• Topic #31166 "Allowable metallic contamination in nickel plating bath"

A. The term "dummying" probably comes from "plating a dummy load". And it means to plate onto scrap (preferably a corrugated steel sheet) at a very low current density to try to get the copper contamination to plate out preferentially to the zinc. Copper, being more noble than zinc, should plate out well at a current density that is too low for much of the zinc to plate out.

A. Dummying, Dummy Plating = Limpieza selectiva

Saludos cordiales,

Thanks a lot for the answers.
Mil Gracias!

A. Not only electroplating baths, electroless plating such as electroless copper, electroless nickel also need dummying during re start-up after bath idle for certain time to consume excess stabilizer and activate the metal ions reduction reaction to prevent skip plating in following production. David Shiu - Singapore Q. How do you dummy an electroless nickel bath after a new make up? I am plating nickel on ceramic capacitors and the first loads usually fail and I get black parts. After a few runs, then I get good results. Thanks Reynaldo Reynaldo Arroyo - Sylmar, California, USA November 8, 2016

A. By the term dummying it generally indicate LCD (Low Current Density) plating for Nickel as Zn and Cu are the most common impurities and can be deposited at Low current. While for Chrome it is done at high voltage and still call as dummying. So we can say that 'plating out' impurities from the main bath can be termed as dummying.
Regards,

A. Hello, Cousin Vu. Dummy plating is one of several ways to deal with contaminants in a plating bath. It is usually used against metallic impurities, especially if the contaminant is more noble than the main metal of the plating bath. For example, copper contamination in a nickel plating bath.

In theory, you simply plate at a low voltage onto scrap cathodes, in hopes that the contaminant metal will plate out preferentially, so you will plate out the contaminant onto the scrap, without plating out too much of contents of the plating bath.

In practice, the dummy cathode is often a sheet of corrugated metal. In the old days, nickel plating tanks often had dummy plating compartments, so that you were continuously plating out copper and other contaminants. These days dummy plating is usually a periodic batch type operation instead. Good luck.

Regards,

A. Hi, Vu. I don't know what a grille cylinder is, but what is used as the dummy cathode may not matter. I do not know why it is suggested to dummy a brand new copper pyrophosphate bath. If this is a proprietary bath there should be a technical data sheet for it that describes whether or not it requires dummying. If it is a "home brew" bath, perhaps the copper pyrophosphate is not pure enough.

I would suggest plating Hull Cell panels and seeing if they look good without dummying.

Regards,

A. Hi Neelakandan.

You did not mention what kind of plating you are doing, so it is hard to answer your question. But in acid zinc plating it is usual to add peroxide to precipitate the iron, and filter it out rather than dummying. If that is your situation please see our library article "Improving Your Chloride Zinc Plating Operation". Good luck.

Regards,

A. Hi Sastry. Plain steel corrugated roofing sheets ought to be fine. Good luck.

Regards,

A. Hi Sastry. Yes, 5 ASF (amps per square foot) ought to be okay. Please see brief excerpt from the nickel plating chapter of "Electroplating Course Manual - Basic Practical Electroplating" published by the Garden State Branch of American Electroplaters' and Finishers' Society Inc., edited by F.J. LaManna

Regards,

A. Some dummy regularly and some run forever without ever dummying.

IMO dummying is necessary only if contaminants (primarily lead, zinc and copper) are present, or if anode and cathode densities are unreasonable.

However there was at one time a well known supplier who sold a self-contaminating nickel brightener.

A. Good day Dave.

I think dummying requirements are directly proportional to good housekeeping and proper process control.

That is a very interesting explanation regarding the oxide formation on HCD areas of the anode producing brightener oxidation. I would think the anode/cathode ratio is at play here regarding HCD oxidation. I would also think the anode ratio is too small, as it is producing HCD oxides.

