1, with rough generations
The important couplings on the machine, such as the drive shaft, fly shaft, etc., use bolts with fine thread. When missing parts during maintenance, some people replaced them with coarse bolts. Due to the large internal diameter of the fine tooth bolts, the pitch and the external angle are smaller, and they have the advantages of high strength, good self-locking performance, and the ability to withstand shocks, vibrations, and exchange loads; after loose tooth bolts are used instead, they are easy to loosen or break off and break. .
2, the torque does not match
Many people think that bolts should be "never tight", so they consciously increase the tightening torque of the bolts. As a result, the bolts are slipped. On the other hand, for the important bolts that require tightening with the torque, there are people who can use the adjustable wrench to save time. To screw, the result is often loose due to insufficient torque, causing mechanical problems.
3, thickening nuts
Some people often mistakenly believe that thickening the nut can increase the number of working turns of the thread, thereby improving the reliability of the coupling. In fact, the thicker the nut, the more uneven the load distribution between the threads of each ring, the more likely to cause loosening of the coupling.
4, the washer is too large
Sometimes due to the lack of suitable gaskets, someone replaced the gasket with a larger inner diameter. As a result, the contact area between the bolt head and the washer is small, and the bearing pressure or locking force of the washer is reduced. Under the action of vibration and impact loads, the bolt is easy to loosen.
When choosing fasteners, first use the options from the national standard specification, and then select in the industry. When last resort, design according to the special needs of the host. In these requirements, prevention and prevention of breakage are the two main conditions for consideration.