Tribological Mechanism of Graphene and Ionic Liquid Mixed Fluid on Grinding Interface under Nanofluid Minimum Quantity Lubrication

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.

Tribological Performance of Different Concentrations of Al_(2)O_(3)Nanofluids on Minimum Quantity Lubrication Milling

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.

Effect of Surface Roughness on Lubrication Performance of Bump-Type Gas Foil Bearings

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.

Achieving oxidation protection effect for strips hot rolling via Al_(2)O_(3) nanofluid lubrication

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.

Multifunctional Lubricant Additive Improves Lubrication and Antioxidation Properties of Tung Oil

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.

Assessment of Lubrication Property and Machining Performance of Nanofluid Composite Electrostatic Spraying(NCES)Using Different Types of Vegetable Oils as Base Fluids of External Fluid

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.

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

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

矩形沟槽结构参数对水润滑轴承润滑性能的影响

为了研究矩形沟槽结构参数对水润滑轴承弹流润滑性能的影响,建立水润滑轴承流固耦合(FSI)分析模型,采用有限元法,通过比对轴承周向水膜压力、最大水膜压力、摩擦系数、承载力、偏位角和轴承最大径向变形等参数,阐述了矩形沟槽结构参数对轴承润滑性能的变化规律。结果表明,沟槽宽度或深度越大的轴承,其承载性能越差。通过合理调整沟槽的宽深比,可以有效地改善轴承的润滑状态。在相同流水槽总断面积下,沟槽宽深比过大或过小均不是轴承弹流润滑的最好状态,沟槽宽度对轴承承载性能的影响要高于沟槽深度对轴承的影响。

利用SRV试验机研究温度对润滑剂摩擦学性能的影响

介绍了一种自行研究建立的测定润滑剂抗擦伤失效温度的试验方法,这是摩擦学领域性能评价的一个新发展。利用该试验方法评价了几种润滑剂摩擦因数随温度变化的情况并确定抗擦伤失效温度,对典型样品摩擦学性能随温度变化的情况进行了机理探讨,以期为相关润滑剂研发人员提供帮助和指导。

粗糙度和轴向运动对艉轴承混合润滑性能的影响

针对大型船舶航行过程中出现船体变形时艉轴承的磨损状态异常这一问题,本文探究磨损表面粗糙度变化和轴向运动对于艉轴承混合润滑性能的影响,建立了耦合轴向运动和表面粗糙度的混合润滑模型,通过数值模拟得到轴承润滑特征的分布,分析轴向运动和粗糙度对轴承混合润滑特性的影响,并对该润滑模型进行验证。计算结果表明:在轴向运动和轴颈倾斜耦合作用下,油膜厚度沿轴向方向非线性减小,油膜压力和接触压力在局部出现峰值,轴瓦在局部出现较大变形;轴向速度增加会加强动压润滑效应,轴向运动对润滑特性的影响程度随着倾角的增大而增加;粗糙度越大承载能力越强,同时接触情况越严重,会加速轴承的局部磨损。

聚(桐油-甲基丙烯酸甲酯)多功能润滑油添加剂的合成

以桐油(TO)、甲基丙烯酸甲酯(MMA)为原料,偶氮二异丁腈(AIBN)为引发剂,采用Schlenk装置合成了聚(桐油-甲基丙烯酸甲酯)(PTOM)共聚物。采用红外光谱(FT-IR)和核磁共振氢谱(1H NMR)表征了共聚物的结构,利用凝胶渗透色谱仪(GPC)测定了共聚物的相对分子质量及其多分散性指数,利用热重分析仪(TGA)测定了共聚物的热稳定性,并对共聚物的降凝、增黏和抗磨性能进行了评价。结果表明:当桐油与甲基丙烯酸甲酯质量比为1.5∶8.5、引发剂用量为1.0%(在单体中的质量分数)、反应温度为80℃、反应时间为6 h时,共聚物的收率较高(44.99%),其重均相对分子质量为28289。润滑油馏分(350~395℃)中添加质量分数0.8%的共聚物时,可将其凝点(T_(SP))降低6℃,将磨斑直径降低0.314 mm;添加质量分数0.5%的共聚物时,可将其黏度指数(VI)提高69。所合成的聚(桐油-甲基丙烯酸甲酯)可作为一种具有良好降凝、增黏和抗磨性能的多功能润滑油添加剂。

