Aerostatic Porous Bearings Research Articles

Integrating experimental and theoretical investigations of porous graphite materials with scanning electron microscope image processing

Accurate determination of fractal dimension (FD) and permeability of porous graphite materials (PGM) is essential for applications like porous aerostatic bearings (PABs). This study addresses the need for improved measurement methods by employing image processing and computer vision (IPCV) techniques to enhance FD and permeability accuracy. We aimed to refine these measurements by analysing the effects of image size and magnification on accuracy. The research developed theoretical models based on fractal theory, Darcy's law, and a modified Hagen-Poiseuille gas equation to evaluate these effects. A dual-path X-ray imaging detection system was used for experimental validation. The gauge pressure was varied across the surface of the PGM and volume flow rate was measured. MATLAB was utilized for IPCV, enabling precise FD determination and underscoring the importance of image parameters. Results showed that FD values stabilize at specific image sizes and magnifications, improving accuracy. Linear relationships between pressure gradient and volume flow rate were observed, with permeability stabilizing at high pressures. Porosity values varied among materials: Toyo Carbon (15 %), SGL Graphite (17 %), Super Carbon Graphite (27 %), and poplar porous (30 %). FD obtained through theoretical and scanning electron microscope (SEM) methods had a maximum error of 0.08. The study also found a positive correlation between relative density and image grayscale at the macroscopic level. The findings emphasize the importance of optimizing image size and clarity for accurate PGM analysis, providing crucial insights for PAB design and other advanced applications.

On the static performance of aerostatic elements

Porous aerostatic bearings and seals offer several advantages in precision engineering applications. The static performance of aerostatic elements, i.e., bearings and seals, is investigated both experimentally and numerically. This study presents a method, a test setup, and a measurement of the air gap pressure distribution with high spatial and temporal resolution. This study presents experimental and numerical results of the load capacity, air gap height, static stiffness, air consumption, and air gap pressure distribution. The experimental results are compared to a numerical model based on the modified Reynolds equation. Furthermore, boundaries for the operating parameter space of the investigated seal are determined by stiffness and leakage. The experimental results and the numerical model showed good correlation, providing corroborative evidence for the accuracy of the measurement setup and the feasibility of the pressure measurement method.

Multifunctional silicon carbide/cement-based composites for porous aerostatic bearings

Multifunctional silicon carbide/cement-based composites for porous aerostatic bearings

Evaluation of the performance characteristics of aerostatic bearing with porous alumina (Al2O3) membrane using theoretical and experimental methods

Instruments with high levels of precision commonly use aerostatic bearings. Moreover, the use of porous (Al2O3 membrane) material validates that the pressure is spread uniformly throughout the air film region. The impression of applied load on the thickness of the air film of the aerostatic bearings was evaluated using a certain experimental technique. As the applied load rises, the thickness of the air film expands, and as the compressive stress rises, it contracts. The theoretical model parameters were set using the experimental stipulations. It was discovered that the theoretical model and the experimental data were consistent. The pressure gradient induced in the air film and the air bearings’ capacity for carrying loads were calculated using a theoretical simulation. The results of theoretical modeling and experimental comparison of the different characteristics of porous (Al2O3 membrane) aerostatic bearings based on stiffness and load-carrying capacity are graphically illustrated in this study. Porous aerostatic bearings with Al2O3 membranes have a number of potential applications, including high-speed spindles, precision instruments, microelectromechanical systems, vacuum pumps, cryogenic applications, etc.

Permeability prediction of porous aerostatic bearings through 3D morphology and fractal calculation method

AbstractPorous ceramics for aerostatic bearing restrictors were fabricated using carboxymethyl cellulose and polystyrene microspheres as pore formers. The three‐dimensional morphology of the porous ceramics was nondestructively obtained using laser scanning confocal microscopy, and the processing information was eliminated by fitting the pore area fractal dimensions at different heights. A mathematical model was developed based on the assumption of elliptical tortuous capillaries to relate microstructural pore parameters to permeability by combining fractal theory, Darcy's law, and the gas conservation equation. The calculated permeability closely matched the experimental results, with an error of less than 3.5%. This method has promising potential as an alternative to pressure drop experiments. Moreover, the capacity of the fractal calculation model to establish a correlation between microstructural parameters and permeability paves a new way to design future porous aerostatic bearings.

