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Guide for selection of machine tool spindle bearings

Time:2022-12-16 13:39:49click:1236

Bearing is the core component of the machine tool spindle, which has a direct impact on the operation of the machine tool. Its performance determines the rotation accuracy, rotation speed, rigidity, temperature rise and noise of the machine tool, and has a decisive impact on the dimensional accuracy and surface roughness of the parts,
Machine tool spindle bearing
The spindle bearing of machine tool usually requires an accuracy of more than ISO P5. If CNC machine tools and machining centers must work at high speed and high precision, their spindle bearings need to be above ISO P4;
The bearings used for main shaft bearings are usually angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.
Precision angular contact ball bearing
Precision angular contact ball bearings are most widely used in machine tool spindles. It can provide higher speed, smaller heating and higher accuracy. Hybrid ceramic ball bearings are also required for special ultra-high-speed spindle applications. The rolling element of ceramic material brings it good performance of high rigidity, high speed, high temperature resistance and longer service life.
At present, the contact angles of angular contact ball bearings are 15 ° and 25 °; 15 ° contact angle can bring higher rotational speed, while 25 ° contact angle can provide higher axial load. Selection of preload of precision angular contact ball bearing: medium or heavy bearing preload shall be selected for the requirements of high load and high rigidity; For high speed and high precision, light preload is generally selected.
Precision tapered roller bearing
For applications such as raw mill, threading machine, heavy lathe and milling machine, which need to bear heavy load and high speed at the same time, precision tapered roller bearing is usually selected. It can provide high rigidity and load, reduce the running torque and heat, and ensure the speed and accuracy of the main shaft. During installation, SKL tapered roller bearing can also adjust the axial clearance, which is convenient for customers to adjust the bearing clearance.
For precision selection, ISO P5 is usually selected in traditional lathes and milling machines; In machining center, grinding machine and other applications, ISO P4 or above is usually selected. There are usually two types of taper roller bearing layouts for the main shaft.
First, a tapered roller bearing is installed face to face at the front end and rear end, which is characterized by compact structure, high rigidity and easy installation and adjustment.
The second is to install two tapered roller bearings face to face at the front end of the main shaft, and use a bearing with two outer rings and two single inner rings at the rear end; It is characterized by floating capacity, bearing the axial thermal expansion of the main shaft, and good accuracy of the machine tool.
Precision cylindrical roller bearing
Double-row precision cylindrical roller bearings are usually used in combination with precision angular contact ball bearings or thrust bearings on the main shaft. It can bear large radial load and high speed. The fluctuation frequency during rotating operation is much higher than that of single-row bearings.
Double-row precision cylindrical roller bearings usually have two forms: NN30, NN30K series inner ring with retaining edge, and outer ring can be separated; The outer ring of NNU49 and NNU49K series is provided with a rib, and the inner ring can be separated. NN30 and NNU49 are cylindrical bore bearings. During installation, interference fit is used to reduce the clearance or preload the bearing. NNU49 bearing with detachable inner ring is installed behind the main shaft. Finishing the raceway can improve the rotation accuracy of the main shaft.