Dynamic Behaviour of Rotor Roller Bearing System with Bearing Defects

Abstract

Rotating machinery is becoming faster and light weight due to the advanced technologies made in engineering and materials sciences. It is required to run them for longer periods of time. The detection, location and analysis of faults are highly recommended in highly reliable operations. The high speed rotor bearing system often shows unpredictable dynamic response due to manufacturing defects. As it is not possible to produce perfect surface or contour even with the best available machine tools so imperfection such as surface waviness in the rolling element and races developed during manufacturing process cannot be avoided. The radial and axial clearance provided in the design of bearings to compensate for thermal expansion, can also be a source of vibrations and introduce nonlinearity in the dynamic system. Using vibration analysis, the condition of a machine can be periodically monitored. In this study, dynamic behaviour of rotor roller bearing system with bearing defects, like radial clearance, declining of roller and localized inner race defect. The nonlinear bearing forces of a roller bearing under two dimensional loads and develops 2-DOF dynamics equation of a rotor-roller bearing system. The contacts between the rolling elements and the races are considered as non-linear springs, whose stiffness is obtained by using Hertzian elastic contact deformation theory. The system shows the nonlinear characteristics under dynamic condition. The equation of motion in radial and axial condition is obtained for shaft and rolling elements and they are solving by numerical integration technique Newmark-? method. Vibration of rolling element in the radial direction is analyzed time and frequency domain. Characteristics defects frequency and their components can be seen in the frequency spectrum of roller element vibration. As the clearance increases the dynamic behaviour becomes complicated with the number and the scale of instable region becoming larger.