Stability analysis of double porous and surface porous layer journal bearing

The linear stability analysis of double porous and surface porous layer journal bearing based on long and short bearing approximations is presented. The Brinkman model is employed in the porous region and the infinite permeability porous layer is simulated as surface layer. The coefficients of load, threshold speed and critical whirl frequency ratio are computed for double porous and surface porous layer configurations. The coefficients obtained using long and short bearing approximations yield same results. Higher threshold speed is obtained for double layer configurations of (i) high permeability bearing adsorbent porous layer topped with low permeability porous layer, and (ii) surface porous layer lubricant film.     

Influence of wear on the performance of a multirecess conical hybrid journal bearing compensated with orifice restrictor

In the present work, an analytical study concerning the influence of wear on the performance of a four-pocket hybrid conical journal bearing compensated with an orifice restrictor has been presented. The Reynolds equation governing the flow of lubricant in the clearance space of bearing has been solved using FEM and the Newton Raphson method. The static and dynamic performance characteristics have been presented for the various values of external load, wear depth parameter and for the various values of semi-cone angle. The numerically simulated results suggest that, the performance of the conical bearing is greatly affected by the wear defect.     

Stability of journal bearing systems using non-Newtonian lubricants: a non-linear transient analysis

The effect of the non-Newtonian behaviour of lubricants, resulting from the addition of polymers, on the performance of hydrodynamic journal bearings is investigated. The model of non-Newtonian lubricant developed by Dien and Elrod is taken into consideration. An attempt has been made to evaluate the mass parameter (a measure of stability) besides finding out the steady-state characteristics of finite journal bearings with non-Newtonian lubricants. A non-linear time transient analysis is carried out for the stability analysis.     

Study of hole-entry hybrid journal bearing system considering combined influence of thermal and elastic effects

A theoretical model is developed to study the performance of a hole-entry hybrid journal bearing system by considering variation of viscosity due to temperature rise of the lubricant in the analysis. The deformation of bush due to fluid-film pressure and temperature has been considered to establish the modified fluid-film profile. The journal temperature is computed on the basis of the fluid-film temperature. The relevant governing equations have been solved using the finite element method and a suitable iterative technique. The thermoelastohydrostatic performance of an orifice compensated symmetric and asymmetric hole-entry hybrid journal bearing configurations has been studied for the chosen bearing operating and geometric parameters. The results presented in the study indicate that the variation of viscosity due to temperature rise of the lubricant fluid-film have a quite appreciable influence on the static and dynamic performance of a hole-entry hybrid journal bearing system.     

Journal bearing housing design—A statistical study with FEM

When designing journal bearing housings for construction equipment, one goal is to get an even pressure distribution over the length of the bushing. This is to avoid excessive wear due to contact pressure peaks.A housing that is considered good, does not allow the pin to deflect and keeps the stresses low in the weld. To do this it must be stiff and this will lead to high contact pressures on the edges of the bushing, which is not preferable since wear is highly dependent on the contact pressure level.If the distribution of the contact pressure could be smoothed out over the bushing, the material might be used more efficiently. The normal way to do this is to crown the bushing to allow for pin deflection. However this leads to reduced area in contact. Another method to avoid high pressures in the bearing is to optimize the bearing housing for optimum stiffness.This paper describes one way to optimize journal bearing housings in regard to the contact pressure in the tribo-contact. A statistical approach was applied to a parameterized finite element model with contact elements. Three parameters were analyzed at different loads; set ring thickness, set ring width and fillet weld size.The contact pressure distributions were evaluated in two different ways to a single value to meet the statistical demand of measurable result. The results show that the set ring thickness and width are the parameters that influence most the contact pressure distribution. To reduce the maximum contact pressure the set ring thickness should be kept small.     

The restrictive effects of capillary compensation on the stability of the Jeffcott rotor-hybrid bearing system

The influence of restriction parameters, recess depth and land-width ratios on the load capacity and stability of a Jeffcott rotor supported by single-row, six-recessed hybrid bearings with capillary compensation is studied. The finite difference method is used to solve Reynolds equation, whilst the determination of stability threshold uses the Routh-Hurwitz method. The load capacity, stability threshold, and the critical whirl ratio, versus the changing restriction parameters, are each simulated for both shallow-recessed and the deep-recessed bearings with various land-width ratios. Simulated results indicate that small land sizes are necessary for shallow-recessed bearings in order to yield good performance, and these bearings are superior to deep-recessed bearings. Furthermore, both load capacity and stability threshold become correspondingly greater with a decrease in the restriction parameters. Nevertheless, the appropriate design of both restrictor and land size in deep-recessed bearings might well induce both load capacity and stability threshold greater than in shallow-recessed bearings.     

