Predictions of friction and flash temperature in marine gears based on a 3D line contact mixed lubrication model considering measured surface roughness

Wear and scuffing failures often occur in marine transmission gears due to high friction and flash temperature at the interface between the meshing-teeth.In this paper,a numerical solution procedure was developed for the predictions of transient friction and flash temperature in the marine timing gears during one meshing circle based on the 3D line contact mixed lubrication simulation,which had been verified by comparing the flash temperature with those from Blok’s theory.The effect of machined surface roughness on the mixed lubrication characteristics is studied.The obtained results for several typical gear pairs indicate that gear pair 4-6 exhibits the largest friction and the highest interfacial temperature increase due to severe rough surface asperity contacts,while the polished gear surfaces yield the smallest friction and the lowest interfacial temperature.In addition,the influences of the operating conditions and the gear design parameters on the friction-temperature behaviors are discussed.It is observed that the conditions of heavy load and low rotational velocity usually lead to significantly increased friction and temperature.In the meantime,by optimizing the gear design parameters,such as the modulus and the pressure angle,the performance of interfacial friction and temperature can be significantly improved.

Parametric analysis of mixed lubrication characteristics in work zone of strip rolling

A theoretical model for mixed lubrication with more accurate contact length has been developed based on the average volume flow model and asperity flattening model,and the lubricant volume flow rate and outlet speed ratio are determined by integrating differential equations based on rolling parameters.The lubrication characteristics at the roll-strip interface with different surface roughness,rolling speed,reduction and lubricant viscosity are analyzed respectively.Additionally,the average volume flow rates of lubricant under different rolling conditions are calculated and used to explain the change rule of lubrication characteristics.The developed scheme is able to determine the total pressure,lubricant pressure,film thickness and real contact area at any point within the work zone.The prediction and analysis of mixed lubrication characteristics at the interface is meaningful to better control the surface quality and optimize the rolling process.

A MIXED LUBRICATION MODEL MODIFIED BY SURFACES' FRACTAL CHARACTERISTICS

Fractal characteristics are introduced into solving lubrication problems. Based on the analysis of the relationship between roughness and engineering surfaces' fractal characteristics and by introducing fractal parameters into the mixed lubrication equation, the relationship between flow factors and fractal dimensions is analyzed. The results show that the pressure flow factors' values increase, while the shear flow factor decreases, with the increasing length to width ratio of a representative asperity γ at the same fractal dimension. It can be also found that these factors experience more irregular and significant variations and show the higher resolution and the local optimal and the worst fractal dimensions, by a fractal dimension D , compared with the oil film thickness to roughness ratio h/R q . As an example of application of the model to solve the lubrication of the piston skirt in an engine, the frictional force and the load capacity of the oil film in a cylinder were analyzed. The results reveal that the oil film frictional force and the load capacity fluctuate with increasing fractal dimension, showing big values at the small D and smaller ones and slightly variable in the range of bigger one, at the same crank angle.

Numerical analysis on mixed lubrication performance of journal-thrust coupled microgroove bearings with different bottom shapes

The purpose of the present study is to establish a mixed lubrication model for the journal-thrust coupled microgroove bearings(also referred as coupled bearings)used for the ship shaftless rim-driven thrusters.During the hydrodynamic modelling,the coupling hydrodynamic pressure between the journal bearing and the thrust bearing is considered.The mixed lubrication performances of the microgroove journal-thrust bearing with five different bottom shapes,including rectangle,semi-ellipse,right triangle,isosceles triangle and left triangle,are compared.Based on the numerical results,the optimal microgroove bottom shape of the journal bearing and tilting angle of the thrust pad are determined.Additionally,the comparative analysis shows that the coupled bearing with left triangle microgroove bottom shape exhibits the optimal mixed lubrication performance.The numerical result also indicates that the optimal inclination angle of the thrust bearing pad is 0.01°for the current simulation case.

