关于拧螺栓这件事，用什么方法拧?拧紧需要遵守怎么的流程?不是装配工人自己定的，而是设计师定义好的，用什么工具?怎么操作?都是有标准规范的。
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 action
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.
螺栓的分类
Classification of bolts
螺栓按照性能等级分为3.6、4.8、5.6、6.8、8.8、9.8、10.9、12.9八个等级，其中8.8级以上(含8.8级)螺栓材质为低碳合金钢或中碳钢并经热处理(淬火+回火)，通称高强度螺栓，8.8级以下(不含8.8级)通称普通螺栓。
Bolts are divided into 8 grades according to performance grades: 3.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium carbon steel and heat treated (quenching + tempering), which are generally referred to as high-strength bolts, and bolts below grade 8.8 (excluding grade 8.8) are generally referred to as ordinary bolts.
螺栓按照性能等级分为3.6、4.8、5.6、6.8、8.8、9.8、10.9、12.9八个等级，其中8.8级以上(含8.8级)螺栓材质为低碳合金钢或中碳钢并经热处理(淬火+回火)，通称高强度螺栓，8.8级以下(不含8.8级)通称普通螺栓。
Bolts are divided into 8 grades according to performance grades: 3.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium carbon steel and heat treated (quenching + tempering), which are generally referred to as high-strength bolts, and bolts below grade 8.8 (excluding grade 8.8) are generally referred to as ordinary bolts.
用于紧固高强度扭剪螺栓，并且在紧固完成后将剪断的梅花头保留在套筒内部不掉落，随后扣动扳机将梅花头弹出，动力为220V或110V交流电源，相比较与传统六角螺栓，扭剪螺栓配合电动电动扭剪扳手，施工方便快捷，扭矩控制准确并且方便检查。
It is used to fasten the high-strength torsion shear bolt, and keep the cut plum blossom head inside the sleeve after fastening, and then pull the trigger to pop up the plum blossom head. The power is 220V or 110V AC power supply. Compared with the traditional hexagonal bolt, the torsion shear bolt is matched with the electric torsion shear wrench, which is convenient and fast in construction, accurate in torque control and convenient for inspection.
电动扭矩扳手专用于紧固有扭力要求的六角螺栓，动力为220v或110v交流电源，带有扭矩控制器，在一定范围内输出扭矩可调。且控制精度高，重复精度高可达±3%，摒弃电机反正转，采用更加先进机械式反正转，减少电机损耗，提高可靠性。
Electric torque wrench is specially used to fasten hexagon bolts with torque requirements. The power is 220V or 110V AC power supply, with torque controller, and the output torque is adjustable within a certain range. The control precision is high, and the repetition precision can reach ± 3%. Instead of the motor reverse rotation, the more advanced mechanical reverse rotation is adopted to reduce the motor loss and improve the reliability.