Author: Li Binbin, et al.
As the bearing speed increases, problems such as increased friction and heat generation in the bearing, slippage of the cage and rolling elements, damage to the rolling surface, cage stability, and reduced fatigue life will occur. For bearing condition monitoring, speed, load, temperature rise, vibration, and lubrication are all important functional parameters. Among them, if the temperature (temperature rise) of the bearing can be accurately measured under different working conditions, it will be helpful to evaluate the operating status and performance of high-speed rotating bearings.
Different temperature measurement and testing methods can be selected based on factors such as range accuracy, sensitivity, life, size, cost, reliability and measurement feasibility required to measure bearing temperature. The following focuses on the introduction of high-speed rotating bearing temperature measurement technologies such as thermocouple temperature measurement method, infrared radiation temperature measurement method, fiber Bragg grating sensor temperature measurement method, and LC electronic oscillation temperature measurement method 4.
1 Thermocouple temperature measurement
The thermocouple temperature measurement method is a contact temperature measurement method that uses the principle of the thermoelectric effect to convert the temperature signal into a thermoelectromotive force signal. Thermocouples have the advantages of simple structure, high temperature measurement accuracy, easy remote measurement and control, and low price. They are currently a widely used temperature measurement method in the field of bearing temperature measurement. However, the thermocouple temperature measurement method is a point temperature measurement method and cannot reflect changes in regional temperature distribution, which has certain limitations.
Installation of thermocouples (oil film bearings)
2 Infrared radiation thermometry
Infrared radiation thermometry is a temperature measurement method based on the fact that all objects with temperatures higher than thermodynamic zero have the characteristic of radiating energy outward in the form of electromagnetic waves. Based on the temperature effect of infrared light, Planck's distribution law is used to convert infrared light into digital signals. The infrared radiation temperature measurement method is safe, fast, reliable and convenient. It is a non-contact temperature measurement method and can obtain the dynamic change characteristics of the bearing temperature during the bearing operation.
As shown in the figure below, a miniaturized, low-power infrared temperature sensor and vibration signal sensor are integrated into the outer ring of the bearing. The sensor module is bonded to the bearing to be monitored with epoxy resin. The probe of the infrared temperature sensor is aligned with the inner ring of the bearing to measure the temperature of the inner ring of the bearing and realize real-time intelligent monitoring of the operating status of the bearing.
Integration of bearings and sensors
Wave-based measurement methods include: Surface Acoustic Wave (SAW), which is a sound wave that propagates along the solid surface and is an elastic wave whose energy is concentrated near the solid surface. The propagation speed of surface acoustic waves is much slower than that of electromagnetic waves. Therefore, it is easy to sample and convert signals along the propagation path of surface acoustic waves. Using this feature, surface acoustic waves can be used to simulate various functions of electronics.
Measurement principle
Comparison between wireless temperature measurement system and traditional temperature measurement method
The literature [5] establishes a multispectral temperature measurement method. Establish a thermodynamic model of high-speed bearings based on the Palmgren model, use the principle of radiation heat transfer to analyze the influence mechanism of high-speed bearing thermal radiation sources and background thermal radiation sources respectively, and use the graphical method to solve the angular coefficient of the background thermal radiation source on the bearing being measured, thereby establishing a multi-spectral temperature measurement model of the bearing and realizing the measurement of bearing temperature rise.
3 Fiber Bragg Grating Sensor Temperature Measurement Method
The fiber Bragg grating sensor temperature measurement method uses the photosensitive properties of optical fiber materials to cause the refractive index of the optical fiber to undergo periodic or non-periodic permanent changes along the axial direction, forming a spatial phase grating in the fiber core. The fiber grating temperature measurement method has the characteristics of small size, light weight, no electromagnetic interference, high sensitivity, corrosion resistance, and long transmission distance.