MoSe_(2)/石墨烯-不锈钢自润滑材料的减摩机理

为克服不锈钢摩擦副零件摩擦因数大、易磨损的不足,利用粉末冶金不锈钢基体贯通孔隙特征和异质结纳米润滑剂超滑效应,采用真空浸渍和水热合成两步法工艺制备出了MoSe_(2)/石墨烯-不锈钢自润滑材料,并对其摩擦学特性与减摩机理进行了研究。研究发现:摩擦过程中,加入到基体孔隙的MoSe_(2)/石墨烯异质结润滑剂在摩擦表面形成了均匀润滑膜,显著减小了摩擦副的摩擦因数和磨损率。在常温、载荷40 N、转速100 r/min工况下,MoSe_(2)/石墨烯-不锈钢自润滑材料的摩擦因数低至0.106,磨损率降至6.45×10^(-5)mm^(3)/(N·m),与不锈钢基体相比,其摩擦因数和磨损率分别降低了86%和93%。

石墨烯纳米颗粒润滑性能分子动力学分析

文中为了研究基础油液蓖麻油中加入石墨烯纳米颗粒后蓖麻油的润滑性能改变情况,运用分子动力学知识和LAMMPS仿真软件进行了粒子数密度、粒子径向分布势函数及热导率分析,同时探究了混合石墨烯的蓖麻油对切削加工后材料表面的形貌影响。仿真和试验结果表明:石墨烯纳米颗粒具有亲油性,蓖麻油分子在石墨烯周围呈层状分布,形成润滑油膜,此油膜具有良好的导热性和抗压性,以及良好的润滑效果,石墨烯的加入改善了蓖麻油的润滑性能。

分形粗糙面的主轴承弹流脂润滑分析

为探究弹性流体动压润滑(弹流润滑)状态下RV减速器主轴承接触表面之间的润滑特性,基于润滑脂的非牛顿特性以及粗糙表面分形理论,提出一种主轴承的点接触弹流脂润滑数值模型。首先,对该模型进行数值求解,得到脂膜压力、脂膜厚度的分布规律;然后,将其分别与其他点接触弹流润滑模型的数值结果和实验结果进行对比,验证了所建模型的正确性;最后,分析了主轴承表面光滑和粗糙状态下流变指数、分形维数、卷吸速度、载荷和润滑脂黏度对润滑性能的影响。结果表明:润滑脂的非牛顿性越明显,脂膜厚度越小且颈缩现象愈加不明显,接触区附近脂膜压力越符合赫兹压力分布,二次压力峰逐渐消失;考虑主轴承分形粗糙表面的弹流润滑特征更切合实际,增大分形维数,接触区真实接触面积增大,有利于降低脂膜压力,增加脂膜厚度;卷吸速度、载荷和润滑脂黏度对脂膜厚度分布的影响显著,对脂膜压力分布的影响较小;脂膜厚度以及最小膜厚越大,主轴承接触区脂膜不易破坏且越容易形成动压润滑。

医用介入导丝用疏水和亲水涂层的研究进展

医用介入导丝被广泛应用于各类介入手术,是目前经皮冠状动脉成形(PTCA)术及经皮血管成形术(PTA)中常用的医疗器械之一。在医用介入导丝表面添加亲水或疏水涂层,可以减小导丝在临床应用中的组织摩擦和组织损伤,有效提高导丝的通过性、抗菌性和生物相容性,减少炎症。综述了近年来国内外医用介入导丝亲水和疏水涂层材料,介绍了这些涂层的机理、附着力优化、抗菌修饰等方面内容,重点介绍了聚四氟乙烯、聚乙烯吡咯烷酮、聚丙烯酰胺、聚乙二醇、聚对二甲苯等涂层材料体系的研究进展,介绍了不同材料体系在医用导丝亲水和疏水涂层的作用机理和实际应用,同时介绍了亲疏水涂层的制备工艺,重点阐述了层层自组装、紫外光接枝、等离子体接枝和化学气相沉积等制备方法的可操作性、优势和劣势。最后在总结前人研究成果的基础上,对医用介入导丝涂层的现状及面临的问题进行了探讨,并对医用介入导丝涂层的发展方向及提高涂层综合性能等方面进行了展望。