The tribological behavior of Ni–Cu–Ag-based PVD coatings for hybrid bearings under different lubrication conditions

In a cryogenic environment, components like bearings with interacting surfaces in relative motion (tribosystems) often generate undesired heat and experience high wear. Because the properties of conventional bearing materials like stainless steel cannot be applied to this temperature range, the PVD coating based on metal–metal pairs with better frictional properties must be employed. To test the suitability of the Ni–Cu–Ag-based PVD coatings of hybrid bearings for liquid rocket engine turbopumps and to obtain reliable coating material data in the extreme environment, the tribological behaviors of coatings under the cryogenic fluid (liquid oxygen and liquid nitrogen) and water lubricated conditions are studied, respectively. In the paper, the specimens are in a vibrocryotribometer with the ball-on-plane contact type, and various running conditions in terms of lubricants, contacting loading, and contacting velocity are examined. The simulated experiment for testing the actual tribological performance of Ni–Cu–Ag-based PVD coatings for hybrid bearings is tested. The results of the tests indicate that the coatings can be suitable for cryogenic tribosystems of turbopumps. In the cryogenic environment, the volume wear rate of coatings increases rapidly with the contacting loading, but 15 min later, the volume wear volume of coatings turns into 2.5–15×10⁻⁴ mm³. Besides, under the liquid oxygen condition in simulating the liquid rocket engine turbopumps environment, the friction coefficients are 0.03–0.1.     

The influences of orifice restriction and journal eccentricity on the stability of the rigid rotor-hybrid bearing system

The influences of restriction parameter and eccentricity on the stability of the rigid rotor supported by single-row, six-recessed hybrid bearings with orifice compensation are studied. The load capacity, stability threshold, and the critical whirl ratio versus the change of restriction parameter are each simulated for both small and large eccentricity ratio cases, also for both the shallow-recessed and the deep-recessed bearings in various land-width ratios.Simulation results will reveal that the significant influence of design parameters. The appropriate selections of restriction parameter and land-width ratio for the design of a hybrid bearing, superior load capacity and stability threshold can be obtainable. The simulated results have been concluded for the design of hybrid bearing and its restrictors.     

Stability characteristics of an externally adjustable fluid film bearing in the laminar and turbulent regimes

This paper deals with the effect of turbulence on stability characteristics of an externally adjustable fluid film bearing having a design configuration as illustrated by Shenoy and Pai. The time dependent form of Reynolds equation is solved numerically using the finite-difference method. Linearized turbulence model of Ng and Pan is incorporated in the solution scheme. Dynamic coefficients are determined using the method of linearization of bearing reactions. A study with various adjustments predicts that a bearing with negative radial and negative tilt adjustment configuration and operating in turbulent regime results in superior stability as compared to a conventional fluid film bearing.     

Analysis of hybrid journal bearing for non‐Newtonian lubricants

The performance characteristics of capillary compensated hole‐entry hybrid journal bearing systems have been studied theoretically. The analysis considers the generalized Reynolds equation governing the flow field of lubricant, having variable viscosity, taking the equation of lubricant flow through a capillary restrictor as constraint. The non‐Newtonian lubricant is assumed to follow the cubic shear stress law. The results obtained from the study suggest that bearing static performance characteristics can be optimized for the particular bearing operating conditions by proper selection of parameters such as bearing land width ratios (ā_b), the restrictor design parameter (C̄_s2), and the non‐linearity factor (K̄). Copyright © 2006 John Wiley & Sons, Ltd.     

Investigations on a permanent magnetic–hydrodynamic hybrid journal bearing

In the present work, a permanent magnetic–hydrodynamic hybrid journal bearing is developed. The force of the journal bearing comes from the hydrodynamic film and the permanent magnetic field. When a hydrodynamic film does not form, such as during starting and stopping a machine, the journal bearing relies on the magnetic force to support the rotor system. This paper studies a model of the permanent magnetic force and develops an experimental rig of the journal bearing. Experiments show that the hydrodynamic film force uncouples with the magnetic force in the journal bearing. Predictions from the model are compared with experimental data.     

动静压轴承油楔最佳加工方法的探讨

介绍了动静压轴承油楔在磨床上加工工装的改进,将原来的偏心套工装,改为工件与偏心轴通过四杆机构连动进行油楔磨削的方式,使磨削油楔的形状和尺寸更容易控制和高速,从而提高轴承精度.该工装的改进为磨床行业动静压轴承油楔的加工提供更有价值的借鉴.     

