Film Stiffness Research Articles

Dynamic characteristics analysis of cylindrical roller bearing considering joint excitations from micro-geometry topography and marco-extended spalling

Abstract Spalling is a type of marco-failure observed in cylindrical roller bearings (CRBs). Traditionally, failure models such as rectangular or polygon shapes have been utilized to characterize the appearance and extension of spalling. However, these models often exhibit inconsistencies with real-world observations due to the simplification of the contact interface between the roller and spalling. This simplification ignores the intricate effects between the micro-geometry topography and the presence of oil film, which significantly influence the contact characteristics and dynamic behaviors of the bearing system. To settle this problem, a new dynamic model of CRB considering coupled excitations from micro-geometry topography and marco-extended spalling is established. Based on the proposed model, the investigation delves into the effects of the micro-geometry topography and marco-extended spalling on contact characteristics and dynamic behaviors. Results indicate that as the ring roughness intensifies, the oil film stiffness and damping exhibit a increasing trend. During the extension of the spalling, the micro-geometry topography of the ring introduces additional oscillations in the waveforms of acceleration, contact force, and friction force. Notably, sideband modulation and high-frequency oscillation phenomena emerges in the acceleration patterns, aligning well with the experimental results. One of the primary factors contributing to the dynamic responses of the bearing is the time-varying contact force stemming from the combination of the micro-geometry topography and marco-extended spalling.

An axial elastic deformation of ceramets on elastohydrodynamic lubrication of wavy-tilt-dam mechanical face seals

PurposeThis paper aims to investigate the lubrication characteristics of siliconized graphite with a wavy-tilt-dam (WTD) pattern applied to the hydrodynamic face seals.Design/methodology/approachIt focuses on two friction pairs, carbon graphite versus tungsten carbide (CG-TC) and siliconized graphite versus siliconized graphite (SG-SG), through a three-dimensional elastic hydrodynamic lubrication numerical model that integrates finite difference method and finite element method. The consequence of axial elastic deformation of sealing pair materials on film thickness, film pressure, cavitation and sealing performance for a WTD mechanical face seal under full working conditions of ΔP = 0.8, 5.3 and 15.8 MPa are analyzed theoretically.FindingsThe nuclear hydrodynamic WTD face seal generates a convergent gap and exhibits a dual-characteristic behavior of hydrodynamic and hydrostatic effects under various ΔP. Compared to the CG-TC, the SG-SG shows a lower minimum film thickness, decreasing by 3.9%, 17.3% and 35.1%. The flow leakage rate decreases by 47.8%, 52.1% and 75.4%. In addition, the film stiffness increases by 46.8%, 49.8% and 97.8%. Thus, the SG-SG better deals with the dynamic tracking problem, and the sealing performance is stable. The strength and hardness of siliconized graphite enhance WTD sealing performance and improve cavitation control in high-pressure applications.Originality/valueThe lubrication characteristics of the siliconized graphite with a WTD pattern could inform the future design of hydrodynamic shallow groove wavy seals in boiler feedwater engineering implements under high-pressure conditions for the nuclear power industry.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2024-0382/

Study on partial ER fluid hybrid two-lobe hole-entry journal bearing with genetic algorithm for bionic surface

This work focuses on ER (Electrorheological) fluid-based hybrid hole-entry journal bearings, which studies the effect of ER fluid with partial electric field on the tribological nature of two-lobe bearings with bionic textured surfaces. The design of bionic textures, by virtue of their capacity to influence fluid flow, load capacity, and friction reduction for the enhancement of bearing performance, has been analytically investigated. The integration of ER fluid subjected to partial electric field along with bionic textured surfaces displays an optimistic improvement in performance metrics of bearings, which clearly manifests through preliminary results. Notably, the optimization of bionic textures through genetic algorithms resulted in a 13.04% reduction in friction coefficient and a significant increase in load capacity. The combination of partial ER fluid lubrication and bionic textures also improved fluid film stiffness by up to 66.11%, further enhancing stability and overall bearing efficiency. The obtained results are expected to further enhance design and development activities of high-performance hybrid journal bearings for numerous industrial applications.