Simulation analysis of wear characteristics of connecting rod bearing bush based on improved mixed lubrication model

The failure rate of crankpin bearing bush of diesel engine under complex working conditions such as high temperature,dynamic load and variable speed is high.After serious wear,it is easy to deteriorate the stress state of connecting rod body and connecting rod bolt,resulting in serious accidents such as connecting rod fracture and body damage.Based on the mixed lubrication characteristics of connecting rod big endbearing shell of diesel engine under high explosion pressure impact load,an improved mixed lubrication mechanism model is established,which considers the influence of viscoelastic micro deformation of bearing bush material,integrates the full film lubrication model and dry friction model,couples dynamic equation of connecting rod.Then the actual lubrication state of big end bearing shell is simulated numerically.Further,the correctness of the theoretical research results is verified by fault simulation experiments.The results show that the high-frequency impact signal with fixed angle domain characteristics will be generated after the serious wear of bearing bush and the deterioration of lubrication state.The fault feature capture and alarm can be realized through the condition monitoring system,which can be applied to the fault monitoring of connecting rod bearing bush of diesel engine in the future.

Theoretical analysis based on a modified mixed-film lubrication model for metal forming processes

An analytical model for metal rolling in the mixed lubrication regime was developed based on Wilson and Chang’s asperity flattening model and Von Mises homogenous deformation model. A more rigorous average Reynolds equation was used to calculate the hydrodynamic pressure. The variations of the yield stress with strain were considered in the model. An efficient iteration procedure was developed to solve the contact area, film thickness and hydrodynamic pressure. The model is more practical with fewer assumption and converges quickly. It is applicable to a wider range of rolling regimes. The calculation results using the model agree well with the literature as well as with measured data from a rolling mill.

Design and Engineering Application of Direct Mixing Lubrication System for Emulsion Pipeline in Secondary Cold Rolling Mill

With the benefit fierce competition in the steel industry market in recent years,double cold reduction products have been developed towards strength improvement and thickness reduction.The traditional cold-rolling lubrication process with a fixed flow rate and concentration cannot solve the problems,which are uncontrollable plate shape and the excessive consumption of lubricating oil.Moreover,based on the analysis of the traditional direct aplication lubrication system of double cold reduction mill,a set of design scheme suitable for the emulsion pipeline direct mixing lubrication system of double cold reduction mill unit was proposed.The design completed the selection of key components,which included the static mixer and atomization nozzle selection,pump and oil pump design selection,pipeline design selection,flow type selection,pressure gauge selection,electronic control cabinet design selection and other eight aspects.Equipment of the emulsion pipeline direct mixing lubrication system of double cold reduction has been developed.Comparing with characteristics of the traditional direct aplication lubrication system,the emulsion pipeline direct mixing lubrication system was better applied to the production practice of a 1220 double cold reduction mill.The consumption of ton of steel was reduced by 9.6%.The rolling energy consumption and fuel consumption comprehensive costs decreased by 10.7%,and the strip steel section thickness difference was reduced by 19.3%.In addition,the plate shape quality defect rate decreased by 25.6%,otherwise creating a large economic benefit for the unit and promoting the application value.

基于MixedEHL啮合齿轮润滑特性研究

为了改善和提高齿轮传动系统综合传动性能和疲劳寿命,以某直齿轮传动为研究对象,运用专业齿轮润滑仿真软件MixedEHL建立啮合齿轮混合润滑有限元仿真模型;对啮合齿轮油膜压力、油膜厚度分布、接触齿面平均粗糙度、接触刚度等啮合齿轮接触面的润滑特性进行仿真分析。仿真结果表明:啮合齿轮油膜压力呈现单波峰的形式,油膜厚度呈现双波峰的形式;在不同方向上,油膜压力和油膜厚度不同;接触齿面平均粗糙度较小,接触刚度呈现先增加再基本保持不变最后减小的趋势;该研究为直齿轮传动混合润滑特性、接触特性的改善提供理论依据。

Precision loss of ball screw mechanism under sliding-rolling mixed motion behavior

The sliding-rolling mixed motion behavior degrades the ball screw’s precision at different levels.Based on the sliding-rolling mixed motion between ball and screw/nut raceway,the ball screw’s precision loss considering different given axial loading and rotational speed working conditions was investigated.Since creep and lubrication relate to sliding and rolling motion wear,the creep and lubrication characteristics are analyzed under different working conditions.Besides,the precision loss was calculated considering the sole influence of sliding behavior between ball and screw and compared with the results from other current models.Finally,research on precision loss owing to the sliding-rolling mixed motion behavior was realized under given working conditions,and suitable wear tests were carried out.The analytical results of precision loss are in good agreement with the experimental test conclusions,which is conducive to better predicting the law of precision loss in stable wear period.

