2023 May the First Week KYOCM Technical Knowledge: Overview of Fault Diagnosis Methods for Rolling Bearings

Abstract: Rolling bearings have many advantages. They are not only very convenient to use and maintain, but also have a certain degree of stability and good starting performance during operation. Especially at moderate speeds, the load-bearing capacity is relatively good. However, compared to sliding bearing handles, rolling bearings have larger radial dimensions, poorer shock absorption ability, and higher noise and noise. At the same time, there are also certain faults in rolling bearings, which restrict the development of bearings. In view of this, the article will mainly discuss the diagnostic methods for rolling bearing faults.

Keywords: Rolling bearings; Fault; diagnosis; method

1. Analysis of Main Faults of Rolling Bearings

The structure of rolling bearings has a certain degree of complexity, mainly composed of outer rings, inner rings, rolling elements, cages, and other parts. Therefore, there may be many problems in the specific operation, which can cause the failure of rolling bearings, and even lead to problems such as foreign objects and corrosion in the rolling bearings. Although it is in a normal state during installation and lubrication, after a period of operation, the bearings may not function properly due to fatigue and wear. Generally speaking, bearing failures are mainly manifested in the following aspects:

Firstly, it is fatigue pitting and plastic deformation of rolling bearings. Under the load of gravity, certain contact occurs between the inner and outer rings of the rolling element, and the force generated by the contact between the inner and outer rings is called contact stress. When the contact stress of the inner and outer rings reaches a certain value, fatigue pitting corrosion will form on the rolling surface of the inner and outer rings.

Fatigue pitting is one of the main faults of rolling bearings, and its harm is mainly manifested in the loss of bearing working ability. This is commonly referred to as bearing failure. At the same time, there is also a problem of plastic deformation in the failure of rolling bearings. The so-called plastic deformation mainly refers to bearing scratches caused by excessive impact loads on the shaft, or additional loads caused by bearing thermal deformation and foreign object invasion. The occurrence of these problems can cause serious noise and vibration in the actual operation of bearings. In addition, once the bearing has indentation, it will cause the surface of the area near the impact load to fall off.

Secondly, it is the wear and fatigue peeling of rolling bearings. Rolling bearings may experience certain malfunctions due to increased usage time and frequency. For example, during use, the presence of foreign objects or dust can cause relative motion between the rolling bearing and the rolling element, leading to surface wear of the rolling element, increasing the gap between the bearings, and making the surface of the bearings rougher, reducing the operating accuracy of the bearings and the motion accuracy of the machine. At the same time, there may also be some noise during operation.

For bearings in some precision machinery, it can also shorten the length of time and service life of the machinery to a certain extent. There are also some wear issues caused by slight vibrations. The main reason is that when the bearing is not rotating, there will be slight contact between the rolling element and the raceway. After continuous contact, it will cause wear problems in the raceway, resulting in unnecessary wear marks. And fatigue peeling mainly refers to the problem caused by the load on the inner and outer raceways of rolling bearings and the surface of rolling bodies. Mainly manifested in deep cracks and surface peeling. The provisions in the test procedure indicate that if a fatigue peeling pit with an area of 0.5mm appears on the raceway or rolling element, it is considered the end of bearing life. From this, it can be seen that fatigue peeling has a significant impact on the service life of machinery and will to some extent adhere to its service life.

Once again, it is the rust problem and adhesion of rolling bearings. The most serious problem in rolling bearing failures is timely corrosion of the rolling bearing. Rust problems can cause high-precision bearings to form rust problems on the surface, thereby losing the ability to continue working. Usually, the direct invasion of moisture and acidic substances can cause corrosion problems of bearings to a certain extent. Once the bearing stops working due to corrosion issues, the temperature of the bearing will decrease, and the water droplets on top will fall on the surface of the bearing, leading to corrosion.

At the same time, due to the passage of current inside the bearing, contact may occur when it comes into contact with the raceway and rolling element, causing electrical corrosion of the oil film on top, resulting in the formation of some uneven pits on the surface of the bearing. The adhesion problem of rolling bearings is mainly caused by poor lubrication and friction heating caused by high-speed and heavy-duty work. The heat generated by this friction can cause the components of the bearing to reach a very high temperature in a short period of time, leading to metal adhesion from one component to another on the surface of the bearing. This phenomenon is called gluing.

