Air-lubricated Bearings Research Articles

An Experimental Study of High-Speed Rotors Supported by Air-Lubricated Foil Bearings—Part 2: Response to Impact and to Periodic Excitation

A high-speed rotor, supported by an air-lubricated foil bearing is stable at speeds up to and in excess of 60,000 rpm. “Natural frequencies” are determined at various rotational speeds from records of response following impact of the rotor housing. The foil-rotor system is subjected to periodic, unidirectional excitation by means of a vibrator (shake table) and the in-line and transverse responses are obtained in a frequency range 50–2000 cps. The behavior of the system is similar to that of a simple, damped oscillator, characterized by a single resonance in the low-frequency range. Experimentally determined values of resonant frequencies are in fairly good agreement with predicted results, based on a simplified theoretical formulation of the problem. Responses of rotors to (a) excitation of variable amplitude at resonance and to (b) excitation of variable amplitude at frequency equal to half the rotational speed are investigated. It is found that excitation and rotor excursion are nearly colinear, except in the neighborhood of resonance. Excitation at frequency equal to half the speed of rotation is not associated with large amplitudes of motion, wherein the foil bearing compares favorably with other types of fluid-film bearings.

A recording, air‐bearing torsion pendulum

AbstractA recording torsion pendulum has been designed which allows the measurement of storage modulus and loss modulus for weak gels. The gel is held in a cone–plate geometry. The 5° cone, along with the inertial elements of the pendulum, is supported by an air‐lubricated bearing. The decay of oscillations is sensed by a Proximeter which does not touch the moving apparatus and which converts the amplitude of oscillation into a de signal of several volts. Storage moduli as low as 40 dyn/cm2 and log decrements as low as 0.0054 have been measured.

Some factors affecting the whirl instability of a Journal bearing (part 2) : R. M. Bouwman, L. C. Collingwood and J. W. Midgley, Second Convention on Lubrication and Wear, 1964, Paper 5. To be published in the Proc. Inst. Mech. Engrs., London, 1964/1965; 8 figs., 1 table, 4 refs.

The paper contains the description of the test rig and first experimental data regarding the mechanical and the thermal behaviour of a 7 kg rotor, 460 mm long and with a diameter of 50 mm, supported by externally-pressurized air-lubricated bearings. The rig allows to load the rotor radially and axially both in static and dynamic conditions and to measure the orbits on the supports. The rotating imbalance response at different speeds has been measured up to 60,000 rpm. The orbits are always synchronous with the rotational speed and their shape changes also with temperature (though this effect is almost negligible). The rotor is stable and does not present whirl instability.

Investigation of Whirl in Externally Pressurized Air-Lubricated Journal Bearings

The nature of whirl of a rigid rotor in externally pressurized air-lubricated journal bearings, including self-acting bearings as a special case, is discussed and an experimental investigation described. Rotor unbalance leads to synchronous whirl which can persist through one or more critical speeds. Self-excited whirl is likely when the rotational frequency is about twice the lowest critical frequency. We discuss the effects of supply pressure, number and location of sources, rotational speed, mass, unbalance, and load upon the onset of self-excited whirl, and describe first-order prediction techniques.

A special analytical study of air-lubricated bearings for jet aircraft engines : George M. Robinson. Final Technical Report. Prepared on NACA Contract NAw-6473 Laboratories for Research and Development, Franklin Inst. Report F-A 1914. (Ask for N-79697) March 7, 1956 to February 15, 1957. 75. pp., diagrs.

A special analytical study of air-lubricated bearings for jet aircraft engines : George M. Robinson. Final Technical Report. Prepared on NACA Contract NAw-6473 Laboratories for Research and Development, Franklin Inst. Report F-A 1914. (Ask for N-79697) March 7, 1956 to February 15, 1957. 75. pp., diagrs.

Air-lubricated bearings for high-speed motors and turbines. (in Russian) : S. A. Sheinberg and A. M. Kharitonov. Vestnik mashinostroeniia, v. 38, no. 9, Sept. 1958, p. 14–17

Air-lubricated bearings for high-speed motors and turbines. (in Russian) : S. A. Sheinberg and A. M. Kharitonov. Vestnik mashinostroeniia, v. 38, no. 9, Sept. 1958, p. 14–17

An Experimental Investigation of the Pressurized Air-Lubricated Journal Bearing in the High-Speed Range

Experimental apparatus has been developed and used to study the friction characteristics of an externally pressurized air-lubricated journal bearing. The effects of variations in speed, load, diametral clearance, and inlet pressure have been studied over a wide range at high speeds. The experimental friction coefficients have been compared with those given by the well-known Petroff (1)† formula, and a reasonable degree of correlation has been found. Bearing air consumption has been measured and a linear relationship between air-mass flow and inlet pressure is indicated. Curves relating load-carrying capacity to various ratios of inlet pressures are included, the applied loads being carried by hydrostatic flotation in all cases. The bearings used were plain, cylindrical bushes of diameter in. and length in. Compressed air was admitted through three sets of radial-inlet holes around the bush circumference, pressures being adjusted to keep the shaft and bush as close to concentric as possible.

