Effect of Tilted Misalignment on Tribo-Characteristics of High-Speed Ball Bearings in Liquid Hydrogen

Abstract

When radial load applied to the bearings was high, ball excursion occurring in the retainer ball-pockets became large due to ball-speed-variation (BSV). Such BSV was also caused by inclination of the outer race to the shaft (tilted misalignment). If pocket clearance was smaller than maximum ball excursion, large force was imposed on the ball-retainer contact, resulting in retainer damage. The objective of this experimental and analytical research was to determine the effect of tilted misalignment on the tribo-characteristics of 40-mm-bore ball bearings in liquid hydrogen. The bearings used a retainer having elliptical-shaped ball pockets to restrain the ball-retainer contact due to high BSV. Various ball-pocket clearances (1.75, 1.95, 2.15 mm) were tested under high tilted misalignment conditions in a level of 1.9-3.5 × 10-3 mm/mm at speeds up to 50,000 rpm and thrust loads of 590-2,650 N. Testing showed that, the retainer having a pocket clearance of 2.15 mm, the clearance of which was possibly larger than the maximum ball excursion emphasized by high tilted misalignment, enabled to stabilize the bearing torque and the bearing temperature at a speed of 50,000 rpm. Based on the results, the threshold of the ball-retainer contact occurred by tilted misalignment was discussed.

Keywords

• cryogenic
• liquid hydrogen
• solid-lubrication
• high-speed ball bearing
• retainer failure
• misalignment
• elliptical ball-pocket
• ball-speed-variation
• bearing torque
• bearing temperature