气体静压小孔节流与多孔质节流性能的比较

本文给出了传统的小孔节流和多孔质节流轴承的理论分析，分析了外部供压气体轴承的进气形式对轴承性能的影响，对于不同类型的小孔节流和多孔质节流的轴承，本文给出了实验结果，并对轴承的性能参数即承载能力，刚度等进行了比较，作者分析了小孔节流和多孔节流止推轴承的承载能力和刚度，结果表明多孔质止推轴承同小孔节流轴承相比，具有高的承载能力。     

小孔节流静压气体轴颈轴承主轴系统的动态特性分析

通过对小孔节流静压气体轴颈轴承的雷诺方程与描述主轴系统的动力学数学模型联立直接进行数值求解,分析了轴承系统的动力学特性,研究了在不平衡质量作用下轴承主轴系统的响应。结果表明,由于精密离心机小孔节流静压气体轴承的支承刚度大,承载能力高,旋转主轴的运动是稳定的。但在一定条件下,旋转主轴有可能出现不稳定现象,这取决于主轴绕固联坐标系各轴之转动惯量间的关系、轴承支承刚度、主轴旋转速度和不平衡质量控制等因素。该方法用于精密离心机静压气体轴承主轴系统动力学的数值计算,提高了计算精度和可靠性。     

Design procedures for orifice compensated gas journal bearings based on experimental data

This paper presents a method for designing externally pressurized gas journal bearings with orifice compensation. The design procedures include a basis for prediction of bearing stiffness, load, and flow rate for a range of typical bearing configurations, and allow an interactive procedure whereby the designer can visually interpret the effects of various design changes. Guidance is given on bearing geometry to maximise load carrying capacity. Recommendations are also given to enable the designer to select the number of orifices to achieve the predicted load carrying capacity, as well as guidance concerning pocket geometry to minimise the possibility of pneumatic hammer instabilities. The effects on design performance due to variations of bearing clearance and orifice diameter are included and provides a basis for the tolerancing procedure which is proposed     

Stability of the rotor supported in gas journal bearings with a chamber feeding system

This paper describes the results of numerical investigations of the stability problem of the rigid symmetrical rotor supported in two externally pressurized gas journal bearings. The bushes of the bearings are mounted on a system of linear springs and viscous dampers. When the stiffness and damping coefficients of these springs and dampers are chosen correctly, it is possible to avoid the self-excited vibrations of the rotor. Such vibrations, which are caused by the phenomenon of a half-synchronic whirl, are the major obstacle to the widespread application of gas bearings. The results of authors numerical experiments have shown that the elastic support of the bearing bushes can be designed as an additional externally pressurized air ring, surrounding the bush. The set of parameters of such a ring is optimal when the bearing has a chamber feeding system.     

不同孔式节流器对圆盘止推气体轴承静特性的影响

采用保角变换有限元方法计算采用相同供气孔径的不同孔式节流器对静压圆盘止推气体轴承静特性(包括承载力特性、静刚度特性及流量特性)的影响。对承载力和流量特性的分析结果与Kazim ierski的研究结果一致,即:采用相同供气孔径的简单孔式和环形孔式节流器止推轴承,在其他几何参数和工作参数相同的条件下,前者的承载力系数高于后者,但后者的单位载荷气体消耗率要小于前者。对静刚度特性的分析结果表明,同尺寸供气孔径的简单孔式节流器与环形孔式节流器止推轴承,在其他几何参数和工作参数相同的条件下,可以实现的最大静刚度相当,但前者最大静刚度点对应的气膜高度大于后者,因此采用简单孔式节流器时,止推轴承的设计工作点对应的气膜高度可以大一些,这意味着可在一定程度上降低对轴承制造精度的要求。     

Analysis of orifice compensated externally pressurized gas bearings

Dynamic performance of orifice compensated externally pressurized gas bearings is considered. By adopting the finite element method and modifying the perturbation formulation of Lund, stiffness coefficients, damping coefficients, critical mass and threshold speed for various bearing eccentricities and design parameters have been computed.     

