AYA FASTENERS Guide | Common Misunderstandings in The Use Of Bolt Fasteners, How Many Have You Hit?

1. Use Coarse Thread Bolts Instead Of Fine Thread Bolts

There are many important connecting parts on the machine, such as drive shafts, etc. Most of the bolts are fine thread. If there are missing parts during maintenance, some maintenance personnel will use coarse-toothed bolts instead, which should be avoided. Because the inner diameter of the fine thread 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 shock, vibration, and exchange loads is also relatively strong. Once the coarse-toothed bolts are used instead, it is easy to loosen or fall off, dismantle, and even cause mechanical accidents.

 

2. Bolt Hole Does Not Fit Bolt

 

The bolts on the machine that are subjected to lateral loads and shearing forces, such as drive shaft bolts and flywheel bolts, have a transition fit with the bolt holes, and the assembly should be strong and reliable and can withstand lateral forces. Some people do not pay attention to the inspection during the assembly process and continue to install 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 to 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, and the easier the coupling is to loosen.

 

4. One nut with multiple washers

 

 

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 be broken due to uneven force during the firming process, so that the pre-tightening force of the bolt is reduced, and an eccentric load may be generated, which reduces the reliability of the bolt connection.

 

 

 

 

5. The tighter the tightening, the better

 

Many staff members have such a misunderstanding: they think that the bolts should be "would rather be tightened than unscrewed", so they deliberately increase the tightening torque, resulting in the bolts slipping. In addition, some important bolts need to be tightened with torque, some people use an adjustable wrench to save time, resulting in insufficient torque, resulting in loose bolts, and even mechanical failures.

 

6. Washers that are too large don't get in the way

 

Sometimes there is a lack of a suitable size washer, and some workers will replace it with a washer with a larger inner diameter. In this case, the contact area under the bolt head with the washer is small, which will reduce the bearing pressure or locking force of the washer, if there is vibration and shock in the working environment, the bolts are easy to loosen.

 

 

 

7. Inappropriate anti-loosening device

Important bolts should be locked with anti-loosening devices after assembly, which is divided into four cases to illustrate. If a split pin is used for locking, it should not be locked with a thin split lock or a half-piece split lock; if a spring washer is used for locking, the washer opening should not be too small; if a locking plate is used, the locking plate should not be locked in corners of the nut. If double nut locking is used, the thinner nut must not be installed on the outside.

8. False tightening

 

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

 

 

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