A novel parallel capillary-cavity model for the analysis of pneumatic hammer vibration in porous aerostatic bearings

Porous aerostatic bearings (PABs) are widely used in high-speed applications and ultra-precision machinery owing to their frictionless motion and remarkable stability. In this paper, a novel parallel capillary-cavity model based on the intricate pore structure characteristics is established to characterize air flow in PABs and analyze the pneumatic hammer vibration. An experimental setup is constructed to measure the pneumatic hammer vibration of PABs. The experimental results exhibit a strong agreement with the predictions. The effects of various factors, including different loads, air pressures and porosities on the pneumatic hammer vibration are thoroughly discussed. The results show that higher air supply pressures, larger loads, and increased porosity are more likely to trigger pneumatic hammer vibration in PABs.

Manufacturing and static performance of porous aerostatic bearings

According to the common body of knowledge, aerostatic bearings invariably need narrow manufacturing tolerances to ensure maximal load capacity and high stiffness. This study experimentally investigates the manufacturing of porous material aerostatic bearings and the effect of manufacturing parameters on the performance properties of the bearings. During the study, samples were manufactured using different methods, and the geometrical and performance properties of each sample were inspected. The bearing performance measurement device developed during the study is introduced. The results present the dependence between manufacturing parameters and bearing properties under varying load and operating pressure conditions. The results clearly suggest that effect of bearing surface roughness on load capacity is small; meanwhile, surface planarity has a major impact on load capacity.

Study on Static Characteristics of Aerostatic Bearing Based on Porous SiC Ceramic Membranes.

The porous aerostatic bearing is a new supporting structure that is widely used in precision and ultraprecision engineering and the aerospace and other fields. The aerostatic bearing has a good bearing capacity and static stiffness. In this work, the numerical and experimental research on the static characteristics of an aerostatic bearing based on a porous SiC ceramic membrane is presented. The porous ceramic membrane prepared by reactive sintering, with a porosity of 25.8% and a pore size of 20.55 μm, was used as the restrictor to fabricate the aerostatic bearing. It was found that the ceramics have good permeability, and the permeability coefficient reached 2.78 × 10−13 m2 using permeability-test experiments. The effects of the gas-supply pressure and permeability coefficient on the static characteristics of the aerostatic bearing based on porous ceramics were analyzed using Fluent simulation calculation. When the gas-supply pressure was 0.5 MPa and the gas-film thickness was 6 μm, the static stiffness of the aerostatic bearing reached a maximum of 20.9 N/μm, while the bearing capacity was 632.5 N. The numerical results of the static characteristics of the aerostatic bearing are highly consistent with the experimental results, which verifies the accuracy of the Fluent simulation, and provides convenience for studying the static characteristics of aerostatic bearings.

Numerical and experimental study on the effect of surface damages on the performances of porous aerostatic bearings

External high-pressure air can still flow from the partly scratched or blocked surface of porous aerostatic bearings to form lubrication film. Hence, studying the effect of surface damages on the performances of porous aerostatic bearings systematically is essential. In this study, a novel whole-region porous model is proposed. The clearance is considered as the virtual porous material disc and will be coupled with the original porous material disc. The damages change the partial shape and permeability of two discs based on this model. Numerical results show that the damages decreased the local pressure in the bearing clearance evidently. It determines the load capacity of the damaged bearings being smaller than that of the non-damaged bearings. Moreover, the blockage decreases the load capacity more significantly. The influence of the damages on stiffness is complicated. However, the damages decrease the stiffness as a whole. Moreover, the influence of the damages becomes more significant with the increase in the size of the damages and the decrease in the original porous disc thickness and permeability. Lastly, the damaged and non-damaged bearings are manufactured and tested experimentally. The experimental results of pressure distribution and load capacity obtained agree with the predictions greatly. Numerical and experimental results prove that the surface damages have significant influence on the bearing performances, but the surface damaged bearings can still offer effective levitation force. The results presented in this study can assess the availability of the damaged bearings and offer the advices for designing bearings with diminishing the influence of the damages on the bearing performance.

Theoretical and Numerical Investigations on Static Characteristics of Aerostatic Porous Journal Bearings

To investigate the static characteristics of aerostatic journal bearings with porous bushing, the flow model—in which the compressibility of lubricating gas is considered—is established based on the Reynolds lubrication equation, Darcy equation for porous material, and continuity equation. With the finite difference method, difference schemes for non-uniform grids, relaxation method, and virtual node method, the numerical method for the governing equations of compressible flow in porous journal bearings is proposed. The effects of nominal clearance of bearings and compressibility of gas on the static characteristics are analyzed. Under the same minimum film thickness and the same gas compressibility, as the nominal clearance widens, the load capacity, mass flow rate, and power consumption increase. Under the same minimum film thickness and the same nominal clearance, with the increase in gas polytropic index, the load capacity strengthens, while the mass flow rate and power consumption decline. This study could provide a reference for the design of porous journal bearings.

