Common faults of rolling bearings and their vibration signal characteristics

Abstract: Bearing is one of the key components of mechanical equipment. Bearing damage will directly affect the normal operation and production efficiency of equipment. This paper analyzes the causes and forms of common faults of bearings, and summarizes the fault detection methods and vibration signal characteristics of bearings.

Keywords: bearing fault vibration signal

China Library Classification Number: TH 133 Document Identification Number: A Document Number:1672-3791(2012) 06 (c)-0085-02.

Timely maintenance and replacement of key components of the system can, to a certain extent, avoid the economic loss and personal injury caused by system failure caused by the damage of key components during system work. Rolling bearing is the key component of rotating machinery, and its running state directly determines the efficiency and safety of rotating components. This paper summarizes the common fault types of rolling bearings and bearing fault detection methods, and analyzes the characteristics of bearing vibration signals. This paper provides reference for bearing fault diagnosis and equipment maintenance, and is helpful to predict the causes and types of bearing faults in advance.

Failure form and cause analysis of 1 bearing

During the working process of rolling bearings, improper assembly, insufficient lubrication, foreign body intrusion or overload operation may cause bearing damage, or overload operation may cause bearing damage, or fatigue peeling or natural wear after long-term work may lead to system failure. Common bearing faults can be classified into two categories: damage and wear. Common damage faults include fatigue spalling, plastic deformation, bearing burn, corrosion, fracture and gluing. Wear failure is a progressive failure caused by long-term normal operation of bearings.

1. 1 fatigue spalling

The typical failure mode of rolling bearing is simple fatigue spalling of rolling contact. When working, the contact surface of bearing roller and raceway rolls relatively and presses each other at the same time. Coupled with the effect of periodic alternating load, after long-term work, the contact surface of bearing parts will produce small peeling pits, which will eventually develop into large-scale peeling, called fatigue peeling. .

1.2 plastic deformation

When the working load is too heavy, uneven pits are formed on the surface of bearing raceway due to the excessive impact force and static load borne by rolling bearings, which mainly occurs on bearings rotating at low speed. In addition, the additional load caused by thermal deformation may also cause plastic deformation of the bearing [1].

1.3 fracture

Excessive load is the main reason for the fracture of bearing internal parts. In addition, excessive thermal stress caused by friction will also cause the fracture of bearing parts.

1.4 Bearing burn

When the bearing assembly has large deflection, it is easy to cause the bearing temperature to rise and the bearing to burn. In addition, poor bearing lubrication, unqualified or deteriorated lubricating oil, and too tight assembly will all cause bearing burns. Designers lack consideration of thermal expansion in assembly design, which leads to smaller and smaller clearance during operation and also causes bearing burn. The raceway and rolling body of the burned bearing are tempered.

1.5 corrosion

Causes of bearing corrosion caused by moisture intrusion. When the bearing works, its temperature is higher than the ambient temperature. When the bearing stops working, the bearing temperature drops, and the moisture in the air is easy to condense on the bearing surface. Failure to clean in time will lead to bearing rust. Due to improper protection, water directly enters the bearing, which is also the cause of bearing corrosion.

1.6 gluing

Under the condition of high speed, high load and lack of lubrication, the heat generated by friction can make the bearing parts heat up rapidly, and when it reaches a certain temperature, the metal surfaces contacted by the bearing parts can adhere to each other. This phenomenon is called gluing.

In the working process of worn bearing, the extrusion force generated by the relative movement of bearing roller and raceway and impurities invading bearing raceway will cause the surface wear of bearing, and poor lubrication will accelerate the surface wear. Wear will increase the clearance of the rolling bearing, increase the roughness of the working surface of the bearing and reduce the running accuracy, which will lead to the decrease of the working accuracy of the rotating system and the increase of the working noise.

2 Common fault detection methods for rolling bearings

2. 1 oil sample analysis method

By extracting and analyzing the size and shape of metal particles in bearing lubricating oil, the cause and position of particles are judged, so as to judge the running state of bearings. This method is limited to oil-lubricated bearings, which is greatly influenced by the environment, such as external metal chips splashing into bearing lubricating oil.

2.2 Temperature monitoring method

By monitoring the temperature of the parts near the bearing, such as the temperature of the bearing seat or box, observe whether the bearing operates normally. Temperature monitoring is very sensitive to excessive temperature caused by bearing overload and poor lubrication, and is often used in alarm systems.

The acoustic emission method will make a sound when the rolling bearing passes through the peeling position, which is periodic. The fault type and location can be judged by analyzing the detection period.

2.3 Vibration method

The vibration sensor collects the vibration signal of the rolling bearing, and processes and analyzes the signal. According to the obtained signal characteristics, the type and location of bearing fault are judged. Vibration method is suitable for rolling bearings under various working conditions. The testing and processing of vibration signals are simple and intuitive, and the bearing fault diagnosis results are reliable.

In addition, there are some methods to judge the working state of bearings through experience. When the equipment is running, it is normal to touch the bearing bush by hand, and its temperature sense is not hot. On the contrary, the bearing temperature is too high. Periodic impact sound indicates that the bearing has peeling dents, and harsh chirp sound indicates that the bearing is not lubricated enough or the rolling parts are assembled too tightly.

3 Characteristics of vibration signals of faulty bearings

According to the characteristics of bearing vibration signal, the failure forms can generally be divided into surface damage and wear damage. See table 1 for the main characteristic frequencies generated during bearing operation.

3. 1 Surface damage fault

When the damage point rolls over the surface of the bearing element, it will produce an impact pulse force in the form of a sudden broadband signal, which will make the high-frequency vibration frequency of the bearing system resonate, thus generating impact vibration. This is one of the basic characteristics of damage fault vibration signal, and the fault characteristic frequency is generally below 2kHz.

Damage of bearing inner ring: When the bearing inner ring is damaged, if the rolling bearing has no radial clearance, it will produce impact vibration with the frequency of nf6. Usually, rolling bearings have radial clearance and are loaded unilaterally. Because the contact position between the damaged part and the rolling element is different, the vibration amplitude will change periodically, that is, amplitude modulation will occur. If it is modulated by shaft frequency, its vibration frequency is.

Damage of bearing outer ring: Damage of bearing outer ring will also produce impact vibration. The vibration frequency is.

Roller damage: when the roller is damaged, the defective part will generate impact vibration when passing through the raceway surface, and it will be modulated with revolution frequency, and its vibration frequency is.

3.2 Failure related to wear

Wear failure is a progressive failure of bearings after long-term work. The vibration signal produced by the wear of bearing working surface has the same properties as that of normal bearing, and the waveforms of both are regular. However, the vibration signal amplitude of worn bearing is obviously higher than that of normal bearing, which is the basic feature that the vibration signal of worn bearing is different from that of normal bearing.

4 conclusion

There are many kinds of rolling bearing faults. In this paper, the reasons and types are classified and summarized, which is helpful to diagnose bearing faults in time and take reasonable treatment methods. After collecting and analyzing the vibration signal of the bearing, the fault position of the bearing can be diagnosed according to the characteristics of the obtained vibration signal, and with the assistance of the real-time signal processing system, it is easy to realize real-time monitoring of the bearing state.

refer to

[1] Fault analysis and discussion of rolling bearing [M]. Internal combustion engine parts, 2000(3).

[2] Fault analysis, inspection and maintenance of rolling bearings [J]. Science and technology communication, 20 10.5 (1).