Some knowledge about bearing temperature

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Friction: Under the action of an external force, when one object moves relative to another or tends to move, the tangential resistance that arises at the contact surface between the two objects and hinders their movement is called friction. This phenomenon, in which motion is hindered and energy is consumed in the area where two objects come into contact, is called friction. Based on the lubrication condition between the surfaces of the friction pair, friction states are classified into: dry friction, fluid friction, boundary friction, and mixed friction. Friction can be divided into sliding friction and rolling friction. Wear: Friction between moving parts leads to the gradual loss of material from the surface of those parts; this phenomenon is known as wear. Wear and tear can reduce a machine’s efficiency and reliability, affect product quality; in severe cases, it can even lead to the machine becoming unusable, forcing it to stop operating or shutting down the entire production line. This results in lost production time, delays in delivery dates, and even serious safety incidents, so we must treat this issue with caution. Reasons for high bearing temperature: a poor working environment, with excessive dust accumulation that hinders heat dissipation. High impurities in the lubricant cause it to lose its original lubricating properties, leading to difficulties in lubrication and excessive frictional heating. Overloaded operation. Oiling (the height is too high); insufficient clearance. Low oil level. The bearing is severely worn or damaged. The coupling is not aligned (not centered), resulting in high friction from the oil seal. What is the maximum temperature that a standard roller bearing can withstand? 1. When it comes to the high temperatures that ordinary roller bearings can withstand, their heat resistance is related to the tempering temperature of the bearings: if the bearing rings are tempered at 200°C, the operating temperature can reach 150°C; if they are tempered at 250°C, the operating temperature can reach 200°C; if they are tempered at 300°C, the operating temperature can reach 250°C; and if they are tempered at 350°C, the operating temperature can reach 300°C. 2. In practical use, taking into account the loss of lubricant and the play in the bearings, the temperature rise is generally kept around 40 degrees, with a maximum recommended temperature of no more than 80 degrees. The inspection of bearings mainly includes the following points: (1) The quality of the bearings. During the disassembly of the bearing housing, it is first necessary to check whether the lubricating grease is deteriorated, caked, contaminated, or otherwise defective; this serves as an important indicator for determining the cause of bearing damage. Secondly, check whether the bearing is damaged or worn; examine the surface finish of the inner and outer rings, rolling elements, and cage of the bearing, as well as look for any defects such as cracks, rust, peeling, dents, or discoloration due to overheating. Measure the bearing’s clearance to ensure it is within acceptable limits; also check the shaft sleeve for wear, dents, or peeling. If any of these issues are present, a new bearing should be installed. 　　(2) Bearing fit 　　When installing bearings, it is very important that there be a proper fit between the inner diameter of the bearing and the shaft, as well as between the outer diameter and the housing. If the fit is too loose, relative sliding occurs at the contact surfaces, a phenomenon known as creep. Once creep occurs, it will wear the mating surfaces, damage the shaft or housing, and the wear particles will enter the bearing, causing heating, vibration, and damage. When the interference is too large, it causes the outer diameter of the outer ring to decrease or the inner diameter of the inner ring to increase, thereby reducing the internal clearance of the bearing. To select a suitable combination for the intended purpose, various factors such as the nature and magnitude of the bearing load, temperature conditions, and the rotational states of the inner and outer rings must be taken into consideration. 　　(3) Adjustment of the clearances between various parts of the bearing 　 When the bearing clearances are too small, excessive shear friction losses due to the grease present in those clearances can also cause the bearing to overheat. Additionally, when the clearances are too small, the amount of oil available decreases, and it is not sufficient to remove the heat generated by friction, which further increases the bearing’s temperature. However, if the clearance is too large, it will alter the dynamic characteristics of the bearing, causing unstable rotation of the rotor. Therefore, it is necessary to select the appropriate bearing clearance based on different equipment and operating conditions. Unit #8 of Guohua Taicang had a persistent issue of high bearing temperatures during its operation; during the Unit C-level maintenance in 2008, a thorough inspection was carried out to address this problem. The inspection revealed that the bearing lubrication, the static balance of the impeller, and the alignment of the coupling were all normal; therefore, the focus of the investigation was shifted to the clearances in various parts of the bearing. Measurement showed that the bearing thrust clearance was only 0.07 mm; it was analyzed that the low thrust clearance was the cause of the high bearing temperature. A grinder was used to grind the partition ring in the thrust bearing by 0.07–0.08 mm, thereby increasing the thrust clearance; this raised the bearing’s thrust clearance to 0.14–0.15 mm. The bearing temperature remained normal during operation, and the defects that had persisted for a long time were completely eliminated, ensuring the safe and stable operation of the equipment. The bearing of the induced draft fan in Unit #1 of Yunnan Phosphorus Power has experienced persistently high temperatures, ranging from 80 to 90°C, which has **reduced** the bearing’s service life; multiple replacements of the bearing have failed to resolve the issue. During the Class C maintenance in 2008, it was found that the gap between the shaft and the shaft seal on the end cover was too small. During cold-state testing, the bearing temperature was normal; however, when the unit was operating under hot conditions, the shaft expanded due to heat, resulting in friction with the shaft seal on the end cover. Analyzing this as the reason for the persistently high bearing temperature, the end cover holes were turned by 0.5 mm, increasing the clearance between the shaft and the end cover seal by 0.25 mm, thereby preventing friction between them due to the shaft’s thermal expansion during operation. After the treatment, the problem of excessively high bearing temperatures was fundamentally resolved; the bearing temperatures remained normal during both cold and hot operation, and there was no oil leakage from the bearing housing. This ensured favorable operating conditions for the bearings, reduced the frequency of replacement, and saved on maintenance costs.