2022 October the Fourth Week ITS Technical Knowledge: Detection and Control of Abnormal Sound of Deep Groove Ball Bearing

Abstract: The research on abnormal sound of deep groove ball bearings in China is reviewed. The generation mechanism, essential characteristics, detection methods, causes of abnormal sound and measures to control the abnormal sound are reviewed and analyzed.

Key words: deep groove ball bearing; Vibration; Abnormal sound; testing


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Since the early 1980s, China has carried out a comprehensive quantitative control of ball bearing vibration. At present, the dynamic performance of domestic ball bearings has gradually approached the international advanced level, and began to develop from low vibration value to low noise value, and then to quiet bearings without abnormal sound. In this process, in the mid-1990s, the problem of abnormal sound of domestic ball bearings began to emerge. The measured results show that although the vibration value and noise of some domestic low-noise deep groove ball bearings are equivalent to those of foreign countries, the dispersion of domestic bearing samples is large, and the abnormal noise of the samples is as high as 50%.

 

Bearing technology leading countries have completed the progress of low vibration and low noise of ball bearings in the 1960s and 1970s. As early as 1963, Kosurido and Okui studied the abnormal sound of ball bearings. At present, although our country has also revised the national standard of bearing product vibration quality, developed a "abnormal sound" detector for deep groove ball bearings, and the qualified rate of products without abnormal sound reaches 90%, there are still many problems that have not been solved.

 

1 Characteristics of abnormal bearing sound

The vibration acceleration signal of normal bearing is a zero mean random signal subject to Gaussian distribution. Its RMS can describe the "intensity" of bearing vibration to identify the product quality level The vibration acceleration signal of abnormal acoustic bearing deviates from the Gaussian distribution, and its mean value is also zero, but it contains non periodic or periodic damping ring attenuation oscillation signal with large peak value.

 

Literature uses time-frequency spectrum as the mathematical model of abnormal sound, and uses time, frequency and intensity as three basic parameters and effective value as auxiliary parameters to evaluate.

 

Based on the analysis of one-dimensional single degree of freedom mass elastic damping vibration model, a two-dimensional motion differential equation is used to describe the abnormal vibration of bearings in reference. Its adoption δ As the mathematical model of the impact force that causes abnormal sound, the pulse function discusses the abnormal vibration of the bearing caused by periodic or non periodic impact during the operation of the bearing. The vibration waveform of the theoretical analysis is consistent with that of the actual measurement.

 

2 Detection of abnormal sound

Bearing vibration is closely related to noise, and bearing noise is the result of human auditory perception of its vibration propagation in the air. Although the research results on the correlation between bearing vibration and noise are rarely reported, the relationship diagram between motor noise and Andrew value of vibration measuring instrument provided by Luoyang Bearing Research Institute and NSK Technology Research Institute in Japan in 1998 in China's technical exchange shows that there is a good correlation between bearing vibration and noise.

 

2.1 Determination of abnormal sound evaluation parameters

The determination of abnormal sound detection parameters is the key work for abnormal sound detection, evaluation and control. Through a large number of practical tests, Chinese researchers have statistically analyzed the correlation between the abnormal sound of the bearing and the effective value, peak value and wave crest factor of the vibration, revised the measurement method of rolling bearing vibration, and formulated the technical conditions for the vibration value of deep groove ball bearing and the technical conditions for the vibration wave crest factor of deep groove ball bearing.

 

The early bearing vibration measuring instrument in China can only detect the effective value of vibration, is not sensitive to the pulse wave response of vibration, and can not effectively judge whether there is abnormal sound in the bearing [5]. According to the statistical analysis of a large number of measured data in the literature [6 - 10], the following conclusions are drawn: the error rate of using the effective value of vibration to evaluate the abnormal sound of bearings is high; The peak value of abnormal acoustic bearing vibration is significantly different. Literature  holds that:

(1) The wave crest factor value of bearings with normal quality is 3-5, while that of bearings with abnormal noise can reach 6-10. (2) Pulse counting is very effective for evaluating the influence of mechanical impurities in lubricating grease on bearing vibration. (3) At the same time, the effective value and the maximum peak value (or wave crest factor value) of vibration can be used to identify the abnormal sound of bearing quantitatively. Literatureconsiders that it is possible to misjudge the bearing abnormal sound only by using the effective value or wave crest factor.

 

According to literature, the obvious feature of abnormal acoustic bearing vibration is that the peak value is large, so there is a theoretical basis for taking the peak value as a characteristic parameter of abnormal sound; At the same time, since the wave crest factor is proportional to the peak value and independent of the bearing vibration measurement value, it can also be used as a characteristic parameter of abnormal sound; The kurtosis of normal bearing is close to the standard value 3, while that of abnormal acoustic bearing is greater than 3. Therefore, kurtosis is also taken as an auxiliary characteristic parameter of abnormal sound. However, some studies show that when the defects of bearings are serious, the kurtosis value of their vibration returns to 3, indicating that the kurtosis value cannot be used as an evaluation parameter of bearing abnormal sound alone.

