缠绕提升钢丝绳微动摩擦试验研究

为了掌握多绳多层缠绕提升钢丝绳层与层之间微动摩擦磨损机制,设计矿井提升机钢丝绳综合摩擦试验台,在其缠绕提升机钢丝绳摩擦试验装置上开展滑动摩擦试验,以6×19+FC热镀锌钢丝绳为研究对象,探究不同接触载荷、接触角度下钢丝绳滑动摩擦磨损规律及钢丝绳摩擦接触处温升变化规律。研究结果表明：钢丝绳滑动摩擦因数随时间经历了快速增长阶段、缓慢递增阶段和平稳波动阶段;摩擦因数随着载荷增加先减小后增大,在250 N时最低为0.59,但摩擦因数随载荷变化范围不大,维持在0.68左右;摩擦因数随接触角度的增大先迅速增大后呈缓慢增长趋势,最终稳定为0.58,其中接触角度为45°时摩擦因数最小,仅为0.15;钢丝绳滑动摩擦温升集中在接触区域内,接触点温升随着接触角度的增加而增加,最高温升为8.5 ℃,随载荷的增加呈先减小后增大最后减小的波浪形变化趋势,最高温升为10.4 ℃。     

接触角与接触载荷对缠绕提升钢丝绳摩擦特性的影响

为了掌握多绳多层缠绕提升钢丝绳层与层之间微动摩擦磨损机制,设计矿井提升机钢丝绳综合摩擦试验台,在其缠绕提升机钢丝绳摩擦试验装置上开展滑动摩擦试验,以6×19+FC热镀锌钢丝绳为研究对象,探究不同接触载荷、接触角度下钢丝绳滑动摩擦磨损规律及钢丝绳摩擦接触处温升变化规律。研究结果表明:钢丝绳滑动摩擦因数随时间经历了快速增长阶段、缓慢递增阶段和平稳波动阶段;摩擦因数随着载荷增加先减小后增大,在250 N时最低为0.59,但摩擦因数随载荷变化范围不大,维持在0.68左右;摩擦因数随接触角度的增大先迅速增大后呈缓慢增长趋势,最终稳定为0.58,其中接触角度为45°时摩擦因数最小,仅为0.15;钢丝绳滑动摩擦温升集中在接触区域内,接触点温升随着接触角度的增加而增加,最高温升为8.5℃,随载荷的增加呈先减小后增大最后减小的波浪形变化趋势,最高温升为10.4℃。     

双粗糙面滑动摩擦热力耦合有限元分析

建立了双粗糙分形表面滑动摩擦的热力耦合模型,综合考虑了随温度变化的材料性能、材料的弹塑性变形及摩擦副的磨损失效等因素,以摩擦材料的性能参数及设定的材料损伤参数为实例对双粗糙分形表面滑动摩擦全过程的温度场、应力场及磨损进行了数值模拟,分析得到了滑动摩擦过程中摩擦界面最高接触温度、接触应力的分布、磨损率及其变化规律,实现了对双粗糙面摩擦磨损情况的模拟及预测。     

双粗糙接触模型的表面温度在滑动摩擦过程中变化分析

建立三维双粗糙体分形表面的热力耦合接触模型,在固定滑动速度工况下综合考虑了钛合金材料的磨损失效、界面粘着及接触过程中的热力耦合,动态探讨了粗糙体在滑动过程中接触表面的温度变化情况。运用有限元方法对滑动过程的温度场进行模拟仿真并得出:滑动摩擦初始时刻摩擦表面接触温度急剧上升,随着滑动距离的增加,最高接触温度处于波动状态;界面剪切强度越大,最高温度越高。通过研究接触表面的温度场分布情况,以探索滑动过程钛合金材料摩擦磨损的真正起因。将结果与相关文献实验进行比较,得出了模拟仿真的合理性。     

材料光谱发射率精密测量装置

采用光栅单色仪方案研究了光谱发射率的测量装置,以加热方式将材料样品温度控制在473～1 000 K,可在2～15 μm测量样品的定向光谱发射率.应用锁相放大技术和统计测量方法提高样品与黑体的辐射亮度比较测量的信噪比.对测量装置性能进行了评价实验,并提出一种双黑体法评价光谱辐射测量系统的线性度.测量了氧化不锈钢样品和高发射率涂料的光谱发射率并进行了不确定度评定,合成标准不确定度小于0.04.     