Dynamic characteristics of hydrostatic thrust bearing with tilting oil pad under eccentric load

Abstract During the processing of heavy machine tools, due to the effect of eccentric load, the oil film thickness changes, which directly affects the lubrication performance of the bearing. Therefore, this study takes the tiltable double rectangular oil pad hydrostatic thrust bearing as the research object and explores its dynamic characteristics. The study involves the analysis of oil film displacement response under eccentric loading conditions at different offset distances, loads and sudden loads. Through analysis, the oil film damping coefficient and oil film dynamic stiffness of each oil cavity can be determined under different offset distances and loads. The research results show that the change of oil film thickness has a significant effect on the oil film stiffness. As the oil film thickness increases, the stiffness decreases, the ability to resist deformation becomes weaker, and the displacement response time becomes longer. Moreover, the dynamic stiffness is affected by the offset distance and the loading frequency. When the offset distance is 200 mm, the load is 24 tons, and the loading frequency is 50 rad/s, the oil film stiffness of the oil cavity 1 reaches 180×108 N/m. It is worth noting that the increase in dynamic stiffness of the sinking side is significantly greater than that of the floating side. Ultimately, this study provides a theoretical reference for evaluating the stability of hydrostatic thrust bearing systems under eccentric loads.

Investigation on the influence of rotational speed on oil film stability of hydrostatic rotary table

PurposeThe purpose of this study is to investigate the influence of rotational speed on the oil film stability of the hydrostatic rotary table having double rectangular oil pads. The oil film stability is evaluated based on the oil film stiffness under constant load condition and the displacement response amplitude of the oil film under disturbance load condition.Design/methodology/approachThe oil film stability theoretical equations of the double rectangular oil cavity are deduced such as oil film stiffness, damping and dynamic equations. A simulation model is developed to analyze the relationship among oil film temperature, oil film pressure fields and oil film stability. The user-defined function programs are used to control the rotational speed, lubricant viscosity and oil film thickness during the simulation. In addition, an experimental rig is built to test the simulation results.FindingsThis study shows that oil film stability decreases with increasing rotational speed under constant load and disturbance load. The trend of oil film stability decreased slowly within 30 r/min, and then rapidly. However, since the hydrodynamic pressure effect, the decrease rate of stability is mitigated under constant load and high rotational speeds.Originality/valueThe conclusions can provide a theoretical basis for improving the oil film stability of machines with similar hydrostatic support structure.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2024-0267/

Flow Characteristics and Experimental Verification of T-Groove Dry Gas Seal Under Different Flow States

With the improvement of dry gas seal efficiency in high-parameter fields, the flow pattern of gas film lubrication is complicated. Based on gas lubrication theory, the Reynolds equation of compressible gas was established with a bidirectional T-groove dry gas seal as the research object. The Reynolds equation was solved to obtain a modified turbulent film pressure distribution law that affects gas lubrication. The effectiveness of the calculation program was verified by experimental tests. The results show that with an increase in operating parameters, the turbulence effect caused the gas film pressure fluctuation in the T-groove region to intensify, resulting in gas film flow instability. In addition, the inertia effect improved, which slowed down the leakage and affected the change law of stiffness and the rigid leakage ratio. When the fluid speed and gas pressure were low, the inertia effect could be ignored. When the groove depth was increased to 8 μm, the height difference between the trough and non-T-groove region became larger due to the combination of the turbulence and inertia effects. Further, when the gas film thickness was 3 μm, the opening force and gas film stiffness were high due to the dynamic pressure effect in the small film thickness groove. An increase in the gas film thickness weakened the turbulence effect and reduced the gas film pressure fluctuation.

