plating, anodizing, & finishing Q&As since 1989
Chemical activation of tool steels (EDM machined areas) for HCP
Our company hard chrome plates plastic injection molds and machine tools. When plating mold parts, it is customary to glass bead the areas that have been EDM machined so as to better clean the rough area and more importantly reactivate the "passive" EDM burn. One of our customers has voiced strong concern over the use of the glass bead, one because it could break the sharp corners needed on the part and secondly, the hazing or dulling of the quality ground surfaces surrounding the EDM pocket.
What are my options for reactivating the steel chemically. Has anyone had similar difficulties when plating EDM machined surfaces?
Thank you.Jeff Hanaway
- Pennsylvania US
YOUR CUSTOMER IS RIGHT. WE PLATE PLASTIC INJECTION MOLDS AND OTHER TOOLS THAT HAVE EDGES AND SURFACES THAT MUST BE KEPT SHARP. IN THESE CASES WE NEVER USE BLASTING.
INSTEAD, TRY IMMERSION IN 30% H2SO4, 40-50 °C. FOR ENOUGH TIME TO SEE UNIFORM GASSING COMING OUT FROM ALL SURFACES FOLLOWED BY A RINSE AND A WOODS NICKEL STRIKE. 300 g/L NiCl + 300 mL/L HCl +H2O FORWARD POLARITY ROOM TEMP. 10-40 A/SQ.FT. FOLLOWED BY RINSE AND CHROME PLATING WITH NO REVERSE.
YOU MIGHT ALSO TRY, IF GEOMETRY ALLOWS YOU, A NORMAL REVERSE ETCH FOLLOWED BY A STRONG KICK OF 1 SECOND IN YOUR PLATING CHROME TANK AT UNUSUALLY HIGH AMPERAGE IF AVAILABLE, SAY 30AMP/SQ.IN!.
ANOTHER LESS ELEGANT BUT VALID OPTION IS TO CHECK FOR ACTIVE SURFACE BEFORE PLATING BY SOAKING THE EDM AREAS WITH A SOLUTION OF CuSO4+H2SO4 (COPPER IMMERSION). THIS WILL LET YOU ACTUALLY SEE. IF YOU HAVE AN ACTIVE STEEL SURFACE IT WILL COLOR UNIFORMLY PINK. THEN DISSOLVE COPPER DEPOSIT WITH AMMONIUM HYDROXIDE. THIS LAST METHOD NOT FOR 300 SERIES STAINLESS STL. IF YOU STILL HAVE PROBLEMS I WILL GLADLY HELP AT NO CHARGE ON THIS SITE. BILL MARRUFO.Guillermo Marrufo
Monterrey, NL, Mexico