Plastic-elastic Model for Water-based Lubrication Considering Surface Force

Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based superlubricity.To enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based lubrication.Considering the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic flow.The results of the two models show good agreement.Plastic deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.

Influence of Oil Film Inertia on Piston Skirt Lubrication in High Speed Engine

By an iteration method, the influence of oil film inertia on piston skirt lubrication in a high speed engine is investigated. By alternately solving the Navier-Stocks equations and the Reynolds equation, the new iteration method can trace the variations of velocity field and pressure field with time. Based on this, the mixed-lubrication model suitable for the piston skirt of high engines is proposed. By introducing the inertia coefficient, the new lubrication model includes the inertia term in oil film. The model can be also used to solve for the lubrication performances of a piston skirt in low or medium speed engines and for lubrication problem in general excluding the inertia term of oil film , when the inertia coefficient is put equal to zero. The calculation results show that the influence of oil film inertia on the friction force increases with the ratio of the piston skirt's length to its diameter, the inertia coefficient and the eccentricities of the lower and the upper piston skirt, with other conditions kept constant, while the influence of it on the load capacity of oil film is small.

Linear polymer aqueous solutions in soft lubrication:From boundary to mixed lubrication

In order to better understand linear polymer aqueous solutions in soft lubrication from boundary to mixed lubrication,poly(ethylene glycol) and sodium hyaluronateare used as model polymers were investigated by using UMT-2 tribometer with the ball-on-disk mode. The relationship between the master Stribeck curves of the polymer aqueous solutions and the influence factors were investigated. Experimental results indicated that soft lubrication is determined by lubricant rheological properties and surface-lubricant interactions, e.g., wetting behavior of polymer aqueous solution on tribological surfaces.

Analysis of the coated and textured ring/liner conjunction based on a thermal mixed lubrication model

For the ring/liner conjunction, well‐designed surface texturing has been regarded as a potential means to improve its tribological performance, as well as the application of coating. However, so far most researchers focused on the one of these aspects. In this study, the combined effect of coating and texturing on the performance of ring/liner conjunction is numerically investigated. A thermal mixed lubrication model is presented. The effects of the coating's thermal and mechanical properties on the tribological performance are studied under the cold and warm engine operating conditions. Along with the increasing coating thickness, the effects of the coating's thermal properties on friction loss are found to be significant, as well as the effects of the coating's mechanical properties. It is also found that a soft coating with a lower thermal inertia has a greater ability to reduce the friction loss of the textured conjunction.

Investigation on Relationship between Lubricating Performance and Stability of Emulsion for Cold Strip Rolling

The influence of the ratio and content of emulsifiers on the stability of anion emulsions for cold strip rolling was investigated in this paper. The present study also investigated the effects of HLB （hydrophile-lipophile balance） value and emulsifier content on the stability of no-ionic emulsions. Based on the effects of different stabilities and different concentrations of emulsions on the adsorptivity and friction coefficients, good lubricating performance was obtained when the amount of the separated oil and soap （SOS） accounted for 2.5%. The wearing scar of the steel balls also indicated the improvements in tribological properties after using the emulsion. Thus, the preparation of emulsion should be regulated according to different rolling conditions.

Simulation of temperature distribution of point contacts in mixed lubrication

The numerical simulation of temperature distribution of point contacts in mixed lubrication is presented. The calculating includes two steps. First, temperature rises on two surfaces are obtained by a temperature integration method of transient point heat source. Second, the partition coefficients of heat flux are determined by matching the temperature of two surfaces. Similar to the calculation of elastic deformation, double linear interpolation function is used to get a better accuracy, and moving grid method is used to increase the efficiency of the computation. Due to the symmetry of influence coefficient matrix in the direction perpendicular to the velocity, storage and computational work are further reduced by 50%. Numerical samples validate the algorithm and program. The calculating results of the cases of smooth surface and isotropic sinusoidal surface are presented.

Wear law in mixed lubrication based on stress-promoted thermal activation

Although several empirical wear formulas have been proposed,theoretical approaches for predicting surface topography evolution during sliding wear are limited.In this study,we propose a novel wear-prediction method,wherein the energy-based Arrhenius equation is combined with a mixed elastohydrodynamic lubrication(EHL)model to predict the point-contact wear process in mixed lubrication.The surface flash temperature and contact pressure are considered in the wear model.Simulation results are compared with the experimental results to verify the theory.The surface topography evolutions are observed during the wear process.The influences of load and speed on wear are investigated.The simulation results based on the Arrhenius equation relationship shows good agreement with the results of experiments as well as the Archard wear formula.However,the Arrhenius equation is more accurate than the Archard wear theory in some aspects,such as under high-temperature conditions.The results indicate that combining the wear formulas with the mixed EHL simulation models is an effective method to study the wear behavior over time.

