Tribo-Characteristics of Cryogenic Hybrid Ceramic Ball Bearings for Rocket Turbopumps: Self-Lubricating Performance

Experiments were conducted to investigate and compare the self-lubricating performance of two types of modified, 25 mm-bore ball bearings: a hybrid bearing with Si 3 N 4 ceramic balls, and an all-steel bearing. The modified bearings had a single outer land-guided retainer with elliptical pockets and a narrow axial pocket clearance to reduce wobbling of the retainer. The bearings were tested under high thrust loads to 2840 N and at speeds up to 50,000 rpm in liquid hydrogen (LH 2 ), liquid oxygen (LO 2 ), or liquid nitrogen (LN 2 ). Testing showed that the bearing torque of the modified all-steel bearing was drastically decreased to about one-half that of the conventional double outer land-guided bearing at a speed of 50,000 rpm in LH 2 Furthermore, the hybrid bearing had relatively stable variation of bearing torque and better load capacity than those of the all-steel bearing in both LH 2 and NH 2 . However, in LO 2 , the all-steel bearing exhibited excellent performance with high load capacity at high speeds, contrasted with poor self-lubrication by the hybrid bearing. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13-17, 1996