The effect of surface profile and groove bottom profile on steady-state performance of dry gas seals

PurposeThe purpose of this paper is to improve the film stiffness of a dry gas seal (DGS) through the proper design of 3D macroscopic surface structures based on numerical study.Design/methodology/approachA novel generalized three-dimensional (3D) geometric model is proposed to characterize macroscopic surface structures of a DGS, including grooves, waviness, radial taper and step. The mathematical model is established to simulate film pressure distribution. The effect of the surface profile and groove bottom profile on the steady-state performance of DGSs at different working conditions is investigated.FindingsThe unidirectional groove surface has the largest film stiffness at different speed conditions and the largest opening force at medium and high speed, whereas the annular groove has the largest opening force at static pressure. For obtaining the maximum film stiffness, unidirectional combined variable depth groove surface when ns = 0.4 and k = 0.5 outperforms the other unidirectional groove surfaces, whereas circumferential waviness when ns = 1 and k = 1 is the best choice among annular groove surfaces.Originality/valueThis study proposes a novel generalized 3D geometric model to characterize macroscopic surface structures of a DGS. The optimal groove bottom profile for different surface profiles of DGS is presented.

Influence of the Purification Degree of Cellulose from Posidonia oceanica on the Properties of Cellulose-PLA Composites

PLA biocomposites, incorporating 5% wt. of lignocellulosic fibres (LF) from Posidonia oceanica waste with different degrees of cellulose purification, were obtained by melt blending and compression moulding. The LF were obtained after removing part of the non-cellulosic components by subcritical water extraction at 150 and 170 °C and after bleaching the extracted residues with hydrogen peroxide or sodium chlorite. The non-bleached LF provided the composites with a brown colour and opacity, while the bleached LF impacted the optical properties of composites to a lower extent, depending on their whiteness. The LF composition had a noticeable effect on the composites’ mechanical and barrier properties. All LF reduced the water vapour barrier capacity while promoting the oxygen barrier of the films. Bleached LF enhanced the film stiffness and reduced extensibility and resistance to break, whereas non-bleached LF had lower impacts on the tensile parameters. Considering the mechanical and barrier performance of the composites, the fibres obtained at 170 °C and bleached with sodium chlorite exhibited the best behaviour. Nevertheless, if transparency and colour are not limiting for the use of the films, untreated LF allowed for good preservation of the water vapour permeability of PLA films and enhanced the oxygen barrier capacity, with a similar mechanical response as the other non-bleached fractions.

Modeling of Multibody Lubrication Dynamics in Cylindrical Roller Bearings

As a typical multibody system, rolling bearing consists of several lubricated frictional pairs that transmit motions and forces among components. In this paper, a multibody lubrication dynamics (MLD) model of cylindrical roller bearings (CRBs) is developed by coupling the bearings dynamics submodel and several lubrication submodels of each frictional pairs in real-time. The lubrication submodels are discretized by using finite difference and solved by numerical iteration methods of Gauss-Seidel with line relaxation and discrete convolution-fast Fourier transform (DC-FFT) technique. Additionally, a parallel algorithm is also designed to enhance the calculation efficiency. Its results are validated by the experimental results in literature and further compared by the results from other dynamics models. It revealed that the film formation alters not only friction but also geometrical constraints and pressure distribution, which may introduce additional load inside bearing and increase rolling friction under high-speed conditions. As the dynamic oil film stiffness and damper are took into account by MLD, the cage has a lower whirl frequency and forces. The curve-fitting formulas of elastohydrodynamic lubrication (EHL) film thickness are overestimates of the thickness value and, thus, change the load distribution and friction between roller and raceway.

