1. The requirements of precision hardware shaft for matching machine parts
Since the precision of the precision hardware shaft itself is within 1μm, it is required to have high dimensional accuracy and shape accuracy of its mating parts (shaft, bearing seat, end cap, retaining ring, etc.), especially the accuracy of the mating surface should be controlled at the same level as the bearing, which is crucial and most easily ignored.
Must also pay attention to the precision hardware shaft of the matching machine parts if it fails to meet the above requirements, often make the precision hardware shaft in the installation than the original bearing error occurs several times, or even 10 times more than the error, completely does not become its precision hardware shaft, the reason is that the error of the matching machine parts is often not simply superimposed on the error of the bearing, but with a different multiplier amplification added to the.
2、Precision hardware shaft fit
In order to ensure that the bearing does not produce excessive deformation after installation, it must do the following.
(1) The roundness of the shaft and the seat hole and the verticality of the retaining shoulder should be required in accordance with the corresponding accuracy of the bearing.
(2) To accurately calculate both the amount of interference of the rotating collar fit and the amount of suitable fit of the fixed collar.
Rotating collar burning interference amount in the possible range is also appropriate to obtain a small. As long as the effect of thermal expansion at operating temperature and the effect of centrifugal force at the highest speed is practically guaranteed, it will not cause creep or sliding of the tightly fitted surface. Fixed collar according to the size of the working load and bearing size, choose a very small gap fit or interference fit, too loose or too tight are not conducive to maintain the original precise shape.
(3) bearing such as in high-speed conditions, and high working temperature, should pay special attention to the rotating collar fit can not be too loose to prevent eccentric vibration, as well as fixed collar fit can not appear clearance, in order to prevent the collar under load deformation and excitation vibration.
(4) the fixed ring to take a small interference with the condition of the matching surface both sides have high shape accuracy and small roughness, otherwise it causes installation difficulties and disassembly more difficult, in addition, also need to consider the impact of spindle thermal elongation.
(5) use pairs of angular contact ball bearing spindle, most of the load is lighter, its fit interference such as large, then its internal axial preload will be significantly larger, resulting in adverse effects. The use of double row short cylindrical roller bearing spindle and tapered roller bearing spindle, the load is relatively large, so its fit interference is also relatively large.
3、Ways to improve the actual fit accuracy
In order to improve the actual fit accuracy of the bearing installation, we must use the measurement method and measurement tools that do not deform the bearing, the actual precision measurement of the bearing bore and outer circle with the size of the surface, you can measure the inner diameter and outer diameter of the measurement items are measured, and the measured data to make a comprehensive analysis, based on this, precision for the shaft and seat hole bearing installation parts of the size. The actual measurement of the corresponding size and geometry of the shaft and housing should be carried out under the same temperature conditions as when the bearings are measured. In order to ensure a high practical fit, the roughness of the surfaces of the shaft and the seat bore with the bearing should be as small as possible.
In the above measurement, should be in the bearing of the outer circle and bore, and the corresponding surface of the shaft and seat hole, in close to the assembly chamfer on both sides, respectively, to show the maximum deviation direction of the two groups of marks, so that in the actual assembly, so that the maximum deviation of the two parties to align the same orientation, so that after the assembly, the deviation of both sides can be partially offset.
The purpose of making two sets of orientation marks is that the compensation of deviation can be considered comprehensively, so that the respective rotational accuracy of the two end supports can be improved, and the coaxiality error of the seat hole and the two end journals between the two supports can be partially eliminated. The implementation of surface strengthening measures on the mating surface, such as sandblasting treatment, with a slightly larger diameter precision plug plug once the bore, etc., are conducive to improving the accuracy of the mating.