Letter 41057

Brown Spots appear 1 week after nickel electro-plating on brass coils  

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Hi folks,

I have some age old problems with nickel electroplating on Brass coil.

After send in for plating, there are brownish/ yellowish spots erupting rom the surface.

I wonder if it is plating or material problems?

The plater told me its the pores of the brass coil and the sulphuric acid can't even clean away the impuriites but "trapped" in the tiny grains of the material and start appearing as yellow spots...

Is that a feasible?

I have seen black and white spots appearing on the coils 2 to 3 years ago but never see yellow spots before...

Hope some of you can assist me with this long pressing problems.

Yours sincerely,

Alan Chow
Coil Slitting - Singapore

Hi Alan,
It is very possible what the plater is saying is correct, but it sounds like they could be using a better pre-dip than sulfuric acid or a sulfuric acid based pre-dip. There are proprietary peroxide based dips that offer different degrees of etching and brightness, and are easy to waste treat. They do a great job in cleaning the surface of the brass. What is the thickness of the nickel plate? Insufficient plating thickness could also be a cause of the problem. The plater should be investigating better cleaning techniques and try to solve the problem, rather than inferring "it's the nature of the beast". You could try sending a sample lot to a reputable plater, and let them know the problems you currently have. If they want your business they will do everything to get it right. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York

Dear Mark Baker,

Thanks for your advice & expertise.

Instead of using 1.27um Nickel, we are only adopting 0.5 um Nickel undercoat before adding Bright Tin.

Is that the industry standards of using 1.27 um for Nickel undercoat in order to cover colored spots?

We do not have black spots erupting , my old samples tat are 2 years back did not show any signs of spots erupting....

I need your advice... it may be coil material or cleaning agent?

Yours sincerely
Alan
Coil Center

Alan Chow
- Singapore

You have simple galvanic corrsion setting up in the pits. YOu may retard this tendency by dipping in a weak solution of hex chromi acid. The rinse following a chromate or chrome plate will greatly reduce the tendency for these pits to bloom. The brown color is copper oxide diulted with the zinc and nickel salts in the area. HOt-cold-hot-cold rinsing before dippping in the chromic acid will further increase the protection.

Robert H Probert Robert H Probert Technical Services Garner, North Carolina Editor's note:        Mr. Probert is the    author of Aluminum How-To / Aluminio El Como

Hello again Alan,
In your first posted question you had said "send in for plating". Does your company have it's own plating department or are you using a jobshop plater? The reason I ask is to determine how much control you actually have to rectify this problem. If you have your own plating shop, the responses given on this site can be implemented by you or your plating manager. As Mr. Probert and I have mentioned the problem stems from the substrate material (brass). To alter the types of plating and the thickness of the Ni, is like putting on a band-aid, hoping to stop the bleeding. The issue of pore corrosion has to be dealt with first. Reducing the Ni thickness to 0.5um is not a good idea regardless of what the final plate is. I would concentrate on the pre-plate cleaning cycle, before you change anything else. You've been given a few recommendations to begin with. Good luck!

Mark Baker
Process Engineer - Syracuse, New York

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