螺栓和螺柱连接  文件类型：PPT/Microsoft Powerpoint   文件大小：字节

Chapter 7 Screws, Bolts and Studs Fastening
螺钉,螺栓和螺柱连接
7.1 Screw threads 螺纹
7.1.1 General conception 概述
7.1.2 Screw thread terms 螺纹术语
7.1.3 Classification of screw thread 螺纹的分类
7.1.4 The conventional representation of screw threads
螺纹的规定画法
7.1.5 The specification of screw threads 螺纹的标记
Screw threads 螺纹
major diameter 螺纹大径
minor diameter 螺纹小径
thread profile 螺纹牙型
pitch 螺距
lead 导程
left-hand threads 左旋螺纹
right-hand threads 右旋螺纹
nominal diameter 公称直径即螺纹大径
Standard screw thread 标准螺纹
nonstandard screw thread 非标准螺纹
Special screw thread 特殊螺纹
Key words
7.1 Screw threads 螺纹
7.1.1 General conception 概述
In all fields of engineering and industry, separate parts
have to be held together. This leads to the requirement of
permanent (永久的)fastenings(连接), removable(可拆装的)
fastenings.
Although there are many ways of fastening or joining
parts together, yet the most important one is screw thread.
It is one of the six mechanical powers which have served
as a tool for human being since primitive(原始的) time,
(The other five mechanical powers are the lever(杠杆), pulley
(滑轮), wheel, inclined plane(斜面) and wedge(楔)).
Metal fasteners(金属连接件) with screw threads are the
most common of all machine parts. They are used so
widely that it is necessary to know the standard system
of screw threads how they are represented (表达) on
drawings and how they are specified (详细说明).
7.1.2 Screw thread terms 螺纹术语
A screw thread is a ridge (脊) of uniform (相同的) section in the form of a helix (螺旋线) on the external (外部的) or internal (内部的) surface of a cylinder (圆柱) or a cone (圆锥) or frustum of cone (圆台).
In other words, if the vertices of a plane figure such as a triangle (三角形) or a rectangle (矩形) draw helices of the same pitch along the surface of a cylinder, then a screw thread can be generated.
(1) The formation of a helix 螺旋线的形成
A helix is a curve generated (产生) by a point moving
uniformly around a cylinder and uniformly parallel to the
axis of the cylinder.
jaws
chuck
Work pieces
Lathe tools
External thread
Internal thread
(2) Major diameter 螺纹大径
The largest diameter of the internal or external thread. It
is the crest (顶) diameter of a external thread or the root
diameter of a internal thread.
(3) Minor diameter 螺纹小径
profile
crest
crest
root
root
(4) Pitch diameter 螺纹中径
The pitch diameter is the diameter of an imaginary cylinder
whose surface would pass through the threads at such points
as to make equal the width of the threads and the width of the
spaced cut by the surface of the cylinder. It is not shown in
drawing but used when the thread is designed.
The smallest diameter of the external or internal thread. It is the root
diameter of a external thread or the crest (顶) diameter of a internal thread.
(5) Thread profile 螺纹牙型
The longitudinal section (纵剖面) of the screw thread.
(6) Thread angle 螺纹角
The angle of thread is the angle included between the
sides of the thread measured in an axial plane. The thread
angle of a metric thread (米制螺纹,公制螺纹) is 60°.
(7) Pitch 螺距
The pitch is the distance from a point on a screw thread
to a corresponding point on the next thread.
Pitch=lead
Pitch
Lead
(8) Lead 导程
The lead is the distance a screw thread advances (前进)
axially in one turn.
On a single-start (or single-
thread) screw(单线螺纹), the lead
and pitch are identical(相等的);
on a two-start (or double-thread)
screw(双线螺纹), the lead is twice
(两倍) the pitch; on a three-start
(or triple-thread) screw(三线螺纹),
the lead is three times the pitch.
Pitch=lead
Pitch
Lead
(9) Direction of the threads 螺纹的旋向
Threads can be made right-hand (右旋) or left-hand (左旋). The threads mostly used are right-hand, it turns in a clockwise direction (顺时针) to enter a threaded part when views(观察者) from the outside end.
A left-hand thread is on which turns in a counter clockwise direction (逆时针) when views from the outside end.
