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Lubricant viscosity and lubrication method of spindle bearing

by:JNSN     2021-12-24
Lubrication must be obtained: Sufficient spindle bearing life, wear-free operation and low vibration An important prerequisite is the formation of a lubricating oil film in the contact area that separates the rolling elements from each other. In order to achieve this, it is necessary to ensure that there is a certain amount of lubricant at each contact point. To meet the speed requirements, choose the right lubrication method and choose the right lubricant. Lubricant viscosity The condition of the lubricant film depends on the viscosity ratio κ, which is the ratio of the working viscosity ν to the reference viscosity ν1. The reference viscosity ν1 is a function of bearing size and speed, which can be found in Figure 1. The working viscosity is the actual viscosity of the lubricant during operation. It is a function of the operating temperature and the viscosity of the lubricant base oil and can be found in Figure 2. Grease lubrication needs to consider the base oil viscosity. The viscosity of the lubricant at operating temperature should be at least twice the reference viscosity, that is, κ u003d ν/ν12. Too high a viscosity ratio will not improve the lubricating oil film more, but will increase friction. Lubrication method The choice of lubrication method should be based on the maximum operating speed to be achieved by the bearing. The data sheet in this catalog gives the limiting speed of the two most important lubrication methods (grease lubrication and oil lubrication) of super-precision bearings. The allowable speed of a bearing set with a rigid preload arrangement can be multiplied by a reduction factor by the limit speed of a single bearing, see Figure 14. Most super-precision bearings use grease lubrication. The main advantages of grease lubrication include: low friction, lifetime lubrication, simple design, low system cost. If the spindle speed exceeds the limit speed of bearing grease lubrication, the least amount of oil can be used for lubrication. When the high speed index lasts for a long time, it makes sense to use the least amount of oil for lubrication, so that a guaranteed lubricant service life can be obtained. In some cases, grease lubrication can also meet the speed requirements, but since the service life of the grease (Figure 5) decreases with the increase in speed, in this case, it is more appropriate to use the least amount of oil lubrication. Lubricating greases and bearings are being researched at a rapid pace, and all aspects of performance have been significantly improved, especially the increase in speed. Now the speed index n · dm can reach 2 000 000 mm.r/min. The use of primary-installed life-long grease and seals for spindle bearings has more advantages, such as effectively preventing pollution and ensuring cleanliness inside the bearing. In addition, installation is easier. The grease suitable for super-precision bearings is shown in Table 3. ARCANOL L075 is a high-performance grease that is widely used in spindle bearings with outer ring constant temperature at high speed and no more than 80°C. Due to the effect of liquid cooling, it is difficult for the temperature of the electric spindle to rise to 80°C. L075 has become the standard grease for spindle bearings. ARCANOL L210 is another high-speed grease. Because of its high base oil viscosity, it can be used in occasions where the temperature exceeds 80°C and can reach 100°C. ARCANOL L055 is a high-load grease, which is most commonly used in the configuration of ball screw-driven shaft end bearings, turntable bearings, and lathe tailstock central bearings. Practice has proven to be very effective. Grease Addition Different types of bearings require different amounts of grease. The recommended values u200bu200bgiven in Table 4 are not affected by the rotating elements, but mainly depend on the bearing volume. Information on grease lubrication can be found in the installation instructions section (see page 204).
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