Aerostatic Thrust Bearings Research Articles

Structure Optimization of Aerostatic Thrust Bearing Based on Air Film Pressure Field Characteristics Analysis

The air film pressure field (AFPF) of aerostatic thrust bearings significantly determines the working performance of the bearings, and the characteristics of AFPF are closely related to the bearing structure parameters. This study carried out the structure optimization of aerostatic thrust bearing based on the analysis of the AFPF characteristics. The influence law of the number, distribution and the outlet shape of the orifices, as well as the bearing diameter on the static performance of the bearing was investigated. The relationship between bearing structural parameters, AFPF characteristics and bearing static performance was established and effectively used for the structure optimization of aerostatic thrust bearing. The simulation results were verified by the experiment. The results show that the static performance analysis of the aerostatic thrust bearing based on the AFPF characteristics can effectively provide a theoretical basis for the design and optimization of the bearing structure, and improve the bearing performance.

Effects of correction of thermal properties on 3D conjugate heat transfer of aerostatic thrust bearings

Effects of correction of thermal properties on 3D conjugate heat transfer of aerostatic thrust bearings

Design and Development of Different Applications of PATB (Porous Aerostatic Thrust Bearing): A Review

In several applications demanding precise and ultra-precision movements, porous aerostatic thrust bearings had been employed as a crucial precision engineering component and enabling technology. By acting as a lubricant between the moving part and the stationary part in aerostatic bearings, pressurized air almost completely eliminates friction. Since air acts as the lubricant, oil-based lubricants leave no debris behind. The air prolongs the life of the substances by preventing them from slipping and wearing. The aerostatic type uses graphite as a porous film to disrupt the air uniformly over the surface, or a tiny hole is drilled through the centre of the bearing to let the air circulate and produce a thin layer between the components. With an increased reliance on computational and mathematical methodologies for design and bearing performance optimization, this review paper aims to present the state-of-the-art in aerostatic bearings advancement and research. It also conducts a critical analysis of their future research directions and development trends in the next ten years and beyond. Air bearings are utilized in the production of tools like lathes, CMM, and grinders because they are highly precise in their operation and decrease mistakes and production time. Air bearings are available in a variety of forms and sizes. The assessment of future trends and obstacles in aerostatic bearings investigation, as well as their prospective applications in the precision engineering sectors, concludes the study.

Research Developments of Aerostatic Thrust Bearings: A Review

In aerostatic thrust bearings (ATBs), a high-pressure gas film with a certain bearing capacity and stiffness is formed by passing high-pressure gas between the moving surface and the static surface. Aerostatic bearings have outstanding advantages in the following aspects: high precision, high speed, and long service life, etc. They are widely used in many fields, such as high-speed air spindles, precision machine tools, air-bearing guideways, turbine machinery, and high-speed drills. With the pursuit of higher efficiency and high-precision machining machinery, there is an increasing demand for high-performance ATBs. Much effort has been spent on the study of ATBs, such as improvements in load capacity and stiffness, and the enhancement of stability. Some significant progress has been achieved. In this paper, the research developments of ATBs are summarized from several aspects, such as theoretical models and experimental methods, static performance, dynamic performance, and applications. In addition, insights on the breakthrough and development trends of ATBs are put forward. It is hoped that this paper can provide some guidance for the design and application of ATBs.

A newly treated boundary conditions to enhance accuracy of finite element analysis for orifice-type aerostatic bearings

Although numerical approaches have been extensively employed for solving the Reynolds equation in order to predict the performance of air bearings, we found inappropriate boundary settings can cause significant numerical errors if the grid-dependent condition is ignored. The current scrutiny is focused on crucial procedures for adopting the finite element method to assess the performance of orifice-type aerostatic bearings. To this end, numerical models for a single orifice-type are established and then checked by varying mesh sizes, mesh types, and boundary conditions (BCs). The obtained results reveal that those numerical models with a single-source node are grid-dependent, and the relative error is so large that the results are not credible compared with the analytical solution and becomes worse with denser meshes. This peculiar phenomenon can be mathematically interpreted by a one-dimension finite difference model calculated manually and auxiliary sources have proved to be an effective technique to reduce single-source numerical error to an acceptable level. Additionally, a physical explanation is given based on engineering systems modeling. By this view, rules of setting high pressure on the edge of recess are proposed and three types of grid-independent BC settings are proposed. Stiffness test experiments based on manufacturing a rotary table adopting multi-orifice aerostatic thrust bearings are further carried out to validate these numerical models, and the discrepancy between measured and calculated stiffness is reported to be lower than 5%.

