Super-precision bearings must be able to withstand loads at extremely high speeds with high precision. They are selected based on the following factors: Accuracy Rigidity Running performance These performances can only be achieved if there is no wear over the entire life cycle. This depends on the formation of a hydrodynamic lubricant film in the rolling contact area. Under these conditions, rolling bearings reach their maximum life in various applications. But this reliable life is usually limited by the life of the lubricant (as shown in 5). In this respect, the Hertzian stress at the contact point and the dynamic behavior of the bearing play a decisive role. It is best to determine the arrangement of each bearing with the aid of a special calculation program, especially for high-performance bearing units. In practice, since super-precision bearings will not fail due to fatigue, it is no longer appropriate to determine the service life of bearings based on the rated life L10 calculated by DIN ISO 281. Bearing load static load For super precision bearings, the static load, ie the load when the bearing is not rotating, is rarely checked. The stress factor fs used to measure the static load can be obtained from the following formula: fs u003d C0/P0fs u003d static stress factor C0 u003d static load rating [kN] P0 u003d equivalent static load [kN] The equivalent static load is based on the axial and Radial loads are calculated (shown below). When there are several bearings on the shaft, the distribution of the external load on a single bearing is shown in Figure 8. In each case, the load-carrying capacity of the bearing bearing the highest load needs to be checked. Spindle bearing contact angle u003d 15P0 u003d Fr [kN] when Fa/Fr 1.09P0 u003d 0.5 Fr + 0.46 Fa [kN] when Fa/Fr 1.09 Contact angle u003d 25P0 u003d Fr [kN] when Fa/Fr 1.31P0 u003d 0.5 Fr + 0.38 Fa [ kN ] Axial and radial forces calculated from external loads when Fa/Fr 1.31 bearings are in contact with each other or positioned with spacers. In order to ensure the accuracy of the bearing, the static stress index should be greater than 3.0. The fs 1 can only be used in hybrid ball bearings for very short periods of time and under a central axial load (unloading force). Two-way angular contact thrust ball bearing P0 u003d Fa stress factor should be higher than 2.5. Floating displacement bearings and cylindrical roller bearings P0 u003d Fr static stress factor should be higher than 3.0. Durability Strength To test the durability strength, the static stress coefficient fs* u003d C0/P0*P0* can be calculated according to the following formula, which can be calculated using the equivalent static load formula; just use the same dynamic load as the equivalent load for calculation. The stress factor is used to determine whether the bearing will fail under specific application conditions. If the factor fs* 8, the bearing is considered to have infinite life. It is more accurate to use a calculation program to calculate the Hertzian contact stress and to check the dynamic properties of the bearing (see appendix, p. 226). In the case of conditions with a continuous lubricating oil film (κ 2) and very high cleanliness, no rating life calculation is required. The cleanliness level of the oil is the basis for evaluating whether circulating particles can reduce bearing life and can be determined by lubricating oil samples provided by filter manufacturers and academic institutions. The required level of cleanliness has been achieved if the entire amount of oil can flow through the filter within a few minutes. To ensure a very high degree of cleanliness, the bearing must be cleaned before running. For example, a filtration ratio of β3 200 means that in what is commonly referred to as a multiple filtration test, only 1 in 200 particles with a diameter of 3 μm will pass through the filter. To avoid damage to other components of the lubricating oil circulation system, filters larger than β3 75 should not be used. If the above conditions are not fulfilled, the corrected life calculated by hand according to DIN ISO 281 appendix 1 or by a computer-aided program according to DIN ISO 281 appendix 4 can be used to evaluate the effect of lubrication and contamination on the bearing life. Cleanliness is very important for precision bearings, because for general light-loaded bearings, cleanliness has a great impact on service life, and contamination can increase wear. Reference values u200bu200bfor lubricant cleanliness for oil lubricated bearings are taken from the hydraulic field and can be obtained from Table 9. In practice, extreme cleanliness is guaranteed if the bearings are greased and sealed by the manufacturer. The inner and outer rings of super-precision bearings with operating temperature can ensure geometric stability when the temperature is not higher than 150 C. If this value is not exceeded, the effect of temperature on material properties does not need to be considered. Attention must be paid to cage, seal and lubricant limit temperatures (see table 10). For applications of super-precision bearings at higher temperatures, please consult Schaeffler Group Industrial Applications.