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1、Part I Connections,TypesStatic connectionReleasable connections such as thread,key and pin connections;Non-detachable connections such as weld,bonding and riveting c-onnections,Motion connectionKinematic pair,51 Thread,Right-hand and left-hand threads:A right-hand thread is one that advances into a
2、nut when turned clockwise(figure a).A left-hand thread is on the advances into a nut when turned counterclockwise(figure b).A thread is always considered to be right-handed unless specified otherwise.A left-handed thread is always labeled(LH)on a drawing.,(I)Main parameters of threads:,Single and Mu
3、ltiple Threads:A single thread is composed of one ridge(脊)and the lead is equal to the pitch(齿距)(figure a).A double thread is composed of two ridges and the lead is equal to twice the pitch(figure b).A triple thread is composed to three ridges and the lead is equal three times the pitch(figure c).,T
4、hree diameters：(Major Dia.(大径)Standard Dia.(标准直径)；1(Minor Dia.(小径)；2(Pitch Dia.(中径),Two heights：p(pitch,螺距)；(Lead,导程)；(Number of threads,螺旋线数);n p;(Helix angle,升角);a(Thread angle,牙型斜角);tgn p2,(II)Types and applications of threads(Table 5-1),Connecting threads(联接螺纹):Plain thread,Gas thread(管螺纹)Transm
5、ission threads(传动螺纹):Rectangular thread,trapezoidal thread(梯形);Saw-tooth thread(锯齿形),1.Connecting(triangular)threadsPlain thread(普通螺纹):60large leads to large f,easy to self-lock Coarse thread(粗牙):small d1,big Thury thread(细牙):large d1,small,more easy to self-lock,Gas thread：(British system,英制)55tigh
6、t(Metric system,米制）60tight,2.Transmission thread small,big,multiple threads,high efficiency Trapezoidal thread(Tr)30 15Saw-tooth thread(S)33w3nw30Rectangular thread(R)(or 1),Working surface,Feed screw of a machine tool,Forcing press(压力机),IFundamental types of the threaded connection*,52 Types of the
7、 threaded connection and the standard connecting pieces,1.Bolt Connection(螺栓联接),Plain bolt connection:There is clearance between the hole and the bolt,it is conveni-ent to install and commonly used.,Connection with reamed hole(铰制孔),hole basis(基孔制)，transition fit(过渡配合,H7/m6,H7/n6）：No clearance,with h
8、igh costs,2.Studded Connection(双头螺柱联接),It is used when one of the connection pieces is very thick,3.Screw connection(螺钉联接),4.Holding screw connection（紧定螺钉连接）,5.Special screw connection Ground screw connection(地脚螺钉联接)Lifting bolt connection(吊环螺钉联接),IStandard components of threaded connections Bolt Bo
9、lt；Screw；Threaded stud；Holding screw,Nut(螺母)Hexagon nut(六角螺母)；Round nut;Round nut with groovesGasket(垫片)Flat gasket(平垫片)；Spring shim(弹簧垫片)；Bevel washer(斜垫片)；Spherical washer(球形垫片),According to GB/T 3103.1-1982,components of threaded connections includes three accuracy classes,i.e.,A-class,B-class an
