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Letter 16081
Galling of press-fit assemblies
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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, USA
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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 susrface 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.
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