Speed, stiffness and deformation of FAG super-precision bearings

The rotational speed that can be achieved with any bearing arrangement depends on the proper fit between the elements, balancing the overall energy. The number of bearings, their location, internal stress (clearance or preload), external stress as well as lubrication and heat dissipation are all decisive factors. The attainable speeds given in the bearing tables are guidelines and can be higher or lower, depending on the above-mentioned conditions. The limiting speed given in the FAG spindle bearing table is the speed capability of a single bearing under elastic preload. These speeds cannot be reached with rigidly preloaded bearings, bearing pairs or bearing sets. Its deceleration coefficient is shown in Figure 14. Cylindrical roller bearings For cylindrical roller bearings, the maximum speed is obtained by adjusting the radial clearance. Instructions are included in the Installation Instructions section, see Table 8 on page 210. Deformation and stiffness Bearing set stiffness depends on bearing arrangement and preload. The stiffness of the overall system of the machine tool depends more on the stiffness of the shaft and the bearing seat than the bearing stiffness. Axial stiffness ca Axial stiffness is the ratio of axial load to axial displacement. ca u003d Fa/aca u003d Axial stiffness [N/μm]Fa u003d Axial load [N]a u003d Axial displacement [μm] Unloading force KaE If a bearing set is subjected to an axial force through the shaft, the bearing is loaded Deformation will occur when the contact angle direction is opposite to the load direction and the bearing installed in the opposite direction will be unloaded. The unloading force KaE is defined as the axial force that reduces the preload of the bearing set to the unloaded condition through the center of the bearing. The displacement of the bearing set of the spindle bearing is almost proportional to the unloading force that the bearing bears. The axial stiffness ca given in the bearing tables applies to bearing sets arranged back-to-back or face-to-face. The radial stiffness cr can be estimated from the axial stiffness. cr 6 ca here u003d 15cr 2 ca here u003d 25 For bearing sets with more than two bearings, the stiffness value and load capacity increase. Figure 15 shows the approximate values u200bu200bof axial stiffness and bearing capacity under axial load on the shaft. The radial stiffness of a bearing set subjected to a radial center load can be estimated from Figure 16. For double-directional angular contact thrust ball bearings of the 2344.. series, the axial stiffness values u200bu200bca given in the bearing tables apply if the axial force on the bearing does not exceed 2.2% of the bearing dynamic load rating C.