Hybrid Bearings Research Articles

Effect of Temperature and Surface Roughness on the Tribological Behavior of Electric Motor Greases for Hybrid Bearing Materials

Greased bearings in electric motors (EMs) are subject to a wide range of operational requirements and corresponding micro-environments. Consequently, greases must function effectively in these conditions. Here, the tribological performance of four market-available EM greases was characterized by measuring friction and wear of silicon nitride sliding on hardened 52100 steel. The EM greases evaluated had similar viscosity grades but different combinations of polyurea or lithium thickener with mineral or synthetic base oil. Measurements were performed at a range of temperature and surface roughness conditions to capture behavior in multiple lubrication regimes. Results enabled direct comparison of market-available products across different application-relevant metrics, and the analysis methods developed can be used as a baseline for future studies of EM grease performance.

Grease Performance in Ball and Roller Bearings for All-Steel and Hybrid Bearings

Grease life in hybrid bearings is longer than that in all-steel bearings. This will be shown in this article by means of grease life tests with a large number of greases for both deep groove ball bearings (DGBBs) and cylindrical roller bearings (CRBs). The results show that grease life for hybrid bearings is always larger than that for equivalent all-steel bearings and that this varies between a factor of 2 and 9 depending on the grease type used. For cylindrical roller bearings, grease life does not increase with decreasing speed below a minimum value. However, at these relatively low speeds, hybrid bearings give a longer grease life than all-steel bearings.

Inclination angle effect of tribological performance for hydrostatic bearing having tilting oil pad under variable viscosity conditions

In order to improve tribological performance of hydrostatic bearing, an innovative hydrostatic bearing structure having tilting oil pad is designed. During the operation, the semicircular boss at the bottom of the oil pad can realize the circumferential micro-motion. It generates additional dynamic pressure, and forms the static and dynamic pressure mixing support, make up for the static pressure loss, and solves the problems such as low precision and unstable operation of the numerical control equipment under the high speed and heavy load conditions. According to the tribological principle and lubrication theory, bearing capacity, flow rate, oil film thickness equation and oil film stiffness for hydrostatic and dynamic hybrid bearing are derived under variable viscosity conditions. The simulation model of hydrostatic bearing having tilting oil pad is established. ANSYS software is used to analyze the distribution of oil film temperature field and oil film pressure field under different inclination angles. The effects of tilting oil pad inclination angle on oil film tribological performance and oil film stiffness are obtained. The results show that the hydrostatic bearing having tilting oil pad can generate additional dynamic pressure in high speed operation, make up the loss of static pressure. When the inclination angle is 0.0044°, oil film temperature rise is 34.8 ℃, the average pressure is 622.2 KPa, oil film stiffness is 54104 N/µm, the comprehensive lubrication performance is optimal, the oil film stiffness is the largest, and the operation accuracy and stability of hydrostatic bearing are improved.

Empirical correlation of heat generation in hybrid ball bearings, depending on the operational conditions in the aero-engine rotor supports

Modern gas turbine bearings operate at high rotational speeds. Their speed index reaches dmn=3…3, 5-106 mmrpm, where dm = bearing mean diameter, and n = rotational speed. At high speeds, significant heat is generated in conventional steel bearings, and substantial cooling oil consumption may be required. A promising solution to this problem is using hybrid bearings with steel rings and ceramic rolling elements. Due to ceramic’s relatively small coefficient of thermal expansion, hybrid bearings retain radial clearance in a wide temperature range. Hybrid ball bearings, with an inner diameter of 130mm and 150mm, were tested in the bearings test rigs at the Central Institute of Aviation Motors (CIAM). From these tests, an empirical method for determining the thermal state of the bearings was developed. The calculated values correspond well with the experimental data presented in the extant literature.

