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Assembly of FAG Double Row Cylindrical Roller Bearings for Spindle

Source: FAG bearings  Tags: News

Double-row cylindrical roller bearings with tapered bore are linear contact bearings. Their load-carrying capacity and rigidity are higher than point contact angular contact bearings. They are often used for medium and large bearings with larger loads and higher rigidity, but the speed is relatively low. , Heavy-duty machine tool spindle system. Next, Eric Bearing Limited will share with you the assembly and adjustment method of FAG double row cylindrical roller bearings used in the spindle system.

1. The selection of FAG rolling bearings for spindles.

Both the spindle and FAG bearings have manufacturing errors, which will inevitably affect the rotation accuracy of the spindle assembly. When assembling the spindle assembly, if the influence of the errors of the two are partially offset each other, the rotation accuracy can be further improved. Since the inner ring of the rolling bearing rotates with the main shaft, its radial runout (or runout) has the greatest impact on the bearing rotation accuracy. Therefore, generally only adjust the relative position of the bearing inner ring and the spindle journal.

(1) Front FAG bearing selection: Since the radial runout of the main shaft at the front support has the greatest impact on the rotation accuracy of its end, the bearing selection method should be used first to reduce the radial runout at the front support.

The actual operation process is to measure the inner ring and main shaft journal of a batch of rolling bearings separately before assembling, and type markings at the respective high points (bearings in some countries, the high points have been marked, in recent years In order to improve the accuracy of the bearing, the mark is removed); then grouped according to the actual radial runout, and the one with similar runout is selected for assembly, so that the two high points are opposite to each other to complete the selection of the front bearing. Widely application for bearing  FAG 7311-B-TVP-UO , ERIC BEARING LTD are professional FAG brand bearing distributor , if you interested , pls click here : 

(2) Rear FAG bearing selection: After the front bearing is selected, the rear bearing can be selected to further improve the rotation accuracy of the spindle assembly. Since the main shaft uses the same datum to grind each shaft journal, the high points of the front and rear shaft journals beating against the main shaft axis are often in the same direction.

Therefore, as long as the high points of the rear bearing and the front bearing are arranged in the same axial plane and on the same side of the axis, better results can often be obtained. If the radial jump points of the outer ring of the front and rear bearings are installed in the same direction and opposite to the high point of the seat hole, the rotation accuracy of the spindle can be further improved.

2. The clearance (clearance) of the spindle FAG rolling bearing and its adjustment.

The amount of clearance (clearance) of the spindle rolling bearing has an important influence on the performance of the spindle assembly and the life of the bearing. When the bearing is working under a large gap, it will cause the deviation of the spindle position (radial or axial) and directly affect the machining accuracy. At this time, the bearing area of ​​the bearing is also small, and the load is concentrated on one or several rolling elements in the direction of the force, resulting in greater stress concentration, causing the bearing to mature and increase wear and reduce its life.

In addition, the rigidity and vibration resistance of the spindle assembly are also greatly weakened. When the bearing is adjusted to zero clearance, the load-bearing area increases, the force of the rolling elements tends to be uniform, and the rotation accuracy of the main shaft is improved. When the bearing preload (pre-cutting load) is adjusted to a negative gap, the rolling elements are elastically deformed, and the contact area with the raceway is increased, so that the load-bearing area is expanded to 360°, and the rigidity and vibration resistance of the spindle assembly can be Obviously improved.

Therefore, keeping a reasonable amount of clearance in the rolling bearing is an important measure to improve the rotation accuracy, stiffness and vibration resistance of the spindle assembly.

The static stiffness of the main shaft assembly increases as the amount of bearing clearance decreases. The stiffness change (the slope of the curve) of the bearing near the zero gap is the largest, and then the stiffness increases slowly. However, the impact of the bearing clearance on the dynamic characteristics of the spindle assembly is more complicated. The damping value of the main shaft assembly (the ratio of the actual damping value to the critical damping value is that the damping ratio first increases with the reduction of the bearing clearance, and the damping value at the zero clearance is the largest, and then the interference increases as the clearance decreases. Large), the damping value will decrease instead.

This is because the bearing gradually tends to be "rigid", which reduces the structural damping, and more of the internal friction damping characteristics of the material. The static stiffness and damping characteristics affect the overall dynamic response of the spindle assembly. There is an optimal gap position. At this time, the resonance amplitude of the front end of the spindle is the smallest, the static stiffness and resonance frequency are both high, and the roundness error and roughness of the machined surface Also smaller.

When the amount of clearance is too small, the increase in stiffness is not significant, but the wear and heat of the bearing is greatly increased, thereby reducing the life of the bearing and worsening the conditions of use. It can be seen that the selection of the best bearing clearance should not simply consider the static stiffness, but also consider the damping value at the same time, so as to obtain the smallest shaft end resonance value, higher stiffness, resonance frequency and machining accuracy. According to experience, the bearing clearance of the spindle of general medium and large machine tools should be adjusted from -0.005 to -0.015mm.

3. Inspection and adjustment of the installation correctness of the inner and outer rings of FAG bearings.

The ratio of diameter to width of double-row cylindrical roller bearings is generally between 4 and 7. Due to the relatively large diameter and width of double-row cylindrical roller bearings, the guiding performance when installed in the spindle box hole and on the spindle is poor. Furthermore, the size and quality of large-scale machine tool parts are relatively large, which brings certain difficulties to the assembly work, and easily causes uneven force when installing the bearings.

The above various reasons cause the installation position of the inner and outer rings of the spindle bearing to shift, and the bearing rolling elements are in poor contact with the inner and outer rings of the bearing, which reduces the rigidity and rotation accuracy of the spindle. The method to verify the installation correctness of the inner and outer rings of the spindle bearing is as follows: During the process of pre-tightening the inner ring of the bearing, continuously rotate the spindle while observing the rotation of the bearing rolling elements.

If the main shaft rotates easily, and the rolling elements of the bearing rotate with the rotation of the main shaft, the inner and outer rings of the bearing should be installed correctly; if the main shaft has a certain amount of preload, it feels blocked during rotation, and the individual rolling elements of the bearing do not follow If the main shaft rotates and rotates, or the individual rolling elements are loosened by hand, it should be caused by the deviation of the inner ring or outer ring of the bearing.

You can install the magnetic meter seat on the main shaft box and the main shaft respectively, rotate the main shaft and observe the change of the indicator value of the dial indicator (see Figure 1, Figure 2), adjust the position of the inner ring and outer ring of the bearing to make the dial indicator The indication value changes the least (generally should be less than 0.01 ~ 0.04mm, related to the size of the bearing)