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Common Misunderstandings In The Selection Of Fasteners, See How Many Items You Have Won

Mar 10, 2021

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-threaded. 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 the 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 by coarse-threaded bolts, it is prone to loosening or detachment, disassembly, and even mechanical accidents.


The pores are not matched. The bolts on the machine that bear the lateral load and shearing force, such as drive shaft bolts and flywheel bolts, are matched with the bolt holes as transitional fits. 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.


Thickened nuts increase connection reliability. Some people mistakenly believe that thickened nuts 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.


One female with 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 solidification process. As a result, the pre-tightening force of the bolt is reduced, and an eccentric load may be generated, which reduces the reliability of the bolt connection.


The tighter the tightening, the better. Many staff members have a misunderstanding: that the bolts should be “tighter than loose”, so they deliberately increase the tightening torque, which results in the bolts slipping. In addition, 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, which causes the bolts to loosen, and even causes mechanical failure.


If the washer is too large, it doesn’t get in the way. Sometimes there is a lack of a suitable size washer. Some workers will use a washer with a larger inner diameter instead. Stop force, if there is vibration and shock in the working environment, the bolt is easy to loosen.


The locking is improper, the important bolts should be locked with anti-loosening device after the assembly is completed. 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 a 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 error; if a lock plate is used for locking, the lock plate must not be locked in At the edges and corners of the nut; if a double nut is used for locking, the thinner nut must not be installed on the outside.


It is false and strong. 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, they appear to be tightened on the surface, but in fact the couplings are not really tightened. Under such false solidity, the bolts will loosen quickly if vibration, load shock and temperature change occur.