Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphe...Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.展开更多
TiN-Ag composite coatings were prepared by pulsed bias arc ion plating.X-ray diffraction(XRD)and energy dispersive X-ray spectroscopy(EDS)were applied to analyze the compositions of the coatings.Tribological propertie...TiN-Ag composite coatings were prepared by pulsed bias arc ion plating.X-ray diffraction(XRD)and energy dispersive X-ray spectroscopy(EDS)were applied to analyze the compositions of the coatings.Tribological properties of the coatings were studied using an MFT-R4000 ball-on-disk friction tester in the presence of lubricating greases containing multilayer graphene.Scanning electron microscopy(SEM),Raman spectroscopy,and X-ray photoelectron spectroscopy(XPS)were used to analyze the worn surface compositions of the lubricating films.The results show that with the decrease in Ag in the film,hardness increased but electrical conductivity decreased.The coating with 10 at%Ag content shows the best friction-reducing and anti-wear properties,which can be attributed to the moderate content of Ag embedded in the TiN crystal gap that enhanced the grain bonding force to improve the anti-wear and self-lubricating ability.Graphene can be adsorbed on the coating as a solid lubricant.展开更多
The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact’s film-forming capacity.An elastohydrod...The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact’s film-forming capacity.An elastohydrodynamic lubrication(EHL) test rig with two interferometry microscopes,which could simultaneously monitor two different contact locations in the finite line contact,was constructed in order to study the influences of the grease thickener formulation on the film thickness and lubrication condition.By using the relative light intensity method,the thickness maps of the grease-lubricated film were calculated from the interferometer images captured by the two microscopes.The test results revealed that the grease thickener’s formulation had remarkable effects on film formation and the perturbation of film thickness.For the lithium-based grease,the film’s thickness near the two ends of the roller was prone to severe perturbation caused by the conglomeration of clumps that were hard to shear.For the aluminum-complex-based grease,the fibers tended to accumulate in the middle of the roller rather than at the two ends.The urea-based grease could be easily sheared into smaller particles.In addition to the straight-line profile rollers,the logarithmic profile rollers were tested and found to effectively enhance the axial grease flow,increase the axial shear stress,and thus shear more fibers into particles within the contact area.展开更多
A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thi...A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thickener concentration, alkyl-tetralin content and type of blend oils on the rheological and tribological performance of lithium grease was investigated. The microstructures of soap fibers were measured to reveal the structure-property correlations. The concentration of thickener and alkyl-tetralin content obviously affect the lubricating performance of lithium grease, while the molecular structure of alkyltetralin has no obvious impact on their properties. It was found that alkyl-tetralin could significantly enhance the thickening ability of PAO8 base oils, and decrease the amount of thickeners by 1.5%(mass).Lithium greases prepared using 20%(mass) alkyl-tetralin as co-base oil exhibited high colloidal stability,excellent rheological behaviors and tribological properties.展开更多
Graphene has superhigh thermal conductivity up to 5000 W/(m·K),extremely thin thickness,superhigh mechanical strength and nano-lamellar structure with low interlayer shear strength,making it possess great potenti...Graphene has superhigh thermal conductivity up to 5000 W/(m·K),extremely thin thickness,superhigh mechanical strength and nano-lamellar structure with low interlayer shear strength,making it possess great potential in mini-mum quantity lubrication(MQL)grinding.Meanwhile,ionic liquids(ILs)have higher thermal conductivity and better thermal stability than vegetable oils,which are frequently used as MQL grinding fluids.And ILs have extremely low vapor pressure,thereby avoiding film boiling in grinding.These excellent properties make ILs also have immense potential in MQL grinding.However,the grinding performance of graphene and ionic liquid mixed fluid under nano-fluid minimum quantity lubrication(NMQL),and its tribological mechanism on abrasive grain/workpiece grinding interface,are still unclear.This research firstly evaluates the grinding performance of graphene and ionic liquid mixed nanofluids(graphene/IL nanofluids)under NMQL experimentally.The evaluation shows that graphene/IL nanofluids can further strengthen both the cooling and lubricating performances compared with