Volume 49,2024 Issue 7

• The Influence of Ionic Liquid on Tribological Properties of WS2 Nano Lubricating Oil
  HOU Xianjun; QIAN Yucong; JIANG Hua; YU Qifan
  Abstract:Nano tungsten disulfide has excellent lubrication performance,but its easy agglomeration in lubricating oil affects its anti-wear and friction reduction performance.To improve the anti-wear and friction reduction performance of nano WS2,a phosphate ionic liquid was added to WS2 nano lubricating oil,and its frictional properties were tested using four-ball friction tester.XPS,EDS,and electron microscopy were used to characterize the worn surface of the steel balls.The results show that although the friction coefficient of nano lubricating oil is slightly increased after adding ionic liquid,compared to the base oil,ionic liquids can still reduce the friction coefficient by a maximum of 28%,and can significantly reduce the wear scar diameter,with a maximum reduction of 44%.In the friction process,the ionic liquid reacts with WS2 to generate PW,which acts as a catalyst to accelerate the oxidation reaction in the friction process,and the generated compound acts as a chemical friction film to reduce wear and improve the anti-wear and friction reduction performance of lubricating oil.

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• Structural Optimal Design of Spiral Wound Gasket Based on Section Parameters R(R1,R2)
  ZHANG Zheng; GUO Yanbao; WANG Deguo
  Abstract:Flexible graphite spiral wound gaskets(SWGs) are widely used in static sealing of pipeline flanges,and their structure has an important effect on the mechanical properties and sealing performance.Based on the commonly used "V" type simplified model of SWGs,an improved simplified model of R(R1,R2) section parameter was proposed,which can better meet the process requirements.Taking the contact pressure,equivalent stress and compression-recovery of the flexible graphite sealing tape as key performance indicators,the basic objective function and constraint equations for the geometric structure optimization of SWGs were constructed.The simulation analysis of the improved model was carried out using AN-SYS software.The influence of different gasket structure parameters on the key performance indicators was explored,and the optimal structure of the SWG under multi-constraint conditions was determined by using response surface method.

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• Analysis of Floating Ring Bearing Performance under Bottom Pressure of Well
  ZHONG Lin; LENG Xiaodong; WANG Guorong; WANG Juan; WEI Gang; WU Xiaolong
  Abstract:In order to investigate the rotational speed ratio at equilibrium,tribological properties,and oil film pressure distribution of the floating ring bearing of an 215.9 mm cone bit with an inner and outer gap ratio under bottom pressure of well,Reynolds boundary conditions were modified by considering the actual downhole environmental pressure of the floating ring bearings and the seal pressure difference of the cone bit.The Reynolds equation of floating ring bearings was numerically solved by using the PDE Toolbox in MATLAB,and the influence of the internal and external gap ratios on the rotational speed ratio at equilibrium,oil film pressure,and friction coefficient of floating ring bearings was analyzed.The results show that when the ambient pressure is 60 MPa and the seal pressure difference is 20 MPa,the equilibrium rotational speed ratio of the floating ring increases first and then decreases with the increase of the inner and outer clearance ratios.Taking the bearing′s friction coefficient and oil film pressure as a comprehensive evaluation index,when the internal and external gap ratio of floating ring bearings is 2.0,the friction coefficient of the bearing is smaller,the pressure of the oil film is higher,and the overall performance of the bearing is better.When the internal and external gap ratio is 2.0,with the rise of environmental pressure,the torque and friction coefficient of the floating ring bearing increase,thereby accelerating the wear of the bearing.This study provides basic theoretical support for structural parameter optimization and performance improvement of cone-bit floating ring bearings under special boundary conditions.

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• Research on Axial Vibration of Non-contact Mechanical Seals Based on Newmark-β Method
  JIN Saisai; SUN Jianjun; MA Chenbo
  Abstract:Vibration has an important impact on the performance of non-contact mechanical seals,such as collision and leakage.A seal vibration system model was built,which included static ring,liquid film,dynamic ring and elastic element,and the displacement of the static ring,dynamic ring,and elastic components of the sealing system,as well as the leakage and collision of the sealing system under three types of excitations,such a free attenuation vibration,self-excited vibration,and seismic extreme vibration,were explored.The results show that the axial stability and sealing performance of the sealing system are good under free attenuation vibration without external excitation.After being disturbed by self-excited vibration in the form of harmonic vibration excitation force,the displacement of the sealing system significantly increases,which will significantly affect the sealing performance.Under the influence of random and stable ground motion with a certain seismic intensity,the displacement of elastic components increases significantly,leading to seal failure.Vibration has a significant impact on the performance of non-contact mechanical seals.It is necessary to ensure that the liquid film thickness between the sealing faces is stable and small enough to maintain the long-term operation of the sealing system.

