Load Capacity Of Bearing Research Articles

Discontinuous grooves in thrust air bearings designed with CAPSO algorithm

Spiral groove thrust air bearings suffer from low load capacity. Although there have been studies on optimizing the groove geometry of spiral groove thrust air bearings to enhance the load capacity, all of them found so far have focused on continuous grooves only. Here, a novel groove optimization method, which allows the flexibility of generating either continuous or discontinuous grooves, is introduced for maximizing the load capacity of spiral groove thrust air bearings. In the proposed method, computational fluid dynamics is combined with the chaos-enhanced accelerated particle swarm optimization algorithm to search for the optimal groove geometry. A case study is given where the optimization of an initial spiral groove thrust air bearing is implemented. The optimized grooves are found to be discontinuous and of new geometry. Numerical analysis shows that the optimized discontinuous grooves can achieve higher load capacity than the optimized continuous grooves, the conventional herringbone, and the initial spiral grooves. The effect of the proposed method is further verified in experiments.

Tilting-Pad Journal Bearing Subjected to Fuzzy Type-2 Uncertain Parameters

Abstract This paper evaluates the effects of uncertainties on the load capacity of a four-pad tilting-pad journal bearing, in which the pad radius, oil viscosity, and radial clearance are considered as uncertain information. The hydrodynamic supporting forces at the bearing pads are obtained by solving the Reynolds equation. In this case, the uncertain parameters are modeled as fuzzy type-2 variables. Fuzzy type-2 sets have been widely used due to their ability to model higher orders of uncertainties as compared with the fuzzy type-1 approach. They allow for inaccurate knowledge to be included in the membership functions used to describe the uncertain parameters. In the present contribution, the so-called α-level optimization was associated with the fuzzy type-2 technique for uncertainty analysis purposes. A sensitivity analysis was also carried out as an additional assessment of the considered uncertain parameters. The numerical results allowed to understand how the uncertain parameters affect the bearing supporting forces for three shaft speeds, namely, 3000, 9000, and 15,000 rpm. It was demonstrated that the effect of the uncertain parameters on the supporting forces increases according to the shaft speed. Additionally, the load capacity revealed to be more sensitive to variations on the oil viscosity and radial clearance than to the pad radius concerning the adopted uncertain interval. Consequently, the obtained results can provide suitable information for the design, manufacturing, and maintenance of tilting-pad journal bearings.

Hydrostatic Journal Bearing With Porous Pads and Improved Properties

Abstract A hydrostatic journal bearing with porous pads to improve its performance is designed. The porous pads, which are embedded in recesses of the hydrostatic journal bearing, not only allow lubricant to flow through them but also form a complete cylindrical surface with the bearing land. The load capacity of the hydrostatic bearing is thus maintained and the hydrodynamic effects strengthened. A theoretical model of the porous pads bearing is tested with the simulation software, and the parameters that critically affect the bearing performance are studied. Thus, the results obtained indicate that the porous pads bearing has higher load capacity and higher stiffness than a typical hydrostatic bearing with lower friction and lower end flow rate at high rotating speed.

A numerical method to investigate the mixed lubrication performances of journal-thrust coupled bearings

PurposeThis paper aims to present a numerical model to investigate the mixed lubrication performances of journal-thrust coupled bearings (or coupled bearings).Design/methodology/approachThe coupled hydrodynamic effect (or coupled effect) between the journal and the thrust bearing is considered by ensuring the continuity of the hydrodynamic pressure and the flow field at the common boundary. The mixed lubrication performances of the coupled bearing are comparatively studied for the cases of considering and not considering coupled effect.FindingsThe simulated results show that the hydrodynamic pressure distributions for both the journal and thrust bearing are modified due to the coupled effect. The decreased load capacity of the journal bearing and the increased load capacity of the thrust bearing can be observed when the coupled effect is considered. And the coupled effect can facilitate in reducing the asperity contact load for both the journal and thrust bearing. Additionally, the interaction between the mixed lubrication behaviors, especially for the friction coefficient, of the journal and the thrust bearing is significant in the elastohydrodynamic lubrication regime, while it becomes weak in the mixed lubrication regime.Originality/valueThe developed model can reveal the mutual effects of the mixed lubrication behavior between the journal and the thrust bearing.

