外加电场作用下双电层电粘度对水润滑特性的影响

根据双电层理论,建立了外电场作用下流体润滑中的双电层引起的电粘度效应的数学模型,并通过组合滑块水润滑试验考察了双电层的电粘度效应对流体润滑性能的影响。结果表明,外加电场作用下,双电层电粘度效应对摩擦因数具有明显影响;当速度较低时,随着外加电压的增加,摩擦因数明显增大;随着速度的增加,摩擦因数增大幅度减小;试验结果同所建立的数学模型相符。     

薄膜油润滑中电粘度效应影响研究

利用组合滑块油润滑试验考察了双电层的电粘度效应对薄膜润滑性能的影响，采用施加外加电场和添加添加剂两种方法以改变润滑剂中离子浓度进行试验研究。结果表明：双电层引起的电粘度效应对摩擦因数有明显影响，摩擦因数随着外加电场的增强而变大，当外电场增大到一定程度时摩擦因数开始减小；在离子浓度较小时，摩擦因数随着离子浓度的增加而增大，当离子浓度增大到一定程度时摩擦因数开始减小。     

薄膜润滑中双电层效应影响分析

根据Poisson—Boltzmann双电层理论,详细推导了润滑区中双电层产生的流动电场,并进一步建立了考虑双电层电粘度效应的薄膜润滑数学模型。然后,对润滑中双电层效应进行了数值分析,对不同的电粘度公式进行了比较,结果表明薄膜润滑中,双电层的电粘度效应使流体粘度显著增加,同时润滑膜厚也明显增加。     

离子双电层动态输运特性及电场对液体油膜压力的影响

随着流体动压润滑向纳米尺度发展,离子双电层对润滑性能的影响不能忽视。考虑到润滑过程中摩擦副相对速度是可变的,提出一种考虑离子动态输运特性与流场及电场耦合的离子双电层润滑模型,分析摩擦副相对运动速度和Zeta电势差对润滑膜的影响。分析结果表明：摩擦副相对运动造成了电势不均衡分布,平衡电势偏向于运动壁面Zeta电势,且相对速度的增大加剧了不均衡性;Zeta电势差对润滑液体承载能力影响显著,当Zeta电势差从0开始增大时,双电层电黏度效应及润滑液体承载能力先增大后减小。提出的模型实现了速度可变的双电层润滑瞬态仿真,为变工况下的双电层润滑性能分析奠定理论基础。     

提升机盘形制动器闸瓦材料摩擦性能实验研究

用XDZ-A型摩擦材料制样机将石棉闸瓦材料制备成试验所需的标准试样,用X-DM型调压变速摩擦试验机模拟实际工况,对标准试样开展不同正压力、不同滑动速度和多种温度下的组合实验,全面研究了石棉闸瓦材料与16Mn钢摩擦盘对磨的摩擦学特性。实验结果表明:随着正压力、滑动速度和温度的变化,闸瓦材料摩擦因数均发生变化;摩擦因数随正压力的升高而增大,随滑动速度的增加而减小,但滑动速度对摩擦因数的影响大于正压力的影响;摩擦因数随温度的升高而减小,在200℃左右,摩擦因数下降比较明显。     

双粗糙面滑动过程摩擦因数的变化分析

采用W-M函数建立具有分形特征的三维双粗糙面接触模型,考虑了接触界面间的黏着效应,在滑动速度、法向载荷及界面剪切强度等参数变化下,运用有限元方法探讨了粗糙体在滑动过程中摩擦因数的变化情况。结果显示,滑动速度、法向载荷及界面剪切强度等参数对摩擦因数的变化有一定的影响,边界润滑工况下平均摩擦因数为0.28,无润滑工况下平均摩擦因数为0.713,最大界面剪切强度时的平均摩擦因数为0.73;随着界面剪切强度的减小、法向载荷的增大、滑动速度的增加,滑动摩擦因数有所减小。与相关文献结论或实验结果进行比较,证明了上述结果的正确性。分析结果可为摩擦学设计和摩擦材料的制备提供理论参考。     

