机械设计第四章摩擦磨损及润滑概述

1、机械设计第四章摩擦磨损及润滑概述第1页，共25页，2022年，5月20日，3点29分，星期四Lubrication（润滑）The condition of having been made smooth or slippery by the applicat-ion of a lubricant such as oil or grease (脂)Tribology（摩擦学）The branch of engineeri-ng that deals with the interaction of surfaces in relative motion (as in bearings or gea

2、rs): their design and friction and wear and lubrication第2页，共25页，2022年，5月20日，3点29分，星期四II Friction (摩擦)1. Classification Classified by whether two parts have relative movementStatical friction(静摩擦)friction between two or more solid objects that are not moving relative to each other；Kinetic friction(动摩

3、擦)occurs when two objec-ts are moving relative to each other and rub together (like a sled(雪橇) on the ground). 第3页，共25页，2022年，5月20日，3点29分，星期四Classified by movement type（important）Sliding friction（滑动摩擦）occurs when two objects slide across from one another；Rolling friction (滚动摩擦)occurs when a body (su

4、ch as a ball, tire, or wheel) rolls on a surface.第4页，共25页，2022年，5月20日，3点29分，星期四Classified by lubricant （important）Dry friction (干摩擦)resists relative lateral motion of two solid surfaces in contactFluid friction（流体摩擦）the friction between layers within a viscous fluid that are moving relative to each

5、other； 第5页，共25页，2022年，5月20日，3点29分，星期四Boundary friction（边界摩擦）occurs when a surface is at least partially wet, but not so lub-ricated that there is no direct friction between two surfaces;Mixed friction（混合摩擦）a kind of friction including both boundary friction and fluid fric-tion.第6页，共25页，2022年，5月20日，3

6、点29分，星期四III Wear(磨损)Three stages of wear *run-in wear(磨合磨损)（useful）Stable wear (稳定磨损)（work）Severe wear (剧烈磨损)（failure）Wear rate ：=q t q Wear magnitude Design or use a machine, you should do your best to reduce run-in time, increase stable wear time and postpone the arrival of severe wear.第7页，共25页，20

7、22年，5月20日，3点29分，星期四1.Adhesive wear (粘着磨损)3.Fatigue wear (疲劳磨损) Pressurelocal temperature increasesadhesion (weld) Friction forceavulsion, shearmaterial transfer Fluctuating stressescrack propagatio-nsurface delamination (表面剥落) pit（pitting corrosion, 疲劳点蚀）2.Abrasive wear (磨料磨损)Surface material drops

8、off, oil contains impurity (杂质), rigid grains become abrasive grains(磨料)4.Corrosion wear (腐蚀磨损)5.Erosion (冲蚀磨损)A state of deterioration in metals caused by oxidation or chemical actionErosion caused by gas and fluid第8页，共25页，2022年，5月20日，3点29分，星期四IV Lubrication（润滑）Decrease friction, reduce wear；Preven

9、t parts from rust；Heat output and temperature reduction（circulation oil ,循环油）；Cushion and absorb shock (缓冲吸振)；Seal （Grease lubricant）1. Effects of Lubrication (润滑的作用)第9页，共25页，2022年，5月20日，3点29分，星期四2、Lubricant and its index（润滑剂及主要指标)（1） Lubricating oil（润滑油） Animal oil, vegetable oil, Mineral oil and c

10、hemical synthesis oil Viscosity（粘度）Resistance of a liquid to shear forces (and hence to flow) 第10页，共25页，2022年，5月20日，3点29分，星期四Newtonian fluid friction law (牛顿流体摩擦定律)：A move with a speed V ，and B is hold still, so that fluid close to A move with a speed V, and fluid close to B plate is static. The mov

11、ement of the fluid is laminar flow, there exist relative slip between arbitrary two layers, shear stresses exist at the interface of laminar flow, i.e., 第11页，共25页，2022年，5月20日，3点29分，星期四A. Kinetic viscosity （动力粘度） Unit：Pas（ISO），Ns/m2（C.G.S, 厘米-克-秒制单位）B、Kenimatic viscosity (运动粘度) Unit：m2/s Fluid densit

12、yC、Specific viscosity (条件粘度)E Unit：Engler degree (恩氏度, Et） Oil number(Table4-1): According to GB/T314-1994, oil number is the central value of kenimatic viscosity at 40C第12页，共25页，2022年，5月20日，3点29分，星期四Influencing factor of viscosity (影响粘度的因素)Temperature：high temperature causes low viscosity；Pressure：

13、Viscosity increases with increasing press-ure. When pressure is lower than 20MPa, its effects can be ignored. When pressure exceeds 20MPa, they must be considered.pViscosity under pressure p， Pas；0Viscosity under pressure 105Pa， Pas； Pressure viscosity coefficient (粘压系数)， （13）10-8 m2N。第13页，共25页，2022

14、年，5月20日，3点29分，星期四Oiliness (油性) Physical or chemical absorption film (吸附膜) decrease friction and wear Extreme pressure property (极压性) Create wear-resisting, high pressure resisti-ng chemical boundary film Oxidation resistance (氧化稳定性) The ability to resist oxidation Flash point（闪点）and Solidifying Poin

15、t（凝固点） It is important to work in high or low temperature 第14页，共25页，2022年，5月20日，3点29分，星期四（2） Lubricant grease（润滑脂） Calcium base (钙基) grease, Sodium (钠基) base grease，lithium base (锂基) grease, aluminum base (铝基) grease Penetration (针入度) Lower penetration increases bearing capacity Dropping point (滴点)

16、Measure the high thermal resistance of the grease第15页，共25页，2022年，5月20日，3点29分，星期四（3）Additive（添加剂）Effects of the additive Improve oiliness, extreme pressure property and work ability under extreme operating conditions； Defer ageing and prolong service life； Improve physical propertyTypical additive：de

17、tergent dispersant (清净分散剂), antioxidant (抗氧化剂), oiliness additive (油性添加剂), extreme-pressure and antiwear additive (极压与抗磨添加剂), pour inhibitor(降凝剂), tackifier (增粘剂)第16页，共25页，2022年，5月20日，3点29分，星期四Lubricating methods (oil and grease lubrication）1. Oil lubrication (油润滑)Force filling oil cup (压注油杯）Oil pot

18、 with turning sleeve（旋套油杯）第17页，共25页，2022年，5月20日，3点29分，星期四（1）Drip feed lubrication (滴油润滑)Oil pot with needle valve (针阀油杯)Wick oiler(油芯注油器)第18页，共25页，2022年，5月20日，3点29分，星期四（2）Oil-ring lubrication (油环润滑)（3）Splash lubrication (飞溅润滑)（4）Pressure circulation (压力循环润滑)第19页，共25页，2022年，5月20日，3点29分，星期四 2. Grease

19、lubrication (脂润滑)Grease cup with turning sleeve(旋盖式油脂杯)Grease gun(油脂枪)第20页，共25页，2022年，5月20日，3点29分，星期四 44 Hydrodynamic and hydrostatic lubrication (液体动力润滑和流体静力润滑)I. Newtonian law of friction (viscosity) 牛顿流体摩擦的摩擦定律（粘性定率）Tangential stresses in any point of fluid are directly pro-portional to local velocity gradientProportionality coefficients (比例系数) Kinetic viscosity of the fluid Shear resistance per unit area (单位面积的剪切阻力):第21页，共25页，2022年，5月20日，3点29分，星期四I