Showing papers on "Fluid bearing published in 2016"

Aerostatic thrust bearings active compensation: Critical review

Abstract: Aero-static thrust bearings are widely used in high precision conventional applications, e.g., in machine tools, measuring instruments, precise positioning systems, manufacturing and medical equipment. Their appeal is due to the absence of contact between moving and stationary parts, which ensures their low friction, limited heat generation and long life. Moreover, the use of air bearings usually does not contribute to the environmental contamination. However, aerostatic thrust bearings have usually lower stiffness and load capacity than rolling or oil bearings. For this reason, active and passive compensation are currently used to enhance these properties, thus extending the bearing's operating range. Recently, active compensation methods have become more popular thanks to improvements in mechatronics technology, and because they can provide the very high accuracy required by current high precision applications. This paper reviews the state of the art of the active compensation method and provides general classification criteria, outlining dissimilarities and the pros and cons of the available solutions. The paper concludes with several considerations and comments regarding the main performance features of each solution.

Hydrodynamic lubrication of partial textured sliding journal bearing based on three-dimensional CFD

Abstract: Purpose – The purpose of this study is to investigate the effects of partial texture location and dimple depth on load carrying capacity (LCC), friction coefficient and circumferential flow of journal bearing. Design/methodology/approach – Based on the Navier-Stokes equation, the methodology used computational fluid dynamics (CFD). A phase change boundary condition was applied on fluid domain, and the negative pressure at divergent region of oil film was considered. Findings – It has been found that texture located at lubricant inlet area can improve the performance of the bearing, and the effect of shallow dimples is superior to the deep ones. However, the bearing performance will be reduced due to the texture located at the maximum pressure area. When texture is located at the lubricant outlet area, there will be two different situations: the part of the texture located within the oil film divergent area can improve the LCC, while the part that is beyond the divergent region will make the LCC decrease. ...

Analysis on design parameters of water-lubricated journal bearings under hydrodynamic lubrication

Abstract: The article aims to investigate the relationship between eccentricity ratio and the Sommerfeld number based on hydrodynamic water-lubricated journal bearings. Considering the differences between wa...

Minimizing Frictional Losses in Crankshaft Bearings of Automobile Powertrain by Diamond-like Carbon Coatings under Elasto-hydrodynamic Lubrication

Abstract: An efficient powertrain technology contributes to sustainable lowering of greenhouse gas emissions in terms of reducing mechanical losses and saving fossil fuels Minimization of frictional losses of highly loaded components in automobile powertrain as crankshaft plain bearings and gears offers massive potential for target achievement Application-related investigations of diamond-like carbon (DLC) coatings ZrCg (a:C-H/ZrCg) and nanocomposite (nc)-ZrC (a‑C:H/ZrC) in lubricated rolling-sliding contacts in twin-disc and gear efficiency test-rig revealed great potential of ZrCg for efficiency improvement in automobile gearboxes by reducing mechanical losses up to 39 % under elasto-hydrodynamic lubrication (EHL) compared to uncoated gears With regard to plain bearings, ZrCg and nc-ZrC coated modified prototype bearings exhibited a friction advantage of up to 36 % in EHL compared to standard bearings in an engine test bench This yet largely unknown favorable effect of DLC coatings under rolling-sliding conditions in EHL opening doors to new possibilities in tribology and efficiency improvement was attributed to the thermophysical properties of DLC coatings and was confirmed by simulations of rolling-sliding contacts

Investigations on the Influence of Surface Texturing on a Couple Stress Fluid–Based Journal Bearing by Using JFO Boundary Conditions

Abstract: The present study was conducted to examine the effect of laser surface texturing combined with couple stress fluids on the hydrodynamic lubrication of finite journal bearing in this work. The Jakobsson-Floberg-Olsson (JFO) boundary conditions were engaged instead of Reynolds boundary conditions to achieve realistic results. Moreover, the results were computed and authenticated with the previous published work. It was observed that the load-carrying capacity is increased with couple stresses for smooth journal bearings at different eccentricity ratios. However, the increment in load-carrying capacity with texture affects only at low eccentricity ratios. The combined effects of texturing with couple stress fluids lower the performance of journal bearings at different eccentricity ratios.

Theoretical and experimental research on the friction coefficient of water lubricated bearing with consideration of wall slip effects

Abstract: Researches of the nature of friction coefficient of water lubricated bearing are carried out in this paper. Based on the experimental results of composite material bearing under hydrodynamic lubrication by water, we calculate the Stribeck curves as the function of load and speed, deviate the modified Reynolds equation considering wall slip effects in Cartesian coordinate system, put forward the essential model of friction coefficient, the composition of friction coefficient and essential changing correlation between them. Numerical results are in good agreement with experimental results, which verifies existence of wall slip. Researches indicate that there is always an appropriate working condition which friction coefficient is minimum. Comparison of the theoretical and experimental results shows that they are consistent on the overall trend but still exist some deviations under certain operating conditions. Reasonable explanations are given to illustrate the correctness of theoretical model.

A study on the stability performance of noncircular lobed journal bearings with micropolar lubricant

Abstract: In this paper, steady-state and stability performance characteristics of circular and noncircular two-, three-, and four-lobe journal bearings with micropolar fluids are presented. For this purpose...

