Bearing Clearance Research Articles

Optimization of crankpin bearing lubrication under dynamic loading considering effect of micro asperity contact

Purpose To improve the lubrication and tribology performance (LTP) of the crankpin bearing, this paper aims to propose the optimization of the crankpin bearing parameters considering effect of the high-speed dynamic load and micro asperity contact. Design/methodology/approach A numerical simulation method combined by the slider-crank-mechanism dynamic and lubrication models is applied to solve the dynamic and lubrication equations of crankpin bearing. These equations are then computed via an algorithm program written in Matlab software. The contact force (Wac) in the asperity contact region, friction force (Ff) and friction coefficient (μ) of crankpin bearing are chosen as objective functions. The original parameters and experimental data of the engine are used for the simulation to enhance the reliability of the research results. The parameters are then optimized to obtain the minimum values of Wac, Ff and μ. Findings The research results show that the LTP is significantly improved with optimized parameters. Particularly, the maximum values of Wac and Ff are greatly decreased by 27 and 32%, respectively. Originality/value Reducing the width, radius and surface roughness and increasing the radial clearance of crankpin bearing can improve better the LTP. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0072/

Dynamic characteristics of spindle with water-lubricated hydrostatic bearings for ultra-precision machine tools

A key component of ultra-precision machine tools is the spindle. The motivation for this study was to improve machining accuracies in precision cutting and grinding by pursuing improvements in the spindle characteristics by designing a sophisticated spindle with water-lubricated hydrostatic bearings. The static bearing stiffness of the developed spindle was investigated in previous studies. In addition to the static bearing stiffness, the dynamic characteristics regarding bearing stiffness also affect significantly on the machining results. In this study, dynamic characteristics of the developed spindle with water-lubricated hydrostatic bearings were investigated via simulations and experiments. Not only bearing dynamics but also rotor dynamics were considered in this study.In the simulation studies, the spindle dynamic characteristics were analysed based on the transfer matrix method. A spindle rotor supported with hydrostatic bearings was represented by discrete sections of the rotor. The mathematical model of transverse linear vibrations of the spindle rotor was derived with distributed parameters for these discretized rotor sections. As a result of the analysis on the amplitude-frequency characteristic, radial displacements of the rotor due to bearing displacement and bending deformation were defined. Then, the frequency characteristics were represented with Nyquist plots. Resonant frequencies and amplitudes formation in the transverse vibration of the rotor were determined. The influence of rotor bending deformations on spindle compliance was assessed. Furthermore, the study examined the influences of the supply pressure of the lubricating fluid, radial clearance and journal diameter of the hydrostatic bearings on the amplitude of the rotor vibration, and the resonance frequency of the system.Furthermore, the dynamic characteristics of the spindle were examined experimentally. The simulation results were in good agreement with the actual spindle dynamics obtained experimentally. The influence of the structural parameters of the rotor and the operating parameters of the bearings on the spindle dynamic characteristics was also determined. It was verified that the amplitude of the vibration of the rotor overhang part was dominantly affected not by bearing stiffness but by bending stiffness of the bearing journal of the front bearing and the length of the rotor overhang.Then it was verified that the resultant displacement of the rotor in the radial direction due to the influence of the bearing characteristics and the structural effect of the rotor is significantly small. Practical recommendations to improve the spindle design in terms of the dynamic characteristics of the spindle with water-lubricated hydrostatic bearings were also derived.

