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Does electrocleaning cause dezincification or otherwise harm brass parts?




December 1, 2010

Q. I work in the plating field and I have a problem with some highly polished brass parts; I would like to comment:

The problem is that I try to electroclean cathodically; the composition has sodium hydroxide, sodium carbonate / washing soda [affil links], metasilicate, triphosphate and a small quantity of wetting agent.

operated at room temperature
time 30 - 40 secs
if I use the degreaser for a longer period for example 1 minute the parts become plated but I see blisters after some time or during plating

does anybody know the reason for this?

thanks in advance

Daniel Hernandez
Plating shop - Bucaramanga Santander Colombia


A. Hi, Daniel.

Electrocleaning of brass parts must be done with care because they can etch badly, perhaps due to the zinc content. Please be sure that there are no parts that get too much exposure to the anodes.

And if the parts seem to be hurt by being electrocleaned for more than a minute, please remember what the doctor says if you tell him: "it hurts when I do this, doc"  :-)

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2, 2010


A. My guess is that you are plating out trash metals that are not adherent. Bleed and feed or dump the tank. I would try this in the lab first.
Periodic reverse will also help for a while and then you will have the same problem.
Concentration or voltages or temperature may be high enough to actually etch the part, even though it is cathodic.

James Watts
- Navarre, Florida
December 3, 2010



December 6, 2010

Daniel,
The people at finishing.com can help you better if they know :
1. What type of plating you do on the brass?
2. What type of brass?

SK Cheah
- Penang, Malaysia


A. Electocleaning of brass really requires a properly formulated cleaner. Cathodic only cleaning inevitably leads to poor adhesion when getting old as contaminants "plate" on.
It is generally best to follow with a short anodic cycle but at not too high voltage to minimize dezincification.The oxide film formed during the anodic cycle needs to be dissolved with a suitable acid.
Consult a reputable supplier.

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia
December 7, 2010



December 7, 2010

Q. Thanks for your time !

Well the electrocleaner is new, so a discard old contaminants and hexavalent chromium, I guess that due to the cathodic action the electrocleaning bath must be changed more frequently because it builds up in contamination, especially ions of metals that are not good for the plating (especially chromium).

What type of plating I am doing?
Is a watts bath

What type of brass I am plating?
I certainly don't know because my customer does not know either, but is a brass that before polishing is worked on CNC so is must have a little amount of lead so I use a small percent of fluoride in the acid dip after electroclean.

I guess that the reason for the blisters are some type of change due to dezincification on the surface or in the copper or it could be lead passivation. But I am not sure.

So my question is what could be the reason for this.

Also some times after the electroclean I see white spots on the surface, I am using a highly silicated cleaner so I suppose that is due to silicates still present on the part. could be the silicates the reason for the white spots?

thanks
Daniel

Daniel Hernandez
- Bucaramanga Santander Colombia




De-zincification of hexavalent chrome plated brass

Q. Is it more or less likely that brass will lose zinc (dezincification) if it is hexavalent chrome plated?

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California

May 27, 2014


A. Hi, Jim. As you probably know, the chrome plating goes on top of nickel plating -- so the brass will not be exposed to the chrome plating or chrome plating solution, and they will have no effect on it. A poor pretreatment cycle can lead to de-zincification, but I don't think it's a serious concern in the general case. If I'm misunderstanding your question please get back to us.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2014



May 30, 2014

Q. Ted,

Our normal process is to nickel plate, then add a trivalent chrome layer. However, we are concerned with parts from China that have only been hexavalent chrome plated -- no nickel.

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California



A. Hi Jim. Sorry, but I'm still having trouble following you.

Nobody chrome plates without a nickel plated underlayer for a decorative function, do they? It sounds to me like chrome plating directly on brass would offer poor appearance and very little corrosion resistance; it might reduce the corrosion resistance compared to bare brass.

And chrome on brass as a "hard" and wear resistant finish wouldn't seem to make sense unless it was a few thousandths of an inch thick (which is a lot of chrome and takes hours to deposit).

How do you know there is no nickel plating on the Chinese components?

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2014


A. Chromium plating always has cracks or pores through which de-zincafication can take place if the nickel coverage underneath is not continuous.

Lyle Kirman
consultant - Cleveland Heights, Ohio
June 2, 2014


A. Hi.
In mainland China ... anything is possible. I've seen decorative Hexavalent chromium plating directly onto brass. The brass components are manually polished before chrome plating. It offers poor corrosion resistance and appearance compared to the standard nickel / chrome plated parts.
Its not worth the problems that come with the low cost. Go for the proper nickel/chrome plating. Sleep better at night.

SK Cheah
- Penang , Malaysia
June 2, 2014



thumbs up signThank you all for your comments. We will check to see if they nickel plated first before chrome plating the parts.

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California

June 4, 2014


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