01 Vibration classification of sliding bearings
The vibration of sliding bearing can be divided into two forms according to its mechanism:
One is forced vibration, also known as synchronous vibration. It is mainly caused by the imbalance of components on the shafting, the misalignment of the coupling, poor installation and other reasons. The frequency of its vibration is the rotation frequency of the rotor and its double frequency. The amplitude of vibration increases with the increase of the speed before the critical speed of the rotor, and decreases with the increase of the speed beyond the critical speed. There is a resonance peak at the critical speed;
The other kind of vibration is self-excited vibration, also known as subsynchronous vibration. That is, oil film whirl and oil film oscillation, whose vibration frequency is lower than the rotation frequency of the rotor (about half of the rotation frequency of the rotor), often occurs suddenly at a certain speed, which is very harmful.
02 Sliding bearing vibration diagnosis mechanism
In the design, manufacture and installation of the sliding shaft, the problems of reducing the forced vibration source, avoiding resonance and strengthening the dynamic stability of the oil film have generally been considered. Therefore, under normal working conditions, the vibration magnitude of lubricated bearings is limited to a lower level.
If the vibration of the bearing exceeds this level, it will indicate that it has produced some kind of failure. In addition, as a response of the shaft after excitation, according to the frequency keeping characteristic principle of linear system, it is possible to find traces of various vibration sources from the frequency component analysis.
03 Vibration test
There are many kinds of sensors used to measure vibration, such as absolute type, relative type, acceleration type, velocity type, displacement type, etc. In the vibration test of sliding bearings, the selection of sensor type, in addition to considering the sensitivity, dynamic range, frequency response characteristics, environmental adaptability and reliability of the sensor itself, must also consider the installation conditions, measurement point direction and location and other issues. Generally, for sliding bearings with exposed bearing seats, absolute vibration speed or acceleration sensors are mostly selected; For the sliding bearing with the bearing seat hidden inside, the relative vibration displacement sensor is often used. As for the measurement direction, the radial plumb and horizontal are the main ones, and the location of the measurement point should be selected at the place with the shortest vibration transmission path and the most sensitive to the vibration source.
04 Sliding bearing vibration diagnosis method
The commonly used vibration diagnosis methods of sliding bearings include the following categories:
Time domain amplitude diagnosis method: this method mainly calculates the root mean square amplitude in the time domain index of sliding bearing vibration signal. When the root mean square value is greater than a certain limit value, the tested bearing is judged to be faulty. This method is simple and easy, and is often used in simple diagnosis.
Time domain waveform diagnosis method: this method mainly analyzes the law that the direct frequency amplitude of the sliding bearing vibration signal changes with the speed, so as to distinguish whether the vibration of the tested bearing is forced vibration (including resonance) or self-excited vibration. The typical vibration waveforms of several different vibrations are given in the figure below, which can be used as a reference for waveform diagnosis.
Several typical vibration waveforms
1-instability; 2-unbalance; 3-resonance; 4-electromagnetic vibration; 5-The base is loose
Frequency domain diagnosis method: analyze the spectrum of the vibration signal of the sliding bearing. According to the difference between this spectrum (spectrum to be tested) and the vibration spectrum (standard spectrum) of the sliding bearing when it is normal, and the corresponding relationship between the frequency component at the difference and the frequency of the vibration source, the existence, degree, category and cause of the fault can be determined. This is a more precise and reliable vibration diagnosis method. The characteristic frequencies to be diagnosed are generally shaft rotation frequency, half of shaft rotation frequency, frequency doubling of shaft rotation frequency, etc.
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Jiashan Epen Bearing Co., Ltd. is a professional manufacturer of sliding bearings, metal plastic composite bearings business, specializing in adhering to do fine, the better for our customers continue to create value concept, is committed Sliding Bearings, new composite materials research, development, promotion and applications. Company's existing main products for metal-plastic composite series Sliding Bearings, bimetal bearings, sliding bearings single metal series, are widely used in automotive, metallurgy, engineering machinery, construction machinery, plastics machinery, machine tool industry, water conservancy and hydropower 30 a number of areas.