How to screw the bolt? What process should be followed for tightening? It is not determined by the assembler himself, but defined by the designer. What tools are used? How? There are standards and specifications.

拧螺栓这么简单的事情，怎么还定一个操作规范呢?其实拧螺栓没有想象的那么简单，拧螺栓是为了使螺栓获得一个初始的预紧力，这个预紧是起什么作用的呢?

How can an operation specification be set for such a simple thing as tightening bolts? In fact, screwing the bolt is not as simple as expected. Screwing the bolt is to obtain an initial preload. What role does this preload play?

1、传递横向力或扭矩

1. Transfer lateral force or torque

螺栓预紧力使被连接件接触面之间产生压力，接触面之间压力越大，可传递横向力就越大。当接触面压力足够大时，横向力就全部由摩擦力传递了，螺栓仅承受预紧力，不再受剪应力和压应力了，螺栓的安 全性就增加了很多。

The bolt preload generates pressure between the contact surfaces of the connected parts. The greater the pressure between the contact surfaces, the greater the transverse force that can be transmitted. When the pressure on the contact surface is large enough, the transverse force is transmitted by friction. The bolt only bears the preload and is no longer subject to shear stress and compressive stress, and the safety of the bolt is increased a lot.

2密封作用

2 sealing function

当螺栓连接用于压力管道或压力容器时，螺栓需要有足够的预紧力，起到密封作用，总的螺栓预紧力不能小于接触面间流体的压力。

When the bolt connection is used for pressure pipes or pressure vessels, the bolt shall have sufficient preload to seal. The total bolt preload shall not be less than the fluid pressure between the contact surfaces.

3、防止结构开裂

3. Prevent structural cracking

一般受疲劳载荷的螺栓连接是不允许被连接件开缝的，一旦被连接件之间产生缝隙，螺栓拉力就会随着外拉力载荷的增加而快速增加，下图为螺栓拉力与外载荷的曲线图，我们可以看到，在曲线的前半部分，被连接件之间还没有开缝，螺栓拉力增长缓慢，被连接件开缝之后，螺栓拉力快速增加。

Generally, the bolted connections subject to fatigue load are not allowed to be jointed. Once there is a gap between the connected parts, the bolt tension will increase rapidly with the increase of external tension load. The following figure is the curve of bolt tension and external load. We can see that there is no slit between the connected parts in the first half of the curve, and the bolt tension increases slowly, After being slotted by the connector, the bolt tension increases rapidly.

被连接件开缝后，螺栓的交变疲劳载荷幅值也会迅速增加，会大大缩短螺栓的疲劳强度。

After the joint is slotted, the alternating fatigue load amplitude of the bolt will also increase rapidly, which will greatly shorten the fatigue strength of the bolt.

螺栓拧紧从三个方面进行了分析，主要包括：

Bolt tightening is analyzed from three aspects, mainly including:

螺栓预紧后能够防止被连接件的开口分离，提高螺栓连接的疲劳强度;

The bolt pre tightening can prevent the opening separation of the connected parts and improve the fatigue strength of the bolt connection;

防止被连接件的滑动，依靠摩擦力来达到被连接件抵抗外部载荷的作用，避免螺栓受到剪切载荷;

Prevent the sliding of the connected part, rely on friction to resist external load, and avoid shear load on the bolt;

防止压力容器的内部压力泄漏。

Prevent internal pressure leakage of pressure vessel.

以上三点，正好是VDI2230标准中计算螺栓所需预紧力的三个部分，也就是螺栓所需的小的预紧力，从而设计出合适的螺栓规格和性能等级，从而确定螺栓的预紧力。

The above three points are exactly the three parts of vdi2230 standard for calculating the preload required by the bolt, that is, the small preload required by the bolt, so as to design the appropriate bolt specification and performance grade, so as to determine the preload of the bolt.