MQL grinding using ILs only.The specific grinding energy and grinding force ratio can be reduced by over 40%at grinding depth of 10μm.Work-piece machined surface roughness can be decreased by over 10%,and grinding temperature can be lowered over 50℃at grinding depth of 30μm.Aiming at the unclear tribological mechanism of graphene/IL nanofluids,molecular dynamics simulations for abrasive grain/workpiece grinding interface are performed to explore the formation mechanism of physical adsorption film.The simulations show that the grinding interface is in a boundary lubrication state.IL molecules absorb in groove-like fractures on grain wear flat face to form boundary lubrication film,and graphene nanosheets can enter into the grinding interface to further decrease the contact area between abrasive grain and workpiece.Compared with MQL grinding,the average tangential grinding force of graphene/IL nanofluids can decrease up to 10.8%.The interlayer shear effect and low interlayer shear strength of graphene nanosheets are the principal causes of enhanced lubricating performance on the grinding interface.EDS and XPS analyses are further carried out to explore the formation mechanism of chemical reaction film.The analyses show that IL base fluid happens chemical reactions with workpiece material,producing FeF_(2),CrF_(3),and BN.The fresh machined surface of workpiece is oxidized by air,producing NiO,Cr_(2)O_(3) and Fe_(2)O_(3).The chemical reaction film is constituted by fluorides,nitrides and oxides together.The combined action of physical adsorption film and chemical reaction film make graphene/IL nano-fluids obtain excellent grinding performance.展开更多
Nanofluid minimum quantity lubrication(NMQL)is a green processing technology.Cottonseed oil is suitable as base oil because of excellent lubrication performance,low freezing temperature,and high yield.Al_(2)O_(3)nanop...Nanofluid minimum quantity lubrication(NMQL)is a green processing technology.Cottonseed oil is suitable as base oil because of excellent lubrication performance,low freezing temperature,and high yield.Al_(2)O_(3)nanoparticles improve not only the heat transfer capacity but also the lubrication performance.The physical and chemical proper-ties of nanofluid change when Al_(2)O_(3)nanoparticles are added.However,the effects of the concentration of nanofluid on lubrication performance remain unknown.Furthermore,the mechanisms of interaction between Al_(2)O_(3)nanoparti-cles and cottonseed oil are unclear.In this research,nanofluid is prepared by adding different mass concentrations of Al_(2)O_(3)nanoparticles(0,0.2%,0.5%,1%,1.5%,and 2%wt)to cottonseed oil during minimum quantity lubrication(MQL)milling 45 steel.The tribological properties of nanofluid with different concentrations at the tool/workpiece interface are studied through macro-evaluation parameters(milling force,specific energy)and micro-evaluation parameters(surface roughness,micro morphology,contact angle).The result show that the specific energy is at the minimum(114 J/mm^(3)),and the roughness value is the lowest(1.63μm)when the concentration is 0.5 wt%.The surfaces of the chip and workpiece are the smoothest,and the contact angle is the lowest,indicating that the tribological proper-ties are the best under 0.5 wt%.This research investigates the intercoupling mechanisms of Al_(2)O_(3)nanoparticles and cottonseed base oil,and acquires the optimal Al_(2)O_(3)nanofluid concentration to receive satisfactory tribological properties.展开更多
Taking bump-type gas foil bearings as the research object,a deformation model of bump foil and a thin-plate finite element model of top foil were proposed.By solving Reynolds equation and energy equation,the pressure ...Taking bump-type gas foil bearings as the research object,a deformation model of bump foil and a thin-plate finite element model of top foil were proposed.By solving Reynolds equation and energy equation,the pressure distribution and the temperature distribution of gas films in foil bearings were obtained.Further,a numerical method for calculating the lubrication performance of gas foil bearings with considering the surface roughness was proposed.With a specific example,effects of the surface roughness on the bearing lubrication performance were parametrically studied.The results indicate that rougher journal surface can lead to larger fluctuation of the lubrication performance,while surface roughness of top foil has few effects on the fluctuation.Moreover,the mean values of performance parameters almost remain constant at different values of surface roughness.展开更多
