Paper 1: Grease Lubrication of Ball Bearings in Helium

Ball bearings lubricated with a silica gel–mineral oil grease fail prematurely when run in helium at 200°C, failure being mainly in the form of surface damage to the bearings. Various additives have been incorporated into the grease in an attempt to overcome this difficulty, but only a combination of sodium nitrite and sodium stearate has proved completely satisfactory. The sodium nitrite, acting as an oxidizing compound, re-forms the oxide film removed by mechanical abrasion from the bearing surfaces, and the sodium stearate, acting as a boundary lubricant, minimizes this abrasion. These additives do not detract from the high-temperature and radiation-resistant properties of the grease. Depletion of the sodium nitrite, which occurs at high operating temperatures, does not limit the useful life of the grease or bearing. The grease is considered suitable for the lubrication of ball bearings in certain applications in the Dragon nuclear reactor.