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Various factors affecting the life of spindle bearing grease

by:JNSN     2021-12-22
Grease life refers to the time that the bearing can work normally under the condition of proper amount of grease lubrication. Factors that affect life include: Grease amount, grease type, bearing type, speed, temperature, installation, operation, and environmental conditions. In most practical applications of super-precision bearings, the decisive factor for the life of the bearing set is the life of the grease. The impact of bearing fatigue life is relatively small. Can be found in Figure 5. Figure 5 is suitable for high-speed grease. Adverse operating conditions and environmental conditions must be considered in the application, including moisture, vibration, or airflow in the bearing. In variable-speed operation with different durations, the total life of the grease can be calculated by the following formula: Here, qi represents the ratio of working time, and F10i represents the life of the grease at a specific speed in the tachometer. kf u003d 1 for FD, N10 and N19 kf u003d 2 for NN30 NNU49 kf u003d 0.75 for spindle bearings with a contact angle of 15° (C) kf u003d 0.90 for spindle bearings with a contact angle of 25° (E) kf u003d 2.50 is suitable for 2344/2347n u003d speed dm u003d average bearing diameter. Grease distribution and running-in: The first correct operation of a grease-lubricated bearing has a great influence on the performance and service life of the bearing. In order to distribute the grease evenly, it is recommended to perform intermittent start-stop operation. This prevents the contact surface from overheating and causing damage. During the shutdown, the temperature between the bearing components will be balanced and adjusted, so pre-load damage will not be caused. We recommend installing a temperature sensor as close as possible to the outer ring of the bearing to monitor the temperature changes during the grease running-in and subsequent continuous operation. In any case, it is necessary to avoid continuous temperature rise due to excessive preload. Grease running-in is completed when the bearing temperature is stable. The running-in process should initially be started and stopped under the condition of halving the maximum speed. Figure 6 recommends the grease running-in process for open and sealed spindle bearings. Grease consumption table 4 and grease running-in process chart 6 are equipped with plastic shrink packaging cards made in DIN A5 format for workshop use. The running-in process includes several start-stop operations performed at different speeds and durations. The pause time after each run is particularly important. The required number of start-stop operation cycles depends on the bearing size, number of bearings, limit speed and bearing environment and other factors. If necessary, start and stop operations with longer running time and shorter pause time should be carried out until the temperature stabilizes. Minimal oil lubrication: spindle bearings require only a small amount of lubricating oil. If all rolling and sliding contact surfaces are immersed in oil, the amount of oil required is about 100mm3/h. Minimal oil lubrication can minimize frictional power loss. When the spindle speed exceeds the speed range under grease lubrication, oil lubrication can be used. Today's standard lubrication method is oil-air lubrication. The bearing table lists the limit speeds that can be achieved with the least amount of oil lubrication. Lubricants that meet the ISO VG68 + EP standard have a nominal viscosity of 68 mm2/s at 40°C and contain an appropriate amount of extreme pressure additives. Practice has proved very suitable. Figure 7 shows the guideline value of the oil volume when the minimum oil volume is used for lubrication. However, the flow of lubricating oil inside the bearing has a great influence on the amount of oil required.
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