The design of high efficiency flat pad aerostatic bearings using laminar restrictions

The design of flat pad aerostatic bearings is examined to determine the best inlet arrangement to achieve high load capacity. The paper shows that like all other forms of aerostatic bearings, the optimum selection of supply to inlet pressure (K_g) and the optimum position of inlet devices can be achieved. The paper demonstrates a relatively new type of inlet geometry — the capillary inlet slot. Both single thrust pad and opposed flat pad bearings arrangements are examined. A theoretical analysis of the flat pad arrangements has been developed using a finite difference approach previously adopted for the analysis of externally pressurized journal bearing arrangements¹.     

Performance analysis of Pareto optimal bearings subject to surface error variations

A Pareto optimization study was carried out on a flat pad aerostatic bearing design. Some of the Pareto optimal configurations were then subjected to surface profiling errors including tilt, concavity, convexity and waviness and key performance parameters such as load capacity, stiffness and flow rate determined. From these studies it was concluded that multi-orifice aerostatic flat pad bearings are highly sensitive to surface profile variations and these surface profile variations are inherent limitations of the current manufacturing techniques. A technique to account for the sensitivity to manufacturing tolerance within air bearing optimization studies is also proposed.     

Dynamic tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors

Aerostatic rectangular double-pad thrust bearings with compound restrictors have often been used in linear guideway systems of ultra-precision machine tools and precision measuring equipments, because high bearing stiffness is easily achieved in these bearings. However, in actual devices, various dynamic loads as well as static loads are imposed on these aerostatic bearings. Therefore, in this paper, the dynamic stiffness and damping coefficient of this type of bearing for tilt motion of a shaft are investigated, both theoretically and experimentally. It was consequently found that the dynamic tilt characteristics of the aerostatic thrust bearings considered in this paper are greatly influenced not only by design parameters such as the groove position and the groove depth but also by the squeeze effect.     

Analysis of tapered land aerostatic bearings for combined radial and thrust loads (yates' configuration)

In this paper the analysis of tapered land aerostatic Yates' bearings for supporting combined radial and thrust loads is presented. Air flow in the journal and thrust bearings is expressed in terms of the Reynolds equation and the Navier-Stokes equations respectively. The pressure distributions in the bearing clearance are obtained by solving these equations using a finite difference numerical technique. The effects of various design and operational parameters on the performance of the combined journal and thrust bearing are reported. In conclusion, guidelines for the optimal design of such bearings are suggested.     

Static tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors

Aerostatic rectangular thrust bearings with compound restrictors have often been used in ultra-precision machine tools and precision measuring equipment because high bearing stiffness is easily achieved. Compound restrictors combine a feed-hole restrictor with a groove compensation restrictor. This paper investigates, theoretically and experimentally, the static tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors, when coupled loads or offset loads are applied. Furthermore, the usefulness of aerostatic thrust bearings with compound restrictors is clarified by comparison with the characteristics of conventional aerostatic thrust bearing with feedhole restrictors.     

Design and test of a Pareto optimal flat pad aerostatic bearing

This paper discusses the design and assessment of a Pareto optimal aerostatic flat pad bearing. The design of such bearings is a multi-variable, multi-criteria problem. The criteria used were load capacity, flow rate and stiffness. The design technique does not rely on weighting the criteria at the outset but allows a final design to be selected from the Pareto set. The final design was assessed using an automated experimental rig to obtain load/deflection data, mass flow rates, and film pressure profiles for a range of gap heights. The experimental performance of the Pareto optimal bearing is shown to compare well with the theoretical prediction at lower gap heights.     

高速空气静压径向轴承稳定性的试验研究

高速空气静压轴承的稳定性问题实质上是涡动振动问题,它是空气轴承在高速场合应用的一大障碍。本文对空气静压轴承在0～24万转/分范围内。刚性支承的情况下,从介绍测试涡动振幅与频率的关系开始,进行了供气压力、轴承间隙、不平衡量大小等因素对高速稳定性影响的试验分析;比较了沟槽、孔式及切向进气等五种结构轴承的高速特性;给出了试验发现的一些规律;涡动起始速度随间隙的变化关系存在有两个最佳间隙,第二最佳间隙的大小远远超过了一般设计概念所考虑的范围;沟槽节流轴承的稳定性优于孔式节流的;单排轴承的稳定性比双排的优越;沟槽节流轴承也存在所谓“阻塞”的问题。最后指出了高速空气静压轴承设计上的一些基本问题。     

