Eight common errors in fasteners
1. use thick teeth instead of thin teeth
There are many important connecting parts on the machine, such as the drive shaft, and most bolts are fine thread. If parts are missing during maintenance, some maintenance personnel will use coarse teeth bolts instead, which should be avoided. Because the inner diameter of the fine-tooth 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 bear the impact, vibration and exchange load is also relatively strong. Once the coarse tooth bolt is used instead, it is easy to loose or remove, break, and even cause mechanical accidents.
2. the pores do not match
Bolts ON THE machine that BEAR lateral LOADS and shear forces, such as drive shaft bolts and FLYwheel bolts, their fit with the bolt hole is a transition fit, the assembly should be strong and reliable, and can withstand lateral forces. Some people do not pay attention to the inspection in the assembly process, and continue to install when there is a large gap between the bolt and the bolt hole, which is easy to happen bolt loosening or cutting off accident.
3. Thickening nut increases connection reliability
Some people mistakenly believe that thickening nuts can increase the number of turns of thread and improve the reliability of the joint. But in fact, the thicker the nut is, the more uneven the load distribution between the threads of each turn is, and the joint is easier to loosen.
4. a more pad
After the completion of the installation, sometimes there will be too long bolt phenomenon, so someone will install an extra spring washer on the bolt, in this case, the strong process of spring washer uneven force will be broken, so that the bolt preload decreased, and may produce eccentric load, reduce the reliability of the bolt connection.
5. the tighter the better
Many workers have such a misunderstanding: that is, they believe that the bolt should be "rather tight than loose", so they deliberately increase the tightening torque, resulting in bolt slip buckle. In addition, some of the important bolts that need to be tightened with torsion force, but some people use adjustable wrench to screw because of the convenience, resulting in insufficient torque, resulting in bolt loosening, and even mechanical failure.
6. the gasket is too large
Sometimes the lack of a suitable size of the washer, some workers will use a larger diameter of the washer instead, in this case, the head of the bolt and the washer contact area is small, will reduce the washer bearing pressure or locking force, if there is vibration and impact in the working environment, the bolt is easy to loosen.
7. the lock is not suitable
Important bolts should be locked by anti-loose devices after assembly. Here are four cases to explain. If using cotter pin lock, do not use too fine opening lock or half piece opening lock lock; If the spring washer is used to lock, the opening of the washer shall not be too small; If the lock piece is used, the lock piece shall not be locked at the edges and corners of the nut; If a double nut lock is used, thinner nuts should not be mounted on the outside.
8. False firmness
If there is rust on the bolts, nuts or threads, or impurities such as scale and iron filings, it must be cleaned before assembly; The joint surface of the joint part has burr, sediment and other impurities should also be removed. Otherwise, when tightening the bolt, it appears to be tightened, but in fact the joint is not really pressed. Under such false firmness, the bolts will come loose quickly in the event of vibration, load shock and temperature change.