10、d C-class.A-class has the highest degree of accuracy,it is applied for important thread connections requi-ring exact fit and vibration-proof；B-class is used to thread connections subjected to heavy loads or fluctuating loads and those needing frequent adjustment or dismounting.；C-class is often used
11、 to ordinary thread connec-tions.,53 Pretension of thread connection,Purpose：prevent connection from becoming loose improve reliability,strength and tighteness,F0,When screw down(拧紧时)pretightening force(预紧力)F0:,bolt(螺栓)pre-tension(预紧拉力)connecting pieces(被联接件)pre-compression(预紧压力),T1:resisting moment
12、(螺纹阻力矩),T2:frictional resistance moment(摩擦阻力矩)at supporting surface of the nut,Tightening torque T:T1+T2,1F d2/2F0 tg(v)d2/2,TT1T20.2F0d Because F0=5T/d,if d is small，F0 will be big.It is suggested that the major diameter should be larger than M12,T2 fc F0 r m,:Helix angle；Equivalent friction angle
13、v=arctan1.155f,54 anti-loose of thread connection,Tightened v(self-lock)anti-loose？,If impact,vibration and variable loads happen,fricti-on may disappear,so that self-lock by friction is unrel-iable,therefore,anti-loose is necessary,Friction anti-loose:Maintain longitudinal and lateral pressure betw
14、een contact area of threads resistance moment will not disappearMechanical anti-looseConstrain the screw pair by the metal elements being easy to replaceUndetachable anti-loseweld,riveting and bonding,Anti-lose method：Prevent screw pair from relative turning,I Strength calculation of loose bolt conn
15、.(no0),Tight bolt conn.:have pretightening force and operating tension,Loose bolt conn.:no pretightening force,only operating tension,5-5 Strength calculation of bolt connection,Check,Design,Tight bolt conn.,II Strength calculation of tight bolt conn.(have0),Bolts with M10M64：0.5 Calculation stress：
16、ca=,Pretightening force and operat-ing tension,Only pretightening force,Tight bolt conn.,Screw downtightening torqueshear stress Screw downtightening torquetension stress,1.Tight bolt connection with only pretightening force,F0 have relation with lateral loads,2.Pretightening force 0+operating tensi
17、on,Tight bolt conn.,Screw downpretightening tensionLoadoperating tension,Total force F2 0+=？,Tightened:elongate b F0 shorten m F0,Bolt Connecting pieces,Loaded:elongate again relax,Pressure of connecting pieces：Residual pretightening force:F1=F0 F,Total force F2：F2=F0+F=F+F1,Deformation compatibilit
18、y condition：is the same,Cb=F0 b bolt stiffness Cm=F0 m Connecting pieces stiffness,Relative stiffness of the bolt,Relative stiffness should be as small as possible,the recommendation is：metal gasket(or no gasket)0.20.3，leather gasket(皮革垫片)0.7，copper asbestos gasket(铜皮石棉垫片)0.8，rubber gasket(橡胶垫片)0.9。
19、,Relative stiffness of the bolt,（1）Static strength formula：F is a constant,：1）to reduceF2，you must reduce relative stiffness of the bolt，i.e.,Cm Cb 2）to keep tightness of the bolt conn.,F1 must be larger than 0,（2）Formula of fatigue strength：F=0F,F=0FF2=F0 F2,variable stresses are between min max,3
