At present, most fastening connections are made by common hex bolts, hex nuts, spring washers and other fasteners. In order to let you use fastener bolts, nut connection have more understanding, the following to share common fastener bolts, nut anti-loose situation, common fastener bolts, nut failure analysis and automotive comparison of several anti-loose nuts.

 1. Anti-loosening of bolts and nuts of ordinary fasteners

 The main structure types of bolts are: hexagonal flange bolts, increase the contact area; Hexagonal flange face bearing face with teeth bolts, increase the contact area and increase the friction coefficient; Hexagonal head bolt with hole, hexagonal head butterfly rod bolt with hole after assembly through mechanical locking wire;

 The main structure types of anti-loose nuts are: hexagonal flange nut, increase the contact area; Hexagon lock nuts with non-metallic insert and hexagon flange lock nuts with non-metallic insert prevent loosening through insert; All-metal hexagon lock nuts, all-metal hexagon flange lock nuts through the head flange to increase the effective torque; Hexagonal slotted nuts are mechanically stopped with split pins.

 Gasket anti loose structure type is mainly: stop back and increase the elasticity, spring washer, tapered elastic washer, serrated lock washer, etc. In the construction also commonly used thread glue, mechanical locking, such as hole bolts with iron wire fastening, locking plate locking and other anti-loosening measures.

 2. Failure analysis of bolts and nuts of common fasteners

 The frame is the carrier of all parts of the car, all parts are fastened directly or indirectly on the frame, and the car, as a sports equipment, is subjected to load, road force, frame deformation, fastener loosening is a natural thing.

 The analysis of fastener connection failure begins with the analysis of working mechanism. During assembly, the tightening torque of wrench is transformed into the pretightening force of thread through friction force, and only the tightening torque is checked in field quality control. From this process, it can be analyzed that the factors affecting the failure of fasteners are tightening tools, tightening torque, screw structure, fastener quality, connected parts, external force, design and so on.

 The value shown by the tool is not consistent with the actual value, and the effectiveness of the tool is checked regularly. The compressed air pressure does not meet the requirements, check and rectify; Bolts and nuts are tightened online. Bolts and nuts without special requirements can be tightened by an pneumatic wrench. Bolts and nuts with special requirements are tightened by an pneumatic wrench first, and then tightened by a fixed wrench. The friction coefficient of the thread itself directly determines the preload, and the conversion of tightening torque to preload is different at different pressure angles. Fastener quality, such as forging burst, size out of tolerance, friction coefficient deviation, etc. The connecting elements are surface paint film quality, paint film thickness, the gap between the connecting parts, the elasticity of the connecting parts, etc. External force factors mainly show in vibration, impact, stress deformation and so on; The design factors are improper selection of fasteners, small or large preload, shear force and tensile length deformation can not meet the actual demand, etc.

 According to the force analysis of tightening process, the tightening torque must overcome the friction torque of tightening end face, friction torque of thread pair, elastic deformation torque of connected parts, etc., and the rest can be converted into clamping force. Therefore, under the same operating conditions, the key factors 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.

 Visible, the failure of fasteners in loose, adhesion, deformation, fracture, take off a silk, lead to be fitting, dissolution, damaged, or even cause traffic accident, causing injuries and property losses, such as fall off the front of the shaft, the front ground will cause overturned vehicles hold up, turned to the spline shaft bolt loss caused to failure, etc. Fastener assembly is the main work of the whole vehicle assembly, and the variety and quantity of fasteners are important factors affecting the whole vehicle assembly, which can not be ignored.

 3. Comparison of several anti-loose nuts for vehicles

 3.1 Common hexagon nuts

 Hexagon bolts and nuts with large production volume, mature technology and low cost will still be the mainstream of automotive fasteners. Over the years, many fastener manufacturing enterprises are committed to the research of thread locking, also for regular hexagon bolt, nut loose problem made a special analysis, analyses the common hexagonal nut in manufacturing factors that influence the pre-tightening force of prestressing force influence the main reason is that the tooth shape, such as friction coefficient, the preliminary analysis, for the average standard thread, thread on the most The load is concentrated on the thread surface of the first and second teeth, with uneven distribution and large dispersion of friction coefficient (see Figure 1). Users often have the misconception that more friction is better. In fact, otherwise, the smaller the friction coefficient between the friction pairs, the greater the axial clamping force, the better the fastening performance. According to the theory that the influence of the change of friction coefficient on tightening efficiency and fastening degree shows the trend of “scissors difference”, and verified by the test, the “median” friction coefficient is adopted, that is, the friction coefficient smaller than the current bolt and nut, we call it the small friction coefficient. However, in mass production, it is impossible to maintain a fixed value for all parts. Through joint design of public relations with suppliers and process improvement, the friction coefficient can be kept fluctuating within a reasonable range as far as possible.

3.2 Never loosen the nut

 Many fasteners produced by enterprises are declared to be immovable, such as DTFLOCK (Shibiro) LOCK nut from the United States, HARDLOCK(HARDLOCK) LOCK nut from Japan, Disc-lock LOCK washer from the United States, Nord-Lock LOCK washer from Sweden and so on. By comparing the final selection of low friction coefficient nuts,DTFLOCK lock nuts and Japanese HARDLOCK nuts.

 1) DTFLOCK nut

 DTFLOCK nuts have a 30° wedge-shaped bevel at the bottom of the teeth of the internal thread. When the bolt and nut are tightened, the tooth tip of the bolt is pressed against the wedge-shaped bevel of the nut, resulting in a large locking force. Because the Angle of the tooth changes so that the normal force applied to the contact between the threads is at an Angle of 60° to the bolt shaft (see Figure 2), rather than the 30° Angle of normal threads, the normal pressure of DTFLOCK threads is much greater than the clamping pressure, and therefore the anti-loosening friction generated must be greatly increased.

2) HARDLOCK nut

 HARDLOCK is a double nut (see Figure 3) with an eccentric protrusion on the outside of the inner nut. The outer nut is a common nut structure, and its inner side is provided with concentric grooves; When the outer nut is ready, the outer convex of the nut is different from the bolt. The eccentric protuberance of the inner nut and the bolt are squeezed by the outer nut to produce radial force. It is equivalent to adding a wedge in the thread gap, and the screw is locked in all directions.