聚脲润滑脂噪音特性的衰退机制研究

低噪音润滑脂是高速电主轴、高速电机及高端家电中高精密轴承广泛使用的润滑介质. 当前有关低噪音润滑脂的研究大都集中在基础油、稠化剂和生产工艺等因素对润滑脂噪音特性的影响，而对长期使用过程中润滑脂噪音性能的变化行为及其微观机制则缺乏足够关注. 本论文中围绕低噪音聚脲润滑脂，基于FE9轴承测试台架，结合润滑脂噪音检测技术，考察了低噪音聚脲润滑脂在使用过程中噪音特性的衰退行为. 结果表明，静音性能优异的聚脲基低噪音润滑脂在轴承试验开始的100 h内，噪音等级已由GN4级衰减为GNX级，丧失减振降噪能力. 对取样润滑脂的微观结构表征发现，润滑脂噪音等级的衰退与聚脲润滑脂内稠化剂团聚体的形成高度关联. 团聚体的形成破坏了稠化体系的结构连续性，导致稠化网络的结构保持性显著下降，失去束缚的大尺寸团聚体随基础油流入轴承运动界面，进而引发高速轴承的振动和噪声. 热分析结果表明该低噪音聚脲稠化剂可能为一种亚稳态聚脲结构，在受热条件下会向组装度更高的团聚体发展. 本论文中的研究表明低噪音润滑脂的噪音寿命与轴承试验中得到的服役寿命相关度并不高，充分评估热作用对润滑脂微观结构及噪音特性的影响，对于保障高速精密轴承的长期可靠运行具有重要意义.

Low-noise grease is a widely used lubricating medium for high-precision bearings in high-speed electric spindles, high-speed motors and high-end home appliances. Current studies on low-noise grease mostly focus on the effects of base oil, thickener, production process and other factors on the noise characteristics of grease, but there is insufficient attention paid to the change behavior of grease's noise performance and its microscopic mechanism during long-term service. In this paper, focusing on low-noise polyurea grease, based on the FE9 bearing test rig and combined with grease noise detection technology, the decay behavior of noise characteristics of low-noise polyurea grease during use was investigated. The results show that the polyurea-based low-noise grease with excellent noise reduction performance had its noise grade attenuated from GN4 to GNX within the first 100 hours of the bearing test, losing its vibration and noise reduction capability. Microstructural characterization of the sampled grease revealed that the decay of grease noise grade is highly correlated with the formation of thickener aggregates in polyurea grease. The formation of aggregates disrupts the structural continuity of the thickening system, leading to a significant decrease in the structural retention of the thickening network. The unbound large-sized aggregates flow into the bearing motion interface along with the base oil, thereby triggering vibration and noise in high-speed bearings. Thermal analysis results indicate that this low-noise polyurea thickener may be a metastable polyurea structure, which will develop into aggregates with a higher degree of assembly under thermal stress. The research in this paper shows that the noise lifetime of low-noise grease has low correlation with the service life obtained in bearing tests. Fully evaluating the impact of thermal action on the microstructure and noise characteristics of grease is of great significance for ensuring the long-term reliable operation of high-speed precision bearings.