气浮主轴轴向闭式支承系统静特性数值分析

求解气体润滑问题的最大难点在于如何获得雷诺方程的精确解。为了提高气浮主轴轴向支承系统的设计精度,在建立小孔节流气体静压止推轴承润滑数学模型的基础上,运用有限元方法对雷诺方程进行离散化。基于MATLAB7.0工具平台,采用超松弛迭代法,开发求解气体静压止推轴承压力方程与静特性的数值仿真软件。以某气浮主轴轴向闭式支承系统静特性参数设计为例,通过数值仿真,获得单侧止推轴承润滑气膜的压力分布,及不同节流孔直径与不同供气压力下的静特性性能;以刚度最大为优化目标,确定该气浮主轴止推轴承的结构参数与操作参数,并由此获得闭式支承系统的静特性。     

Air Vortices and Nano-Vibration of Aerostatic Bearings

Small vibration on the order of nanometers poses challenges for the application of aerostatic bearings in ultra-precision machine tools and metrology equipments. In this article, the flow field in aerostatic bearings is numerically investigated and air vortices in the recess are analyzed. Vibration of the aerostatic bearing is also experimentally measured. Design and functioning parameters are varied to study their effects on the air vortices and nano-vibration of aerostatic bearings, and a direct relationship is established between the gas vortices and nano-vibration in aerostatic bearings. It is demonstrated that vibration energy of the aerostatic bearing increases with the strength of air vortices.     

Prevention of fluttering fatigue damage in a tilting pad journal bearing

Tilting pad journal bearings have been widely used to support high-pressure/fast rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damage in the upper unloaded pads and the break of locking pins by pad fluttering continuously take place in actual steam turbines. The purpose of this paper is to develop a bearing model that can prevent bearing problems effectively using pad fluttering in a tilting pad journal bearing. A developed bearing model with a wedged groove is suggested from studies of a fluttering mechanism performed in previous research. The fluttering characteristics of the upper unloaded pad are studied experimentally in order to verify the reliability of the bearing model. It was found that very little pad fluttering nearly occurs in the bearing model under various experimental conditions. In addition, no type of bearing failures by pad fluttering was detected in applications involving actual steam turbines.     

Comparison of power loss and pad temperature for leading edge groove tilting pad journal bearings and conventional tilting pad journal bearings

A study was undertaken to compare power loss and pad temperature characteristics between LEG (leading edge groove) tilting pad journal bearings and conventional tilting pad journal bearings with and without a seal tooth. All test bearings were double tilting type with six-pad LOP (Load On Pad), 300.6 mm inner diameter, and 120.0 mm effective length. Pad temperatures and power losses were compared and evaluated versus rotor rotational speed, oil flow rate, and static load. Four kinds of tilting pad journal bearings were evaluated, conventional tilting pad journal bearings with and without a seal tooth and LEG tilting pad journal bearings with and without a seal tooth.Test results indicate that tilting pad journal bearings without a seal tooth have lower power loss and pad temperature than tilting pad journal bearings with a seal tooth. Especially, conventional tilting pad journal bearing without a seal tooth has the lowest power loss and pad temperature among the test bearings.     

On the design and development of hybrid journal bearings: a review

This paper presents a comprehensive review of developments in the design and application of hydrostatic and hybrid journal bearing systems during the last few decades. Revolutionary changes have taken place in the applications of hydrostatic and hybrid journal bearings, from very low‐speed radar to very high‐speed turbo‐machinery and ultra‐precision machine tools requiring high stiffness to improve accuracy. Hydrostatic and hybrid bearings are of interest because of their potential at very high operating speed and heavy load‐carrying capacity. This paper also outlines the analyses done of these types of journal bearings in practical application, which has led to improved bearing design. This review critically discusses the parameters that significantly affect the static and dynamic performance of a journal bearing. This review includes coverage of recent publications in the literature pertaining to hydrostatic and hybrid journal bearings focusing on the influence of parameters such as bearing geometry, supply pressure, flow control devices, fluid compressibility, fluid inertia, journal misalignment, bearing flexibility, surface roughness, and thermal effects. Copyright © 2006 John Wiley & Sons, Ltd.     

空气静压轴系支承的数值分析

采用有限差分技术,对精密轴系中的径向和轴向空气静压轴承进行了数值分析。主要针对有多个供气孔的径向轴承的复杂流场,沿周向展开承载曲面以雷诺方程为气体润滑的控制方程。同时根据质量守恒原理,制定出每个供气孔出口压力边界条件逐轮修正的迭代路线,计算出不同偏心率和供气压力下的压力分布、承载能力及流量。该技术成功地用于轴系支承精确设计并制造出精密模块化主轴轴系。     

Improvement of static characteristics of an aerostatic journal bearing using the elastic deformation of an O-ring

A new type of aerostatic journal bearing in which the elastic deformation of an O-ring is used to improve its static characteristics is proposed. The static characteristics of this bearing are determined theoretically by both the finite difference method and the small perturbation method. Effects of parameters on the static characteristics are shown, and the optimum design method for the static characteristics is discussed. Further, theoretical results are compared with experimental results to confirm the validity of theoretical predictions. It is consequently found that the new type of bearing possesses higher static stiffness and greater load capacity than conventional point source bearings with inherently compensated feeding holes.     