Online Bearing Clearance Monitoring Based on an Accurate Vibration Analysis

Accurate diagnosis of incipient faults in wind turbine (WT) assets will provide sufficient lead time to apply an optimal maintenance for the expensive WT assets which often are located in a remote and harsh environment and their maintenance usually needs heavy equipment and highly skilled engineers. This paper presents an online bearing clearance monitoring approach to diagnose the change of bearing clearance, providing an early and interpretable indication of bearing health conditions. A novel dynamic load distribution method is developed to efficiently gain the general characteristics of vibration response of bearings without local defects but with small geometric errors. It shows that the ball pass frequency of outer race (BPFO) is the primary exciting source due to biased load distribution relating to bearing clearance. The geometric errors, including various orders of runouts on different bearing parts, can be the secondary excitation source. Both sources lead to compound modulation responses with very low amplitudes, being more than 20 dB lower than that of a small local defect on raceways and often buried by background noise. Then, Modulation Signal Bispectrum (MSB) is identified to purify the noisy signal and Gini index is introduced to represent the peakness of MSB results, thereby an interpretable indicator bounded between 0 and 1 is established to show bearing clearance status. Datasets from both a dedicated bearing test and a run-to-failure gearbox test are employed to verify the performance and reliability of the proposed approach. Results show that the proposed method is capable to indicate a change of about 20 µm in bearing clearance online, which provides a significantly long lead time compared to the diagnosis method that focuses only on local defects. Therefore, this method provides a big opportunity to implement more cost-effective maintenance works or carry out timely remedial actions to prolong the lifespan of bearings. Obviously, it is applicable to not only WT assets, but also most rotating machines.

Clearance and design optimization of bio-inspired bearings under off-center load

Wear due to over-pressure is a well-known phenomenon that appears on bush bearing under off-center load. In this context, this paper proposes a methodology to develop a new bearing inspired from a lamb elbow. This bio-inspired bearing could replace bush bearing from helicopter's system. The method starts with the analysis of the contact surfaces of the biological joint from 3D scans. That allowed to extract a revolute profile for the bio-inspired bearing. Finite element simulations were then realized to find the best clearance specification to reduce contact pressure. The bio-inspired bearing is after optimized using Design Of Experiments method.

The impact of clearance in roller bearings on the power contact between its elements

The impact of clearance in roller bearings on the power contact between its elements

Dynamic modeling of a planetary gear system with sun gear crack under gravity and carrier-ring clearance

The large load capacity, compact size and high-power density have made planetary gearboxes widely applied in heavy machinery such as wind turbines. Although well designed, planetary gearboxes are vulnerable to fatigue crack because of harsh working environment such as high loads. Fatigue crack may eventually cause failures of planetary gearboxes if not detected early. This study investigates the dynamics of a planetary gear system with a crack in a sun gear tooth. This paper considers the gravity effect, carrier-ring bearings clearance, gyroscopic and centrifugal forces that reported studies have not considered together yet. Simulation results reveal that gravity produces a sinusoidal shift in the dynamic response of a planetary gearbox in the time domain. The carrier-ring bearing clearance causes crack-induced impulses to be more apparent. These results can help researchers develop more effective fault diagnosis strategies especially for early crack in the sun gear.

A radial clearance adjustable bearing reduces the vibration response of the rotor system during acceleration

Abstract A radial clearance adjustable bearing is proposed in this study. The structure and working principles of the adjustable bearing are introduced. This adjustable bearing can change the dynamics characteristics of the bearing by adjusting the radial clearance. In this paper, a simple rotor bearing finite element model is used to study the vibration response of the rotor system. When the rotational speed does not reach the critical speed, reducing the radial clearance can effectively reduce the vibration of the rotor, and the vibration suppression effect can reach 67%. When the rotational speed approaches the critical speed, increasing the radial clearance can significantly reduce the resonance amplitude of the rotor, and the vibration suppression effect reaches about 37%. The amplitude response of the system decreases almost equally in the vertical and horizontal directions. In addition, when the rotational speed increases to twice the critical speed, the oil whip occurs under light load condition, and the oil film instability can be suppressed by increasing the radial clearance. The current study has achieved manual adjustment of the bearing's clearance; furture work includes developing an intelligent controller that enables active adjustment of the clearance.

