Leaded Brass One More Time

Ask an Expert From: Products Finishing, ,

Posted on: 10/1/2003

Question: Our plating shop plates many parts made of brass.

Question:

Our plating shop plates many parts made of brass. We plate these parts with a number of different materials including copper, sulfamate nickel and electroless nickel. Most of the time our plating results are excellent but we seem to have trouble with certain parts. The plating flakes or peels off. When that happens, we strip the bad plate and send the parts through the process again, usually with the same results. Obviously this is expensive and certainly non-productive. Any suggestions as to what we are doing wrong? D. S.

Answer:

Alas, you are probably suffering from a problem that should not be a problem in the year 2003! Simply put, do you know what your substrate is made of? You are correct: There are many different brass alloys and as you have found out, they all do not plate the same way.

In a modern plating shop, the first thing you must do when starting a new plating job is to find out the specifications for the plated part. This includes the material the parts are made off.

If you know the composition of the substrate, you can then determine the proper way to clean the parts prior to plating.

In your particular case, I am willing to bet that the parts that fail during the plating process are made from a leaded brass. Leaded brasses cannot be cleaned in the same way as non-leaded brasses. Leaded brasses usually have very small globules of lead near the surface. During the machining and manufacturing process, some of the lead gets smeared over the surface of the part.

An alkaline cleaner will do a good job of removing soils but will not touch the lead on the surface. In order to get good adhesion to the surface, this smeared lead must be removed. A specially formulated acid dip must be used. The best way of doing this is to dip the leaded brass parts in a 10-30% solution of fluoboric acid for no more than two minutes. Cleaners can also be formulated using fluoborate salts instead of the acid. People have also successfully used sulfamic, citric and dilute nitric acid to remove the lead from the surface.

I recommend a formulated alkaline cleaner and if possible a formulated acid based cleaner. Discuss this with your chemical vendor or look for vendors in Products Finishing Directory and Technology Guide, under Cleaning Chemicals, aqueous (www.pfonline.com/suppliers).



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