Preload and stiffness of FAG super-precision bearing arrangement design and application examples

In practical applications, a large number of different types of spindle bearings are used. The choice of FAG spindle bearing type and arrangement depends on the characteristics of the application: such as turning, milling, grinding, etc. However, operating conditions and economy also play a decisive role in the final selection and technical requirements. In order to achieve high precision requirements (P4 or higher), bearings must generally be run with preload or at least zero clearance. The temperature rise that occurs at maximum speed should be as low as possible (speed index, up to n~dm u003d 2~106 mm/min. with grease lubrication, 3,1~106 mm/min. with oil lubrication) . The above requirements can be achieved by using super-precision bearings and corresponding precision mating parts. The following information can assist in selecting the most suitable bearing and bearing arrangement for an application, including the following: Preload Stiffness Contact angle Rolling element size and material Bearing spacing Sealing Steps in bearing design Bearing arrangement comparison Bearing samples. Preload: Rigid preload bearings are sensitive to changes in temperature difference between the shaft and the housing, especially when the bearing spacing is small. If the floating bearing fails to float in the axial direction, the preload in the bearing set will be greatly increased, and even the internal clearance of the bearing will be completely eliminated; radial stress will also be generated, especially for the spindle bearing with a contact angle of 15. These phenomena occur in cylindrical roller bearings and in sliding-fit spindle bearing sets. In contrast, if elastic preload is used, the bearing set with a contact angle of 25 and a larger bearing spacing is selected to be less sensitive to temperature differences. Generally, ceramic ball bearings operate at a lower temperature, and the temperature rise T in rigid preload systems is smaller than that of steel ball bearings. The speed reduction factor (see table 2) is for use with rigid preloaded bearings. In elastic preloading (by spring or hydraulic pressure), the bearing speed can reach the values u200bu200bin the bearing data table due to the reduced thermal sensitivity. The preload must be at least as high as that of a medium preload bearing (with suffix M) (see bearing data table). Stiffness: The stiffness of the bearing system is affected by the diameter of the shaft, the number of bearings, the size of the bearings, the magnitude of the preload and the contact angle. Although the radial stiffness of the 15 contact angle bearing is 10% higher than that of the 25 contact angle bearing, its axial stiffness is 45% lower. If the whole system of main shaft bearing and cantilever is considered, the radial stiffness of the former is better than that of the latter because the supporting span of the 25 contact angle bearing arrangement is larger than that of the 15 contact angle bearing. Due to the effect of installation, the rigidity of the rigid preloaded bearing after installation is higher than the data in the sample. During operation, due to high-speed centrifugal force and thermal expansion of the shaft and inner ring, the bearing ring expands and the rigidity increases.