1 Error factors affecting the rotation accuracy of rolling bearing spindle

The rotation accuracy of mechanical spindle is the key content of mechanical accuracy. The main index to evaluate the spindle rotation accuracy is the radial circular runout and axial runout of the spindle front end. The rotation accuracy of the spindle is directly affected by the manufacturing accuracy of the spindle itself and the bearing accuracy, as well as the installation, adjustment and other factors of the bearing.

1.1 Factors of bearing accuracy

(1)For the radial runout and shape error of the raceway, the bearing and raceway surface determine the spindle rotation axis, while the inner hole of the bearing determines the geometric axis position of the spindle. The shape error of the bearing raceway (roundness and amplitude, etc.) will cause radial runout of the spindle axis.

(2) Inconsistent diameter and shape error of each rolling element, diameter and shape error of rolling element will cause radial circular runout of spindle axis. Every time the largest rolling element passes through the bearing area once, the spindle rotation line will have a maximum radial circular runout. The cycle of axis runout is related to the rotation speed of the cage, and the rotation speed of the cage is always lower than that of the inner ring. Therefore, this radial circular runout can only be repeated once after the spindle rotates for several revolutions.

It can be seen from the above that the radial circular runout of the rotating shaft caused by the error of the raceway and the rolling body is a complex periodic function of the spindle rotation angle. This periodic function contains not only the frequency components equal to the spindle speed n, but also the frequency components lower than and higher than n.

(3) Bearing clearance, the existence of bearing clearance has a great impact on the spindle rotation accuracy. It not only makes the spindle produce a displacement that changes with the direction of the external force under the action of external force, that is, the drift movement of the rotation axis, but also its displacement will change periodically.

1.2Main shaft accuracy and precision factors of mating parts

(1) The size and shape errors of the main shaft journal and the support seat hole, because the inside and outside of the bearing is a thin-walled elastic element, when the roundness error of the journal and the support hole is too tight, it will inevitably cause the corresponding deformation of the inner and outer ring raceway, which will reduce the rotation accuracy of the main shaft during operation.

(2) The coaxiality error of the spindle taper hole and centering journal to the spindle journal, which includes the eccentric error and the tilt error of the centerline, will cause the radial runout error of the corresponding surface of the spindle.

(3) The coaxiality error between the bearing seat hole and the front and rear journals of the main shaft will cause the relative inclination of the inner and outer race raceways of the bearing, which will cause the radial runout and axial displacement of the rotary axis.

4. The end face vertical error of the nut, transition sleeve, washer and main shaft that adjust the clearance will cause the distortion of the raceway due to the uneven force when the bearing is assembled.

2 Assembly adjustment for improving the rotation accuracy of the main shaft of rolling bearing

measures

(1) The matching method is adopted to further improve the matching accuracy of rolling bearing, journal and support hole, and reduce the influence of the shape error of mating parts on the bearing accuracy.

(2) The rolling bearing can be preloaded during assembly as required to eliminate the bearing clearance and produce certain interference, which can improve the rotation accuracy and stiffness of the bearing.

(3) During assembly, the maximum radial runout error direction of the bearing and the maximum runout error direction of the relevant surface of the spindle can be assembled in a certain direction, that is, the so-called error oriented assembly method is used to make the errors compensate each other (rather than accumulate), so as to improve the rotation accuracy of the spindle.

2.1 Directional Assembly Method of Rolling Bearing Spindle

In machinery, when the surface such as the centering taper hole at the front end of the main shaft requires high rotation accuracy (the runout tolerance of the radial ring is less than 3 Λ m), the fitting and fixing of the main journal of the inner ring of the rolling bearing can adopt the error oriented assembly method.

Before assembly, check the radial runout of the bearing inner race and the deviation of the centering surface measured at the front end of the spindle from the radial runout of the common axis of the front and rear journals of the spindle, and mark the position of the highest (low) radial runout point.

2.2 Inspection method for radial runout of rolling bearing inner race (see Fig1). When checking, the outer ring is fixed, an appropriate load is applied to the end face of the inner ring, and the inner ring is rotated, then the radial runout and its direction of the same hole surface can be measured by the indicator.

The inspection method for the coaxiality deviation direction of the measured center surface such as the center of the spindle taper hole relative to the common axis of the spindle journal (see Figure 2). During the inspection, place the main shaft journal on the "V" shaped iron, support it on the angle iron bracket with steel balls in the axial direction, insert the inspection rod into the taper hole of the main shaft, and rotate the main shaft to measure the deviation direction of the central line of the key hole at the end near the main shaft and L from the main shaft with an indicator.

During assembly, select the assembly position of the bearing according to the following principles:

① The bearing inner race with large radial circular runout shall be placed on the rear support.

② The highest point of the radial circular runout of each bearing inner race in the front and rear supports. It is placed in the same direction in the same axial section, and the deflection direction of the common axis between the supplementary centering surface and the journal at the front end of the main shaft. On the contrary, make the center of the measured surface close to the actual rotation center. After the bearing is assembled according to the directional assembly method, its inner ring and shaft shall be strictly kept from relative rotation, otherwise the acquired adjustment accuracy will be lost.

More about FRC Needle Roller Bearings:

It is known that FreeRun Bearing is one of popular manufacturers and suppliers of needle roller bearings in China. FreeRun needle roller bearings include drawn cup needle roller bearings, heavy duty needle roller bearings, one way clutch bearings, needle roller and cage assembles, needle roller thrust bearings, aligning needle roller bearings, inner rings, loose needle rollers and track rollers.

Needle bearing is a roller bearing with cylindrical rollers. Compared with its diameter, the rollers are thin and long. This kind of roller is called needle roller. Although it has a small section, the bearing still has high load bearing capacity. The needle roller bearing is equipped with thin and long rollers (roller diameter D ≤ 5mm, L / D ≥ 2.5, l is the roller length). Therefore, the radial structure is compact. When its inner diameter size and load capacity are the same as other types of bearings, the outer diameter is the smallest, which is especially suitable for the supporting structure with limited radial installation size.

According to different application occasions, the bearing without inner ring or needle roller and cage assembly can be selected. At this time, the journal surface and shell hole surface matched with the bearing are directly used as the inner and outer rolling surfaces of the bearing. In order to ensure that the load capacity and operating performance are the same as those of the bearing with ferrule, the hardness, machining accuracy and surface quality of the raceway surface of the shaft or outer shell hole should be similar to that of the bearing ferrule. This kind of bearing can only bear radial load.