Повышение надёжности приводных асинхронных машин на электроподвижном составе

The problem of failures of traction machines used in the electric rolling stock (ERS) is considered. In the course of ERS operation with microprocessor control and the use of electric drives with semiconductor converters and induction traction motors (ITMs), it is observed that the service life of bearings reduces from the 2 million km declared by the manufacturer, to 200-600 thousand km. The study of bearings shows the following types of damage: dulling of rolling elements and tracks of the outer and inner rings, grooving, and lubricant degradation. An analysis that was carried out shows that in the majority of cases, the bearings fail as a consequence of a current flowing through them. The currents flowing through bearings are generated due to different mechanisms. A classification of bearing currents is proposed, and possible current flow loops are analyzed. Based on an analysis of literature sources, methods for reducing the bearing currents are given, and their effectiveness is evaluated. To enhance the ITM reliability, several measures to prevent electric current from passing through the bearings have been developed, including the method of plasma deposition of aluminum oxide on the outer ring, which insulates the bearing outer ring from the motor body, and hybrid bearings with ceramic rolling bodies. To select the optimal solution and determine the difference between the outer ring insulation concept and the hybrid concept, operational tests were carried out. Conclusions have been drawn about the expediency of using hybrid bearings with rings made of bearing steel and rolling elements made of bearing silicon nitride (Si3N4).

Методы повышения надёжности работы подшипниковых узлов в тяговых асинхронных машинах

The problem of electric rolling stock traction machinery failures caused by electrical erosion of bearings is addressed. Damages inflicted to traction machinery bearings as a result of electric current flowing through them have been known since long ago. In recent time, however, damages of this kind have become more frequent, because frequency and voltage converters for control of three-phase inductor motors are widely used in the electric rolling stock. An overview of factors causing the occurrence of stray currents generated in frequency converter driven traction motors and sources of these currents is presented. Electric current flows through rolling bearings in the area of the contact between the rolling elements with inner and outer rings, thus causing damage to the bearing metal components' rolling surfaces and degrading the quality of lubricants. To study and analyze the currents through bearings, the stray capacitances existing in traction machines are determined, and their calculation methods are defined, the necessity of which is stemming from the fact that these capacitances influence the generation of parasitic currents. The stray capacitances in traction machines include the capacitance between the stator windings and the stator core pack, the capacitance between the stator windings and the rotor, the capacitance between the rotor and the stator core pack, and the capacitances of the bearings. From the electrical point of view, bearings may also be regarded as capacitances. As long as there is a continuous lubricant film between the inner ring and outer rings and the rolling elements, the bearings behave as capacitors. A difference of potentials across the bearing elements may lead to electrostatic discharges and, hence, to discharge currents through the bearings. One of possible ways to enhance the reliability of traction machine bearing units is to use insulated bearings. The change in the impedance of bearings with ceramic coating and hybrid rolling elements depending on the applied voltage frequency and operating temperature is calculated and analyzed. Conclusions regarding the expediency of using hybrid bearings having rings made of bearing steel and rolling elements made of bearing silicon nitride (Si3N4) are drawn.

Numerical and experimental investigation on the performance of hybrid porous gas journal bearings

AbstractAs the progress of the high‐speed performance requirement for porous gas journal bearings continuing, the aerodynamic effect, which plays a key role in the state of lubrication, causes the porous gas journal bearings being gradually to be used as hybrid bearings. This paper firstly presents a theoretical analysis on the lubrication mechanism of the hybrid bearings. The gas flow in the porous and clearance is modelled by using the mass continuity equation. Two experimental test rigs are designed to systematically test the static and dynamic characteristics of the hybrid bearings. The numerical results are corroborated by the experimental data. Results show that there is optimal clearance for hybrid bearings to obtain maximum load capacity. The load capacity of the hybrid bearings is increased by the aerodynamic effect to be higher than that of pure aerostatic bearings especially at higher rotational speed and larger eccentric ratio. However, due to the occurrence of the aerodynamic effect, the hybrid bearings show clear cross‐coupling dynamic coefficients, which may lead to bearing instability. It is interesting to note that the direct dynamic stiffness and damping coefficients are both influenced by the aerodynamic and aerostatic effects. Higher rotational speed and external supply pressure will result in higher direct dynamic coefficients.

