Newton's internal friction law, shear stress between liquid layers (internal friction force F between adjacent liquid layers, contact area A between liquid layers, velocity gradient between liquid layers) "viscosity" 1 dynamic viscosity, also known as absolute viscosity, The unit is, the formula is 2 kinematic viscosity: the ratio of the kinematic viscosity to the density of the liquid, expressed as the unit, the hydraulic oil with the formula L-HL46 at 40 o'clock, the central value of the kinematic viscosity is 46. 4. The viscosity temperature characteristic The nature of the viscosity of an oil as a function of temperature is called the viscosity-temperature characteristic. The effect of temperature on the viscosity of the oil is relatively large, the temperature rises, and the viscous text drops significantly. Other physical and chemical properties of the oil include: flame resistance, anticoagulability, oxidation resistance, foam resistance, emulsification resistance, rust prevention. Sex, lubricity, thermal conductivity, compatibility and purity 4. There are many types of hydraulic oil, there are three main types: mineral oil type, emulsified type, and synthetic type. Hydraulic transmission system oil should generally meet the requirements: appropriate viscosity, good viscosity and temperature characteristics; good lubricity, good rust resistance; pure texture, less impurities; good compatibility with metal and seals; good oxidation stability It is not easy to deteriorate; it has good anti-foaming and anti-emulsification properties; it has high burning point, low solidification, harmless to human body and low cost. 5. The basic knowledge of hydrostatics 1. The pressure of liquid The hydraulic force per unit area is called pressure, which is called the concept of pressure in physics, but it is customary in hydraulic technology to be called pressure. At a certain point, a normal force acts on a small area. The static pressure P at that point is such that the static pressure of the liquid has two important characteristics: (1) the static pressure of the liquid acts on the bearing surface along the normal force ( 2) The static pressure at any point in the stationary liquid is equal in all directions. 2. The pressure distribution of the stationary liquid under gravity (1) The pressure at any point in the stationary liquid consists of two parts: one part is the pressure on the liquid surface, The other part is the pressure created by the weight of the liquid above this point. When the liquid surface is only subjected to atmospheric pressure, then the pressure at any point in the liquid is: (2) The pressure in the static liquid is linearly distributed with the depth of the liquid (3) The pressure at the same point from the liquid depth is equal, forming An isobaric surface (for the horizontal plane) 3. The representation and unit of pressure are based on the metric. The liquid pressure is divided into absolute pressure and relative pressure. The pressure measured on the basis of absolute vacuum is called absolute pressure; then the pressure measured by atmospheric pressure as the benchmark is relative pressure. On the surface of the earth, all objects subject to the atmosphere, the role of atmospheric pressure is self-phase equilibrium, so the general pressure instrument reads zero in the atmosphere, and the pressure measured by the pressure gauge is obviously relative pressure. Therefore, the relative pressure is also called the gauge pressure. If the absolute pressure at a point in the liquid is less than atmospheric pressure, then the value that is less than atmospheric pressure is called vacuum. Absolute pressure, relative pressure and vacuum relationship absolute vacuum relative pressure (positive) absolute pressure relative pressure (negative) vacuum absolute pressure atmospheric pressure> http://news.chinawj.com.cn
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