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Description of super precision bearing speed and fit

by:JNSN     2021-12-15
Super-precision bearings can be used at the highest speed. If grease lubrication is adopted, the speed index n · dm can reach 2.0 · 106 mm/min, and if oil lubrication is adopted, it can reach 3.0 · 106 mm/min or even higher. Such high speed will generate high centrifugal force, which acts on the inner ring to expand it. The expansion of the inner ring will cause its inner diameter to increase, which affects the fit between the inner ring and the journal. The possible results from this are: wear and corrosion the inner ring slips on the journal, the journal loses its guidance and is prone to vibration, and the eccentricity may reduce bearing performance. The above-mentioned situations can be avoided by tightly fitting the bearing and the journal. The required interference can be calculated from Table 11 or from the BEARINX® program. For the value obtained by this method, an interference of 1 μm is still required at the highest speed. The interference will increase the preload, especially for the rigidly adjusted bearings. This will lead to increased heat generation in the bearing arrangement and affect the speed capability. Such increased preload must be compensated by appropriate methods. If fw · n2 1.2 (red area in Figure 11), it is best to consult the Schaeffler Group Industrial Application Department. The value fw can be obtained directly from Figure 12 (for B, HCB and XCB bearings) and Figure 13 (for HS, HC and XC bearings). If n2 · fw 1.2, the resulting journal size is as follows: Example: HCS71914E.T.P4S.UL Speed u200bu200bn u003d 16 000 min1 The actual size of the inner ring: 70 mm 3 μm u003d 69.997 mm. (The size deviation of the inner ring is marked on the bearing ring). Hollow shaft with a bore diameter of 35 mm (50% of shaft diameter) fw u003d 4.30 · 109 (according to Figure 13 for HS, HC and XC bearings) n2 · fw u003d 1.1 Value 1.1 and hollow shaft 50% curve (Figure 11 ) The required interference is 9 μm. Therefore, the actual size of the shaft should be 70.006 mm to ensure that the inner ring is still fastened on the shaft when the speed n u003d 16 000 min1.
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