Finally, there is a problem of damage to the cage of the rolling bearing. The problem of cage damage is mainly caused by improper mechanical assembly or improper use of bearings. This type of fault can to some extent cause deformation of the cage and increase friction between rolling elements. It can even cause the problem of jamming between rolling elements, resulting in the inability of the rolling elements to roll. At the same time, it may also cause friction between the retainer and the inner and outer rings of the rolling bearing, further leading to noise and heating of the rolling bearing, and causing damage to the rolling bearing.

2. Discussion on Fault Diagnosis Methods for 2 Rolling Bearings

With the development of science and technology, many methods have emerged for fault diagnosis of rolling bearings, specifically including the following diagnostic methods:

One is the shock pulse method. The so-called impact pulse method mainly refers to the low-frequency impact effect that occurs when the rolling element contacts the rolling zone of the inner and outer surfaces, which also causes resonance of the sensor to a certain extent. The signal generated by this shock action is the shock pulse signal. Currently, the impact pulse method is considered the most practical method for diagnosing local damage to rolling bearings. It overcomes the difficulty of selecting the filtering center frequency and broadband. However, this method also has certain limitations. After all, the resonance frequency of the structure caused by local damage to rolling bearings is not fixed and unchanging. The resonance frequency of the damage has different resonance reactions at different stages, and even different reactions can occur at different parts. Therefore, in practical use, when the background noise is strong or reacts with other shock sources, it will lead to poor diagnostic performance of the shock pulse method and lose its practical value.

The second method is resonance demodulation. The so-called resonance demodulation method mainly involves envelope analysis and high-frequency resonance technology. This method is the most effective way to deal with high-frequency signals caused by mechanical shock. When a mechanical malfunction causes intermittent high-frequency impulse signals, hardware can be used to monitor its high pass filtering. By filtering and extracting the peak value of the signal detection signal, the main faults in the bearing can be analyzed. However, it should be noted that a wider frequency band can bring noise to a certain extent, leading to poor noise reduction performance of bearings. Although the frequency of noise can be analyzed to a certain extent through the analysis of envelope signals, it can also cause the phenomenon of sum and difference frequencies, making the situation of envelope analysis very complex and difficult to accurately identify. At this time, the envelope analysis method cannot evaluate the severity of the fault.

The third is intelligent diagnostic technology for fault signals. With the development of science and technology, the diagnostic technology of rolling bearings is also constantly developing. At present, the fault diagnosis technology of rolling bearings in China mainly uses the expert system, knowledge engineering and genetic algorithm in artificial intelligence technology to diagnose and monitor the parameters and signals of rolling bearings in a timely manner. Through a large number of experiments, it has been shown that intelligent diagnosis technology for fault signals can achieve effective monitoring and diagnosis of bearing faults by analyzing parameters such as peak and effective values. However, its main drawback is that the computational speed is relatively slow, making it difficult to meet the monitoring needs of bearing faults. However, for some early signal monitoring, intelligent diagnosis technology for fault signals plays an important role and can also produce good monitoring results, thereby achieving real-time monitoring of bearing faults.

Fourthly, it is necessary to extract data features in a timely manner. Based on the time-domain data analysis of bearings, some parameter data with certain characteristics can be used to extract these features, so as to diagnose faulty rolling bearings in a timely manner and ensure that the use of bearings is within normal and reasonable range values. In view of this, it is necessary to conduct a comprehensive analysis of the mean, variance, peak value, etc. of time-domain data. It is necessary to calculate the difference between time domains, compare normal peaks, and analyze faults based on the characteristic quantities with significant errors.

3. Conclusion

In summary, the structure of rolling bearings has a certain degree of complexity, and there may be many problems during specific operation, which can cause the failure of rolling bearings and even lead to foreign objects and corrosion in the rolling bearings. Therefore, it is necessary to conduct timely analysis based on different faults in bearings and use correct monitoring methods. Specifically, various methods such as impact pulse method, resonance demodulation method, and intelligent diagnosis technology for fault signals are mainly used to achieve fault diagnosis of rolling bearings, thereby extending the service life of rolling bearings.

More about KYOCM Cylindrical Roller Bearing:

KYOCM cylindrical roller bearings can meet the challenges of applications faced with heavy radial loads and high speeds. Accommodating axial displacement (except for bearings with flanges on both the inner and outer rings), they offer high stiffness, low friction and long service life. KYOCM cylindrical roller bearings include single row cylindrical roller bearings, double row cylindrical roller bearings and four row cylindrical roller bearings.

Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life. Split bearings are intended primarily for bearing arrangements which are difficult to access, such as crank shafts, where they simplify maintenance and replacements.