Increasing environmental concerns about limiting harmful emissions has necessitated sulfur-and phosphorus-free green lubricant additives.Although boron-containing compounds have been widely investigated as green lubri...Increasing environmental concerns about limiting harmful emissions has necessitated sulfur-and phosphorus-free green lubricant additives.Although boron-containing compounds have been widely investigated as green lubricant additives,their macromolecular analogs have been rarely considered yet to develop environmentally friendly lubricant additives.In this work,a series of boron-containing copolymers have been synthesized by free-radical copolymerization of stearyl methacrylate and isopropenyl boronic acid pinacol ester with different feeding ratios(S_(n)-r-B_(m),n=1,m=1/3,1,2,3,5,9).The resulting copolymers of S_(n)-r-B_(m)(n=1,m=1/3,1,2,3,5)are readily dispersed in the PAO-10 base oil and form micelle-like aggregates with hydrodynamic diameters ranging from 9.7 to 52 nm.SRV-IV oscillating reciprocating tribological tests on ball-on-flat steel pairs show that compared with the base oil of PAO-10,the friction coefficients and wear volumes of the base oil solutions of S_(n)-r-B_(m)decrease considerably up to 62%and 97%,respectively.Moreover,the base oil solution of S_(1)-r-B_(1)exhibits an excellent load-bearing capacity of(850±100)N.These superior lubricating properties are due to the formation of protective tribofilms comprising S_(n)-r-B_(m),boron oxide,and iron oxide compounds on the lubricated steel surface.Therefore,the boron-containing copolymers can be regarded as a novel class of environmentally friendly lubricating oil macroadditives for efficient friction and wear reduction without sulfur and phosphorus elements.展开更多
Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials....Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials. Iron-based samples were prepared by die wall lubricated warm compaction at 135 ℃ and 175 ℃, using polytetrafluoroethylene (PTFE) emulsion as die wall lubricant. A compacting pressure of 700 MPa and 550 MPa were used. The admixed lubricant concentration ranging from 0 to 0.6 wt.% was used in this study. Compared with non-die wall lubricated samples, the die wall lubricated samples have higher green densities. Results show that in addition to the decrease in ejection forces, green density of the compacts increased linearly with the decrease in admixed lubricant content. Mechanical property of the sintered compacts increase sharply when the admixed lubricant concentration reduced to 0.125 wt.% or less. Ejection force data indicated that samples with die wall lubrication show lower ejection forces when compared with samples without die wall lubrication. No scoring was observed in all experiments even for samples contain no admixed lubricant. Our results indicated that under experimental condition used in this study, no matter at which compaction pressure, compaction temperature, graphite and lubricant contents in the powder the die wall lubricated warm compaction would give the highest green density and lowest ejection force. It can be concluded that combination of die wall lubrication and warm compaction can provide P/M products with higher density and better quality. It is a feasible way to produce high performance P/M parts if suitable die wall lubrication system was applied.展开更多
Nano-copper used as lubrication oil additive has good tribological property and active self-repairing effect for friction pairs. The reduction in liquid phase for preparing nano-additive is one of the most common meth...Nano-copper used as lubrication oil additive has good tribological property and active self-repairing effect for friction pairs. The reduction in liquid phase for preparing nano-additive is one of the most common method. Nano-copper was prepared by reduction in liquid phase. The different project and routine practice for preparing nano-copper were researched. The dispersion problem of nano-copper was investigated by surface treatment and high dispersion. The particles dimension, the dispersion stability and the purity of nano-copper were characterized by TEM and XRD. The conclusion indicates that the methods of the preparation and dispersion can obtain 20nm copper additive with good dispersion property in lubrication oil.展开更多
Considering the effect of viscosity-temperature relationship and cavitation of micro-scale film,the influencing factors on hydrodynamic lubrication performance of upstream pumping mechanical seal were investigated bas...Considering the effect of viscosity-temperature relationship and cavitation of micro-scale film,the influencing factors on hydrodynamic lubrication performance of upstream pumping mechanical seal were investigated based on the theory of hydrodynamic lubrication.N-S equation,energy equation,viscosity-temperature equation and vapor transport equation were solved with the finite volume method by using Fluent software,which was performed to analyze the influence of the viscosity-temperature and cavitation effect on hydrodynamic lubrication failure of the film.The research demonstrates that it will lead to the