Improvement of Durability of Hybrid Ceramic Ball Bearings in Liquid Hydrogen at 3 Million DN (120,000 rpm)

Abstract

The durability of a hybrid ceramic 25-mm-bore ball bearing having a single outer land-guided retainer was evaluated and improved in liquid hydrogen at speeds up to 120,000 rpm (120,000 min -1 ) (3 million DN) by comparing the propagation of superficial thermal microcracks on Si 3 N 4 balls at various speeds. To select a tough Si 3 N 4 ball capable of restraining crack propagation, bearing tests were conducted for three kinds of the Si 3 N 4 balls with different jet-cooling systems. The test results showed that the Si 3 N 4 ball having high fracture toughness as well as high thermal shock resistance could restrain the propagation of wide-ditch microcracks. With regard to the jet-cooling system, four nozzles were better than two nozzles with increasing jet speed. Furthermore, the jet flow aimed at the retainer was superior to that aimed at the inner race, and its result indicated that microcracks might be generated at the trace in contact with the outer raceway under insufficient cooling conditions with a large centrifugal force. Thus, decreasing the maximum contact stress of the outer race to 2.0 GPa by a limited race curvature of 0.51 could restrain the propagation of superficial microcracks.

Cryogenic Tribology in High-Speed Bearings and Shaft Seals of Rocket Turbopumps

“…The components of the hybrid ceramic bearing were in excellent condition with regard to wear at a speed of 120,000 rpm with a thrust load of 3,140 N in LH 2 [40]. On the contrary, the seized all-steel bearing exhibited severe adhesive wear.…”

“…Furthermore, under the same cooling rate, the four nozzles achieved a higher cooling ability than the two nozzles with increasing jet speed above 208 m/s. The jet-speed of nozzles reached to the twice of the sliding speed of 108 m/s at the retainer outer-land [40].…”

“…Furthermore, sufficient cooling at the outer raceway was gained by a proper clearance of the outer land of the retainer. Decreasing the maximum outer-race stress to 2.0 GPa (thrust load, 1,960 N) in conjunction with sufficient cooling through a narrow outer land clearance could prevent the propagation of superficial micro-cracks even under insufficient cooling conditions [40]. …”

Modeling and Position-Sensorless Control of a Dual-Airgap Axial Flux Permanent Magnet Machine for Flywheel Energy Storage Systems

“…Each of the upper and lower stators carries a set of three-phase copper windings which are the double-layer type with 2 slots per pole per phase [29]. Rotation of the flywheel is supported radially by the two main bearings which can be either based on conventional steel or on advanced ceramic materials [30], [31]. Another set of auxiliary bearings, named the mechanical supporting system, provides axial support.…”

Tribological Behaviour of Solid Lubricants in Hydrogen Environment

“…For better performance and rotational speeds up to 100,000 rpm hybrid ceramic bearings with Si 3 N 4 balls and steel rings are used. Such bearings were developed for the space shuttle (Gipson, 2001), the future VINCI launcher in Europe, and the Japanese LE-7 rocket engine (Nosaka et al, 2010). Hybrid ball bearings with ceramic balls can be operated up to 120,000 rpm in liquid hydrogen.…”