Common misconceptions in the use of fasteners

Common misconceptions in the use of fasteners:

1. Replace fine with coarse

Important connecting parts on machines, such as drive shafts, flyshafts, etc., often use fine thread bolts.

. When parts are missing during maintenance, someone replaces them with coarse threaded bolts. Due to the large inner diameter, small pitch and outer angle of fine tooth bolts, they have the advantages of good strength, good self-locking performance, and good ability to withstand impact, vibration, and exchange loads; After replacing with coarse threaded bolts, it is easy to loosen, detach, or break, causing mechanical accidents

2. Pore mismatch

The bolts on the machine that bear lateral loads and shear forces (such as drive shaft bolts and flywheel bolts) should have a transitional fit with the bolt holes, and the assembly should be sturdy and able to withstand lateral forces.

. Someone did not pay attention to inspection during assembly and still installed when there was a large gap between the bolt and the bolt hole, resulting in bolt loosening or cutting accidents

3. Thickened Nut

Some people often mistakenly believe that thickening nuts can increase the number of working turns of threads, thereby improving the quality of the connector. In fact, the thicker the nut, the more uneven the load distribution between the threads of each turn, which is more likely to cause the connector to loosen.

4. One mother with multiple washers

During installation, sometimes the assembled bolts may become too long. Therefore, some people install many spring washers on one bolt, which causes uneven force on the spring washers during the fastening process, and some may break, reducing the pre tightening force of the bolt;

; Or it may generate eccentric loads, reducing the optimal connection of bolts

5. The gasket is too large

Sometimes, due to a lack of suitable gaskets, some people use gaskets with larger inner diameters instead.

. In this way, the contact area between the bolt head and the washer is small, and the bearing or locking force of the washer decreases. Under vibration and impact loads, the bolt is prone to loosening

6. Inconsistent Torque

Many people believe that bolts should be tightened rather than loosened, so they consciously increase the tightening torque of bolts, resulting in bolt slippage. On the other hand, for important bolts that require torque tightening, some people try to save time by using adjustable wrenches to tighten them, but often loosen due to insufficient torque, leading to mechanical failures.

7. Improper locking

Important bolts should be locked with anti loosening devices after assembly.

. When using open-ended locking, a common mistake is to use overly thin open-ended locks or half piece open-ended locks for locking; The common mistake of using spring washers for locking is that the opening of the washer is too small and loses elasticity; The common mistake in using locking plates is to lock the locking plates at the corners of the nut; The common mistake with double nut locking is to install thinner nuts on the outside and not tighten them tightly

8. False firmness

There are rust stains, scale, iron filings, sand particles and other impurities in the threads of bolts, nuts or screw holes, or burrs, mud and other impurities on the joint surface of the connecting parts, which are not removed before assembly. When tightening the bolts, due to the blocking effect of impurities, the surface is tightened very tightly, and the torque value meets the requirements, but in reality, the connecting parts are not really tightened;

; In addition, there is another situation where due to the jacking effect of impurities such as oil sludge and scale in the screw hole, although the bolt torque meets the requirements, the workpiece is not tightened. Under such false firmness, vibration, load impact, and temperature changes often cause bolts to loosen quickly