Air Film Thickness Research Articles

Numerical simulation and experimental study of the influence of disk groove structure optimization on the air film flow field signature of an air-cushion sandwich belt conveyor

A new type of disk groove mechanism was developed and manufactured. The effects of the structural and operating factors of the disk groove on the air film loading performance were examined using single factor and orthogonal experimental methods. The results of numerical simulation and experimental studies showed that the air film loading performance correlated positively with the orifice diameter and inlet pressure, with the orifice spacing and diameter having the most significant effects, and that the belt speed boosted the air film uniformity. Meanwhile, a comparative analysis of the corresponding level values showed that an air film thickness of 0.8 mm, orifice diameter of 5 mm, orifice spacing of 30 mm, inlet pressure of 8000 Pa, and conveyor speed of 5 m/s were the optimal parameter combinations for the maximum loading capacity. To verify the accuracy of the model, a field experiment was conducted at Jiangmen Southern Conveying Machinery Engineering Co., Ltd. The air film pressure at the experimental position matched the numerical simulation results. In addition, when the number of rows was one and the air volume was 10 m3/h, the smallest value of traction resistance was obtained under minimum power consumption.

Nonlinear dynamic analysis of high-speed precision grinding considering multi-effect coupling

The aerostatic spindle is widely used in the field of precision grinding because of its excellent machining stability and machining accuracy. The spindle is jointly affected by multiple excitation effects in the high-speed grinding process. In order to study the dynamic characteristics of the aerostatic spindle under high-speed precision machining, it is necessary to analyse the nonlinear response of the aerostatic spindle with multi-physical field coupling. In this paper, the nonlinear dynamic model of the aerostatic spindle system under multi-effect coupling is established by considering three aspects: fluid-structure coupling, mass eccentricity excitation coupling, and vibration-grinding force coupling. Firstly, the instantaneous nonlinear air film force excitation is calculated by the derivation of the dynamic air film thickness model with multi-degree-of-freedom vibration responses coupling. The mass eccentricity excitation considering dynamic deflection angle is derived through the eccentric-load relationship. Afterwards, the dynamic precision grinding force model under the full surface of the tool is established based on judging the material removal mode, which considers the grain-workpiece interaction relationship under the influence of the nonlinear vibration. Finally, the accuracy and effectiveness of the coupled model is verified by high-speed precision grinding experiments, and the nonlinear dynamic behaviour under different operating parameters is analysed.

Study of the Static Characteristics of Gas-Lubricated Thrust Bearings Using Analytical and Finite Element Methods

A study was conducted to develop a porous aerostatic rectangular thrust bearing model, with the aim of assessing how different operational conditions and geometric factors influence its static capabilities. Initially, the Reynolds equation was analytically solved. Subsequently, simulations were performed on the rectangular air bearing model. Analyzing the impact of throttle hole configurations, air film thickness, orifice size, and supply pressure revealed their significant effect on the bearing’s load capacity, air consumption, peak airflow speed in the air film gap, and rigidity. Experimental validations were further conducted on manufactured bearings, corroborating the theoretical findings. It was observed that extending the length of the rectangular throttle hole array progressively increases gas consumption and diminishes stability, while the load capacity and stiffness initially surge then taper off. A thinner air film enhances load capacity and reduces gas flow, contributing to increased stability. Conversely, enlarging the orifice diameter boosts both load capacity and stability but escalates mass flow and diminishes stiffness. Elevating gas supply pressure enhances load capacity, flow rate, and stiffness, albeit at the cost of reduced stability. A comparative analysis among experimental data, finite element analysis, and analytical solutions showed strong congruence, affirming the precision of the latter two methods for predicting the bearing’s performance. This investigation aids with refining bearing design for precision devices and offers insights to enhance bearing efficiency and lifespan and to reduce friction and wear. Given its lower computational demands, the analytical approach provides a rapid means to assess static characteristics, underscoring its utility alongside finite element techniques for optimizing aerostatic bearing parameters.

Stability of orifice-compensated air bearing with rectangular shape considering air film thickness

A theoretical model of the orifice-compensated air bearing with rectangular shape is built to study the stability, the stiffness and the air consumption considering the air film thickness. The study shows that, the pocket volume ratio of less than 0.03 is recommended to avoid the pneumatic hammer. The stability is good and the air consumption is small when the bearing has the high stiffness. Strict control of the structural deformation is crucial as it can significantly affect the stability. Increasing the nozzle number can improve the stability and avoid the choked flow. The findings are of great importance for the design of the orifice-compensated air bearing.