20、Tight bolt conn.under shear stresses,Reamed hole bolt:the lateral force F is equilibrated by shear and pretighting loadings,Crushing strength between the bolt and the hole：,Notice：1）d0 is the diameter of a shear plane 2）Lmin is minimum height of the compressive plane 3）pis the smaller of the materia
21、ls,Shear strength of the bolt：,Notice：1）d0 is the diameter of a shear plane 2）Lmin is minimum height of the compressive plane 3）pis the smaller of the materials,Homework,Problem 5-9 on page 102(8th Edition),Performance rate(性能等级)of Bolts,the screws and double-screw boltsincluding ten levels(Table 5-
22、8)the digits before the decimal point indicate sB/100,and after the decimal point ss/sB E.g.,4.8 indicates B=400Mpa and s=320Mpa Performance rate of the nutsincluding 7 levels(Table 5-9)The digits indicate roughly smin/100,I Materials of conn.pieces,5-7 Materials and allowable stresses of Conn.Piece
23、s,II Allowable stresses of conn.pieces,S、S、SpSafety factor(Table 5-10)：To search safety factors for Tight bolt conns.,pilot calculation(试算)is necessary.,Aim：Shapes of adjoining planesymmetrical,convenient for manufacture,same centroid(形心)Bolt arrangementenough space and edge distan-ce for a wrench(扳
24、手),see Table 5-5,I Structural design of the bolt groups,56 Design of bolt groups,Processing and installationDiameter and length of the bolts is the same Amount of bolts on the circumference should be 4,6 and 8,Adjoining plane and boltuniform stress distribution,avoid additional bending moment.,Later
25、al loads,Axial loads,II Mechanical analysis on bolt groups,Loading types,Aim：Find out the bolt subjected to the largest force and solve the force,Torque,Bending moment,Equilibrium condition：f F0 z iKs FF0 Ks F z i f KsAnti-skid coefficient,Ks=1.11.3 iNumber of adjoining planesffriction coefficient(T
26、able 5-6),The force of each bolt：F=F z znumber of bolts,1）Reamed-hole bolt conn.,1 Bolt groups subjected to lateral load F,Tightened pretighting force F0 friction force between adjoining planecarry loads,2）Plain bolt conn.,Discussion:if f=0.2,z=1,i=1,Ks=1.2,then F0=Ks F z i f=6 F,1）Loads in plain bo
27、lts are larger than those in hinged bolts，in this moment the latter should be selected 2）If you use plain bolts，load-shedding keys,pins and sleeve,1）Hinge hole bolt conn.,2 Bolt groups subjected to torque T,Shearing deformation of a bolt is in direct proportion to the distance ri to the centroid o,s
28、o that the shear-ing force Fi is also in direct proportion to ri.The di-rection of Fi is perpendicular to the radius vector(向径)to the centroid o.,Torque equilibrium condition：,Maximum working shearing force：,2）Plain bolt connection,Analysis：it is assumed that the pretightening force F0 in each bolt
29、is the same,so that the friction between the adjoin-ing plane is also the same.,z numberri radius Ksanti-skid factor,Torque equlibrium condition：,f F0 r1+f F0 r2+f F0 rz KsT,Pretightening force need in each bolt:,螺栓受拉力为：F=F z,3 Bolt groups subjected to axial loading F,：Apart from working tensile for
30、ce F,the bolt also carries pretightening force F0,No M：only F0Apply M：tensile force increases on one side,and decreases on another side,4 Bolt groups subjected to bending moment M,Equlibrium condition：,1）loads in bolts,Working loads in the bolt subjected to maximum load:,Lidistance to central line o
31、-o,Total central force F2:,2）Connecting pieces and base plate,防止接合面被压溃：pmax=p+pmax p,防止接合面出现缝隙：pmin=p-pmax 0,0,p查表57,W抗弯截面系数,螺栓联接的受力分析,指出图中受力最大的螺栓,Homework,Problem 5-5,5-6 on page 101(Edition 8),一 降低影响螺栓疲劳强度的应力幅,58 提高螺栓联接强度的措施(四种),降低螺栓的刚度：增加螺栓长度 采用腰状杆螺栓或空心螺栓,增大被联接件的刚度：不用垫片或采用 刚度较大的垫片,3 同时采用三种措施：预紧力、
32、螺栓刚度、被联接件刚度,二 改善螺纹牙上载荷分布不均匀的现象,原因：螺母与螺栓的变形性质不同 螺母与螺栓的刚度不同,改善措施：采用均载螺母（悬置螺母、内斜螺母等）使螺母受拉或改变螺母牙受载位置 采用钢丝螺套，利用其弹性来均载,三 减少应力集中的影响,措施：采用大圆角、卸载槽，加工 支承面、加球面垫圈,采用冷镦和滚压方法，提高疲劳强度,四 采用合理的制造工艺方法,一.类型:按传导螺旋传递运动为主,高的运动精度用传力螺旋传力为主,以小T大的轴向力Q途调整螺旋调整零件间相对位置细牙M,59 螺 旋 传 动,按 滑动螺旋=0.30.4，简单，精度低摩擦滚动螺旋0.9，复杂高精度、高效性质静压螺旋,二、
33、滑动螺旋的结构和材料（了解）,结构运动转变方式有：螺杆转动，螺母移动,机床进给丝杆,起重螺旋,螺母转动，螺杆移动螺母固定，螺杆转动及移动,螺杆固定，螺母转动及移动,螺母结构,整体螺母结构简单，但由磨损产生的轴向间隙不能补偿，只是用于精度要求较低的螺旋。组合螺母结构复杂，但可以定期地调整，以消除轴向间隙，避免反向转动时的空行程。,剖分式螺母结构复杂，但可以补偿旋合螺纹的磨损。,材料,a、螺杆低速轻载：不经热处理的Q235、Q275、45；较高速重载：热处理的40Cr、65Mn、20CrMnTi；精密传导：热处理的9Mn2V、CrWMn、38CrMoAl。b、螺母一般传动：ZCuSn10Pl、ZC
34、uSn5Pb5Zn5重载低速：ZCuAl9Fe4Ni4Mn2、ZCuZn25Al6Fe3Mn3重载调整：35、球墨铸铁低速轻载：耐磨铸铁大尺寸：钢或铸铁做外套，内孔浇铸青铜高速：钢或铸铁做外套，内孔浇铸巴氏合金。,三、螺旋传动的设计计算,失效形式及校核内容主要失效形式：磨损(Wear)校核：受力较大的传力螺旋：校核螺杆危险剖面及螺纹牙的强度(Strength)；精密的传导螺旋：校核螺杆的刚度(Rigidity)；长径比很大的螺杆：校核其稳定性(Stability)；高速长螺杆：校核其临界转速(Critical speed)；要求自锁的螺杆：校核其自锁性(Self-locking)。,耐磨性计算
35、(Wearing resistance),工作面上的压力p：,A螺纹承压面积（mm2）；,d2螺纹中径（mm）；,h螺纹工作高度（mm）；,u螺纹工作圈数，uHP H螺母高度（mm）,P螺距（mm）；,F轴向力（N）；,令 Hd2，则 Hd2，代入整理后得,矩形和梯形螺纹，h0.5P，则,30的锯齿形螺纹，h0.75P，则,：整体螺母：1.22.5；剖分螺母，兼作支承螺母：2.53.5；传动精度高、载荷大、寿命长：4。螺纹工作圈数不易超过10圈。,（设计公式）,自锁条件,螺杆的强度计算,式中：,FAxial Direction Pressure（N）；AArea of Dangerous Se
36、ction（mm2）；WTAnti-torsional Section Modulus(mm3)；TTorque（Nmm）；Admissible stress of material（MPa）。,螺母螺纹牙的强度计算,剪切强度：,弯曲强度：,式中：b牙根部的厚度(mm)，,矩形螺纹b0.5P，梯形螺纹b0.65P，锯齿形螺纹b0.75P；,l弯曲力臂(mm)，,螺母外径与凸缘强度计算,a、bb剖面拉伸应力,b、凸缘与底座接触表面挤压强度,考虑摩擦力,c、凸缘根部的弯曲强度,螺杆的稳定性验算,稳定条件：SSCFcrFSS SSC稳定性计算安全系数 SS 稳定性安全系数,Fcr螺杆临界压力 按Sl
37、i 选用不同的Fcr,传力：SS3.55.0传导：SS2.54.0精密或水平：SS4,在Sli公式中：螺杆长度系数，查表5-14；l 螺杆工作长度(mm)，,i螺杆危险剖面的惯性半径(mm),两端支承，取支点间的距离，一端螺母支承，支点取螺母中点；,s100，且B480 Mpa的优质碳钢,s100，且B380 Mpa的普通碳钢,s40时，不必进行稳定性校核。,s100,按Sli 选用不同的Fcr的公式：,Ssc,稳定条件：SSCFcrFSS,不满足此条件怎么办？,Fcr,增大螺杆小径d1,小 结1.螺纹主要参数及分类，螺纹联接基本类型。2.螺纹联接的拧紧目的及防松方法。3.螺栓联接的受力分析和
38、强度计算,螺栓联接,紧螺栓,松螺栓轴向载荷F=FA,铰制螺栓横向载荷、转矩 剪切和挤压,普通螺栓,预紧力F0横向载荷、转矩=1.3 F0 A,预紧力+轴向力F 螺栓轴向载荷=1.3 F2 A F2=F1+F,A=d124,Design of Screw prop（螺旋千斤顶设计）,Reference book:Guidebook for Machine Design(洪家娣主编 机械设计指导 Page 292）Your should hand in the following materials:(1)Instruction book for design calculation(设计计算说明书);(2)Assembly diagram(装配图)(A3)Deadline:20 Oct.,1.大径 中径 小径.2.内径;55;60.3.(3);(1);(1);(3)4.A B C;C.5.(3).6.(4).7.C.8.(2),