significant difference of the temperature field by considering the coupling of temperature and viscosity.When the film thickness decreases and the rotating speed rises,cavitation regions and viscous friction heat increases,the opening force of the film is also enhanced.However,the growth rate is restricted to the cavitation regions and viscous friction heat,and the opening force begins to decline to a certain extent,and thereby being insufficient to open the surfaces of the seals and leading to the failure of automatic adjustment function and severe wear,lubrication failure occurrs.Through comprehensive research on the influences of viscosity-temperature and cavitation effect on hydrodynamic lubrication performance,the theories of failure and design of upstream pumping mechanical seal are further developed.展开更多
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 ...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.展开更多
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 r...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.展开更多
The thermal elasto-hydrodynamic lubrication characteristics of the internal meshing gears in a planetary gear train under vibrations were examined considering the influence of the modification coefficient and time-var...The thermal elasto-hydrodynamic lubrication characteristics of the internal meshing gears in a planetary gear train under vibrations were examined considering the influence of the modification coefficient and time-varying meshing stiffness.Based on dynamic theory of the gear system,a dynamic model of the planetary gear train was established.The lubrication performances of modified gear systems under vibrations and static loads were analyzed.Compared with other transmission types,the best lubrication effect could be produced by the positive transmission.A thicker lubricating oil film could be formed,and the friction coefficient and oil film flash temperature are the smallest.Increasing modification coefficient improves the lubrication performance continuously but intensifies the engage-in and tooth-change impact.For the planetary and inner gears,the increase in the modification coefficient also leads a decrease in the oil film stiffness.展开更多
In order to analyze the lubricating characteristics at different meshing points in the cycloid pin wheel transmission process,the cycloid gear teeth were discretized,combined with the kinematic analysis of the cycloid...In order to analyze the lubricating characteristics at different meshing points in the cycloid pin wheel transmission process,the cycloid gear teeth were discretized,combined with the kinematic analysis of the cycloid pin gear transmission and the contact analysis of the gear teeth.The progressive mesh densification method(PMD)was used to numerically solve the film thickness.The influence of the design parameters and process parameters on the lubrication characteristics was analyzed.The elastohydrodynamic lubrication and mixed lubrication characteristics at different contact points were obtained.The optimal meshing area of the cycloid gear tooth was determined,and the film thickness ratio,contact load ratio,maximum contact pressure at different points,average film thickness and roughness after contact deformation were analyzed.The conclusion of this study provides effective guidance for the research on the modification of cycloid gear teeth.展开更多
External return mechanism is a mechanical structure applied to axial piston pumps.To study its lubrication characteristics,the Reynolds equation applied to an external return spherical hinge pair was deduced based on ...External return mechanism is a mechanical structure applied to axial piston pumps.To study its lubrication characteristics,the Reynolds equation applied to an external return spherical hinge pair was deduced based on the vector equation of relative-motion velocity of the external return spherical hinge pair under the influence of external swash plate inclination and offset distance.The results show that the total friction,axial leakage flow,and maximum value of the maximum oil-film pressure increase with increasing pump-shaft speed and decrease with increasing offset distance in one working cycle when the external-swash-plate inclination is constant.However,the varying offset distance has little effect on the axial leakage flow.The maximum value of the maximum oil-film pressure decreases with increasing external-swash-plate inclination and the total leakage flow increases with increasing external-swash-plate inclination in one working cycle when the offset distance is constant.It can be seen that the abovementioned parameters are important factors that affect the lubrication characteristics of external return spherical hinge pairs.Therefore,the complex effects of different coupling parameters should be comprehensively considered in the design of the external return mechanism.展开更多