混合陶瓷球轴承多目标优化

混合陶瓷球轴承(Hybrid Ceramic Ball Bearing,HCBB)用Si3N4陶瓷球替换钢球,这两种材料性能差距较大,导致轴承寿命和发热量发生显著变化,需对HCBB进行多目标优化设计。提出高速HCBB多目标优化模型,目标函数为疲劳寿命和直接表征发热的自旋摩擦功率。用Ioannides-Harris理论计算HCBB寿命,用非劣排序遗传算法-II求解该多目标优化问题。结果显示优化的HCBB显著优于当前设计。     

圆柱浮环液体动静压轴承止推环性能的有限元分析

本文对圆柱浮环液体动静压轴承的止推环静动态特性进行了有限元分析。提出了保证浮环正常工作的平衡条件,并据此给出了浮环轴承的设计准则;在有限元分析中求解了该轴承内、外膜压力场;用小扰动法分析了动态雷诺方程,得到内外膜的刚度系数和阻尼系数;在求得浮环静压、动压平衡的基础上,得到了该轴承的静、动态特性及稳定性参数。     

Performance of worn non-recessed hole-entry hybrid journal bearings

Non-recessed journal bearings have been successfully used in various engineering applications because of their good performance over a wide range of speed and load, besides their relative simplicity in manufacturing. Due to many starts and stops in its lifespan, the bearing bush wears progressively on account of rubbing, which affects bearing performance. The present work is an attempt to analytically study the performance of a worn non-recessed (hole-entry) capillary-compensated hybrid journal-bearing system. FEM has been used to solve the Reynolds equation, governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation using suitable iterative technique. A study is conducted for two configurations, i.e., symmetrical and asymmetrical hole-entry journal-bearing system. The simulated results of bearing characteristics parameters in terms of maximum fluid-film pressure, minimum fluid-film thickness, flow rate, frictional torque, rotor dynamic coefficients, stability threshold speed and whirl frequency ratio, etc. have been presented for the wide range of various values of load and speed. The results indicate that the wear affects the bearing performance considerably; therefore, a due consideration of wear defect should be given for an accurate prediction of the bearing performance over a number of cycles. The computed results further indicate that the influence of wear defect on journal bearing performance may be minimized if a designer selects a suitable bearing configuration.     

Materials failure mechanisms of hybrid ball bearings with silicon nitride balls

A modified Shell four-ball apparatus was used to determine failure mechanisms and estimate time to failure of hybrid ball bearings using silicon nitride and zirconia balls. The machine was set up to hold a hybrid bearing containing three ceramic balls, instead of the usual 14 in order to increase contact pressure. Five kinds of silicon nitride ceramics, which differed in terms of surface roughness, porosity as well as the amount and chemical composition of additives were investigated. The goal of this study was to establish a quality criterion for silicon nitride for industrial use in hybrid ball bearings. Lifetime and failure mechanisms varied between the five bearings with silicon nitride balls and a dependance was found on the porosity and chemical composition of the materials, whereas surface roughness did not seem to influence their performance.     

Stability analyses and experiments of spindle system using new type of slot-restricted gas journal bearings

A new type of slot-restricted gas journal bearing with non-uniform slot clearance in the circumferential direction is proposed in this paper. The stability characteristics of the new type of slot-restricted gas bearing are obtained by solving linear equations of motion of rotor with two degrees of freedom supported by one bearing to prove that the proposed new type of the slot-restricted gas journal bearing is much more stable than a conventional slot-restricted bearing. For comparisons with experimental results, the stability characteristics of four degrees of freedom rotor-bearing system are judged by the non-linear transition analyses. The instability threshold speed tests of the rotor-bearing system are performed. The instability threshold speed experimentally obtained is compared with theoretical results to confirm the validity of the numerical analyses. As a result of the analysis and experiment, it was shown that the proposed new type of slot-restricted gas journal bearing is much more stable than a conventional slot-restricted bearing due to non-uniform slot clearance.     

Influence of orifices on stability of rotor-aerostatic bearing system

This paper has studied the influences of both the number and locations of entry holes on the stability of a rigid rotational rotor supported by two double-row, orifice compensated aerostatic bearings. The air is assumed to be perfect gas, undergoing the adiabatic process and passing through entry holes into the bearing clearance, is governed by Reynolds equation including the coupled effects of wedge due to rotor rotation and squeezed film due to rotor oscillation. The Ph-method is used to analyze Reynolds equation which is then solved by the finite difference method and numerical integration to yield static and dynamic characteristics of air film. The equation of motion of the rotor-bearing system is obtained by using the perturbation method and the eigen-solution method is used to determine the stability threshold and critical whirl ratio. The eccentricity, rotor speed, and restriction parameter are considered in the analysis of the whirl instability of the rotor-aerostatic bearing system for the comparisons between various designs in the number and locations of entry holes of aerostatic bearings.