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

Choosing the best bearing spacing If the structure allows, it is recommended to choose a suitable spacing of the bearing arrangement under rigid preload. The radial and axial thermal expansion of the shaft can be compensated by pretensioning. For a spindle bearing with a contact angle of 25°, the most suitable bearing distance L is approximately 3 times the shaft diameter d; for a bearing with a contact angle of 15°, it is approximately 5 times the shaft diameter d. However, the advantages of the above design are questioned due to the fact that the long axial distance between the shafts does not contribute to the axial thermal expansion. Therefore, these designs are relatively rare in practical applications.

  Sealing: Spindle bearings, especially at the end of the spindle, must be effectively sealed. The non-contact labyrinth seal with a dust cover has a compact radial clearance (h8/C9), a wide axial clearance (clearance width ? 3 mm) and a drain hole, all of which enable the bearing to be operated and non-operating. Effectively isolates cutting fluids, metal chips and dust. Sealed, grease lubricated bearings enhance the effect of the labyrinth seal and prevent air from flowing in the bearing arrangement.

 The design steps of the bearing arrangement 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) 2. Select the bearing arrangement according to the application and requirements (eg table 6) 3. Determine lubrication (see Lubrication section, page 176) 4. According to speed (see Speed ​​chapter, page 189), install space and lubrication Select bearing type and size 5. Check grease life (see Lubrication Table 5, page 180 in the chapter) 6. Calculate the load distribution on the bearing 7. Check the maximum working life of the bearing arrangement (see section Life calculations). If you can use the calculation program, you can follow the following steps: 8. Calculate the bearing kinematic parameters (rotation/roll ratio, sphere drift motion) and contact pressure (P0), and compare with the design limit (as shown in Table 5) 9. Estimate operating life, consider lubrication and cleanliness 10. Calculate shaft, deformation and stiffness 11. Recalculate natural frequency and limit speed 12. Optimize bearing arrangement.

  Rotation/rolling ratio maximum 0.5 depends on the internal design of the bearing 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 500MPa For material Cronidur 30: 1 900 MPa.