Selection and Sealing of Optimum Bearing Spacing for FAG Super Precision Spindle Bearings

Choosing the best bearing spacing If the structure allows, it is recommended to choose a bearing arrangement with a suitable spacing under rigid preload. The radial and axial thermal expansion of the shaft can be compensated by preloading. For a spindle bearing with a contact angle of 25, the most suitable bearing spacing L is about 3 times the shaft diameter d; and for a bearing with a contact angle of 15, it is about 5 times the shaft diameter d. However, the advantage of the above design is questioned because the long bearing spacing makes the axial thermal expansion of the shaft less effective. Therefore, these designs are relatively rare in practical applications. Sealing: Spindle bearings, especially at the ends of the spindle, must be effectively sealed. The non-contact labyrinth seal with dust cover has a compact radial clearance (h8/C9), a wide axial clearance (gap width 3 mm) and drain holes, which enable the bearing to operate and not operate Effective isolation of cutting fluid, metal chips and dust. Sealed grease lubricated bearings enhance the labyrinth seal and prevent air flow in the bearing arrangement. Bearing Arrangement Design Steps To design the spindle bearing arrangement, the following steps must be followed: 1. Determine the operating conditions (speed, load, continuous operation time, spacing, diameter, temperature, ambient environment) 2. Select the bearing arrangement according to the application and requirements (see table 6) 3. Determine lubrication (see Lubrication chapter, page 176) 4. Select bearing type and size based on speed (see Speed u200bu200bchapter, page 189), mounting space and lubrication 5. Check grease life (see Lubrication Table 5 in chapter, page 180) 6. Calculate the load distribution on the bearing 7. Check the maximum service life of the bearing arrangement (see chapter on life calculation). If a calculation program is available, the following steps can be followed: 8. Calculate the bearing kinematics (rotation/roll ratio, ball drift motion) and contact pressure (P0), and compare with the design limit values u200bu200b(as shown in Table 5) ) 9. Estimate operating life, consider lubrication and cleanliness 10. Calculate shaft, deformation and stiffness 11. Recalculate natural frequency and limiting speed 12. Optimize bearing arrangement. Rotation/rolling ratio max. 0.5 depends on the bearing's internal design Hertz contact pressure Fatigue life limit: Point contact: For material 100Cr6: 2 000 MPa For material Cronidur 30: 2 500 MPa Line contact: For material 100Cr6: 1 500 MPa For material Cronidur 30: 1900 MPa.