工艺参数对铝合金板筋摩擦因数的影响

利用自行研制的新型摩擦测试装置,对铝合金板成形过程拉深筋部位摩擦因数进行了测试实验.探讨了压边力、拉延速度、润滑状态等3种工艺参数对拉深筋部位摩擦因数的影响.实验结果表明,在润滑状态下,摩擦因数随拉延速度的增加先增大后减小,随压边力的增加先减小后增大;在无润滑状态下,虽然在拉延初期摩擦因数随拉延速度的增加呈不规则变化,但是当拉延速度达到9 mm/s以后摩擦因数随拉延速度的增加而减小,随压边力的增加先增大后减小.在某些条件下,润滑状态下的摩擦因数反而比无润滑状态下的大,主要原因是润滑油膜对铝合金板与模具表面之间有较大的吸附力.     

浸渍石墨配对9Cr18密封摩擦副的摩擦特性

针对无压喷油运行工况下机械密封端面磨损严重问题,基于多功能摩擦磨损试验机开展浸呋喃树脂石墨M180K和浸锑石墨M181D配对9Cr18金属环的摩擦磨损试验。探讨操作工况参数轴向载荷和线速度对浸渍石墨摩擦因数和摩擦扭矩两摩擦特性参数的影响,对比研究不同摩擦状态下线速度对两摩擦特性参数的影响,并基于三维形貌仪采集2种浸渍石墨试验前后的表面形貌。结果表明：低黏油润滑工况,一定范围内提高pv值有助于减小浸渍石墨摩擦因数,但轴向载荷的增加提高了摩擦扭矩;而较大轴向载荷时,增加线速度有助于减小摩擦扭矩;相同操作工况和摩擦状态下,浸锑石墨摩擦因数显著小于浸呋喃树脂石墨对应值且表面磨损轻微;相比而言,浸锑石墨的耐磨性更优异,更适用高参工况。     

Ag膜在干摩擦、油和脂润滑下的摩擦学性能研究

精密运转部件表面沉积一层软金属银和银基固体薄膜可以有效地降低摩擦、减小磨损。通过钢球/镀Ag膜摩擦盘在干摩擦、4122油和L252脂润滑条件下的球-盘摩擦学试验,研究Ag膜在油和脂复合润滑下的摩擦学性能,分析润滑条件、载荷、速度对Ag膜摩擦因数的影响。试验结果表明:在4 N法向载荷和油、脂润滑下,与干摩擦相比,镀Ag膜摩擦副的最大静摩擦因数分别减小了10.7%和6.1%;在0～2 000 r/min转速范围内,Ag膜摩擦因数随转速增加而减小,与干摩擦相比,油润滑下Ag膜摩擦因数减小9%～48%,脂润滑下Ag膜摩擦因数减小17%～52%。Ag膜在干摩擦、4122润滑油和L252润滑脂复合润滑下,摩擦因数均随载荷增加而降低;Ag膜摩擦副/钢球在油、脂复合润滑下启动摩擦力矩小,摩擦副在宽转速范围内摩擦因数变化小,运转平稳。     

内衬厚度对水润滑橡胶艉轴承摩擦性能的影响

基于流固耦合的基本理论,考虑橡胶衬层弹性变形因素,构建出水润滑艉轴承橡胶内衬有限元模型,利用MATLAB软件数值分析橡胶内衬厚度对水膜厚度和水膜压力的分布状况及摩擦性能的影响规律,并在SSB-100型艉轴承试验机上进行试验验证。研究结果表明:在相同的工况下,随着内衬厚度的增加,橡胶衬层弹性变形增大,水膜厚度增大,水膜压力减小;相应地,流体润滑效果越好,摩擦因数越小;在相同厚度下,随着转速的增大,摩擦因数先减小后趋于平稳。试验结果验证了仿真分析的正确性。     

Theoretical analysis and experimental study on the influence of electric double layer on thin film lubrication