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• Effect of Thermal Properties of Surface Coatings on Point Contact Elastohydrodynamic Lubrication
  SU Zhenhua; CUI Jinlei; CAO Fengshuo; LIU Xiaoling
  Abstract:To investigate the influence of thermal characteristic parameters of coating materials on point contact elastohydrodynamic lubrication,three diamond-like carbon (DLC) coatings prepared by different methods and zirconia ceramic coatings were selected,and the point contact elastohydrodynamic lubrication model considering the thermal properties of coating was established to analyze the effects of coating materials,coating thickness and rheological properties of lubricant on the lubrication properties of the contact zone.The results show that the four surface coatings with different thermal characteristics under elastohydrodynamic lubrication state result in differences in film thickness,and the solid surface temperature and lubrication zone temperature field will vary with the thermal inertia of the coatings.The DLC coating with minimal thermal inertia can achieve higher film thickness when it is covered on the faster surface.With the increase of coating thickness,the temperature of solid surface will rise,and the friction will decrease.The non-Newtonian fluid has little influence on the pressure and film thickness,but results in relatively lower temperature compared with the Newtonian fluid.It is beneficial to reduce friction and increase film thickness when coating is covered on the faster surface under elastohydrodynamic lubrication state.

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• Research on Roller Bearing Parameters Based on Elastohydrodynamic Lubrication
  HUANG Jiaming; GU Chunxing
  Abstract:The influence of structural parameters of cylindrical roller bearings on their lubrication characteristics was studied based on the theory of elastohydrodynamic lubrication.By combining the elastic contact deformation equation and the fluid dynamics lubrication equation,an elastohydrodynamic lubrication model suitable for roller bearings was established to study the changes in frictional properties of roller bearings under different parameters,such as ellipticity,load,entrainment speed,and viscosity.The results show that the ellipticity,load,suction speed,and viscosity will affect parameters such as pressure peak and secondary pressure peak to varying degrees.As the ellipticity increases,the oil film thickness and pressure significantly increase,as the load increases,the overall pressure,pressure peak,secondary pressure peak and their sharpness significantly increase,but the minimum oil film thickness slightly decreases.There is a significant positive correlation between viscosity and minimum oil film thickness and pressure.There is a weak positive correlation between entrainment velocity and oil film thickness,and a weak negative correlation between entrainment velocity and oil film pressure.Therefore,increasing the ellipticity and reducing the load to a certain extent is beneficial for improving lubrication performance.

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• Study of Oil Film Characteristics of Ultra-high Speed Liquid Hybrid Bearings Considering Fluid-solid Coupling Effect
  ZHAO Ziheng; TAN Yanqing; MA Lianjie; XU Pengyang
  Abstract:Consider the influence of the viscosity temperature effect of lubricating oil on hybrid bearings,the oil-film-shaft fluid-structure coupling model of ultra-high-speed liquid hybrid bearing was established,the pressure and temperature fields of the oil film of the hybrid bearing were obtained by solving the continuity equation, energy equation and Navier-Stokes equation with computational fluid dynamics (CFD) method.The two-way fluid-structure coupling analysis method was used to calculate the hybrid bearing,and the effect of bearing elastic deformation on the oil film characteristics was analyzed.The results show that the oil film pressure and maximum deformation of the hybrid bearing increase with the increase of speed and oil supply pressure,and increasing the oil supply pressure can intensify the flow of lubricating medium,thus reducing the oil film temperature to a certain extent.After considering the effect of fluid-structure coupling,the actual bearing load capacity and oil film pressure of the hybrid bearing are reduced to a certain extent.

