What is the EP grease?
Here I'm going to explain it to you. EP is the abbreviation of extreme pressure, meaning "extreme pressure", EP grease is extreme pressure grease, suitable for heavy load, impact or vibration occasions, this kind of grease is generally added with extreme pressure additives. Grease is composed of base oil, thickener and additives. The performance of extreme pressure grease is determined by thickener, base oil and additives. Extreme pressure greases are recommended only when needed, Please check the recommendation of EP grease manufacturer before use.
1. Extreme pressure performance of base oil and grease:
Base oil is the main component of grease, and attention should be paid to the fluidity of base oil at low temperature. In general, oil increases viscosity (thickens) and becomes less fluid at low temperatures. If the low temperature performance of the base oil is not good, it will significantly affect the low temperature performance of the grease, resulting in the grease can not fully reach the lubrication point. The viscosity of synthetic oils is more stable than that of mineral oils in temperature changes. For example, PAO has good low temperature fluidity and high viscosity index. Using PAO (also known as SCH, synthetic hydrocarbon) as base oil can improve the performance of extreme pressure grease.
2. Extreme pressure performance of additives and grease:
Some additives are added to the grease to improve the performance of the grease. The extreme pressure additive is one of them. The role of extreme pressure agent is mainly to prevent wear and protect the friction surface under extreme pressure or boundary lubrication conditions. At present it is common to use 3%~5% molybdenum disulfide, and there are other types of extreme pressure agents. In general, extreme pressure agents need to be activated at a certain temperature to be effective, and the temperature required will vary with different types of extreme pressure agents. By using multiple types of extreme pressure agents, extreme pressure properties can be exploited at different temperatures. There are 4 Ball wear testing and Timkin OK Load tests to test the extreme pressure performance of grease. Different test methods have different test conditions, should be compared with the actual use of working conditions, and then refer to the performance results obtained from the experiment. Extreme pressure additives may corrode yellow metals, so for copper-containing parts, it is important to know whether extreme pressure grease has a corrosive effect on copper-containing parts.
3. Extreme pressure performance of thickener and grease:
Thickener will affect the performance of extreme pressure grease, grease is named according to the type of thickener, there are many kinds of thickener, such as lithium based thickener, calcium based thickener, aluminum based thickener, polyurea, composite lithium based thickener and so on, each of the thickener has different characteristics, some high temperature resistance, some have good water resistance, Some are more balanced in all aspects such as lithium based and composite lithium based thickeners. Chosen characteristics of grease should be suitable for the conditions of use, or if the grease in use because of the changes in temperature or other reasons cause thickener degeneration, dry, pumping based oil flow is bad, difficult to transport at low temperature, high temperature, extreme pressure agent is not fully reach the friction surface, these conditions will influence the extreme pressure performance of the grease.
For some types of greases, the thickener itself has extreme pressure properties, that is, in the absence of extreme pressure agents, the thickener itself has a certain extreme pressure wear resistance, such as complex calcium sulfonate greases. For extreme pressure additives that require a certain temperature to be activated, at low temperatures, if the extreme pressure agent does not work, then the grease itself also has extreme pressure wear resistance.