Gas Journal Bearings Research Articles

The experimental investigations for the stiffness of the herring-bone grooved gas journal bearings.

Results are presented from an experimental investigation of the load and displacement characteristics of the Herring-bone Grooved Gas journal Bearings. The attitude and the bearing stiffness are measured for various rotations, clearances and groove depths, and the experimentally obtained characteristics are compared with the theoretically predicted characteristics. It is shown that the experimental results have good agreement with the theoretical prediction. But the tangential component of bearing stiffness is relatively larger than that predicted, so the herring-bone grooves are not so effective for pumping the fluid as the theoretical prediction indicates.

The unbalanced whirl of herring-bone grooved gas journal bearings. (2nd report. Expertimental investigations).

An experimental investigation is carried out to study the unbalanced whirl of herring-bone grooved gas journal bearings. The unbalanced whirls of both the cylindrical mode and the conical mode are measured individually by arranging the gap sensors at the appropriate positions along the rotor, and the relation of rotating frequency and whirl frequency is shown by measuring the acceleration of the bearing. These experimental results are compared with the theoretical predictions. This paper also describes the influence of the rotor centrifugal expansion on the whirl characteristics.

An investigation into the stability of herring-bone grooved gas journal bearings. 2nd report. Experimental study.

This paper presents a study for the self-excited whirl of Herring-bone grooved gas journal bearings. A comparison of the stability between the conical mode and the cylindrical mode is theoretically carried out for the experimental rotating system. These theoretical predictions are experimentally verified by measuring the whirl attitude. It is confirmed that the conical mode is more stbale. Also the characteristics of the self-excited whirl, such as the stability limit and the whirl frequency are measured, and these results are compared with conventional theoretical predictions.

Study of Conical Whirl Instability of Self-Acting Porous Gas Journal Bearings Considering Tangential Velocity Slip

The purpose of the present work is to study theoretically the conical whirl instability of unloaded self-acting porous gas journal bearings considering the tangential velocity slip at the bearing-film interface. The hydrodynamic pressure developed in the bearing clearance due to angular displacements of the journal at the midplane of the bearing is obtained by the simultaneous solution of equation of continuity in the porous medium and the modified Reynolds equations, satisfying the appropriate boundary conditions. With the help of the dynamic tilting stiffness and damping coefficients, stability characteristic is obtained. The effects of various parameters on conical stability parameter have been investigated for a nongyroscopic system.

The theoretical investigations for the stability of herring-bone grooved gas journal bearings. 1st report. Conical mode analysis.

The stability characterisitics of radially unloaded herring-bone grooved gas journal bearings are numerically analyzed by taking the angular mode bearing mechanical impedance into consideration. The influences of the construction of the rotating system and the effects of the polar mass moment of inertia of the rotor on the conical mode stability are discussed. Results show that the rotating system suspended by two bearings with a long span is fairly advantageous for the conical mode stability compared with the system suspended by a bearing. Also, it is found that the polar mass moment of inertia has great effects on suppressing the conical mode instability.

ポケット付きオリフィス絞りを有する静圧気体ジャーナル軸受の静特性

Recently, gas bearings have been used in high technology industry. But, conventional bearings have obliged mean clearance to be as wide as 20-30 μm by the use of inherently compensated restrictors. In this paper, an externally pressurized gas journal bearing is made as an experiment, and load capacity, stiffness and gas flow rate are measured. The test bearing is 30 mm in length, 30 mm in diameter, 3 mm in pocket diameter and 0.05, 0.1 and 0.2 mm in orifice diameter respectively. Following conclusions are obtained. (1) By the use of pocketed orifice restrictors, the stiffness is the highest at 7-13 μm in mean radial clearance without generating pneumatic hammer instability. (2) As the bearing can be operated with a narrow clearance, gas flow rate is about 4 L/min with 0.1 mm in orifice diameter and 10 μm in radial clearance at supply pressure of 0.6 MPa.

The unbalanced whirl of herring-bone grooved gas journal bearings. 1st Report. The theoretical analysis.

A method for estimating the unbalanced whirl characteristics of herring-bone grooved gas journal bearings by solving the appropriate dynamics equations is outlined. This method covers both cylindrical mode and conical mode whirl, and the interference of the two modes is considered. Here, also, the theoritical analysis for the bearing angular stiffness is presented.

Static characteristics of externally pressurized gas journal bearings with circular slot restrictors

The static characteristics of an externally pressurized gas journal bearing with a circular slot restrictor are described. The slot configuration is circumferentially continuous and is simpler than that of the journal bearing with discrete slots proposed by Dee and Shires 1. Here, the optimum design conditions for the load capacity are theoretically determined and it is shown that gas journal bearings with a circular slot restrictor possess a load capacity comparable to designs which have discrete slots.

Hybrid Porous Gas Journal Bearings: Steady State Solution Incorporating the Effect of Velocity Slip

A theoretical analysis is presented to predict the steady state performance characteristics of externally pressurized rotating gas journal bearings incorporating the effect of velocity slip at the porous interface. The governing equation for flow in the porous media and the modified Reynolds equation derived from the Navier-Stokes equations satisfying the velocity slip boundary condition, are solved simultaneously for film pressure distribution. Due to the nonlinearity of modified Reynolds equation the solution is obtained by perturbation method using finite difference technique. The dimensionless load capacity, attitude angle and mass rate of flow are computed numerically for different operating parameters. The effect of slip on the static characteristic is discussed. Comparison of the results with similar available solution for the no-slip case shows good agreement.