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• Study on Wear Properties of Impregnated Graphite Materials under Different Normal Loads
  SONG Wei; LI Kaimin; MA Rongrong; LI Wanjia; DING Xuexing; CHEN Haoxiang
  Abstract:The effects of normal load on the friction and wear characteristics of impregnated graphite under different friction systems were investigated.The surface wear morphology and wear profile were characterized by scanning electron microscope and laser confocal microscope,respectively,and the friction and wear mechanism between impregnated graphite and dual balls (GCr15 steel ball and Si3N4 ceramic ball) were evaluated.The results show that the wear marks deepen and widen with the increase of normal load.The wear rate is negatively correlated with the normal load,while the friction coefficient and wear volume is positively correlated with the normal load.The wear mechanism of graphite under small load is adhesive wear and abrasive wear,while the main wear mechanism under large load is adhesive wear,oxidation wear and fatigue wear.Compared to the friction pairs of Si3N4/graphite,the friction pairs of GCr15/graphite have lower wear rates and form a complete and more continuous "third body" lubricating film during the friction process,which reduces wear and protects the graphite matrix.

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• Design Optimization of the Mechanical Performances of the Aerostatic Journal Bearing
  LI Yifei; HUANG Weiping; SANG Ran
  Abstract:To improve both the static and the dynamic performances of the aerostatic journal bearing,the flow characteristics in the bearing clearance,the displacement impedance,as well as the load carrying capacity were analyzed and optimized.The flow structures in the bearing clearance were analyzed by numerical simulation method.The supersonic region in the flow field of the air film was eliminated to suppress the micro-vibration.The stiffness and damping of the bearing air film were calculated,and the displacement impedance was further achieved based on the Engineering Simplification Algorithm-Computational Fluid Dynamics method.The influences of bearing parameters on the displacement impedance were discussed.It is found that the pressure in the air film decreases from the orifice to the outlet of the air film,and the formation of the shock waves at the outlet of the orifice can induce the vortex flow and then cause the occurrence of the micro-vibration.The formation mechanism of the micro-vibration is similar with that of the thrust bearing.The mathematic model for optimization was established,the displacement impedance and the load carrying capacity were both considered as design objectives,and the elimination of the micro-vibration was also considered.Several cases with different eccentricity ratio and excitation frequency were discussed.Through optimization,the mechanical performances of the journal bearing are improved,and the optimization and analysis process can provide a reference for engineering application of design of the aerostatic journal bearing.

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• Analysis of Friction Reducing and Leakage Characteristics of Plunger Pair with Pangolin Scale Texture
  GUO Mengxian; GUO Yong; CHEN Jiaxin
  Abstract:In order to solve the problem that the wear and leakage of the plunger pair of the inner curve radial motor restrict the efficiency of the hydraulic-electric energy recovery system,a method to simulate the pangolin scale texture on the surface of the plunger structure to reduce friction and leakage.The mathematical model of pangolin scale texture was characterized by double parabola translation method,and the simulation model of oil film bearing capacity and friction coefficient was established based on Reynolds equation.The oil film pressure and friction coefficient of non-textured and textured plungers were compared,and the relationship between gap leakage of plunger pair and texture area ratio was analyzed.The results show that the textured plunger has higher bearing capacity and lower friction coefficient,and its oil film pressure is 10% to 35% higher than that of the non-textured plunger.Compared with the non-textured plunger pair,the leakage of the textured plunger pair is reduced by 13.8% to 27.8%, indicating that the texture has a certain improvement effect on the sealing performance of the plunger pair.Pangolin scale texture plunger structure hydraulic motor has a significant effect on improving the efficiency of hydro-electric energy recovery system.

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• Thermodynamic Coupling Simulation Study of Proton Exchange Membrane Fuel Cell Sealing System
  CHEN Zhi; XING Yanfeng; ZHANG Xiaobing; YANG Fuyong; CAO Juyong
  Abstract:Temperature affects the sealing performance and mechanical behavior of proton exchange membrane fuel cell (PEMFC),thus affecting their service life and reliability.To study the sealing performance and mechanical behavior of PEMFC under thermodynamic coupling,two-dimensional models of PEMFC single-cell and multi-cell structures were established to study the stress-strain distribution of the sealing system at different operating temperatures.The effects of rubber sealing ring compression ratio,bipolar plate misalignment and sealing gasket size on the sealing performance and mechanical properties of the PEMFC were discussed.The results show that temperature has a significant effect on the Mises stress of the sealing gasket and the contact pressure of the membrane electrode assembly (MEA) frame.The sealing performances of single-cell and multi-cell structures at different operating temperatures are similar,and the differences in stress and contact pressure distribution are not significant.Therefore,the research conclusion of single-cell structure can be extended to multi-cell structure.The fuel cell sealing performance is improved with increasing compression ratio and size of the rubber sealing ring.The misalignment of the bipolar plates exacerbates the deformation of the MEA frame.The high stress area appears inside the cross section of the rubber sealing ring,which can easily lead to local stress concentration and sealing failure.

