01 Replace thin with thick
For important connecting parts on the machine, such as drive shaft and flying shaft, the bolts are usually threaded with fine teeth. When missing parts during maintenance, someone replaced them with coarse bolts. Due to the large inner diameter, small pitch and external Angle, fine tooth bolt has the advantages of high strength, good self-locking performance, strong ability to bear impact, vibration and exchange load; After replacing with coarse bolts, it is easy to loosen or take off or break, resulting in mechanical accidents.
02 Pore mismatch
The bolts (such as drive shaft bolts and flywheel bolts) that bear the transverse load and shear force on the machine shall be fitted with the bolt hole for transition, and the assembly shall be solid and reliable, and able to bear the lateral force. Some people do not pay attention to the inspection in the assembly, the bolt and bolt hole between the large gap is still installed, the result of bolt loose or cut off the accident.
03 Thickening nut
Some people often mistakenly think that the thickening nut can increase the number of working rings of the thread, so as to improve the reliability of the connection, in fact, the thicker the nut, the load distribution between the rings of thread is more uneven, the more likely to lead to the loosening of the connection.
04 One mother many pads
In the installation, sometimes there will be too long phenomenon of bolt assembly, so someone will install many spring washers on a bolt, so that in the firm process of spring washers uneven force, some will break, so that the bolt preload down; Or produce eccentric load, reduce the reliability of bolt connection.
05 Washer is too large
Sometimes due to the lack of a suitable gasket, someone will use a larger diameter gasket instead. In this way, the contact area between the bolt head and the washer is small, the pressure of the washer or the locking force drops, and the bolt is easy to loose under the action of vibration and impact load.
06 Torque is inconsistent
Many people think that bolts should be "rather tight than loose", so they consciously increase the tightening torque of bolts, resulting in bolt sliding. On the other hand, for the important bolts that need to be tightened by torsion, some people try to save trouble by using adjustable spanner to twist, and the result is often loose due to insufficient torque, leading to mechanical failure.
07 Improperly locked
After assembling important bolts, adopt anti-loosening device to lock them. When using split pin lock, the common mistake is to use too thin open lock or half open lock lock; The common mistake is that the opening of the washer is too small and loses its elasticity. The common mistake is to lock the locking plate in the corner of the nut; For double nut locks, a common mistake is to have the thinner nut on the outside and not tightly screwed.
The euro strengthened
Bolt, nut or screw hole threads inside the rust stains, scale, iron filings, sand and other impurities, or join a joint surface impurities such as burrs, sediment, and not be removed before assembly, when tightening bolts, due to the effect of blocking of the impurity, on the surface of screw tightly, torque value meet the requirements, but actually has not really compact connection; In addition, there is another case, because of the top support effect of impurities such as mud and scale in the screw hole, although the torsion of the bolt meets the requirements, the working parts are not pressed. Vibration, load shock, and temperature changes often cause bolts to loosen quickly under such sturdiness.