Control of hybrid electromagnetic bearing and elastic foil gas bearing under deep learning.

The hybrid electromagnetic and elastic foil gas bearing is explored based on the radial basis function (RBF) neural network in this study so as to improve its stabilization in work. The related principles and structure of hybrid electromagnetic and elastic foil gas bearings is introduced firstly. Then, the proportional, integral, and derivative (PID) bearing controller is introduced and improved into two controllers: IPD and CPID. The controllers and hybrid bearing system are controlled based on the RBF neural network based on deep learning. The characteristics of the hybrid bearing system are explored at the end of this study, and the control simulation research is developed based on the Simulink simulation platform. The effects of the PID, IPD, and CIPD controllers based on the RBF neural network are compared, and they are also compared based on the traditional particle swarm optimization (PSO). The results show that the thickness, spread angle, and rotation speed of the elastic foil have great impacts on the bearing system. The proposed CIPD bearing control method based on RBF neural network has the shortest response time and the best control effect. The controller parameter tuning optimization starts to converge after one generation, which is the fastest iteration. It proves that RBF neural network control based on deep learning has high feasibility in hybrid bearing system. Therefore, the results provide an important reference for the application of deep learning in rotating machinery.

Controlling the characteristics of the hybrid bearing by means of an electromagnetic actuator

The increase in the power and efficiency of the newly developed rotating mechanisms is inextricably linked with the growth of their rotation speeds and the overall level of vibration. Gas-dynamic foil bearings have a higher priority for use in high-speed mechanisms due to their practically unlimited maximum speed, the absence of an additional lubrication system, low friction power losses, etc. However, increased friction and low load-carrying capacity during the start-stop period is a problem for the further application of gas-dynamic foil bearings. The hybrid bearing studied in this work includes a rolling-element bearing, a gas-dynamic foil bearing and actuators. The hybrid bearing studied in this work includes a rolling-element bearing, a gas-dynamic foil bearing and actuators. Actuators allow during operation to switch from one type of bearing to another, as well as to control the radial gap of the gas-dynamic foil bearing, changing the dynamic characteristics of the hybrid bearing. The new designed hybrid bearing was manufactured and tested on a rotordynamic test rig in this study. A theoretical model of the hybrid bearing rotor system was built and demonstrated by the experiment results.

Research and applications of active bearings: A state-of-the-art review

Controllable/active bearings are mainly associated with active magnetic bearings (AMBs), whereas active bearing control is also found in many types of bearings, e.g. fluid, gas and hybrid bearings. The article presents a review of the literature describing the structure and results of studies of active bearings. Active control brings a number of benefits resulting in the fact that their use as a support for rotors becomes increasingly common. This article introduces readers to the different methods of controlling radial bearings and provides detailed information on various technical solutions. Furthermore, the paper presents the characteristics of bearings as well as the basic advantages, disadvantages and possibilities offered by active control of various types of bearings. The influence of active control on rotor dynamics as well as on bearing friction, temperature control, permissible operating time, the environment (possibility of using safer lubricants) and operating safety is presented. The final part of the article presents possible directions of development of active bearings (ABs).

Microstructure and Wear of Cathodic Arc Physical Vapour Deposited on TiAlN, TiCrN and n TiAlN Alpha Si3N4 Films

Present study examined the microstructural features, hardness and wear performance of TiAlN, TiCrN and n-TiAlN/α-Si3N4 coatings deposited by cathodic arc physical vapour deposition (CA-PVD) technique on M-50 steel keeping in mind a possible application of hybrid bearings in next generation aero-engine. Microstructural features of the coatings were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy. Hardness was measured using microhardness tester. Wear test was carried out with the help of ‘Bruker’ tribometer. Worn surfaces were characterised employing SEM. Results show that TiCrN coating has crystalline columnar structure and other coatings have nano-crystalline structures. Besides improved hardness, TiAlN has best wear resistance and TiCrN coating exhibits least friction coefficient.

