In the article of the screw ts, see the ili area â–¡ Liu Yun bolt is used to connect the fasteners, which is one of the most used standard parts in machine repair. In daily repairs, some people save trouble or take it for granted. They do not assemble according to technical requirements, and often loosen the bolts in the machine work and the joints fail. Here are some common problems that are expected to attract the attention of maintenance personnel.
The drive shaft bolts of the inferior superior motor vehicles, the flywheel bolts of the engine, the main bearing bolts, the connecting rod bolts, etc., must be used with special bolts due to the large alternating load during the work. These bolts are made of high quality carbon steel. Made by quenching and tempering and finishing. When the bolts are missing during maintenance, someone replaces them with ordinary bolts. Because the tensile and shear strength of ordinary bolts can not meet the design requirements, after the replacement, the bolts are loosened and broken, resulting in serious mechanical accidents.
In the coarse coupling machine, such as the transmission shaft, the flywheel, etc., the bolts are mostly made of fine thread. When there is a missing piece in the repair, someone replaces it with a coarse bolt. Due to the large inner diameter of the fine bolt, the pitch and outer angle are small, the strength is high, the self-locking performance is good, and the ability to withstand impact, vibration and alternating load is strong; after being replaced by the coarse tooth bolt, it is easy to loose or fall off and break. , causing mechanical accidents.
å½åŒ•P shore: +! Bolts (such as drive shaft bolts and flywheel bolts) on the machine that are subjected to lateral loads and shear forces, and their mating with the bolt holes are a transition fit, which makes the assembly robust and able to withstand lateral forces. Some people did not pay attention to the inspection during the assembly. When there was a large gap between the bolt and the bolt hole, it was still edited by the editor: Tao Liran installed, and the bolt loosened or cut off.
Thickened nuts Some maintenance personnel often mistakenly believe that thickening nuts can increase the number of working turns of the thread, thereby improving the reliability of the coupling. In fact, the thicker the nut, the more uneven the load distribution between the threads of each ring, the easier it is to cause the connection. The pieces are loose.
In the repair, sometimes the bolts after assembly are too long. Then someone put a lot of spring washers on a bolt. In this way, the spring washer is unevenly stressed during the fastening process, and some may be broken to reduce the pre-tightening force of the bolt; or an eccentric load is generated, which reduces the reliability of the bolt connection. Incidentally, sometimes the bolts are too short, and the bolts and bolts of the bolts fail to extend the nuts 1 to 3, and the effective locking ability of the bolts is reduced, and it is easy to loosen.
If the map is too large, sometimes someone replaces it with a gasket with a larger inner diameter due to the lack of a suitable gasket. In this way, the contact area under the bolt head with the washer is small, the bearing pressure or the locking force of the washer is lowered, and the bolt is easy to loose under the action of vibration and impact load.
False fastening bolts, nuts or screw holes have rust, scale, iron filings, sand and other impurities, or the joint surface of the coupling has burrs, sand and other impurities, which are not removed before assembly. When tightening the bolts, Due to the blockage of impurities, the surface is tightened tightly, and the torque value is required, but in fact the coupling is not actually pressed; in addition, there is a case of impurities such as sludge, scale and the like in the bolt hole. For the top support, although the bolt torque is in compliance, the workpiece is not pressed. Under such false tightening, vibration, load rush, t, and temperature changes often cause the bolt to loosen quickly.
The torque does not match many people think that the bolt should be “never tightâ€, so the bolt tightening torque is consciously increased, resulting in the bolt slip and the locking force is reduced. On the other hand, for the important bolts that need to be tightened with a torque wrench, the smashing figure is used to wind the wrench, and the result is often loosened due to insufficient torque, causing mechanical failure.
Improper locking The important bolts should be locked after the bolts are assembled. When using the open n pin lock, the common mistake is to use a thin open u pin or a half piece open u pin lock; the use of spring washer lock, the common mistake is that the washer open ri wrong distance is too small, the loss of elasticity; The common mistake of locking with the locking piece is to lock the locking piece at the corner of the nut; the common mistake of locking with a double nut is to install the thinner nut and not tighten it tightly.
During the assembly process, the white deceived people realized that the connection problem of a certain bolt, such as the thread has been slipped, etc., but it is too troublesome to disassemble the new assembly, so he listened to it and pretended not to have this situation. I am lucky to myself, thinking that only one or two bolts are defective, and there is always no problem. As everyone knows, some large faults are often caused by the looseness of one or two threaded connections. live
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