Left-hand threads
Right-hand threads
(10) Developing a helix 螺旋线的展开
In developing a helix the hypotenuse (斜边) of a right
triangle (直角三角型) will form one turn of a helix if
wrapped (环绕) around a cylinder(圆柱), if the base of the
triangle is equal to the circumference(圆周) of the cylinder.
The altitude will be the pitch of the helix. β is called
the spiral(螺旋的) angle(螺旋角) of the helix and αthe helix
angle(升角) of it.
The nominal diameter(公称直径即螺纹大径), pitch (螺距) and the profile(牙型) are called the three essential elements of the thread.
7.1.3 Classification of screw thread 螺纹的分类
According to the screw thread standard GB4459.1-84 of
our country, screw threads can be classified as follows:
(1) By its profile 根据牙型分
a. Standard screw thread 标准螺纹
The profile (牙型), major diameter (大径) and thread pitch (螺距) of such threads are all standard (标准).
b. Nonstandard screw thread 非标准螺纹
The profile of such threads are not standard.
c. Special screw thread 特殊螺纹
The profile is standard but the major diameter or pitch
is not standard.
The standard screw thread profiles:
标准螺纹的牙型 (Tab.7-1 p216)
a. Metric thread 普通螺纹(米制螺纹)
coarse series
普通粗牙螺纹
fine series
普通细牙螺纹
b. pipe thread 管螺纹
cylindrical pipe
圆柱管螺纹
conical pipe
圆锥管螺纹
They are connecting threads. (连接螺纹)
c. Trapezoidal thread 梯型螺纹
Tr
d. Buttress thread 锯齿型螺纹
They are transmitting threads.
(传动螺纹)
(2) By the surface in which a helix is formed
根据螺旋线产生的表面分
a. External thread 外螺纹
It is made on the external surface of a cylinder (圆柱),
cone (圆锥), or frustum of cone (圆台).
b. internal thread 内螺纹
It is made on the internal surface of a cylinder (圆柱),
cone (圆锥), or frustum of cone (圆台).
(3) By its use 根据用途分
a. Connecting thread 连接螺纹
It is used to hold parts together such as metric thread,
pipe thread.
b. Transmitting thread 连接螺纹
It is used to transmit (传递) motion (运动) or power(动力) and to hold the force in line with the axis such as trapezoidal thread, buttress thread.
7.1.4 The conventional representation of screw threads 螺纹的规定画法
1. Standard screw thread 标准螺纹
The following figure shows the conventional
representation of the visible external thread. Its major
diameter is drawn with full lines and its minor diameter
is drawn with thin lines.
The figure shows the conventional representation of the
visible internal thread(threaded hole)(此处指剖视图). Its major
diameter (大径) is drawn with thin lines (细实线) while its
minor diameter (小径) is drawn with full lines (粗实线). The
section lines should always be drawn up to the full lines.
For both external and internal threads chamfers (倒角) need not be shown in the side view (左视图).
If the external or internal thread is invisible(不可见), then
dashed line (虚线) are used to represent both the major and
minor diameter(大,小径).
2. Nonstandard screw thread 非标准螺纹
In case that a nonstandard screw thread is occured, a
broken-out section (局部剖) or an additional view (附加视图)
(p218 Fig.7-3(b))should be added to show its profile (牙型).
3. Special screw thread 特殊螺纹
In view that the profile (牙型) of special screw thread is
standard (标准的), its representation (表达) is identical(相同的)
with the standard one, and its profile need not be shown in
the drawing.
4. Representation of the mating threads
螺纹的连接画法
If two threads, one external and the other internal of the same diameter and pitch(螺距) are assembled(装配) together, then their mating (配合) portions(部分) should be drawn in the same manner(方法) as the single external thread(单个外螺纹) does.
a. Standard screw thread 标准螺纹
Designation (指明,标示) for standard screw thread is
shown in Tab. 7-1(p216).
(1) Metric , trapezoidal and buttress threads
7.1.5 The specification of screw threads 螺纹的标记
Examples:
12(p6): lead(pitch)
(2) pipe threads
G: symbol for
cylindrical pipe thread
(查表p318表5-4)
1or 1/2: nominal dia.
R: internal conical
pipe thread
Rc: external conical
pipe thread
Rp: internal
cylindrical pipe thread
b. Nonstandard screw thread 非标准螺纹
The profile(牙型) needs to be shown and
dimensioned(标尺寸).
c. Special screw thread 特殊螺纹
The word "Special" should be added before the symbol of profile to distinguish (区别) it from the standard screw thread.
Goodbye!