Plating Defect Pin Holes
Q. Shaft made from EN9 material and induction hardened and ground. 15 to 20 microns hard chrome plating carried out on shaft. We observed many pin holes on plated O.D. after deplating these holes are not visible and if we do plating again then same pin holes are visible through out the area.
A. A high population of pinholes can mean several things, most likely
1.) inadaquate reverse etch, check cathode contact, anode condition, anode spacing and using a hand held DC meterm verify the proper DC current (amps/volts) is flowing to the part during etch.
2.) verify pre-plate steps, recommend solvent or stoddard cleaning, then grit blast prior to chrome plating with a medium to fine grit aluminum oxide at 60-80 psi to uniformly abrade the base material and remove any microscopic patterns from the hardening or grinding process.
Hardened steels benefit from a "warm up" step in the chrome plating solution prior to the application of reverse current. This warm up should be commensurate with part size. (example 1" solid shaft warm up 2-3 minutes, 4" solid shaft 5-7 minutes and so on).
Best of luck.