二硫化钼自润滑涂层性能及制备工艺的研究进展

MoS_(2)是过渡族金属二硫化物中的一员,其涂层材料因独特的层状结构而表现出优异的摩擦学性能。MoS_(2)自润滑涂层在刀具以及空间部件材料的表面减磨和保护上发挥着重要作用,但是MoS_(2)涂层对湿度的敏感性、附着力差以及耐磨寿命有限等问题限制了其应用。国内外学者在MoS_(2)涂层的摩擦学研究上做了大量工作,目前的研究重点主要是不同温度、湿度、气体介质的多环境下的摩擦学行为分析,以及通过纳米多层体系的设计实现对晶体结构的可控。本文概述了2010年以来有关MoS_(2)自润滑涂层材料的研究进展,主要综述了MoS_(2)自润滑涂层的摩擦学性能以及不同元素掺杂对其性能和结构的影响。总结了MoS_(2)涂层的组成结构、性能、制备工艺,并对其在表面润滑领域的研究和应用前景进行了展望。本文对MoS_(2)自润滑涂层的研究和工程应用具有参考意义。

复合纳米自润滑金刚石砂轮磨削SiC陶瓷的试验研究

提出一种复合纳米自润滑金刚石砂轮的制备方法,并对制备的砂轮进行SiC陶瓷的磨削试验,分析砂轮表面不同质量分数的复合纳米颗粒对磨削性能的影响。使用MoS2、TiO2纳米颗粒作为自润滑砂轮基底的填充材料,采用复合纳米自润滑金刚石砂轮和传统金刚石砂轮进行磨削对比试验,研究复合纳米自润滑金刚石砂轮的润滑机制。研究结果表明,复合纳米自润滑金刚石砂轮自释放的纳米颗粒有效地参与了磨削区间的润滑,砂轮的法相力、切向力降低,提升了工件表面质量。在磨削深度为2~8μm内,复合纳米自润滑金刚石砂轮的具体表现为法向磨削力降低18.6%~38.7%、切向磨削力降低11.2%~28.6%,工件表面粗糙度降低13.9%~41.5%。根据本试验所得数据,当砂轮表面复合纳米颗粒质量分数为8%时,润滑性能和工件表面质量最佳。

浸渍石墨材料在不同法向载荷下的磨损性能研究

研究不同摩擦体系下法向载荷对浸渍石墨的摩擦磨损特性的影响,采用扫描电子显微镜和激光共聚焦显微镜分别表征摩擦表面磨痕形貌、磨痕轮廓,对浸渍石墨与对偶球(GCr15钢球和Si_(3)N_(4)陶瓷球)的摩擦磨损情况与机制进行评估分析。结果表明:磨损痕迹随着施加载荷的增加而加深加宽,磨损率与法向载荷呈负相关,而摩擦因数、磨损体积则与法向载荷呈正相关;小载荷作用下石墨的磨损机制为黏着磨损和磨粒磨损,大载荷下则主要表现为黏着磨损、氧化磨损以及疲劳磨损;GCr15/石墨摩擦副相比于Si_(3)N_(4)/石墨摩擦副磨损率较低,在摩擦过程中形成完整、连续性更好的“第三体”转移膜减轻了磨损,对石墨基体起到保护作用。

斜齿轮啮合弯矩对风电齿轮箱行星轮滑动轴承瞬态润滑性能影响分析

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以系统观念推进合成润滑油脂发展的思考

随着中国式现代化建设的推进,“双循环”新发展格局的形成,设备用润滑油呈现高端化、绿色化、长寿命化发展趋势,合成润滑油脂发展迎来了国产化替代机遇和高端增长机遇。本文运用系统观念的基础性思想和工作方法,对中国石化合成润滑油脂业务发展现状进行了分析,就推进合成润滑油脂前瞻性技术创新、产业链贯通式开发、全面润滑管理服务、全价值链管理、全产业链发展提出了措施和对策。