Why do bearings experience high temperatures?

Thread Content

Through measurement, if it is found that the operating temperature of the bearing exceeds the allowable value (such as 95°C) or is rising rapidly, further measures and analyses should be carried out to identify the cause and address it. Below, the motor is used as an example to explain the reasons for the high temperature. 1) The bearing has poor quality or was damaged during transportation and handling prior to operation. The deepest indentation in the axial middle section of the inner and outer raceways of the NU-type roller bearing shown in Figure 1a was caused by the bumpy road conditions during transportation, which led to the rotor moving up and down and thus causing the bearing rollers to impact the outer raceway of the bearing. With this type of damage, a rhythmic \"clang, clang\" sound can be heard from the bearings while the motor is running. 2) The coaxiality between the bearing and the shaft or bearing housing does not meet the requirements, as shown in Figure 1b. 3) The outer ring of one of the end bearings, which should be able to move axially, is pressed down by the bearing cover, as shown in Figure 1c. When the rotating shaft expands due to rising temperature, it causes the inner ring of the bearing to move away from its original axial position, thereby compressing the raceways where the balls roll and generating more heat. 4) The bearing is too tightly fitted to the shaft or bearing housing, causing the inner or outer ring of the bearing to be compressed and deformed; this reduces the radial clearance, makes rolling difficult, and generates more heat, as shown in Figure 1d. 5) The bearing is too loosely fitted to the shaft or bearing housing, causing the inner ring of the bearing to slide rapidly on the shaft and the outer ring to slide rapidly within the bearing housing (sliding of the inner ring is absolutely not allowed, while slow sliding of the outer ring is generally harmless), as shown in Figure 1e. This friction generates a large amount of heat, causing a sharp rise in temperature; in severe cases, it can damage the bearings in a very short time, leading to serious accidents such as contact between the stator and rotor and winding overcurrent that results in burnout. 6) Excessive, insufficient, or deteriorated grease. In the bearing housing structure with an oil baffle (see Figure 2c), if grease is not replenished in a timely manner, a gradual shortage of grease will occur. Furthermore, using high-temperature-resistant grease at low temperatures generates relatively more heat due to its higher viscosity. 7) Dust in the environment enters the bearings through the gap between the bearing cover and the shaft, which can significantly reduce the lubricating effect of the grease, increase frictional resistance, and generate more heat, as shown in Figure 1f. 8) Overheating of the rotor due to various reasons causes heat from the rotor to be transferred to the bearings, raising the temperature of the lubricant in those bearings to its dripping point; as a result, the lubricant turns into a liquid and is lost, leaving the bearings without lubrication and generating excessive heat