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The main performance indicators of lubricants

(1) Viscosity

Viscosity indicates the viscosity of lubricating oil. It refers to the internal frictional resistance generated when relative displacement occurs between oil molecules, and the size of this resistance is expressed by viscosity.

There are two types of viscosity: absolute viscosity and relative viscosity. The absolute viscosity is divided into dynamic viscosity and kinematic viscosity.

What we commonly use is kinematic viscosity. Since the viscosity of lubricating oil varies with temperature, it must be indicated at what temperature the viscosity was measured. The commonly used test temperature is 40°C, at which the viscosity is measured and used as the grade of lubricating oil.

(2) Flash point and ignition point

When the lubricating oil is heated under certain conditions, the evaporated oil vapor is mixed with air to reach a certain concentration when it comes into contact with the flame, and the lowest temperature at which short-term flicker occurs is called the flash point.

If the flash point time is extended for more than 5 seconds, the temperature at this time is called the ignition point. The flash point is a safety index for the storage, transportation and use of lubricating oil. Generally, the maximum working temperature should be 20-30℃ lower than the flash point. There are two methods for flash point determination: open and closed methods. The results of the open method are generally 20-30°C higher than the closed method.

(3) Penetration

Indicates the degree of softness and hardness of the grease, which is an important basis for classifying grease grades.

Test method: A standard cone with a weight of 150 grams is sunk into the grease within 5 seconds at a temperature of 25C (unit: 1 I 10 mm), which is called the penetration of the grease. The deeper the plunge, the softer the grease and the smaller the consistency; conversely, the smaller the penetration, the harder the grease and the greater the consistency. The penetration of lubricating grease increases with the increase of temperature, and the selection should be based on temperature, speed, load and working conditions.

(4) Dropping point

Indicates the heat resistance of grease.

Put a sample of grease into a dropping point meter and heat it under specified conditions. The temperature when the first drop of oil drops after the grease melts is used as the dropping point of the grease.

The dripping point of grease determines its working temperature. Grease with a dripping point 20-30℃ higher than the working temperature should be selected for application.