Tailoring of the bearing stiffness to enhance the performance of gas-lubricated bump-type foil thrust bearing:

Abstract: This study aims to tailor the bearing stiffness for enhancing the load-carrying capacity of foil thrust bearings. New architectures for the bump foil are introduced with structural stiffness tailor...

"Fluid bearing" effect of enclosed liquids in grooves on drag reduction in microchannels

Abstract: Vortical structures form in an enclosed fluid within transverse grooves along a laminar flow in a microchannel, and act as fluid bearings on the boundary for lubrication. The fluid bearings generated from low-viscosity fluids can be used to transport high-viscosity fluids for drag reduction.

A comparative study for lubrication of surface textured porous journal bearing with two different non-Newtonian fluid models

Abstract: A study of two non-Newtonian fluid models viz., power law fluid model and couple stress fluid model on the hydrodynamic lubrication of porous journal bearing has been investigated. In addition, sinusoidal type of surface texturing is incorporated at different configurations on the bearing surface to find the performance of the bearing in both cases. The modified Reynolds equation with Darcy model using Reynolds boundary conditions is solved by central differencing technique of finite difference method. The bearing performance characteristics are calculated numerically and are compared with each other. A direct comparison between the two models has been shown graphically. The power law index (n) has taken in the range 1.0 to 1.2 while couple stress parameter (l*) has taken in the range 0 to 0.6. Numerical results show that both models significantly improve the load carrying capacity (W) and reduce coefficient of friction (COF). The results are more effective for low eccentricity ratios instead of high eccentricity ratios. It has also been observed for surface texturing that configuration 3 (72° to 144°) gives optimum results for both load carrying capacity as well as COF, when compared with all other configurations.

Analysis of the operating load of foil-air bearings in the gas generator of the turbine engine during the acceleration and deceleration maneuver

Abstract: The paper examines loads acting on the drive unit of an unmanned helicopter during maneuvers of acceleration and braking. Particular attention is paid to loads of gas generator bearings nodes of a turbine engine which is applied in the helicopter designed. The study is based on the time courses of changes in velocity of the manned PZL W3-Falcon. The correlation of flight velocity change and time was approximated by the least squares method to determine changes in acceleration. This enabled to determine the values of the forces acting on gas generator bearings under static and dynamic conditions. These values were compared with the values obtained for jump-up and jump-down maneuvers. The investigation enabled to determine the extreme components loading of the drive unit, including gas generator bearings nodes.

Experimental Study on the Dynamic Performance of a New High-Speed Spindle Supported by Water-Lubricated Hybrid Bearings

Abstract: The dynamic performance of a new high-speed spindle supported by water-lubricated hybrid bearings is experimentally studied on a test rig. The present design allows the speed of the spindle up to 30,000 rpm, with a bearing internal diameter of 40 mm, which makes it possible to simulate many actual machining processes. Some experiments have been presented to study the mechanical and thermal behaviors of the spindle and its supporting hybrid bearings. The maximum temperature rise is less than 15°C with a speed of 30,000 rpm and a water supply pressure of 2.5 MPa. The spindle radial run-out of the rotational frequency is about 1 µm. Stability of the spindle system has been improved. The experimental results indicate that water-lubricated hybrid bearings are valuable choices to replace ceramic bearings and air bearings as support for spindles under high-speed, high-precision, and heavy-load machining conditions.

Dynamic modeling method for air bearings in ultra-precision positioning stages:

Abstract: Air bearings have been widely used in ultra-precision positioning stages due to the property of nearly zero friction or wear. Small vibration of the bearing reduces the overall moving and positioni...

THD Analysis of Rolling Piston and Journal Bearings in Rotary Compressors

Abstract: A numerical analysis of the thermohydrodynamic lubrication of a rolling piston and two misaligned journal bearings in a rotary compressor has been carried out. The temperature rise of the oil film was calculated according to the transient energy equation of viscous fluid, and coupled analysis with the hydrodynamic lubrication of the rolling piston and journal bearings was conducted by using the finite element method and finite difference method. The distributions of the pressure and temperature rise of the oil film for several cycles were calculated. The analysis results show that for the journal bearings, the temperature of the oil film rises with the increase in pressure, the highest temperature appears around the region of the maximum pressure, whereas for the rolling piston bearing, there is a sharp peak in the temperature distribution. The maximum temperature in the oil film varies periodically with the rotation of the crankshaft, and after several cycles the balance between viscous heating a...

Method for increasing load capacity on a porous aerostatic bearing with a two-phase fluid

Abstract: A method for increasing load capacity on a porous aerostatic bearing through use of a two-phase fluid that is less viscous than lubrication oils and the bearing gap is of the size of air bearings. The porous material throttles vapor and liquid. As liquid goes through the porous media, the pressure drop from the porous media resistance causes it to vaporize. The increased volume flow in the bearing gap reduces the vapor flow rate through porous media, resulting in higher pressure in gap. As the vapor-liquid mixture escapes from bearing gap, another vaporization occurs at the end of bearings which retards escaping, and further increases pressure in the gap. The liquid portion of the two-phase fluid in the bearing gap increases the load capacity and stiffness, similar to hydrostatic bearings fed with liquid. The vaporization absorbs heat generated by bearing friction to allow higher relative speed between bearing surfaces.