聚脲润滑脂噪音特性的衰退机制研究

Degradation Mechanism of Noise Characteristics of Polyurea Grease

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.

As one of the most important industrial basic parts,the rolling bearings greatly determine the performance and reliability of equipment.Nowadays,low operating noise is an important technical requirement for high quality bearings.Therefore,low-noise lubricating greases have been widely used in high precision bearings in high-speed spindles,high speed motors and high-end household appliances.Among low-noise greases,the polyurea grease is thought as the most promising one due to the high thermal stability and long service life.At present,most of the research on the low-noise polyurea greases focuses on the influence of the base oil,thickener,production process and impurities in the noise characteristics,while the evolution behavior and relevant micro-mechanism for the grease noise in the long-term use process are neglected.In this study,based on the FE9 bearing test rig and combined with the grease noise tests,the degradation of noise characteristics of low-noise polyurea grease during use were investigated.The results showed that the color of grease deepened and became nonuniform after bearing test,and the noise grade of polyurea grease with excellent noise performance degraded from GN4 to GNX within 100 h after the FE9 bearing test started,indicating that the grease lost the ability to reduce the bearing vibration and noise.It was pointed out by the academics that the microstructure of thickener was the critical factor that affected the low-noise property of greases.Thus,the microstructure of grease samples was characterized via optical microscope and scanning electron microscope.The microstructure of the aged greases indicated that the degradation of noise level was highly correlated with the formation of thickener aggregates in the grease.The differential scanning calorimetry implied that the thickener may be a metastable polyurea structure,which aggregated into higher assembly degree under heating conditions.The rheological characterizations showed that the aged grease had higher composite modulus,while the yield point and flow point were significantly reduced,indicating that the continuity of the thickener was destroyed due to the formation of aggregates,which induced the weakened structural retention ability of the thickener network.Large aggregates without constraints could flow into the bearing interface with the base oil,thus causing vibration and noise.Confirmed by the noise and structural characterizations of grease samples in the static thermal aging test was that the degeneration of noise grade was mainly caused by the thermal action.This study showed that the noise life of low-noise grease was not highly correlated with the service life obtained from the bearing test,and evaluating the influence of thermal on the microstructure and noise characteristics of the grease was significant for the long-term reliability of high-speed precision bearings.