Externally pressurized gas journal bearing with slot restrictors arranged in the axial direction

doi:10.1016/j.precisioneng.2017.05.016

Precision Engineering

Volume 50, October 2017, Pages 286-292

https://doi.org/10.1016/j.precisioneng.2017.05.016 Get rights and content

Highlights

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We proposed an externally pressurized gas journal bearing with slot restrictors arranged in the axial direction.
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The angular stiffness of the proposed bearing was then compared with that of a conventional bearing. The proposed bearing stiffness was improved compared with the conventional bearing.
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A rotational test was conducted. The rotational speed of the rotor reached a maximum of 380 Hz (22,800 rpm), at which the rotor vibration was stabilized. This bearing can be expected to operate more higher rotation speed.
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The proposed bearing is suitable for use for various rotary machines.

Abstract

In this study, a novel rectangular slot restriction-type externally pressurized gas journal bearing was developed for use in high-speed rotating machinery, such as medical devices and industrial machines. The proposed bearing has several rectangular slot restrictors arranged in the inner surface of the bearing. To measure the bearing characteristics, a model was developed for the numerical calculation of the pressure distribution in the bearing clearance and the static characteristics of the bearing. The proposed bearing, which consists of two parts, was designed and can be manufactured using appropriate techniques. In this study, a prototype bearing with eight slots in its surface was manufactured as a test piece for fundamental tests. The diameter and length of the test bearing are 30 and 40 mm, respectively. The roundness of the bearing was measured using a three-dimensional coordinate measuring machine, and the results were used in the analysis. The pressure distribution and static characteristics obtained experimentally were found to be in good agreement with the calculated values. In the rotational tests, the rotor speed exceeded 380 Hz (22,800 rpm), and whirl vibration did not occur. During testing, the maximum rotor vibration amplitude was 0.002 mm, corresponding to an eccentricity ratio of 0.3.

Introduction

Externally pressurized gas journal bearings have advantages such as high-precision rotation, low frictional loss, and high rotational speeds. These bearings have been used in practical applications and have been studied for high-precision and high-speed devices, such as rotating machine tools and cryogenic turbo machines. Particularly, slot restrictors have been shown to produce a high load capacity and bearing stiffness [1]. Yoshimoto et al. have investigated and proposed a circular slot-restricted journal bearing and have numerically and experimentally clarified its static characteristics [2], [3]. Park et al. have conducted stability analyses and experiments on a spindle system using nonuniform slot-restricted gas journal bearings [4]. Their results showed that this bearing is much more stable than a conventional slot-restricted bearing because of the nonuniform slot clearance. Sharma et al. have researched a slot restriction-type journal bearing for incompressible fluid [5], [6]. They reported that asymmetric slot arrangements provide an improved stability threshold speed margin in comparison with asymmetric journal bearings. Ise et al. have researched the characteristics of a slot-restricted bearing with an asymmetric gas supply and an asymmetric bearing area and demonstrated that this bearing has a higher load capacity than conventional slot-restricted bearings [7], [8], [9], [10], [11].

The present authors have been developing new slot restrictor arrangement in a bearing that rotates at several tens of thousands of revolutions per minute with the aim of further performance improvement. In this study, the basic characteristics of the proposed bearing were verified as a first step in the development process. This report presents the calculation of static characteristics, an experimental verification of the pressure distribution and load capacity, and rotational test results. The results of this study demonstrate the sufficient practicality and effectiveness of the proposed bearing.

