In the excavator hydraulic system, the hydraulic oil not only serves as the working medium for transferring energy, but also has the function of lubricating and cooling the transmission system. Therefore, whether the quality and variety of hydraulic oil meet the requirements directly affects the life and work efficiency of the entire machine.
General physical properties of hydraulic oil
1. Oil viscosity
When the liquid flows, the resistance to mutual adhesion and friction between molecules is called viscosity. The physical quantity that expresses the viscosity is called viscosity. There are three units for measuring viscosity: dynamic viscosity, kinematic viscosity and relative viscosity. Our country mainly adopts kinematic viscosity.
(1) Two layers of liquid with a dynamic viscosity area of 1 cm2 and a distance of 1 cm. When one of the layers moves relative to the other layer of liquid at a speed of 1 cm/sec, the resistance between the two is called It is the dynamic viscosity, and its physical unit is poise (dynes/cm) and centipoise (1/100 poise).
(2) Kinematic viscosity At the same temperature, the ratio of the dynamic viscosity of the liquid to its density is called the kinematic viscosity. The physical unit is stoke (cm2/s); the engineering unit is m2/s. 1 m2/sec = 104 stokes (cm2/sec) = 10° centistokes.
Kinematic viscosity and kinematic viscosity are based on measuring their absolute value, so it is also called absolute viscosity.
(3) Relative viscosity Relative viscosity is also called conditional viscosity, usually measured by Engel's method. That is: the ratio of the time required to flow through a thin tube with a diameter of 2.8 mm using 200 cm3 of test liquid and 200 cm3 of distilled water at 20°C. This is the conversion between the Engel's viscosity °E viscosity unit of the test fluid.
2, viscosity index
Viscosity Index is a way of expressing the viscosity-temperature properties of oil. The viscosity of the oil is inversely proportional to the temperature of the oil, and directly proportional to the pressure of the oil (but not much change). A high viscosity index means good viscosity-temperature performance and a wide temperature range of use. Otherwise, the range of use is small. Generally, the viscosity index of hydraulic oil is required to be above 90, and the excellent one is above 100.
3, heavy oil
The weight per unit volume of oil is called gravity. The mineral oil generally used has a weight of 0.86 to 0.93 g/cm.
4. Specific heat of oil
The specific heat of oil refers to the amount of heat required per unit weight of oil when the temperature rises by one degree. The specific heat of mineral oil is generally 04~0.5 kcal/kg degrees.
