scholarly journals Rational Design and Porosity of Porous Alumina Ceramic Membrane for Air Bearing

Membranes ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 872
Author(s):  
Jianzhou Du ◽  
Duomei Ai ◽  
Xin Xiao ◽  
Jiming Song ◽  
Yunping Li ◽  
...  

Air bearing has been widely applied in ultra-precision machine tools, aerospace and other fields. The restrictor of the porous material is the key component in air bearings, but its performance is limited by the machining accuracy. A combination of optimization design and material modification of the porous alumina ceramic membrane is proposed to improve performance within an air bearing. Porous alumina ceramics were prepared by adding a pore-forming agent and performing solid-phase sintering at 1600 °C for 3 h, using 95-Al2O3 as raw material and polystyrene microspheres with different particle sizes as the pore-forming agent. With 20 wt.% of PS50, the optimum porous alumina ceramic membranes achieved a density of 3.2 g/cm3, a porosity of 11.8% and a bending strength of 150.4 MPa. Then, the sintered samples were processed into restrictors with a diameter of 40 mm and a thickness of 5 mm. After the restrictors were bonded to aluminum shells for the air bearing, both experimental and simulation work was carried out to verify the designed air bearing. Simulation results showed that the load capacity increased from 94 N to 523 N when the porosity increased from 5% to 25% at a fixed gas supply pressure of 0.5 MPa and a fixed gas film thickness of 25 μm. When the gas film thickness and porosity were fixed at 100 μm and 11.8%, respectively, the load capacity increased from 8.6 N to 40.8 N with the gas supply pressure having been increased from 0.1 MPa to 0.5 MPa. Both experimental and simulation results successfully demonstrated the stability and effectiveness of the proposed method. The porosity is an important factor for improving the performance of an air bearing, and it can be optimized to enhance the bearing’s stability and load capacity.

RSC Advances ◽  
2018 ◽  
Vol 8 (24) ◽  
pp. 13567-13577 ◽  
Author(s):  
Yang Liu ◽  
Weiya Zhu ◽  
Kang Guan ◽  
Cheng Peng ◽  
Jianqing Wu

The traditional dip-coating method for preparation of ceramic membranes requires a long drying time and easily produces drying defects. In this work, an improved dip-coating process was proposed.


2015 ◽  
Vol 35 (11) ◽  
pp. 3187-3194 ◽  
Author(s):  
Zhiwen Zhu ◽  
Jin Xiao ◽  
Wei He ◽  
Tsinghai Wang ◽  
Zhaoling Wei ◽  
...  

2007 ◽  
Vol 339 ◽  
pp. 371-376 ◽  
Author(s):  
Xiao Feng Zhang ◽  
Bin Lin

The load capacity and stiffness of the aerostatic rectangular guideways, which apply annular orifice restrictor and porous restrictor respectively, were analyzed with finite difference method in this paper. A program for solving the pressure distribution, load capacity and stiffness is programmed with VB. The calculated results show that the rise of supply pressure is good for improving the load capacity and stiffness of guideways. The decrease of the orifice diameter in annular orifice restriction and the permeability in porous restriction is advantageous to improve the stiffness of guideways, but both the corresponding bearing clearance and load capacity decrease. In both the annular restriction and porous restriction, the best film thickness which make the stiffness maximum exists under the definite supply pressure and parameter of the restrictor. Under the same supply pressure, the load capacity and stiffness of porous restriction is higher than the orifice restriction. Meanwhile, the design and manufacture of porous restrictor is simple. The porous restrictor is the perfect restrictor of aerostatic guideways.


2014 ◽  
Vol 657 ◽  
pp. 544-548
Author(s):  
Marius Pascu ◽  
Gheorghe Stan

A very important parameter which must be considered when designing a hydrostatic guideway of high stiffness is the pressure from the hydrostatic pockets. Modifications of this parameter during functioning are caused by variations of flow and supply pressure and also by the defective geometry of the hydrostatic pockets. The pocket pressure has a major importance for achieving the hydraulic sustentation, because it determines the load capacity, which thenceforth determines the film thickness and the flow. The latter is used for determining the hydraulic resistance of lands and also for deciding the geometry of the hydrostatic guideway as a whole. Based on these considerations, the analysis of the pocket pressure variations represents an important criterion which should be taken into account when designing a hydrostatic guideway with a very high stiffness. The present paper contains a new method for analysing the hydrostatic guideway behaviour with regard to its stiffness, for different pocket pressure values. The experimental research was carried out on a closed hydrostatic guideway, with the moving element having the dimensions of 500x260 [m and the pocket dimensions of 150x88 [m.