Antibubble formation through single drop impact: Effect of density difference

The antibubble has emerged as a promising tool for the microdroplet manipulation since the intermediate air film can protect the inner globule from external contaminants. Moreover, the antibubble structure allows the convenient package and release of microdroplets since the intermediate air film would not hinder the separation between the inner globule and the liquid surface. Despite the development of various methods for antibubble formation, the initial approach involving single drop impact on a free liquid surface has received limited attention in subsequent studies, partly due to the challenges in replicating this phenomenon in practical applications. This paper presents an experimental investigation into antibubble formation via single drop impact on a liquid surface. Experimental results imply that antibubble formation requires the droplet to penetrate deeply into the liquid bath before the intermediate air film collapses or the deformed liquid surface contracts. A theoretical analysis is introduced to emphasize the crucial role of the density difference between the droplet and the liquid bath. A higher density of the droplet results in an increased penetration speed into the liquid bath, facilitating the formation of antibubbles. Notably, this study repeats the experimental results reported by Hughes and Hughes in 1932. Moreover, the method provides a means to control antibubble parameters such as diameter and air film thickness. This control offers valuable insight for subsequent investigations on antibubbles, establishing a foundation for further exploration and application of this intriguing phenomenon.

Experimental Study on the Influence of Air Conveyor System Parameters on Vibration of Glass Substrate

In this paper, the method of experimental research is used to minimize the micro-vibration amplitude of 0.6 mm thick glass substrates in the air conveyor system. The optimal parameter combination of the small orifice throttling glass substrate air conveyor system is obtained as follows: orifice diameter 0.25 mm, orifice spacing 60 mm and air-film thickness 50 μm. Secondly, based on the orthogonal experimental data, the influence of the main parameters of the air conveyor system at the micro vibration of the glass substrate is analyzed by variance analysis technology. The results show that the three principal parameters of the air conveyor system have significant influence on the vibration of the glass substrate. Among them, the thickness of the air-film has the greatest influence on the vibration of the glass substrate, the diameter of the orifice has the second influence, and the spacing of the orifice has the least influence. Finally, the influence of the three key parameters of orifice diameter, orifice spacing and film thickness on the micro vibration of glass substrate in the orifice throttling air flotation support system was studied and discussed, and the relationship curves between the maximum amplitude of micro-vibration of glass substrate and the main parameters of air flotation system were obtained.

Development and Investigation of Non-Destructive Detection Drive Mechanism for Precision Type Cylindrical Roller Dynamic Unbalance

In the process of dynamic unbalance detection for precision cylindrical rollers, challenges such as difficulty in achieving effective driving and susceptibility to surface damage during driving significantly impact the accuracy of unbalance detection. This hinders the industry’s ability to achieve the non-destructive detection of cylindrical rollers. Therefore, this paper proposes a novel driving method to enable non-destructive driving of precision cylindrical rollers. The structural principles of the driving mechanism are presented, and a mechanical model for the cylindrical roller is established to analyze the force distribution. Subsequently, a mathematical model for the air film bearing the cylindrical roller is developed to study the variation characteristics of the air film’s load-bearing capacity. The optimal air film thickness is determined, and the rationality of the mathematical model is validated through simulation analysis. Finally, an experimental platform for non-destructive driving is constructed to further verify the effectiveness of the proposed method. This research provides a prerequisite for the non-destructive detection of dynamic unbalance in precision cylindrical rollers.

Effect of drainage on antibubble collapse

Antibubbles are a special spherical structure generated in liquids surrounded by a thin air film. The collapse of antibubbles has been regarded as a feasible method for generating microbubbles. This paper demonstrates an experimental study on the antibubble collapse focusing on the effect of rupture time and location. With the help of a high-speed camera, the detailed collapse dynamics for different rupture times and locations was presented. The collapse velocity was found to vary significantly with the rupture time and location. An upgraded theoretical model was proposed to elucidate the effect of the air film thickness distribution due to drainage on the collapse velocity. This study should stimulate further investigation on the antibubble collapse, especially the size distribution of the generated microbubbles.

