I work with a Dominion made Minton Pulp Dryer that is under 18" of vacuum. A number of years ago the dryer can bearings were switched over to Chevron Ultiplex Synthetic grease and later to Mobil Mobilith SHC PM from Chevron Clarity 220 oil. The reason for changing to grease was because the Oil was being pulled into the machine and contaminating the Product Sheet. We now appear to be having a problem with the oil seperating prematurely from the soap and leaving a hard crust where the grease once was. My question is does anyone have any experience with grease under these kinds of conditions and is there a grease that can handle this job.

G'day Ken,

The difficulty is as you most likely know the vacuum lowers the boiling point of the greases base oil allowing the lighter ends to vapourise off leaving the heavier fractions and the grease thickener as you have seen,
For a grease to cope with these conditions the base oil must have the highest boiling point possible and that leads us to polyflouroethers for base oils.
Typically most of the polyflouroethers are thickened with Teflon as the two will slide together into a homogeneous fluid of the NLGI rating required varied by the ratio of thickner to base fluid.
We are not that satisfied by the teflon thickened greases as the fluorene part of the teflon often cause heavy corrosion,
there is one manufacturer in Australia that thickens with a proprietary system
(J&M Speacialized Products PL,
This system has a backup in the thickner that is if the base oil vaporises over time the thickner will not allow metal to metal contact and that system may prove to be very suitable for your application,
our lab web site has a wall chart of his products ,
www.rttech.com.au,
please feel free to check out, he also has extremely good knowledge and advice in these areas.

Regards Rob S

KenG,
You could also test a 220 from Lubricant Engineers www.le-inc.com

Robo