1. what is grease?

Grease is a stable solid or semi-solid product composed of a thickener dispersed in a liquid lubricant. Uniform lubricants have also observed that people are used to calling grease "butter" in daily production ".

Grease is mainly composed of thickener, liquid lubricating oil, additives and fillers.

What is the role of 2. thickener? What types are there?

The role of the thickener is to disperse and form a structural skeleton in the base oil, so that the base oil is adsorbed and fixed in the structural skeleton, thereby forming a solid or semi-solid grease.

The main types of thickeners are soap-based thickeners and non-soap-based thickeners.

Soap-based thickeners can be divided into three categories: single soap-based fat made of metal soap as a thickener, such as calcium-based fat, sodium-based fat. -Mixed soap base-a grease made by mixing two or more single metal soaps at the same time as a thickener, such as calcium-sodium grease. Complex soap-based soap crystals or soap fibers are made by co-crystallization of two or more compounds. Complex causes changes in grease characteristics and is marked by an increase in the dropping point, such as lithium complex and aluminum complex grease. Non-soap thickener: hydrocarbon, inorganic, organic

3. how to judge the soap base fat and non soap base fat?

This can be distinguished by determining whether there is a clear dropping point. Soap base grease has dropping points, and some have excellent radiation resistance, resistance to chemical media and other characteristics.

What are the types of additives used to 4. grease? Can all additives in lubricating oils be used to lubricate grease?

Grease additives are divided into two categories: one is the physical performance improvement agent, such as structural improvers (alcohol, water, glycerin, etc.); the other is the chemical performance improvement agent, such as anti-wear agent, rust inhibitor and so on.

Among the lubricating oil additives, additives that may damage the colloidal structure of the grease cannot be used in the grease; although some additives have poor oil solubility and are limited in the lubricating oil, they have good sensitivity in the grease and can be used in the grease.

5. what is filler and what is its role?

Filler is a solid filler added to increase some special properties of grease, most of which are inorganic powders with lubrication and thickening effect. Most of the filler itself can be used as a solid lubricant, adding grease can improve the lubricating ability of grease, in the grease lubrication film by short-term impact load or high heat, they can play a reinforcing role. Commonly used fillers are: graphite, aluminum powder, molybdenum disulfide, copper powder, etc.

What are the main properties of 6. grease?

① Rheological properties

② High temperature performance

③ Bearing performance

④ Lubrication performance

⑤ Protective performance

The low temperature performance.

How are the rheological properties of 7. greases measured?

Rheology is the study of the deformation or flow of matter under the action of an external force. Rheological properties of grease depends on its composition and structure, but also with the shear rate, temperature, grease flow properties mainly through the grease thixotropy, similar viscosity, strength limit and other properties to assess.

8. what are the thixotropy and strength limits of a grease?

The fat is subjected to shear, and at a certain shear rate, with the increase of shear time, the consistency decreases and the fat becomes thinner; when the shear stops, the structural skeleton gradually recovers and the fat becomes thicker. The phenomenon of thinning and thinning is called thixotropy. Its value depends on the thickener type, concentration and dispersion state, and has no direct relationship with the viscosity of the base oil. A slight thixotropy of the grease is beneficial for use.

The strength limit is the minimum shear stress required to start the grease to flow.

Since the grease has an irregular strength limit, it will not be affected by gravity to change its shape and flow automatically. Even in the friction parts that are not tightly sealed, it will not be lost. It can resist the centrifugal effect during mechanical work and will not be thrown out from the surface of the parts. The strength limit of grease is a function of temperature. The higher the temperature, the smaller the strength limit of grease, and the lower the temperature, the larger the strength limit of grease. The strength limit of the fat depends on the type and content of the thickener and is also related to the process.

What is the basis for 9. grease consistency classification and brand classification?

Consistency is an important indicator related to the ability and sealing performance of grease at the lubrication site, as well as the delivery and filling of grease, and its size is divided by penetration.

At present, the internationally accepted consistency grade is divided according to the consistency grade of the American Grease Association (NLGI). The consistency of the grease is divided into nine grades: 000, 00, 0, 1, 2, 3, 4, 5, 6. Consistency grades are measured by cone penetration.

10. what is the shear stability of a grease?