2020 ◽  
Author(s):  
Fangcheng Xu ◽  
Liukai Hou ◽  
Bin Wu ◽  
Zeda Dong ◽  
Yongliang Wang

Abstract Air thrust foil bearings are key bearings of micro turbo-machinery (such as micro gas turbines, turbo blowers, and air compressors). The bearing load capacity is affected by many factors, and the taper inlet height of bearing structure is closely related to the load capacity. In many previous literature the taper inlet height, as a constant value, was used to calculate film thickness distribution. However, the reality is that the foil will be squeezed by the pressure generated between runner disk and top foil, which makes taper inlet height change during iteration. Therefore, the actual bearing taper inlet height should be chosen properly instead of the constant taper inlet height when iterating. In this paper, an improved computational model of film thickness for adjusting the taper inlet height in real-time is proposed. The relationship between the maximum bearing load capacity and taper inlet height at different rotor speeds of two models is obtained through numerical simulation. It is found that the optimal taper inlet height of the new model is larger than that of the old model. Three types of bearings with different taper inlet height (20μm, 70μm, 114μm) had been tested and the maximum load capacity at different rotor speeds had been obtained. Finally, test data and the simulation results of the two models are compared. It is found that the simulation results of the two models are quite different when the taper inlet height is near the optimal taper inlet height, and the new model is more agree well with the test data.


2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Tomohiko Ise ◽  
Mitsuyoshi Osaki ◽  
Masami Matsubara ◽  
Shozo Kawamura

A rotor supported by gas bearings vibrates within the clearance. If the static imbalance of the rotor is large, even if the rotation speed is low, large amplitude vibration is generated by the centrifugal force. This is a serious problem because the risk of bearing damage increases. In order to solve this problem, an externally pressurized gas journal bearing with asymmetrically arranged gas supply holes has been developed. This type of bearing has a large load capacity as compared with the conventional symmetric gas supply bearing because pressurized gases are supplied to the loaded and counter-loaded side bearing surfaces via asymmetrically arranged gas supply holes. The bearing has a new gas supply mechanism in which gas is supplied from the rotor through inherent orifices. The characteristics of the developed bearing are beneficial from the viewpoint of using the bearing in rotational-type vibration exciters. In other words, this rotor has a large static imbalance. Numerical calculations of the characteristics of this bearing were performed, and the resulting characteristics were compared with those of a conventional symmetric gas supply journal bearing. The bearing load capacity of the developed bearing is considerably larger than that of conventional symmetric type bearings. The load capacity increases owing to the asymmetry of the gas supply holes. In the controlled gas supply pressure condition, rotor radial vibration during rotation can theoretically be zero. A test rig and gas control system to realize vibration reduction was constructed. A rotational test under the gas pressure control condition was conducted using a large unbalanced rotor taking advantage of this property. The control program was constructed using matlab and simulink. The devices were driven by a digital signal processor. The magnitude of the unbalance of the rotor is 13.5 × 10−3 kg m. The bearing diameter and length were 60 and 120 mm, respectively. The rotational vibration amplitude decreased at a high rotational frequency under the proposed bearing configuration, although the amplitude increases monotonically with the frequency in the conventional bearing. When the gas supply pressure was controlled synchronously with the rotation frequency modulation of the large unbalanced rotor, the amplitude of the vibration amplitude was greatly reduced. The rotor of the test rig was safely supported by this bearing, and effective data for practical operation were obtained.


2017 ◽  
Vol 32 (7) ◽  
pp. 731 ◽  
Author(s):  
XIE Yu-Zhou ◽  
PENG Chao-Qun ◽  
WANG Xiao-Feng ◽  
WANG Ri-Chu ◽  
LUO Feng

2018 ◽  
Vol 20 ◽  
pp. 16-33 ◽  
Author(s):  
J. Saraiva de Souza ◽  
S. José dos Santos Filho ◽  
Severino Rodrigues de Farias Neto ◽  
A.G. Barbosa de Lima ◽  
H.A. Luma Fernandes Magalhães

Innovative technologies are needed to attend the increasingly strict requirements for produced water treatment, since most of the separation processes are limited to particles larger than 10 μm. Separation processes using ceramic membranes are attracting great interest from academic and industrial community. Nevertheless, few studies, especially numerical, regarding the inorganic membrane’s application for the polluted water separation have been reported. In the present work, therefore, a study of fluid-flow dynamics for a laminar regime in porous tubes (tubular porous ceramic membrane) has been performed. The mass, momentum and mass transport conservation equations were solved with the aid of a structured mesh using ANSYS CFX commercial package. The velocity of local permeation was determined using the resistance in series model. The specific resistance of the polarized layer was obtained by Carman-Kozeny equation. The numerical results were evaluated and compared with the results available in the literature, where by a good agreement with each other was found. The numerical results, obtained by the proposed shell and tubular membrane separation module, indicate that there is facilitation of mass transfer and hence a reduction in the thickness of the polarized boundary layer occurs.


1998 ◽  
Vol 4 (3) ◽  
pp. 188-194
Author(s):  
Takahiro KAWAKATSU ◽  
Toshikuni YONEMOTO ◽  
Mitsutoshi NAKAJIMA

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