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• Study on Sealing Performance of Single-Lip Seal Ring for Shield Machine Main Drive
  HE Bo; LI Zhenlian; HE Wenhao; LU Zhibin; WANG Tingmei
  Abstract:Taking the main driving single-lip seal ring of shield machine under typical working conditions as the research object,the material parameters of Yeoh third-order model were determined by using the stress-strain curve obtained from the uniaxial tensile test of nitrile rubber material.The two-dimensional axisymmetric finite element model of single-lip seal ring was established,and the effects of medium pressure,pressure difference,friction coefficient and temperature on its sealing performance were simulated was studied.The results show that the medium pressure mainly affects the maximum contact stress,and the maximum contact stress increases linearly with the increase of the medium pressure.The maximum contact stress and contact length are mainly affected by medium pressure difference,and with the increase of medium pressure difference,the maximum contact stress first increases linearly and then basically remains unchanged,while the contact length increases nonlinearly.The influence of temperature change on sealing performance can be ignored.Under the conditions considered,the maximum contact pressure between the lip and the rigid body of the single-lip seal ring is always greater than the medium force,and the sealing performance is good.

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• Study on the Wear of Ti(C,N)-based Cermet Matching Seals for Cone Bit
  ZHOU Yi; LEI Xinlin; TANG Yifeng; WANG Ruchen; YAN Zhaoqiang; WU Bing
  Abstract:The metal sealing rings of cone bits usually uses the same metal materials,which have poor wear performance,and can easily cause the metal seal to fail due to severe wear.Ti(C,N)-based cermet was proposed to use as the sealing pair of roller bits.The friction and wear performance,and wear form of the friction pair surface were studied by the wear tests on different material pairs.A numerical wear model suitable for metal sealing materials of cone bit was established,and the numerical simulation of the bimetal sealing performance of Ti(C,N)-based cermet and matching materials was carried out.Based on the wear model,the wear volume of Ti(C,N)-based cermet matching materials for cone bits after test for 30 h was predicted.The test results show that when Ti(C,N)-based cermet is used as a moving pair and 9CrSi is used as a stationary pair,the average wear volume on the surface of the metal ring is the smallest,while the friction coefficient is smaller,and the wear performance is better.By comparing experimental and simulation data,it is verified that the established numerical wear model is suitable for bimetallic seals.The simulation results show that when Ti(C,N)-based cermet is used as a moving metal ring and 9CrSi is used as a static metal ring,the wear volume of the seal end surface is minimal,and the wear performance of the metal seal is significantly improved.The maximum contact stress is 23.243 MPa,which can meet the sealing requirements.

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• Structural Parameter Optimization of Spring Metal C-Ring Based on Sealing Characteristics
  YU Xiaoming; SHEN Chao; MA Zhigang; ZHANG Bin; SHAO Chunlei; GU Cheng; NIE Jiawei; GU Boqin
  Abstract:There are low stress areas of C-ring in the sealing process,and these areas are difficult to ensure the sealing reliability.In order to study the sealing characteristics of C-ring,it is necessary to analyze the effective contact stress and region.The C-ring with 318 mm outer diameter was selected as the research object.Using equivalent wall thickness instead of coil spring wire diameter,the equivalent model of C-ring was established.The rationality of the model was verified by compressive and resilient test.The effects of silver layer thickness,cladding layer thickness and equivalent thickness（spring wire diameter） on the sealing performance of C-ring were studied by finite element method.The results show that the effective contact width of the silver layer surface increases with the increase of the silver layer and cladding layer thickness,and the effective contact stress decreases with the increase of the silver layer and cladding layer thickness.The increase in equivalent wall thickness can simultaneously increase the effective contact width and effective contact stress.The structural parameters of C-ring were optimized by orthogonal experiment.The results show that the silver layer thickness and the wall thickness have significant influence on the effective contact stress and effective contact width.The optimal design parameters of silver layer thickness,coating thickness and spring wire diameter are 0.2 mm,0.5 mm and 3.1 mm,respectively.The leakage rate test result indicates that the optimized C-ring has better sealing performance.