Development of aerostatic porous bearings manufactured using metal 3D printing technology

Aerostatic porous bearings have been applied widely in precision devices to achieve higher accuracy of motion. Conventional aerostatic porous bearings are made of porous graphite, porous ceramics or sintered metal porous material, having a thickness of several millimetres and a surface-restricted layer. However, during mass production of porous bearings, the time required for the production of the porous materials and the surface restriction treatment leads to an increase in the manufacturing time and cost of the porous bearings. Accordingly, to overcome this problem, an aerostatic porous bearing with a layer thickness of several hundred µm and a support member, manufactured using metal 3D printing technology, is proposed. In this study, the optimum conditions for manufacturing the proposed aerostatic porous bearings with a direct metal laser sintering method 3D printer were investigated, and characteristics of the prototype of the proposed bearings were investigated experimentally.

Parameter Sensitivity Analysis on Dynamic Coefficients of Partial Arc Annular-Thrust Aerostatic Porous Journal Bearings

Aerostatic bearings are widely used in high-precision devices. Partial arc annular-thrust aerostatic porous journal bearings are a prominent type of aerostatic bearings, which carry both radial and axial loads and provide high load-carrying capacity, low air consumption, and relatively low cost. Spindle shaft tilting is a resource-demanding challenge in numerical modeling because it involves a 3D air flow. In this study, the air flow problem was solved using a COMSOL software, and the dynamic coefficients for tilting degrees of freedom were obtained using finite differences. The obtained results exhibit significant coupling between the tilting motion in the x-and y-directions: cross-coupled coefficients can achieve 20% of the direct coefficient for stiffness and 50% for damping. In addition, a nonlinear behavior can be expected, because the tilting motion within 3°, tilting velocities within 0.0012°/s, and relative eccentricity of 0.2 have effects as large as 20% for direct stiffness and 100% for cross-coupled stiffness and damping. All dynamic coefficients were fitted with a polynomial of eccentricity, tilting, and tilting velocities in two directions, with a total of six parameters. The resulting fitting coefficient tables can be employed for the fast dynamic simulation of the rotor shaft carried on the proposed bearing type.

Three-dimensional flow state analysis of microstructures of porous graphite restrictor in aerostatic bearings

Porous aerostatic bearings as a new type of supporting component used in ultraprecision equipment. The study of porous models is essential as they are a basis for porous aerostatic bearings. However, the effects of micropore structure and flow state inside a material have not been addressed in previous studies. Herein, we propose a high-accuracy and low-cost method using deep learning to reconstruct a three-dimensional (3D) porous model and obtain the 3D flow state inside a porous material. It can reveal richer flow states such as the flow track and movement in three directions, which have not been revealed previously. This new method is effective for studying the properties of porous materials, micro-flow state, and simulation of parameters in detail.

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.

Assessment of compacted-cementitious composites as porous restrictors for aerostatic bearings

Cementitious composites reinforced with silica, silicon carbide or carbon microfibres are designed, manufactured, characterised and tested as porous restrictor for aerostatic bearings. Carbon microfibres are residues obtained from the cutting process of carbon fibre-reinforced polymers. Porosity, permeability, flexural strength and stiffness are quite relevant in the design of aerostatic porous bearings. A 3141 full factorial design is carried out to identify the effects of particle inclusion and water-to-cement ratio(w/c) factors on the physical and mechanical properties of cementitious composites. Higher density material is achieved by adding silicon carbide. Higher porosity is obtained at 0.28 w/c level when silica and silicon carbide are used. Carbon microfibres are not effective under bending loads. Higher compressive strength is reached especially when silica particles are combined with 0.33 or 0.35 w/c. According to the permeability coefficient values the cementitious composites consisted of CMF (0.28 w/c), silica (0.30 w/c) or silicon carbide (0.30 w/c) inclusions are promising as porous restrictor; however, carbon microfibre porous bearings achieved the lowest air gap variation under the tested working conditions.