A new mathematical model for thin film lubrication is established by taking into account the effect of an electric double layer. In the present paper, experiments are carried out on a self-made tester. With a composite block and a rotating disk, influence of electric double layer on thin film lubrication is studied. Two different methods are used to reconstruct the field of electric double layer so as to change its effect. One is to change the ionic concentration of lubricants by adding additives, and the other is to apply an external electric field on friction pairs. According theoretical analysis, both the methods will apparently change the electro-viscosity of the lubricant film so as to change the lubrication performances. After theoretical calculation of electro-viscosity is amended according to the experimental results, the equations of electro-viscosity are presented. The results show that the equivalent viscosity of fluid induced by the effect of electric double layer apparently increases with the decrease of thickness of the film while the lubrication film is thin enough. The effect of electro-viscosity is weakened as the thickness of the film increases. Moreover, the effect of electro-viscosity increases with the increase of external electric field at first. When the voltage reaches a certain value, the electro-viscosity begins to decrease. __________ Translated from Tribology, 2005, 25(6) (in Chinese)     

润滑液对电控摩擦的影响研究

研究了二氧化硅/黄铜摩擦副在不同水基润滑液中的摩擦行为对外加电场的响应,发现中性的盐类水溶液做润滑液时外加电压使摩擦副的摩擦因数大幅增加。不同的盐溶液做润滑液时,摩擦因数对外加电压的响应速度不同,其中溶解度高的长链有机钠盐溶液做润滑液时二氧化硅/黄铜的摩擦因数对电场的响应速度快且稳定性好。而碱类和酸类溶液做润滑液时,外加电压使二氧化硅/黄铜摩擦副的摩擦因数减小。     

Complementary effects of solid lubricants in the automotive brake lining

An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb₂S₃). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test.     

外加电场对3种陶瓷/金属摩擦副摩擦行为的影响

使用自制面接触往复式滑动摩擦磨损实验机,采用质量百分比浓度为１％的硬脂酸锌水基乳化液作为润滑剂,研究了边界润滑状态下外加直流电场的几处施加方式对３种摩擦副在低速滑动时摩擦行为的影响。实验结果显示,外加电压的存在显示地改变了３种摩擦副的摩擦系数以及摩擦系数曲线的平稳程度,摩擦系数是最大相对增加量和最大相对减少量分别达到２００％和４０％。摩擦系数的改变与外加直流电压的通断是对应的,不同摩擦副对电压接通     

Modeling and analysis of interfacial electro-kinetic effects on thin film lubrication

At the interface between a solid and a following liquid, charge migration within the electric double layer causes an electro-viscous force to develop which manifests itself as an enhanced fluid viscosity. Based on the Poisson–Boltzmann equation, a new mathematical model of the electro-viscosity is developed. Numerical analysis is carried out taking into account the influence of the electric double layer on thin film lubrication. Analysis results show that the electro-viscosity leads to a significant increase in the film thickness in the thin film regime (below 100 nm).     

材料摩擦因数的可控性研究

在边界润滑状态下采用轴承钢、黄铜等不同摩擦副材料，对一些通用和特殊润滑材料在外加电场作用下摩擦因数的变化进行试验研究，探讨了它们的摩擦控制性能。结果表明：尽管外加电场都能改变这些润滑剂的摩擦因数，但只有BH－1型铁磁流体具有比较理想的摩擦控制性能，说明摩擦可控性并不是润滑材料普遍具有的性质。     

EXPERIMENTAL EVALUATION OF FRICTION COEFFICIENT AND LIQUID NITROGEN LUBRICATION EFFECT IN CRYOGENIC MACHINING

Cryogenic machining is considered an environmentally safe alternative to conventional machining where cutting fluid is used. However, the improved machinability in cryogenic machining has been attributed to the cooling effect of liquid nitrogen (LN2) in past research. Our recent studies indicate that LN2 may possess a lubrication effect in machining, as evidenced by a reduction of tool wear, the apparent coefficients of friction calculated by a mathematical model, and the secondary deformation in chip metallurgy. However, there is a need for a direct proof of LN2's lubrication effect before it can be claimed to be a lubricant in cryogenic machining. This paper presents the methodology and data from an experiment that measures the normal force and friction force directly in an altered machining setup. This procedure simulates the pure frictional behavior of the tool-chip interface in cryogenic cutting. The results show that LN2 cooled condition has a significantly lower coefficient of friction than dry conditions in all cases. The data also shows that the friction is lower for Ti-6Al-4V but mixed results obtained for mild steel AISI 1018 when LN2 is applied properly as in the experiment setup as compared to traditional emulsion flooding. Based on the unique pattern of the friction behavior in the sliding tests, possible lubrication mechanisms using liquid nitrogen are proposed.