Recurrence-based diagnostics of rotary systems

Rotary mechanisms are commonly used for transferring rotational movement in diverse industrial applications in mechanical engineering. Components such as gears and rolling bearings have found their purpose in various automotive, machinery or agriculture systems. During operation in mechanisms, they are subjected to defects or changes of their key parameters. This paper considers the application of recurrence plots (RP) and recurrence quantification analysis (RQA) in the detection of teeth crack in a planetary gear system and radial internal clearance (RIC) in a double row self-aligning ball bearing. Raw signals are obtained from accelerometers installed in test rigs. The analysis consists of a statistical analysis approach and calculations of basic RQA parameters i.e. recurrence rate, determinism and length of the longest diagonal. In the paper, we extract information about the fault detection in one of the rotary systems and about bearing operational parameters with nonlinear dynamics identification.

Theoretical Study on the Influence of Planet Gear Rim Thickness and Bearing Clearance on Calculated Bearing Life

Abstract Planetary gearboxes are becoming more popular due to their high-power density and potentially high efficiency. When the planet bearings are internally mounted, the body of the planet gear has to be hollow. The demand for large outer diameters due to high-load requirements might result in a small planet rim thickness. Depending on the rim thickness, its rigidity may become very low. Due to the low stiffness and the special load conditions caused by the double meshing, the deformation of the planet and its bearings are unique. In this paper, the influence of rim thickness on bearing load and lifetime is examined. The analysis is performed with a finite element method (FEM) model of a planet rim with a built-in cylindrical roller bearing. With the resulting planet deformation from the FEM calculation, the load distribution on the rolling elements in the bearing and the bearing lifetime according to ISO/TS 16281:2008 has been evaluated.

Vibration Modelling and Verification for Rotor-Support-Casing Coupling System with Misalignment Fault

Misalignment is one of the common malfunctions that occur in rotating machines. Effects of misalignment on the casing vibration response of a rotor-support-casing (RSC) coupling system is investigated in detail. The model of an RSC coupling system is established using the lumped mass method. The coupling effects between the rotor, support and casing are fully considered. A misalignment model is proposed, and equivalent misalignment force is applied on corresponding lumped mass points. Nonlinear factors of bearing, such as the clearance of bearing, oil film force, nonlinear Hertzian contact force, and the varying compliance vibration are developed. The influences of oil film thickness and bearing size are considered in the nonlinear oil film force model. By using a numerical method, the governing equations of the system are solved to obtain the steady-state vibration. The simulation results from a coupling model are compared with the experimental results and the effectiveness of the new model is verified. It has been found that spectrums and orbit plots are effectively used to reveal the unique nature of misalignment faults, leading to reliable misalignment diagnostic information.

Research procedure of radial clearances in rolling bearings

In the result of the rolling bearing research it has been found that the bearing radial clearance, especially with a small number z of rolling elements z<15 besides technological factors depends on the rolling element location in the bearing during measurement. During operation the simple rolling bearing design is characterized by complex dynamic processes. In theoretical mechanics general technical calculations are carried out for absolutely rigid bodies that are not deformed during the working load application. This position is completely used in design diagrams as the deformations of races and rolling elements are not taken into consideration. If the bearing is manufactured and operated with a nominally reasonable value of the radial clearance, then the probability of its successful operation will be very high. During the bearing manufacturing it’s necessary to take into consideration the radial clearance as a geometric parameter along with other dimensions of the bearing. Analytical expressions for the radial clearance calculation have been obtained for the first time for odd and even layouts of the rolling element location in the bearing operating area. The calculation results for definite bearings are given. The justification of initial clearances and creation of the analytical method for the radial clearance determination represent a crucial task of the rolling bearing theory.

Dynamical Behavior Analysis of Rubbing Rotor System under Asymmetric Oil Film Force

Rubbing is one of the most common and significant faults that exist in the rotor system. It exhibits extremely complicated dynamic behavior. Existing dynamic models are primarily based on the symmetrical rotor structure, in which the oil film forces at both ends of support are considered identical. However, in practice, the oil film force may be differently affected by multiple factors (e.g., viscosity of lubricants, the thickness of oil film, and clearance of journal bearing). In this study, a novel dynamic model of the rubbing rotor system under asymmetric oil film force was developed. Furthermore, based on the nonlinear rotor dynamic theory, its dynamic behavior with different parameters was analyzed, and the corresponding chaotic features were extracted. The results indicated that the evolution law of chaotic motion was more complicated, and the chaotic region of system response was obviously wider under the asymmetric oil film force than the symmetrical oil film force.