Lubricating greases are widely used in e.g.open gear drives and gearboxes with difficult sealing conditions.The efficiency and heat balance of grease-lubricated gearboxes depend strongly on the lubrication mechanisms ...Lubricating greases are widely used in e.g.open gear drives and gearboxes with difficult sealing conditions.The efficiency and heat balance of grease-lubricated gearboxes depend strongly on the lubrication mechanisms channeling and circulating,for which the grease flow is causal.The computational fluid dynamics opens up the possibility to visualize and understand the grease flow in gearboxes in more detail.In this study,a single-stage gearbox lubricated with an NLGI 1-2 grease was modeled by the finite-volume method to numerically investigate the fluid flow.Results show that the rotating gears influence the grease sump only locally around the gears.For a low grease fill volume,the rotation of the gears is widely separated from the grease sump.For a high grease fill volume,a pronounced geargrease interaction results in a circulating grease flow around the gears.The simulated grease distributions show good accordance with high-speed camera recordings.展开更多
It was discovered the application of Al_(2)O_(3) nanofluid as lubricant for steel hot rolling could synchronously achieve oxidation protection of strips surface.The underlying mechanism was investigated through hot ro...It was discovered the application of Al_(2)O_(3) nanofluid as lubricant for steel hot rolling could synchronously achieve oxidation protection of strips surface.The underlying mechanism was investigated through hot rolling tests and molecular dynamics (MD) simulations.The employment of Al_(2)O_(3) nanoparticles contributed to significant enhancement in the lubrication performance of lubricant.The rolled strip exhibited the best surface topography that the roughness reached lowest with the sparsest surface defects.Besides,the oxide scale generated on steel surface was also thinner,and the ratio of Fe_(2)O_(3) among various iron oxides became lower.It was revealed the above oxidation protection effect of Al_(2)O_(3) nanofluid was attributed to the deposition of nanoparticles on metal surface during hot rolling.A protective layer in the thickness of about 193 nm was formed to prevent the direct contact between steel matrix and atmosphere,which was mainly composed of Al_(2)O_(3) and sintered organic molecules.MD simulations confirmed the diffusion of O_(2) and H_(2)O could be blocked by the Al_(2)O_(3) layer through physical absorption and penetration barrier effect.展开更多
Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematical...Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematically using a rheometer,scanning electron microscope,X-ray diffraction,Fourier transform infrared spectrometer,oscillating tribometer,and 3D surface profiler measurements.The results showed that suitable synthetic conditions are two quenching cycles,and the synthetic temperature and time is 240℃for 12 h.The rheological analysis showed that thickener content and different proportions of the two PP molecular weights have a significant influence on the rheological properties of PP grease.High molecular weight PP(H-PP)has a stronger thickening ability than low molecular weight PP(L-PP).The higher the amount of H-PP in the fixed thickener content or the higher the thickener content with a specific proportion,the higher the viscoelasticity of PP grease.The tribological performance is related to the rheological properties.The proportion of two different molecular weight PPs in the thickener content should be appropriate;excessive H-PP content leads to lubrication failure.展开更多
It is of considerable significance to develop efficient and environmentally friendly machinery lubricant additives because of the increasing depletion of petrochemical resources and severe environmental problems.Herei...It is of considerable significance to develop efficient and environmentally friendly machinery lubricant additives because of the increasing depletion of petrochemical resources and severe environmental problems.Herein,we proposed a facile strategy to synthesize a multifunctional vegetable oil-based lubricant via the lignin derivative vanillin coupled to amine and diethyl phosphite to produce a lubricating additive with both extreme pressure and antioxidant properties.Compared with pure tung oil,the lubricating and antioxidant performance of tung oil is significantly improved after adding additives.Adding the 1.0 wt%additive to the tung oil reduced the friction wear coefficient and the volume,and the oxidation induction time was much longer than pure tung oil.展开更多