表面润湿性对橡胶滑动接触界面摩擦特性的影响

针对橡胶滑动接触界面,利用自主研制开发的光学原位观测线性往复式摩擦试验机,通过控制蒸馏水与添加剂的配比,对不同润湿性液体润滑条件下的橡胶滑动摩擦过程进行了试验性探究,在此基础之上建立了固-液接触角与橡胶滑动摩擦因数之间的关联性,以期从微观界面润湿的角度解释湿滑条件下橡胶滑动摩擦因数变化的原因。研究表明:当润滑液进入橡胶滑动接触界面时,橡胶的黏滞效应大幅度降低,导致摩擦因数出现断崖式下跌,稳态摩擦因数减小;随着添加剂配比的降低,固-液接触角逐渐增大,润滑液在固体表面上的铺展与润湿性变差,润滑作用减弱,稳态摩擦因数逐渐增大。另外试验结果分析表明,固-液接触角与稳态滑动摩擦因数具有一定的线性相关性(R~2≈0.92),摩擦因数随着接触角的增大而增大。     

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。     

高分子材料齿轮的热力耦合模型及接触界面瞬态温度场数值分析

基于高分子复合材料齿轮啮合传动过程的热力学分析和动力学分析,建立了其热力耦合模型,研究了齿轮本体温升和摩擦界面瞬态温升的变化规律。采用有限元软件LS-PrePost对齿轮进行摩擦热仿真分析,分析了影响分子复合材料齿轮啮合传动过程温升场分布的主要因素;并采用红外线热像仪对本体温升和瞬时温升进行实时测量。结果表明,摩擦因数越大,本体温升变化越显著,随着外载G的增大,接触界面瞬时温升变大,理论计算值与实测值基本吻合。     

超声波电动机接触界面梯度设计模型

超声波电动机是依靠定转子接触界面间的摩擦传递动力的新型驱动器,摩擦材料作为接触界面的重要组成部分,它的设计和磨损控制是超声波电动机的关键问题.建立一个超声波电动机定转子简化接触模型,研究摩擦材料磨损对定转子接触参数与驱动摩擦力的影响,得出保持接触宽度稳定时,摩擦材料磨损后应具有的性能,提出设计超声波电动机梯度摩擦材料的构想,并建立梯度摩擦材料理论结构模型.模拟分析表明:超声波电动机摩擦材料的弹性模量应具有在法向上由表及里呈现梯度递减的趋势,可保持定转子接触宽度的稳定,维持超声波电动机输出性能,延长超声波电动机性能寿命,为超声波电动机摩擦材料选择与研究开辟新领域.     

基于双波段比能量法的非接触测温系统的研究

为实现表面发射率未知但稳定的材料的中高温(300～550℃)温度的精确测量,提出了一种双波段比能量测温法,并基于该方法设计了一套非接触测温系统。非接触测温系统选用工作波段为0.9～1.65μm和5.5～14.5μm的红外辐射传感器,传感器将2个波段的能量信号转化为电压信号,并将电压信号做比值,得到和温度相关的K因子,使用面源黑体炉和金属样板对系统进行标定及测试。实验结果表明:使用双波段比能量测温法的非接触测温系统不需要知道目标发射率,也能较为精确地得到中高温物体的真实温度,且温度误差在10℃以内。基于该方法的非接触测温系统对中高温物体真实温度的精确测量具有重要的研究意义。     

Frictional performance of lithium 12‐hydroxystearate greases with different soap fibre structures in sliding contacts

The effect of the fibre structure of the grease on the frictional performance of lithium 12‐hydroxystearate greases with different fibre lengths was investigated in face, line, and point contact sliding tests. At high sliding speeds where the lubrication regime was practically hydrodynamic, the coefficient of friction of the base oil alone was lower than that of the greases. The coefficient of friction was roughly estimated as follows: base oil < long‐fibre grease < medium‐fibre grease < short‐fibre grease. The supply or replenishing capability of the grease played a critical role in maintaining hydrodynamic lubrication. At high contact pressures, the short‐fibre grease was superior in frictional performance to the long‐fibre grease due to the firm fibre network structure of the latter. In mixed and boundary lubrication regimes, the greases were superior in frictional performance to the base oil, since the soap fibres of the greases had a superior load‐carrying capacity. The long‐fibre grease, with a firm fibre structure, offered better frictional performance than the short‐fibre one.     

