機(jī)械設(shè)計基礎(chǔ) 精品課程 滑動軸承

1、第十二章Sleeve bearings 滑動軸承§12-1 General considerations 概述§12-2 Materials of sleeve bearings(materials of bearing shells and inserts滑動軸承材料(軸瓦及軸承襯材料§12-3 Simplified calculations for bearings operating with non-fluid friction非液體摩擦軸承設(shè)計計算§12-4 Load-carrying mechanics of thehydrodynamic

2、lubrication bearings液體動壓潤滑軸承承載機(jī)理§12-1 general considerations概述一、Types of sleeve bearings分類I With respect to friction condition:按摩擦狀態(tài)分1Non-fluid friction bearings非液體摩擦軸承2Fluid friction bearings液體摩擦軸承II With respect to load-carrying direction 按承載方向分:1Thrust bearings 推力軸承:FA 2Radial bearings 向心軸承:

3、F rRadial bearings 向心軸承:F rSolid bearings :used for low speed and light load shaft (the clearance in the bearing can not be adjusted and it is difficult to assembly整體式:低速輕載(間隙不可調(diào),安裝困難Split bearings: common application剖分式:一般應(yīng)用Solid shellSplit shells二、Characteristics and applications特點(diǎn)和應(yīng)用1、AdvantagesO

4、perating steady , reliably and noiselessly工作穩(wěn)定、可靠、無噪音Under fluid friction, friction and wear are smalland oil film has a marked damping effect液體摩擦?xí)r,摩擦、磨損小,油膜吸振2、ShortcomingsHigh starting torque 起動阻力大3、Applications 應(yīng)用Shafts running at exceptionally high speeds or requiring high-precision guidance or

5、carrying heavy load (fluid friction bearings高速、重載、精密(液體摩擦滑動軸承Shafts running at low speed noncritical mechanisms (non-fluid friction bearings 低速、輕載、精度要求低時(非液體摩擦滑動軸承Special occasion:for example, split shell is required or operating in aggressive media.特殊場合:如必須剖分或者宇航、探海等三、Contents of the chapter本章內(nèi)容Sel

6、ection of the bearing materials軸承材料選擇Design of non-fluid friction bearings非液體摩擦滑動軸承設(shè)計計算Load-carrying mechanics of thehydrodynamic lubrication bearings 液體摩擦軸承承載原理§12-2 Materials of sleeve bearings (materials of bearing shells and inserts 滑動軸承材料(軸瓦及軸承襯材料 Bearing shell:Element contacting directly

7、with journal軸瓦:軸承直接與軸頸相接觸的零件Bearing insert: thin layer which is adhered on bearing shell by casting or pressuring in.軸承襯:有的軸瓦是在軸瓦整體上用澆鑄或壓合的方法粘附上一層另一種材料,這一薄層材料稱為軸承襯。一、Requirements for bearing materials:Small friction coefficient, good heat conductivity and low linear expansion coefficient(efficiency

8、high, stable dimension and small temperature increase operating 摩擦系數(shù)小,導(dǎo)熱性好,熱膨脹系數(shù)小(效率高、尺寸穩(wěn)定、溫升小High wear resistance, good corrosion resistance and anti-seizing耐磨、耐蝕和抗膠合性好Enough mechanical strength(anti-impact, anti-press and anti-fatigue (prevent from press and fatigue failures 足夠機(jī)械強(qiáng)度(沖擊、抗壓、疲勞(避免壓潰和疲

9、勞破壞Capacity for being run in readily and low modules of elasticity 一定順應(yīng)性和嵌藏性順應(yīng)性:適應(yīng)軸偏斜的能力 減小偏載嵌藏性:容納異物的能力避免軸頸傷和磨損(彈性模量小塑性增加順應(yīng)性和嵌藏性好Good processing properties, such as castability, manufacturability, etc良好的工藝性(容易鑄造和加工.二、Major bearing materials常用材料1、軸承合金(白合金、巴氏合金babbittsbased on tin 錫銻軸承合金:ZChSnSb11-6b

10、ased on lead 鉛銻軸承合金:ZChPbSb16-16-2 Advantages:Small friction coefficient and high anti-seizing Used for high speed and heavy load摩擦系數(shù)小,抗膠合性好用于高速、重載Shortcomings:High cost and low strength Used forbearing inserts價格高、強(qiáng)度低用作軸承襯2、Bronzes 軸承青銅Tin bronzes 錫磷青銅:ZCuSn10P1Leaded bronzes 錫鋅鉛青銅:ZCuSn5Pb5Zn5 Alum

11、inum-iron bronzes 鋁鐵青銅:ZCuAl9Fe4Ni4Mn2 Advantages:High strength, high wear resistance and good thermal conductivity. Used for bearing shell and inserts強(qiáng)度高、耐磨性好、導(dǎo)熱性好,即可用于軸瓦,又可以作軸承襯3、Brass: used for low speed and medium load黃銅:低速中載4、Cast iron: used for low speed and light load鑄鐵:低速輕載5、Bearings filled