Bearing Clearance in Design Calculation for Porous Aerostatic Thrust Bearings

It has been reported that porous aerostatic bearings behave as if they were operating at a clearance larger than the measured bearing clearance, leading to pressure decrease within the gap and to flow rate increase. This implies that it is difficult to predict the bearing performance theoretically at a design stage, because bearing clearances effective for the design are not known. For one porous metal and three porous carbon bearings, theoretical air film pressures calculated by using the finite element method are compared to experimental ones and it is shown that applying an additional gap is a simple way to compensate the difference in the pressure between theory and practice. Taking into consideration the fact that the porous surface texture resembles Plateau texture, it is reasonable to apply the additional gap of the same magnitude to the parameters derived from the areal material ratio curve, in particular, for porous carbon bearings.

Thermal Characteristic Analysis of Aerostatic Porous Journal Bearings with Surface-restricted Layer

Thermal Characteristic Analysis of Aerostatic Porous Journal Bearings with Surface-restricted Layer

The effect of the arc on annular-thrust aerostatic porous bearings

PurposeAerostatic porous bearings are important for guide rails and spindles. It is well-known that flow restrictors made of porous materials offer major advantages over conventional restrictors in such bearings, including design and manufacturing, load-carrying capacity, stiffness, damping and dynamic stability. Thus, this work numerically investigates the effect of the arc on a new combined annular-thrust aerostatic porous bearing.Design/methodology/approachThe static characteristics of an annular-thrust aerostatic porous bearing were studied using a fast finite element scheme. The pressure distribution, radial load and thrust load were analyzed as functions of the arc, permeability and eccentricity.FindingsThe results reveal that the radial load achieves maximal values at an optimal arc value between 200 and 300, and the thrust load increases monotonically with increasing arc.Originality/valueThis work developed a new combined annular-thrust aerostatic porous bearing to investigate the effect of arc on the annular-thrust aerostatic porous bearings to increase the load-carrying capacity.

Numerical analysis and experimental investigation into the effects of manufacturing errors on the running accuracy of the aerostatic porous spindle

Abstract In ultra-precision machine tool, the running accuracy of aerostatic bearings has a great influence on the machined surface topographies. However, the mechanism of aerostatic bearings running accuracy has not been fully understood. In this paper, a method based on computational fluid dynamic (CFD) method and dynamic mesh technology (DMT) was proposed to quantitatively study the effects of manufacturing errors on the running accuracy of aerostatic porous bearings. The different types of waviness errors and non-flatness errors are modeled based on the actual measurement results of spindle and thrust bearing, respectively. The DMT was applied in CFD method to simultaneously solve the Navier-Stokes (N-S) equations and the Newton's law. The calculation results show that the radial running accuracy of journal bearing can be improved by reducing the waviness amplitude or spatial wavelength, the axial running accuracy of thrust bearing increased with the decrease of non-flatness amplitude. Besides, a nanometer system for measuring the running accuracy of aerostatic porous bearings was constructed based on the Donaldson reversal method. The bearing rotation movement trajectory of calculation results was very similar with the experiment results, which verified the validity of calculation method proposed in this study. Both the calculation results and experimental data confirmed that the effect of waviness errors on the bearing running accuracy was much more obvious than non-flatness errors, which provide the useful guidance for the design and manufacturing of aerostatic porous bearings.

Effects of manufacturing errors on the static characteristics of aerostatic journal bearings with porous restrictor

Numerical and experimental research on the effects of manufacturing errors on the static performance of aerostatic porous journal bearings is presented. The effects of circumferential waviness, taper, concavity, and convexity on the bearing film thickness were modeled based on the experimental results. The effects of amplitude and spatial wave length on the bearing film pressure, load capacity and stiffness were investigated by solving the Darcy-Forchheimer law and Navier-Stokes equations. Both the numerical results and experimental data show that the bearing static characteristics were significantly influenced by the manufacturing errors. Circumferential waviness errors caused the obvious inhomogeneity of the flow field and the transformation of morphology of the high-pressure region, whereas axial errors had a significant impact on the area and location of the high-pressure region. The bearing load capacity and stiffness can be improved by increasing the amplitude of the manufacturing errors, except for the concavity errors. Both the bearing load capacity difference and stiffness difference increased with an increase in the axial errors' amplitude. For the manufacturing errors, the calculation results are close to the measurement data. Therefore, it is necessary to consider the influence of manufacturing errors on the bearing static characteristics in numerical calculations.