Friction torque in grease lubricated thrust ball bearings

Thrust ball bearings lubricated with several different greases were tested on a modified Four-Ball Machine, where the Four-Ball arrangement was replaced by a bearing assembly. The friction torque and operating temperatures in a thrust ball bearing were measured during the tests. At the end of each test a grease sample was analyzed through ferrographic techniques in order to quantify and evaluate bearing wear.A rolling bearing friction torque model was used and the coefficient of friction in full film lubrication was determined for each grease, depending on the operating conditions.The experimental results obtained showed that grease formulation had a very significant influence on friction torque and operating temperature. The friction torque depends on the viscosity of the grease base oil, on its nature (mineral, ester, PAO, etc.), on the coefficient of friction in full film conditions, but also on the interaction between grease thickener and base oil, which affected contact replenishment and contact starvation, and thus influenced the friction torque.     

Consequence of contact local kinematics of sliding bodies on the surface temperatures generated

When studying contact with friction between two bodies, it is not possible to obtain data on real contact conditions on the basis of steady-state situations. Indeed, contacts with friction usually lead to dynamic instabilities generated at the contact interface. It is therefore necessary to take into account contact dynamics in order to better understand the phenomena involved during sliding with friction. The explicit dynamic finite element code PlastD in 2D is used to simulate the contact between two bodies. A constant Coulomb friction coefficient is imposed at the interface. The simulations carried out permitted identifying local contact conditions (kinematics, tribological state, stresses, etc.). They revealed that different instability regimes can be generated (stick–slip, slip–separation, stick–slip–separation, etc.). Local contact stresses and the sliding velocity oscillate through time when instabilities are generated and their maximum values can be much higher than those expected for steady-state conditions. The aim of this paper is to analyse the frictional instabilities and their consequences on the heat generated in the contact. First, the influence of the different instability regimes is studied on a simple contact. Then, an industrial mechanism is studied (wheel–rail contact) to investigate the influence of local contact conditions on the temperature of the rail surface.     

Contact and thermal analysis of an alumina—steel dry sliding friction pair considering the surface roughness

In the present study, finite element transient contact and thermal sliding simulation and temperature measurement of dry sliding friction were performed in order to analyse the real contact area and temperature developed in the contact region. Real 3D surface worn topographies were taken into consideration, at macro and intermediate stages. The calculated real contact area has been changing in time and space in the course of sliding. The sliding components were high purity alumina ceramic palettes and 100Cr6 steel with constant accelerated motion. The calculated temperature results are in good agreement with the temperature data measured. Heat partition was changing in time during sliding. The developed algorithm based on incremental FE technique can characterize real processes.     

表面微凹坑和纹理方向对界面摩擦的耦合影响

选取三种不同纹理的铝合金试样,并在试样上加工不同面积占有率的规则圆形微凹坑,利用自制的摩擦试验装置,在油润滑条件下以不同接触压力进行摩擦试验,试验过程中滑动方向与表面纹理方向的夹角分别为0°、45°、90°。利用非接触式三维轮廓仪测量试验前后试样的三维表面形貌,并选取Sa、Str、Vvv、Vvc等表面表征参数来分析滑动接触界面表面形貌的变化。结果表明：表面纹理方向的差异导致铝合金表面在滑动接触摩擦过程中表现出各向异性,而在其表面加工不同面积占有率的微凹坑,减弱了铝合金表面纹理方向性对界面摩擦的影响,反映出表面微凹坑和纹理对界面摩擦的耦合作用。同时界面摩擦对试件的表面形貌也有明显的影响,Str、Vvv、Vvc在试验后发生了规律性的变化。     

Investigation of disc/pad interface temperatures in friction braking

Maintaining appropriate levels of friction interface temperature is important for the overall operating effectiveness of modern friction brakes, and implicitly the safety of the vehicle. Measurement and prediction of the distribution and magnitude of brake friction interface temperatures are difficult. A thermocouple method with an exposed hot junction configuration was used for interface temperature measurement, and the magnitude and distribution of the friction interface temperature were investigated in this study. Using a designed experiment approach, the factors affecting the interface temperature, including the number of braking applications, sliding speed, braking load and type of friction material were studied. It was found that the number of braking applications had the strongest effect on the friction interface temperature. The real contact area between the disc and pad, i.e. pad regions where the bulk of the kinetic energy is dissipated via friction, had a significant effect on the braking interface temperature. For understanding the effect of real contact area on local interface temperatures and friction coefficient, finite element analysis (FEA) was conducted, and it was found that the maximum temperature at the friction interface does not increase linearly with decreasing contact area ratio. This finding is potentially significant in optimising the design and formulation of friction materials for stable friction and wear performance.     