Dynamic Modeling of Angular Contact Ball Bearing with Local Defects under EHL Considering Impact Force

In order to analyze the operating status of angular contact ball bearings(ACBBs) with local defects in more detail, a dynamic model of ACBB with local defects considering impact force under elastohydrodynamic lubrication conditions is proposed. Firstly, an elastohydrodynamic lubrication model for defective bearings considering spin is established, the film thickness and film stiffness of the defective bearings are calculated, and then time-varying displacement excitation model and time-varying stiffness model for local defects in angular contact ball bearings is presented. Based on this, an instantaneous impact force function related to defect size and bearing speed is established. Secondly, based on Hertz contact theory and impact force function, a dynamic calculation method for ACBBs with local defects on the outer ring is proposed. Finally, the vibration characteristics of ball bearings with faults are investigated, and the influence of different parameters on the dynamic response of the bearings is analyzed. The calculation results show that under lubrication conditions, the impact force on the vibration of the bearing is significantly weakened. With the increase of defect size and load, the frequency of bearing fault characteristics remain unchanged, but its amplitude increases. As the bearing speed increases, the characteristic frequency and amplitude of bearing faults increase.

Fuzzy PID Composite Control of Hydrostatic Center Frame

To control the oil film stiffness of a hydrostatic center frame precisely, an electrohydraulic servo oil film thickness control system was designed. It employs multiple groups of controllable oil cavities to regulate and control the oil film thickness. A mathematical model of the control system was established, and system model identification and verification were performed. A two-stage self-correcting fuzzy proportional-integral-derivative (PID) control strategy was devised and used in the model obtained by identification. An online fuzzy inference algorithm was designed for real-time online adjustment of the fuzzy control rules. Finally, a MATLAB simulation model was established. Compared with conventional fuzzy PID control, two-stage self-correcting fuzzy PID composite control has faster dynamic response characteristics, smaller overshooting, and higher steady-state accuracy. It significantly improves the synchronous control of the film thickness in the oil film control process.

TVMS calculation model for gear tooth tip chipping failure with EHL

TVMS calculation model for gear tooth tip chipping failure with EHL

The thermal-mechanical deformations of CO2 mixture gases dry gas seal based on two-way thermal-fluid-solid coupling model

PurposeThis study aims to investigate the influence mechanism of thermal-mechanical deformations on the CO2 mixture gases dry gas seal (DGS) flow field and compare the deformation characteristics and sealing performance between two-way and one-way thermal-fluid-solid coupling models.Design/methodology/approachThe authors established a two-way thermal-fluid-solid coupling model by using gas film thickness as the transfer parameter between the fluid and solid domain, and the model was solved using the finite difference method and finite element method. The thermal-mechanical deformations of the sealing rings, the influence of face deformation on the flow field and sealing performance were obtained.FindingsThermal-mechanical deformations cause a convergent gap between the two sealing end faces, resulting in an increase in the gas film thickness, but a decrease in the gas film temperature and sealing ring temperature. The axial relative deformations of rotating and stationary ring end faces caused by mechanical and thermal loads in the two-way coupling model are less than those in the one-way coupling (OWC) model, and the gas film thickness and leakage rate are larger than those in the OWC model, whereas the gas film stiffness is the opposite.Originality/valueThis paper provides a theoretical support and reference for the operational stability and structural optimization design of CO2 mixture gases DGS under high-pressure and high-speed operation conditions.

Lubrication Characteristics of Dry-Gas Seals with Spiral Grooves

To obtain an optimal range of structural parameters for dry-gas seals with good performance, this study employed advanced sensing technology to monitor and analyze the internal flow characteristics of dry-gas seals in real time. Additionally, the validity of the calculation program was verified through experimentation. Using steady-state performance parameters as evaluation indices, a calculation model with lubrication characteristics was developed. The results indicate that when there are 12 grooves, the gas film pressure distribution is uniform and has a high value. At pressures greater than 2 MPa, the opening force, leakage, and gas film stiffness change significantly due to enhanced dynamic pressure effects with high-pressure differences, which reduces the local contact forces and frictional forces. At a constant speed, decreasing the gas film thickness increases the pressure difference while increasing both the opening force and film stiffness; however, at higher rotational speeds where the gas flow becomes non-uniform, the stability of the gas film is affected, leading to increased frictional forces. When there are between 10 and 16 grooves with depths ranging from 5.0 to 6.0 μm, dynamic pressure effects caused by pressure gradients become apparent, resulting in good dry-gas sealing performance being achieved. This research provides a theoretical reference for optimizing the design of dry-gas seals, as well as their steady-state seal performance.

