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中南大学Chapter 5 Screw joints and screw drive51 Screw thread52 Types of Screw thread and Standard joint53 Pre-tightening of screw joints55 Strength calculation of screw joint57 Material and admissible stress of screw bolt58 Measures of improving intensity of screw bolt joint 59 Screw drive54 Looseness preventing of screw joint56 Design of joint of screw bolt groupChapter 5 Screw joints and1中南大学 Forming of screw thread51 Screw threadd2Helical line-the locus of a moving point which rotates around axis,and at the same time moves along the axis in constant velocity on the surface of cylinder。Screw thread-A plane figure moves along a helical line and keeps itself through the axis of the cylinder when moving.Then screw thread is formed.Screw thread Forming of screw thread512中南大学According to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionRectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadAccording to the type of tooth3中南大学 The type of tooth of screw thread Square threadTriangle threadTrapezoidal threadButtress thread1530330 The type of tooth of screw4中南大学Rectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadright-hand threadleft-hand thread According to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionRectangle screw threadright-ha5中南大学Rectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadright-hand threadleft-hand thread single-start threadmulti-start threaddouble-start threadsingle-start threadPSS=2PPSPS=Pn thread:S=n P n 4 According to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionRectangle screw threadright-ha6中南大学Rectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadright-hand threadleft-hand threadsingle-start threadmulti-start threadexternal threadinternal threadscrew pairAccording to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionRectangle screw threadright-ha7中南大学 external threadinternal thread external internal thread 8中南大学Rectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadright-hand threadleft-hand threadsingle-start threadmulti-start threadexternal threadinternal threadscrew pairAccording to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionJoint screw threadDriving screw threadScrew driveRectangle screw threadright-ha9中南大学Joint screw threadDriving screw thread Joint screw threadDriving scre10中南大学Rectangle screw threadTriangle screw threadTrapezium screw threadHackle screw threadright-hand threadleft-hand threadsingle-start threadmulti-start threadexternal threadinternal threadscrew pairAccording to the type of tooth of screw threadTypes of screw threadAccording to the direction of rotation of screw threadAccording to the number of helical lineAccording to inside and outside surface of solid of rotationAccording toThe function of screw threadAccording tothe shape of body of revolutionJoint screw threadDriving screw threadScrew driveparallel screw threadtaper screw threadRectangle screw threadright-ha11中南大学(1)major diameter d 与外螺纹牙顶(或内螺纹牙底)相重合的假想圆柱体的直径。(2)minor diameter d1 与外螺纹牙底(或内螺纹牙顶)相重合的假想圆柱体的直径。(3)pitch diameterd2 也是一个假想圆柱的直径，该圆柱的母线上牙型沟槽和凸起宽度相等。d1d2d(4)thread pitch P 相邻两牙在中径线上对应两点间的轴向距离。(5)Lead S S=nP(6)lead angle 中径d2圆柱上，螺旋线的切线与垂直于螺纹轴线的平面的夹角(7)included angle 轴向截面内螺纹牙型相邻两侧边的夹角。牙型侧边与螺纹轴线的垂线间的夹角。tg=d2 nP flank angle d2S同一条螺旋线上的相邻两牙在中径线上对应两点间的轴向距PPrimary geometry parameters of screw threadSPP/2P/2(8)contact height h 内外螺纹旋合后，接触面的径向高度。h(1)major diameter d 与外螺纹牙顶(或12中南大学 The major diameter of regular screw threads is the nominal diameter.There are a variety of thread pitches of the same nominal diameter.Thereinto the screw thread having the maximal thread pitch is called coarse thread,and the rest are called fine threads.60Precision grade of screw thread:A gradeB gradeC gradeUsing in such occasion:small tolerance,highest precision,using in the occasion that the fit is preciseUsing in such occasion:Bearing heavy load and being disassembled or adjusted frequently or bearing variable load/fluctuating loadUsing in general joint,in most common useCoarse thread is applied most widely.The advantages of fine thread:lead angle is small;minor diameter is great;the capability of self locking is good;and degree of strength is high.The disadvantages of fine thread:wear resistance is poor and easily wear。Application:thin wall part,the joint bearing variable load and fine regulation mechanismPdCoarse threaddPFine threaddPFine thread The major diameter of r13中南大学 Trapezium screw threadTrapezium screw threadHackle screw thread 30330为了减少摩擦和提高效率，这两种螺纹的牙侧角比三角形螺纹的要小得多。用于剖分螺母时，梯形螺纹可消除因摩擦而产生的间隙，应用较广。锯齿形螺纹的效率比矩形螺纹高，但只适合单向传动。Hackle screw threadUsually using in transmission。=15=3 Basic dimensions of regular coarse thread、regular fine thread and trapezium screw thread vide post tables(or refer to correlated manuals of machine design).Basic dimensions of screw thread:Trapezium screw threadTrapezi14中南大学 Diameter and pitch,basic dimensions of coarse thread mmDiameter and pitch,basic dimensions of coarse thread mm3 0.5 2.675 2.459 3 0.5 2.675 2.459 Nominal diameterNominal diameter（major diametermajor diameter）coarse thread fine thread coarse thread fine thread D d thread pitch P pitch diameter D D d thread pitch P pitch diameter D2 2 d d2 2 minor diameter Dminor diameter D2 2 d d2 2 thread pitch P thread pitch P 4 0.7 3.545 3.242 4 0.7 3.545 3.242 5 0.8 3.545 4.1345 0.8 3.545 4.1340.350.350.50.56 1 5.350 4.918 6 1 5.350 4.918 8 1.25 7.188 6.647 8 1.25 7.188 6.647 10 1.5 9.026 8.376 1.25,1 0.75 10 1.5 9.026 8.376 1.25,1 0.75 12 1.75 10.863 10.106 1.5,1.25 0.5 12 1.75 10.863 10.106 1.5,1.25 0.5(14)2 12.701 11.835 (14)2 12.701 11.835 1.5,11.5,116 2 14.701 13.835 16 2 14.701 13.835 (18)2.5 16.376 15.294 (18)2.5 16.376 15.294 20 2.5 18.376 17.294 20 2.5 18.376 17.294 (20)2.5 20.376 19.294 (20)2.5 20.376 19.294 24 3 22.052 20.752 24 3 22.052 20.752 (27)3 25.052 23.752 (27)3 25.052 23.752 30 3.5 27.727 26.211 30 3.5 27.727 26.211 2,1.5,12,1.5,1Note:the nominal diameter in the bracket is the second seriesNote:the nominal diameter in the bracket is the second seriesH=0.866P dH=0.866P d2 2=d-0.6495P d=d-0.6495P d1 1=d-1.0825P=d-1.0825PD D1 1、d d1 1-minor diameter of internal and external thread-minor diameter of internal and external threadD D2 2、d d2 2-pitch diameter of internal and external thread-pitch diameter of internal and external threadD D、d d -major diameter of internal and external thread-major diameter of internal and external threadP-thread pitchP-thread pitchExample of markExample of mark：M24(regular coarse threadM24(regular coarse thread、diameter24diameter24、pitch3)pitch3)M24X1.5(regular fine threadM24X1.5(regular fine thread、diameter24diameter24、pitch1.5)pitch1.5)P PP/8P/8P/8P/8P/8P/8H/4H/4D dD dD D2 2 d d2 2 D D1 1 d d1 1 P/2P/2P/4P/43030 6060 9090 Diameter and pitch,basic dime15中南大学 Basic dimension of regular fine thread mmBasic dimension of regular fine thread mmPitch P pitch diameterDPitch P pitch diameterD2 2、d d2 2 minor diameterD minor diameterD1 1、d d1 10.35 d-1+0.773 d-1+0.621 0.35 d-1+0.773 d-1+0.621 0.5 d-1+0.675 d-1+0.459 0.5 d-1+0.675 d-1+0.459 0.75 d-1+0.513 d-1+0.188 0.75 d-1+0.513 d-1+0.188 1 d-1+0.35 d-2+0.918 1 d-1+0.35 d-2+0.918 1.25 d-1+0.188 d-2+0.647 1.25 d-1+0.188 d-2+0.647 1.5 d-1+0.026 d-2+0.376 1.5 d-1+0.026 d-2+0.376 2 d-2+0.701 d-3+0.835 2 d-2+0.701 d-3+0.835 3 d-2+0.052 d-4+0.752 3 d-2+0.052 d-4+0.752 Basic dimension of regular f16中南大学 Basic dimension of Basic dimension of trapezium screw thread mm mmExample of markExample of mark：Tr48X8Tr48X8(trapezium screw thread(trapezium screw thread，diameter 48diameter 48，pitch 8)pitch 8)Thread Thread tooth height 牙顶牙顶clearanceclearance nominal diameter d nominal diameter d pitch diameterpitch diameter minor diameter of internal threadminor diameter of internal thread pitch pitch P P h h3 3=H=H4 4 a ac c 1 1stst series 2 series 2ndnd series D series D2 2 d d2 2 D D1 1 12 6.5 0.5 9012 6.5 0.5 90、100 85100 85、95 d-6 d-12 95 d-6 d-12 10 5.5 0.5 4010 5.5 0.5 40、7070、80 3880 38、4242、65 d-5 d-10 65 d-5 d-10 8 6.5 0.5 488 6.5 0.5 48、52 4652 46、50 d-4 d-8 50 d-4 d-8 4 2.25 0.25 164 2.25 0.25 16、20 18 d-2 d-4 20 18 d-2 d-4 5 2.75 0.25 245 2.75 0.25 24、28 2228 22、26 d-2.5 d-5 26 d-2.5 d-5 6 2.25 0.5 326 2.25 0.5 32、36 3036 30、34 d-3 d-6 34 d-3 d-6 Internal threadInternal threadExternal threadExternal threadd dP PR R1 1R R2 2D D1 1D D4 4H H1 1D D2 2 d d2 2d d3 3a ac ca ac c3030 H H4 4R R2 2 Basic dimension of trapeziu17中南大学 d dd d2 2d d1 1P PGas thread using screw sealRegular fine threadRegular fine threadgas threadGas thread not using screw sealGas thread not using screw seal（shell of cylindrical pipe=55）Gas thread using screw sealGas thread using screw seal（shell of conical pipe=55）60conical gas threadNominal diameter-nominal diameter of pipe hole强调与普通螺纹不同55 55 Gas thread not using screw seald dd d2 2d d1 1P P2 dd2d1PGas thread using scr18中南大学 52 Types of screw joint and standard jointer Basic types of screw jointBolted jointBasic types eaal1 1l1 1可承受横向载荷。Remaining length of thread l1Reamed hole boltClearance between hole and body of screwStatic load l1=(0.30.5)d;Variable load l1=0.75d;Reamed hole bolt l1 0;用于经常拆装易磨损之处。ddShock load or bending load l1 d;Extension elongation of thread a=(0.20.3)d;Distance between the axis of bolt and the edge e=d+(36)mm 52 Types of screw joint19中南大学 Screw jointScrewing depth in the base H，When the material of screw hole is：ae ee eStud joint 件厚，允许拆装。Steel or bronze H=d;Cast iron H=(1.251.5)dAluminium alloy H=(1.52.5)dDepth of screw hole H1=H+(22.5)P;Depth of drilling H2=H1+(0.51)d;Parameters l1、e、a is the same as boltsl1 1l1 1H HH HH H1 1H H1 1H H2 2H H2 2结构简单，省了螺母，不宜经常拆装，以免损坏螺孔而修复困难。d52 Types of screw joint and standard jointer Basic types of screw thread jointBolted jointBasic types Screw jointScrewing depth i20中南大学 holding screw jointholding screw joint Screw jointStud joint52 Types of screw joint and standard jointer Basic types of screw thread jointBolted jointBasic types holding screw jointholding sc21中南大学 Screw thread fastener Screw thread fastenerboltScrew Screw thread thread fastenerfastenerStructure of boltLL0dhexagon headLdL0Small hexagon head Screw thread fastenerboltS22中南大学dL0L1LL1-length of one end fitting in the baseL0-length of another end fitting in the nutstud Screw thread fastener Screw thread fastenerboltScrew thread fastenerdL0L1LL1-length of one en23中南大学End structureHead end structureScrew、holding screwstud Screw thread fastener Screw thread fastenerboltScrew Screw thread thread fastenerfastenerEnd structureHead end structur24中南大学 foundation bolt Hoisting boltSpecial screw thread jointT type boltScrew、holding screwstud Screw thread fastener Screw thread fastenerboltScrew Screw thread thread fastenerfastener foundation bolt Hoisting bol25中南大学hexagon nutFlat hexagon nutThick hexagon nutround nut用于经常拆装易磨损之处。用于尺寸受限制之处。