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• Effect of Coiled Tubing Wear on Sealing Performance of Packer in the Stripper
  CHEN Ting; HU Zilong; MA Weiguo; DENG Lin; LI Chen
  Abstract:To study the effect of the coiled tubing wear on the sealing performance of the coiled tubing stripper, the common wear forms of the outer wall of coiled tubing were summarized,and the wear geometric models were constructed.Taking the coiled tubing stripper with diameter of 38.1 mm as an example,the constitutive model parameters of packer material were obtained through experiments,and the finite element model for sealing the coiled tubing with packer was established.Using the effective contact stress and maximum Mises stress as the evaluation indexes of sealing performance,the effects of the wear form,wear depth,wear length and off-wear angle on the sealing performance of the tube were analyzed.The results show that the off-wear forms of coiled tubing have great influence on the sealing performance of the packer,and when the length of coiled tubing off-wear section is larger than the height of the packer and the depth of the off-wear is greater than 1 mm,the sealing capacity of the packer cannot meet the wellhead sealing requirement.The off-wear angle will affect the stress distribution of the packer and thus affecting the sealing performance.

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• Analysis of Sealing Performance of Cross-Scale Composite Structured Friction Pair End Faces
  FAN Zhichao; MUTELLIP Ahmat; ZHANG Tingkun
  Abstract:By introducing a cross-scale composite texture combining large-scale grooves and small-scale micropores on the surface of the sealing pair,a composite textured mechanical seal end face combining elliptical micropores and T-shaped grooves was proposed,and a lubricating film fluid model was created.A mathematical model was established according to the mass conservation cavitation boundary conditions,and the finite element method was used for numerical solution.The influence of the composite of elliptical micropores of different length and short axis ratios and T-shaped grooves on the sealing performance was studied,and the optimal composite configuration was determined.The variation of the sealing performances such as opening force and leakage of different textured end face seals under different operating conditions was compared and studied.The results show that the optimal composite configuration is a combination of elliptical micropores with length and short axis ratio of 1.8 and T-shaped grooves.Under the same operating parameters,the cross-scale composite textured end face seal has stronger dynamic pressure lubrication effect,lower leakage,higher liquid film opening force and better overall sealing performance than a single texture.The results of the study can be applied to the design and optimization of the textured friction face of the mechanical seal.

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• Influence Mechanism of Ashless Organic Friction Modifier to the Hydrodynamic Lubrication Performance
  YOU Yue; MA Jiandong; WANG Weiwei
  Abstract:Ashless organic friction modifier can reduce the friction coefficient of hydrodynamic lubrication,which provide new idea to improve the hydrodynamic lubrication performance.The monoolein glycerol,oleic acid,pentaerythritol tetraisostearate and Span 80 were used as ashless friction modifier.Four kinds of lubricant samples were prepared by mixing 5% mass fraction of ashless friction modifier with base oil PAO 5,and their hydrodynamic lubrication performances were studied by fluid dynamic pressure lubrication test rig.Results show that the ashless friction modifiers have certain friction reduction effects under boundary lubrication and mixed lubrication,while the friction reduction effect is more significant under hydrodynamic lubrication.The lubricant containing 5% mass fraction of pentaerythritol tetraisostearate shows the best friction reduction performance,which reduces the friction coefficient of hydrodynamic lubrication by 19.6% compared with base oil.Molecular dynamic simulation results show that the ashless friction modifier produces boundary slip phenomenon on friction surface,reduces the intertwine of carbon chains between molecules,and thus reduces the friction coefficient under hydrodynamic lubrication.

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• Experimental Investigation on the Influence of Surface Texture of Pins on the Skidding of Cam-roller Unit
  Guixiang; SUN Nannan; CHAO Shen; TAN Ruiliang; HUANG Jisong; LIU Chenglong; GUO Feng
  Abstract:To improve the tribological performance of the cam-roller/roller-pin unit in an internal combustion engine so as to reduce the power consumption of the valve train,a triangle texture was fabricated on the pin,and the skidding characteristics of the roller follower and the influence of the texture of the pin on the skidding of the roller were measured by a custom-made cam-roller measurement system.The results show that the roller skidding increases first and then decreases with increasing speed,and high oil temperatures and heavy loads can inhibit the roller skidding.Under conditions of fully flooded oil supply,the surface texture of the pin can effectively reduce the skidding of the roller.Under conditions of insufficient oil supply and high speeds,when using an original pin,the lubricating oil loss increases over time,leading to an increase in the slip rate of rollers.While the pin with triangle texture can effectively improve the lubrication between the pin and the roller by guiding the oil flow at the oil feeding port through triangle texture and the oil storage of the texture,thus skidding of the roller is reduced.Moreover,the skidding does not change much with running time.

