Generally in acid zinc plating when compare to yellow passivation little much excess brightener show its effects on blue passivation. Control your brightener additions you can solve your problem easily.

Shoban Kesarapu
plating chemicals supplier - Secunderabad, A.P., India
October 2, 2008

I agree with Shoban. Excess of brighteners without any question. I've never met more than 4 liters per 10 kAh. The ratio 1:1 also seems to be improper. Please verify the ratio in TDS and reduce replenishment.

Janusz LABEDZ
- Warsaw, Poland
October 5, 2008