带有圆周方向均压槽的静压气体止推轴承的气锤自激

通过开设均压槽,可以增加静压气体轴承的承载能力和刚度,但是如果气体轴承的均压槽等参数设计不合理,会出现一种振动现象——气锤自激振动,尤其是设计高压重载气体止推轴承时。针对常用的圆盘止推气体轴承,建立轴承活动件的动力学方程,再运用小扰动方法和流量连续性方程得到了气锤自激振动的稳定性判别方程。通过求解稳定性判别方程,发现供气压力越大,自激振动的倾向性越强;气膜间隙在一定范围内容易引起自激振动;节流孔直径越大,自激振动的倾向性越强;当止推轴承的外径和内径的比值比较小时,容易发生气锤自激。通过计算得到了不发生气锤自激振动的轴承设计参数,可用于高压重载气体止推轴承的设计。     

Pneumatic hammer in an externally pressurized orifice-compensated air journal bearing

An experimental study was made of the occurrence of pneumatic hammer in an externally pressurized air journal bearing having double plane admission. Various parameters affecting the onset of pneumatic hammer were investigated. These were:- supply recess depth, supply orifice diameter and bearing mass. In general, pneumatic hammer is relatively easily avoided in journal bearings. However, achievement of repeatable results proved difficult, because of the effects of external damping and support stiffness. These factors are not incorporated in the existing theory. There were a significant number of instances where pneumatic instability was not apparent, although existing theory gave a strong indication of its occurrence. When pneumatic hammer did occur, there was broad agreement between experimental results and predicted trends as regards supply recess volume and supply orifice diameter, but not as regards bearing mass. The effects of external damping were important.     

Theoretical analysis and experimental verification on the static properties of externally pressurized air-bearing pads with load compensation

Load compensation can lead to externally pressurized bearings with infinite stiffness at the operating conditions. Calculations and experiments carried out on these bearings are discussed in this paper for two types of circular bearing pads with compliant surfaces. The mathematics is amply treated in appendices, and the numerical procedures are illustrated in diagrams. The experimental set-up is explained.     

一种球面气体静压轴承的建模与仿真

介绍了一种小孔节流式球面气体静压轴承,该轴承的加工工艺性较好,而且在各个方向上都有较大的支承力;针对该轴承支承力的计算提出了一种有限划分计算方法,在建模中考虑到气膜压力分布的不对称性,将轴承根据节流孔的数目划分为数个等分,对每个等分再进行有限划分,若划分数足够多,可以认为在每个小等分中的气膜压力沿划分方向无变化,以小等分中心的压力代替,从而简化了轴承的气膜压力分布的求解;借助MATLAB软件队轴承的支承性能进行了仿真计算,并通过实验进行比较验证,实验结果与仿真结果基本一致。     

The combined effects of the centripetal inertia and the surface roughness on the hydrostatic thrust spherical bearings performance

This paper deals with the surface roughness and the predominant centripetal inertia terms due to the shaft rotation of the externally pressurized thrust spherical bearings. The solutions are presented for the fitted type of bearings, un-recessed and recessed hemispherical and partial hemispherical seats, with capillary tube and orifice restrictors. On the basis of the stochastic theory, Reynolds equation is developed. The bearing surfaces are assumed to have randomly distributed roughness. Expressions for the pressure distribution, load carrying capacity, volume flow rate, frictional torque, friction factor, power factor, power losses and stiffness factor are obtained. The paper shows the combined effects of the centripetal inertia and the surface roughness on the bearing performance. An optimum design based on the minimum power losses, minimum flow rate and optimal restrictor dimensions is theoretically examined.     

均压槽与静压气体轴颈轴承承载特性的关系研究

主要研究通过开设不同结构形式的均压槽来提高静压气体轴颈轴承的承载能力和刚度,利用加权余量法和有限元离散化方法求解雷诺方程进行数值计算和仿真,针对单排孔和双排孔轴颈轴承,分析不同长度的周向均压槽,以及不同数量、不同位置和不同长度的轴向均压槽对轴承承载能力和刚度的影响规律。结果发现:开设周向均压槽和轴向均压槽都可以提高轴承的承载能力,相比开设周向均压槽,开设轴向均压槽对提高轴承的承载能力更为有效,而且只开设一条或两条轴向均压槽就能显著提高轴承的承载能力,通常将轴向均压槽置于气膜间隙较小的位置时能使轴承的承载能力和刚度最大。数值仿真结果通过试验进行验证,研究结果可用以指导高承载和高刚性静压气体轴颈轴承的设计。     

Analysis of externally pressurized gas bearings with journal rotation

Theoretical studies of rotating externally pressurized gas bearings with multiple pressure sources have been made. The solution is obtained for finite bearings by using pressure perturbation theory. Theoretical results are compared with experimental data. The theory allows good prediction of bearing load capacity, stiffness and attitude angle.     

