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Galling of press-fit assemblies

We are pressing a 17-7 stainless steel shaft into a hole in unplated 12L14 steel. The hole is bored and burnished, and the interface is pre-lubed with a thin film of teflon-filled silicon grease. The shaft has a surface finish of 16 RMS or better. Periodically, the assembly galls during the pressing operation. What factors influence the galling? Is speed of pressing a factor? The interference tolerance is closely controlled, but does that have a great effect on whether it galls or not? Is surface finish and/or material hardness a factor?

Thanks.

Al Mirolo
- Vandalia, Ohio
2002

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Stainless steels are well known for galling. Suggest you try plating both surfaces with electroless nickel, high phosphorus type. You could try plating one surface only to see if that solves the problem, if not plate both surfaces. Thickness of about 12 microns. Both metals will require a Woods or low pH sulfamate nickel strike for good adhesion of the EN deposits.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2002