The Failure Analysis Of Ordinary Bolts And Nuts

In the previous article, we introduced The Loosening Resistance Of Ordinary Bolts And Nuts. As a professional fastener manufacturer, we Xinchi Fastener Company will continue to share the failure analysis of ordinary bolts and nuts in this article.

The frame is the carrier of the automobile parts, that is, the parts are directly or indirectly fastened on the frame. As sports equipment, it is natural for the automobile frame to deform and fasteners to loosen when subjected to the force of load and road surface.

The fastener connection failure analysis should first be analyzed from the working mechanism. The tightening torque of the wrench during assembly is transformed into the pre-tightening force of the thread through the friction force, and the field quality control only checks the tightening torque. From this process, it can be analyzed that the factors affecting fastener failure include tightening tools, tightening torque, screw thread structure, fastener quality, connected parts, external force, design, etc.

The value shown by the tool is inconsistent with reality, requiring the tool to be validated regularly. The compressed air pressure does not meet the requirements, which need to be checked and rectified. Bolts and nuts without special requirements can be tightened by a pneumatic wrench; The bolts and nuts with special requirements are tightened by a pneumatic wrench first, and then tightened by a fixed wrench. The failure reason is simple, that is, the torque does not meet the technical requirements. The friction coefficient of the thread itself directly determines the pre-tightening force, and the tightening torque of different pressure angles is also different. Fastener quality problems, such as forging burst, size out of tolerance, friction coefficient deviation, etc. The factors of the connected parts, such as the surface paint film quality, paint film thickness, the gap between the connected parts, and the elasticity of the connecting parts, etc. The external factors are mainly manifested in vibration, impact, stress deformation and so on. Design factors are reflected in improper selection of fasteners, small or large preload, shear force and tensile length deformation, which can not meet the actual demand.

From the force analysis of the tightening process, the tightening torque needs to overcome the friction torque of the tightening end face, the friction torque of the threaded pair, the elastic deformation torque of the connected parts, etc., before the remaining part is converted into the clamping force. Therefore, under the same service conditions, the key factor that determines the tightening force should be the structure and essential quality of the thread itself, such as structure, material, heat treatment, surface treatment, quality control, etc.

It can be seen that the failure of fasteners is mainly manifested in loosening, adhesion, deformation, descaling and fracture, which leads to unstable fixation, disintegration and damage of the connected parts, and even leads to traffic accidents, injuries and property losses. For example, if the front of the drive shaft falls off, the front end of the ground will prop up the vehicle and cause the rollover, and the steering spline shaft bolt falls off and causes steering failure. Fasteners seem to be insignificant small parts in automobile structure, but fastener assembly is the main work of vehicle assembly. Besides, the variety and quantity of fasteners are large, which is an important factor affecting vehicle assembly and should not be ignored.

Xinchi Fastener Company is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.