摩擦磨损及润滑概述.ppt

中南大学,4-1 Friction,4-2 Wear,4-3 Lubricant、additive and lubrication methods,4-4 Introduction of fluid lubrication principle,4-0 Overview,Chapter 4 The overview of friction、wear and lubrication,中南大学,4-0 Overview,Tribology-study friction 、wear and lubrication of two surfaces moving relatively 。It is an edge principle 。, frictionTwo surfaces moving relatively hinder each other；, wear-material of object surface loses or transmit because of friction；,lubricationthe method reducing friction and wear。,About 1/31/2 energy in the world is consumed in friction。,The majority of machine elements are rejected and replaced because of excessive wear 。,中南大学,2、types of friction,Internal friction：the phenomenon of hindrance of relative movement of molecule。,External friction：the phenomenon of hindrance of relative movement of surface。,Static friction：friction having relative moment tendency。,Dynamic friction：friction having relative moment。,Sliding friction：The movement between two surfaces is relative sliding。,Rolling friction：The movement between two surfaces is relative rolling。, “mechanical theory” the friction is hindrance action of convexo-concave surface；, “molecular theory” the friction is the attractive force of molecule of material surface；,1、principle of friction, “mechanical-molecular theory” both action。,4-1 Friction,中南大学,(1) Dry friction,The surfaces of two elements contact directly，many cold-scoring points caused by high press of part area may be sheared when moving。,No dry friction！,(2) Boundary friction,3、Sliding friction,consumption of power,wear,temperature,damage the sleeve,There is a sheet of oil film between the two surfaces of pair. The thickness of oil film is less then 1m The oil film cant separate completely the two surfaces of metal body 。,f 0.1 0.3,The surface of pair have a sheet of press oil film that can separate the surface of two metal body。It is an ideal condition。,(3) Fluid friction,f 0.001 0.01,中南大学,4. Mixture friction,The friction condition of two surfaces is between boundary friction and mixture friction。The friction coefficient of mixture friction is more less than that of boundary friction。,在一般机器中，处于后三种情况的混合状态。,Friction feature curve,n/p -bearing parameter - kinematical viscosity ， p-pressure ，n-rotating speed,Boundary friction and mixture friction are very difficult to differ in engineering and always called non full-film friction。,recent development of Tribology： Millimicron Tribology,reach： f 0.001 -super-lubrication friction condition。,中南大学,wearthe material of element surface disappeared or removed because of friction。,Wear curve,4-2 Wear,The process of wear：,run-in wear period-It results from the roughness of processing surface。,stable wear period-The wear speed of element is steady and slow。,sharp wear period-the gap of pair increase and cause the vibration of machine 。The element may be rejected 。,effectlower the efficient and reliability of machine。,While designing the machine ,we wish the run-in wear period were shorten，the stable wear period were prolonged and sharp wear period were put off。,中南大学,Abrasive wear,types of wear：,Fatigure wear,Adhesive wear,Erosion wear,Corrosion wear,Fret wear,Types of wear,according to the wear theory,according to the appearance of wear surface,Pitting wear,Scorching wear,Scoring wear,中南大学,wear theory：,Abrasive wearIt is also called wear.The dust in the air and metal particle wear the element surface and produce many scores。,中南大学,wear theory：,Adhesive wearIt is also called scorching 。The friction surface interact each other and the material is removed from one metal surface to another because of “cold welding” caused by instant rise of temperature and pressure 。,中南大学,wear theory：,Fatigure wearIt is also called pitting 。The process of pitting： early fatigure crackextend particle drop and form pit。,中南大学,wear theory：,Erosion wearThe hard particles in flow fluid or gas pound the element surface。 