Common mistakes when installing and using nuts

1. Replace fine with coarse: Replace fine bolts of important connectors on the machine with coarse bolts. Fine bolts have larger inner diameters, smaller pitches and external angles, and have the advantages of high strength and good self-locking performance. They can withstand strong impact, vibration and exchange loads. When replaced with coarse bolts, they are easy to loosen or fall off or break, causing mechanical accidents.
2. Pore mismatch: The match between the bolts and bolt holes that bear lateral loads and shear forces on the machine should be a transition match. If you do not pay attention to inspection during assembly, when there is a large gap between the bolts and the bolt holes, they are still installed, and bolt loosening or cutting accidents may occur.
3. Thickening nuts: It is believed that thickening nuts can increase the number of working turns of the thread, thereby improving the reliability of the connector. However, the thicker the nut, the more uneven the load distribution between the threads, which is more likely to cause the connector to loosen.
4. One nut with multiple washers: Installing many spring washers on a bolt will cause the spring washers to break due to uneven force during the tightening process, which will reduce the preload of the bolt; or produce eccentric loads, which will reduce the connection reliability of the bolt.
5. Too large washers: Using washers with larger inner diameters instead of suitable washers will reduce the contact area between the bolt head and the washer, reduce the bearing pressure or locking force of the washer, and the bolt will easily loosen under vibration and impact loads.
6. Torque mismatch: On the one hand, it is believed that bolts should be "tighter than looser", and the tightening torque is consciously increased, resulting in bolt slippage; on the other hand, for important bolts that need to be tightened with torque, they are tightened with adjustable wrenches for the sake of convenience, which often loosens due to insufficient torque, causing mechanical failures.
7. Improper locking: When using a split pin for locking, use a too thin split lock or a half-piece split lock; when using a spring washer for locking, the washer opening is too small and loses elasticity; when using a lock plate for locking, lock the lock plate at the corner of the nut; when using a double nut for locking, install the thinner nut on the outside and do not tighten it tightly.
8. False firmness: There are rust stains, scale, iron filings, sand and other impurities in the threads of the bolts, nuts or screw holes, or there are burrs, mud and other impurities on the joint surface of the connector, which are not removed before assembly. When tightening the bolts, it is tightened on the surface and the torque value meets the requirements, but in fact the connector is not really tightened; or due to the top support of impurities such as sludge and scale in the screw hole, the bolt torque meets the regulations, but the working part is not tightened. Under this false firmness, vibration, load impact and temperature changes often cause the bolts to loosen quickly.