Bolts and nuts fastening methods are widely used in connection with parts of the design of mechanical equipment. Because of low cost and flexible installation, this connection gets wide range of applications. But this connection will occur automatically fall off when the device is experiencing severe vibration, resulting in fastener failure and equipment failure. Many of the major quality accidents are caused by the small fasteners loose.
To solve the problem, many scientists and engineers used a variety of auxiliary locking approaches such as washers, chemical glue, pins, locking plate, nylon lock, physical deformation, etc., but those Methods can only play a temporary solution to the problem, do not solve the problem from the root –loose.
The locking principle of thread fasteners is the key to the structure of the shape of the thread. American engineers studied the structure and the forces of thread fasteners, and redesigned the geometry of nut thread, invented this variant thread which is now called 30° variable tooth type locking thread, a fundamental solution to the problem of the loose of fasteners.
30° variable tooth type thread has a unique anti-loosening screw thread structure, the tooth bottom of the female thread has a wedge slope of 30 degrees, when tightening the bolt clasp nut to each other, the cusp of the bolt tightly press on 30° wedge ramp of the variable tooth nut , resulting in a lot of petty clamping force. Since the variable in the angle of the tooth shape, the direction of the method force produced by the contact between bolt and nut and the axis of the thread is angle of 60 degrees, instead of 30 degrees of common thread. This thread form makes the method pressure of 30 °variable tooth type thread is far greater than the fastening pressure, so the friction generated by the method pressure greatly add. Meanwhile, when thread engagement happens between the crest of the male thread and the female thread of 30° tooth type locking thread, the prongs of the crest appears to local elastic deformation, in which the load is evenly distributed on the contact line length of the coil (see Figure 1), avoiding the phenomenon of more than 80% of the total load is concentrated on the surface of the thread of the first and second teeth as common standard thread engagement. Therefore, the thread coupling Vice of 30° variable tooth type locking thread not only overcome the shortcomings of coupling Vice of the ordinary standard thread easy loosening under vibration conditions, but also greatly extend the life of the bolt.
NASA and a number of research institutions have done the research on 30° variable tooth type locknuts, they used (JUNKERS) vibration test machine to do the lateral load vibration test, showing that it has a very excellent vibration capability (Figure 2 three kinds of nuts contrast). They tested three basic nuts: 30° variable tooth type locknuts, ordinary standard nut and effective torque locknuts. They do the test on the same testing machine using the same standard bolt, the same amplitude frequency, the same tightening torque load, the test time was two minutes. The results are that all the ordinary standard nut loose; effective torque locknuts have lost 70 percent of locking capability; while 30° variable tooth type locknuts remained above 75% of residual axial force, and verify its reliable self-locking capability.
On the basis of the above experiment, repeated use of the three threads for further lateral vibration test: after tooth nut torque wrench to tighten and loosen repeatedly, 30° variable tooth type locknuts still does not reduce the locking force, maintaining the original nut locking effect, which proves that it can be reused; after a few moments tightening and loosen, the locking force of the general standard nut and effective locknut continues to decrease until the complete loss of lock ability, proving that they can not be reused.
In China, the Shanghai Zhengao (ZG) commissioned by China Machinery Industry General Parts Product Quality Supervision Center done lateral load vibration test for its production of 30° variable tooth type locknut with Anbuneike lateral vibration testing machine. Test results show that 30° variable tooth type locknut has a strong locking capability for high loads, severe vibration and shock occasions. Experimental details see below "test report" (CITA pass word No. 101884).
Figure 2 The contrast of the three kinds of nuts
