I can testify that Krytox oil freezes to rock a long, long way before
you reach liquid nitrogen temperatures. Something under -60C sounds
about right, but I don't recall exact numbers. (I'd assume the same
about Krytox grease, but I don't know that from personal experience.)
I very much would not assume any graphite-based lube is LOX-compatible.
The others, I have no idea.
Henry
On 5/2/2016 7:15 PM, Robert Watzlavick wrote:
I'm preparing for some more cold / LN2 tests of my semi-custom ball
valves. I was reading Bal Seal TR-75 (Shaft and housing materials,
coatings, and lubricants for optimal cryogenic sealing) and it says:
"Wet lubricants may be used at temperatures to –77 F (–60 C). At lower
temperatures, dry lubricant should be used. Dry lubricants are
recommended for cryogenic service because they improve seal performance
and create a protective film between the seal and sealing surface. The
protective film reduces friction and seal wear, minimizes galling, and
improves sealing ability."
For dry lubricants, it recommends:
Microseal (Metal Improvement Co.)
Molydisulfide Spray Coating (Anadite, Inc.)
Graphite Spray-On Coating (Crest Coating, Inc. ) - is graphite oxygen
compatible?
I need some lubrication to assemble the spring loaded stem seal but I've
always used Krytox (actually I use Tribolube-16 because it's cheaper).
Now I'm wondering if the grease makes the problem worse by turning rock
hard and keeping the seal from staying formed around the shaft. I was
considering Dow Molykote Z because it is readily available.
Anybody have experience on the best lubricant for a cryogenic shaft seal?
-Bob