Stability analysis of externally-pressurized gas-lubricated porous bearings with journal rotation Part 2. Conical whirl

The stability analysis of externally pressurized gas journal bearings under conical mode of vibration has been obtained using a first-order perturbation method. The effect of journal speed, feeding parameter, supply pressure, porosity parameter and length-to-diameter ratio on the conical whirl and whirl ratio has been investigated.

Dynamic Properties of Externally-Pressurized Gas Journal Bearings with Circular Slot Restrictors

The externally-pressurized gas journal bearings with circular slot restrictors are investigated theoretically and experimentally to determine their dynamic properties. The theoretical analyses are presented for a single-row admission bearing and a double-row admission one. respectively, by using Reynolds equations in which inertial forces of a gas film are considered. The accuracy of the theoretical method is consequently shown that the present theoretical method can accurately predict the dynamic properties of a gas journal bearing with a circular slot restrictor.

Stability of a Rigid Rotor supported by Externally Pressurized Gas Journal Bearings with a Circular Slot Restrictor

In this paper, the stability of a rigid rotor supported by externally pressurized gas journal bearings with a circular slot restrictor is theoretically determined by the use of the small perturbation method with respect to whirling amplitude. In the theoretical analysis, influences of the inertia forces of the gas film on the dynamic properties of this kind of bearing are investigated and theoretical results are compared with experimental data. Good agreement between the theoretical and experimental results is obtained and it is found that the effects of various factors which affect the stability of a rigid rotor supported by this kind of bearings can be accurately predicted by the present method.

静圧気体ジャーナル軸受の負荷容量増加に関する一考察

In externally pressurized gas journal bearings, to avoid pneumatic hammer instability, a large pocket in the bearing surface cannot be used, and compressed air is supplied to the bearing surface through inherently compensated restrictor or pocketed orifice restrictor. Therefore, load capacity of gas bearings is less than that of hydrostatic bearings. This paper deals with externally pressurized gas journal bearing with the large land area in the pocket, and the improvement of load capacity without occurring pneumatic hammer instability. The test bearing is 46 mm in length, and 50 mm in diameter and out of roundness of the bearing diameter is less than 0.4 μm. The pocket is about 0.1 mm in depth, and the orifice is 0.2 mm in diameter. The following conclusions are obtained. (1) In case of no rotation, the test bearing with a pad in the pocket has the same load capacity as hydrostatic journal bearing with the same geometry. (2) Due to the hydrodynamic effects on the pad and the land, load capacity increases with the shaft rotational speed.

Theoretical Considerations of Molecular Mean Free Path Influenced Slip in Self-Acting Gas-Lubricated Plain Journal Bearings

The purpose of this paper is to study the effect of slip under the influence of molecular mean free path on the steady state and dynamic performance characteristics of plain gas journal bearings. The theoretical investigations have been made over a wide range of compressibility number. It is found that slip usually impairs the bearing performance, particularly at low compressibility numbers, A; the effect of slip, however, diminishes with increasing values of A. In fact at high compressibility numbers, theory suggests that slip has a beneficial effect of improving the dynamic performance of the bearing.

Circumferentially Grooved Hydrostatic Gas Journal Bearing

This paper presents static characteristic of a cicumferentially grooved hydrostatic gas journal bearing which is characterized by two circumferential grooves located near its ends wherein compressed gas is supplied through a small number of supply ports. Bearing efficiency, optimum clearance and flow rate of the novel bearing are analyzed numerically and its superiority in load capacity, stiffness and flow rate to the conventional discrete source bearing is shown at low supply pressure of less than about 105N/m2. Optimum design method is discussed. The numerical results are verified experimentally.

Analysis of Gas-Lubricated Foil Journal Bearings

This work is concerned with an evaluation of the performance of a gas journal bearing using a spring supported compliant foil as the bearing surface. The analysis, conducted for both single and multipad configurations, is concerned with the effects that the various structural, geometric, and operational variables have on bearing behavior. Following the solution of the relevant differential equation, tabular or graphical solutions are provided for a range of relevant geometric and operational parameters. The solutions include values of the colinear and cross-coupled spring coefficients due to both structural and hydrodynamic stiffness. Desirable design features with regard to start of bearing arc, selection of load angle, number of pads and degree of compliance are discussed.

Stability of Unsymmetrical Rigid Rotor Supported by Self-Acting Gas-Lubricated Journal Bearings

In order to determine the threshold of instability for an unsymmetrical rigid rotor supported by two identical self-acting, plain-cylindrical gas journal bearings, a theoretical approach is made by the use of the quasi-static nonliner PH method. Influence of various parameters affecting the threshold of instability of the unsymmetrical rotor is experimentally shown and compared with the theoretical results. The experimental variables considered in this paper include bearing load, bearing length, bearing clearance, the axial deviation of the center of gravity from the center of the rotor span. Good agreement was obtained between the experimental and theoretical results.

Graphical design procedures for slot entry hybrid gas journal bearings

The important parameters for the design of slot-restricted journal bearings are defined in this paper. A feature of the paper is the attention to tolerances on bearing clearance which have a significant effect on bearing performance and flow rate. A graphical design procedure is presented which removes the need for complex calculation by the designer and in addition allows the designer to assess the effects of adjusting certain parameters for his convenience. The design procedure presented is illustrated by a design example.

Dynamic performance of plain gas journal bearings

This paper presents dynamic performance characteristics of plain gas journal bearings. The perturbation formulation suggested by Lund has been modified to obtain stiffness and damping properties. Since rotor bearing axes are never perfectly parallel, the effect of skew has also been considered. Stability studies have been carried out for selected compressibility parameters

Dynamic Properties of Externally-Pressurized Gas Journal Bearings with Circular Slot Restrictors

Dynamic Properties of Externally-Pressurized Gas Journal Bearings with Circular Slot Restrictors