An elastic foil under tension is wrapped partly around a rotating cylinder and is supported on a thin film of air. Capacitance probes, coincident with the surface of the cylinder, scan the air gap along the arc of wrap. The cylinder can be traversed across the width of the stationary foil, so that the topography of the air gap can be determined from a series of circumferential scans. Experimental results are compared quantitatively with theoretical predictions for the perfectly flexible and for the elastic foil bearing of infinite width [8, 12]. A comparison is also made with theory, for the case when the angle of wrap is small and the entrance and exit transition zones merge [9]. The effect of foil and gap width on side leakage is illustrated. The last part of this study deals with elastic foil bearings of finite width and with the characteristic “edge effect” in particular. The influence of various parameters on the nature of the displacement field of foils is demonstrated and related to recent analyses [13].
The subject of this paper is the stability of externally pressurized gas bearings. The pertinent equations of motion are linearized and the stability criteria stated in terms of small deviations from the equilibrium operating point. The flow in the bearing clearance is treated on a distributed rather than on a lumped-parameter basis. Results obtained from present analysis when compared with those previously arrived at by means of simplified analyses [1, 3] show a marked divergence in the limiting values of parameters which influence the stability of the bearing. These results and divergences are discussed in terms of permissible compression volume, pressure ratios, supply-nozzle size, length of annular clearance, and bearing mass.
Novel thrust bearings, with spiral-groove, flexible membranes mounted on resilient supports, were designed and their performance convincingly demonstrated. Advantages of surface compliance were thus combined with the superior load-capacity of the spiral-groove geometry. Loads of 127–150N (29–33 lb) were comfortably supported on an area 42 cm2 (6.5 in.2), at speeds 43,000–45,000 rpm and mean clearances 15–20 μm (600–800 μin.), by these self-acting and air-lubricated bearings. Support-worthiness was proved under exacting conditions, when tested in conjunction with foil journal-bearings and a 19N (4.3 lb)-rotor, excited in a pitching mode by a total unbalance of 43 μm.N (6100 μin.oz).
A high-speed rotor, supported by an air-lubricated foil bearing, is rotated in both the vertical and horizontal attitudes at speeds in excess of 60,000 rpm. The rotor is stable and free from “half-frequency” or “fractional-frequency” whirl instability encountered in conventional gas bearings. External pressurization is applied to separate the foil surfaces from the journal during the initial and final stages of rotation, with adequate self-acting support and foil separation established at relatively low transition speeds. In the pressurized mode of operation, the system is characterized by a series of ultra-harmonic resonances, of sharply defined frequencies, related by fractions to speeds of synchronous resonance. In the self-acting mode of operation, the response of the system to residual imbalance is influenced by both the foil bearing and by the pressurized thrust bearings. The magnitude of the air gap (clearance) is determined at various rotational speeds and compared with theoretically predicted results. The temperature rise of the foil with speed is measured at various locations in order to assess its contribution to clearance growth. The journal and foil surfaces are examined and it is found that the foil bearing is endowed with excellent wipe-wear characteristics.
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