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.

擰螺栓這么簡單的事情，怎么還定一個操作規(guī)范呢?其實擰螺栓沒有想象的那么簡單，擰螺栓是為了使螺栓獲得一個初始的預緊力，這個預緊是起什么作用的呢?

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、傳遞橫向力或扭矩

1. Transfer lateral force or torque

螺栓預緊力使被連接件接觸面之間產生壓力，接觸面之間壓力越大，可傳遞橫向力就越大。當接觸面壓力足夠大時，橫向力就全部由摩擦力傳遞了，螺栓僅承受預緊力，不再受剪應力和壓應力了，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

當螺栓連接用于壓力管道或壓力容器時，螺栓需要有足夠的預緊力，起到密封作用，總的螺栓預緊力不能小于接觸面間流體的壓力。

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、防止結構開裂

3. Prevent structural cracking

一般受疲勞載荷的螺栓連接是不允許被連接件開縫的，一旦被連接件之間產生縫隙，螺栓拉力就會隨著外拉力載荷的增加而快速增加，下圖為螺栓拉力與外載荷的曲線圖，我們可以看到，在曲線的前半部分，被連接件之間還沒有開縫，螺栓拉力增長緩慢，被連接件開縫之后，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.

被連接件開縫后，螺栓的交變疲勞載荷幅值也會迅速增加，會大大縮短螺栓的疲勞強度。

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.

螺栓擰緊從三個方面進行了分析，主要包括：

Bolt tightening is analyzed from three aspects, mainly including:

螺栓預緊后能夠防止被連接件的開口分離，提高螺栓連接的疲勞強度;

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

防止被連接件的滑動，依靠摩擦力來達到被連接件抵抗外部載荷的作用，避免螺栓受到剪切載荷;

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

防止壓力容器的內部壓力泄漏。

Prevent internal pressure leakage of pressure vessel.

以上三點，正好是VDI2230標準中計算螺栓所需預緊力的三個部分，也就是螺栓所需的小的預緊力，從而設計出合適的螺栓規(guī)格和性能等級，從而確定螺栓的預緊力。

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.