In the vertical turning equipment, the rotary table is one of the core structures that reflects the overall performance of the machine tool and realizes the machining accuracy of the workpiece. We require it to operate at high speed and bear heavier workpieces, while possessing precise running accuracy and very high anti-overturning moment capability. The slewing bearing supporting the worktable is the key to accomplish this important mission. Previously, most of the domestic workbenches chose thrust bearings and radial bearings to cooperate. This arrangement has a complicated structure and uses more materials. Especially when large box parts are placed, the space of the entire machine tool is larger. It is also difficult to install and adjust the pre-tightening of the slewing bearing, the alignment is more difficult to guarantee, and the overall accuracy of the worktable is difficult to improve.
Therefore, more designs are now beginning to choose cross-roller bearings with a more compact structure, which not only saves material costs, but also simplifies the design, higher limit speed, better operating accuracy and stability, and stronger load-bearing capacity and rigidity. This article introduces how to apply cross roller bearings on vertical lathes to achieve their perfect engineering performance.
1. Runout accuracy
Bearing runout can be divided into synchronous runout and asynchronous runout. The impact of synchronous runout on the overall runout of the workbench can be minimized by grinding the work surface, but the impact of asynchronous runout cannot be eliminated in this link. It is mainly It is determined by the outer diameter tolerance and roundness of the roller. Therefore, the better the asynchronous runout control of the bearing, the smaller the final radial and axial runout of the worktable, that is, the higher the running accuracy. When selecting bearing brands and accuracy grades, it is recommended not to only focus on the bearing assembly runout, but to have a thorough understanding of the accuracy standards that affect the asynchronous runout of the bearing.
2. Bearing fit
When selecting the bearing, it is recommended that the inner ring and the shaft, and the outer ring and the gear ring are tightly fitted. Since the outer ring is a rotating part, the tight fitting amount should be slightly larger. The inner ring will be pressed down by the end cap and adjusted to a certain pre-tightening amount, so the tight fitting amount should be slightly smaller. However, if the inner ring is considered to be a static part, and the inner ring and the shaft are designed to be loosely fitted, there is a radial gap between the inner ring and the shaft, it is possible that the inner ring may be deflected when the inner ring is installed, locked or the bearing is loaded. Oblique, that is, eccentricity occurs. This eccentricity will cause stress concentration on the boundary of the contact area between the roller and the raceway, causing serious scratches, cratering and peeling, and ending the bearing life earlier.
Three, shape and position tolerance
The mounting surface of the shaft and the gear ring is required to have the same flatness, perpendicularity, roundness and cylindricity as the precision bearing. Controlling these shape and position tolerances can not only achieve better assembly accuracy, but also avoid excessive eccentricity of the inner and outer rings of the bearing to cause stress concentration, and extend the service life of the bearing. Regarding the processing standards of the form and position tolerances, it is recommended to consult the bearing supplier and match its bearing accuracy.
Fourth, the axial preload
In the cutting test of the vertical turning, the end face and the outer circle roughness of the workpiece are very concerned, and one of the keys to determine the advantages and disadvantages is the rigidity of the system. 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.
Therefore, it is particularly important to fully consider the effects of temperature and load and reasonably set the axial preload of the bearing.