Design approach for optimization of a piston ring profile considering mixed lubrication

To reduce the friction of a piston ring while maintaining a large oil film load-carrying capacity,an approach comprising of the inverse method and the sequential quadratic programming algorithm was proposed.The approach considers the variation of mixed lubrication and variable lubricant viscosity with temperature along the engine stroke,is developed to optimize the profile of a piston ring.A piston ring profile is represented by a polynomial function.A case study of the second piston ring shows that the proposed method can be applied for the optimization of a piston ring profile.In addition,this paper illustrates the effects of the degree of a polynomial function.The results show that the minimization of friction and maximization of oil film load-carrying capacity can be balanced simultaneously when the degree of the polynomial is 2 and 5.

Contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions

Existing studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions.However,most lubricated transmission components operate in the mixed lubrication region,indicating that both the asperity contact and film lubrication exist on the rubbing surfaces.Herein,a novel method is proposed to evaluate the time-varying contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions.This method is sufficiently robust for addressing any mixed lubrication state regardless of the severity of the asperity contact.Based on this method,the transient mixed contact stiffness and damping of spiral bevel gears are investigated systematically.The results show a significant difference between the transient mixed contact stiffness and damping and the results from Hertz(dry)contact.In addition,the roughness significantly changes the contact stiffness and damping,indicating the importance of film lubrication and asperity contact.The transient mixed contact stiffness and damping change significantly along the meshing path from an engaging-in to an engaging-out point,and both of them are affected by the applied torque and rotational speed.In addition,the middle contact path is recommended because of its comprehensive high stiffness and damping,which maintained the stability of spiral bevel gear transmission.

Iteration framework for solving mixed lubrication computation problems

The general discrete scheme of time-varying Reynolds equation loses the information of the previous step,which makes it unreasonable.A discretization formula of the Reynolds equation,which is based on the Crank-Nicolson method,is proposed considering the physical message of the previous step.Gauss-Seidel relaxation and distribution relaxation are adopted for the linear operators of pressure during the numerical solution procedure.In addition to the convergent criteria of pressure distribution and load,an estimation framework is developed to investigate the relative error of the most important term in the Reynolds equation.Smooth surface with frill contacts and mixed elastohydrodynamic lubrication is tested for validation.The asperity contact and sinusoidal wavy surface are examined by the proposed discrete scheme.Results show the precipitous decline in the boundary of the contact area.The relative error suggests that the pressure distribution is reliable and reflects the accuracy and effectiveness of the developed method.

Molecular dynamics simulation of the Stribeck curve: Boundary lubrication, mixed lubrication, and hydrodynamic lubrication on the atomistic level

Lubricated contact processes are studied using classical molecular dynamics simulations for determining the entire range of the Stribeck curve.Therefore,the lateral movement of two solid bodies at different gap height are studied.In each simulation,a rigid asperity is moved at constant height above a flat iron surface in a lubricating fluid.Both methane and decane are considered as lubricants.The three main lubrication regimes of the Stribeck curve and their transition regions are covered by the study:Boundary lubrication(significant elastic and plastic deformation of the substrate),mixed lubrication(adsorbed fluid layer dominates the process),and hydrodynamic lubrication(shear flow is set up between the surface and the asperity).We find the formation of a tribofilm in which lubricant molecules are immersed into the metal surface—not only in the case of scratching,but also for boundary lubrication and mixed lubrication.The formation of a tribofilm is found to have important consequences for the contact process.Moreover,the two fluids are found to show distinctly different behavior in the three lubrication regimes:For hydrodynamic lubrication(large gap height),decane yields a better tribological performance;for boundary lubrication(small gap height),decane shows a larger friction coefficient than methane,which is due to the different mechanisms observed for the formation of the tribofilm;the mixed lubrication regime can be considered as a transition regime between the two other regimes.Moreover,it is found that the nature of the tribofilm depends on the lubricant:While methane particles substitute substrate atoms sustaining mostly the crystalline structure,the decane molecules distort the substrate surface and an amorphous tribofilm is formed.