Numerical study on the rotational and machining accuracy of an end-milling process with spindles supported by aerostatic bearings

Aerostatic bearings are widely used for spindles in ultra-precision machining tools. These spindles consist of a pair of aerostatic thrust bearings and several aerostatic journal bearings. The rotational accuracy of aerostatic spindles depends largely on the arrangement and performance of the individual bearings, but the evaluation of the rotational accuracy is mainly carried out experimentally using a prototype machine, which poses challenges in terms of the time and cost of building a prototype. Therefore, a real need exists to evaluate the spindle characteristics by numerical calculation. In this study, we developed a method to numerically calculate the trajectory of the spindle rotator which is supported by aerostatic bearings. The method was developed to numerically investigate and determine the effects on the rotational accuracy of the spindle during end milling when the cutting force is applied to the rotating rotor. A comparison was made regarding the amount of runout of the rotating shaft when side milling was performed using a spindle with a shaft diameter of 22 mm and a small end mill with a diameter of 1 mm, concerning three different spindles with different arrangements of thrust and journal bearings. The effects of rotational speed, radial depth of cut, and the number of tool teeth on the runout of the rotating shaft were numerically verified. As a result, it was found that a spindle structure in which the thrust bearing is placed on the tool side and the journal bearing span is lengthened is desirable.

An Improved Dynamic Modeling Approach of Aerostatic Thrust Bearing Considering Frequency-Varying Stiffness and Damping of Air Film

Abstract The damped mass-spring model is often used for the dynamic modeling and vibration analysis of aerostatic bearing systems by taking the air film as equivalent springs, especially when the bearing is used as a key component in mechanical equipment. However, the stiffness and damping of the air film are frequency-dependent, making the commonly used approach of taking static stiffness or fixed value as the spring coefficient no longer applicable for a bearing subject to a complex external force containing different frequencies. To address this issue, this paper develops the damped mass-spring model for the aerostatic thrust bearing considering the frequency-varying stiffness and damping by means of the linear superposition method. It indicates that the air bearing is still a linear system under a micro disturbance despite the frequency-dependent character of dynamic coefficients because the bearing vibration satisfies the superposition principle. The improved dynamic modeling approach is able to accurately and efficiently predict the overall dynamic response of the thrust plate with both axial and tilting motion when the plate is subjected to a multi-frequency vibration. In solving the overall dynamic response, the stiffness and damping associated with the responses of the transient part and steady part correspond to the natural vibration frequency and external disturbance frequencies, respectively. The feasibility and accuracy of the improved modeling approach are partly or completely verified by the direct trajectory calculation method, the computational fluid dynamics, dynamic mesh simulation, and a modal test. The proposed modeling method provides an effective way for the vibration analysis of air bearings, and in the meantime avoids the possible numerical errors caused by the traditional modeling approach.

Development of a CFD based parametric GUI for the design of the rectangular aerostatic thrust bearings

The CFD method is capable to investigate the influence of the geometrical parameters of the air film and the manufacturing error on the performance of aerostatic bearings. To facilitate the CFD based design of the aerostatic bearings, a parametric GUI for analyzing the performance of aerostatic bearing is developed, by which the performance of aerostatic bearings with varying geometrical parameters and manufacturing errors can be simulated efficiently. Furthermore, as a case study, the influence of the key geometrical parameters and the manufacturing errors on the performance of rectangular aerostatic bearings is investigated, which provides guidance for the design and manufacturing process of an aerostatic stage. Finally, the experimental test was conducted to verify the simulation result.

Structure design and performance analysis of aerostatic thrust bearing with compound restrictors

Aerostatic thrust bearing compensated by multi-orifices and porous material restrictor simultaneously is proposed to improve the static performance of the bearing. Load Carrying Capacity (LCC), stiffness and the flow field characteristics of the bearing are obtained by Computational Fluid Dynamic (CFD) simulation. The influences of supply pressure, orifice number, orifice diameter, orifice distribution, porous material thickness and permeability coefficient on the bearing performance are analysed. It is indicated that LCC and stiffness of the bearing with compound restrictors are much higher than those of the bearing with porous material restrictor or multi-orifice restrictor if gas film thickness is in rational range. The bearing with compound restrictors has better stability than that of the bearing with multi-orifice restrictor. Moreover, the optimum bearing parameters with compound restrictors are given to improving the performance of aerostatic thrust bearing.

