Aerostatic Thrust Bearings Research Articles

Aerostatic Thrust Bearing with a Self-Controlled Restrictor Employing a Floating Disk. Static Characteristics.

In this paper, the static characteristics of a new type of aerostatic thrust bearing with a self-controlled restrictor is proposed in order to establish a very high stiffness (nearly infinite stiffness).The self-controlled restrictor used in this bearing makes use of the balance of fluid-film forces acting on both sides of the floating disk to control the gas flow entering a bearing clearance. Since various design parameters influence the static characteristics of the proposed bearing, the effects of these parameters are discussed theoretically and experimentally. Then the optimum design method to obtain higher stiffness is also discussed. It is consequently demonstrated that the proposed bearing can have a very high static stiffness, about ten times as high as that of a conventional aerostatic thrust bearing.

Zero-compliance aerostatic bearing for an ultra-precision machine

A new type of active air film restrictor is proposed for obtaining a zero-compliance aerostatic thrust bearing. The moving member in the active retrictor is sopported elastically. This active restrictor can therefore be called an aerostatically controlled-restrictor (ACR). Experiments show that the compliance of the thrust bearing with the ACR can be less than 1 nm N −1 when the frequency of the applied load is less than 2 Hz. Pneumatic hammer does nor occur during the experiments.

A Design Methodology for Obtaining Infinite Stiffness in an Aerostatic Thrust Bearing

The desire to maintain high positional accuracy has led to many unique bearing designs which achieve high, and even infinite, stiffness. This paper presents a design procedure for an aerostatic thrust bearing and demonstrates that infinite stiffness may be attained by proper selection of the bearing’s geometric parameters. The bearing is comprised of two main components; the bearing housing and a flexible membrane that deflects due to changes in load. The current analysis employs plate equations to approximate the behavior of the membrane. Optimization techniques are utilized in the design algorithm and the results are presented in the form of a design chart or nomograph. Additionally, so that the results may be extended to other bearing sizes and gas properties, scaling laws are developed based on a dimensional analysis of the associated variables.

Design of aerostatic flat pad bearings using annular orifice restrictors

Design charts are presented for use in the design of aerostatic thrust bearings which use annular orifice restrictors. Annular orifices are preferred when pneumatic hammer instability is a potential problem. The design procedures presented are based upon analyses produced using finite difference equations to the compressible form of the Reynolds equation. The method provides the designer with a graphical technique that enables him to take into account bearing stiffness, clearance, number of orifices and bearing dimensions in obtaining a satisfactory solution to his problem.

Analysis of tapered land aerostatic thrust bearings under conditions of tilt and rotation

In this paper the theoretical analysis of tapered land aerostatic thrust bearings operating under conditions of tilt and rotation is reported. For a known bearing geometry, the radial and circumferential pressure distributions in the bearing are obtained by solving the Reynolds equation using a finite difference numerical technique. The effects of various design and operational parameters, such as the taper, size of pad, supply pressure, tilt angle and speed of rotation, on the load-carrying capacity, stiffness and mass flow rate of the bearings are reported.

Design of aerostatic flat pad bearings using pocketed orifice restrictors

Design charts are presented to enable the design of aerostatic thrust bearings which use pocketed orifice restrictors. Attention has been paid to ensuring that pneumatic hammer instability is avoided by providing design information on the maximum depth and diameter of the orifice pocket. The design procedures presented are based upon analyses produced using finite difference equations to the compressible form of the Reynolds equation. The procedures presented provide the designer with a graphical technique that enables him to take into account stiffness, clearance, number of orifices and bearing dimensions when deriving a satisfactory solution to his problems.

Steady-State Characteristics of Aerostatic Porous Rectangular Thrust Bearings Incorporating the Effects of Velocity Slip, Anisotropy and Tilt

A generalized solution is presented in order to predict the steady-state performance characteristics of aerostatic porous rectangular thrust bearings of finite pad thickness. The analysis takes into account the Beavers-Joseph criterion for velocity slip at the bearing interface, the anisotropy of the porous material and the tilt of the bearing. Dimensionless load capacity, mass flowrate of the gas and static stiffness are computed numerically for different operating parameters and bearing dimensions and presented in the form of design charts. The effect of slip is to reduce the load capacity and increase the mass rate of flow.

A Simplified Procedure for Predicting the Performance of Inherently Compensated Aerostatic Thrust Bearings

Simplified theoretical predictions of load capacity, flowrate and stiffness are compared with measured performance. Reasonable agreement is achieved if the roughness of the bearing surfaces and an empirical discharge coefficient for the equivalent restrictor are taken into account.

Static Axial Characteristics of Aerostatic Annular Porous Thrust Bearings with Tilt

A theoretical analysis is presented to predict the static axial performance characteristics of a porous circular thrust bearing with a central hole for both open and sealed ends, taking into consideration the tilt of the runner pad. The flow in the bearing matrix is considered to be three-dimensional. The governing equations of gas flow through the porous pad and the bearing clearance are solved simultaneously using the finite difference technique to obtain pressure distribution in the bearing clearance. The load capacity, mass rate of flow and static axial stiffness are calculated numerically for various bearing dimensions and supply conditions and presented in graphical form. The bearings with sealed ends have comparatively better load capacity over those with unsealed ends. The effect of tilt is to decrease the load capacity and increase the mass flowrate.

Static Characteristics of Aerostatic Porous Rectangular Thrust Bearings With Offset Load

A theoretical analysis for the static characteristics of an aerostatic porous rectangular thrust bearing with an offset load, for both open and sealed end configurations, is presented considering three-dimensional flow in the porous matrix. Static characteristics for different operating parameters are calculated numerically and presented in dimensionless form as design charts. The effect of tilt is discussed.

Dynamic Characteristics of Aerostatic Thrust Bearings with Porous Inserts

A first-order perturbation method is adopted to find the dynamic behaviour of an aerostatic circular thrust bearing having a central porous insert as a restrictor. The linearized gas film stiffness and damping are derived and used to study their behaviour with other design variables.

Analysis of aerostatic thrust bearings with offset load

A general solution of an aerostatic multirecess thrust pad with offset load is obtained. The generalized Reynolds' equation is solved numerically with the aid of a digital computer. Design curves are given for the performance of a four-recessed square thrust bearing. Experimental evidences show the validity of the method.

An instrument for measuring the mean surface profile of seal faces

The design, construction and performance of an instrument for measuring the surface profile of nominally flat seal-rings associated with an experimental mechanical seal are described. The device, which utilizes the principles of the aerostatic thrust bearing, is capable of measuring profiles of a few microinches amplitude superimposed on a face run-out greater by two orders of magnitude.