The current study of minimum quantity lubrication(MQL)concentrates on its performance improvement.By contrast with nanofluid MQL and electrostatic atomization(EA),the proposed nanofluid composite electrostatic sprayin...The current study of minimum quantity lubrication(MQL)concentrates on its performance improvement.By contrast with nanofluid MQL and electrostatic atomization(EA),the proposed nanofluid composite electrostatic spraying(NCES)can enhance the performance of MQL more comprehensively.However,it is largely influenced by the base fluid of external fluid.In this paper,the lubrication property and machining performance of NCES with different types of vegetable oils(castor,palm,soybean,rapeseed,and LB2000 oil)as the base fluids of external fluid were compared and evaluated by friction and milling tests under different flow ratios of external and internal fluids.The spraying current and electrowetting angle were tested to analyze the influence of vegetable oil type as the base fluid of external fluid on NCES performances.The friction test results show that relative to NCES with other vegetable oils as the base fluids of external fluid,NCES with LB2000 as the base fluid of external fluid reduced the friction coefficient and wear loss by 9.4%-27.7%and 7.6%-26.5%,respectively.The milling test results display that the milling force and milling temperature for NCES with LB2000 as the base fluid of external fluid were 1.4%-13.2%and 3.6%-11.2%lower than those for NCES with other vegetable oils as the base fluids of external fluid,respectively.When LB2000/multi-walled carbon nanotube(MWCNT)water-based nanofluid was used as the external/internal fluid and the flow ratio of external and internal fluids was 2:1,NCES showed the best milling performance.This study provides theoretical and technical support for the selection of the base fluid of NCES external fluid.展开更多
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 stat...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.展开更多
Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials ...Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials one of the most important research candidates for alternative paper packaging materials for oil resistance.These bio-based materials have excellent oxygen and oil barriers,which are critical for food packaging.Moreover,they are biodegradable,naturally renewable,and safe.In this artical,two main groups of bio-based oil repellents for paper food packaging,including polysaccharide-based biopolymers and protein-based biopolymers,are enumerated,and the advantages and weaknesses of bio-based oil repellents are discussed,and effective solutions are proposed.Finally,research status and prospects on the development of bio-based oil-resistant coatings for the food packaging industry are presented.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.52075458 and U2141211).
文摘Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.
基金supported by the Natural Science Foundation of Beijing Municipality(2172053)the National Natural Science Foundation of China(51575181)。
文摘TiN-Ag composite coatings were prepared by pulsed bias arc ion plating.X-ray diffraction(XRD)and energy dispersive X-ray spectroscopy(EDS)were applied to analyze the compositions of the coatings.Tribological properties of the coatings were studied using an MFT-R4000 ball-on-disk friction tester in the presence of lubricating greases containing multilayer graphene.Scanning electron microscopy(SEM),Raman spectroscopy,and X-ray photoelectron spectroscopy(XPS)were used to analyze the worn surface compositions of the lubricating films.The results show that with the decrease in Ag in the film,hardness increased but electrical conductivity decreased.The coating with 10 at%Ag content shows the best friction-reducing and anti-wear properties,which can be attributed to the moderate content of Ag embedded in the TiN crystal gap that enhanced the grain bonding force to improve the anti-wear and self-lubricating ability.Graphene can be adsorbed on the coating as a solid lubricant.
基金funded by the twelfth five-year projects of China for science and technology under Contract D50-0109-12-001the Key Innovational Program of Shanghai Municipal Education Commission(No.11ZZ89)
文摘The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact’s film-forming capacity.An elastohydrodynamic lubrication(EHL) test rig with two interferometry microscopes,which could simultaneously monitor two different contact locations in the finite line contact,was constructed in order to study the influences of the grease thickener formulation on the film thickness and lubrication condition.By using the relative light intensity method,the thickness maps of the grease-lubricated film were calculated from the interferometer images captured by the two microscopes.The test results revealed that the grease thickener’s formulation had remarkable effects on film formation and the perturbation of film thickness.For the lithium-based grease,the film’s thickness near the two ends of the roller was prone to severe perturbation caused by the conglomeration of clumps that were hard to shear.For the aluminum-complex-based grease,the fibers tended to accumulate in the middle of the roller rather than at the two ends.The urea-based grease could be easily sheared into smaller particles.In addition to the straight-line profile rollers,the logarithmic profile rollers were tested and found to effectively enhance the axial grease flow,increase the axial shear stress,and thus shear more fibers into particles within the contact area.
