Abstract: The traditional research on the dynamic characteristics of rotor system with loose fault mainly focus on the looseness of the non-rotating parts. However, the loose fault of the rotating parts is neglected. Based on this deficiency, a rotor-disc rubbing model is established by Hertzian impact-contact theory, and the motion equation of rotor system with loose disc is also established. The fourth-order Runge-Kutta method is used to solve this equation. The influence factors of the disc motion state, disc vibration characteristics, variation of displacement between loose disc and shaft, and trajectory of shaft and disc are discussed. The research results show that some factors, such as the shaft speed, elasticity modulus of shaft and disc, clearance between loose disc and shaft, shaft damping, disc damping, rotational damping, and initial speed of loose disc have a major effect on the motion state of loose disc. The waveform of the rotating shaft may have the phenomenon of beat vibration at certain rotating speed, this phenomenon may be caused by the loose disc and shaft’s vibration or collision. Some high frequency multiplication occurs in the spectrum, and the multiplication of high frequency increases with the increases of disc and shaft’s speed difference. The displacement between loose disc and shaft tends to be stable as the turntable speed tends to be stable. The sawtooth phenomenon occurs in the trajectory diagram of the loose disc and shaft. The change of the frictional force of the disc-shaft leads to the inconsistency of the saw tooth direction, and the sawtooth phenomena of disc is more obvious. The research results have an important reference value for the research of dynamic characteristics of rotor system with loose disc.

Key words: rotors with loose disc, nonlinear vibration, hertz contact, fault diagnosis, dynamic characteristic