Example: air high pressure pump。,近年来，由于燃气涡轮机的叶片、火箭发动机的尾喷管这样一些部位的破坏，才引起人们对这种磨损形式的特别注意,中南大学,wear theory：,Corrosion wearThe friction pairs is corroded and move relatively in the chemical and electrochemical environment 。,中南大学,wear theory：,Fret wearIt is a compound wear formed by all the above-mentioned theories when the friction pairs have slight shock。,example：interference fit joint of axial and hole、working surface of rivet。,中南大学,1、 lubricant,function：to lower power consumption、to decrease wear、to cool the element、to absorb vibration、to be rustproof and so on。,types,Liquid lubricant-lubricating oil,Semi-solid lubricant-lubricating grease,Solid lubricant,1) Lubricating oil,The mineral oil is widely used because it is sufficient、cheap and stable。,types,Gas lubrication-air,Organic oil-animal oil 、vegetable oil,Mineral oil-petroleum products,Chemical synthesis oil,4-3 Lubricant、additive and lubrication method,中南大学,在轴承中，润滑油最重要的物理参数是粘度，它是选择润滑油的主要依据。粘度表征液体流动的内摩擦特性。,A、B两板之间充满了液体，B板静止，A板水平移动速度为v。由于液体与金属表面的吸附作用，A板表面的液体速度为v，而B板表面的液体速度为0。两板之间的速度呈线性分布。,The friction shear stress between fluid layers：,-shear stress is proportional to velocity gradient。,- Dynamic viscosity,unit： N s /m2 (Pa s) is called poise 。,or centipoise：1P=1 dyn s /cm2,Experiment result：,分析位置y处薄层的受力,viscosity-it is an important index 。The higher the viscosity is ，the thicker oil is 。,types,Dynamic viscosity,Kinematical viscosity,Conditional viscosity,(1) Dynamic viscosity,-Newton fluid theory,1 poise=100 centipoise,中南大学,Kinematical viscosity (convenient):,unit： m2 / s,is called stoke St：cm2 /s,or centistoke cSt：1St=100 cSt,(2) Kinematical viscosity,中南大学,(3) Conditional viscosity,We use viscosimeter to measure the time the oil pass through the fixed hole under given condition to determine the viscosity。,Common use：,恩氏度（ Et） -Chinese,赛氏通用秒（SUS）-American,雷氏秒 (R)-English,The relations between Kinematical viscosity and Conditional viscosity：,The lubricant trademark relates to the kinematical viscosity 。The kinematical viscosity of L-AN10 lubricant at 40 is 10 cSt。,中南大学,Characteristics of lubricant：,(1)viscosity-temperature,Temperature t ,Pressure p , ,p 100Mpa has little change., ,viscosity-temperature diagram,L-TSA32,L-TSA32,L-TSA32,L-TSA32,Choice principle：,1) Temperature t load ,2) load 、speed .,The viscosity of lubricant not only influence the obstruction of friction pair but also play an important part in forming the oil film。,中南大学,(2)oiliness,A sheet of boundary oil film is formed and adheres to the metal surface by the absorption action.This can lower the friction and wear。,(3)polar pressure,When the polar compound which contains sulphur and phosphorus is put into the lubricating oil ,the polar molecule will improve the boundary lubricity 。,(4)flash point,When the lubricating oil is heated,the oil steam may flash at certain temperature。The working temperature of machine should lower 3040 than the flash point。,(5)pour point,When the temperature of lubricating oil is lowered,the oil cant flow freely at certain temperature。This will influence the machine to start。,中南大学,2)lubricating grease,A lubricating grease is a solid or semisolid lubricant consisting of a thickening agent in a liquid lubricant. Soaps of calcium 、sodium and aluminum are the major thickening agent 。,Advantage： (1)less frequent lubricant application is necessary; (2)less sensitive to the temperature and speed 。,Disadvantage：The machine efficiency is low 。