Porous Thrust Research Articles

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 Performance of an Externally Pressurized Porous Thrust Bearing Employing Different Pocket Shape

Dynamic Performance of an Externally Pressurized Porous Thrust Bearing Employing Different Pocket Shape

Effect of the deformation of porous materials on the performance of aerostatic bearings by fluid-solid interaction method

Aerostatic porous bearing is a new supporting structure gradually used in ultra-precision machine tools. Considering the relatively lower Young's modulus of porous, there are few references about the effect of deformation. Here, the deformation of porous thrust bearings is numerically and experimentally analyzed. The fluid-solid interaction method is proposed with the governing equations. The permeability of the porous is obtained by the experiment for accurate simulation. The effect of supply air pressure, material thickness, and Young's modulus are studied on the porous deformation and the bearing static performance. The simulation results were verified by the experiment. Finally, a double-layered porous restrictor is proposed to suppress deformation and the various thickness combinations of double layers are also discussed.

Effect of Variation of Gap Thickness of the Thrust Bearing on Gap Pressure and Stiffness of the Aerostatic Spindle in Vertical Milling

When the partially porous aerostatic thrust bearing and the journal bearings of an aerostatic spindle in a vertical milling machine are subjected to cutting load and gravitational force, the thicknesses of gaps between the thrust plate and the spindle flange will change. This study applied CFD software to analyze the effect of variations of gap thickness and rotating speed on the pressure in the gaps of the bearings and the stiffness of the spindle. The results revealed that, when the thrust plate and the spindle flange were pushed back and forth by external loading, the pressure in the gap between the spindle flange and the thrust plate was affected significantly. The pressure in the gap between the spindle and the journal bearing was slightly affected. When the spindle rotated faster, the pressure on the surface of spindle became higher and the stiffness of spindle was increased.

Static Characteristics of Aerostatic Thrust Bearings With Multiple Porous Inlet Ports

Aerostatic porous bearings have been applied successfully to various precision devices, such as precision machine tools and precision measuring equipment, to achieve higher accuracy of motion. Recently, large aerostatic porous thrust bearings have been used as essential components in a lithography machine for large liquid crystal display (LCD) glasses. Conventional aerostatic porous bearings are made of porous material that covers the whole of the bearing surface area, requiring a large piece of such material for large bearings. However, making large pieces of porous material requires the use of a large electric furnace, which is a very expensive part of the bearing's manufacturing cost. To overcome this problem, this paper proposes an aerostatic thrust bearing with multiple porous inlet ports. The proposed bearing has a number of small porous inlet ports on the bearing surface, thereby avoiding the need for large electric furnaces. The static characteristics of the proposed bearings are investigated numerically and experimentally. The results show that the proposed aerostatic thrust bearing is potentially very useful for the manufacture of large aerostatic thrust bearings, where it would have advantages over conventional aerostatic porous thrust bearings.

Theory of gasostatic thrust bearing with an isotropic porous throttle

This paper considers a flat gasostatic thrust bearing with feeding of compressed gas through an annular throttle made of homogeneous isotropic porous material. A two-dimensional equation in partial derivatives that determines the pattern of distribution of the pressure in the porous body is solved using splines. The equation for the pressure in the lubricating layer adjacent to the porous wall is solved numerically by the Runge-Kutta method. The algorithm for calculating the integral characteristics of the support is given and the examples of optimization of this support for the maximum rigidity are considered. Graphs of the dependence of the load-carrying capacity, rigidity, and flow of compressed gas from various operating parameters are constructed and conclusions regarding the specifics of operation of the porous thrust bearing are drawn.

磁流润滑推力轴承的摩擦学研究

本文介绍了磁流润滑多孔推力轴承，开展了相关摩擦学试验并对实验结果进行了分析。通过实验分析证明其减轻了非均布振动、载荷冲击与长期重载运行对承载能力、工作可靠性与抗疲劳寿命的影响。 Magnetic fluid lubrication porous thrust bearing has been introduced in this paper, and related tribology experiments and the experimental results were analyzed, which could reduce the influ-ence on the bearing capacity, work reliability and fatigue life because of the vibration, load impact and long-term overload operation.

