Report 19: Testing of Bearing Materials and Lubricants under Cavitation Conditions

Abstract

A novel adaptation of magnetostriction oscillator technique to lubricant and bearing material testing is described. This consists of vibrating the end of a transducer at right angles to a stationary specimen surface, causing formation and collapse of cavitation bubbles in the separating fluid film, In order to control the temperature and properties of the separating film, a flow is introduced through a central hole in the stationary specimen. This limits the temperature rise, ensures the removal of the debris and supplies continuously fresh working fluid. A steady state condition with regard to loss of material can be reached within about an hour with a white metal specimen in a lubricating oil. It has been found that the temperature at the specimen face is not critically affected by changes in the rate of flow over a range from 10 cm³/s to 20 cm³/s. The actual temperature rise is quite moderate, being of the order of 2°C for water and 15°C for Shell Vitrea 33 oil operating at 26°C inlet temperature. With the oil flow interrupted, the temperature rises by about 50°C in 2 minutes with a tendency of the rise to continue. It is suggested that the method offers a unique opportunity for controlling the cavitation environment of bearing materials and lubricants.