Non-contact Measuring System for Surface Wear Dent of Journal Bearing

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Wear dents are often found on the surfaces of journal bearings in use for long, and these concave shapes are made because journals, make direct metal-to-metal contact with bearing surfaces while hydrodynamic oil films remain too thin during start-up or shut-down operation. Once the wear dent is formed, the oil film changes its shape, and the minimum oil film thickness may decrease, endangering bearing into seizure. Furthermore the rotordynamic coefficients would change, causing a self-excited vibration of rotor supported in the bearings before rated speeds are reached. Consequently, wear dent profiles on the bearing surfaces must be measured precisely to estimate the degradation of the bearing performance. However there exists no suitable measuring system available on the sites where bearings are installed.This research project aimed to develop a new handy measuring system for practical use that can easily and rapidly detect surface wear dents of journal bearings of large diameter with the resolution of some micrometer. A gap sensor of eddy-current type is used to detect the distance between the sensor and the bearing surface. The sensor is mounted on a rotating arm which, in turn, is fixed on a beam. The beam can move in a linear actuator. Thus the sensor can scan the bearing surface in the circumferential and also axial directions. The distance data collected are real-time processed on-line in a small-size computer, and wear dent profiles are calculated automatically by means of a computer program installed in the computer. The program was newly developed and coded. The results are presented graphically and numerically on a monitor screen. This system was used to measure various wear dents machined artificially on the surfaces of model journal bearings, and proved to function satisfactorily with precise measurements.