Numerical Investigation of Static and Dynamic Characteristics of Water Hydrostatic Porous Thrust Bearings

A moving table supported by aerostatic bearings can achieve excellent accuracy of motion because of its noncontact support and, hence, it is used in various precision machine tools and measuring equipment. However, because of low viscosity of air, the damping coefficient of aerostatic bearings is not very high, causing vibration with nanometer-order amplitudes. The accuracy of machine tools and measuring equipment could deteriorate because of this vibration. It is expected that water hydrostatic bearings would have a higher damping coefficient than aerostatic bearings due to the higher viscosity of water. In addition, water, like air, does not pollute the environment. In this paper, the static and dynamic characteristics of water hydrostatic thrust bearings using porous material were numerically investigated and comparedwith conventional pocket hydrostatic bearings with a capillary restrictor. Hydrostatic porous bearings can be easily constructed because the porous material becomes a viscous restrictor itself. It was consequently found that water hydrostatic porous thrust bearings have higher maximum load capacity and slightly lower stiffness than water bearings with a capillary restrictor.

Experimental Study on Water Lubrication Characteristics of Porous Thrust Bearing with Partial Filled Parts

In order to support a load, conventional bearings have geometrical wedge which produces the squeeze effect to generate the pressure. In this study, a porous flat thrust bearing with partial non-porous parts (Land) filled by a cyanoacrylate is developed. The bearing effect of this bearing is achieved only by alternate layout of porous surface and non-porous surface. And the pressure is generated to compensate the discontinuous shear flow rate at the interface of porous part (slippery part) and non-porous part (free from slip flow). Therefore, this structure enables the flat thrust bearing that has no geometrical wedge such as conventional bearings. This bearing has considerably lower friction coefficient than porous surface over a wide range of bearing characteristic number. Especially, eight land thrust bearing achieves the lowest friction coefficient of 0.02 which is 4% of that of fine test piece and the friction surface is almost free from the wear. These results suggest a potential of which porous thrust bearing having some filled parts functions well with a low friction coefficient.

1115 水潤滑多孔質静圧スラスト軸受に関する研究(テクスチャリングと低摩擦(1),一般講演)

1115 水潤滑多孔質静圧スラスト軸受に関する研究(テクスチャリングと低摩擦(1),一般講演)

Analysis of Dynamic Stiffness and Damping of Partial Porous Aerostatic Thrust Bearings

Porous materials have been successfully used in an aerostatic bearing. In this paper, the dynamic stiffness and damping of partial porous aerostatic thrust bearings are analyzed by numerical calculation method. Firstly, the pressure distribution function of the bearing is divided into the static and dynamic pressure distribution functions through minor perturbation method. Then, the static and dynamic pressure distribution functions are calculated by FEM. Finally, the dynamic stiffness and damping coefficients of the bearing are solved. The result indicates that the dynamic stiffness increases obviously with the increment of supply pressure and first increases then decreases with the increment of frequency, and that there is negative damping in the low frequency band and the supply pressure has a great impact on the stability of the bearing.

B35 水潤滑多孔質静圧スラスト軸受に関する研究(OS-2 最新機械要素技術(2))

B35 水潤滑多孔質静圧スラスト軸受に関する研究(OS-2 最新機械要素技術(2))

3039 給気ライン中に絞りを挿入した表面絞り型多孔質静圧気体スラスト軸受の軸受特性に関する研究(S81-1 トライボロジーの基礎と応用(1),S81 トライボロジーの基礎と応用)

Recently, linear guide way systems supported by the surface-compensated aerostatic bearings are widely used for ultra-precision machines, such as semiconductor photolithography machines and ultra-precision measurement machines. In the previous paper, authors proposed the new type of surface-compensated aerostatic thrust bearings using porous material and improvement method of static stiffness of this type of bearings. It was found that proposed method is effective in increasing the static stiffness. In this paper, dynamic characteristics of surface-compensated aerostatic porous thrust bearings with 2nd restrictor inserting into an air feed port is investigated.

2916 オリフィスの挿入による深溝付多孔質静圧気体スラスト軸受の静剛性向上法に関する研究(S64-1 トライボロジーの基礎と応用(1),S64 トライボロジーの基礎と応用)

2916 オリフィスの挿入による深溝付多孔質静圧気体スラスト軸受の静剛性向上法に関する研究(S64-1 トライボロジーの基礎と応用(1),S64 トライボロジーの基礎と応用)

Static and Dynamic Characteristic of Aerostatic Porous Thrust Bearings with Deep Feed Groove

Recently, lithographic technologies using electron-beam (EB) or extreme ultra violet (EUV) illumination source have been developed as a next generation advanced lithography. Generally, aerostatic bearings have been used in the lithography machine because they have a very higher accuracy of motion. However, lithography technologies using EB or EUV illumination source have to operate in a high vacuum and require higher precision accuracy than current lithography technology. Therefore, in this paper, an aerostatic porous bearing with deep feed groove is proposed to achieve required accuracy in the next generation lithography technology. Aerostatic porous bearing have relatively high stiffness and higher damping coefficient than another types of aerostatic bearings. In addition, the proposed bearings can supply pressurized air from a stationary guide-way to a moving table through a deep feed groove without any disturbances of air supply tubes. The static and dynamic characteristics of aerostatic porous bearings with a deep feed groove are investigated theoretically and experimentally.