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• Effect of Radial Clearance on Fatigue Life of Cylindrical Roller Bearings
  WEI Yangang; ZHAO Xia; LV Haiting; XU Kai; YAO Jinchi
  Abstract:Applying the classic rolling bearing theory and the basic idea of the "slicing method",taking the output shaft bearing of a large MW wind turbine gearbox as an example,using the Romax Designer engineering analysis software,the calculations were conducted on the internal load distribution,contact stress,equivalent dynamic load of the ring and raceway,and life of the cylindrical roller bearing under different radial clearances.The effect of radial clearance on the service life of bearing ISO/TS 16281 was analyzed.The results indicate that the radial clearance not only affects the lifespan of the bearing by affecting the internal load distribution,contact stress,and equivalent dynamic load of the ring raceway,but also by influencing factors such as the life correction coefficient.The research results can provide reference for the optimization design of roller bearings.

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• Parametric Analysis of Magnetic Liquid Seal Pressure Resistance
  ZHANG Miaotian; JIN Licong; LI Shicong
  Abstract:Aimed at the magnetic liquid seal of aircraft,the COMSOL finite element analysis software was used to establish a magnetic liquid sealing model of different structural parameters.The structure parameters such as sealing gap,polar teeth width,polar teeth height,and polar teeth positions are calculated and analyzed respectively.Second,based on the formula for calculating pressure resistance,combine with the results of the finite element analysis,calculate the strength difference between the magnetic field of the seal under different parameters,and then judge the resistance capacity of different magnetic liquid sealing structures.Studies are obtained that the sealing gap and polar teeth width have a greater impact on the sealing resistance capacity of magnetic liquids,polar teeth height and polar teeth positions have less impact on the magnetic liquid sealing capacity.The sealing effect is best when the polar teeth shape is trapezoidal.Finally,through comparative analysis,select the optimal magnetic liquid sealing structure parameters,which provides theoretical basis for the study of magnetic liquid sealing resistance.

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• Influence of Structural and Material Parameters on the Reliability of Rotary Shaft Lip Seal
  HAN Zhao; ZHANG Fuying; WU Jihao; YANG Pengwei
  Abstract:A mixed lubrication numerical model of the oil seal sealing area was established using flow factor statistical methods.The finite element software was used to solve the model,and the influence of structural and material parameters on the reliability of oil seal was analyzed.The results show that within the range of parameters studied,the reliability of static sealing increases with the increase of waist thickness,waist length,air side lip angle,spring elastic modulus,and rubber hardness,but decreases with the increase of interference,oil side angle,and theoretical contact width.When the interference is 0.4 mm to 0.55 mm,the theoretical contact width is 0.3 mm to 0.6 mm,the oil side angle is 35°to 50°,the air side lip angle is 15° to 30°,the waist thickness is 1.0 mm to 1.3 mm,the waist length is 0.9 mm to 1.2 mm,the spring modulus is 1 175 MPa to 1 250 MPa,and the rubber hardness is 70HA to 85HA,it is beneficial to improve the reliability of the oil seal.Within this range of values,the reliability of dynamic sealing increases with the increase of interference,oil side lip angle,rubber material hardness,waist thickness,and theoretical contact width,while decreases with the increase of spring elastic modulus,waist length,and air side lip angle.

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• Preliminary Study on Friction Properties of SiC/PI System Using Liquid Crystals as Lubricant
  ZHANG Liang; GAO Xinlei; SHI Miaomiao; CHENG Yuwei; WANG Tingting
  Abstract:In order to explore the lubricating effect of liquid crystal as lubricant on the silicon carbide/polyimide(SiC/PI) rubbing pair system and the factors affecting the friction reduction performance of the system,monomolecular liquid crystal 4-cyano-4′-n-pentylbiphenyl（5CB）and mixed liquid crystal of 90% 5CB and 10% 4′-cyano-［1,1′-biphenyl］-4-yl 4-ethylcyclohexane-1-carboxylate(2CEPPN) were selected as lubricants respectively,and the tribological performances of the system were investigated by UMT-3 micro-friction tester.The results show that both the monomolecular liquid crystal and mixed liquid crystal have better friction reduction effects as lubricant on SiC/PI rubbing pair,and can even reach the superlubricity state.The mixed liquid crystal has better friction reduction effect than the monomolecular liquid crystal,it can achieve good friction reduction effects at low loads and high speeds,and can enable SiC/PI rubbing pair to achieve superlubricity for a long time.

