Speed, stiffness and deformation of super-precision bearings
The speed that any kind of bearing configuration can obtain depends on the proper cooperation between the components to balance the overall energy. The number of bearings, position, internal stress (clearance or preload), external stress, lubrication and heat dissipation are all decisive factors. The achievable speed given in the bearing table is a reference value and can be higher or lower, depending on the above working conditions. The limit speed given in the spindle bearing bearing table is the speed capability of a single bearing under elastic preload. Rigidly preloaded bearings, bearing pairs or bearing sets cannot reach these speeds. The deceleration factor is shown in Figure 14. Cylindrical roller bearings For cylindrical roller bearings, the maximum speed is obtained by adjusting the radial clearance. There are related instructions in the installation instructions, see Table 8 on page 210. Deformation and stiffness The stiffness of the bearing set depends on the arrangement and preload of the bearing. In addition to the rigidity of the bearing, the rigidity of the overall system of the machine tool depends more on the rigidity of the shaft and the bearing seat. Axial stiffness ca Axial stiffness is the ratio of axial load to axial displacement. ca u003d Fa/δaca u003d Axial stiffness [N/μm] Fa u003d Axial load [N] δa u003d Axial displacement [μm] Unloading force KaE If a bearing group bears the axial force passing through the axis, then the bearing is loaded Deformation occurs 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 group to the unloaded condition through the bearing center. The displacement of the spindle bearing bearing group is almost proportional to the unloading force borne by the bearing. The axial stiffness ca given in the bearing table 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 where α u003d 15°cr 2 · ca where α u003d 25° For bearing groups with more than two bearings, the stiffness value and load capacity will increase. Figure 15 shows the approximate values u200bu200bof the axial stiffness and bearing capacity under the axial load of the shaft. The radial stiffness of the bearing group subjected to the radial center load can be estimated according to Figure 16. For the 2344.. series of double-direction angular contact thrust ball bearings, if the bearing's axial force does not exceed 2.2% of the bearing's rated dynamic load C, the axial stiffness value ca given in the bearing table applies.