Effect of Porous Thrust Surfaces on Detonation Transition and Detonation Tube Impulse

As pulse detonation engine development matures, it becomes increasingly important to consider how practical details such as the implementation of valves and nozzles will affect performance. Inlet valve timing and valveless inlet designs may result in flow of products back upstream and, consequently, reduction in impulse over the ideal case. Although proper inlet design or operation under flowing conditions may minimize these losses, our study addresses the worst-case effect that a porous thrust surface may have on the measured impulse. A series of single-cycle tests have been carried out to measure the impulse in stoichiometric ethylene–oxygen mixtures, initially between 20 and 100 kPa, in a detonation tube with a porous thrust surface. The tested thrust surfaces had blockage ratios ranging from completely solid (100% blockage ratio) to completely open (0% blockage ratio). A 76% loss in impulse was observed with a thrust surface blockage ratio of 52% at an initial pressure of 100 kPa. The time to detonation transition was found to be more dependent on the mixture’s initial pressure than on the thrust surface blockage ratio. A model of the impulse in detonation tubes with porous thrust surfaces was developed.

Numerical and experimental analysis of aerostatic thrust bearings with porous restrictors

The finite element method is used to predict the performance of aerostatic thrust bearings with a complete porous surface. Results obtained by a 1D and 3D source flow model derived from D’Arcy’s law are compared for rectangular porous bearings having an infinite width. It turns out that the 1D source flow model is adequate for practical design parameters. For a circular aerostatic porous thrust bearing results calculated with several mathematical models for the source flow and slip flow are compared with experimental results. A relatively simple model incorporating unflatness and deformation of the bearing surface correlates well with the experimentally determined bearing performance.

Static and Dynamic Characteristics of Aerostatic Circular Porous Thrust Bearings (Effect of the Shape of the Air Supply Area)

Recently, graphite porous material has been used successfully in an aerostatic bearing. In actual bearing design, it is often necessary to reduce the thickness of porous material to make the bearing smaller. However, a reduction in thickness results in a reduction in the strength of the porous material. In particular, when the diameter of porous material is large, it is difficult to supply the air through the full pad area of porous material because it deforms. Therefore, in this paper, two types of air supply method (the annular groove supply and the hole supply) in a circular aerostatic porous thrust bearing are proposed to avoid the deflection of the bearing surface. The static and dynamic characteristics of aerostatic porous bearing with these air supply methods are investigated theoretically and experimentally. In addition, the effects of a surface restricted layer on the characteristics are clarified.

Experimental Study on the Mechanism of Lubrication in Hydrodynamic Porous Thrust Bearings With a Wavy Surface

Hydrodynamic fluid lubrication theory is applied to thrust bearings with three-dimensional, wave-shaped axial end surfaces. Optimizations of the wave height and surface porosity are experimentally determined using lubrication characteristics such as the friction coefficient and worn-out surface conditions. Lubrication characteristics such as the friction coefficient, temperature rise, thrust flotation, and oil consumption rate are evaluated for an estimation of life expectancy. In this research, the results of this theoretical application on thrust bearings clearly showed considerable improvement over conventional thrust bearings. Furthermore, this experimental research has clarified the lubrication conditions of various thrust-loaded axial end surfaces.

Experimental Study on the Mechanism of Lubrication in Hydrodynamic Porous Thrust Bearings. 2nd Report. Experimental Research of Various Thrust Loaded Surface Shapes and Lubrication Conditions.

The application of hydrodynamic fluid lubrication theory is attempted to the porous thrust bearings with various hydrodynamic shaped axial end surfaces. The superior one within the hydrodynamic shaped axial end surfaces such as, PUMPIN, PUMPOUT, HERRINGBONE, TPDLND (Tapered Land) and HWB (Hydro Wave Bearing) are experimentally determined concerning lubrication characteristics. The measurements of lubrication characteristics such as, a friction coefficient, the temperature rise, floating height, floatation and oil consumption rate for estimation of life expectancy etc. are evaluated. In this research, the results of this application on the end surfaces of thrust bearings clearly showed considerable improvement over the conventional thrust bearings. Furthermore, this experimental study clarified the load carrying capacities and lubrication conditions of the respective shape of the axial end surfaces.