Eight common misunderstandings about fasteners

Time:2023-10-30

Fasteners are widely used and are often called standard parts in the market. There are not only many types of fasteners, but also a huge demand. During use, we need to choose the appropriate type according to the specific actual situation to fasten and connect mechanical parts. Through understanding, here are the common misunderstandings about fasteners and The principles for selecting various types of fasteners, I hope it will be helpful to everyone.

Eight common misunderstandings about fasteners

1. Use coarse teeth instead of fine teeth
There are many important connecting parts on the machine, such as transmission shafts, etc., and most of the bolts have fine threads. If parts are missing during maintenance, some maintenance personnel will use coarse-threaded bolts to replace them, which should be avoided. Because the fine thread bolt has a large inner diameter, small pitch and outer angle, high strength, good self-locking performance, and a relatively strong ability to withstand impact, vibration and exchange loads. Once coarse-thread bolts are used instead, they will easily become loose, detached, or broken, and may even cause mechanical accidents.

2. Mismatch of pores
The bolts on the machine that bear lateral loads and shear forces, such as drive shaft bolts and flywheel bolts, have a transitional fit with the bolt holes. The assembly should be strong and reliable, and can withstand lateral forces. Some people do not pay attention to inspection during the assembly process and continue to install when there is a large gap between the bolts and the bolt holes. This may easily cause bolt loosening or cutting accidents.

3. Thickening the nut increases connection reliability
Some people mistakenly believe that thickening the nut can increase the number of working turns of the thread and improve the reliability of the connection. But in fact, the thicker the nut, the more uneven the load distribution among the threads, and the easier it is for the coupling to loosen.

4. One mother and multiple pads
After the installation is completed, sometimes the bolts are too long, so someone installs additional spring washers on the bolts. In this case, the spring washers will break due to uneven force during the strengthening process, thus reducing the predetermined strength of the bolts. The tightening force decreases, and eccentric loads may occur, reducing the reliability of bolt connections.

5. The tighter the screw, the better.
Many workers have the misunderstanding that the bolts should be "tightened rather than loose", so they deliberately increase the tightening torque, resulting in the bolts slipping. In addition, some important bolts that need to be tightened with torque, but some people use adjustable wrenches to save trouble. As a result, the torque is insufficient, causing the bolts to loosen, and even cause mechanical failure.

6. It doesn’t matter if the gasket is too big.
Sometimes there is a lack of washers of suitable size, and some workers will use washers with larger inner diameters instead. In this case, the contact area between the bottom of the bolt head and the washer is small, which will reduce the bearing pressure or locking force of the washer. If the working environment There is vibration and impact, and the bolts can easily loosen.

7. Improper locking
Important bolts should be locked with anti-loosening devices after assembly is completed. Here are four situations to explain. If a cotter pin is used for locking, do not use an overly thin cotter lock or a half-piece cotter lock; if a spring washer is used for locking, do not use a washer with an opening that is too small; if a locking plate is used for locking, do not lock the locking plate in the The edges and corners of the nut; if double-nut locking is used, the thinner nut must not be installed outside.

8. False solidity
If there is rust on the bolts, nuts or threads, or impurities such as scale, iron filings, etc., they must be cleaned before assembly; burrs, sediment and other impurities on the joint surfaces of the joints must also be removed. Otherwise, when tightening the bolts, it will appear to be tightened on the surface, but in fact the coupling is not really tightened. Under such false solidity, the bolts will loosen quickly if vibration, load impact and temperature changes occur.