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Status monitoring and fault diagnosis of rolling bearings
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| Time：2016.08.30 News Sources：Shandong Xinkaite bearing Co.,Ltd. Views：
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Rolling is an important part of rotating machinery, statistics show that the use of rolling bearings in rotating machinery, about 30% of mechanical failures are caused by rolling bearings. With state detection and fault diagnosis technology, the accident rate can be reduced to 75%, maintenance costs can be reduced by 25% to 50%.
A failure in the form of a rolling bearing
(A) fatigue spalling
Inside and outside of the rolling bearing raceways and rolling elements alternately enter and exit the bearing area, these parts for a long time alternating loads of action, first fatigue cracks from the contact surface the following maximum alternating shear stress at the contact surface and then extended to the surface dot peeling, flaking and gradually developed into a large, called fatigue spalling.
(B) wear
Due to the relative movement of dust and foreign matter raceways and rolling elements caused by surface wear, poor lubrication will be increased wear, resulting in the bearing clearance increases, the surface roughness increases, reducing the bearing running accuracy, thus reducing the movement accuracy of the machine, to increase the performance level of vibration and noise.
(C) scratch
Since the hard particles or microscopic projections on the inner and outer bearing raceways and rolling elements contact surface the contact surface uneven force, in poor lubrication, high-speed heavy load conditions, due to the heat generated by friction caused by partial local deformation and contact surfaces friction welding, metal surface may be severe localized melting of the contact surface of the friction force of the partial tear weld from the substrate.
(Iv) fracture
Suffered when the bearing load, the vibration is too large, the location of the defect in the inner and outer rings of the rolling elements repeated shocks, the gradual expansion of the defect and fracture.
(E) corrosion
Water or acid, alkaline substances can cause invasive direct bearing corrosion. When the bearing shaft current through the contact point in the raceways and rolling elements caused by sparks generated electrical erosion, washboard-like irregularities formed on the surface.
Second, the failure process of rolling bearings
Bearing failure is usually divided into four stages:
(A) First stage: the stage bearing ultrasonic frequency vibrations
The earliest bearing failure is reflected in the range of 250kHz ~ 350kHz ultrasonic frequency vibration anomalies, with the development of failure, abnormal frequency decreased gradually moved to 20kHz ~ 60kHz, this time bearing tiny fault may be the impact of the envelope and AE the method detects the impact envelope value up 0.5gE (enveloped acceleration, vibration analysis represents the amplitude of an acceleration indicator).
(B) Second stage: the natural frequency of vibration of the stage bearing
With the operation of the bearing, the rolling bearing surface will have a slight defect, the vibration caused by these minor flaws will arouse the natural frequency of the bearing member (fn) resonance vibration or bearing support structure, generally vibration frequency in 500Hz ~ 2kHz. Meanwhile, the frequency is also used as the carrier frequency modulation failure of the bearing. At first only observe this frequency itself late performance occurs in the vicinity of the natural frequency side frequency. If the acceleration detected by the envelope will find the envelope value will rise to about 0.5 ~ 1.OgE. In this case, the bearing is still safe operation.
(C) The third stage: the bearing defect frequency and its harmonic vibration stage
With the further expansion of the bearing tiny defects, bearing defect frequency and its harmonics began to appear, with the further development of bearing wear, more octave frequency defects began to appear, doubling the number of side bands around these natural frequencies and the bearing member also gradually increased. At this time bearing vibration has been more obvious, consideration should be given as soon as possible to replace the bearings.
(D) Phase IV: Broadband random vibration bearing stage
Bearing is close to complete failure, bearing life is nearing completion, and even frequency is also influenced by rises and produces many frequency multiplier, while the original discrete bearing defect frequency and natural frequency Start "disappear" is replaced by random broadband high frequency "noise and vibration", the high-frequency noise and vibration envelope values declined, but just before the final failure of the bearing envelope impact value will increase significantly.
Third, the rolling bearing vibration characteristics analysis
(A) characteristic parameter method
Advantages characteristic parameter method is that only a small number of indicators used to interpret the bearing condition, results of analysis of simple and convenient. Commonly used in the diagnosis of rolling bearings feature a variety of parameters, including frequency domain parameter RMS, peak and other time domain parameters of frequency and gravity.
(Iii) the frequency spectrum analysis
Rolling bearing vibration frequency component is very rich, containing both low-frequency component, also contains high frequency components. Each corresponding to a particular fault are specific frequency component, through appropriate signal processing method of a specific frequency component separated, thus indicating the presence of specific faults.
(C) The envelope method
Advantages include envelope method can distinguish occur simultaneously in the same bearing fault feature of several features, remove the fault-related signal from the high-frequency modulation signal, thereby avoiding confusion with other low-frequency interference, with a very high reliability and sensitivity of the diagnosis.
When the bearing surface of a component is a partial injury in the course of the operation by the carrier to the impact it is in contact with the surface of an impact pulse force. Since the band impulse force is very wide, including the bearing assembly, the bearing, the natural frequency of the machine structure and the sensor, it is bound to arouse resonance vibration measurement system. Therefore, the vibration acceleration measured signals comprise a plurality of resonant frequency of the carrier, as well as fault characteristic frequency modulation thereon and its harmonic components. Thereby selecting a resonant frequency according to the actual situation of the center, so that weak fault signal bearing mounted in the resonant frequency high amplitude pass out, and then the absolute value of the measured signal is processed, after low-pass filtering, modulation can be obtained envelope signal, and then carry out a fast Fourier transform FFT, you can get the low-frequency envelope signal containing fault characteristic frequency and its harmonic component of the envelope signal spectrum analysis can easily be diagnosed bearing failure, this process is also known as resonance demodulation.
IV Conclusion
Learn bearing failure stage of development in the form and bearing failure, bearing failure diagnosis is essential. Master bearing fault diagnosis analysis principles and methods is a prerequisite for accurate diagnosis of bearing failure.
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