Grindability Evaluation of Ultrasonic Assisted Grinding of Silicon Nitride Ceramic Using Minimum Quantity Lubrication Based SiO_(2)Nanofluid

Minimum quantity Lubrication(MQL)is a sustainable lubrication system that is famous in many machining systems.It involve the spray of an infinitesimal amount of mist-like lubricants during machining processes.The MQL system is affirmed to exhibit an excellent machining performance,and it is highly economical.The nanofluids are understood to exhibit excellent lubricity and heat evacuation capability,compared to pure oil-based MQL system.Studies have shown that the surface quality and amount of energy expended in the grinding operations can be reduced considerably due to the positive effect of these nanofluids.This work presents an experimental study on the tribological performance of SiO_(2)nanofluid during grinding of Si_(3)N_(4)ceramic.The effect different grinding modes and lubrication systems during the grinding operation was also analyzed.Different concentrations of the SiO_(2)nanofluid was manufactured using canola,corn and sunflower oils.The quantitative evaluation of the grinding process was done based on the amount of grinding forces,specific grinding energy,frictional coefficient,and surface integrity.It was found that the canola oil exhibits optimal lubrication performance compared to corn oil,sunflower oil,and traditional lubrication systems.Additionally,the introduction of ultrasonic vibrations with the SiO_(2)nanofluid in MQL system was found to reduce the specific grinding energy,normal grinding forces,tangential grinding forces,and surface roughness by 65%,57%,65%,and 18%respectively.Finally,regression analysis was used to obtain an optimum parameter combinations.The observations from this work will aid the smooth transition towards ecofriendly and sustainable machining of engineering ceramics.

Fluorographene with Narrow Lateral Size and Thickness Distributions Prepared for Enhancing Lubrication Performance of Bentonite Grease

Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the lubricating performance of bentonite grease enhanced by the as-prepared FG.The results showed that the coefficient of friction and the wear volume of bentonite grease with 0.3 wt%FG were decreased by 20.4%and 44.9%,respectively,as compared to those of the base grease.The main reason is that FG can promote the formation of the tribo-chemical reaction film consisting of complex carbon oxide,Fe_(2)O_(3)and FeF_(3)on the friction surface,which can remarkably improve the performance of friction reduction and prevent the appearance of severe wear.

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.

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.

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.

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.

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%。

纤维材质对UHMWPE水润滑轴承复合材料摩擦学性能的影响

超高分子量聚乙烯(Ultra-high molecular weight polyethylene, UHMWPE)在水润滑轴承领域具有巨大的发展潜力,然而单一的UHMWPE难以满足水润滑轴承的耐磨性需求,尤其是在低速重载工况下.通过纤维改性的方法可以提高其摩擦学性能,但是纤维材质的不同特性对于复合材料摩擦学性能的影响存在差异.通过热压模具分别制备剑麻纤维(Sisal fiber,SF)、碳纤维(Carbon fiber,CF)和聚酯纤维(Polyester fiber,PETF)与UHMWPE混合的定向纤维复合材料,并与纯UHMWPE做对照试验.利用R-tec往复摩擦试验机模拟不同载荷(5和10 N)和不同速度(20、40和60 mm/s)下铜球与不同复合材料的摩擦过程,通过邵氏硬度和极限抗弯强度试验对复合材料力学性能进行表征测试,采用接触角测试复合材料的浸润性,试验结束后用扫描电子显微镜观察表面磨损形貌.结果表明:纤维的力学性能,尤其是硬度和抗弯强度是影响定向纤维复合材料摩擦学性能的关键因素,所添加纤维在复合材料中强有力的支撑作用使摩擦学性能显著提高,纤维的耐磨性和浸润性是次要因素.试验工况下,CF/UHMWPE摩擦系数最低,且在低速重载(载荷10 N,速度20 mm/s)时的摩擦系数与纯UHMWPE相比降低了36.92%;添加耐磨性强的PETF纤维后,复合材料磨损体积与纯UHMWPE相比降低了30.56%.

