Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation.
Spots on Nickel/Chrome-Plated Parts
Q. After brazing a powdered metal part onto an
alloy steel shaft, the entire part is nickel chrome plated and on a percentage of
the parts, raised "hive like" spots appear along the length of the square
shaft, usually only on two of the four faces. Any ideas on what would cause
A. Possibly flux residue from the brazing operation is leaching out or is otherwise present on the substrate. If so, delamination, as you described, is possible. To fix this problem, you may need to change your pre-plate methods. Here are a couple of suggestions to try:
Pre-clean using fluoroboric acid dip (40%:60% acid::water). Perform a 1.0 minute warm up in the chrome tank. Step voltage/amperage to desired level.
As an alternative, after fluoroboric acid pre-clean, go directly into chrome bath with "live current" at 2.0 to 2.4 volts and
then step the voltage/amperage to desired level.