Application of cross roller bearing in CNC vertical vehicle
- 2020/4/20 15:15:45
Application of cross roller bearing in CNC vertical vehicle
China is a big machine tool demand, is also a big production country, but only in the low-end field to meet the domestic industrial needs more fully, the high-end field has been involved in less.With the development of the industry and the upgrading of the competition, it is the best choice for the long-term development of enterprises to improve the technical content of products and own independent patents and designs.Therefore, as far as CNC vertical vehicle is concerned, how to realize the product from low-end to high-end, from primary processing to advanced manufacturing is the direction of enterprise transformation tide should be thought and efforts.
In the vertical vehicle equipment, the rotary table is one of the core structures to reflect the overall performance of the machine tool and realize the machining accuracy of the workpiece.We require it to operate at high speed and bear heavy parts at the same time, with precise operating accuracy and very high anti-overturning torque ability, and the bearing supporting the workbench is the key to complete this important mission.Before most of the domestic workbench choice thrust bearing and radial bearing to use together, this arrangement form structure is complex, with more materials, especially in the placement of large box parts, the space volume of the entire machine tool is larger.Bearing installation and preload adjustment is also more difficult, more difficult to ensure the overall accuracy of the workbench is difficult to improve.
With the development of science in recent years, high precision and high speed machine tools are favored by the market.Also makes the vertical machining precision to a new height.The cross roller bearing plays a key role in improving the machining accuracy of vertical car.
Beat accuracy
Bearing run-out can be divided into synchronous run-out and asynchronous run-out, in which the influence of synchronous run-out on the overall run-out of the table can be reduced to the greatest extent by grinding the work surface, but the impact of asynchronous run-out in this part can not be eliminated, it is mainly determined by the roller outer diameter tolerance and roundness.Therefore, the better the bearing asynchronous run-out control, the smaller the final radial and axial run-out of the workbench, that is, the higher the running accuracy.In the choice of bearing brand and precision level, it is recommended not only to focus on the bearing assembly run-out, but should have a deep understanding of the bearing asynchronous run-out accuracy standards.
Bearing fit
It is suggested that the inner ring and shaft, outer ring and gear ring should be closely matched when selecting bearings.Since the outer ring is a rotating part, the compact weight should be slightly larger;The inner ring will be pressed down by the end cap to move down and adjust to a certain amount of pre-tightening, so the amount of tightening should be slightly smaller.However, if the inner ring is considered to be a stationary part, and the design of the inner ring and the shaft is loosely fitted (there is a radial gap between the inner ring and the shaft), it is possible to install the inner ring, locking the inner ring or bearing load when the inner ring deflection, that is, eccentric.This eccentricity will cause stress concentration at the boundary of the contact area between the roller and raceway, resulting in serious scratches, craters and spalling, and an early end to the bearing life.
The mounting surface of shaft and gear ring is required to have the flatness, perpendicularity, roundness and cylindricity consistent with the precision bearing.Controlling the shape and position tolerances can not only obtain better assembly accuracy, but also avoid excessive eccentricity of bearing inner and outer rings which may cause stress concentration and prolong the service life of bearing.As for the machining standard of shape and position tolerance, it is suggested to consult the bearing supplier to match the bearing precision.
Axial preload
In the cutting test of vertical lathe, the roughness of the end face and the outer circle of the workpiece are paid much attention to.The system rigidity includes the rigidity of the frame structure, the rigidity of the supporting bearing, etc. The rigidity of the bearing often depends on its axial preload.
Matters needing attention for bearing installation
This section focuses on the operational details that require additional attention during installation:
1. When the lower inner ring of the bearing is loaded into the shaft seat and returned to room temperature, it is necessary to check the clearance between the inner ring and the block shoulder with a 0.025mm feeler to ensure that it has been installed in place.The outer ring is the same, if not in place, the steel bar of medium hardness is used to hit the end face, so that it is in place, in order to avoid the inner and outer ring due to installation is not in place and eccentric, damage to the bearing.
2. After the installation of the lower inner ring, outer ring and roller of the bearing, adjust the parallelism between the end face of the gear ring and the end face of the main shaft (the plane shown by the red line in the figure) to make the lower inner ring and the outer ring parallel;After the installation of the upper inner ring, the front and back bearings shall be rotated to make the rollers and spacers correctly positioned, and then the parallelism between the end face of the ring and the end face of the upper inner ring shall be adjusted to ensure that the three bearing rings are all level, so as to avoid the eccentricity between the bearing rings, resulting in stress concentration and bearing damage.
3. Complete the inner ring is installed, must be positive and negative rotation bearings, roller and spacer automatically straighten, add the gasket and the end cover lock.If there is no rotation and make the arrangement of skew roller bearing on the rolling path and lock, can appear when bearing is running a serious fever, raceway burns, cuts, and loss of accuracy.
4. Lock the end cover bolts one by one in a diagonal order (as shown in FIG. 6). The locking torque can be increased by 3 to 4 times to the final locking amount, so as to avoid the eccentricity of the inner ring due to uneven or excessive forces on both sides when the end cover is pressed.At the same time, you can also check the levelness of the end cover again after each round of locking to eliminate eccentricity as far as possible.