基金financially supported by the National Natural Science Foundation of China (U1910202, 21978194)the Key Research and Development Program of Shanxi Province (202102090301005)+1 种基金the Fund for Shanxi “1331 Project”the Shanxi Natural Science Foundation for Young Scientists (202103021223064)。
文摘A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thickener concentration, alkyl-tetralin content and type of blend oils on the rheological and tribological performance of lithium grease was investigated. The microstructures of soap fibers were measured to reveal the structure-property correlations. The concentration of thickener and alkyl-tetralin content obviously affect the lubricating performance of lithium grease, while the molecular structure of alkyltetralin has no obvious impact on their properties. It was found that alkyl-tetralin could significantly enhance the thickening ability of PAO8 base oils, and decrease the amount of thickeners by 1.5%(mass).Lithium greases prepared using 20%(mass) alkyl-tetralin as co-base oil exhibited high colloidal stability,excellent rheological behaviors and tribological properties.
基金Supported by Shandong Provincial Natural Science Foundation of China(Grant Nos.ZR2022ME208,ZR2020QE181)National Natural Science Foundation of China(Grant Nos.51705272,52005281)+1 种基金China Postdoctoral Science Foundation(Grant No.2018M642628)111 project(Grant No.D21017).
文摘Graphene has superhigh thermal conductivity up to 5000 W/(m·K),extremely thin thickness,superhigh mechanical strength and nano-lamellar structure with low interlayer shear strength,making it possess great potential in mini-mum quantity lubrication(MQL)grinding.Meanwhile,ionic liquids(ILs)have higher thermal conductivity and better thermal stability than vegetable oils,which are frequently used as MQL grinding fluids.And ILs have extremely low vapor pressure,thereby avoiding film boiling in grinding.These excellent properties make ILs also have immense potential in MQL grinding.However,the grinding performance of graphene and ionic liquid mixed fluid under nano-fluid minimum quantity lubrication(NMQL),and its tribological mechanism on abrasive grain/workpiece grinding interface,are still unclear.This research firstly evaluates the grinding performance of graphene and ionic liquid mixed nanofluids(graphene/IL nanofluids)under NMQL experimentally.The evaluation shows that graphene/IL nanofluids can further strengthen both the cooling and lubricating performances compared with MQL grinding using ILs only.The specific grinding energy and grinding force ratio can be reduced by over 40%at grinding depth of 10μm.Work-piece machined surface roughness can be decreased by over 10%,and grinding temperature can be lowered over 50℃at grinding depth of 30μm.Aiming at the unclear tribological mechanism of graphene/IL nanofluids,molecular dynamics simulations for abrasive grain/workpiece grinding interface are performed to explore the formation mechanism of physical adsorption film.The simulations show that the grinding interface is in a boundary lubrication state.IL molecules absorb in groove-like fractures on grain wear flat face to form boundary lubrication film,and graphene nanosheets can enter into the grinding interface to further decrease the contact area between abrasive grain and workpiece.Compared with MQL grinding,the average tangential grinding force of graphene/IL nanofluids can decrease up to 10.8%.The interlayer shear effect and low interlayer shear strength of graphene nanosheets are the principal causes of enhanced lubricating performance on the grinding interface.EDS and XPS analyses are further carried out to explore the formation mechanism of chemical reaction film.The analyses show that IL base fluid happens chemical reactions with workpiece material,producing FeF_(2),CrF_(3),and BN.The fresh machined surface of workpiece is oxidized by air,producing NiO,Cr_(2)O_(3) and Fe_(2)O_(3).The chemical reaction film is constituted by fluorides,nitrides and oxides together.The combined action of physical adsorption film and chemical reaction film make graphene/IL nano-fluids obtain excellent grinding performance.
基金Supported by National Natural Science Foundation of China(Grant Nos.51806112,51975305)PhD Research Startup Foundation of Qingdao University of Technology,China(Grant Nos.JC2022-012,20312008).