润滑条件对TC4钛合金切削加工影响的实验研究

为了研究冷却润滑条件及切削参数对TC4钛合金的切削力和表面粗糙度的影响,分别开展CMQL、冷风、浇注式冷却润滑条件的TC4钛合金高速切削实验、四种不同润滑环境的粗/半精/精加工实验以及CMQL条件下TC4钛合金正交切削试验,通过单因素分析和正交试验法研究冷却润滑条件及切削参数对切削加工性的影响。研究表明:CMQL冷却润滑条件可在TC4钛合金高速切削时有效降低切削阻力和改善表面粗糙度,并在高速精车削阶段体现出降低切削阻力的优势。考虑CMQL条件下高速精车TC4钛合金加工效率,最佳参数组合为较高的切削速度、较小的精加工余量和合适范围内较大的进给量。

基于红外光谱技术智能识别润滑油的研究进展

机器学习作为人工智能发展的核心,在各行业得到快速发展,近年来也成为润滑油领域研究的热点之一,标志着润滑油的研究不再局限于大规模的试验研究,高通量数据、机器学习、优化算法开始应用于润滑油的研究。文章介绍了基于红外光谱技术在润滑油种类鉴别、润滑剂筛选、润滑性能评估和润滑监测等方面的研究进展,并对未来基于红外光谱技术应用于智能识别润滑油的研究进行了展望。

航空发动机滑油系统LRU级故障树建模与分析

滑油系统是航空发动机的关键系统之一,一旦发生故障,严重影响飞行安全。滑油系统结构复杂,排故难度较大。对滑油系统进行LRU级故障树建模和分析,能够为快速定位LRU级故障源提供指导性建议。根据滑油系统工作原理、组成与运行特点,构建了以LRU级故障为底事件故障树模型,运用下行法求解故障树最小割集,采用不交化的最小割集表达式,计算滑油系统顶事件故障发生概率,以及滑油压力异常、油液污染、滑油消耗量大、滑油系统部件损坏等典型故障发生概率;在不交化最小割集矩阵中,与求顶事件概率相对应,分析LRU级故障树底事件概率重要度和相对概率重要度;通过概率重要度分析明确航空发动机滑油系统的易损部件,为日常维护与管理提供参考。

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。

中国润滑油行业现状及发展趋势分析

随着我国经济的持续增长,世界各大润滑油企业都将我国润滑油市场作为其重点发展的区域,国内市场已形成跨国润滑油公司,中国石化,中国石油和地方民营润滑油企业相互竞争的格局,行业竞争日益激烈,如果润滑油企业不能抓住机遇并及时提升竞争力以应对更为激烈和复杂的市场竞争,产品的市场占有率和盈利水平将面临下降的风险。从基础油,添加剂及市场方面对中国润滑油行业的现状及发展趋势进行了分析。目前国外品牌依然占据我国润滑油的高端市场,但随着我国润滑油技术的进步,国内品牌润滑油正在逐渐取代国外品牌润滑油的垄断地位,市场占有率不断提升,预计在未来的5年内,我国自主润滑油的国内市场占有率将达到65%,将实现润滑油品牌的战略化转移。

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。

PEG/PPG共聚醚酯的制备及其润滑性能

聚醚类基础油一般通过环氧化物的开环聚合反应制备,但由于环氧化物易燃易挥发的特性,对安全生产要求较为严苛。为解决上述问题,以氯化亚锡为催化剂,聚乙二醇、聚丙二醇和琥珀酸共缩聚后脱酸制备共聚醚酯,并通过红外光谱、核磁共振和凝胶渗透色谱对其结构和相对分子质量进行表征。利用运动黏度测试仪、四球摩擦试验机和3D白光干涉仪对共聚醚酯的黏温特性和润滑性能进行考察。结果表明:所制备的聚醚酯在40℃下运动黏度约为170 mm^(2)/s,黏度指数可达220左右;在392 N、30 min、1450 r/min条件下,四球试验钢球磨斑直径为0.55 mm,平均摩擦因数为0.057,说明聚醚酯的减摩效果显著优于商用基础油。