Tribological characteristics of bisphenol S bis(diphenyl phosphate) as a high‐performance antiwear additive in lubricating greases at elevated temperature

Bisphenol S bis(diphenyl phosphate) (BSDP) was synthesised and characterised, and its tribological behaviours as additives in polyurea grease and lithium complex grease were evaluated for steel/steel contact at 200 °C. The results indicated that BSDP could dramatically reduce the friction and wear of sliding pairs in the base grease of polyurea, and the tribological performances of BSDP in polyurea grease were significantly superior to the normally used molybdenum disulfide‐based additive package. Furthermore, BSDP in polyurea grease has better tribological behaviour than that in lithium complex grease at a constant load of 100 N. X‐ray photoelectron spectroscopy analysis indicated that boundary lubrication films composed of Fe(OH)O, Fe₂O₃, Fe₃O₄ and FePO₄ compounds containing the P–O bonds and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance. Copyright © 2016 John Wiley & Sons, Ltd.     

铁路轮轨润滑脂的研制

采用IR、XRD、SEM-EDS等手段,对常用铁路轮轨润滑脂进行剖析,得到润滑脂的基础油种类和添加剂组成。研制一种新型铁路轮轨润滑脂,并与常用铁路轮轨润滑脂的性能进行比较。结果表明:研制的润滑脂的最大无卡咬负荷为863 N,比常用铁路轮轨润滑脂的大一倍多,其摩擦因数为0.008～0.032,明显小于常用铁路轮轨润滑脂的0.039～0.051,但烧结负荷小于常用铁路轮轨润滑脂;研制的润滑脂具有更好的胶体稳定性和耐热性。     

Effect of the Abrasive Size on the Friction Effectiveness and Instability of Brake Friction Materials: A Case Study with Zircon

The friction-induced vibration triggered at the sliding interface between the gray iron disk and brake friction material was studied by changing the size of the zircon particles in the friction material. The friction tests were performed using a reduced brake dynamometer and the friction characteristics of the friction materials containing zircon particles with sizes of 3, 50, and 100 μm were analyzed. Our results show that the properties of the sliding surface were strongly affected by the entrenchment of the abrasive particles in the friction layers during sliding. The friction effectiveness was inversely proportional to the size of the abrasive, while friction instability was pronounced when smaller zircon particles were used. The smaller zircon particles produced larger plateaus on the sliding surface with low contact stiffness. However, the contact plateaus with the low contact stiffness showed higher amplitudes of the friction oscillations, suggesting a surface with low stiffness also can produce high propensity of friction instability during sliding. Based on the friction stability diagram and surface properties, such as contact stiffness and surface roughness, it was suggested that the static coefficient of friction, which was changed as a function of dwell time, was crucial to understand the cause of friction-induced force oscillations and propensity of friction instability of brake friction materials.     

The Film Behaviors of Grease in Point Contact During Microoscillation

Microoscillation is a typical case of transient motion, which occurs in many machine elements, including rolling or sliding element bearings, cams, and gears. Wear is easy to occur on the surface of such elements, particularly at the end point of the stroke, where the surfaces are momentarily static. In the present work, an experimental investigation is conducted to explore the grease film behavior of point contact lubrication during microoscillation in the case of pure rolling or pure sliding. The technique of relative optical interference intensity was used to monitor the variation of the grease film thickness and the motion of the grease in the contact area through analyzing the captured interferograms. Experimental results indicate that a crescent-shaped grease film can form along the motion direction in the contact area under microoscillation. The grease film is formed in the inlet region, and the film thickness remains while moving in the Hertzian contact area. In the case of pure rolling, the crescent-shaped grease film and the initial entrapped grease film are carried by a tow effect of moving interfaces in the contact area. However, in the case of pure sliding, there are relative motions in the sliding direction at the two interfaces of the grease/ball and the grease/disk in the Hertzian contact area. The shape of the entrapped grease remains almost unchanged while moving in the Hertzian contact area. During the repetition of microoscillations, the crescent-shaped grease film thickness drops gradually.