I've got an interesting problem in thermal expansion.  We have a 304
stainless steel shaft running through a High Density Polyethylene bearing
block, with about 0.020" clearance.  Turns like a greased doorknob at room
temperature.  But the thing is in a cryo chamber that gets -200C, and at
some temperature in the middle the bearing latches onto the shaft and quits
turning.

My old CRC handbook does not see fit to list thermal expansion coefficients
of either material, so I'm off on a search for that info.

Once found, I'm trying to figure out what to do with it.  Would the inside
of the plastic bearing contract at the:

1.  Coefficient of expansion rate  or

2. Coefficient of expansion times Pi or something like that, since it is a
circle?

Hmmm.  Shouldn't have slept through Physics.


-- Lawrence Lile
Sr. Project Engineer
Salton inc. Toastmaster Div.
573-446-5661 Voice
573-446-5676 Fax

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