In the process of using fasteners, many people think that a small fastener replacement will not make a big difference. As everyone knows, this idea is not correct. Fasteners, as important parts of machinery, must be installed strictly in accordance with the requirements of different types in the process of use. If similar fasteners are replaced, it is likely to lead to mechanical equipment accidents, or even safety accidents. Therefore, we must pay attention to the use of fasteners. According to the understanding of Zhonghua Standard Parts Network, we tell you that in these eight cases, many people will mistake the use of fasteners for the correct, in fact, it is not.
In these eight cases, the fastener is not used correctly:
First, use thick teeth instead of thin teeth
There are many important connecting parts on the machine, such as the drive shaft, and most of the bolts are fine tooth threads. If parts are missing during maintenance, some maintenance personnel will use coarse teeth bolts instead, which should be avoided. Because the fine tooth bolt has large inner diameter, small pitch and outer Angle, high strength, good self-locking performance, and strong ability to withstand impact, vibration and exchange load. Once the coarse tooth bolt is used instead, it is easy to loose, take off, disassemble, and even cause mechanical accidents.
Two, the pore is not fit
The bolts on the machine that bear the transverse load and shear force, such as the drive shaft bolts and flywheel bolts, should be fitted with the bolt holes for the transition fit, the assembly should be strong and reliable, and can withstand the side force. Some people do not pay attention to check during the assembly process, and still continue to install when there is a large gap between the bolt and the bolt hole, which is easy to loose or cut off the bolt accident.
3. Thickened nuts increase connection reliability
Some people mistakenly believe that thickened nuts increase the number of threads and improve the reliability of the coupling. But in fact, the thicker the nut, the more uneven the load distribution between the threads of each ring, the more easily the coupling loose.
Four, a mother multi pad
After the installation is complete, sometimes the bolt is too long, so someone will install extra spring washer on the bolt. In this case, the uneven force of the spring washer will be broken in the solid process, so that the preload of the bolt decreases, and may produce eccentric load, reducing the reliability of the bolt connection.
Five, the tighter the better
Many staff have such a misunderstanding: that is, they think that the bolt should be "rather tight than loose", so they deliberately increase the tightening torque, resulting in bolt slip. In addition, some important bolts that need to be tightened with torsion force are tightened by some people with adjustable wrenches to save trouble. As a result, the torque is insufficient, leading to the loosening of the bolts and even mechanical failure.
Six, the washer is too big is not in the way
Sometimes there is a lack of a suitable size of the washer, some staff will use a larger diameter of the washer instead, in this case, the head of the bolt below the washer contact area is small, will reduce the bearing pressure or locking force of the washer, if there is vibration and impact in the working environment, the bolt is easy to loosen.
Seven, the lock is not appropriate
Important bolts should be locked by anti-loosening device after assembly, which can be explained in four cases. If the cotter pin lock is used, it shall not be closed with a thin opening lock or half a piece of opening lock; If the spring washer is used to lock, the washer opening should not be too small; If the lock piece is used, the lock piece shall not be locked at the corner of the nut; If double nut locks are used, thinner nuts must not be fitted outside.
Eight, false firm
If the bolts, nuts or threads are rusted, or scale, iron filings and other impurities, be sure to deal with clean before assembly; The joint surface of the connector has burr, sediment and other impurities to be removed. Otherwise, when tightening the bolt, it appears that it is tightened, but in fact, the connecting parts are not really compressed. Under such false firmness, the bolt will quickly loosen if there is vibration, load impact and temperature change.