12、with oil 含油軸承: Sintered metal powders粉末冶金材料Porous structure、Filled with oil Self-lubrication多孔、含油自潤滑Bad roughness 韌性差Used for steady load and places which is difficult or impossibleto lubricate 平穩(wěn)無沖擊、難于用油潤滑處Iron-graphite Fe石墨Bronze-graphite Cu石墨6、Plastics軸承塑料Advantages:small friction coefficient, se

13、lf-lubrication and low modules of elasticity摩擦系數(shù)小,自潤滑性和嵌藏性好Shortcomings:bad heat-resistance and lowthermal conductivity. When they absorb moisture,sizes expansion takes place. Otherwise, undercommon load, dramatic deformation will takeplace in plastics bearings.耐熱性、導(dǎo)熱性差,吸水膨脹,易變形常用作軸承襯三、Structures of

14、 bearing shell 軸瓦結(jié)構(gòu)Bearing inserts are used 加軸承襯1、Bearing shells 軸瓦Single metal shell單金屬軸瓦Double metals shell雙金屬軸瓦Three metals shell三金屬軸瓦2、Oil hole, oil groove and oil chamber油孔、油溝、油室Oil hole 油孔 For supplying oil 供油Oil groove 油溝Conveying oil 輸送油Distributing oil 分布油Equispacing oil 均布油Reserving oil 貯油

15、Steadily supplying oil穩(wěn)定供油Oil chamber 油室Oil grooves are cut in zones where there are not force or there are smaller force in order to supply oil easily and prevent from reduce load-carrying ability at same time.油溝開于不受力或者受力較小區(qū),以利供油,同時避免降低承載能力§12-3 Simplified calculations for bearingsoperating wi

16、th non-fluid friction非液體摩擦軸承設(shè)計計算一、Types of failures and design criteria失效形式和設(shè)計準(zhǔn)則Wear boundary film do not lose磨損邊界膜不破裂This has many affecting factors andanalyses are considerably complicated simplified calculation因素多,復(fù)雜條件性計算FdBRadial bearings 徑向軸承:Average pressure is limited (prevent from oil to be

17、force out 限制平均壓強(qiáng)(防油擠出過度磨損(p p MPa p dB F p 只校核低速或間歇轉(zhuǎn)動軸承,=Only check p<p for low speed or pause rotating bearingspv is limited: (prevent from excessive temperature increasing oil film lose excessive wear 限制pv 值(防溫升t 過大油膜破裂過度磨損m/sMPa pv 2000F 100060dB F pv 1B n nd T =vv m/s (Prevent from excessives

18、peed quick wear (p 較小時(防v 過大加速磨損v 100060v dn =p、pv、vP161表9-1Thrust bearings 推力軸承(:油環(huán)數(shù)-=-=Z m/sMPa pv Z d d 0003Fn pv MP p Z d d 4F p m/s MPa pv pv MPa p p 0202 (液體軸承起動、停車:混和摩擦狀態(tài)§12-4 Load-carrying mechanics of the hydrodynamiclubrication bearings液體動壓潤滑軸承承載機(jī)理一、Basic equation of hydrodynamiclubri

19、cation-Reynolds equation (1886年液體動壓潤滑基本方程雷諾方程30h h h V 6-=x p1、Assumptions假設(shè)Compared with forces of viscous shear, inertia and gravity of the fluid are very small and are neglected與粘滯阻力相比,流體慣性力、重力很小,忽略Flow of lubricant belong to laminar flow潤滑油為層流流動yv =-服從牛頓剪切定律:Forces of viscous shear developed in

20、the layers can be determined by Newton s law of viscous flow.Sliding do not exist between lubricant and planes 潤滑劑與板面無滑動The dimensions in the direction perpendicular to the drawing are assumed to be infinitely large 軸承無限寬(Z向無流動Viscosity and density of the oil do not depend on pressure流體粘度、密度與壓力無關(guān)2、I

21、ntroduction 推導(dǎo) By means of:Equilibrium equation of the oil 流體平衡方程N(yùn)ewtons law of viscous flow 牛頓內(nèi)摩擦定律Principle of continuity of flow 流體流動連續(xù)性方程yv=-xqx=Reynolds equation 雷諾方程Equilibrium equation of the oil流體平衡方程0F x=(假設(shè)1.yx p 0dydxdz y(dxdydz x p (p dxdz pdydz -=+-+-+Newtons law of viscous flow 牛頓內(nèi)摩擦定律

22、(假設(shè)2=-.y v x p y v 22-=By integrating twice and substituting the boundary conditions 積分 x p 122dy x p 2(vdy q 43h 0h 0x -h Vh y h y h y h V =無側(cè)漏:量(假設(shè)面單位寬度面積上的流單位時間內(nèi)流經(jīng)任一剖The volume of oil flowing per second through a clearance of height h and unit width is (side leakage do not existBy means of principle of continuity of flow處的=方程(假設(shè)用不可壓縮流體連續(xù)性h p h (2Vh q 0x p :p p const q 0xq 5max 000max x x =(雷諾方程30h h h V 6-=x p-=>而且是收斂楔形。(相