Bearings: Technology and needs
A brief status report on bearing technology and present and near-term future problems that warrant research support is presented. For rolling element bearings a material with improved fracture toughness, life data in the low Lambda region, a comprehensive failure theory verified by life data and incorporated into dynamic analyses, and an improved corrosion resistant alloy are perceived as important needs. For hydrodynamic bearings better definition of cavitation boundaries and pressure distributions for squeeze film dampers, and geometry optimization for minimum power loss in turbulent film bearings are needed. For gas film bearings, foil bearing geometries that form more nearly optimum film shapes for maximum load capacity, and more effective surface protective coatings for high temperature operation are needed.
Fatigue life of high-speed ball bearings with silicon nitride balls
Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. The five-ball fatigue tester was used to test 12.7-mm- diameter silicon nitride balls at maximum Hertz stresses ranging from 4.27 x 10 to the 9th power n/sq m to 6.21 x 10 to the 9th power n/sq m at a race temperature of 328K. The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.
Rolling-Contact Studies with Four Refractory Materials to 2000 F
Four refractory materials were tested in the five-ball fatigue tester to study their behavior under repeated stresses applied in rolling contact: hot-pressed alumina, cold-pressed-and-sintered alumina, self-bonded silicon carbide, and nickel-bonded titanium carbide cermet. The failures that developed in all four materials were shallow, eroded areas of apparent surface origin unlike fatigue spalls found in bearing steels. The load capacity of hot-pressed alumina was the highest of the four materials tested but was only about 7% of that of a typical bearing steel. Preliminary tests at elevated temperatures indicated that hot-pressed alumina is capable of rolling-contact operation at temperatures up to 2000 F without gross wear or plastic deformation. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Washington, D.C., October 13–16, 1964.