Section snippets

Configuration of the proposed bearing

The proposed bearing configuration is shown in Fig. 1(a) [12]. The bearing consists of two parts. To ensure the accuracy of the slot restrictor clearance after assembly, pins for positioning were installed on the end faces of each part. Pressurized gas is supplied from an outer source to the gas channel in the outer ring of the bearing. Then, the gas flows to rectangular slot restrictors (orange areas in Fig. 1(a)). The restrictors have a very narrow clearance in the axial direction and are

Calculation method

The calculation model for the proposed bearing is shown in Fig. 2. To calculate the static characteristics of the bearing, the divergence formulation method was applied [13], [14], [15]. In Fig. 2, the eccentricity ratio is defined such that positions below the geometrical center are positive. Moreover, the circumferential angle is defined as θ = 0 at the bottom and increases with counterclockwise rotation. The supplied gas flows from the slot inlet to the bearing edge via the slot and bearing

Experimental setup

The pressure distribution obtained using the above calculation method and the experimentally obtained pressure distribution were compared. The experimental setup used in this study is shown in Fig. 4. The test bearing was installed in a casing. The shaft could be moved in the axial and circumferential directions. The shaft is supported by a guide bearing. The pressure was measured through a small hole (diameter of 0.05 mm) using a pressure gauge. Pressure propagated through the inner channel of

Experimental setup

Fig. 7 shows a schematic of the experimental setup used to measure the static characteristics. The test rotor was fixed horizontally to the high-stiffness frame, and the test bearing was set at the center of the rotor. Pressurized gas was supplied to the bearing from an external source through a mist separator, an air filter, a regulator, a flow meter, and a pressure meter. A load was applied to the bearing housing via a load screw from the lower side. The load was measured using a load cell

Experimental setup

A schematic of the experimental apparatus used in the rotation test is shown in Fig. 11. The proposed bearing and rotor were positioned vertically. The test bearing was installed in a bearing casing. Both ends of the rotor were supported by externally pressurized gas thrust bearings. Pressurized air was supplied to the bearing from a gas compressor through a mist separator, an air filter, a regulator, and a pressure meter. The rotor was driven by an impulse turbine containing eight nozzles with

Conclusion

In this study, an externally pressurized gas journal bearing with slot restrictors arranged in the axial direction was developed. The gas restrictors in this bearing are in a novel configuration. To verify the fundamental bearing characteristics, the pressure distribution and static characteristics were experimentally measured and compared with the corresponding numerically calculated values; the measurement and calculation results were found to be in good agreement. The angular stiffness of

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(1971)
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Stability of a rigid rotor supported by externally pressurized gas journal bearings with a circular slot restrictor
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(1984)
S. Yoshimoto
Static characteristics of an aerostatic journal bearing with partially gas-fed slot restrictors: on the double-row admission bearing using feeding slits
Bull JSME
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J.K. Park et al.
Stability analyses and experiments of spindle system using new type of slot-restricted gas journal bearings
Tribol Int
(2004)
S.C. Sharma
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Tribol Int
(1999)
S.C. Sharma
Influence of elastic effects on the performance of slot-entry journal bearings
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Hydrostatic asymmetric journal gas bearings for largely unbalanced rotors of seismic ACROSS transmitters
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There are more references available in the full text version of this article.

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View full text

Externally pressurized gas journal bearing with slot restrictors arranged in the axial direction

Highlights

Abstract

Introduction

Section snippets

Configuration of the proposed bearing

Calculation method

Experimental setup

Experimental setup

Experimental setup

Conclusion

The current state of the art of fluid bearings with discrete slot inlets

Trans ASME Ser F

Stability of a rigid rotor supported by externally pressurized gas journal bearings with a circular slot restrictor

Bull JSME

Static characteristics of an aerostatic journal bearing with partially gas-fed slot restrictors: on the double-row admission bearing using feeding slits

Bull JSME

Stability analyses and experiments of spindle system using new type of slot-restricted gas journal bearings

Tribol Int

A study of slot-entry hydrostatic/hybrid journal bearing using the finite element method

Tribol Int

Influence of elastic effects on the performance of slot-entry journal bearings

Tribol Int

Hydrostatic asymmetric journal gas bearings for largely unbalanced rotors of seismic ACROSS transmitters

J Adv Mech Des Syst Manuf