Study on the effect of mechanical shearing on the microstructure and performance of lithium complex grease

Abstract This paper focuses on the effect of mechanical shearing on the structure and properties of complex lithium greases with or without zinc dialkyl dithiophosphate (ZDDP). The base grease and grease with additives were first mechanically sheared by a roller shear tester, and then the tribological properties, rheological properties, micro-structure changes and noise properties of the samples were tested by a four-ball tester, rheometer, field emission scanning electron microscope and Bequiet+ noise tester, respectively. The results indicated that mechanical shear significantly reduced the mechanical stability and colloidal stability of the lithium grease, and the tribological properties of the two greases (with or without ZDDP) showed opposite trends. The rheological performance test showed that the structural strength of the grease was significantly reduced and the micro-structure became loose after shearing. In addition, the grease containing ZDDP showed a slight decrease in noise compared to the base grease due to the favorable reduction of the intermediate frequency of the complex lithium grease. This study provided theoretical guidance for the precise design and performance optimization of low noise greases.