Nonlinear dynamic characteristics analysis method of planetary gear train torsional vibration considering meshing oil film force

Planetary gear train is an important part of automatic transmission. The oil film between teeth is one of the key factors affecting the torsional vibration of planetary gear train. Selecting the appropriate oil film stiffness is of great significance for analyzing the nonlinear dynamic characteristics of planetary gear train. A method for analyzing the nonlinear dynamic characteristics of planetary gear system torsional vibration considering the oil film force between teeth is proposed in this paper. A 3-DOF torsional vibration model of planetary gear train considering oil film is established. In this model, the oil film between teeth is equivalent to a time-varying nonlinear spring-damper element, and nonlinear factors such as backlash and meshing error are also considered. The effects of meshing oil film thickness on oil film stiffness and damping are analyzed, and the torsional vibration characteristics of planetary gear train under different meshing stiffness, meshing damping ratio, and rotational speed are analyzed based on bifurcation diagrams. The results show that in one meshing cycle, the meshing oil film thickness first becomes larger and then becomes smaller. When the meshing oil film thickness increases, the meshing oil film stiffness and the equivalent meshing oil film damping become smaller. The torsional vibration of planetary gear train can be effectively reduced by increasing meshing stiffness, damping ratio, rotational speed within a certain range. This method provides technical support for reducing torsional vibration of planetary gear train and realizing stable transmission of planetary gear train.

Optimization of twin grooved two-lobe textured hydrodynamic journal bearing design by using genetic algorithm

Surface texture plays a role in enhancing the performance of hydrodynamic journal bearings by reducing friction coefficients and increasing load-carrying capacity. However, its impact on the dynamic performance of the bearings remains largely unexplored. This study aims to fill this gap by investigating the optimized surface texture of twin-grooved two-lobe hydrodynamic journal bearings using genetic algorithms. Through the optimization of surface texture, significant enhancements in the dynamic performance of the bearings, including improvements in fluid film damping, stiffness, and omega threshold speed, are achieved. Utilizing GA optimization, textured bearings demonstrate a remarkable enhancement in dynamic performance, with an impressive increase of 195.55% in omega threshold speed. These findings provide valuable insights for enhancing bearing designs and stability, thereby contributing to advancements in tribological engineering.

Effect of oil film stiffness on vibration of full ceramic ball bearing under grease lubrication

PurposeThis paper aims to understand the vibration characteristics of full ceramic ball bearings under grease lubrication, reduce the vibration of the bearings and improve their service life.Design/methodology/approachThe Hertz contact stiffness formula for full ceramic ball bearings is constructed; the equivalent comprehensive stiffness calculation model and vibration model of full ceramic ball bearings are established. The dynamic characteristic test of full ceramic ball bearing under grease lubrication was carried out by using the bearing life testing machine, and its vibration was measured, and its vibration acceleration root-mean-square was obtained by software calculation and compared with the simulation results.FindingsAt the rotational speed of 12,000 r/min, the root-mean-square value of vibration acceleration is maximum 10.82 m/s2, and the error is also maximum 7.49%. As the rotational speed increases, the oil film stiffness decreases. In the radial load of 600 N, the vibration acceleration root-mean-square is minimum 6.40 m/s2, but its error is maximum 6.56%. As the radial load increases, the vibration of the bearing decreases and then increases, so under certain conditions increasing the radial load can reduce the bearing vibration. With different types of grease, the best preload is also different; low-speed heavy load should be used when the viscosity of the grease is large, and high-speed light load should be used when the choice of smaller viscosity grease is made.Originality/valueIt provides a theoretical basis for the application of full ceramic ball bearings under grease lubrication, which is of great significance for reducing the vibration of bearings as well as enhancing the service life of bearings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0094/