I must agree with Jeffrey regarding metallics. Dependent on the substrate, one will get contamination depending on load size and ASF. Parts do fall in the solution, and as you well know, they are not always discovered/removed.
They will dissolve in solution and cause shelf roughness issues = dummying.
Proprietary brighteners/additives can address copper contamination in LCD areas as darkness.
A brightener overload will cause LCD problems/darkness/poor throw/coverage = dummying.
Just thought I might throw in my two cents.

Regards,

A. High current density dummying removes sulfur from the bath. So if your Ni deposits are compressively stressed, high CD dummying will make them less compressive and eventually tensile.

Only drawback is that high CD dummying is expensive.

A. Rich,

I never heard dummy chrome to take out zinc contamination, but you can decant chrome solution to cut contamination out.
Make sure LCD dummy does not create trivalent chrome problem ; once you create trivalent chrome you cannot chrome plate on the part.

A. Doubt you'll have much luck dummying out Zn.

Try a porous pot purifier.

A. Hi Ragul. The zig zag shape is preferred both because it offers a bit of range in current density, and because it offers more surface area than a flat sheet. Why it might be done at high current density was explained by Pat Mentone. But as others have said, it's usually low current density, about 5 ASF or lower. But you haven't yet told us what kind of plating you are doing nor what kind of contaminants you are trying to remove, so it's hard to expand upon the good information already offered. Good luck.

Regards,

A. In many cases a current density of only 3 ASF is used and the current density is calculated on the projected area of the zig-zag plate (as if it was a flat sheet) not the actual area.

A. You dummy a chromium bath to activate the anodes and reduce trivalent chromium.
If you are using dummying to remove impurities at low CD often best to do a Hull Cell first and see if there is a dark band and then estimate the CD that that band is and then "dummy' at that average CD. Don't use too sharply corrugated sheets as you will waste too much metal on the high CD areas, and not get at enough at the targeted CD.
In the case of nickel always plate at normal CD first to get a coherent coat before lowering to the dummy CD so you get a coherent coat first as often the contaminated coating is porous and non adherent.
Don't dummy continuously unless you know you have a need, as you will just waste metal and power.
There are many other alternatives to "DUMMYING'

A. Hi cousin Mark. There is no "such as" in this situation ... there are only specific suggestions for specific impurities in specific baths :-)

This thread started with a discussion about using dummying to remove copper from acid zinc, and in an earlier response I suggested adding hydrogen peroxide to acid zinc to precipitate the iron and make it filterable. There may be other approaches if you have a problem with these suggestions. Good luck!

Regards,

A. Hello Brian, nickel nor iron will co-deposit with copper. Are you experiencing poor throwing power? My suggestion would be to decant the bath, add back the bath constitutes.

A. Hello Brian, I apologize for the delay on your second question. What I have had to do in the past is to figure the percentage you want to decrease the concentration of Ni and Fe contamination. Let's say it's a 20% desired reduction. You would pump out 20% of the solution and waste treat it. The amount of solution that is pumped out must be replaced. Refer to your tech data sheet for the amount of each chemical to add back to the bath plus water of course. I don't think the Ni or Fe will settle to the bottom of the tank overnight without using a precipitator, which I am not aware of any.

A. Hi Anton. Ideally, a corrugated sheet is used for dummying because it offers more surface area than a flat sheet (π/2 x as much if the corrugation is a true sine wave), as well as various current densities. In a Hull Cell you already have a great range of current density so the corrugation probably isn't important.

You haven't told us yet whether the tin plating bath is MSA, stannate or what, but ... do you have reason to believe that all those contaminants are present, that they are responsible for whatever problems you are having, and that they can be dummied out of that type of bath? I tend to doubt that you can dummy zinc out.

Regards,

A. Hi again Anton. Although, it doesn't discuss those metallic impurities specifically, Charles Rosenstein's article "Methane Sulfonic Acid as an Electrolyte for Tin ..." does say that dummying can be done to reduce metallic impurities.

But a Hull Cell is used to predict what will happen in the actual process tank, and it doesn't seem constructive to me to employ a Hull Cell test in a manner which is unrepresentative, so I think you should use pure tin anodes in the Hull Cell. Good luck.

Regards,