,Calcium grease,-widely used in engineering,types,Aluminum grease ,Soda grease,中南大学,polyvinyl fluoride resin,appliance situation：used in the situation in which lubricant oil can not work，such as high temperature、low speed and heavy load、the situation in which clean environment is required.,graphite,molybdenum disulfide(MoS2）,-steady performance、when t 350 begin to oxidize， can work in water.,-low frictional coefficient，used in wide-range of temperature (-60300 )，But the performance reduce as soon as meeting water.,-low frictional coefficient ,being half of that of graphite,the methods of use：,(1).mixed with oil；,(2).coated、sintered on friction surface to form covering film；,(3).mixed with metal or plastic powder,then sintered to form bearing,其应用日渐广泛,3)solid lubricant and its choice,characteristics：solid film is formed on slide surface,中南大学,Oiliness agent,types,Additive -in order to improve the property of lubricant ,we always add some materials。,2、additive,function-limit chemical change、improve oiliness、prolong use life and so on。,Polar agent,Antifoam agent,Oxidation inhibitor,Pour depressant,Viscosity-index improver,中南大学,The lubricating oil is used very universally in engineering 。,3、lubrication methods,Lubrication methods,manual lubrication；,drip-feed lubrication；,splashing lubrication,oil jet lubrication,oil jet lubrication,drip-feed lubrication；,lubrication in oil bath,splashing lubrication,lubrication in oil bath,中南大学,4、lubrication equipments,1) oil cup,中南大学,2) oil ring,中南大学,1、fluid hydrodynamic lubrication,先分析平行板的情况。板B静止，板A以速度向左运动，板间充满润滑油，无载荷时， 液体各层的速度呈三角形分布，近油量与处油量相等，板A不会下沉。但若板A有载荷时，油向两边挤出，板A逐渐下沉，直到与B板接触。,4-4 Introduction of fluid lubrication principle,While moving relatively , the two friction surfaces separate completely by the viscosity oil film。The pressure of oil film bears the load。,hydrodynamic oil film,The pressure oil cant exit between two parallel plates！,如两板不平行板。板间间隙呈沿运动方向由大到小呈收敛楔形分布，且板A有载荷， 当板A运动时，两端速度若程虚线分布，则必然进油多而出油少。由于液体实际上是不可压缩的，必将在板内挤压而形成压力，迫使进油端的速度往内凹，而出油端的速度往外鼓。进油端间隙大而速度曲线内凹，出油端间隙小而速度曲线外凸，进出油量相等，同时间隙内形成的压力与外载荷平衡，板A不会下沉。这说明了在间隙内形成了压力油膜。这种因运动而产生的压力油膜称为动压油膜。各截面的速度图不一样，从凹三角形过渡到凸三角形，中间必有一个位置呈三角形分布。,中南大学,Essential condition of formation of hydrodynamic oil film：,1) There is wedge-shaped clearance between two element surfaces；,2) There is sufficient liquid between two element surface；,3)The two element surface must slide relatively。The liquid must flow from big cross section to small one。, Fy =F Fx 0, Fy =F Fx = 0,example-formation of hydrodynamic oil film of radial sliding bearing：,static,climb,raise the shaft转速继续升高,revolve stably达到工作转速,e -eccentric distance,中南大学,2、hydrodynamic lubrication of elastic fluid,hydrodynamic lubrication of elastic fluid -study the mechanical characteristics of hydrodynamic lubrication of elastic subjects which contact on point or line。,pressure and thickness distribution of oil film,the premise of fluid hydrodynamic lubrication:,-suitable for the low pair，,Viscosity doesnt change with the pressure.,friction surface is rigid body；,中南大学,While two cylinder rolling on each other ,the lubricant is brought into the clearance。Because the pressure of contact area is very big, the parallel clearance forms and smaller clearance of oil exit emerges。 When the oil film forms, the second pressure of peak value appears。,Dry friction contact,Theory of hydrodynamic lubrication of elastic fluid,中南大学,Working principle：The high pressure oil is pressed into the bearing clearance by the oil feeding device and the oil film is formed。,characteristics： Hydrostatic bearing is fit for any operating mode。,flow control valve,Key elements： flow control valve,Function of low control valve ：adjust automatically the oil pressure。,3、hydrostatic lubrication,1) Hydrostatic bearing,中南大学,2) Air bearing,Air is also one kind of fluid lubricant。The viscosity of air is only 1/4000 of L-AN7 lubrication oil。The air resistance is very small 。 The air bearing can revolve at 100000r/m。,The working principle of air bearing is the same as that of fluid bearing。It can be divided into static-pressure bearing and dynamic bearing 。,Thickness of gas film-20m,Manufacture precision,Filtrate seriously,Advantage：1)dont change with temperature, fit for high temperature or low temperature；,2)dont have oil pollution；,3)Revolve precision is high and noise is low。,disadvantage：The bearing capacity is not big .It is difficult to seal 。,