Theoretical and Experimental Investigation on Air Film Pressure Field Characteristics of Aerostatic Thrust Bearing

This paper studied the air film pressure field (AFPF) characteristics of aerostatic thrust bearing, in which we proposed the measurement equipment for the 2D AFPF and successfully verified the theoretical simulation results. The experimental results agreed well with the theoretical results. However, in the area between the distribution circle of orifice to the air film outlet boundary, the experimental air film pressure (AFP) was slightly higher than the theoretical one. While for the area between the distribution circle of orifice and the center of the bearing, it showed the opposite law. Besides, the increase ratio of the AFP was close to that of the external load with its increase.

Dynamic Performance of Partially Orifice Porous Aerostatic Thrust Bearing.

The aerostatic thrust bearing’s performance under vibration brings certain changes in stiffness and stability, especially in the range of 100 to 10,000 Hz, and it is accompanied by significant increase in fluctuations due to the changes in frequency, and the size of the gas film damping. In this research work, an analysis is carried out to evaluate the impact of throttling characteristics of small size orifice on stiffness and stability optimization of aerostatic thrust bearings. There are two types of thrust bearing orifices such as: partial porous multiple orifice and porous thrust bearings and their effects on variations in damping and dynamic stiffness are evaluated. A simulation based analysis is carried out with the help of the perturbation analysis model of an aerostatic thrust bearing simulation by using FLUENT software (CFD). Therefore, two models of aerostatic thrust bearings—one with the porous and other with partial porous orifice are developed—are simulated to evaluate the effects of perturbation frequencies on the damping and dynamic stiffness. The results reveal a decrease in the amplitude of dynamics capacity with an increase in its frequency, as well as a decrease in the damping of partial porous aerostatic thrust bearings with an increase in the number of orifices. It also reveals an increase in the radius of an orifice with an increment of damping of bearing at the same perturbation frequency and, with an increase in orifice height, a corresponding decrease in the damping characteristics of bearings and in the dynamic stiffness and coefficient of damping of bearing film in the frequency range less than 100 Hz.

Dynamic Characteristics of Aerostatic Thrust Bearing Based on Fluid-structure Interaction

Dynamic Characteristics of Aerostatic Thrust Bearing Based on Fluid-structure Interaction

Effect of Surface Waviness on the Performances of an Aerostatic Thrust Bearing with Orifice-Type Restrictor

Effect of Surface Waviness on the Performances of an Aerostatic Thrust Bearing with Orifice-Type Restrictor

Research status and developing trends of gas bearing in recent years

As one kind of support elements for rotational machines, gas bearings that use air or gas as lubricant, have many attractive advantages such as low power loss, wide work temperature range, high rotating speed and low maintenance cost. However, gas bearings also have some disadvantages including low carrying load at low speed, wear at start-stop procedure, not easy to predict bearing performance due to the complex bearing structure and so on.The purpose of this paper is to explore the research status of gas bearing based on the Web of Science datasets and related tools, meanwhile, the developing trends emerged in gas bearing are further studied. The results shows that: 1) the top ten productive countries published 85% papers in the studies of gas bearing; 2) there are eight research clusters emerged in the topics analysis visualization and the top three largest clusters are #1 metal mesh foil bearing, #1 bump-type foil bearing and #2 aerostatic thrust bearing respectively; 3) Comparing to other research topics, foil bearings (metal mesh type and bump type)and aerostatic thrust bearing may be further explored in the future. This study presents intuitive state of research of gas bearings and proposes a fresh perspective for relevant researchers to perform research in the future.

Dynamic Quality of an Aerostatic Thrust Bearing with a Microgroove and Support Center on Elastic Suspension

The disadvantage of aerostatic bearings is their low dynamic quality. The negative impact on the dynamic characteristics of the bearing is exerted by the volume of air contained in the bearing gap, pockets, and microgrooves located at the outlet of the feeding diaphragms. Reducing the volume of air in the flow path is a resource for increasing the dynamic quality of the aerostatic bearing. This article presents an improved design of an axial aerostatic bearing with simple diaphragms, an annular microgroove, and an elastic suspension of the movable center of the supporting disk. A mathematical model is presented and a methodology for calculating the static characteristics of a bearing and dynamic quality indicators is described. The calculations were carried out using dimensionless quantities, which made it possible to reduce the number of variable parameters. A new method for solving linearized and Laplace-transformed boundary value problems for transformants of air pressure dynamic functions in the bearing layer was applied, which made it possible to obtain a numerical solution of problems sufficient for practice accuracy. The optimization of the criteria for the dynamic quality of the bearing was carried out. It is shown that the use of an elastic suspension of the support center improves its dynamic characteristics by reducing the volume of compressed air in the bearing layer and choosing the optimal volume of the microgroove.