Fiber Bragg Grating Sensor Layout
4 LC Electronic Oscillation Thermometry
The LC electronic oscillation temperature measurement method is a temperature measurement method that uses an LC sensor composed of fully passive components and temperature-sensitive materials to convert the measured temperature into the resonant frequency of the LC resonant circuit for measurement. This temperature measurement method no longer relies on various line signals and can be applied to bearing temperature measurement in complex and harsh working environments.
Installation of temperature sensor on ball bearing
(No battery, wireless sensing technology)
Summary
(1) The thermocouple temperature measurement method is relatively mature, with simple structure, high temperature measurement accuracy, easy remote measurement and control, low price, and is widely used in the field of bearing temperature measurement. However, thermocouple temperature measurement can only reflect the temperature of the monitoring point, but cannot study the regional temperature distribution of the bearing, and the dynamic temperature measurement accuracy of thermocouples is not high.
(2) As a non-contact temperature measurement method, infrared radiation thermometry can reflect the temperature distribution of bearings and monitor dynamic characteristics. However, the infrared radiation temperature measurement method is susceptible to interference from environmental background radiation, resulting in low temperature measurement accuracy. It is necessary to compensate and correct the bearing infrared temperature measurement results.
(3) Fiber Bragg grating sensor temperature measurement method, as a temperature measurement method for passive sensitive components, has the characteristics of small size, light weight, large measurement range, high sensitivity, explosion-proof, flame-proof, and anti-electromagnetic interference. However, fiber Bragg grating sensors are expensive, and the reliability of bearing temperature measurements in harsh environments with high temperatures and high rotational speeds needs further verification.
(4) The LC electronic oscillation temperature measurement method is based on the characteristics of passive devices and can be used to measure bearing temperature in harsh working environments. However, further breakthroughs are needed for accurate measurement of bearing temperature in ultra-high rotation speed environments.
(5) The development of accurate measurement technology for bearing temperature under ultra-high-speed rotation conditions such as aerospace engines will be one of the key research directions that require breakthroughs in the field of bearing temperature measurement. The recent CdTe quantum dot temperature sensor is theoretically not limited by the bearing speed and has been successfully used to monitor the temperature of bearings at ultra-high rotation speeds 15 000 r/min. It is expected to have good development potential in the field of bearing temperature measurement under ultra-high-speed rotation conditions such as aerospace engines.
References:
[1] Li Binbin, Kou Zhihai, Guo Yuhang. Review of Temperature Measurement Technologies for High-Speed Rotating Bearings [J]. Technology Innovation and Application, 2022, 12(20):160-164. DOI:10.19981/j.CN23-1581/G3.2022.20.038. [2] Li Yi. Application of Surface Acoustic Wave Technology to Compressor Bearing Temperature Measurement [J]. Control and Instruments in Chemical Industry, 2022, 49(02):246-249.
[3] Xie Hui, Ma Mingfei. Temperature measurement method of rolling bearing micro-contact area based on medium-wave infrared technology [J]. Measurement and testing technology, 2022, 49 (04) :45-47.DOI:10.15988/j.cnki.1004-6941.2022.4.014.
[4] Li Yanchao, Yang Binghua, Liu Huan, Man Weiwei. Rolling bearing temperature field measurement system based on infrared technology [J]. Bearings, 2020(09):63-66.DOI:10.19533/j.issn1000-3762.2020.09.013.
[5] Wu Hongmei, Jia Ning. High-speed bearing temperature measurement method based on multi-spectral radiation [J]. Instrument technology and sensors, 2018 (12): 96-100.
[6] Su Qi. Research on bearing temperature measurement based on fiber Bragg grating sensing [D]. Hebei Science and Technology Normal University, 2018.
[7]CHEN J，ZHANG W，WANG H. Intelligent bearing structure and temperature field analysis based on finite element simulation for sustainable and green manufacturing [J]. Journal of Intelligent Manufacturing，2021，32（3）：745-756.
Source: Bearing Magazine
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