Influence of 3D surface irregularities on the performance of hydrostatic rectangular tilted thrust pad bearing configurations

Tribological behavior of tribo-pairs is strongly dependent on the surface topography. Further, the structural deformation, manufacturing, and assembly errors cause the hydrostatic thrust pad bearings to tilt slightly. The work in this article is aimed to study the effect of tilt and three-dimensional (3D) surface irregularities on the performance of hydrostatic rectangular thrust pad bearings (HRTPB) compensated with capillary restrictors. The 3D surface irregularities are assumed to follow cosine curve. To perform the analysis, a source code has been developed in MATLAB and the Finite Element Method has been used to solve the governing Reynold's equation. The numerical simulation results indicate that the effect of tilt reduces the value of fluid film reaction, fluid film stiffness, and fluid film damping coefficients. The study reveals that 3D surface irregularities results in a higher value of fluid film stiffness and damping coefficient as compared to that of smooth-bearing surfaces.

Effect of Chain Orientation on Coupling of Optical and Mechanical Anisotropies of Polymer Films

Polymer films have broad applications in different industries with specific requirements for their optical and mechanical properties. In mass production, processing conditions during film formation that apply forces and motions in various directions to the film tend to manifest preferred molecular chain orientation in the film microstructure, which unavoidably produces optical and mechanical anisotropies. In this paper, we investigate the effect of such macromolecular orientations on the optical and mechanical anisotropies of several polymer films, including polystyrene, poly(methyl methacrylate), poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ether ether ketone), poly(ether sulfones), poly(ethylene chlorotrifluoroethylene), poly(phenylsulfone), and polycarbonate, at temperatures well below their respective glass transitions (Tg). The film mechanical responses, including elasticity, yielding, and post-yield behaviors, were obtained for the in- and out-of-plane directions utilizing tensile and nanoindentation testing methods, respectively. In addition, the net chain orientation within the films was evaluated by birefringence through analyzing the film optical refractive indices, which were verified and complemented by wide-angle X-ray scattering (WAXS) measurements. The results reveal a considerable quantitative correlation between the birefringence and the degree of elastic anisotropy and a qualitative correlation between the chain orientation and the film post-yield tensile instability (necking). These observations corroborate the interrelationship between the microstructure of polymer films and their optical and mechanical properties. In addition, they emphasize that process conditions can be selected to tune the optical and mechanical anisotropies to best serve the material performance in specific devices. We also propose an empirical equation to approximate the out-of-plane film stiffness based upon the optical and in-plane mechanical properties.

Influence of Natural Gas Composition and Operating Conditions on the Steady-State Performance of Dry Gas Seals for Pipeline Compressors

A dry gas seal (DGS) is one of the key basic components of natural gas transmission pipeline compressors, and the sealing performance of a DGS dealing with complex multi-component pipeline natural gas is different from that dealing with conventional nitrogen medium. In this paper, a spiral groove DGS of the compressor in natural gas transmission pipeline systems is taken as the research object. The thermal hydrodynamic lubrication model of the DGS is established considering turbulence effect and choking effect. Based on the finite difference method, the temperature and pressure distributions and the steady-state performance of the DGS are obtained by simulating. The influence of unitary impurity compositions such as light hydrocarbon, heavy hydrocarbon, non-hydrocarbon, and their contents on the steady-state performance of the DGS is analyzed. The steady-state performance of the DGS dealing with multi-impurity natural gas such as in the West-East gas transmission is investigated under different operating conditions. The results show that turbulence had a significant effect on the DGS, while choking had a weak effect. Increasing the content of light hydrocarbon such as C2H6 and heavy hydrocarbon such as C5H10 resulted in an increase in the gas film stiffness, leakage rate, and the temperature difference between the inlet and outlet, while non-hydrocarbon, such as N2, reduced the temperature difference between the inlet and outlet. The greatest impact on seal performance was produced by the heavy hydrocarbon, followed by the light hydrocarbon, and the least was produced by the non-hydrocarbon.