Investigation of Structural Conformity in a Three-Pad Adaptive Air Foil Bearing With Regard to Active Control of Radial Clearance

Abstract Various solutions for the design of oil-free bearings are discussed in the literature. Adding hydrodynamic preload to the foil bearings by profiling the inner bore of the bearing is one of the most frequently investigated methods for improving the bearing stability and damping character of the entire system. However, this approach leads to a reduced load capacity and thus to an increased lift-off speed of the foil bearings. Observations of this kind lead to the presentation of various solutions for active bearing contour adjustment, which benefits from different profiles of the lubricant film. Most of these concepts use piezoelectric stack actuators to generate the required alternating force, although the influence of the stiffness of adaptive elements on bearing performance is not fully discussed in the literature. The focus of this study is on the investigation of structural conformity, i.e., the harmonization of stiffness with respect to the requirements for shape control and load capacity of an adaptive air foil bearing (AAFB). The result may be a basis for the consideration of additional degrees of freedom in any concept with shape control as the main design framework in interaction between the lubricant and compliant structure in an air foil bearing from both static and dynamic points of view.

Analysis on the steady state performance of a multi pad externally adjustable fluid film bearing

PurposeThis study aims to investigate the performance characteristics of an externally adjustable bearing with multiple pads in steady state conditions. The proposed adjustable bearing geometry can effectively control the hydrodynamic operation in bearing clearances by adjusting the pads in radial and tilt directions. These pad adjustments have a significant role in improving the bearing characteristics such as load capacity, attitude angle, side leakage, friction variable and Sommerfeld number, which will be analysed in this paper.Design/methodology/approachThe adjustable bearing is designed with circumferentially spaced four bearing pads subjected to similar radial and tilt adjustments. Tilt angles are applied along the leading edges of bearing pads. A modified film thickness equation is used to incorporate the pad adjustments and accurately predict the variation in film profile. Finite difference approximation is adopted to solve the Reynolds equation and discretize the fluid film domain.FindingsFor negative radial and tilt adjustments, higher hydrodynamic pressures are generated in bearing clearances, which increases the bearing load capacity at different eccentricity ratios. From comparative analysis for different pad adjustments, superior bearing performance is observed for bearing pads under negative radial and negative tilt adjustments.Originality/valueThis research presents a detailed theoretical approach to analyse the performance capability of a four pad adjustable bearing geometry, which is not available in literatures. Improved bearing performances with negative pad adjustments can attract bearing designers to implement the proposed adjustability-bearing concept in rotating machineries.

Load capacity of foil gas dynamic bearings with conical surfaces lubricated with low-viscosity cryogenic fluids

The present paper features a mathematical model of load capacity and static characteristics calculation of foil gas dynamic bearings with conical surfaces lubricated with cryogenic fluids based on equations of thermophysics, hydrodynamic and elasticity theory. Algorithmic model is presented. Original software is presented that is used to calculate load capacity and static characteristics of the bearings in question.

IRON POROUS SLIDE BEARINGS IMPREGNATED WITH A SELECTED IONIC LIQUID

This article presents some selected results of the research on the slide porous bearings, sintered from the iron powder Höganas NC.100.24, with 2.5% of copper addition by weight, impregnated with selected ionic liquids, through comprehensive and detailed research works [L. 1–6]. The research was carried out within the framework of PBR/15-249/2007/WAT-OR00002904 Research Project financed by the Ministry of Science and Higher Education, during 2007–2011 [L. 7]. Several times higher load capacities and durabilities were obtained in comparison with standard ø25/ø35×20 mm sleeves lubricated with previously used oils, including perfluoropolyether oils. To date, there were no bearings sintered from the iron powder and impregnated with ionic liquids. The durability and load capacity of such bearings are higher, and that is why it was decided to submit a proper patent claim to the Polish Patent Office [L. 8].

Performance Study of Conical Hydrodynamic Bearing Under Different Semi Cone Angle on Conical Hydrodynamic Bearing Performance With Air Lubrication

Bearing plays crucial role in the functioning of almost all industries such as chemical, petrochemical, automotive, and various process industries. Bearing supports, guides, and reduces the friction of moving machine parts. The lubrication in fluid film journal bearing is used to separate two relatively sliding surfaces with a thin film. The fluid wedge between shaft and bearing causes pressure built to support the load. Conical bearing supports load in both axial and radial direction over separate cylindrical journal bearing and thrust bearing. Conical bearing replaces two bearings with one. The present study related to performance analysis of conical hydrodynamic bearing with air as lubricant. In this paper, semi-cone angle effect is analyzed on the pressure distribution of air lubricated conical bearing. The performance is carried out with semi cone angle of 5, 10, 20, 45, 60 and 80 degrees using ANSYS workbench. Results shows maximum pressure distribution is obtained for the semi cone angle between 5 to 10. Bearing load capacity in radial direction reduces after 450 angle.