Real-Time Dynamics Modeling of Cryogenic Ball Bearings With Thermal Coupling

Abstract Real-time dynamic modeling of cryogenic ball bearings, where the rotating inner race accelerates to the operating speed, is based on integration of classical differential equations of motion of bearing elements, when experimentally measured ball/race traction behavior is used to compute the imposed acceleration on the rolling elements. The dynamic performance simulation provides a realistic coupling between traction behavior in the ball-to-race contacts and dynamics of bearing element motion as the bearing goes through the transient speed variation. However, due to vastly different mechanical and thermal time scales, heat generation in the bearing is time-averaged over a relatively large thermal time-step to model temperature fields as a step change, while the bearing motion is simulated in real-time. The emphasis is on dynamic modeling with thermal coupling in a static sense. Under stable conditions, the step change in temperature field converges to operating value as the bearing approaches a dynamic steady-state condition, which demonstrates acceptable significance of the dynamic simulation with coupled thermal interactions. Both all steel and hybrid ball bearings for liquid oxygen (LOX) turbo pump applications are modeled. Bearing performance simulations are closely modeled over experimental time cycles in both transient and steady-state domains. Steady-state solutions are shown to be independent of initial conditions to demonstrate acceptable convergence of time domain integrations. Model predictions of heat transferred to circulating LOX is within the range of variation in experimental data. Parametric evaluation of bearing performance as a function of operating conditions demonstrate that while the ball/race contact stress is higher in a hybrid bearing, contact heat generation is significantly lower in comparison with that in the all steel bearings.

Rolling Friction of Hybrid Ceramic–Steel Pairs under Different Lubrication Conditions

We present the results of a study of a model rolling tribosystem with ceramic balls making a point “ceramic–steel” contact with a flat movable thrust ring under dry rolling friction and under lubrication. The results of laboratory tribotechnical tests enabled a comparative assessment of the wear rate of hybrid “steel–ceramics–steel” model rolling tribosystems with balls made of different ceramic materials. We ranked the studied material in terms of efficiency and improved the technology of rolling elements for hybrid ball bearings. We manufactured prototype hybrid bearings that undergo bench durability tests.

Fabrication of micro-texture on cylindrical inner surface and its effect on the stability of hybrid bearing

In this paper, a removable through-mask electrochemical micromachining (EMM) is proposed for fabricating the microstructures with different sizes and structures on the inner surface of the hybrid bearing. By optimizing the machining parameters of EMM, micro-textures with considerable area consistency and excellent surface quality are obtained on the inner surface of the hybrid bearing. Subsequently, the stability tests of the non-textured bearing and other three textured bearings with various area ratios are carried out on the setup of hybrid rotor-bearing system to study the influence of micro-texture on the vibration characteristics and stability of the bearing rotor. The time domain, frequency domain, and axis trajectory of the rotor are compared and analyzed. The experiment results show that at low speed (2400 rpm), the micro-texture has little effect on the amplitude of bearing-rotor system. As the rotational speed increases, the amplitude of the rotor-bearing system gradually increases. It should be noted that the amplitude of specific micro-texture bearings is smaller than the non-textured bearing, but not all types of micro-texture perform like that. At 9000 rpm, the relative amplitude of one sample decreases by 22.6% compared with the non-textured bearing rotor system. Therefore, the micro-texture with reasonable size and structure could significantly reduce the vibration of the rotor-bearing system under the water film condition, which is of considerable significance to improve the stability of liquid film and provides a potential application background for high-speed bearing lubrication.