国标罗列有六十余种不同结构的螺母NutSpecial screw thread jointScrew、holding screwstud Screw thread fastener Screw thread fastenerboltScrew Screw thread thread fastenerfastenerhexagon nutFlat hexagon nutThi26中南大学 Other nuts：Other nuts：27中南大学 Other nut：Other nut：28中南大学washerplain washerthin plain washerA type plain washer B type plain washer Bevel washerSpring washerclamping washer using by round nutFunction:to increase the bearing area in order to decrease pressure,to avoid scratching the surface while tightening up,to prevent looseness.NutSpecial screw thread jointScrew、holding screwstud Screw thread fastener Screw thread fastenerboltScrew Screw thread thread fastenerfastenerwasherplain washerthin plain w29中南大学553 Pre-tightening of screw thread jointPre-tightening force：the majority of screw thread joint need to be tightened while fitting in order to bear load before supporting service load.This load is called pre-tightening force.The aim of pre-tightening:to enhance the reliability and tightness of joint,to prevent appearance of gap or relative move after bearing load.Principle of determination of pre-tightening force:the pre-tightening stress after tightening up is not more than the 80 percent of the materials limit of yielding s ss.Overview一般螺纹联接在装配时都必须拧紧，这时螺纹联接受到预紧力的作用。对于重要的螺纹联接，应控制其预紧力，因为的大小对螺纹联接的可靠性，强度和密封均有很大影响。Carbon steel bolt:Qp(0.60.7)s A1Alloy steel bolt:Qp(0.50.6)s A1A1-the area of minimum life section-the area of minimum life section，A1 dd2 21 1/4/453 Pre-tightening of screw t30中南大学 tightening torqueT T1 1conquer resistance torque while conquer resistance torque while relatively rotatingrelatively rotatingT T2 2conquer friction resistance torque on the conquer friction resistance torque on the supporting area of nutsupporting area of nutIf axial force is Fa或预紧力（不受轴向载荷）fc cfriction coefficient.while having no friction coefficient.while having no lubricationlubrication：fc c=0.15=0.15rf fradius of supporting arearadius of supporting area rf=(=(dw w+d0 0)/4)/4Simplified formulaSimplified formula：适用于M10M60的粗牙螺纹，f=0.15,fc=0.15,T 0.2 F 0.2 Fa a dF Fa aFa是由联接要求决定的，为了发挥螺栓的工作能力和保证预紧 可靠，应取：General torque：Notice:For important joint,the M12 bolt should be adopted to the best of ones abilities.Td0ddw tightening torqueT1conquer 31中南大学 measuring torque spanner Control methods of pre-tightening force:联接用三角形螺纹都具有自锁性，在静载荷和工作温度变化不大时，不会自动松脱。但在冲击、振动和变载条件下，预紧力可能在某一瞬时消失，联接仍有可能松动。高温下的螺栓联接，由于温度变形差异等，也可能发生松脱现象（如高压锅），因此设计时必须考虑防松。即防止相对转动。F Ffixed torque Spanner通常螺纹联接拧紧是凭工人的经验来决定的，重要螺栓则必须预紧力进行精确控制。L LS S1)depend on experience；2)measuring torque Spanner；3)fixed torque Spanner；4)Measuring elongation amount。L LM ML LS S measuring torque spanner Cont32中南大学 联接用三角形螺纹都具有自锁性，在静载荷和工作温度变化不大时，不会自动松脱。但在冲击、振动和变载条件下，预紧力可能在某一瞬时消失，联接仍有可能松动而失效。高温下的螺栓联接，由于温度变形差异等，也可能发生松脱现象（如高压锅），因此设计时必须考虑防松，即防止相对转动。Functions of looseness preventing：1.Looseness preventing using additional frictionfelt cylinder locknutSpring washeropposite vertical nut53 Looseness preventing of screw jointLooseness preventing to prevent relative rotation of screw-pair 联接用三角形螺纹都具有自锁性，在静载荷和工作温度变化不大时33中南大学 cotter pin&hexagon slotted nutseries connection steel wire2.Looseness preventing using special element clamping washer by round nut clamping washer cotter pin&hexagon slotted34中南大学3.Other looseness preventing functions11.5PTo punch 2-3 dots using punch pinlooseness preventing by punched dotslooseness preventingby agglutinateLaying bond on3.Other looseness preventing 35中南大学55 Strength calculation of screw jointMain failure formsBolt bearing tensile stressplastic deformation 螺纹部分fatigue fractureBolts bearing shear stressshearingcrash 螺杆和孔壁的贴合面fracture-axial variable loadOften dismounted wear55 Strength calculation o36中南大学 螺栓与螺母的螺纹牙及其他各部尺寸是根据等强度原则及使用经验规定的。采用标准件时，这些部分都不需要进行强度计算。所以，螺栓联接的计算主要是确定螺纹小径d1，然后按照标准选定螺纹公称直径d及螺距P等。Strength calculation of loose bolt jointStrength condition：In formula:d1-thread minor diameter mm，allowable stress Strength calculation of tightened bolt jointFaFa力除以面积Design formula：装配时须要拧紧，在工作状态下可能还需要补充拧紧。