In the present study,the effect of reduction of cutting fluid consumption on the surface quality and tool wear was studied.Mathematical models were developed to predict the surface roughness using response surface met...In the present study,the effect of reduction of cutting fluid consumption on the surface quality and tool wear was studied.Mathematical models were developed to predict the surface roughness using response surface methodology(RSM).Analysis of variance(ANOVA)was used to investigate the significance of the developed regression models.The results showed that the coefficient of determination values(R^2)for the developed models was 97.46%for dry,89.32%for flood mode(FM),and 99.44%for MQL,showing the high accuracy of fitted models.Also,under the minimum quantity lubrication(MQL)condition,the surface roughness improved by 23%−44%and 19%−41%compared with dry and FM,respectively,and the SEM images of machined surface proved the statement.The prepared SEM images of tool rake face also showed a considerable decrease in adhesion wear.Built-up edge and built-up layer were the two main products of the adhesion wear,and energy-dispersive X-ray spectroscopy(EDX)analysis of specific points on the tool faces helped to discover the chemical compositions of adhered materials.By changing dry and FM to MQL mode,dominant mechanism of tool wear in machining aluminum alloy was significantly decreased.Breakage wear that led to early failure of cutting edge was also controlled by MQL technique.展开更多
The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated,including the influence of the modification coefficient and vibrations.Based on the dynamic t...The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated,including the influence of the modification coefficient and vibrations.Based on the dynamic theory of gear systems,a six-degree-of-freedom tribo-dynamics model was established.Thermal elastohydrodynamic lubrication characteristics of a modified gear system under vibrations and a static load were analyzed.The results showed that the positive transmission gear system exhibited the better lubrication effect compared with other transmission types.A thick lubricating oil film could be formed,and the friction coefficient between the teeth and the oil film flash temperature were the smallest.As the modification coefficient increased,the lubrication condition was continuously improved,and the scuffing load capacity was enhanced.The increment of the modification coefficient increased the meshing stiffness of the gear system but reduced the stiffness of the oil film.展开更多
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 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.展开更多
Based on the theory of unsteady hydrodynamic lubrication and relevant mathematic and physical methods, a basic model was developed to analyze the unsteady lubrication film thickness, pressure stress and friction stres...Based on the theory of unsteady hydrodynamic lubrication and relevant mathematic and physical methods, a basic model was developed to analyze the unsteady lubrication film thickness, pressure stress and friction stress in the work zone in strip rolling. The distribution of pressure stress and friction stress in the work zone was obtained. A numerical simulation was made on a 1850 cold rolling mill. The influence of back tension stress and reduction on the distribution of pressure stress and friction stress between the roll gaps was qualitatively analyzed by numerical simulation. The calculated results indicate that the higher the back tension, the lower the pressure stress and the friction stress in the work zone, and the largest friction stresses are obtained at the inlet and outlet edges. The pressure and friction gradients are rather small at high back tension. The pressure-sensitive lubricant viscosity increases exponentially with the increase of pressure. The unsteady lubrication phenomenon in the roll bite is successfully demonstrated.展开更多
Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly...Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.展开更多
Due to the biological risks of using the conventional lubricants,the vegetable oils have been considered nowadays.Besides,to improve the tribological properties of the vegetable oils in various applications like metal...Due to the biological risks of using the conventional lubricants,the vegetable oils have been considered nowadays.Besides,to improve the tribological properties of the vegetable oils in various applications like metal forming processes,nanoparticles have been used as additives.This research evaluated the lubrication performance of the Al2O3 and TiO2 nanoparticles dispersed in rapeseed oil during the parallel tubular channel angular pressing (PTCAP) process.The experimental PTCAP tests have been fulfilled under three lubrication conditions and the comparison between the PTCAP processed tubes has been performed in terms of the maximum forming force,surface roughness,and microhardness.The experimental results indicate that adding the mentioned nanoparticles has caused at least a 50% reduction in the maximum deformation load.Moreover,a remarkable decrement in the surface roughness of the formed tubes has been obtained.展开更多
