At present, most of the fastening connections for vehicles are connected by ordinary hexagonal bolts, hexagonal nuts, spring washers and other fasteners. In order to let you know more about the connection of bolts and nuts of automotive fasteners, we share the anti-loosening situation of ordinary fasteners, bolts and nuts, failure analysis of ordinary fasteners, bolts and nuts, and automotive fasteners. Comparison of several lock nuts.
1. Ordinary fastener bolts and nuts against loosening
The main types of bolt anti-loosening structures are: hexagonal flange bolts, which increase the contact area; hexagonal flange bearing toothed bolts, which increase the contact area and increase the friction coefficient; hexagonal head bolts with holes and hexagonal head butterfly bolts. The rod with hole bolt is mechanically locked by steel wire after assembly;
The main types of nut anti-loosening structures are: hexagonal flange surface nut to increase the contact area; non-metallic insert hexagonal locking nut, non-metallic insert hexagonal flange surface locking nut to prevent loosening through the insert; all-metal hexagonal locking nut Nuts and all-metal hexagonal flange face locking nuts increase the effective torque through the head flange; hexagonal slotted nuts use cotter pins for mechanical backstop.
Gasket anti-loose structure type is mainly: stop and increase elastic force, there are spring washers, conical elastic washers, external sawtooth lock washers and so on. Anti-loosening measures such as thread gluing and mechanical locking are also commonly used in construction, such as bolts with holes being fastened with iron wires, and locking pieces being locked.
2. Failure analysis of common fastener bolts and nuts
The frame is the carrier of the various parts of the car, and each part is directly or indirectly fastened to the frame, and the car, as a sports equipment, is subjected to loads and road forces, the frame is deformed, and the fasteners are loose. It is a natural thing.
The failure analysis of fastener connection starts from the analysis of the working mechanism. During assembly, the tightening torque of the wrench is converted into the pre-tightening force of the thread through frictional force, and the on-site quality control only checks the tightening torque. From this process, it can be analyzed that the factors affecting the failure of fasteners include tightening tools, tightening torque, thread structure, quality of fasteners, connected parts, external force, design, etc.
If the indicated value of the tool does not match the actual value, the tool should be checked regularly; if the compressed air pressure does not meet the requirements, check and rectify; the bolts and nuts should be tightened online; The pneumatic wrench is tightened, and then the fixed-value wrench is used to re-tighten. The reason for the failure 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 conversion of the tightening torque into the pre-tightening force at different pressure angles is also different. ;Quality of fasteners, such as forging burst, size out of tolerance, friction coefficient deviation, etc.; the factors of the connected parts include the quality of the surface paint film, the thickness of the paint film, the gap between the connected parts, the elasticity of the connecting parts, etc.; the main performance of external force factors In vibration, impact, force deformation, etc.; design factors are shown in improper selection of fasteners, small or large preload, shear force, tensile length deformation can not meet the actual needs and so on.
From the analysis of the force in the tightening process, the tightening torque needs to overcome the friction torque of the tightening end face, the friction torque of the thread pair, the elastic deformation torque of the connected parts, etc., and the remaining part is converted into the clamping force. Therefore, under the same conditions of use, the key factor determining 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, wire removal, and fracture, resulting in poor fixation, disintegration, and damage to the connected parts, and even traffic accidents, resulting in personal injury and property damage, such as the front of the drive shaft. Falling off, the front end of the vehicle is propped up to cause a rollover, and the steering spline shaft bolt falls off, causing steering failure, etc. Fasteners seem to be inconspicuous small parts in the structure of automobiles, but the assembly of fasteners is the main work of the assembly of the whole vehicle, and the variety and quantity are large, which is an important factor affecting the assembly of the whole vehicle and should not be underestimated.zj-junyue.com