Thermal effect on stability and minimum oil film thickness of a deep/shallow pockets conical bearing

PurposeThis paper aims to study the influence of thermal effect on the performance for a high-speed conical hybrid bearing including stability and minimum oil film thickness.Design/methodology/approachA thermal hydrodynamic (THD) model and dynamic model of single mass rigid rotor system were established by taking conical hybrid bearing with shallow and deep pockets as the research object, dynamic coefficient and stability parameters of bearing-rotor system were obtained by using finite element method (FEM) and finite difference method (FDM) to solve computational models of Reynolds equation, energy equation and viscosity-temperature equation. Minimum oil film thickness was obtained based on bearing force balance. Dynamic coefficient was compared with previous findings.FindingsAfter considering thermal effect, the dimensionless critical mass decreases, a significant decrease in the instability speed, and the stability of the system decreases greatly; the minimum oil film thickness decreases because of thermal effect.Originality/valueThe thermal effect is combined with dynamic characteristics to analyze stability of the rotor system for a conical hybrid bearing. Influence of thermal effect on minimum oil film thickness is studied.Peer reviewThe peer review history for this article is available at:https://publons.com/publon/10.1108/ILT-12-2019-0542/

Active hybrid bearings as mean for improving stability and diagnostics of heavy rotors of power generating machinery

The article describes a theoretical study of basic features of active hybrid bearings used as supports for heavy energy-generating machines equipment, primarily turbine generators and their turbines. Due to the adjustable oil supply pressure and using a controller of a rotor position AHB reduces its vibration level. Vibration velocity can be reduced from several times for smaller rotors to tens of percent for heavier ones. The eccentricity of the rotor position in the bearing also affects the efficiency of vibration reduction. In this case also some nonlinear effects are observed. In addition, AHB can possibly be used as a diagnostic tool for monitoring the health of a heavy power generating machinery due to its ability to generate power test impulses for rotor excitation and further analysis of its response.

Seismic performance analysis of a large-scale single-layer lattice dome with a hybrid three-directional seismic isolation system

A large number of studies and applications have been carried out on horizontal seismic isolation systems, and their effectiveness has been indicated. For long-span spatial structures, vertical seismic load plays an important role. However, vertical seismic isolation technology has not been extensively investigated. In this paper, a hybrid bearing with three-directional seismic isolation effects is proposed, in which the triple friction pendulum component and the viscous damping component are combined in series. Compared with other seismic isolation systems, the advantages of this hybrid seismic isolation system are that it can not only greatly lengthen the structural periods but also dissipate the seismic energy in all three directions. A hybrid numerical modeling method for this hybrid seismic isolation bearing is also developed. The seismic performance of a welded large-scale single-layer lattice dome with this hybrid seismic isolation system subjected to near-field ground motions is analyzed. The results show that the important dynamic demands in the dome are significantly suppressed compared with the base-fixed dome. The seismic isolation effects are evaluated in all three directions, and the effectiveness of the hybrid isolation system is verified. Finally, a comparative study is performed, and the mechanical parameters of this hybrid bearing are discussed. It is found that the damping energy dissipation in the seismic isolation bearings is not the most important factor in reducing structural dynamic demands. The proposed seismic isolation system and its numerical modeling method provide an attractive and effective alternative for the design of long-span spatial structures with hybrid seismic isolation systems.

Modelling the criticality of silicon nitride surface imperfections under rolling and sliding contact

Ceramic rolling elements of hybrid bearings may initially include surface imperfections. In order to provide reliable operation of a bearing, the criticality of such imperfections under rolling contact fatigue is examined by defining them as Star features: intersecting semi-elliptical surface cracks. Parametric study is conducted using Finite Element Method and discussed with help of previously published experimental observations. The effects of the Star feature morphology and configuration, contact pressure and crack face friction are investigated in terms of stress intensity factors. Possible crack propagation scenarios are explained in the present study.

Design features of hybrid bearings with adjustable stiffness

The article considers a mathematical model of a combined bearing assembly, operating on the principle of separation of speeds. The features of the influence of the switching mechanism on the dynamic stiffness coefficients of the bearing assembly are established, the effect of the appearance of resonance on transient conditions is revealed, recommendations are made on the detuning of the rotor-support system from the resonance zone.

Lubrication Characteristics of Hybrid Bearing in Sodium-cooled Fast Reactor

Lubrication Characteristics of Hybrid Bearing in Sodium-cooled Fast Reactor