Hybrid ANFIS-PSO algorithm for estimation of the characteristics of porous vacuum preloaded air bearings and comparison performance of the intelligent algorithm with the ANN

Air bearings are commonly used in systems requiring high precision, including semiconductor manufacturing, optical and electronic devices, and aerospace systems, and the usage of vacuum preloading and porous material provides a homogeneous pressure distribution on the bearing surface. The prediction of the characteristics of these air bearings, such as air film thickness and location, is crucial for designing and optimizing the performance of the systems. They exhibit highly nonlinear behavior and are challenging to accurately predict their characteristics using conventional analytical or numerical techniques. In this study, the characteristics of vacuum preloaded porous air bearings are estimated using a hybrid ANFIS-PSO predictor soft computing method with a certain pressure (410 kPa), vacuum (50.8 kPa), and with three different diameters (50, 75 and 90 mm). The usage of different algorithms in the characteristics and selection and design criteria of air bearing has been applied. Six different cases are simulated with different input and output parameters to predict the air film thickness and location of the air bearing. The location of the air bearing has been determined with two angle parameters, α, and β. The dataset required for training and testing the algorithm was obtained through experimental study. In the training and testing process, 40 and 20 datasets were used, respectively. Before the starting analysis, a sensitivity analysis was executed to find optimum PSO parameters such as the number of particles, acceleration coefficients, number of membership functions, and inertia weight. The proposed hybrid ANFIS-PSO method was compared with classical ANFIS and ANN, and it showed better performance and a more accurate solution to estimate the characteristics of vacuum preloaded porous air bearings in both training and testing phases with the R2 of 0.9958 and MSE value of 0.102. The maximum training performance of the ANFIS-PSO is better than ANFIS and ANN with the ratio of 6.8% and 8.5%, respectively. On the other hand, the maximum testing performance of the ANFIS-PSO algorithm is higher than ANFIS and ANN, with the ratio of 22.2% and 24.1%, respectively.

Investigation of Recirculating Marangoni Flow in Three-Dimensional Geometry of Aqueous Micro-Foams

Experimental investigations of Marangoni flow in micro-foams have faced challenges due to the inherent difficulties in detecting and measuring this flow. The Marangoni flow manifests as small spots within the lamellae films, which makes it hard to accurately analyze. Hence, to elucidate Marangoni flow characteristics, this study introduces and investigates comprehensive three-dimensional models of flow in microscale foams. The geometric models contained Plateau Borders (PB), nodes, and films. The recirculating Marangoni flow was simulated and studied for different interfacial mobilities. Inside the foams, the Marangoni flow velocities were at the same scale with the PB flow velocity for mobile interfaces. However, for a more rigid interface, the magnitude of the Marangoni flow was considerably less than that of the PB owing to the combined effect of high surface hydraulic resistance on the Marangoni flows and nature of the Marangoni flow as a surface-only flow type. Furthermore, the effect of the film thickness on the Marangoni flow was analyzed. Thicker films have a stronger effect in reducing the Marangoni flow than PB flow. This is due to the higher ratio of gravity body force to the Marangoni-driven surface force for thicker films. Finally, the combined effect of the liquid–air interfacial mobility and film thickness on the Marangoni velocity was studied.

Research on load characteristics of squeeze-film air bearings based on fluid–solid coupling

In order to obtain the loading capacity and its variation of the squeeze-film air bearing, taking an air bearing as the research object, the structure model and the equivalent disk model of the squeeze-film air bearing are established. The modal analysis of the designed structure is carried out, and the mode of the bearing structure in the ultrasonic frequency range and the working squeeze frequency of the bearing are obtained. At the same time, the influence of air film thickness on the load characteristics of squeeze-film air bearing is analyzed by the fluid–solid coupling method. The relationship between air film thickness and loading capacity, and the relationship between contact area and loading capacity are obtained, respectively, by the above method. The results show that reducing the gap between the bearing bush and the rotor, increasing the amplitude of the bearing bush, and increasing the contact area between the bearing bush and the rotor can improve the loading capacity of the squeeze-film air bearing.

