Dr. A.

Topic: Applying copper to brass

I've been nickel plating for a long time, and we are taking our first dive into copper plating. This is also our first crack at reel to reel plating. We are attempting to copper coat brass-plated wire.The manufacturer of the wire assures us that there is nothing on the wire other than the brass, i.e. no rust preventatives, oils or preservatives.

We have some differing opinions on how to proceed;

1. Anodic alkaline cleaning. Does anyone think it would still be a good idea? I would like to run an alkaline cleaning even though the wire is "clean" but others here do not want to waste the time and energy.

2. Anodic vs. cathodic acid cleaning vs just an acid dip. We had tried a cathodic cleaning, but didn't get good adhesion of the copper to the brass. Anodic was much better. The wire passes through this tank in two seconds, so whatever we are doing has to be done quick. The acid is a 25% solution of hydrochloric. Either way,the cleaning was done at about 1 volt or 150 asf.

3. Material to use to complete the current in the acid. We tried some strip stainless steel, but in the cathodic cleaning, the steel corrodes into solution and I am afraid that very quickly we will be plating a layer of garbage onto the wire. I thought titanium would be better, but not great. What would be a good material?

4. Rinses - the rinses we use right now are closed loop systems located between each step. The rinse is down in a sump, and pumped up to flush the wire, and reused. I would prefer to use a fresh water rinse spray sort of like they use in grocery stores on produce.

5. Does the reversing polarity have any affect on the wire? In other words, the wire is getting an anodic cleaning, rinsed, and then enters the strike. Although these steps are controlled by different rectifiers, does the fact that at one point the wire may have positive current and then be hit with negative current have any affect?

Thanks in advance for the help.

DustinGebhardt

Re: Applying copper to brass

First, I have a question for you: what is the alloy of the brass? Does it contain any lead?

To answer your questions:

1.Yes, I would put in an alkaline anodic cleaner. Just because the wire is "clean" does not mean that it is plating-quality clean. Beware anything with too much caustic, as it can easily oxidize and discolor the brass, making the downstream acid have to work that much better.

2. I love cathodic acid cleaning. I've always used sulfuric acid for this application or a sulfuric acid derivative (GBS acid salt).

3. I've used carbon/graphite anodes. They have a limited amount of current that they can carry, so take this into consideration.

4. Rinsing can be a difficult item to decide upon until the line is actually in production. The primary function of the rinse is to prevent carryover from one process into the next. While fresh water sprays would probably be best, reusing the water should be okay, assuming that the water is changed regularly. A dirty, contaminated rinse is no doing you any favors.

5. I would imagine that stray current issues are common in reel-to-reel lines. I would say that as long as you have good isolation between the stages, you should be fine. Electroplating is all about forcing the electricity to do what YOU want it to do. If you can maintain the circuit loop within each process step, the electricity will have nowhere to go other than where you are forcing it.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC