机械设计5章 螺纹联接与螺旋传动

1、Chapter5: Design of Threaded,Fasteners and Joints,5-1 Basic concepts,5-2 Thread standards and definitions,5-3 Screw fastenings,5-6 Preventing unintentional unscrewing of screw joint,5-5 Bolt tightening and initial torsion,5-7 Screw and thread element design for steady load,5-4 Screwing-up torque, ef

2、ficiency and,self-locking condition,Chapter5: Design of Threaded,Fasteners and Joints,5-8 Design of screw joints subject to loads in the plane of,the joint,5-9 Design of screw joints subject to the overturning,moment,5.10 Bolt tension with external joint-separating force,5.11 Strength classes and ma

3、terials of threaded parts,5.12 Design and processing measures that raise the,strength of screws subject to variable load,5.13 Power screws,螺纹的类型与特点,2,二、,The main parameter of the thread,d,Nominal diameter .,d,1,The minor diameter .,d,2,mean diameter,P,pitch,。,a,thread angle,。,y,helix angle,n,the num

4、ber of thread,S,lead,，,S,=,nP,。,2,2,arctan,arctan,d,nP,d,S,?,?,y,?,?,Thread,联接类型与标准件,1,一、,The main kinds of threaded joints,THE KINDS OF THREADED JOINTS AND STANDERD MEMBER,联接类型与标准件,1,The threaded joints of special construction,：,联接类型与标准件,2,THE KINDS OF THREADED JOINTS AND STANDERD MEMBER,二,the stan

5、dard member of threaded joints,Accuracy class of threaded joint :A,B,C . The,C class is,usually used.,纹联接的预紧,BOLT TIGHTENING AND INITIAL TENSION,We have a force in advance before the component,subject to the work load .,Improving the reliability and tightness,The initial tension of the joint is not

6、less than the,80% yield limit of the material,?,INITIAL TENSION,?,purpose of initial tension,：,?,the principle of determining the initial tension,：,纹联接的预紧,螺纹联接的预紧,?,The control of the initial tension,：,measuring spanner,for force moment,torque wrench,测定螺栓伸长,纹联接的预紧,PRETIGHTENING OF THREADED JOINT,not

7、e,：,for the important joint,，,it is not suitable to use the joint,nominal diameter less than 12mm,d,F,T,0,2,.,0,?,The torque of screwing-up,among,：,For the,favorite bolt we can use the following equation P70,螺纹联接的防松,Preventing unscrewing of screw joints,The reason of nut,unscrewing,：,Under the condi

8、tion of shock ,vibration,variable load,；,high temperature or considerably temperature variation ,the,initial tension and friction of the joint will decrease or disappear,。,特殊的防松方法：,铆冲防松、在旋合螺纹间涂粘合剂防松等。,The method of preventing unscrewing,：,friction method,、,mechanism method,P71,Table 5-3,螺纹联接的强度计算,1,

9、强度计算的目的：,根据强度条件确定螺栓直径。,紧螺栓联接强度计算,1,仅受预紧力的紧螺栓联接,2,受轴向载荷的紧螺栓联接,3,受工作剪力的紧螺栓联接,Failure modes,：,受拉螺栓：螺纹部分的塑性变形、,螺栓杆的疲劳断裂。,65%,20%,15%,受剪螺栓：螺栓杆被剪断、螺栓杆,和孔壁的贴合面被压溃。,The strength calculation of the threaded joints,螺纹联接的强度计算,1,The strength calculation of the threaded joints,The strength calculation of the thr

10、eaded joints,螺纹联接的强度计算,2,The strength calculation of the threaded joints,1,仅受预紧力的紧螺栓联接,2,1,0,4,d,F,?,?,?,预紧力引起的拉应力：,?,?,?,y,?,5,.,0,16,2,),tan(,3,1,2,v,0,?,?,?,d,d,F,螺纹牙间的摩擦力矩,引起的扭转剪应力：,?,?,?,?,?,?,?,2,1,0,ca,4,3,.,1,d,F,强度条件：,?,?,?,?,3,.,1,3,2,2,ca,?,?,?,根据第四强度理论，,螺栓的计算应力,:,F,0,F,0,F,F,螺纹联接的强度计算,2,

11、The strength calculation of the threaded joints,The,measures,of relieving the shear force,：,螺纹联接的强度计算,3,螺纹联接的强度计算,2,受轴向载荷的紧螺栓联接,F,D,D,p,（,推导过程,）,F,F,F,?,?,1,2,?,?,?,?,?,?,?,4,/,3,.,1,2,1,2,ca,d,F,F,C,C,C,F,F,m,b,b,0,2,?,?,?,螺栓的总拉力为：,预紧力,F,0,为：,F,C,C,C,F,F,m,b,m,1,0,?,?,?,强度条件式：,式中,F,1,为残余预紧力，为保证联接的,

12、紧密性，应使,F,1,0,，推荐值见,73,页。,式中：,m,b,b,C,C,C,?,为螺栓的相对刚度，其取值范围为,0,1,，见,74,页。,（,疲劳强度校核,）,设计公式：,?,?,?,?,2,1,3,.,1,4,F,d,?,?,还可以表示为：,螺纹联接的强度计算,3,螺纹联接的强度计算,受轴向载荷的紧螺栓联接强度计算推导：,当螺栓的预紧力为,F,0,，工作拉力为,F,时，螺栓的总拉力,F,2,为：,F,F,F,?,?,1,2,螺纹联接的强度计算,3,螺纹联接的强度计算,受轴向变载荷螺栓的疲劳,强度精确校核：,计算安全系数为：,式中：,材料的对称循环拉压疲劳极限，表,5,7,。,S,安全系

13、数，表,5,10,。,tc,1,?,?,材料常数，碳素钢取,0.1,0.2,；合金钢取,0.2,0.3,。,?,y,拉压疲劳,强度综合影响系数，,，见第三章,。,?,K,?,?,?,?,/,k,K,?,螺纹联接的强度计算,4,螺纹联接的强度计算,3,承受工作剪力的紧螺栓联接,按挤压和剪切强度条件进行计算。,挤压强度条件为：,剪切强度条件为：,式中：,F,螺栓所受的工作剪力，单位为,N,；,d,0,螺栓剪切面的直径，单位为,mm,；,L,min,螺栓杆与孔壁挤压面的最小高度，单位为,mm,；设计时,应使,L,min,1.25,d,0,?,?,P,m,in,0,P,?,?,?,?,L,d,F,?,

14、?,?,?,?,?,?,2,0,4,d,F,F,F,d,0,L,min,螺纹联接组的设计,1,Design of screw joint subject to load,in the plane of the joint,The purpose,：,determine the form of the mating face,、,the number of the screws ,distribution,。,?,联接接合面应设计成轴对称的简单几何形状。,?,螺栓布置应使各螺栓的受力合理。,?,螺栓的排列应有合理的边距、间距。,?,同一圆周上的螺栓数目应取,4,、,6,、,8,等偶数。,一、,t

15、he structural design of the screw joints,螺纹联接组的设计,1,Design of screw joint subject to load in the plane of the joint,?,避免螺栓承受附加的弯曲载荷。,螺纹联接组的设计,2,Design of screw joint subject to load in the plane of the joint,1,Transverse load,2,Torque load,3,Axial load,4,Overturning motion,purpose,：根据联接的结构和受载情况，求出受力

16、最大的螺栓,所受的力，以便进行螺栓联接的强度计算。,suppose,：所有螺栓的材料、直径、长度和预紧力均相同；,受载后联接接合面仍保持为平面。,mode of loads,：,二、,Force analysis of the screw joints,螺栓组的对称中心与联接接合面的形心重合；,F,?,F,?,r,i,O,O,M,T,fF,0,fF,0,F,F,?,螺纹联接组的设计,3,（,1,）铰制孔用螺栓联接（图,b,）,（,2,）普通螺栓联接（图,a,）,式中：,z,为螺栓数目。,1,受横向载荷的螺栓组联接,z,F,F,?,?,?,?,F,K,zi,fF,S,0,fzi,F,K,F,?,

17、?,S,0,或,Design of screw joint subject to load in the plane of the joint,式中,: K,s,为防滑系数，设计中可取,K,s =1.11.3,；,f,为接合面的摩擦系数，见表,5,5,。,F,F,F,F,b),a),每个螺栓所受工作剪力为：,预紧后接合面间所产生的最大摩擦力必须大于或等于横向载荷：,螺纹联接组的设计,4,2,受转矩的螺栓组联接,T,K,fr,F,fr,F,fr,F,s,z,0,2,0,1,0,?,?,?,?,?,?,?,T,r,F,z,i,i,i,?,?,?,1,（,1,）普通螺栓联接，靠联接预紧后在接合,面间

18、产生的摩擦力矩来抵抗转矩,T,。,（,2,）铰制孔用螺栓联接，是靠螺栓的剪,切和螺栓与孔壁的挤压作用来抵抗转矩,T,。,i,i,r,F,r,F,?,m,ax,m,ax,?,?,?,Z,i,i,r,Tr,F,1,2,m,ax,m,ax,?,?,?,z,i,i,r,f,T,K,F,1,S,0,Design of screw joint subject to load in the plane of the joint,螺纹联接组的设计,5,Design of screw joint subject to load in the plane of the joint,3,受轴向载荷的螺栓组联接,各个

19、螺栓受载相同，每个螺栓所受轴向工作载荷为：,当残余预紧力为,F,1,时，每个螺栓所承受的总载荷,F,2,为：,z,F,F,?,?,F,2,=,F,1,+,F,4,2,2,D,p,F,?,?,?,螺纹联接组的设计,6,m,ax,i,m,ax,i,L,L,F,F,?,Design of screw joint subject to load in the plane of the joint,4,受倾覆力矩的螺栓组联接,作用在底板两侧的合,力矩与倾覆力矩,M,平衡。,由此可以求出最大工作载荷：,?,?,?,z,i,L,F,M,1,i,i,?,?,?,Z,i,L,ML,F,1,2,i,m,ax,m,

20、ax,i,i,r,F,r,F,?,m,ax,m,ax,螺纹联接组的设计,7,m,ax,m,ax,p,p,p,p,?,?,?,?,?,?,?,?,A,ZF,P,0,?,?,0,m,ax,m,in,?,?,?,?,p,p,p,?,?,?,螺栓组联接的设计,0,m,ax,P,P,W,M,A,zF,?,?,?,?,?,0,0,m,in,P,?,?,?,W,M,A,zF,?,螺栓的总拉力：,m,ax,m,b,b,0,2,F,C,C,C,F,F,?,?,?,为防止结合面受压最大处被压碎或,受压最小处出现间隙，要求：,式中：,W,M,p,?,?,m,ax,?,得：,螺栓材料的性能等级分为,10,级,螺纹联接

21、件的材料与许用应力,螺纹联接件的材料与许用应力,一、螺纹联接件材料,螺母材料的性能等级分为,7,级,螺纹联接件的材料与许用应力,螺纹联接件的材料与许用应力,常用的材料为：碳素钢,Q215,、,Q235,、,35,、,45,等,合金钢，如,15Cr,、,40Cr,等。,二、螺纹联接件的许用应力,1,许用拉应力,S,s,?,?,?,螺纹联接件的材料与许用应力,螺纹联接件的材料与许用应力,2,许用剪应力和许用挤压应力,3,螺纹联接件的安全系数,?,?,?,S,s,?,P,s,P,S,?,?,?,（被联接件为钢）,P,B,P,S,?,?,?,（被联接件为铸铁）,提高螺纹联接强度的措施,提高螺纹联接强度的措施,影响螺栓强度,的因素主要有以下,几个方面：,?,降低应力幅,F,C,C,C,F,F,m,b,m,1,0,?,?,?,F,C,C,C,F,F,m,b,b,0,2,?,?,?,当外载荷为,0,F,时，,螺栓拉力为,F,0,F,2,提高螺纹联接强度的措施,提高螺纹联接强度的措施,降低应力幅的措施：,?,减小螺栓刚度,?