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Spots on nickel plate over high polished brass

December 16, 2008

I have problems with a very high polished brass,them look spotted.
the procedure is as follows

degrease with naptha
alkaline cleaner
electroclean 3-4 Volts 3 amp/dm2
acid dip very diluted 1% sulphuric acid
nickel plate

do you have any idea about it to narrow range of search.

The piece passes water break test
looks like attack on the base metal but I have tried to take pictures but the spot is difficult to see on the picture.
could it be due to material (more than 45% of zinc on the content)
Could it be due to watts bath composition?
please help

Daniel Hernandez
Plating shop - Bucaramanga, Colombia

Could be due to either lead smear from your free machining brass, if that is what you are using, or it could be dezincification of the brass. The former will look grey and the latter will look copper coloured.
If it is lead smear, you need to dip the brass in fluoboric acid for about 10 seconds. If it is the latter, avoid using strongly alkaline cleaners.
When plating brass, I would suggest using low current live entry.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
January 29, 2009

February 16, 2009

The problem could be due to lead content as it was mentioned already.
But I think it is due to high zinc content. In this case, a cyanide copper layer prior to the Nickel deposit should solve the problem

sara michaeli
sara michaeli signature
Sara Michaeli
Tel-Aviv-Yafo, Israel

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