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• Research Progress on Lubrication Mechanism and Applications of Carbon Quantum Dots as Lubricant Additives
  TENG Jiahuang; ZOU Shuai; PENG Maohui; HUANG Fuchuan
  Abstract:As a new type of zero-dimensional carbon based nanomaterial,carbon quantum dots are considered as a green and efficient lubricating material due to their small size,good designability,excellent biocompatibility,good dispersion and stability,multiple synthesis methods and low cost.Many studies have also confirmed the excellent tribological properties of carbon quantum dots as lubricant additives.The research progress on the lubrication mechanism and functionalization of carbon quantum dots as lubrication additives was reviewed,and the application status of carbon quantum dots as lubricant additives in water-based lubricants,lubricating oils,greases and hydrogels was summarized.The prospects and research directions of carbon quantum dots as new lubricating additives were suggested.Making full use of molecular dynamics simulation technology to explore the lubrication mechanism of carbon quantum dots as lubrication additives,while strengthening research on the versatility of carbon quantum dots,and exploring the compatibility between carbon quantum dots and other additives are the focus of future research.

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• Lubricity and Extreme Pressure Properties of the New Sulfuration Polyester in Deep Hole Drilling Cutting Oils
  XIONG Hongqi; HOU Haiyan; ZHANG Peng; DAI Enqi
  Abstract:The lubricity,wear resistance and extreme pressure of additives such as new sulfuration polyester and chlorinated paraffin in deep hole drilling cutting oil were compared by using four ball extreme pressure and wear resistance tests and tapping torque tests.The feasibility of replacing chlorinated paraffin with new sulfuration polyester in deep hole drilling cutting oil was explored.The results show that compared with chlorinated paraffin,new sulfuration polyester has excellent performance,which can effectively improve the lubricity,wear resistance and extreme pressure of cutting oil,and significantly enhance the sintering load of cutting oil.The new sulfuration polyester can effectively replace chlorinated paraffin as a chlorine free extreme pressure additive for deep hole drilling cutting oil.

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• Research on Optimization Method of PTFE Lip Seal Structure
  YANG Fang; ZHANG Haitao; FENG Tao; HUANG Hongyan; WANG Hu
  Abstract:Based on parametric modeling and neural network technology,an optimization method for double-lip oil seal structure was proposed.With the thickness of the sealing lip and the coordinates of the lip tip as design variables,the parametric model of the double lip oil seal was established.The optimal Latin hypercube sampling method was used to sample the design space and the finite element analysis was combined to carry out the design of experiment.The neural network was introduced to fit the response surface model and approximatively replace the objection function,the influence of each design parameter on contact pressure,radial force and equivalent stress was comprehensively analyzed.Taking the maximum contact pressure,the minimum equivalent stress and redial force as objectives,and using the optimization algorithm to find the optimal solution in the design space,a mathematical model was established for the optimization design of the double-lip seal.The results show that the contact pressure of the optimized oil seal is increased by 6.3% and the contact pressure distribution is more in line with the requirements of a good seal.Both the equivalent stress and radial force are significantly reduced,so as to improve the reliability of the oil seal.The improvement in the performance of the lip seal proves the effectiveness of this optimization method.

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• Design and Test of High Pressure Lubricating Oil Sensors
  SHI Yongsheng; WU Yukuan; ZHANG Bowen; TONG Guanju
  Abstract:The on-line monitoring of lubricating oil pollutants such as water,oxide and metal particles by oil quality sensor is of great significance to the normal operation of large industrial equipment.However,traditional lubricating oil sensor can not be used in many lubricating systems due to its low working pressure.A high-pressure multi-parameter lubricating oil sensor was designed,and taking the detection of water pollution in hydraulic oil as an example,the performance of the sensor under different pressures was tested.Repetitive experiments were conducted using an oil with a water content of 0.8%(mass fraction).It is found that the sensor can operate normally at the pressure range from 0 to 18 MPa,and there is a good linear relationship between the sensor output change and the lubricating oil pressure change.When the oil pressure remains stable,the sensor output has better stability.The sensor can normally detect the change of water content in high-pressure environment,and after high-pressure experiments,the sensitivity change of the sensor under normal pressure is less than 1%,indicating that the sensor has good pressure stability.

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