A transient hydrodynamic lubrication comparative analysis for misaligned micro-grooved bearing considering axial reciprocating movement of shaft

Abstract A transient hydrodynamic lubrication model is proposed to investigate the lubrication performance of micro-grooved journal bearings, considering the axial flow caused by the axial reciprocating movement of the shaft. The lubrication performance of the bearing engineered with three different microgroove distributions, i.e. straight groove, spiral groove, and herringbone groove are compared systematically, including the load capacity and friction coefficient. The results suggest that the herringbone-grooved bearing exhibits the maximum load capacity in the positive axial movement, followed by straight-grooved bearing, and finally spiral-grooved bearing. The spiral-grooved bearing produces the minimum fluctuation amplitude of load capacity and attitude angle in one reciprocating period. The increased frequency of the axial movement can increase the value of load capacity for three micro-grooved bearings during the positive movement of the shaft; however, it does not affect the distribution trends of load capacity among the three micro-grooved bearings. Moreover, the effects of groove angle (β), degree of misalignment (Dm), and misalignment direction angle (α) on the lubrication performance of the micro-grooved bearing are investigated. The results indicate that the herringbone-grooved bearing exhibits better lubrication performance than the spiral-grooved bearing in the positive axial movement at any β. The present study also indicates that the load capacity of considering axial movement is more sensitive to Dm than that of not considering axial movement. The misalignment direction angle will result in the decreased load capacity of the micro-grooved bearing.

ANALYSIS OF BEARING CLEARANCE AND WIDTH OF AN OIL GROOVE ON THE CHARACTERISTIC OF FLUID FILM IN HYDRODYNAMIC MAIN CRANKSHAFT BEARINGS

Paper represents an analysis of the influence of oil groove width and bearing clearance on the characteristics of oil film in a hydrodynamic journal main crankshaft bearing. Analysis was performed to define the influence of bearing clearance and dimensions of oil grooves on static characteristics and manufacturability of half-shelf bearings in industrial high-volume production. Computer simulations were made using an ARTbear program, which was developed in Department of Machine Construction and Vehicle Design in Gdańsk Technical University. The analysis allowed defining the correlation between groove geometry and load capacity and working conditions of bearings. Potential opportunities of possible shortening of production time in high-volume production were also indicated.

Vibration Reduction of Large Unbalanced Rotor Supported by Externally Pressurized Gas Journal Bearings With Asymmetrically Arranged Gas Supply Holes (Verification of the Effectiveness of a Supply Gas Pressure Control System)

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.

Effects of structural parameters on the load carrying capacity of the multi-leaf gas foil journal bearing based on contact mechanics

Abstract In this study, a comprehensive model is introduced to obtain the accurate load carrying performance of the multi-leaf foil bearing. The model considers area contact between foil leaves and also the bearing sleeve constraint and rotor-foil contact. Bearing loading tests are conducted, and the results correspond well with those by simulation. This also indicates that bearing sleeve constraint aids in improving the bearing load capacity. The study analyses the effects of foil thickness, free foil radius, foil overlapping ratio, and radial clearance on the bearing load capacity and aeroelastic characteristics including foil deflections, distributions of gas film thickness and pressure. The results indicate that optimal values of the studied parameters exist to improve the load capacity of multi-leaf foil bearing.

Increasing the load capacity of planar ferrofluid bearings by the addition of ferromagnetic material

Ferrofluid pocket bearings are a type of bearing that are able to carry a load using an air pocket encapsulated by a ferrofluid seal. Previously designed ferrofluid bearings show the great potential of the stick-slip-free and low viscous friction bearings, however until now the load capacity is limited. In this article a method is presented to increase the load capacity in a simple and cost effective way by the addition of ferromagnetic material around the magnet. First, a mathematical model of the bearing is presented and is validated by experiments using an axially magnetized ring magnet surrounded by two steel rings. The model is used to optimize the dimensions of the added ferromagnetic material for maximum load capacity. Depending on the fly height, the load capacity has been increased by a factor three to four by the addition of steel rings to the ferrofluid pocket bearing configuration.

