After the bearing is installed in the main machine, if the radial runout of the main shaft is measured, it can be found that there is a certain change in the measured value at each revolution; When continuously measuring, it can be observed that after a certain number of revolutions, this change will approximately repeat. The indicator for measuring the degree of change is the accuracy of cyclic rotation. The number of revolutions required for the change to approximately repeat represents the "quasi period" of cyclic rotation accuracy. If the magnitude of the magnitude change within the quasi period is large, it is known as poor cyclic rotation accuracy.
If appropriate preloading is applied to the spindle, gradually increasing the speed to close to the working speed to implement the "running in" effect of the bearings, it can improve the cycling rotation accuracy of the spindle.
A method to improve bearing accuracy, such as a trial production instrument in a certain factory, which uses 6202/P2 type bearings for the main shaft but still cannot meet the accuracy requirements. Then, the journal is thickened and a raceway is made on it to replace the inner ring, and the steel balls are measured for density. Each group of steel balls is divided into groups of three sizes, with intervals close to 120 °. Due to the reduction of one machining surface and one matching surface, At the same time, it also improves the stiffness of the shaft bearing system, and the close equidistant distribution of the large and small three steel balls improves the rotational accuracy of the shaft, thus meeting the accuracy requirements of the instrument
Clean the bearing with clean cleaning kerosene. For grease lubrication, first inject a solvent containing 3% to 5% lubricating grease into the bearing for degreasing cleaning, and then use an oil gun to fill a quantitative amount of lubricating grease into the bearing (accounting for 10% to 15% of the bearing space volume); Heat the bearing to raise the temperature by 20-30 ℃, and use an oil press to install the bearing into the shaft end; Press the locking sleeve onto the shaft and press it against the bearing end face with appropriate pressure to achieve axial positioning; Wind the belt of the Spring scale on the outer ring of the bearing, and verify whether the specified preload has a large change by measuring the starting torque (even if the bearing is correct, the preload may also change due to the deformation of the fit or cage).
Install the bearing and shaft assembly into the seat hole and heat the seat hole to raise the temperature by 20-30 ℃. Use continuous and gentle pressure to tighten the bearing? Install the shaft assembly into the seat hole; Adjust the front cover so that the tightening amount of the front cover is 0.02-0.05 μ m. Using the outer end face of the bearing seat as the reference, place the dial gauge head against the surface of the journal, rotate the shaft to measure its runout, with an error of 10 μ Below m; Position the dial indicator on the shaft, with the gauge head touching the inner surface of the rear seat hole. Rotate the shaft to measure the coaxiality of the front and rear seat holes of the bearing seat.
Selectively place the bearing end in a position that may offset the deviation, install it in the support position behind the bearing seat, and try to offset the roundness deviation and coaxiality deviation as much as possible.
