Chrome on Brass
Q. Is it necessary to apply strike or flash (Cu or Ni) on brass prior to chrome plating. What is the general rule to chrome plate brass products? Finish and strike or flash?
A. As far as pure brass is concerned, clean the surface with a solvent,
remove grease, oils, rouge, etc., even buff with a clean dry fine grade
Scotchbrite pad to ensure that the surface is perfectly clean and
fingerprint free. Remember the chrome will mirror the finish you start with,
so the better it is going in, the better the chrome coming out.
When part(s) are clean and prepped, immerse directly into the hard chrome
bath, give it 5-15 seconds to warm and become lightly etched by the hot
chromic acid (no current at first) set your rack or fixture in place, clamp
DC connections then start current at 2.0 to 3.0 volts and raise current in
"5" second increments, stepping voltage up a few tenths of a volt each time
until you reach normal plating rate (generally 5.0 volts with conforming
anodes and 6.0-6.5 volts with "stick anodes". Don't delay stepping voltage,
brass shouldn't set idle in the bath too long.
Pure brass needs no reverse etch or subsequent strike coatings.
Other brass and copper alloys depending on content and hardness may require
a strike of copper or Ni. Generally you can hard chrome straight onto
bronze, Aluminum nickel bronze the same as brass but the cleaning and prep
steps are critical.
Exception to these rules are "leaded Brass, bronze, copper alloys" Most of
these alloys will need an additional cleaning step in fluoroboric acid (also
spelled fluoboric acid) prior to plating.