文摘Nanofluid minimum quantity lubrication(NMQL)is a green processing technology.Cottonseed oil is suitable as base oil because of excellent lubrication performance,low freezing temperature,and high yield.Al_(2)O_(3)nanoparticles improve not only the heat transfer capacity but also the lubrication performance.The physical and chemical proper-ties of nanofluid change when Al_(2)O_(3)nanoparticles are added.However,the effects of the concentration of nanofluid on lubrication performance remain unknown.Furthermore,the mechanisms of interaction between Al_(2)O_(3)nanoparti-cles and cottonseed oil are unclear.In this research,nanofluid is prepared by adding different mass concentrations of Al_(2)O_(3)nanoparticles(0,0.2%,0.5%,1%,1.5%,and 2%wt)to cottonseed oil during minimum quantity lubrication(MQL)milling 45 steel.The tribological properties of nanofluid with different concentrations at the tool/workpiece interface are studied through macro-evaluation parameters(milling force,specific energy)and micro-evaluation parameters(surface roughness,micro morphology,contact angle).The result show that the specific energy is at the minimum(114 J/mm^(3)),and the roughness value is the lowest(1.63μm)when the concentration is 0.5 wt%.The surfaces of the chip and workpiece are the smoothest,and the contact angle is the lowest,indicating that the tribological proper-ties are the best under 0.5 wt%.This research investigates the intercoupling mechanisms of Al_(2)O_(3)nanoparticles and cottonseed base oil,and acquires the optimal Al_(2)O_(3)nanofluid concentration to receive satisfactory tribological properties.
文摘Taking bump-type gas foil bearings as the research object,a deformation model of bump foil and a thin-plate finite element model of top foil were proposed.By solving Reynolds equation and energy equation,the pressure distribution and the temperature distribution of gas films in foil bearings were obtained.Further,a numerical method for calculating the lubrication performance of gas foil bearings with considering the surface roughness was proposed.With a specific example,effects of the surface roughness on the bearing lubrication performance were parametrically studied.The results indicate that rougher journal surface can lead to larger fluctuation of the lubrication performance,while surface roughness of top foil has few effects on the fluctuation.Moreover,the mean values of performance parameters almost remain constant at different values of surface roughness.
基金Supported by the German Research Foundation e.V. (DFG).The presented results are based on the research project STA1198/14-1。
文摘Lubricating greases are widely used in e.g.open gear drives and gearboxes with difficult sealing conditions.The efficiency and heat balance of grease-lubricated gearboxes depend strongly on the lubrication mechanisms channeling and circulating,for which the grease flow is causal.The computational fluid dynamics opens up the possibility to visualize and understand the grease flow in gearboxes in more detail.In this study,a single-stage gearbox lubricated with an NLGI 1-2 grease was modeled by the finite-volume method to numerically investigate the fluid flow.Results show that the rotating gears influence the grease sump only locally around the gears.For a low grease fill volume,the rotation of the gears is widely separated from the grease sump.For a high grease fill volume,a pronounced geargrease interaction results in a circulating grease flow around the gears.The simulated grease distributions show good accordance with high-speed camera recordings.
基金financially supported by the National Natural Science Foundation of China(No.51874036)National Key Research and Development Program of China(No.2021YFB3701305)。
文摘It was discovered the application of Al_(2)O_(3) nanofluid as lubricant for steel hot rolling could synchronously achieve oxidation protection of strips surface.The underlying mechanism was investigated through hot rolling tests and molecular dynamics (MD) simulations.The employment of Al_(2)O_(3) nanoparticles contributed to significant enhancement in the lubrication performance of lubricant.The rolled strip exhibited the best surface topography that the roughness reached lowest with the sparsest surface defects.Besides,the oxide scale generated on steel surface was also thinner,and the ratio of Fe_(2)O_(3) among various iron oxides became lower.It was revealed the above oxidation protection effect of Al_(2)O_(3) nanofluid was attributed to the deposition of nanoparticles on metal surface during hot rolling.A protective layer in the thickness of about 193 nm was formed to prevent the direct contact between steel matrix and atmosphere,which was mainly composed of Al_(2)O_(3) and sintered organic molecules.MD simulations confirmed the diffusion of O_(2) and H_(2)O could be blocked by the Al_(2)O_(3) layer through physical absorption and penetration barrier effect.
