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What are the misunderstandings in the use of fasteners

Fasteners are often hailed as "industrial rice", but how many people will use it correctly? Today, the editor summarized the "Eight Misunderstandings of Using Fasteners", and I hope it will be helpful to everyone.

1. Use coarse teeth instead of fine teeth

There are many important connections on the machine, such as drive shafts, and most of the bolts are fine thread. If there are missing parts during maintenance, some maintenance personnel will use coarse bolts instead, which should be avoided.

Because the inner diameter of the fine pitch bolt is larger, the pitch and outer angle are smaller, the strength is high, the self-locking performance is good, and the ability to withstand impact, vibration and exchange loads is relatively strong. Once replaced with coarse-threaded bolts, it is prone to loosening or detachment, disassembly, and even mechanical accidents.

2. Pore is not matched

The bolts on the machine that bear the lateral load and shearing force, such as the drive shaft bolts and flywheel bolts, are matched with the bolt holes as a transitional fit. The assembly should be strong and reliable, and can withstand lateral forces. Someone does not pay attention to the inspection during the assembly process, and the installation continues even when there is a large gap between the bolt and the bolt hole, which is prone to bolt loosening or cutting accidents.

3. Thicken nuts increase 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 coupling. But in fact, the thicker the nut, the more uneven the load distribution between the threads of each circle, and the easier the coupling is to loosen.

4. One female with multiple pads

After the installation is complete, 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 tightening process, which will make the bolts If the tightening force is reduced, eccentric load may be generated, which reduces the reliability of bolt connection.

5. The tighter the screw, the better

Many workers have this misunderstanding: they think that bolts should be "tighter than loose", so they deliberately increase the tightening torque, which results in bolts slipping. In addition, for some important bolts that need to be tightened with torque, some people use adjustable wrenches to save trouble. As a result, the torque is insufficient, causing the bolts to loosen, and even causing mechanical failure.

6. The washer is too large

Sometimes there is a lack of gaskets of suitable size, and some workers will replace them with gaskets with larger inner diameters. In this case, the contact area under the head of the bolt with the washer is small, which will reduce the bearing pressure or locking force of the gasket. There are vibrations and shocks, and the bolts are easily loosened.

7. Inappropriate locking

Important bolts should be locked with anti-loosening device after assembly. Here are four cases to explain. If a split pin is used for locking, it must not be locked with a thin split lock or half-piece split lock; if a spring washer is used for locking, it must not be used with a washer that has too small an opening; if a lock is used for locking, the lock must not be locked in At the edges and corners of the nut; if double nuts are used for locking, do not install the thinner nut on the outside.

8. False and solid

If the bolts, nuts or threads are rusted, or impurities such as scale, iron filings, etc., must be cleaned before assembly; burrs, sand and other impurities on the joint surface of the coupling must also be removed. Otherwise, when the bolts are tightened, it appears to be tightened on the surface, but in fact the couplings are not really tightened. Under such false solidity, the bolt will loosen quickly if vibration, load shock and temperature change occur.