Fault Diagnosis Method for Deep Groove Ball Bearings 6008, 6208 and 6408 Based on 'Hertz's Contact Theory' Using Engine Oil and Gear Box Oil

Abstract

A bearing is the machine component which allows relative movement between the components of machines and equipment, along with transmitting the load. The most commonly used bearings are the Rolling Element Bearing. Rolling element Bearings generally fail suddenly before giving any indication. Many monitoring methods are in use to monitor the condition of bearings. The existing methods are either very costly or require major changes in the setup. The present work is based on a method, simple and inexpensive and capable for online condition monitoring of rolling element bearings. The methodology includes analytical determination of the Elastohydrodynamic lubricant film thickness based on “Hertz’s Contact theory”. The formula developed includes the Electrical Resistance between balls and races of the bearings and the Electrical Resistivity of the lubricants. The Electrical Resistivity is determined by using a simple Test Rig. Further the Electrical Resistance is also determined by using a simple Electrical Circuit along with measuring instruments on Rolling Element Bearing Test Rig at different loads and speeds. The Electrical Resistance is directly related to the lubricant film thickness present between the balls and races of the bearings, more the thickness, more will be Electrical Resistance. Related formulae of lubricant film thickness were developed for test bearing 6008, 6208, 6408 and test lubricants 20W40 (Engine oil), G 90 (Gearbox oil). Experiments were performed for speed range from 800 rpm to 1200 rpm (in steps of 100 rpm), and load range from 40 Kg to 120 Kg (in steps of 20 Kg), on Rolling Element Bearing Test Rig. Useful conclusions are drawn at the end of the experimental work based on the results.