Air entrainment dynamics of aqueous polymeric droplets from dilute to semidilute unentangled regimes

Recent studies have revealed the air-cushioning effect of droplet impact upon various surfaces and although pure water droplets have extensively been studied, the air entrainment dynamics for aqueous polymeric droplets was the focus of this study. Herein, droplets of low to moderate Weber numbers, We ∼ O(1−10), displayed air film thickness gradients which was strongly influenced by the viscoelastic properties of the aqueous polymeric droplets in the dilute to the semidilute unentangled regimes. Aqueous polyethylene oxide droplets impacting a smooth thin oil film surface formed a submicrometer air layer, moments prior to impact, which was tracked by a high-speed total internal reflection microscopy technique. The radial changes in the air film thickness were related to the polymer concentration, thus providing an alternative tool for comparing the rheometer-derived overlap concentrations with a contactless optical technique.

Ethylene permeance through perforated packaging film: Modelling and effect of air velocity, temperature, film thickness and perforation diameter

Perforation in packaging material is one of the efficient ways to remove ethylene from fresh produce packages for delaying the ripening of climacteric fruit and vegetables. The effect of storage conditions on ethylene permeance has not been studied previously, therefore, this study pursued to investigate and model the effect of cooling air velocity, temperature and perforation size on the ethylene permeance through oriented polypropylene packaging film. Ethylene permeance was estimated from 1.70 ± 0.02 to 4.06 ± 0.03 cm s−1 at different temperatures, air velocities and perforation sizes. The perforation diameter showed an inverse significant impact on ethylene permeance. The model based on the empirical approach and artificial neural network using validation data exhibited an R2 of 0.9515 and 0.9890, respectively. The presented study would be helpful in optimising the perforation size in order to avoid ethylene accumulation inside fruit packages, under different storage conditions.

Research on the pressure field and loading characteristics of air film of air cushion belt conveyor

The power loss generated by the air cushion belt conveyor when transporting materials mainly depends on the diameter of the orifice, the form of arrangement, and the thickness of the air film. A mathematical model of an air cushion belt conveyor is established through mechanical analysis, and the relationship between load distribution, air film thickness, air film carrying capacity, and power consumption is found. Numerical simulations of orifices of different diameters on the disk groove and the formed air film are carried out, and the loading capacity of the air film was analyzed by observing the stress and deformation of the wire rope core. The results show that the air film formed by the selected type of orifice arrangement in this paper carries the load, which causes the least amount of deformation and stress change in the wire rope core, and the stability of the air film loading capacity is also verified by experiments.

Investigation on the influence of structural rigidity on the stiffness of aerostatic guideway considering fluid-structure interaction

The static performances of the aerostatic guideway are significantly influenced by the fluid-structure interaction (FSI) effect. This paper investigates the FSI process between the air film and two-stage cantilever structure of the slider based on a two-way transient FSI model, in which the thickness and shape of actual air film can be acquired. Moreover, the stiffness of the aerostatic guideway system with two different materials 38CrMoAl nitriding steel and 7075 aluminum alloy, is investigated numerically and compared experimentally. It proves that the structural rigidity of the slider has a non-negligible impact on the stiffness of the aerostatic guideway system. The inner mechanism of this phenomenon is further discussed to provide meaningful guidance for the design of the aerostatic guideway system.

Correlated Theory of Cross-Axis Interference of MEMS Devices Based on Parallel Plate and Squeeze Film Air Damping Induced Suppression

Owing to inevitable errors of the material and fabrication process, the cross-axis sensitivity commonly exists in a large number of MEMS devices based on parallel plate structures. Such cross-axis interference results in the non-negligible rotation of the plate that deteriorates the performance of MEMS devices. Therefore, suppressing the cross-axis sensitivity is extremely critical in the device design. This paper proposes a novel theory to identify the interplay between the cross-axis interference and squeeze film air damping, and further develops a correlated theory of the damping induced suppression. The model of tilting plate with a tiny amplitude is set up by exploiting the Reynolds equation coupled with the equations of the mass deflection, and the analytical expressions of corresponding properties are derived to elucidate the suppression mechanism and its characterization. The analytical calculation and numerical simulation analysis demonstrate that the damping induced improvement effect exists objectively and is remarkable in the condition of a large mass and a small air film thickness. The cross-axis sensitivity rendered by the tilt angle quantitatively declines 80% in terms of the air damping. The theoretical underpinning can be utilized to elaborate the ubiquitous interplay between squeeze film air damping and cross-axis interference in non-vacuum MEMS devices, which is of paramount importance for achieving high performance and stability. More importantly, it is not an exclusive method that can be combined with other methods to minimize the cross-axis interference fully.

