In the hydraulic system of the excavator, in addition to being the working medium for transmitting energy, the hydraulic oil also has the functions of lubrication and cooling transmission system. Therefore, whether the quality and variety of hydraulic oil meet the requirements directly affects the life and working efficiency of the entire machine.
General physical properties of hydraulic oil
1. Viscosity of oil
When the liquid flows, the resistance between the molecules bonding and rubbing is called viscosity. The physical quantity representing the viscosity is called viscosity. There are three units for measuring viscosity: dynamic viscosity, kinematic viscosity and relative viscosity. Kinematic viscosity is mainly used in my country.
(1) Two layers of liquid with a dynamic viscosity area of 1 cm 2 and a distance of 1 cm apart. For dynamic viscosity, the physical units are poise (Dyne seconds/cm) and centipoise (1/100 poise).
(2) Kinematic viscosity At the same temperature, the ratio of the kinematic viscosity of the liquid rest to its density is called the kinematic viscosity. The physical unit is Tuo (cm2/sec); the engineering unit is m2/sec. 1 meter 2 / second = 104 staps (cm 2 / second) = 10 ° centistokes.
Dynamic viscosity and kinematic viscosity are based on the determination of their absolute value, so it is also called absolute viscosity.
(3) Relative viscosity Relative viscosity, also known as conditional viscosity, is usually measured by the Eng method. That is: the ratio of the time required for 200 cm 3 of test liquid and 200 cm 3 of distilled water at 20°C to flow through a thin tube with a pore diameter of 2.8 mm. This is the conversion between the test fluid Hughes's viscosity and the unit of viscosity.
2. Viscosity index
Viscosity index is a method to express the viscosity-temperature property of oil. The viscosity of the oil is inversely proportional to the temperature of the oil and directly proportional to the oil pressure (but does not change much). A high viscosity index indicates good viscosity-temperature performance and a wide temperature range. Otherwise, the range of use is small. The viscosity index of general hydraulic oil is required to be above 90 and excellent to 100.
3. The weight of oil
The weight of oil per unit volume is called heavy. The weight of mineral oil generally used is 0.86~0,93 g/cm.
4. Specific heat of oil
specific heat of oil refers to the heat quantity 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.