文摘Increasing environmental concerns about limiting harmful emissions has necessitated sulfur-and phosphorus-free green lubricant additives.Although boron-containing compounds have been widely investigated as green lubricant additives,their macromolecular analogs have been rarely considered yet to develop environmentally friendly lubricant additives.In this work,a series of boron-containing copolymers have been synthesized by free-radical copolymerization of stearyl methacrylate and isopropenyl boronic acid pinacol ester with different feeding ratios(S_(n)-r-B_(m),n=1,m=1/3,1,2,3,5,9).The resulting copolymers of S_(n)-r-B_(m)(n=1,m=1/3,1,2,3,5)are readily dispersed in the PAO-10 base oil and form micelle-like aggregates with hydrodynamic diameters ranging from 9.7 to 52 nm.SRV-IV oscillating reciprocating tribological tests on ball-on-flat steel pairs show that compared with the base oil of PAO-10,the friction coefficients and wear volumes of the base oil solutions of S_(n)-r-B_(m)decrease considerably up to 62%and 97%,respectively.Moreover,the base oil solution of S_(1)-r-B_(1)exhibits an excellent load-bearing capacity of(850±100)N.These superior lubricating properties are due to the formation of protective tribofilms comprising S_(n)-r-B_(m),boron oxide,and iron oxide compounds on the lubricated steel surface.Therefore,the boron-containing copolymers can be regarded as a novel class of environmentally friendly lubricating oil macroadditives for efficient friction and wear reduction without sulfur and phosphorus elements.
文摘Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials. Iron-based samples were prepared by die wall lubricated warm compaction at 135 ℃ and 175 ℃, using polytetrafluoroethylene (PTFE) emulsion as die wall lubricant. A compacting pressure of 700 MPa and 550 MPa were used. The admixed lubricant concentration ranging from 0 to 0.6 wt.% was used in this study. Compared with non-die wall lubricated samples, the die wall lubricated samples have higher green densities. Results show that in addition to the decrease in ejection forces, green density of the compacts increased linearly with the decrease in admixed lubricant content. Mechanical property of the sintered compacts increase sharply when the admixed lubricant concentration reduced to 0.125 wt.% or less. Ejection force data indicated that samples with die wall lubrication show lower ejection forces when compared with samples without die wall lubrication. No scoring was observed in all experiments even for samples contain no admixed lubricant. Our results indicated that under experimental condition used in this study, no matter at which compaction pressure, compaction temperature, graphite and lubricant contents in the powder the die wall lubricated warm compaction would give the highest green density and lowest ejection force. It can be concluded that combination of die wall lubrication and warm compaction can provide P/M products with higher density and better quality. It is a feasible way to produce high performance P/M parts if suitable die wall lubrication system was applied.
文摘Nano-copper used as lubrication oil additive has good tribological property and active self-repairing effect for friction pairs. The reduction in liquid phase for preparing nano-additive is one of the most common method. Nano-copper was prepared by reduction in liquid phase. The different project and routine practice for preparing nano-copper were researched. The dispersion problem of nano-copper was investigated by surface treatment and high dispersion. The particles dimension, the dispersion stability and the purity of nano-copper were characterized by TEM and XRD. The conclusion indicates that the methods of the preparation and dispersion can obtain 20nm copper additive with good dispersion property in lubrication oil.
基金National Natural Science Foundation of China(Grant No.51279067)
文摘Considering the effect of viscosity-temperature relationship and cavitation of micro-scale film,the influencing factors on hydrodynamic lubrication performance of upstream pumping mechanical seal were investigated based on the theory of hydrodynamic lubrication.N-S equation,energy equation,viscosity-temperature equation and vapor transport equation were solved with the finite volume method by using Fluent software,which was performed to analyze the influence of the viscosity-temperature and cavitation effect on hydrodynamic lubrication failure of the film.The research demonstrates that it will lead to the significant difference of the temperature field by considering the coupling of temperature and viscosity.When the film thickness decreases and the rotating speed rises,cavitation regions and viscous friction heat increases,the opening force of the film is also enhanced.However,the growth rate is restricted to the cavitation regions and viscous friction heat,and the opening force begins to decline to a certain extent,and thereby being insufficient to open the surfaces of the seals and leading to the failure of automatic adjustment function and severe wear,lubrication failure occurrs.Through comprehensive research on the influences of viscosity-temperature and cavitation effect on hydrodynamic lubrication performance,the theories of failure and design of upstream pumping mechanical seal are further developed.
