Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation.
Hard Chrome Plating SG Cast Iron
Q. To plate sg cast iron, after pre cleaning should we etch cathodically in sulphuric acid (what concentration) and then load in the bath, which is switched on, followed by a high strike for a few seconds before we come to regular workings (i.e., 1-2 amps per sq inch). If not, what would you recommend?
A. Recommend exceptional degreasing or solvent clean surface, grit blast with "aluminum oxide" blast media to white metal (term given to chemically and mechanically cleaned bare metal), then immerse directly into chrome bath and immediately begin forward DC current at 2.0 volts. Step up .2 Volts every 15 seconds. Continue stepping up through a current strike of at least 4-6 ASI, for a maximum of 2 minutes, then step voltage back down to nominal plating current (2.5 - 4 ASI)
If you experience a coverage problem or miss mark, check position of the lead anode(s). The closer spacing the better throwing power. I would use acid cleaning in forward polarity only as a last resort. The best of luck -