The Performance of Externally Pressurized Bearings Using Simple Orifice Restrictors

The load capacity and vibration characteristics of externally pressurized thrust and journal bearings have been investigated. The bearings used orifices sufficiently recessed back from the bearing surface to ensure that the area of the orifice is the minimum presented to the gas flow. The journal bearings consist of plain cylinders with one or two rows of eight orifices, and the thrust plates of plain discs with six orifices drilled in equispaced circumferential grooves.

The load capacity of the thrust plates agrees with that calculated but the vibrations are greater than predicted. The load capacity of journal bearings is about half that calculated assuming axial flow conditions in the bearing, but circumferential flow can account for the difference. Synchronous and half-speed vibrations of a shaft rotating within these bearings have been measured and found to agree with those calculated on the assumption that the gas films behave as linear springs.     

Externally Pressurized Porous Thrust Bearings

The use of porous material in the bearing surface of externally pressurized thrust bearings leads to a compact design by eliminating the need for an external restrictor and has other potential advantages.

An experimental and theoretical investigation of the performance of such bearings, using liquid lubricants is described: the investigation is limited to static conditions but considers the effect of bearing geometry and variations in material properties on the load and flow rate.

Although the theory and experiment are not in complete agreement for the material used, it is shown that the characteristics can be predicted within reasonable limits.

At present, there are practical problems associated with machining the porous material and in evaluating its properties which may inhibit the use of porous, externally pressurized bearings.     

Externally pressurized gas bearings: A comparison between two supply holes configurations

Radial vibration of a vertical rotor with externally pressurized gas bearings is analyzed. The time-dependent Reynolds equation is solved together with the journal equation of motion to obtain the response characteristics of the bearing system. The bearings are supplied with either one or two sets of supply orifices. Stiffness and flow rate are compared for both cases. Stability maps are obtained at different supply pressures and with different supply orifice diameters. The mass range from orbital stability to instability is studied as a function of supply hole downstream pressure level.     

Discharge coefficient influence on the performance of aerostatic journal bearings

Aerostatic journal bearings need externally pressurized air. The discharge coefficient is usually assumed constant for sonic and subsonic flow conditions. However, some authors found that it is variable as a function of the pressure ratio, orifice throat discharge and supply pressures. The present study is a theoretical investigation of the discharge coefficient influence on the performance of aerostatic journal bearings. The Reynolds equation for compressible fluids is solved by the finite element method with triangular linear elements. For 0.5 eccentricity ratio, the bearing load carrying capacity difference is 0.5%, although the bearing total mass flow rate difference is 7.4%.     

小孔节流静压气体轴颈轴承的静态特性研究

通过对小孔节流静压气体轴颈轴承润滑方程的分析,利用泛函求极值法将二阶偏微分方程降为一阶,采用有限元方法,利用三角单元线性插值函数,简化压力分布方程式的计算,对轴承的参数进行了优化,得到了轴承上各点的压力分布和轴承的承载能力和支承刚度,并分析了轴承间隙和偏心率等因素对承载能力和刚度的影响。     

精密离心机静压气体轴承主轴系统的动力学特性分析

精密离心机静压气体轴承主轴系统的动力学特性分析是保障其标定加速度仪精度的重要研究课题。通过在 小孔节流静压气体轴承的雷诺方程式中加入节流孔的流量项,使计算得以简化;采用了泛函求极值法将二阶偏微 分方程离散化,用有限元法进行了承载能力和刚度的数值求解。把描述静压气体轴承工作的偏微分方程式(雷诺 方程)与建立的静压气体轴承主轴系统的动力学数学模型合并直接数值求解,提高了计算精度和可靠性。     

The design of partially grooved externally pressurized bearings

Most hydrostatic and aerostatic bearings are designed using external restrictors in order to obtain sufficient bearing stiffness. Alternatives such as the shallow pocket or partially grooved externally pressurized bearing are seldom applied, in spite of their advantageous constructive simplicity. In this article a simple analytical model to analyze journal bearings with partially grooved surfaces is described. The results of the analytical model are compared to the results obtained by numerical analysis. Both incompressible and compressible fluids are considered. The formulas derived are of extreme simplicity and helpful in finding the groove dimensions for optimal load capability and calculating approximate bearing characteristics using a simple calculator.