基金Project(51905118)supported by the National Natural Science Foundation of ChinaProject(3072020CF0306)supported by the Fundamental Research Funds for the Central Universities,China。
文摘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.
基金Project(2012BAF09B04)supported by the National Key Technology Research and Development Program of China
文摘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.
基金Projects(51575289,51705270)supported by the National Natural Science Foundation of China。
文摘The thermal elasto-hydrodynamic lubrication characteristics of the internal meshing gears in a planetary gear train under vibrations were examined considering the influence of the modification coefficient and time-varying meshing stiffness.Based on dynamic theory of the gear system,a dynamic model of the planetary gear train was established.The lubrication performances of modified gear systems under vibrations and static loads were analyzed.Compared with other transmission types,the best lubrication effect could be produced by the positive transmission.A thicker lubricating oil film could be formed,and the friction coefficient and oil film flash temperature are the smallest.Increasing modification coefficient improves the lubrication performance continuously but intensifies the engage-in and tooth-change impact.For the planetary and inner gears,the increase in the modification coefficient also leads a decrease in the oil film stiffness.
基金Project(E2019209153)supported by the Natural Science Foundation of Hebei Province,China。
文摘In order to analyze the lubricating characteristics at different meshing points in the cycloid pin wheel transmission process,the cycloid gear teeth were discretized,combined with the kinematic analysis of the cycloid pin gear transmission and the contact analysis of the gear teeth.The progressive mesh densification method(PMD)was used to numerically solve the film thickness.The influence of the design parameters and process parameters on the lubrication characteristics was analyzed.The elastohydrodynamic lubrication and mixed lubrication characteristics at different contact points were obtained.The optimal meshing area of the cycloid gear tooth was determined,and the film thickness ratio,contact load ratio,maximum contact pressure at different points,average film thickness and roughness after contact deformation were analyzed.The conclusion of this study provides effective guidance for the research on the modification of cycloid gear teeth.
基金Project(GXXT-2019-048)supported by the University Synergy Innovation Program of Anhui Province,ChinaProject(51575002)supported by the National Natural Science Foundation of ChinaProject(gxbj ZD11)supported by the Top-Notch Talent Program of University(Profession)in Anhui Province,China。
文摘External return mechanism is a mechanical structure applied to axial piston pumps.To study its lubrication characteristics,the Reynolds equation applied to an external return spherical hinge pair was deduced based on the vector equation of relative-motion velocity of the external return spherical hinge pair under the influence of external swash plate inclination and offset distance.The results show that the total friction,axial leakage flow,and maximum value of the maximum oil-film pressure increase with increasing pump-shaft speed and decrease with increasing offset distance in one working cycle when the external-swash-plate inclination is constant.However,the varying offset distance has little effect on the axial leakage flow.The maximum value of the maximum oil-film pressure decreases with increasing external-swash-plate inclination and the total leakage flow increases with increasing external-swash-plate inclination in one working cycle when the offset distance is constant.It can be seen that the abovementioned parameters are important factors that affect the lubrication characteristics of external return spherical hinge pairs.Therefore,the complex effects of different coupling parameters should be comprehensively considered in the design of the external return mechanism.