Research in the field of roller bearings. (in Russian) : N. A. Spitsyn. Vestnik Mashinostroeniia, v. 38, no. 3, Mar. 1958, p. 3–8

The paper contains the description of the test rig and first experimental data regarding the mechanical and the thermal behaviour of a 7 kg rotor, 460 mm long and with a diameter of 50 mm, supported by externally-pressurized air-lubricated bearings. The rig allows to load the rotor radially and axially both in static and dynamic conditions and to measure the orbits on the supports. The rotating imbalance response at different speeds has been measured up to 60,000 rpm. The orbits are always synchronous with the rotational speed and their shape changes also with temperature (though this effect is almost negligible). The rotor is stable and does not present whirl instability.

Air-lubricated bearings with capillary air-feeder holes : Tokio Sasaki and Haruo Mori. Kyoto University, Memoirs of the Faculty of Engineering, v. 19, Apr. 1957, p. 14–24

Air-lubricated bearings with capillary air-feeder holes : Tokio Sasaki and Haruo Mori. Kyoto University, Memoirs of the Faculty of Engineering, v. 19, Apr. 1957, p. 14–24

空気軸受とその実用性

空気軸受とその実用性

Research on the Air-Lubricated Bearing with Capillary Air-supplying Holes

As reported previously, the stability of air-lubricated bearing operating at high speed was much improved by setting a primary restrictor like a nozzle before the air-supplying hole against the position of the secondary restrictor through which air flows into the bearing clearance just after the air-supplying hole. When the capillary is applied as air-supplying hole, it becomes the primary nozzle and at the same time it possesses the activity of the secondary restriction just before the bearing clearance. In order to obtain a stable air-lubricated bearing, a number of capillary holes are located about the bearing equally spaced around its circumference, because these holes possess the activity which restrains probable vibration of shagt at high speed rotation. Then the air-lubricated bearings with capillary holes have been experimented by measuring frictional coefficient and quantity of air-flow and most suitable design of capillary holes is discussed. After all, the bearings running in very stable condition with extremely slight friction have been obtained.

Air-Lubricated Bearings for Spinning Spindles (1st Report)

Succeeding the previous reports, the new-designed spindle with a radial air-lubricated bearing and a thrust bearing made of a steel ball has been investigated. Such design of thrust bearing is taken owing to the fact that the thrust air-lubricated bearings with conical surface are not sufficient to reduce the frictional power as described in the previous reports. But the design of the upper radial bearing is left as same as it was in the 2nd report, because it had the good characteristic. As an exprimental result, it is clarified that the new spindle is superior to the other spindles especially in the range of high speed rotation, and its frictional power at 12, 000rpm is as small as about 25% of the ordinary oil-lubricated spindle, 60% of the air-lubricated spindle in the 1st report and 80% of the spindle in the 2nd report. And moreover, by measuring the flowing quantity of air and calculating the power required to compress air, the total power of the new spindle, that is the sum of the frictional and air-compressing power, is shown to be less than the power of the ordinary oil-lubricated spindle. This fact shows that the air-lubricated bearing is practically useful for the spinning spindles.

Air-Lubricated Bearings for Spinning Spindles (2nd Report)

Succeeding the research of the 1st report, the design of air-lubricated bearing of the spinning spindle has been changed and specialized, and the operating characteristics of the spindle is inspected, comparing the oil-lubricated spindle with the formerly designed air-lubricated spindle. As an experimental result, it is obtained that the frictional power is reduced to about 30% of that of the oil-lubricated spindles and about 50% of the formerly designed air-lubricated spindle. Such result shows an evident advance comparing with the result of the 1st report.

Air-Lubricated Bearings for Spinnings Spindles (3rd Report)

Air-Lubricated Bearings for Spinnings Spindles (3rd Report)

On the Effects of a Restrictor before the Air-Hole of Air-Lubricated Bearing

It is generally known that the air-flow between the air-hole and the bearing clearance of the air-lubricated bearing is equivalent to the air-flow through a nozzle. In this case, when a restrictor that corresponds to the air-hole and bearing clearance is set before the air-hole, the pressure in front of the air-hole will increase or decrease with the decrease or increase of the bearing clearance same as the gage pressure in the high pressure type pneumatic gage, and then the eccentric motion of shaft will be controlled automatically. Then these effects of a restrictor before the air-hole were clarified by measuring the coefficient of friction, and the cross-sectional area of the restrictor and the air-supply pressure were determined for these effects.