绝大多数螺纹联接在装配时都需拧紧,使联接在未承受工作负荷之前,各联接构件预先受到力的作用(这个预加作用力称为预紧力)。预紧的目的是增强联接的刚性、紧密性及防松能力,以防止受载后被联接件之间出现缝隙或发生相对滑移。对机床齿轮箱、轴承盖等要求较高的螺纹联接应适当选用较大的预紧力以有助于提高联接件的疲劳强度,但预紧力过大又可能使联接过载以至发生断裂破坏。 Most screw connections must be tightened during assembly so that the coupling members are pre-stressed (this pre-energizing force is referred to as pre-tension) before they are subjected to a work load. The purpose of pretensioning is to enhance the rigidity, tightness and anti-loosening ability of the coupling, so as to prevent the occurrence of gaps or relative slippage between the coupling members after being loaded. For machine tool gearbox, bearing cap and other demanding threaded connections should be appropriate to choose a larger pre-tightening force to help improve the fatigue strength of the coupling, but the pre-tightening force is too large and may overload the joint and even the occurrence of fracture damage.