机械设计基础 精品课程 螺纹连接

1、§2 螺纹联接Screw joints§2-1 联接类型和螺纹联接简介Types of the joints and screw joints§2-2 螺纹联接的拧紧和防松Tightening and preventing unscrewing of screw joints§2-3 螺纹组联接的受力分析Forces in group of screw joints§2-4 单个螺栓强度计算Strength calculations for a bolt§2-5 提高螺栓联接强度的措施Measures of increasing jo

2、int strength of bolts螺纹联接设计实例Design example of screw joint§2-1 联接类型和螺纹联接简介Types of the joints and screw joints联接类型Types of the joints螺纹联接简介和应用Screw joints and their applications一、联接类型Types of the jointsScrew jointsKey, spline and pin jointsShaped jointsElastic ring jointsInterference fit joints

3、Riveted jointsWelded jointsAdhesive jointsSeparable jointsJointsPermanent jointsShafthub joints二、螺纹联接简介和应用screw joints and their applications螺纹联接通常有以下几种形式： 螺栓联接Bolt joints双头螺柱联接Stud joints螺钉联接Cap screw joints 紧定螺钉联接Setscrew joints§2-2 螺纹联接的拧紧和防松Tightening and preventing unscrewing of screw join

4、ts螺纹联接的拧紧Tightening of screw joints螺纹联接的防松Preventing unscrewingof screw joints一、螺纹联接的拧紧Tightening of screw joints1.拧紧的目的The purpose of tighteningTightening process of the bolt joints2.PreloadTightening torque factor二、螺纹联接的防松Preventing unscrewingof screw joints1.防松的必要性Necessity of preventing unscrewi

5、ng2.防松的根本问题Basic problem of preventing unscrewing防松的根本问题在于防止螺纹副的相对转动。Prevent relative rotation of the thread pair3. 防松的方法Methods of preventing unscrewing§2-3 螺栓组联接的受力分析Forces in group of bolt joints 任务和假设Task and assumptions 受拉螺栓组联接受力分析Forces in group of bolts subject to tensile strain 受剪螺栓组联接受

6、力分析Forces in group of bolts subject to shear strain一、任务和假设Task and assumptionsTask: find bolt subject to the maximum load among the group of bolts and determine this load。螺栓组受力分析的任务：求出联接中受力最大的螺栓及其载荷Basic assumptions基本假设：1. Parts jointed are sufficiently rigid被联接件是刚体.2. Deformation of the bolts is in

7、 elastic range螺栓的变形在弹性范围内.3. Every bolt has the same tensile and shear rigidity各螺栓的拉伸刚度以及剪切刚度相同（材料、直径和长度均相同）4. Every bolt bears the same preload各螺栓预紧力相同二、Forces in group of bolts subject to tensile strain 受拉螺栓组联接受力分析1. Thegroup of tensile bolts bears transverse forces受拉螺栓组联接承受横向力Transverse forces ar

8、e withstood by friction of the abutting surfacesFriction coefficient Number of boltsNumber of contact surface safety factor2. The group of tensile bolts bears rotating torque受拉螺栓组联接承受旋转力矩By force balance condition of the plate:Preload3. Group of tensile bolts bears axial force受拉螺栓组联接承受轴向力Operating l

9、oadTotal tensile forceStrength checkingformulas4Group of tensile bolts bears inverting moment受拉螺栓组联接承受翻转力矩Taking into account the condition of static equilibrium.According to the condition ofcoinciding elastic displacementsThe bolt 1 and bolt 10 located at the biggest distance from the central axis

10、bear the maximum force :三、Forces in the group of shear boltsLoads are transmitted by sheared bolts and pressing each other between bolts and parts jointed受剪螺栓组联接受力分析受剪螺栓组联接是靠螺栓受剪以及被联接件和螺栓之间的相互挤压传递载荷。1. Group of shear bolts bears transverse force受剪螺栓组联接承受横向力By force balance condition of the plate:2.

11、Group of shear bolts bears rotating torque受剪螺栓组联接承受旋转力矩By force balance condition:According to the conditionof coinciding elasticdisplacements, the force isproportional to the distancefrom where the screws arelocated to the central ofplate.Bolts 1, 4, 5 and 8 bear the maximum force§2-4 Strength

12、 calculations for single bolt单个螺栓强度计算受剪螺栓Shear bolts受拉螺栓Tensile bolts一、Shear bolts受剪螺栓Strength conditionShear forcePress stresses are considered as uniform distribution and strength condition is:二、Tensile bolts受拉螺栓1. Loose bolts 松螺栓Loose bolts can only bear static load andthe bolts are under the loa

13、d only during operating.Strength condition:2. Tight bolts only subject to preload只受预紧力的紧螺栓Thread torqueTensile stressshear stressStrength condition3.Tight bolts subject to preload and operating load预紧力和工作载荷联合作用的紧螺栓According tograph of a relation between force anddeformation we know that the relation

14、s among total tensile force F0, preload F, remaining preload F and operating force F aregivenas follow:由螺栓的力变形关系图，可知螺栓所受的总拉力F0、预紧力F、残余预紧力F和工作拉力F之间的关系如下：When F varies, F0varies along with it. The changing amplitude of the total tensile force is called as tensile force amplitude当工作拉力F为动载荷（0F0F）时，螺栓所受总

15、拉力是变化的（F F0 F F0）。拉力变化的幅度称为拉力幅Fa，由图可知Fa计算公式如下Strength condition of tensile bolts subject to both preload and operating load:预紧力和工作载荷联合作用的紧螺栓强度条件为：（考虑工作状态下的补充拧紧）Taking into account supplementary tightening under operation（工作载荷F变化时使用）Used for variable operating load§2-5 Methods of increasing join

16、t strength of bolts提高螺栓联接强度的措施一、Improving load distribution among thread teeth改善螺纹牙间载荷分布二、Avoid extra bending stresses避免附加弯曲应力（1）Flat supporting surface；支承面平整（2）Avoid eccentric loads 避免偏心载荷。三、Reduce stress concentration减少应力集中（1）Increase the radius of rounding at the root of the thread.增加螺纹牙根圆角半径；（2）

17、Using reasonable manufacturing process采用合理的制造工艺。四、Reduce stress amplitude减小应力幅When the maximum stress is constant, reducing the stress amplitude can increase the fatigue strength of screw joints当最大应力一定时，减小应力幅，可以提高螺纹联接的疲劳强度。We know that reducing rigidity of the bolts or increasing rigidity of parts j

18、ointed can reduce the stress amplitude减小螺栓刚度C1或者增加被联接件刚度C2可以减小应力幅。由螺栓联接的力变形关系图也可以说明这一点。Design example of bolt joints螺栓联接设计实例已知：支架和底板用2个受拉螺栓联接。支架和底板的材料为HT200、螺栓的材料为Q235，支架重量不计。P=3000N、30°、A200mm、B50mm、2l250mm、H1300mm、H2200mm、C60mm，试设计此螺栓联接。Holder and plate are jointed with 2 tensile bolts. Material of the holder and plate is HT200. Material of the bolts is Q235. Weight of the holder can be n