Load Capacity of a Radial Ball Bearing with Increased Radial Clearance

A method is proposed for calculating the load capacity of a radial ball bearing with increased radial clearance.

In-plane friction behaviour of a ferrofluid bearing

Ferrofluid bearings have been demonstrated to be very interesting for precision positioning systems. The friction of these bearings is free of stick-slip which results in an increase of precision. More knowledge on the friction behaviour of these bearings is important for there application in precision positioning systems. This paper demonstrates that the friction of a ferrofluid bearing can be modelled by a viscous damper model and provides a basic model to predict the friction behaviour of a bearing design. The model consists of a summation of a Couette flow with a Poiseuille flow such that there is no net fluid transport under the bearing pads. The model is experimentally validated on a six degrees of freedom stage using ferrofluid bearings. A stiffness in the form of a closed-loop control gain is introduced in the system to create a resonance peak at the desired frequency. The damping coefficient can be identified from the peak height of the resonance, since the peak height is the ratio of total energy to dissipated energy in the system. The results show that the newly derived model can be used to make an estimate of the damping coefficient for small(∼1mm) stroke translations. Furthermore, the model shows that the load capacity of a ferrofluid pocket bearing is affected during sliding.

Effect of environmental pressure on dynamic characteristics of aerodynamic gas bearing of boost turbo expander

Improvement of the environmental pressure of gas bearing can enhance the load capacity of dynamic gas bearing. This study analyzes the effect of environmental pressure on the dynamic characteristics of a bump foil gas aerodynamic bearing. Results show that an increase in the environmental pressure enhances the direct dynamic stiffness Kxx and Kyy and the direct dynamic damping Dxx and Dyy of gas film. The direct stiffness Kxx and Kyy and direct damping Dxx and Dyy of gas film increase with the increase of the environmental pressure of gas bearing. The load capacity of bearing is related to the direct stiffness of gas film. Therefore, the direct stiffness Kyy can be increased by increasing the environmental pressure of gas bearing, consequently improving the load capacity of the bearing.

Effects of humid air on aerodynamic journal bearings

Abstract The development of aerodynamic bearings applications where ambient conditions cannot be controlled (e.g., for automotive fuel cell compressor) raises the question of the effects of condensation in the humid air on performance. A modified Reynolds equation is obtained in relation to humid air thermodynamic equations, accounting for the variation of compressibility and viscosity in the gas mixture. The load capacity and stability of plain and herringbone-grooved journal bearings is computed on a wide range of operating and ambient conditions. In general, performance metrics show an independence on humid-air effects at moderated temperature, although the stability of the grooved journal bearing exhibits strong variations in particular conditions. In consequence, a safety margin of 25% is suggested for the critical mass.

Numerical research of pressure depression in aerostatic thrust bearing with inherent orifice

Abstract The undesirable pressure depression in aerostatic bearing will cause the loss of aerostatic bearing load capacity. Therefore, the method of “separation of variables” (MSV) for solution of laminar boundary-layer equations is utilized to investigate the pressure depression. The influences of supply pressure, orifice diameter, film thickness and pressure ratio on the pressure depression are studied. The results manifest that pressure depression is weakened with decreasing supply pressure and film thickness and increasing orifice diameter. The increase of pressure ratio which is determined by the flow and geometry parameters will weaken the inertial effect and then results in weakening the pressure depression. What's more, when pressure ratio is larger than the critical value 0.9409, the pressure depression will disappear.

Study on Lubrication Performance of Journal Bearing with Multiple Texture Distributions

The lubrication performance of journal bearings with different sorts of uniformly distributed micro-spherical textures are studied in this paper. Geometries and dynamic models of journal bearings with pure concave/convex textures are developed. The validity of the proposed models is verified against the oil film pressure distribution from the literature. The effects of geometry parameters (the texture depth and the area density) on the load capacity and the friction coefficient of the bearing are analyzed and discussed. Results indicate that: the bearing load capacity is reduced by the concave spherical texture, but enhanced by the convex texture; both the concave and convex textures have a very slight influence on the friction coefficient. Aiming to further improve the bearing lubrication performance, a novel concave-convex composite texture is proposed and modelled. Results show that the composite texture can significantly improve both the load capacity and the friction coefficient, because the concave spherical segments among the convex ones protect the oil film from rupture near the main load region. The oil film region is expanded by the composite texture as well.