【作者】 李刚；

【导师】 雒建斌；

【作者基本信息】 清华大学 ， 机械工程， 2010， 博士

【摘要】 在现代工业领域,润滑脂被广泛应用于机械运动系统的润滑,特别适用于低速、重载及非稳态等苛刻条件。脂润滑的深入研究对于节省能源、减少磨损以及延长机械设备的使用寿命具有重要意义。本文为了揭示苛刻条件下的润滑行为,利用相对光强法测量膜厚技术,建立了适于模拟苛刻润滑条件的非稳态润滑综合测量仪。该测量仪可以模拟匀速、变速等多种运动形式,实现了低速（0.04 mm/s）及高接触压力（2 GPa）下接触区动态膜厚测量、润滑行为观测和摩擦力在线测量。选用蓝宝石盘和GCr15钢球为配副材料,研究了润滑脂在低速、重载润滑条件下成膜机理及润滑特性。发现当速度大于4 mm/s时,脂润滑膜厚度变化规律与弹流理论预测结果基本一致;而当速度小于4 mm/s时,润滑脂中的稠化剂纤维对润滑脂成膜起主要作用,润滑脂的成膜能力不受卷吸速度变化的影响,其成膜能力远高于理论预测结果。接触压力的变化对润滑脂的成膜能力及膜厚变化规律影响不明显。在往复摆动的零速瞬间,接触区中心润滑膜厚度比其周围的大,接触区最小润滑膜厚度大于静态润滑膜厚度,最大润滑膜厚度随速度变化率的增加而增大。在一个往复摆动周期中,接触区最小中心润滑膜厚度出现在反向加速运动的初始阶段。润滑脂在高接触压力作用下表现为“类固态”,在微摆纯滑动条件下,接触区受限脂润滑膜中出现无剪切流动层。该无剪切流动层中的各点具有相同的运动速度,只是在两摩擦副表面附近薄层内发生相对滑动。相对滑动对接触区润滑膜形成产生影响。润滑脂中加入MoS₂和TiO₂固体微小颗粒,其流变特性及摩擦学特性都发生了改变。含固体微小颗粒润滑脂的屈服剪切应力随着固体微小颗粒含量的增加而减小,表观粘度随固体微小颗粒含量的增加而增大。含固体微小颗粒润滑脂的减摩抗磨能力明显提高,分析结果表明:磨斑表面生成了与颗粒成份相关的保护层,同时与颗粒的组织结构和物化特性有关。更多还原

【Abstract】 In modern industry, grease is widely employed in many mechanical motion systems, especially under harsh conditions, such as low speed, heavy load and non-steady state. It is of great significance to study the grease lubrication in depth under these conditions to save energy, reduce wear and extend the service life of machinery.In the present thesis, a tribological multi-functional apparatus has been developed by using the technique of relative optical interference intensity to study the lubrication behavior under harsh conditions. The apparatus can simulate the cases at constant speed and variable speed, etc. In addition an ultra-low-speed of 0.04mm/s and a high contact pressure of 2 GPa can be achieved. The dynamic film thickness of the contact area can be measured. The lubrication behavior can be observed and the friction force can be measured online.A sapphire disc and a steel ball （GCr15） are selected as the tribo-pair for studying the film-forming mechanism and the lubrication properties of the grease under the conditions of low speed and heavy load. When the speed is larger than 4mm/s, the variation of the grease film thickness is very close to the theoretical prediction. However, the soap fiber plays an important role in the lubrication process when the speed is lower than 4mm/s. The film forming capacity of the grease at low speeds is far higher than the theoretical prediction, and is not affected by the variation of the entrainment speed. The variation of the contact pressure has no obvious effect on the film forming capacity of grease.During oscillation, the central film is thicker than its peripheries at the moment of zero entrainment speed, and the minimum film thickness is larger than of the static central film thickness. The central film thickness at this moment increases with increasing the rate of the change of entrainment speed. In one oscillation cycle, the minimum central film thickness appears at the initial stage of acceleration. Under micro oscillation sliding condition, there are two thin layers near the interface of the entrapped grease and the two surfaces of the tribo-pairs. The shear flow has a certain effect on the film formation. The rest entrapped grease between the two shear layers shows a solid like state. No shear flow occurs in this layer and the grease in this layer has the same velocity.Micro/Nano MoS₂ and TiO₂ particles are used as additives for the lithium grease. The rheological properties and tribological properties of the modified lithium grease are changed correspondingly. For example, the yield shear stress decreases but the apparent viscosity of the lithium grease increases with the increasing content of the particles. The friction-reduction and anti-wear properties of the lithium grease are improved by adding the particles, and the underlying mechanisms are related to the formation of protective layers on the wear scar and the structure and physicochemical characteristics of the particles.更多还原