1.Tightened bolt joint only bearing pre-tightening force2.tightened bolt bearing axial load3.tightened bolt bearing shearing force装配时不须要拧紧 螺栓与螺母的螺纹牙及其他各部尺寸是根据等强度原则及使用经验37中南大学Bolt bears dual action of axial tensile load F0 and friction torque T1Tensile stress：1.Strength of tightened bolt joint only bearing pre-tightening forceTorsion shear stress：For M10-M64 common steel screw thread,it can be adopted:tg f =0.17，d2/d1=1.04-1.08,tg 0.5 so：0.5 分母为抗剪截面系数Calculated stress：由此可见，对于M10M64普通螺纹的钢制紧螺栓联接，在拧紧时，虽然同时承受拉伸和扭转的联合作用，但在计算时，可以只考虑拉伸强度计算，并将预紧力增大30%来考虑扭转的影响。Intensity condition:Bolt bears dual action of axia38中南大学 While bearing transverse working load,the friction on the joint face generating by pre-tightening load F0 should be more than transverse load F.C-reliability coefficient,usually is C=1.11.3Pre-tightening loadF0：f-friction coefficient,for steel and cast iron,it is f=0.10.15m-the number of joint face 上图m=1,下图m=2If f=0.15，C=1.2,m=1,then：F0 8Fconfiguration dimension is greatFFFF/2F/2F0F0F0F0 While bearing transverse wo39中南大学 FF/2F/22.Intensity of tightened bolt bearing axial loadImprove measure：a.Adopt key,sleeve,pin to bear transverse load.螺栓仅起连接作用b.Adopt reamed hole bolt having no clearance.To suppose that the pressure of liquid is p,bolt number is Z,then the average load of each bolt around the cylinder body is:p D2/4F=ZpFFD FF/2F/22.Intensity of tight40中南大学 Loading deformingEspecial note,axial load:F2 F0+FAfter adding pre-tightening force elongation of bolt is b0shortening of jointed piece is m0After loading F:The total elongation amount of bolt increased toTotal tensile force is：The shortening of jointed piece decreased toThe remnant pre-tightening force decreased to:F1 Obviously:F1F0 被联接件放松了+b0m0-Looseness statePre-tightened stateb0F0F0m0FFF0F0FFFFF2F2F2=F+F1F1F1 Loading Especial note,axial41中南大学 b0Jointer deformingforceBolt deformingforceFbFmBolt deformingforceF2F1FF0F0m0F0b0C0arctgCbarctgCm b0Jointer deformingforceB42中南大学 forceBolt deformingarctgCb -relative stiffness coefficientF=Fb+Fm=(Cb+Cm)Cb+CmCbF2=F0+FCb+CmCbF1=F0 F 1 1-F1=F0-F=F0-Cm F2=F0+Fb=F0+Cb Cb+CmF=FF2FbF0then：Table 5-4 bolts relative stiffness coefficientType of washer metal washer or without washer leather copper sheet rubber0.20.3 0.7 0.8 0.9Cb+CmCbFmF1 forceBolt deformingarctgCb 43中南大学3.3.tightened bolt bearing shearing force 这种联接是利用铰制孔用螺栓抗剪切来承受载荷的。螺栓杆与孔壁之间无间隙，接触表面受挤压。在联接结合面处，螺栓杆则受剪切。Extrusion intensity condition of bolt and hole wall is:Shearing intensity condition of bolt is:Fworking shearing force of bolt,its unit is N;LminReamed bore boltFFd0It should be designed to be:Lmin1.25d0d0diameter of bolts shearing surface(it can be diameter of bolt hole),its unit is mm;Lminthe minimum of height between bolt and hole wall,its unit is mm;3.tightened bolt bearing shea44中南大学556 6 Design of joint of screw bolt group在设计螺栓组联接时，关键是联接的结构设计。它是根据被联接件的结构和联接的用途，确定螺栓数目和分布形式。in order to be convenient to processing and symmetrically in order to be convenient to processing and symmetrically laying bolts,ensure loading uniformly on the joint surface,laying bolts,ensure loading uniformly on the joint surface,the geometry shape of joint face is usually designed to be the geometry shape of joint face is usually designed to be simple axial symmetry geometry shape:simple axial symmetry geometry shape:Structure design of screw bolt group Structure design of screw bolt group jointjointBasic principle:Basic principle:Bolt is used in group in majority of machine.Bolt is used in group in majority of machine.circularity circularity circular ring circular ring rectangle rectangle rectangle rim rectangle rim triangle triangle56 Design of joint of screw 45中南大学Bolt laying should make each bolt bear load reasonablyBolt laying should make each bolt bear load reasonably FFa)For reamed bore bolt joint,dont lay more than 8 bolts in line in parallel with the direction of service load lest load distributing is too unev
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