Fastener tightening requirements
There are usually torque requirements. In most cases, we fix the bolts, tighten only the nuts, and apply torque to the nuts. Common torque requirements are as follows: 1) On the metal cover, the torque requirement for tightening the screws is generally 15-50 lbf.in (lbf.in, Torque unit: pounds inch); 2) on loose materials such as composite materials, honeycomb structures, etc., generally 15-25lbf.in
tips
1 lb = 0.4536 kg = 4.4453 Newtons, 1 inch = 0.0254 meters
1 lb. inch = 0.113 Nm.
Anti-loose thread connection
● Anti-loose purpose. In actual work, the external load has vibration, change, high temperature creep of the material, etc., which will cause mutual friction to decrease. The positive pressure in the thread pair disappears at a certain moment, and the friction force is zero, thus loosening the thread connection, such as After repeated action, the threaded joint will fail. Therefore, it is necessary to prevent loosening, otherwise it will affect the fixing effect and cause an accident.
●The principle of anti-loose
Under static load and normal temperature conditions, the general thread can achieve anti-looseness, on the one hand due to the self-locking condition: for general thread, the spiral rise angle is <6 degrees; the friction at the bearing surface of the nut, bolt head, etc.; Locking, adding friction or mechanical methods, eliminating or limiting the relative motion between the pairs of threads, or increasing the difficulty of relative motion.
● Anti-loose measures.
The fundamental reason to prevent the looseness of the thread is to prevent the relative movement of the thread pair. The main and common methods are:
(1) Using the relative friction action, the specific measures include the tightening nut, the spring washer, the metal lock nut, the nylon ring lock nut, the wedge thread lock nut and the like.
(2) Direct locking method, including the split pin and the slot nut, the stop washer, the series wire (fuse method), and the like. When selecting the split pin, the size and rigidity of the split pin should be considered: the size is about 90% of the hole diameter, and the stiffness meets the requirements; the return pin must be close to the fastener; if the split pin is too long, the excess must be cut off. The foot of the upper bent pin is bent to 1/2-3/4 of the bolt diameter and the excess is cut.
(3) Destroy the relationship of thread pair, mainly including welding, punching and bonding.
(4) The metal self-locking nut is used, that is, one end of the nut is made into a non-circular closing or the opening of the diameter is closed. After the nut is tightened, the opening is opened, and the elastic force of the closing is used to make the screwing tight.
(6) Add a stop washer, or an elastic washer, or a toothed washer.
(7) Use welding or gluing.
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