Selection and sealing of the best bearing spacing for ultra-precision spindle bearings
Select the best bearing spacing. If the structure permits, it is recommended to select a bearing arrangement with a proper 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 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, because the long bearing spacing makes the axial thermal expansion effect of the shaft insignificant, the advantages of the above design are questioned. Therefore, these designs are relatively rare in practical applications. Sealing: The spindle bearing, especially when located at the end of the spindle, must be effectively sealed. The non-contact labyrinth seal with dust cover has compact radial clearance (h8/C9), wide axial clearance (clearance width 3 mm) and drain hole, which can make the bearing in working and non-working conditions Effectively isolate cutting fluid, metal chips and dust. The sealed grease-lubricated bearing enhances the effect of the labyrinth seal and prevents air from flowing in the bearing arrangement. Bearing arrangement design steps To design the spindle bearing arrangement, the following steps must be followed: 1. Determine the working conditions (speed, load, continuous operation time, spacing, diameter, temperature, ambient environment) 2. Select the bearing arrangement according to the purpose and requirements (as shown in the table) 6) 3. Determine lubrication (see Lubrication chapter, page 176) 4. According to speed (see Speed u200bu200bchapter, page 189), installation space and lubrication, select bearing type and size 5. Check grease life (see Lubrication Table 5 in the chapter, page 180) 6. Calculate the load distribution on the bearing 7. Check the maximum working life of the bearing arrangement (see the life calculation chapter). If you can use the calculation program, you can follow the steps below: 8. Calculate the bearing kinematics parameters (rotation/rolling ratio, sphere drifting motion) and contact pressure (P0), and compare them with the design limit values u200bu200b(as shown in Table 5) ) 9. Estimate the operating life, considering lubrication and cleanliness. 10. Calculate the shaft, deformation and stiffness. 11. Recalculate the natural frequency and limit speed. 12. Optimize the bearing arrangement. The maximum rotation/rolling ratio of 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.