Analysis of the dynamic characteristics of downsized aerostatic thrust bearings with different pressure equalizing grooves at high or ultra-high speed

This study adopts the DMT(dynamic mesh technology) and UDF(user defined functions) co-simulation method to study the dynamic characteristics of aerostatic thrust bearings with equalizing grooves and compare with the bearing without equalizing groove under high speed or ultra high speed for the first time. The effects of air film thicness, supply pressure, rotation speed, perturbation amplitude, perturbation frequency, and cross section of the groove on performance characteristics of aerostatic thrust bearing are thoroughly investigated. The results show that the dynamic stiffiness and damping coefficient of the bearing with triangular or trapezoidal groove have obvious advantages by comparing with that of the bearing without groove or with rectangular groove for the most range of air film thickness, supply pressure, rotation speed, perturbation amplitude, especially in the case of high frequency, which may be due to the superposition of secondary throttling effect and air compressible effect. While the growth range of dynamic stiffness decreases in the case of high or ultra-high rotation speed, which may be because the Bernoulli effect started to appear. The perturbation amplitude only has little influence on the dynamic characteristic when it is small, but with the increase of perturbation amplitude, the influence becomes more obvious and complex, especially for downsized aerostatic bearing.

Analysis of Flow Models for Aerostatic Thrust Bearings with Porous Material

The numerical determination of static characteristics of bearings allows a cost-efficient and fast pre-design. In this study, two flow models for aerostatic thrust bearings with pressurized porous material are presented and analyzed. The models are based on the coupling of the Reynolds equation for lubricants (REL) and the determination of pressure drop through porous material by Darcy’s law. The simplified model is based on the assumption of a one-dimensional axial flow through porous media. The extended model considers the three-dimensional flow in the porous body. The analysis includes pressurized air from 4 to 9 bar(a) with nominal clearance of 5 to 60 µm. Commercial CFD software was used to verify the results. The extended model allows a more accurate prediction about the performance in the critical gap range. In total, the results show good agreement with CFD within a short computation time.

Study on static performance of gas-lubricated thrust bearing based on multi-microporous stainless steel plate

A new type of multi-microporous stainless steel plate has been developed, and it has a lot of interconnected micropores on its surface and inside. The test results show that the pore size ranges from 0.1 to 15 μm and has regular shape. It is found that the plate has good air permeability by gas permeation test. The porous aerostatic thrust bearing is prepared by using this material, and the test results show that the bearing has high static bearing capacity. In FLUENT, the static characteristics of the porous gas hydrostatic bearing are simulated, and the simulation result is highly consistent with the experimental data, which verifies the correctness of the simulation and provides convenience for the study of the static characteristics of the porous gas hydrostatic bearing. The multi-microporous stainless steel plate can be used in ultra-high speed and ultra-precision instruments such as air lubricated motorized spindle and air bearing guide rail.

Multi-Field Coupling Dynamics Modeling of Aerostatic Spindle

The aerostatic spindle in the ultra-precision machine tool shows the complex multi-field coupling dynamics behavior under working condition. The numerical investigation helps to better understand the dynamic characteristics of the aerostatic spindle and improve its structure and performance with low cost. A multi-field coupling 5-DOF dynamics model for the aerostatic spindle is proposed in this paper, which considers the interaction between the air film, spindle shaft and the motor. The restoring force method is employed to deal with the times varying air film force, the transient Reynolds equation of the aerostatic journal bearing and the aerostatic thrust bearing is solved using ADI method and Thomas method. The transient air film pressure of aerostatic bearings is obtained which clearly presents the influence induced by the tilt motion of the spindle shaft. The motion trajectory of the spindle shaft is obtained which shows different stability of the shaft under different external forces. The dynamics model shows good performance on simulating the multi-field coupling behavior of the aerostatic spindle under external force. which is quite meaningful and useful for the further research on the dynamic characteristics of the aerostatic spindle.

A FEM based modeling method for analyzing the static performance of aerostatic thrust bearings considering the fluid-structure interaction

The fluid-structure interaction (FSI) phenomenon has significant impact on the performance of aerostatic thrust bearings. To rapidly calculate their performance, this paper proposes a finite element method (FEM) based FSI modeling method. A FEM model of aerostatic bearing and a two dimensional FEM model of thrust plate were built, and the bidirectional data exchange between them was realized. Besides, the change of discharge coefficient caused by FSI phenomenon is considered by adopting a discharge coefficient model. The accuracy of the proposed FSI model is verified numerically and experimentally. The average calculation time is reduced from 9.36 h to 86.2 s for the case study. This research provides an efficient modeling method for the design of aerostatic thrust bearing considering FSI.