SummaryThis paper deals with the problems encountered in the fault diagnosis in damped rotorbearing systems used in centrifugal milk separators. It is shown that direct bearing vibration measurements are more reliable than indirect (through rotor housing) vibration measurements. However, in most cases it is not possible to measure bearing vibrations directly. The factors causing large diagnostic measurement errors, such as the influence of the vibration damping system, step-up gear and electric motor noise are discussed in the paper. It is established that vibration measurements of the damping system are noninformative and cannot be used to diagnose faults in bearings. It is proposed to use the vibration spectra correlation to predict bearing failures in rotor-bearing systems of this type.
Abstract:The paper deals with the fault diagnostic system of centrifugal milk separator's rotor bearings with vibration dampers. The diagnostic system consists of a number of accelerometers attached to the outer ring of the upper bearing of the rotor and the separator's housing. Such a system allows measuring bearing outer ring vibrations directly and indirectly (through the housing) and at the same time it allows to evaluate the impact of bearing vibration dampers. Direct and indirect bearing vibration measurement results and the differences between them are presented in the paper as well as the relationship between the vibration acceleration and excitation force spectra.
This article considers problems arising from conventional techniques used to diagnose faults in the rolling-element bearings of rotor-bearing systems, with dampers used in centrifugal milk processing machinery. Such machines include milk separators and related processing machinery. The article asserts that where the rotor-bearing system is equipped with vibration dampers, conventional fault diagnostic measurements produce inadequate results. Hence, for rotor-bearing systems of this type, this article suggests a different way to diagnose faults in bearings and monitor conditions.
This paper analyses the dynamic behaviour of centrifugal milk separator's bearing-rotor system equipped with vibration absorbers. It is shown that rotational milk motion inside the separator causes a centrifugal force that increases dynamic unbalance of the rotor and has a negative effect on performance of the bearings. Mathematical simulation of bearing-rotor system has shown that the rotor rotates at frequency that is outside the resonant frequency region and the amplitude resonances are associated with the bearings and the components of step-up gear. Investigations of vibration transmissibility of vibration damping system have shown that the resonant frequencies are outside the rotor resonance interval and damping system suppresses the effect of separator with milk on rotor bearings and housing. However, it distorts results of diagnostic measurements. Experimental studies confirmed the last statement and showed that results of indirect (through the housing) vibration measurements cannot be used to diagnose the state of damped bearing-rotor system.
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