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1、Part IV Design of Shafts and Associated Parts Chapter 12 Sliding Bearings Key Terms: sliding bearing journal bearing sleeve, bushing hydrodynamic hydrostatic Liner, lining Bearing Geometry Ratio of bearing width to diameter l/d : 0.31.5 12.1 Types of Sliding Bearing Forces: Radial Bearing Thrust Bea
2、ring Lubrication: Dry rubbing Boundary lubrication Full-film lubricationDry Rubbing triple-layer composite material consists of 3 bonded layers: steel backing, sintered porous tin bronze interlayer and anti-wear surface. high load capacities and low friction rates, and are oil free and anti-wear. Bo
3、undary Lubrication Fnf=0.080.14The oil fills in the volume in the troughs on the mating parts. There is extensive metal-to-metal contact of the peaks and a high rate of friction and wear.Boundary Lubrication BearingFull-film Lubrication FnLubricantf=0.0010.008 Hydrodynamic BearingHydrostatic Bearing
4、Application Extremely high speed; High accuracy position, such as radio antenna or huge telescope; Extremely heavy load or heavy shock; Require split bearing, such as crankshaft Small radial space; Special working condition: water, mud, corrosive medium, etc. 12.2 Bearing Materials Failure Modes: We
5、ar, Seizing, Pitting, CorrosionMaterials: BabbittCast Bronze Cast Iron PorousPlastics: TeflonLubrication Set Lubrication Set 12.3 Construction of Sliding Bearings 1. Construction of Radial Sliding Bearings 1) Solid Bearings Characteristic: 1.Simple construction and low cost; 2.Clearance cant be adju
6、sted; 3.Inconvenient disassemble.Oil holeSleeveHouse2) Split Bearings 1house2cover4bushing5boltCharacteristic: Convenient assemble and disassemble; Clearance can be adjusted by changing thickness of shim;3) Automatic Center Regulating Bearings l / d 1.5Sleeve Forms Solid sleeve Split sleeve Typical
7、groove patterns 2. Construction of Thrust Sliding Bearings 12.4 Design of Boundary-lubricated Bearing 1) Control p Where Fradial load Bbearing width dbearing diameter pbearing pressure pallowable pressure 2) Control pv Where vrelative velocity of journal njournal revolutions per minute pvallowable p
8、v 3) Control vv vCommonly used metal axle bush material performance 4) Design Procedure Select construction and materials; Specify a ratio of bearing width to diameter; B/d=0.51.5 Compute B=d(B/d)=width of bearing; Check the bearing pressure p; Check the pv; Check the v; Select the bearing fit.Slidi
9、ng bearings commonly used coordination and application 12.5 Design of Full-film Hydrodynamic Lubrication Bearing Hydrodynamic Lubrication 1) Concept The film pressure is created by the moving surface itself pulling the lubricant into a wedge-shaped zone at a velocity sufficiently high to create the
10、pressure necessary to separate the surfaces against the load on the bearing.2) Experiment of hydrodynamic lubrication3) An example of hydrodynamic lubrication Hydrodynamic lubrication in the automobile tires on wet roads.4) Newtons Law of Viscous Flow xyu=vu=0uWhere dynamic viscosity 5) Reynoldss Eq
11、uation According to equilibrium of x-direction： According to Newtons Law of Viscous Flow： SoIntegrateBoundary condition: y=0, u=v; y=h, u=0We haveVolume When , p=pmax, h=h0，Reynoldss Equation for one-dimensional flow Univariate Reynolds equation SoReynoldss Equation Where =dynamic viscosity v=relati
12、ve speed h=oil film thickness 6）Conditions to form hydrodynamic lubrication 1)There must be a wedge-shaped space between two relative moving plates;2)There must be a relative sliding velocity between two plates, and the lubricant must flow from big entrance to small exit in the direction of the movi
13、ng plate; 3)The lubricant has sufficient viscosity, and the supply of the lubricant is abundant. 2. Formation of Hydrodynamic Lubrication in a Journal Bearing 3. Parameters Radial clearance: =R-r Relative clearance: = /r Eccentricity ratio: =e/ Minimum film thickness hmin= -e= (1- )=r(1- ) hminh, h=
14、(23)(Rz1+Rz2)4. Load Carrying Capacity Where Cp load carrying capacity coefficient Cp (, B/d) see table 12.2v, ，B， FRatio of Bearing Width to Diameter 5. The Choices of Variables 1) width-to-diameter ratio B/d B/d , F ; B/d =0.31.5Tip: The wide diameter is smaller than the value, the bearing axial s
15、ize is small, carries the aerial drainage quantity to be big, easy to radiate; The wide diameter is bigger than the value, bearing bearing capacity enhances, the friction power loss increases, elevates warm. Therefore, the high speed heavy load takes the small value, the low speed heavy load takes t
16、he great value. 2) relative bearing clearance v, ; F , Tip: The bearing clearance is small, bearing capacity and the rotation precision are higher, but the lubricating oil current capacity is small, the friction power loss is big, elevates warm. When the gap is too small, causes when smallest lubricant film thickness is too small, then with difficulty forms the liquid lubrication. Generally value main basis load and speed selection. The speed is higher, the value should be bigger; The load is bi
