How can grease maintain lubrication for a long time?

Many scholars have conducted a large amount of research work on the lubrication mechanism of grease, especially soap-based grease. However, there is still no unified understanding and further research is needed to solve it in the future.Many scholars have conducted a large amount of research work on the lubrication mechanism of grease, especially soap-based grease. However, there is still no unified understanding and further research is needed to solve it in the future.

Generally speaking, most scholars believe that soap-based grease is a three-dimensional network structure system composed of metallic soap and base oil absorbed in the soap. According to the concept of soap-oil gel particle dispersion, it can be considered that soap-based grease is a structural dispersion system with oil as the dispersion medium and soap oil gel particles as the dispersed phase. Therefore, the following views are gained on the mechanism of grease lubrication.It is generally believed that the base oil is brought to the contact surface of the friction pair due to the action of metal soap or thickener, and the base oil is released by external force on this surface for lubrication. This view only sees that the base oil plays a real lubricating role, and is only proposed based on the following test results, that is, greases made by thickening the same base oil with different bowling agents have the same friction coefficient . Another view is that base oils and thickeners can both provide lubrication. This is based on comparative test results of grease and base oil alone, as well as the relationship between the lubrication properties of the grease and the shear strength of the blockade agent. A more comprehensive view is that the lubrication effect of grease is partly due to the role of the base oil, and more importantly, it depends on the special combination of the gelatinizer and the base oil, which is different from the base oil and the base oil. Lubricating properties of thickeners.

(1) Thixotropy

The basic characteristic of grease is thixotropy. When an external force is applied, the flow of the grease gradually becomes softer, showing a decrease in viscosity. However, once it is stationary, after a period of time (a short period of time), the consistency increases (recovers) again. This characteristic is called thixotropy. This characteristic of grease determines that it can lubricate parts that are not suitable for lubricating oil and show its excellent performance.

(2) Viscosity

Grease is usually expressed by "apparent viscosity or similar viscosity". When describing the viscosity of grease, the temperature and shear rate must be specified. Similar viscosity indicators can be used to control its low-temperature fluidity and pumpability.

(3) Strength limit

The strength limit of grease refers to the small shear stress required to cause the sample to start flowing, also known as the ultimate shear stress. The strength limit of grease is a function of temperature. The higher the temperature, the smaller the strength limit of grease. As the temperature decreases, the strength limit of grease becomes larger. Its size depends on the type and content of the thickener, as well as the grease making process conditions. relation.

(4) Low temperature fluidity

One of the important indicators to measure the low-temperature performance of grease is low-temperature torque, which is the degree to which grease blocks the rotation of low-speed flow bearings at low temperatures (below - 20°C). The low-temperature torque of grease is determined by the starting torque and rotation 60mm The average value of the rear torque is expressed.

(5) Dropping point The low temperature when the grease reaches a certain fluidity under specified conditions is called the dropping point. The dropping point of grease helps to identify the type of grease and roughly estimate the maximum service temperature of the grease. Generally speaking, for soap grease, its service temperature should be 20~30°C lower than the dropping point. The higher the dropping point, The better its heat resistance.

(6) Evaporability

The evaporability (degree) of grease indicates the degree to which the grease oil evaporates when the grease is used for a long time under high temperature conditions. The smaller the evaporability, the better. The evaporability of grease mainly depends on the properties and fraction composition of the lubricating oil.

(7) Colloidal stability

The colloidal stability of grease refers to the grease's ability to maintain a stable colloidal structure under certain temperatures and pressures and prevent lubricating oil from precipitating from the grease, which is also the grease's ability to resist oil separation. The amount of oil precipitated from grease is usually expressed as a mass fraction. The colloidal stability of grease reflects the tendency of grease to separate during long-term storage and actual application. If the colloid stability of grease is poor, serious oil separation will easily occur under the action of heat, pressure, centrifugal force, etc., resulting in a rapid reduction in service life. , and make the grease thicken and dry, losing its lubricating effect.

(8) Oxidation stability

Oxidation stability refers to the ability of a grease to resist the effects of heat and oxygen and maintain its properties without permanent changes when stored for a long time or used at high temperatures for a long time. Due to oxidation, the free alkali content often decreases or the free organic acid content increases, the dropping point decreases, the appearance becomes darker, odor appears, the consistency and strength limit, similar viscosity decreases, corrosive products are generated and the grease structure is destroyed. Substances that cause soap oil to separate. Therefore, during long-term storage of grease, it should be stored in a dry and ventilated environment to prevent sunlight exposure, and changes in free alkali or free organic acids, corrosiveness and other items should be regularly checked to ensure its quality and performance.