§2 螺纹联接Screw joints § 2-1 联接类型和螺纹联接简介 § 2-2 螺纹联接的拧紧和防松

Presentation on theme: "§2 螺纹联接Screw joints § 2-1 联接类型和螺纹联接简介 § 2-2 螺纹联接的拧紧和防松"— Presentation transcript:

1 §2 螺纹联接Screw joints § 2-1 联接类型和螺纹联接简介 § 2-2 螺纹联接的拧紧和防松
§ 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 joint strength of bolts 螺纹联接设计实例 Design example of screw joint

2 § 2-1 联接类型和螺纹联接简介 Types of the joints and screw joints
螺纹联接简介和应用 Screw joints and their applications

3 一、联接类型 Types of the joints
Screw joints Separable joints Key, spline and pin joints Shaped joints Elastic ring joints Joints Interference fit joints Riveted joints Permanent joints Welded joints Adhesive joints Shaft－hub joints

4 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

5 § 2-2 螺纹联接的拧紧和防松 Tightening and preventing unscrewing of screw joints
Tightening of screw joints 螺纹联接的防松 Preventing unscrewing of screw joints

6 一、螺纹联接的拧紧 Tightening of screw joints
1.拧紧的目的 The purpose of tightening

7 Tightening process of the bolt joints
2. Preload Tightening torque factor

8 二、螺纹联接的防松 Preventing unscrewing of screw joints
防松的必要性 Necessity of preventing unscrewing 2.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 pair 3. 防松的方法 Methods of preventing unscrewing

9 § 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 受剪螺栓组联接受力分析 Forces in group of bolts subject to shear strain

10 一、任务和假设 Task and assumptions
Task: 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

11 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 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

12 二、 Forces in group of bolts subject to tensile strain 受拉螺栓组联接受力分析 1
二、 Forces in group of bolts subject to tensile strain 受拉螺栓组联接受力分析 The group of tensile bolts bears transverse forces 受拉螺栓组联接承受横向力 Transverse forces are withstood by friction of the abutting surfaces Friction coefficient Number of bolts Number of contact surface safety factor

13 2. 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: Preload

14 3. Group of tensile bolts bears axial force受拉螺栓组联接承受轴向力
Operating load Total tensile force Strength checking formulas

15 4. Group 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 of coinciding elastic displacements The bolt 1 and bolt 10 located at the biggest distance from the central axis bear the maximum force :

16 三、Forces in the group of shear bolts Loads 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 :

17 2. 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 condition of coinciding elastic displacements, the force is proportional to the distance from where the screws are located to the central of plate. Bolts 1, 4, 5 and 8 bear the maximum force

18 §2-4 Strength calculations for single bolt 单个螺栓强度计算
受剪螺栓 Shear bolts 受拉螺栓 Tensile bolts

19 一、 Shear bolts受剪螺栓 Shear force Strength condition Press stresses are considered as uniform distribution and strength condition is:

20 二、 Tensile bolts受拉螺栓 1. Loose bolts 松螺栓
Loose bolts can only bear static load and the bolts are under the load only during operating. Strength condition:

21 2. Tight bolts only subject to preload 只受预紧力的紧螺栓
Thread torque Tensile stress shear stress Strength condition

22 Tight bolts subject to preload and operating load预紧力和工作载荷联合作用的紧螺栓

23 According to graph of a relation between force and deformation we know that the relations among total tensile force F0, preload F′, remaining preload F″ and operating force F are given as 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：

24 When F varies, F0 varies along with it
When F varies, F0 varies 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（0~F~0~F）时，螺栓所受总拉力是变化的（ 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

25 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 BACK

26 §2-5 Methods of increasing joint 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

27 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 。

28 减少应力集中 三、 Reduce stress concentration
（1） Increase the radius of rounding at the root of the thread. 增加螺纹牙根圆角半径； （2） Using reasonable manufacturing process 采用合理的制造工艺。

29 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。

30 We know that reducing rigidity of the bolts or increasing rigidity of parts jointed 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。

31 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、α＝30°、A＝200mm、B＝50mm、2l＝250mm、H1＝300mm、 H2＝200mm、C＝60mm，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 neglected . Design the group of bolt joints.

32 分析：此螺栓组采用受拉螺栓、并有纵向工作载荷，设计公式如下：
其中受力最大螺栓的总拉力F0 、螺栓的许用拉应力[σ] 为未知量。 [σ] 通过查表得到， F0 通过受力分析获得。 一、螺栓组联接受力分析（求F0）Forces in group of bolt joints. 为计算方便，我们采用后一公式求F0。则首先应求出受力最大螺栓的工作载荷Fmax和预紧力F′。

33 Force system simplify 力系简化
2. Operating force of the bolt subject to the maximum force (upper bolt)受力最大螺栓工作拉力Fmax（上边螺栓FI）

34 3. F′＝？ （1）Condition of preventing from separation of the joints 不离缝条件 （2）Condition of preventing from sliding between contact surfaces 不滑移条件 把相关数据代入①、②式： 4. 计算F0

35 二、Determine bolt sizes 螺栓参数确定
三、 Checking press strength校核挤压强度（有m时） 四、 Checking stress amplitude校核应力幅（变载荷时Under variable load）