基金the financial support provided by the National Natural Science Foundation of China Project (U21A20315,21978186)the Fund for Shanxi“1331 Project” (1331)。
文摘Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematically using a rheometer,scanning electron microscope,X-ray diffraction,Fourier transform infrared spectrometer,oscillating tribometer,and 3D surface profiler measurements.The results showed that suitable synthetic conditions are two quenching cycles,and the synthetic temperature and time is 240℃for 12 h.The rheological analysis showed that thickener content and different proportions of the two PP molecular weights have a significant influence on the rheological properties of PP grease.High molecular weight PP(H-PP)has a stronger thickening ability than low molecular weight PP(L-PP).The higher the amount of H-PP in the fixed thickener content or the higher the thickener content with a specific proportion,the higher the viscoelasticity of PP grease.The tribological performance is related to the rheological properties.The proportion of two different molecular weight PPs in the thickener content should be appropriate;excessive H-PP content leads to lubrication failure.
基金Funding Statement:This work was supported by National Natural Science Foundation of China[No.31901260]Special Fund of Chinese Central Government for Basic Scientific Research Operations in Commonweal Research Institutes[No.CAFYBB2019SY037].
文摘It is of considerable significance to develop efficient and environmentally friendly machinery lubricant additives because of the increasing depletion of petrochemical resources and severe environmental problems.Herein,we proposed a facile strategy to synthesize a multifunctional vegetable oil-based lubricant via the lignin derivative vanillin coupled to amine and diethyl phosphite to produce a lubricating additive with both extreme pressure and antioxidant properties.Compared with pure tung oil,the lubricating and antioxidant performance of tung oil is significantly improved after adding additives.Adding the 1.0 wt%additive to the tung oil reduced the friction wear coefficient and the volume,and the oxidation induction time was much longer than pure tung oil.
基金Supported by National Natural Science Foundation of China(Grant Nos.52175411 and 51205177)Jiangsu Provincial Natural Science Foundation(Grant Nos.BK20171307 and BK2012277).
文摘The current study of minimum quantity lubrication(MQL)concentrates on its performance improvement.By contrast with nanofluid MQL and electrostatic atomization(EA),the proposed nanofluid composite electrostatic spraying(NCES)can enhance the performance of MQL more comprehensively.However,it is largely influenced by the base fluid of external fluid.In this paper,the lubrication property and machining performance of NCES with different types of vegetable oils(castor,palm,soybean,rapeseed,and LB2000 oil)as the base fluids of external fluid were compared and evaluated by friction and milling tests under different flow ratios of external and internal fluids.The spraying current and electrowetting angle were tested to analyze the influence of vegetable oil type as the base fluid of external fluid on NCES performances.The friction test results show that relative to NCES with other vegetable oils as the base fluids of external fluid,NCES with LB2000 as the base fluid of external fluid reduced the friction coefficient and wear loss by 9.4%-27.7%and 7.6%-26.5%,respectively.The milling test results display that the milling force and milling temperature for NCES with LB2000 as the base fluid of external fluid were 1.4%-13.2%and 3.6%-11.2%lower than those for NCES with other vegetable oils as the base fluids of external fluid,respectively.When LB2000/multi-walled carbon nanotube(MWCNT)water-based nanofluid was used as the external/internal fluid and the flow ratio of external and internal fluids was 2:1,NCES showed the best milling performance.This study provides theoretical and technical support for the selection of the base fluid of NCES external fluid.
基金Supported by the National Natural Science Foundation of China(No.52101343)the Aeronautical Science Foundation(No.201834S9002).
文摘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.
文摘Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials one of the most important research candidates for alternative paper packaging materials for oil resistance.These bio-based materials have excellent oxygen and oil barriers,which are critical for food packaging.Moreover,they are biodegradable,naturally renewable,and safe.In this artical,two main groups of bio-based oil repellents for paper food packaging,including polysaccharide-based biopolymers and protein-based biopolymers,are enumerated,and the advantages and weaknesses of bio-based oil repellents are discussed,and effective solutions are proposed.Finally,research status and prospects on the development of bio-based oil-resistant coatings for the food packaging industry are presented.
