Bolt fasteners use common mistakes

- Jun 10, 2019-

First, replace the fine teeth with coarse teeth

There are many important connections on the machine, such as the drive shaft, etc. Most of the bolts are fine threaded. If there is a missing piece during maintenance, some maintenance personnel will use a coarse tooth bolt instead, which should be avoided. Because the inner diameter of the fine bolt is large, the pitch and outer angle are small, the strength is high, the self-locking performance is good, and the ability to withstand shock, vibration and exchange load is also strong. Once replaced with coarse-toothed bolts, it is easy to loosen or take off, break, and even cause mechanical accidents.


Second, the pores do not match

Bolts that are subjected to lateral loads and shear forces on the machine, such as drive shaft bolts and flywheel bolts, are mated with the bolt holes. The assembly should be robust and capable of withstanding lateral forces. Some people do not pay attention to the inspection during the assembly process. If there is a large gap between the bolt and the bolt hole, the installation will continue. This is easy to cause the bolt to loosen or cut off.


Third, thickened 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. However, in fact, the thicker the nut, the more uneven the load distribution between the threads of each ring, and the coupling member is more likely to loosen.


Four, one mother and more mat

After the installation is completed, sometimes the bolts are too long, so some people attach the spring washers to the bolts. In this case, the spring washers will be broken due to uneven force during the sturdy process, thus pre-bolting the bolts. As the tightening force decreases, it is also possible to generate an eccentric load and reduce the reliability of the bolted connection.


Fifth, tighten as tight as possible

Many staff members have such a misunderstanding: that the bolts should be “narrow and not loose”, so the tightening torque is intentionally increased, resulting in a bolt slip. In addition, some important bolts that need to be tightened by torque, some people use the adjustable wrench to save trouble, the result is insufficient torque, resulting in loose bolts, and even caused mechanical failure.


Sixth, the gasket is too big to be in the way

Sometimes there is a lack of a properly sized gasket, and some workers will replace it with a larger inner diameter washer. 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 gasket if the working environment There are vibrations and shocks in it, and the bolts are easy to loosen.


Seven, lock is not suitable

The important bolts should be locked by the anti-loose device after the assembly is completed. There are four cases to explain. If the split pin is used, it must not be locked with a thin opening lock or a half-open lock; if the spring washer is used, the gasket opening should not be too small; if the lock is locked, the lock should not be locked. The corners of the nut; if a double nut is used, the thinner nut must not be placed outside.


Eight, false and solid

If the bolts, nuts or threads are rusted, or impurities such as scales and iron filings must be cleaned before assembly; the joint surfaces of the couplings should be cleaned of burrs, sand and other impurities. Otherwise, when the bolt is tightened, the surface appears to be tightened, but in reality the coupling is not actually compressed. Under such false sturdiness, the bolt will loosen quickly if vibration, load shock and temperature change occur.