文摘In the present study,the effect of reduction of cutting fluid consumption on the surface quality and tool wear was studied.Mathematical models were developed to predict the surface roughness using response surface methodology(RSM).Analysis of variance(ANOVA)was used to investigate the significance of the developed regression models.The results showed that the coefficient of determination values(R^2)for the developed models was 97.46%for dry,89.32%for flood mode(FM),and 99.44%for MQL,showing the high accuracy of fitted models.Also,under the minimum quantity lubrication(MQL)condition,the surface roughness improved by 23%−44%and 19%−41%compared with dry and FM,respectively,and the SEM images of machined surface proved the statement.The prepared SEM images of tool rake face also showed a considerable decrease in adhesion wear.Built-up edge and built-up layer were the two main products of the adhesion wear,and energy-dispersive X-ray spectroscopy(EDX)analysis of specific points on the tool faces helped to discover the chemical compositions of adhered materials.By changing dry and FM to MQL mode,dominant mechanism of tool wear in machining aluminum alloy was significantly decreased.Breakage wear that led to early failure of cutting edge was also controlled by MQL technique.
基金Projects(51575289,51705270)supported by the National Natural Science Foundation of China。
文摘The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated,including the influence of the modification coefficient and vibrations.Based on the dynamic theory of gear systems,a six-degree-of-freedom tribo-dynamics model was established.Thermal elastohydrodynamic lubrication characteristics of a modified gear system under vibrations and a static load were analyzed.The results showed that the positive transmission gear system exhibited the better lubrication effect compared with other transmission types.A thick lubricating oil film could be formed,and the friction coefficient between the teeth and the oil film flash temperature were the smallest.As the modification coefficient increased,the lubrication condition was continuously improved,and the scuffing load capacity was enhanced.The increment of the modification coefficient increased the meshing stiffness of the gear system but reduced the stiffness of the oil film.
基金Project(51975064)supported by the National Natural Science Foundation of ChinaProject(cstc2018jcyj AX0442)supported by the General Projects of Basic Science and Frontier Technology Research of Chongqing,China+2 种基金Projects(2018M631059,2019T120805)supported by the Postdoctoral Science Foundation of ChinaProject(cstc2017zdcyzdzx X0001)supported by the Major Research and Development Program of ChinaProject supported by the Innovation Program on the Common and Key Technologise of Key Industries,China。
文摘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.
基金Project(51175133)supported by the National Natural Science Foundation of China
文摘Based on the theory of unsteady hydrodynamic lubrication and relevant mathematic and physical methods, a basic model was developed to analyze the unsteady lubrication film thickness, pressure stress and friction stress in the work zone in strip rolling. The distribution of pressure stress and friction stress in the work zone was obtained. A numerical simulation was made on a 1850 cold rolling mill. The influence of back tension stress and reduction on the distribution of pressure stress and friction stress between the roll gaps was qualitatively analyzed by numerical simulation. The calculated results indicate that the higher the back tension, the lower the pressure stress and the friction stress in the work zone, and the largest friction stresses are obtained at the inlet and outlet edges. The pressure and friction gradients are rather small at high back tension. The pressure-sensitive lubricant viscosity increases exponentially with the increase of pressure. The unsteady lubrication phenomenon in the roll bite is successfully demonstrated.
基金Project(2016YFB0301402)supported by the National Key Research and Development Program of ChinaProject(CSU20151024)supported by the Innovation-driven Plan in Central South University,China
文摘Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.
文摘Due to the biological risks of using the conventional lubricants,the vegetable oils have been considered nowadays.Besides,to improve the tribological properties of the vegetable oils in various applications like metal forming processes,nanoparticles have been used as additives.This research evaluated the lubrication performance of the Al2O3 and TiO2 nanoparticles dispersed in rapeseed oil during the parallel tubular channel angular pressing (PTCAP) process.The experimental PTCAP tests have been fulfilled under three lubrication conditions and the comparison between the PTCAP processed tubes has been performed in terms of the maximum forming force,surface roughness,and microhardness.The experimental results indicate that adding the mentioned nanoparticles has caused at least a 50% reduction in the maximum deformation load.Moreover,a remarkable decrement in the surface roughness of the formed tubes has been obtained.
