Introduce the accuracy of precision bearings after installation
1. Accuracy improvement method
After the bearing is installed in the main engine, if the radial runout of the main shaft is measured, it can be found that the measured value of each revolution has a certain change; when continuous measurement is performed, it can be found that after a certain number of revolutions, this change will approximately repeat. Appear. The index to measure the degree of this change is the cyclic rotation accuracy. The number of revolutions required for the change to appear approximately repeats represents the “quasi-period” of the cyclic rotation accuracy. The magnitude of the change in the quasi-period is large, which is the poor cyclic rotation accuracy. . If an appropriate preload is applied to the main shaft, the speed is gradually increased to close to the working speed, so as to implement the “run-in” effect of the bearing, which can improve the cyclic rotation accuracy of the main shaft.
2. A method to improve bearing accuracy
A factory trial-produces precision instruments, the main shaft uses 6202/P2 type bearings and its accuracy still cannot meet the requirements, then thicken the journal and make a raceway on it to replace the inner ring, and measure the glutinous density of the steel ball, according to the size Each group of three steel balls is separated by an interval of nearly 120°. Due to the reduction of a heavy machining surface and a heavy matching surface, the rigidity of the shaft-bearing system is improved, and the largest three balls and the smallest three balls are The nearly equidistant distribution of the steel balls improves the rotation accuracy of the shaft, thus meeting the accuracy requirements of the instrument.
3. Comprehensive verification method of installation accuracy
After the angular contact ball bearing is installed into the spindle, the installation accuracy check sequence is as follows (taking an ordinary lathe with a shaft diameter of 60-100mm as an example):
(1) Measure the size of the shaft and the bearing seat hole to determine the matching accuracy of the bearing. The matching requirements are as follows: the inner ring and the shaft adopt an interference fit, and the interference amount is 0~+4μm (0 for light load and high precision) ;The outer ring and the bearing seat hole adopt a clearance fit, and the clearance amount is 0~+6μm (but when the free end bearing uses an angular contact ball bearing, the clearance can also be increased); the surface roundness error between the shaft and the seat hole is less than 2μm, the bearing The parallelism of the end face of the spacer used is below 2μm, the runout of the inner end of the shaft shoulder facing the outer end face is below 2μm; the runout of the bearing seat hole shoulder to the axis is below 4μm; the runout of the inner end of the spindle front cover facing the axis is below 4μm.
(2) For the installation of the front bearing at the fixed end on the shaft, thoroughly clean the bearing with clean cleaning kerosene. For grease lubrication, first inject an organic solvent containing 3% to 5% grease into the bearing for degreasing and cleaning, and then use The oil gun fills a certain amount of grease into the bearing (accounting for 10% to 15% of the bearing space volume); heat the bearing to raise the temperature to 20 to 30°C, and install the bearing into the shaft end with a hydraulic press; press the adapter sleeve on the shaft And press the end face of the bearing with suitable pressure to make it axially positioned; roll the belt of the spring scale on the outer ring of the bearing, and use the method of measuring the starting torque to check whether the specified preload has a large change (even if the bearing is correct). , but the preload may also change due to the deformation of the fit or cage).
(3) Put the bearing-shaft assembly into the seat hole, heat the seat hole to raise the temperature by 20-30°C, and use continuous gentle pressure to install the bearing-shaft assembly into the seat hole; adjust the front cover to make the front cover tight The solid amount is 0.02～0.05μm, based on the outer end face of the bearing seat, the head of the dial indicator is against the surface of the journal, and the shaft is rotated to measure the runout, and the error is required to be less than 10μm; the dial indicator is positioned on the shaft. , the gauge head is against the inner surface of the rear seat hole, and the shaft is rotated to measure the coaxiality of the front and rear seat holes of the bearing seat.