液压与气压传动Chapter_2.ppt

Chapter 2  Fundamental Hydraulic Fluid Mechanics 1. Density (kg/m3)：the ratio of the mass of a given amount of a substance to the volume that this amount occupies . So, viscosity of fluid is the friction on per unit of area fluid under per unit of velocity gradient.There are three methods to describe the viscosity: Absolute viscosity μ, Kinematic viscosityν Relative viscosity OE Fig. 2-2 illustrates the 0E viscometer principle. (4) Viscosity-temperature : For the viscosity less than 15 0E and the temperature 30℃～150℃, the viscosity-temperature formula is describe as following: We also can look up from Fig.2-3. (5) Viscosity-pressure (6) Others performances : physical and chemical, such as anti-inflammability, anti- oxygenation, anti- concreting, anti-foam and anti-corrosion etc 补充：液压油的功能和类型 1）传动 把液压泵所赋予的能量传递给执行元件 2）润滑 润滑液压泵，液压阀，液压执行元件等运动件 3）冷却 吸收并带走液压装置所产生的热量 4）去污 带走工作中所产生的磨粒和来自外界的污染物 5）防锈 防止液压元件所用各种金属的锈蚀。 Request The oil plays two roles of transmission energy and lubrication on the surfaces of working interaction.The requests for the hydraulic fluids are: appropriate viscosity good in property of favorable viscosity－temperature good lubricity chemically and environmentally stabilities compatible with other system materials and so on. 原则： 1.按工作压力 ：p 高，η大； p 低，η小。 2.按环境温度 ：T 高，η大； T 低，η小。 3.按运动速度 ：v 高，η小； v 低，η大。 2.2 Hydrostatics 2.2.1 Characteristics of Hydrostatics 2.2.2 The basic formula of hydrostatics 2.2.3 The principle of Pascal application 2.2.4 Effect of fluid pressure on curved surfaces 2.2.2 The basic formula of hydrostatics 2. The definition and units of pressure Absolute pressure绝对压力 It is based on the absolute vacuum. Relative or gauge pressure 相对压力或表压力 Based on the atmosphere.The pressures measured by a pressure gauge are all relative pressure . Vacuum (negative pressure) 真空度 When the pressure is lower than atmosphere .（+