讲义资料(润滑材目次)英文.xls

LectureLecture ContentsContents 1 Transition for development of solid lubricants1 2 Function and role of solid lubricants1 3 Classification for solid lubricants2 4 Solid lubricants used for Automobiles2 5 Graphite2 5 1 Lubricity of graphite2 3 5 2 An element to affect graphite friction and wear3 4 6 MoS25 WS27 8 Appendix 1 Variety o solid lubricants 9 2 Oxidation rate of graphite MoS2 and WS2 10 3 Definition of tribology and solid lubricants by OECD12 2 On Solid Lubricants 1 On1 On thethe TransitionTransition forfor thethe DevelopmentDevelopment of of SolidSolid ubricantsubricants 1 Before 1930 Physical and chemical structures which are common to slippery materials such as graphite and MoS2 ha been studied materials with slip plane have a great possibility of lublication that a theory governed in those days 2 1940 s The development of aircraft technology caused a plane to be able to fly at higer altitude less air but it happened frequently that a carbon brush used for motor showed an abnormal wear The scientist named Dr Savage at GE discovered the phenomena of graphite lubrication that graphite shows no function of lubrication without air or moisuture absorption He has found that graphite lubrication needs gas absorption but not crystal strucrure of graphite which had been supported for a long time 1948 Vapor lubrication theory 1946 The P T F E was developed and commercialized by Dupont 3 1950 An extension of Savage theory have found the difficulty of application to other solid lubricants such as MoS2 WS2 BN and Talk lubrication mechnism for those materials decided by other new theories 4 1970 s A detailed reseach and development by NASA has found a new type of solid lubricants such as BN and CF Lubrication mechanism of graphite has been found to be different from that of MoS2 5 1980 s to the present Use of metal sulfides Sb2S3 and metal oxide Sb2O3 which have widely been used as high temperature solid lubricants with an excellent friction properties for a long time is regulated owing to an emviromental reasons 2 Function2 Function andand rolerole of of solidsolid lubricantslubricants 1Rationalization and stabilizatoin of by transfering to the mating materials 2 Minimization of wear by protection for friction surfaces 3 Reduction and improvement for NVH by smooth lubrication 3 3 Classification3 Classification forfor solidsolid lubricantslubricants Kinds of solid lubricantsRepresentative solid lubricants 1 Materials with lamellar struactureGraphite Various metal sulfides MoS2 WS2 SnS 2 Materials with non lamellar structurePbO PbS Sb2S3 3 Metals with thin filmLow melting metals such as Pb Bi 4 Organic materialsP T F E 5 Synthtic materialsCF BN 6 OthersFluorides CaF2 BaF2 AlF3 and others 4 4 SolidSolid lubricantslubricants usedused forfor AutomobilesAutomobiles Asbestos age Graphite PbS PbO Sb2S3 MoS2 NAO age Graphite Sb2S3 MoS2 Green friction material Graphite SnS SnS2 P T F E Green friction materials are called for the materials with emviromental problems the use of which is regulated or restricted 5 Graphite5 Graphite The reprsentative solid lubricants with lamellar structure such as graphite and MoS2 are used because of having excellent lubricity Well known is the lubricity of graphite are 1 Graphite with a lamellar structure shows an excellent lubricity in air 2 Graphite is very stable physically and chemically 3 Graphite adheres so strongly to the friction surface to make thin film that it is hardly to be exfoliated 4 Graphite covers friction surface with the film of a low shearing strenght which helps to reduce friction and wear 5 1 Lubricity of graphite A lots of studys for the explanation of graphite lubrication for graphite lubrication have been made but can roughly be divided into the following two theories 1 Internal slip theory The theory to decide the friction of largeness and smallness by slip plane and the strength of shearing force 2 Gas absorbing theory The theory of an absorbed gas to promote lubricity A scientist Bragg has found graphite crystal structure to be hexagonal closed pacage H C P using X ray diffraction and then shearing to be likely to occur at the surface between their weak lamellar bonding strengh and this to be 4 the main causes of lower friction Meanwhile Savage explained that graphite shows lower friction and less wear in air however an abnormal wear and high in vacuum the friction phenomena of which are reffered to gas absorption Eventually he has done has done the various friction tests in different atomospheres and made announcements of test reslts We have not however yet attained the fixed theory of graphite lubrication up to now 5 2 An element to affect graphite friction and wear 1 Crystalization The higher crystallization the more stabilization and the less wear 2 Impurity The less impurities the less wear Graphite with fixed carbon rate more than 99 and its ash impurities less than 1 0 shows a small wear Graphite in fixed carbon rate less 80 shows fluctuation of and increase of wear Graphite with less impurities such as SiO2 Al2O3 shoud carefully be selected because those impurities considerably affect not only friction but also wear 3 Grain size The larger a graphite size is the better lubrticity lower In the application of graphite to brake materials a small size graphite with a large specific surface area and flake graphite with larger specific surface area have an advantage over the large ones when the friction temperature remains within the limit of the temperature not to begin plastic fluidity As a results small graphite shows less wear in both friction materials and its mating one while the friction temperature risin to the temperature over plastic fluidity of the brake binder causes small graphites to be covered by those layers of plastic fluidity And therefore the absence of contact with its mating material causes small size graphite to lose its function entailing wear increase Large size graphites provide us with better friction performance in higher temperature brake applications In an actual brake formulation at leas two different garin sizes of graphite are to be employed to meet the requirements properly to cover a wide range of temperature from low to medium and to high levels Table 1 shows graphite grain sizes and their function 5 Table 1 Example of graphite formulation in brake pads wt Grain Kinds TemAdditionConsiderations size Mesh rangerate SmallNatural150 325 Lower0 4 0 6 having large surface areas SmallArtificial150 325 Middle 0 8 1 4 lubricate wide range of temperature CoarseArtificial20 50Higher3 5Well functionning at high temperature 4 Atmospere dependence Friction materials containinng a lot of graphite such as semi metallic pads are liable to be affected by humidity and for an example friction characteristics are different in winter and summer and a great difference can be seen in NVH issues in particular This indicates that graphite lubricatoin is caused by the gas absorption or the on the surface of graphite of lubrication of gas films as proposed by Dr Savage but not its by graphite crystal structure This tendency differs more or less from the type of graphite An experimental study is shown in the table as follow Table 2 Friction test results in various atmospheres Kinds of graphiteAirDry air Vacuum Natural graphite Air 15 65 Artificial graphite 10 MoS2 Friction characteristocs of MoS2 can be seen to be free Here means 0 1 0 25 0 26 0 40 0 41or more Here means Wear 1 0 1 2 1 21 1 50 1 51or more Graphite shows a high in vacuum atmosphere and much wear irrespective of graphite size And also graphite is unable to display its lubricity in dry conditions 5 Improvement of heat resistance property for graphite Graphite with fine particles and natural graphte with large specific surface areas begin oxidation from a low temperature of 400 and reduce weight To prevent graphite from oxidizing surface of graphite will be coated by phosphate and to prevent graphite surface from direct contact of air a lubrication of graphite can therefore be used up to the higher temperature ranges Oxidation resistance for graphite can be performed by reaction between graphite and phosphate of alkaline metals Friction characteristics and oxidation resistance for graphite are improved by the graphite surface treatment of phosphate magnesium Mg PO3 2 Bibliography 6 1 Graphite lublication mechanism Effect for gas gas absorption R H Savage Graphite lubrication J Appl Phy 19 1 1941 1 2 Graphite lubrication by its crystal structure W A Gragg Introduction to crystal analysis G Bell one is that it is the abrassive material and another is not the material havin