Analysis of Random Factors Affecting Measurement Accuracy of Portable Coordinate Measuring Arm

To improve the measurement and calibration accuracy of Portable Coordinate Measuring Arm, it is very important to accurately identify the system and random errors of the measuring machine. From the kinematic error model, system errors can be identified during calibration. But identifying random errors remains a difficult problem. First, we use the SolidWorks software to analyze the structure of each joint. Second, CETOL 6σ tolerance analysis software is used to calculate the random error of the probe generated by the clearance of bearings in each joint. Finally, the random error due to the systematic uncertainty of the rotary encoder is calculated. The experimental results show that the total value of the random error due to the bearing clearance, the systematic uncertainty of the rotary encoder and the thermal expansion of the mechanical structure according to the temperature variation does not exceed 0.1112 mm. This value is theoretically the limit of the single point repeatability accuracy that can be achieved by this measuring machine. The use of the CETOL 6σ not only allows the design to be carried out scientifically, but also reduces production costs.

Suppression of Rubbing in Rotating Machines by Lemon-Type Bearing

Rotor-to-stator or rotor-to-guide rubbing in rotating machines is a serious problem. The contact (rub and impact) between the rotor and the guide creates an excessive vibration which may lead to permanent damage of the mechanical system. In the present work, the rubbing phenomenon between the rotor and the guide is investigated by simulation and experiment. Two different types of clearance bearings are implemented, which are based on circular and lemon-type guides. Rigorous mathematical models for the lemon-type guide as well as for the traditional circular clearance bearing are derived. Then, a Jeffcott rotor model is simulated for the investigation of the rubbing behavior for the two types of bearings. The numerical model is developed in matlab simulink. For different clearances and friction levels between rotor and guide, and several initial conditions, the rubbing phenomena are studied and evaluated. Finally, a comparison between experimental and simulation work is carried out to validate the overall scenarios in this research work. Results indicate that the lemon-type bearing can reduce the likelihood of sustained rubbing, compared with the circular clearance bearing, for the considered test cases.

Effect of clearances in rolling element bearings on their dynamic performance, quality and operating life

The performance of rolling element bearings is one of the machine quality measures in industry. The fatigue life and performance of rolling element bearings depends mainly on the dynamic characteristics of those bearings. This paper studied the effect of the internal radial clearance on the damping characteristics, natural modes of vibration, and fatigue life of rolling element bearings. Vibration modal analysis was performed on rolling bearings of the same size and type to measure their dynamic characteristics. These dynamic characteristics include the natural frequency of the first mode of vibration, damping, and amplitude of frequency response function at resonance. The internal radial clearances of these bearings were measured. A statistical analysis was performed to study the correlation between the internal radial clearance and the dynamic characteristics of rolling bearings. It was found that the damping ratio of the bearing assembly increased by reducing the internal radial clearance of the bearing. Similarly, rolling bearings that have large internal clearances showed short predicted fatigue life. It is concluded that the dynamic characteristics, and consequently the dynamic performance, of rolling bearings are significantly affected by the internal radial clearance.