The design of aerostatic bearings for application to nanometre resolution manufacturing machine systems

This paper addresses the design of aerostatic bearings for use within machines requiring nanometre precise translation or rotation. The major design parameters which affect aerostatic bearing performance are discussed. The supply pressure ratio and hence, the bearing clearance and the type and specific size of inlet flow control device are shown to require special consideration. Specific information on the tolerance of each of the parameters which have a direct effect on the nano-precision location of these bearings is given. In addition the paper addresses the manufacturing tolerances and manufacturing variations which can occur in practice and places limits on the magnitude that these sources of errors can contribute to the permissible manufacturing variations.     

A new basis for the optimization of hybrid journal bearings

A design strategy is presented for hybrid hydrodynamic/hydrostatic journal bearings which maximizes the hybrid load for minimum total power dissipation. It is shown that the detailed design of hybrid bearings is quite different from the design of recessed hydrostatic bearings. It is found that design for hybrid operation may lead to substantial increases in load support with significantly less total power dissipation than would be required if the designs were developed from hydrostatic bearing procedures.A new technique for optimizing hybrid journal bearings is presented. The method involves the comparison of the bearings to be optimized with a reference bearing on the basis of load/total power, load/pumping power and load/flow.     

Analysis of a tilting pad journal bearing to avoid pad fluttering

This paper describes the investigation into the static and dynamic performance of a tilting pad lightly loaded journal bearing. Some of the bearings were operating with some of the pads fluttering. The analysis of the bearings confirmed the likelihood of pad fluttering and so three possible means to overcome this phenomenon were investigated. Introducing a pad preload would require the installation of a number of shims into the bearing. Similarly, installing pad stops and/or springs introduced more working parts to each bearing. The third option of machining a leading edge taper or relief on each pad was deemed to be the better solution. The geometry of this relief (depth and length around the arc) was found to be an important design parameter. The larger the angular extent of the relief and the deeper it is were found to increase the oil flow rate, thereby reducing the operating temperature of the bearings. The direct stiffness of the bearing is improved by introducing a relief to the leading edge of each pad. Design changes were made to the actual bearings with a significant reduction in bearing operating temperature and wear.     

Theoretical analysis of compliance and dynamics quality of a lightly loaded aerostatic journal bearing with elastic orifices

Active aerostatic bearings, the main advantage of which is their ability to provide negative compliance, are gradually being used in metal-cutting machines as load-bearing structures and as automatic compensators for the deformation of their technological system. The disadvantages of such bearings are an increased tendency to instability and poor dynamics quality. The article proposes a new design and method for improving the quality of the dynamics of aerostatic bearings. The study was made based on the static and dynamic characteristics of an active radial aerostatic bearing, which compensates for lubricant consumption by elastic orifices. The design implements the principle of combined external throttling, the use of which makes it possible to obtain high-quality characteristics in the low, zero, and negative compliance modes of the carrier lubricating gap. It was also established so that the design with rigid orifices provides ideal dynamics quality and can be used instead of conventional aerostatic bearings with simple or ring diaphragms.     

静压孔位置对油膜支承可倾瓦轴承承载性能的影响分析

为了提高汽轮机转子系统中支承轴承的油膜刚度,以三瓦油膜支承可倾瓦轴承为研究对象,研究静压孔相对位置对轴承承载性能的影响规律。建立了油膜支承可倾瓦轴承油膜润滑模型,并运用计算流体动力学方法数值求解三维N-S方程,揭示了不同静压孔相对位置下轴承压力分布、最小膜厚、偏心率、刚度等性能参数的变化规律。分析结果表明：在载荷为890 N的情况下,改变孔的位置可以提高轴承油膜刚度;当静压孔相对位置γ=5°左右时,孔位置接近油膜最大压力分布区,与γ=0°时相比,最小膜厚和偏心率分别减小9.8%和48%,主刚度kyy、kxx接近原结构的1.4倍和1.1倍,此时静压孔位置为相对最优位置区域。依据分析结果开发了新型油膜支承可倾瓦轴承（γ=5°）,通过试验对比分析了普通滑动轴承与新型油膜支承可倾瓦轴承的综合性能,结果表明,高转速时所开发的新型油膜支承可倾瓦轴承具有更好的承载性能与减振性能。研究结果对油膜支承可倾瓦轴承的性能分析具有一定的参考价值,设计轴承静压孔时可根据油膜压力分布规律对其优化以提高轴承性能。