Stainless steel material inherently galls; it is a characteristic of the
soft material. Most stainless steels have a softer surface than steel
screws that rust; most stainless steels don't rust but are generally
weaker than steel screws.
Passivation is a nitric acid process for stainless steels intended to
remove any surface iron particles left from the alloy itself or from
machining tooling; passivation is not a cleaning process and really does
nothing to reduce galling. To test the effectiveness of the passivation
process, sample parts are often tested for many hours in a salt spray
(vapor actually) environment; if red or brown stains are seen after this
test, the passivation process was not adequate. Successful passivation
relies on first effectively cleaning the base stainless steel material,
a fact often overlooked by the treatment facility!
Loctite makes several excellent anti-galling greases with copper or
nickel particles that actually do the anti-galling work. No grease
without these particles will substantially reduce stainless steel
galling, though the grease will reduce friction initially.
Some of the common anti-galling materials discussed for amateur radio
applications were actually developed for use on aluminum wiring
terminations. The Loctite anti-galling materials should be superior for
our mechanical fastener purposes. The Loctite anti-galling materials are
available in small put-ups like grease sticks, about 1-inch diameter and
four inches long. I put this material on every stainless steel fastener
I use, for sure!
I've seen small stainless steel fasteners gall, especially if they were
very clean before assembly, but you often see larger, structural
stainless fasteners 1/4-inch and up gall if not protected by an
anti-gall grease. If there is any microscopic motion in the joint due to
varying stress loading (e.g. wind loading of structures), stainless will
gall for sure! Stainless steels generally don't rust but they do have
other problems.
My experience base? Forty years of precision-instrument mechanical
engineering design.
Larry W6FUB
Grant Saviers wrote:
> Passivated SS, which is frequently the case for machine screw sizes (<
> 1/4-20) is much less likely to gall. Passivation tends to make the
> screws more gray in color and less shiny.
>
> Lanolin is also a "standard" anti gall lubricant for SS and is packaged
> for this purpose and is a lot less messy than anti-seize compounds...
--
Best wishes,
Larry McDavid W6FUB
Anaheim, CA (20 miles southeast of Los Angeles, near Disneyland)
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