The Impact of Journal Bearing Wear on an Electric Submersible Pump in Two-Phase and Three-Phase Flow

Electric submersible pumps (ESPs) provide artificial lift within oil wells. ESPs commonly fail from mechanical vibrations that increase as bearing clearances increase from debris, gas, and liquid pumped through the ESP. In order to understand journal bearing wear within an ESP, three stages of a mixed flow electric submersible pump were subjected to hydraulic fracture sand slurry in water. One hundred seventeen hours were conducted with sand and water, followed by 68 h with air added at 15% inlet gas volume fraction. The journal bearings were severely worn by the end of testing, and pump vibrations increased with increased bearing clearances. Bearing vibrations and clearances became significantly larger than the impeller labyrinth seal vibrations and clearances, indicating that the labyrinth seals became the dominant rotor support once the bearings were worn. Adding air increased the wear and rotor vibration orbit variability. Rotor vibration orbits were entirely independent of gas void fraction by the end of testing, indicating that the lubricant composition no longer directly impacted vibrations. Fine axial cracks from heat checking were observed on the journal of the bearings. Results indicate that controlling journal bearing wear is a critical factor for increasing operating lifetimes. Alternative bearing geometry and materials should be investigated to prevent the occurrence of three-body abrasion, limit the resultant wear rate from three-body abrasion, and limit the damage from heat checking.

Analysis of Main Bearings Lubrication Characteristics for Diesel Engine

In order to study the main bearings lubrication characteristics for diesel engine under elastic deformation conditions, an elastic fluid dynamics simulation model of diesel engine main bearing is established. The law of the load, minimum oil film thickness and maximum oil film pressure of the seven main bearing for the diesel engine is studied. The results show that the minimum oil film thickness decreases gradually with increasing of the bearing clearance of the main bearing, but the maximum oil film pressure gradually increasing. The maximum oil film pressure and the minimum oil film thickness of the main bearing appears in the 3# and 5# main bearings.

Development of a new test rig for the analysis of hydrodynamic bearings for rotors of microGT

The aim of the present work is to design a test rig suited to investigate the dynamic interaction between rotor and hydrodynamic journal bearings in micro gas turbines (microGT), i.e. with reference to small bearings (diameter in the order of ten millimeters). Particularly, the device is capable of measuring the journal location. Therefore, the journal motion due to rotor vibrations can be displayed, in order to assess performance as well as stiffness and damping of the bearings. The new test rig is based on Bently Nevada Rotor Kit (RK), but substantial modifications are carried out. Indeed, the relative radial clearance of the original RK bearings is about 2/100, while it is in the order of 1/1000 in industrial bearings. Therefore, the same RK bearings are employed in the new test rig, but a new shaft has been designed in order to reduce the original clearance. The new shaft enables us to study the bearing behaviour for different clearances, as it is equipped with interchangeable journals. The experimental data yielded by the new test rig are compared with numerical results. These are obtained by means of a suitable finite element (FEM) code developed by our research group. It allows the Thermo Elasto-HydroDynamic (TEHD) analysis of the bearing in static and dynamic conditions. In the present paper, bearing static performances are analysed in order to assess the reliability of the journal location predictions by comparing numerical and experimental results. Such comparisons are presented for both large and small clearance bearings of original and modified RK, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance equal to 8/1000). Nevertheless, rotor alignment is quite difficult with small clearance bearings and a completely new test rig is designed for future experiments.

Intelligent software system for replacing a force sensor in the case of clearance measurement

The aim of this work is to develop a method for measuring radial clearance of bearings during the assembly process. A dedicated measuring device was developed. The clearance can now be measured before, during and after the process of mounting bearings. Furthermore, a corresponding intelligent algorithm developed within the frame of this work adapts to different bearing configurations, replaces the metrological identification of the test load. The curve progression of the test load was abstracted by a mechanical model and the characteristic curve correlated with the clearance. The sensor technology originally required could be replaced by an intelligent software system.

Study of Spiral Groove Bearing Effect on a Mechanical Heart Assist Device by using Computational Fluid Dynamic

Background: Mechanical heart assist device is a viable alternative to the escalating problems of worldwide heart failure. For a long-term support, this device must have an excellent compatibility with blood. However, due to complex flow pattern within the hydrodynamic bearing clearance affect severely on both hemolysis and thrombosis. To tackle this problem, spiral groove bearing was imprinted at the rotor of the blood pump. This hydrodynamically bearing suspends the moving impeller within the blood field thus reduces the mechanical contact (shear stress) as it generated localized pressure.