Rheological properties of grease
author: Ann
2024-12-23
The relationship between shear rate and shear force of Newtonian fluid and non-Newtonian fluid is the flow and deformation characteristics of grease when subjected to external force, which is mainly manifested as follows:
(1) When grease is not subjected to external force, it can maintain a certain shape like a solid, that is, it will not automatically flow when it is stationary.
(2) When subjected to a weak external force, it produces elastic deformation; after the external force is removed, it can return to its original position and shape, showing the elastic characteristics of a solid.
(3) When the applied external force is large enough, the grease deforms and flows, and it can no longer automatically return to its original position and shape. Therefore, the starting torque of grease on the mechanical moving parts is greater than that of liquid lubricants.
(4) During the flow of grease, as the shear stress increases, the soap fibers are oriented to varying degrees, which will cause the apparent viscosity (or similar viscosity) of the system to decrease. At this stage, the apparent viscosity of the grease decreases with the increase of shear rate.
(5) Under extremely high shear stress (high shear rate), the flow of grease is like that of Newtonian fluid, and the viscosity can remain a constant and no longer changes with the change of shear rate.
The significance of rheological properties and thixotropy of grease
The rheological properties and thixotropy of grease are of great significance to the use of grease. In the lubrication process of gears and bearings, the viscosity of grease decreases due to the relative sliding or rolling of the friction pair. Under the action of high shear force, the grease on the friction surface can form a fluid state, which is beneficial to the lubrication of mechanical parts. Once the operation stops, the viscosity of the grease returns to a certain level. For bearings, the grease can be kept inside the bearing without leakage; for gearboxes, the grease that has returned to a certain viscosity can play a sealing role to avoid leakage of the gearbox.
(1) When grease is not subjected to external force, it can maintain a certain shape like a solid, that is, it will not automatically flow when it is stationary.
(2) When subjected to a weak external force, it produces elastic deformation; after the external force is removed, it can return to its original position and shape, showing the elastic characteristics of a solid.
(3) When the applied external force is large enough, the grease deforms and flows, and it can no longer automatically return to its original position and shape. Therefore, the starting torque of grease on the mechanical moving parts is greater than that of liquid lubricants.
(4) During the flow of grease, as the shear stress increases, the soap fibers are oriented to varying degrees, which will cause the apparent viscosity (or similar viscosity) of the system to decrease. At this stage, the apparent viscosity of the grease decreases with the increase of shear rate.
(5) Under extremely high shear stress (high shear rate), the flow of grease is like that of Newtonian fluid, and the viscosity can remain a constant and no longer changes with the change of shear rate.
The significance of rheological properties and thixotropy of grease
The rheological properties and thixotropy of grease are of great significance to the use of grease. In the lubrication process of gears and bearings, the viscosity of grease decreases due to the relative sliding or rolling of the friction pair. Under the action of high shear force, the grease on the friction surface can form a fluid state, which is beneficial to the lubrication of mechanical parts. Once the operation stops, the viscosity of the grease returns to a certain level. For bearings, the grease can be kept inside the bearing without leakage; for gearboxes, the grease that has returned to a certain viscosity can play a sealing role to avoid leakage of the gearbox.
Will the equipment that has been shut down for a long time still operate normally after restarting? What are the "pitfalls" of daily lubrication maintenance?
Grease-specific terminology
