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All types of machines and sub-assemblies will use fasteners during
connecting or assembling operation. Fastener brings convenience to machinery industry, but it has an unavoidable
weakness, i.e. it becomes loose on its own during excessive vibration and thus lead to damage or disassembly of a
component or a complete set of equipment, or even a severe accident. In order to solve the fastener loosening problem, many
scientists and engineers in different countries have conducted extensive tests and researches. They took different kinds
of measures such as locking pieces, pins, nylon inserts, deformed threads, chemical adhesives, etc. These approaches can
prolong to some extent, the service life before the fastener gets loose. But the fastener loosening problem has not been
fundamentally eliminated.
The thread form has an important influence on threaded fastener loosening. For this, US engineers
redesigned geometrical shape of the thread form after studying the shape and the load conditions of fastener thread, and
invented the current “DTFLOCK” thread technology. Since then, the fastener loosening problem has been completely
resolved. The reason why DTFLOCK fastener can effectively prevent thread from loosening is due to its unique
structure. There is a 30° wedge ramp at the root of the female thread. When the bolt and the nut are tightly engaged,
tooth crest of the bolt thread will press tightly against the wedge ramp of the DTFLOCK thread and thus generate large
locking force. Due to change of the thread angle, the angle between the normal force generated at the thread pair and
the bolt axis is now 60° instead of 30° with an ordinary thread. Obviously, normal force of the DTFLOCK thread is far
greater the fastening force. So, the anti-loosening friction force generated by this normal force will become much
greater (See Fig.1).
Fig. 1 DTFLOCK thread
form and Standard thread form For the ordinary threads, the
first two engaged threads bear 70-80% of the total load. The other engaged threads bear only a small fraction of the
total load. So, under vibrating working loads, fastener with ordinary thread form can easily overcome the locking force
generated on the contacting surface and thus generate relative turning. Then the thread will become loose. For DTFLOCK threads, due to its
unique structure, crest of each bolt thread press tightly against the 30° wedge ramp. The load can be evenly distributed
among all engaged threads. So the load can be evenly distributed to each contacting surface or point, and different
parts of the thread can generate almost the same anti-loosening friction force. It can withstand transverse vibration.
So, problems such as loose thread or thread stripping, etc. can be eliminated. In addition, fatigue strength of the
thread can also be greatly improved. The transverse load vibration test was conducted with a Junkers vibration tester in
the laboratory confirmed that the DTFLOCK thread presents outstanding anti-vibration capability (see Fig.2). They tested
3 types of nuts, i.e. ordinary standard nut, effective torque locking nut and DTFLOCK nut. Each nut was tested for 2
minutes with the same standard bolt, the same tightening torque, the same vibration amplitude and frequency, and the
same vibration tester in the same laboratory. The test result was: ordinary standard nut became loose very quickly and
lost all its locking capability, effective torque locking nut lose 70% of its locking capability, while DTFLOCK nut
maintained its locking capability during the whole test duration. Besides, further
transverse vibration tests were conducted to test the reusability of the three types of thread. The test result was: the
DTFLOCK self-locking nut has good reusability since it can maintain its locking force and locking performance after
repeated screwing and unscrewing, while ordinary nut and effective torque locking nut may gradually lose its locking
force and locking capability after several times of screwing and unscrewing.
Fig. 2 Vibration testing results of the 3 types of nuts
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