机械设计4第四章摩擦磨损和润滑概述

u y
A. Kinetic viscosity （动力粘度） Unit：Pa· s（ISO），N· s/m2（C.G.S, 厘米 -克-秒制单位） B、Kenimatic viscosity (运动粘度) Unit：m2/s
＝ ／
——Fluid density
C、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 40º C
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 chemical synthesis oil ① Viscosity（粘度） Resistance of a liquid to shear forces (and hence to flow)
Types of wear
IV Lubrication（润滑）
1. Effects of Lubrication (润滑的作用) • Decrease friction, reduce wear； • Prevent parts from rust； • Heat output and temperature reduction （circulation oil ,循环油）； • Cushion and absorb shock (缓冲吸振)； • Seal （Grease lubricant）
Influencing factor of viscosity (影响粘度的因素)
Temperature：high temperature causes low viscosity；
Pressure：Viscosity increases with increasing pressure. When pressure is lower than 20MPa, its effects can be ignored. When pressure exceeds 20MPa, they must be considered.
② 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 (such as a ball, tire, or wheel) rolls on a surface.
III Wear(磨损)
Three stages of wear * Wear rate ε：ε=△q ／ △t △q ——Wear magnitude run-in wear (磨合磨损) （useful） Stable wear (稳定磨损) Severe wear
Wear
(剧烈磨损)
（failure） （work） Design or use a machine, you should do your
Chapter 4 Summarization of Friction, wear and lubrication I Basic concepts
• Friction force（摩擦力）——The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other • Wear（磨损）——The damage or transfer of the material that is caused by something when it is being used normally
It is important to work in high or low temperature
（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 ① Penetration (针入度) Lower penetration increases bearing capacity ② Dropping point (滴点) Measure the high thermal resistance of the grease
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 movement 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.,
best to reduce run-in time, increase stable wear time and postpone the arrival ossure—local temperature increases— adhesion (weld) wear (粘着磨损) Friction force—avulsion, shear—material transfer 2.Abrasive Surface material drops off, oil contains wear (磨料 impurity (杂质), rigid grains become 磨损) abrasive grains(磨料) 3.Fatigue Fluctuating stresses—crack propagatiowear (疲劳 n—surface delamination (表面剥落)— 磨损) pit（pitting corrosion, 疲劳点蚀） 4.Corrosion wear A state of deterioration in metals caused by (腐蚀磨损) oxidation or chemical action 5.Erosion (冲蚀磨损) Erosion caused by gas and fluid
II Friction (摩擦)
1. Classification ① Classified by whether two parts have relative movement Statical friction(静摩擦)——friction between two or more solid objects that are not moving relative to each other； Kinetic friction(动摩擦)——occurs when two objects are moving relative to each other and rub together (like a sled(雪橇) on the ground).
Lubrication（润滑）——The condition of having been made smooth or slippery by the application of a lubricant such as oil or grease (脂) Tribology（摩擦学）——The branch of engineering that deals with the interaction of surfaces in relative motion (as in bearings or gears): their design and friction and wear and lubrication
p 0 e
p
p——Viscosity under pressure p， Pa· s； 0——Viscosity under pressure 105Pa， Pa· s； ——Pressure –viscosity coefficient (粘压系数)， ＝（1~3）×10-8 m2／N。
② Oiliness (油性)
Physical or chemical absorption film (吸附膜) →decrease friction and wear ③ Extreme pressure property (极压性) Create wear-resisting, high pressure resisting chemical boundary film ④ Oxidation resistance (氧化稳定性) The ability to resist oxidation ⑤ Flash point（闪点）and Solidifying Point （凝固点）
Boundary friction（边界摩擦）——occurs when a surface is at least partially wet, but not so lubricated 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 friction.