TRIBO-CHARACTERISTICS OF CRYOGENIC HYBRID CERAMIC BALL-BEARINGS FOR ROCKET TURBOPUMPS - SELF-LUBRICATING PERFORMANCE

Experiments were conducted to investigate and compare the self-lubrica ting performance of two types of modified 25 mm-bore ball bearings: a hybrid bearing with Si3N4 ceramic balls, and an all-steel bearing The modified bearings had a single outer land-guided retainer with ellipti cal 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 o xygen (LO(2)), or liquid nitrogen (LN(2)). Testing showed that the bea ring torque of the modified all-steel bearing was drastically decrease d 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 bea ring had relatively stable variation of bearing torque and better load capacity than those of the all-steel bearing in both LH(2) and LN(2). However, in LO(2), the all-steel bearing exhibited excellent performa nce with high load capacity at high speeds, contrasted with poor self- lubrication by the hybrid bearing.