Study on Static Characteristics of Annular Array Microporous Aerostatic Bearing

In this paper, an aerostatic bearing model in the form of microorifice annular array is designed to explore the static performance of aerostatic bearing when the orifice diameter and working air film thickness are of the same order of magnitude. Firstly, the simulation model of the new bearing is established, the pressure distribution of the bearing gas film under the influence of the orifice diameter is analyzed by the CFD method, and the performance of the aerostatic bearing is compared with the traditional toroidal throttling method with the orifice diameter of 0.1 mm; at the same time, the effects of air supply pressure, orifice diameter, and orifice number on the static performance of the bearing under different air film thickness are analyzed; finally, a new bearing is developed, and the simulation results are verified by the experimental test. The results show that when the orifice diameter and the air film thickness are of the same order of magnitude, the maximum stiffness of the aerostatic bearing is significantly improved and the microporous throttled aerostatic bearing is more suitable for the field of high stiffness. The greater the air supply pressure, the greater the bearing capacity and stiffness of the bearing. The number of orifices has an effect on improving the bearing capacity of the bearing, but when the number of orifices is large, the effect will become less obvious. This study can provide a new theoretical reference for the design of aerostatic bearing.

Dynamics of 5-DOF aerostatic spindle with time-varying coefficients of air bearing

Aerostatic bearing spindle has been widely used in precision machining processes. This paper presents a time-varying dynamic model of aerostatic spindle due to the change of air film thickness under periodic excitation forces. The effects of the magnitude and frequency of the forces on the dynamic coefficients of air bearing and cutting tool deflection are determined quantitatively. The dynamic properties in both translational and rotational directions are considered. The predicted tool vibration with and without considering the time-varying dynamics are compared. Experiments are conducted to measure the cutting tool displacements under stationary and rotational conditions. It is concluded that the variation of the dynamic coefficients plays a significant role in the spindle dynamics when the force magnitude increases beyond a critical value. The effect of unbalance mass on the spindle vibration is investigated based on the proposed model. The results provide guidance in the structure design for the aerostatic spindle and the process planning to improve the dynamic performance of the precision manufacturing process.

A steady modeling method to study the effect of fluid–structure interaction on the thrust stiffness of an aerostatic spindle

ABSTRACT Under support forces from static pressure bearings, the solid deformations of static pressure spindle or slide systems will affect their performance, especially for those with high load-carrying capacity and stiffness. This paper proposes a steady modeling method to study the effect of fluid–structure interaction (FSI) on the thrust stiffness of an H-shaped aerostatic spindle. The proposed method can be readily applied to different static pressure spindles or slides, and can save a lot of time compared with the transient method, which is generally used to consider the phenomenon of FSI. The method proposed in this study is more suitable for studying the performance of spindles and slides with high load-carrying capacity and stiffness, especially in the design phase. In this paper, solid deformations, pressure distributions and the thrust stiffness are all obtained based on this method. Moreover, the effects of the axial position of the spindle and the air film thickness on the thrust stiffness are studied. The proposed method is verified by experimental results. The calculation error of the proposed method is reduced by nearly 77% compared with the traditional method ignoring FSI.

Chatter stability analysis in Micro-milling with aerostatic spindle considering speed effect

The regenerative chatter is one of the fundamental obstacles in high-speed micro-milling process, which causes tool wear and poor surface quality. In order to predict the chatter stability of micro-milling with aerostatic spindle more accurately, the effects of rotating speed on the dynamic stiffness and damping coefficients of aerostatic journal bearing are investigated firstly. The frequency response functions (FRFs) of aerostatic spindle under different rotating speeds are calculated considering the speed effect of aerostatic bearing, centrifugal force and gyroscopic moment. A method for calculating the stability lobe diagram (SLD) of micro-milling considering the speed effect is proposed in this paper. The speed-dependent SLD is simulated based on tool tip FRFs under different rotating speeds and is verified by micro-milling of aluminum 7075. In addition, the effects of supply air pressure and air film thickness on the SLD are investigated comprehensively. The results provide guidance to improve the chatter stability and cutting efficiency in micro-milling with aerostatic spindle.