 

It can be seen that the main parameters involved in the current evaluation of abnormal bearing sound include the effective value of vibration, peak value, wave crest factor, kurtosis and pulse counting. The RMS, peak value and wave crest factor are the main parameters used to detect abnormal sound.

 

2.2 Abnormal sound evaluation parameters and detection methods

There are two methods to detect abnormal sound: noise detection method and vibration detection method. Vibration detection method is an indirect detection method for abnormal sound, which can be divided into qualitative detection method and parameter quantitative detection method. Among them, qualitative detection methods include monitoring abnormal sound method and observing vibration waveform method.

 

At present, there are many measuring instruments for measuring abnormal bearing sound, including manual measurement and online automatic measurement.

 

3 Causes and control of abnormal sound

3.1 Causes of abnormal sound

There are many factors that cause the abnormal sound of bearings, which are related to the structural design of bearings, the manufacturing quality of bearing parts, and the service conditions. Most researchers believe that the abnormal noise of bearing is mainly caused by the defects of bearing working surface, impurities in lubricant and improper installation during manufacturing and installation. Some researchers believe that abnormal sound of the bearing is related to improper selection of the design parameters of the bearing structure.

 

3.2 Abnormal sound control

The control of abnormal sound involves the structural design of the bearing, the processing technology of the parts, the assembly technology, the inspection and evaluation of the lubricating medium and the bearing quality. China has made certain achievements in controlling abnormal sound. Summarize the reports of relevant literature, and specific measures to control abnormal sound are as follows:

 

(1) Improve product design level.

At present, most enterprises in the bearing industry generally adopt the unified design drawings from the mid-1970s to the early 1980s. Some products cannot meet the needs of the main engine, so the manufacturer should make corresponding improvements to improve the design level.

(2) Fine manufacturing technology improvement [16 - 19] (as shown in Table 2

).

 

(2) Adopt modern manufacturing automation processing technology and equipment (such as grinding ultra short line and assembly line) to produce high-quality bearings with stable large-scale manufacturing process.

 

(3) Strengthen the detection of abnormal sound.

 

4 Conclusion

The research on the abnormal sound of bearings is a problem in the acoustic field. The current detection methods, whether the sound emitted by the vibrometer speaker, the waveform seen from the oscilloscope, or the calculated abnormal vibration parameters, all originate from the radial vibration signal of the bearing, not the real acoustic effect caused by the bearing vibration through the medium. It can be considered that the research on the abnormal sound of bearings involved at present is essentially to study the abnormal vibration of bearings, and there is no real research on acoustics.

 

At present, there is no scientific and rigorous definition of bearing abnormal sound, so there is no clear standard for judging bearing abnormal sound; Abnormal sound detection is mostly qualitative, which is difficult to detect quantitatively; It is difficult to establish the measurement calibration and quantity value transmission system of bearing abnormal sound.

 

At present, the on-site detection of abnormal sound depends on hearing and seeing. There are many human factors and poor reliability. Therefore, it is necessary to further study the detection method of bearing abnormal sound and develop an automatic detection instrument. The actual measurement shows that the vibration waveform of the abnormal acoustic bearing is significantly different from that of the normal bearing. Therefore, the vibration signal of the bearing can be fully used to separate and extract the components that cause the abnormal sound.

 

In the study of bearing abnormal sound, it should be fully noted that abnormal sound is an acoustic concept. The research of abnormal sound based on bearing vibration needs to consider not only the strength of vibration signal, but also the acoustic characteristics such as frequency and waveform, and also the relationship between bearing vibration and its acoustic effect. Therefore, there is still a lot of work to be done to study the abnormal sound of bearings.

 

More about ITS Deep Groove Ball Bearing:

ITS deep groove ball bearing top quality brand has guaranteed production and highly active management.

 

ITS manufactures a full range of deep groove ball bearings (DGBBs). These versatile bearings are the most common type and serve a wide variety of industries.

Besides radial loads, the bearings can take axial loads in both directions and offer low frictional torque and high-speed components ideal for applications requiring low noise and vibration.

 

In addition to open varieties, these bearings can have steel shields or come pre-lubricated with grease maintained by rubber seals installed on one or both sides. Snap rings are sometimes used on the outside diameter of the outer ring.

 

Cages are generally made of pressed steel, though large bearings and bearings designed for high-speeds may use machined brass cages.

 

Deep Groove Ball Bearing 


2022-10-21

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