1、扭矩法

1. Torque method

扭矩法就是利用扭矩与预紧力的线性关系在弹性区进行紧固控制的一种方法。该方法在拧紧时,只对一个确定的紧固扭矩进行控制,因此,因为该方法操作简便,是一种一般常规的拧紧方法。但是,由于紧固扭矩的90%左右作用于螺纹摩擦和支承面摩擦的消耗,真正作用在轴向预紧力方面仅10%左右,初始预紧力的离散度是随着拧紧过程中摩擦等因素的控制程度而变化的,因而该拧紧方法的离散度较大,适合一零件的紧固,不适合重要的、关键的零件的连接。

The torque method is a method of tightening control in the elastic zone using the linear relationship between torque and preload. This method only controls a certain tightening torque during tightening, so it is a general and conventional tightening method because it is easy to operate. However, due to the fact that about 90% of the tightening torque acts on the consumption of thread friction and bearing surface friction, and only about 10% actually acts on the axial preload. The dispersion of the initial preload varies with the degree of control of factors such as friction during the tightening process. Therefore, this tightening method has a large dispersion, which is suitable for the fastening of a part, but not for the connection of important and critical parts.

2、转角法

2. Corner method

转角法就是在拧紧时将螺栓于螺母相对转动一个角度,称之为紧固转角,把一个确定的紧固转角作为指标来对初始预紧力进行控制的一种方法。该拧紧方法可在弹性区和塑性区使用。根据紧固转角和预紧力的关系可知,Q-F曲线斜率急剧变化时,随着紧固转角的设定误差,预紧力的离散度也会变大。因此,在被连接件和螺栓的刚性较高的场合,对弹性区的紧固是不利的;对塑性区的紧固时,初始预紧力的离散度主要取决于螺栓的屈服点,而转角误差对其影响不大,故该紧固方法具有可限度地利用螺栓强度的优点(即可获得较高的预紧力)。

The rotation angle method is a method of controlling the initial preload by rotating the bolt relative to the nut by an angle, known as the tightening angle, using a determined tightening angle as an indicator. This tightening method can be used in both elastic and plastic regions. According to the relationship between tightening angle and preload, when the slope of the Q-F curve changes sharply, the dispersion of preload will also increase with the setting error of tightening angle. Therefore, when the rigidity of the connected parts and bolts is high, it is unfavorable for fastening in the elastic zone; When tightening the plastic zone, the dispersion of the initial preload mainly depends on the yield point of the bolt, while the impact of the angle error on it is not significant. Therefore, this tightening method has the advantage of maximizing the strength of the bolt (i.e., obtaining a higher preload).

应该注意的是该拧紧方法在塑性区拧紧时会使螺栓的杆部以及螺纹杆部发生塑性变形,因此,对螺栓塑性差的以及螺栓反复使用的场合应考虑其适用性。另外,对预紧力过大,会造成被连接件受损的情况时,则需要对螺栓的屈服点及抗拉强度的上限值进行规定。

It should be noted that this tightening method can cause plastic deformation of the rod and threaded rod of the bolt when tightening in the plastic zone. Therefore, its applicability should be considered for occasions where the bolt has poor plasticity and the bolt is repeatedly used. In addition, when excessive preload may cause damage to the connected parts, it is necessary to specify the upper limit values of the yield point and tensile strength of the bolts.

3、扭矩斜率法

3. Torque slope method

扭矩斜率法是以Q-F曲线中的扭矩斜率值的变化作为指标对初始预紧力进行控制的一种方法。该拧紧方法通常把螺栓的屈服紧固轴力作为控制初始预紧力的目标值。该拧紧方法一般在螺栓初始预紧力离散度要求较小并且可限度地利用螺栓强度的情况下使用。但是由于该拧紧方法对初始预紧力的控制与塑性区的转角法基本相同,所以,需要对螺栓的屈服点进行严格的控制。该拧紧方法与塑性区的转角法相比,螺栓的塑性即反复使用等方面出现的问题较少,有一定的优势,但是,紧固工具比较复杂,也比较昂贵。

The torque slope method is a method of controlling the initial preload using the change in the torque slope value in the Q-F curve as an indicator. This tightening method usually takes the yield tightening axial force of the bolt as the target value for controlling the initial preload. This tightening method is generally used when the dispersion of the initial preload of the bolt is required to be small and the bolt strength can be utilized to the maximum extent. However, due to the fact that the control of the initial preload by this tightening method is basically the same as the rotation angle method in the plastic zone, it is necessary to strictly control the yield point of the bolt. Compared to the angle method in the plastic zone, this tightening method has fewer problems with the plasticity of bolts, such as repeated use, and has certain advantages. However, fastening tools are relatively complex and expensive.