The ability to resist changes in consistency under shear is called the shear stability or mechanical stability of the grease. The evaluation methods include the determination of the penetration of the extended working cone and the determination of the stability of the grease roller. The difference between the penetration of 100,000 and 60 working cones is usually used to measure the ability of low fat to resist thinning. The smaller the ΔP, the better the shear stability. △P<30 is excellent, △P = 30-60 is good, △P = 60-100 is acceptable, and △P>100 is inferior. Poor shear stability will lead to increased loss of grease, decreased lubricity and increased grease consumption.

11. What is the difference between grease and lubricating oil viscosity?

Grease is a non-Newtonian fluid, and viscosity is also the most important characterization of grease rheology. The viscosity of lubricating oil does not change with the change of shear speed, but is only a function of temperature, and the viscosity of grease is not only a function of temperature, but also a function of shear speed. Grease viscosity is usually called performance viscosity or similar viscosity. The temperature and shear rate must be indicated when describing the viscosity of the grease. Grease viscosity was measured with a capillary viscometer.

12. What indicators are used to determine the high temperature performance of grease?

Dropping point-evaporability? Oxidation stability ˉ Colloid stability ° High temperature fluidity ± Bearing performance XIII. What is the dropping point? What is the relationship between the dropping point of grease and the actual use temperature?

Dropping point is an important quality indicator. Under normal circumstances, the grease is heated under the specified test conditions, and the first drop of liquid (or the temperature when it flows out of the oil column 25mm) from the grease cup of the instrument is its dropping point. The maximum use temperature of the grease can be roughly estimated by the dropping point. Generally for soap base grease, the use temperature should be lower than the dropping point of 20-30oC, the higher the dropping point, the better the heat resistance. However, some greases are limited by the evaporation of the base oil, or the maximum use temperature is much lower than the dropping point due to the phase transition of the system (becoming a rubber-like gel without adhering to metal). What is the low temperature fluidity of grease?

The indicator of grease fluidity at low temperature is low temperature torque, that is, the degree to which grease blocks the rotation of low-speed ball bearings at low temperatures (below-20oC). The magnitude of low-temperature torque is related to the difficulty and power loss of low-temperature starting of grease-lubricated bearings. The low temperature torque of the grease varies with the type of base oil. If the penetration of the unused cone of the grease is small, the dynamic torque is large. The larger the starting torque, the larger the starting power consumption, the worse the low temperature performance of the grease.

Fifteen, the evaporation of grease is determined by what components?

The evaporative nature of the grease is determined by the type, fraction composition and molecular weight of the base oil. The evaporation loss of fat is too large to cause premature drying up, thus shortening the service life.

What are the factors related to the oxidation stability of grease? What is the difference between the oxidation stability of different types of grease?

The ability of grease to resist oxidation during storage and use is oxidation stability (oxidation resistance), which mainly depends on its component properties, and is related to thickener, base oil and additives.

Non-soap based thickeners are mostly organic or inorganic thickeners with good thermal stability and oxidation stability, which are not easily oxidized and have no catalytic effect on the oxidation of base oil. For the grease prepared by soap-based thickener, its oxidation stability is worse than that of lubricating oil, and for different soap bases, the order of catalytic effect is lithium soap> sodium soap> calcium soap> barium soap> aluminum soap. In the same series of products, the higher the thickener content, the more obvious the catalytic effect.

17. What is the colloidal stability of fat? What factors are related to it?

Oil is a characteristic of grease, any kind of grease has oil phenomenon. The ability of a grease to resist oil separation is often referred to as the colloidal stability of the grease. It mainly depends on the composition and processing technology of the grease, and has a certain relationship with the external conditions. Generally, the smaller the viscosity of the base oil, the less the thickener content, and the lower the thickening ability of the thickener (the thickener is not well dispersed), The easier the grease is to divide the oil. The main external factors affecting oil separation are temperature, pressure and time. With the increase of temperature, the viscosity of the base oil becomes smaller, the molecular movement is accelerated, and the base oil is easy to separate from the fine structure, that is, it is easy to separate the oil. When the pressure increases, the structural skeleton is also easy to separate oil when compressed. An ideal grease needs proper oil separation. The initial oil separation speed is 0.2 h or 2%-10%/500h.

18. How is the lubrication performance of grease reflected?

The oil film formed by the base oil in the grease plays a lubricating role. Under harsh (extreme pressure) conditions, it is mainly lubricated by soap and antiwear agents.