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Precision machine tool spindle bearing selection method

Source:NETAuthor:UN Addtime:2022-05-13 Click:
Rolling bearings are used in machine tools mainly for the following three parts: spindle, ball screw and general drive shaft.
  A. precision machine tool spindle system rotation accuracy
  Rolling bearings for precision machine tool spindle bearing accuracy should be P5 and above, and for CNC machine tools, machining centers and other high-speed, high-precision machine tool spindle support, should be used P4 and above ultra-precision bearings. Spindle bearing as a basic component of the machine tool, its performance directly affects the machine speed, rotary accuracy, rigidity, anti-chatter vibration cutting performance, noise, temperature rise and thermal deformation, etc., which in turn affects the accuracy of the processed parts, surface quality, etc.. Therefore, high-performance machine tools must be equipped with high-performance bearings.
  Spindle system rotational accuracy refers to the machine tool in the no-load manual or motorized low-speed rotation, measured in the spindle front datum radial runout, cross-sectional runout and axial runout accuracy.
  The accuracy of the spindle system is mainly affected by the following factors.
  (1) bearing collar groove radial runout, will correspond to make the spindle system spindle axis radial runout, so that these errors will be part of the complex reflection on the machined surface. 
  (2) bearing rolling body diameter inconsistency and shape error will make the spindle produce regular error. 
  (3) The side swing of the groove to the end face will cause the axial runout of the spindle, the axial runout of the spindle is particularly significant for precision grinding machines, especially bearing grinding machines, if the process of grinding the groove by means of supporting grooves, will make a substantial increase in the scrap rate, noise will also be significantly increased. 
  (4) The size and shape error of the working surface of the bearing installation will cause the corresponding deformation of the bearing raceway, so that the inner and outer rings of the bearing tilt, making the bearing stiffness in all directions is not consistent, which will reduce the rotational accuracy of the spindle system. Adjusting the clearance of the nut, spacer, washer end face are required to grind processing, and the perpendicularity of the axis of rotation with the shaft system should correspond to the accuracy of the installed bearings, otherwise it will reduce the working accuracy of the bearings.
 
  B. precision machine tool spindle lubrication and sealing
  As we mentioned before lubricant is an important part of the bearing configuration, using different lubrication methods, the data of the limit speed of the bearing is different. Lubricant should be replenished according to the design requirements in time (high-speed precision spindle system grease filling amount is generally 10% ~ 20% of the bearing space), a reasonable addition of lubricant, can reduce the friction and wear of the shaft system, extend the fatigue life of the bearing, while the frictional heat of the bearing system can be discharged and play a role in cooling the bearing system; In addition to grease, bearing system lubrication there are liquid oil lubrication, oil mist Oil and gas lubrication has been commonly used in foreign high-speed spindle systems, oil and gas lubrication is oil-saving, pollution-free, and can significantly improve the DN value of the spindle system, and can intelligently control the requirements of the shaft system on the lubricant replenishment amount.
  The design of spindle structure, lubrication and sealing must be used in different forms according to different situations. Seal wear to be replaced in a timely manner, seal lip and rotating body contact at more than 15m / s to use non-contact sealing structure, high-speed precision machine tools mostly use labyrinth seal, and need to design in the appropriate location to dump oil groove, because contact sealing will not only make the seal contact friction loss and overheating, and will have an impact on the bearing system rotational accuracy.
  Third, ball screw as a precision, efficient and sensitive transmission components, in addition to the use of high-precision screw, nut and ball, should also pay attention to the use of high axial stiffness, low friction torque, high running accuracy of the bearing. In the past, ball screw bearing commonly used two-way thrust angular contact ball bearings, tapered roller bearings, needle roller and thrust roller combination bearings, deep groove ball bearings and thrust ball bearings. At present, the most used ball screw bearing is single row thrust angular contact ball bearing with 60° contact angle, moreover, the accuracy level is also P4 and above mainly.

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