|
Letter 12008
Creating brass on bbl plated zinc
castings
We are barrel plating zinc die castings with copper nickel,using a
strike. We are getting blisters that all have a brass deposit on the
base metal when cut open. The blisters appear to be casting blisters,
but any testing to raw castings will not produce blisters, yet the
blister is under a layer of zinc. Is is possible that the plating
process is creating brass? This is only happening on round parts. Any
ideas would be greatly appreciated.
John M. Mahaney
- East Berlin, PA, USA
The brass you are seeing is normal due to diffusion of the copper
into the zinc die casting. The copper plate should be heavy enough
that you still have a true copper layer. Many times blistering in
zinc die cast is due to the surface preparation of the casting and/or
lead in the casting. Although you may be told that there is no lead
in the casting, often some is and it comes to the surface. Use of a
10% fluroboric acid predip after usual acid pickel is helpful at
removing lead from the surface so that the deposit does not blister
in the areas where lead is present.
Gene Packman
process supplier - Great Neck, New York
Dear Reader, please --
- Post a
question on a different
subject.
-
- Answer or follow-up on this
subject (in non-commercial
fashion).
-
 |