Bolt as a tool commonly used in fixture, application is very extensive, but long-term use will also bring many problems, such as connection slack, insufficient clamping force, bolt rust and so on. The quality and efficiency of the machining will be affected because of the loose connection of bolts during the machining of parts. So how to loosen the bolt?
There are three commonly used anti-loosening methods: friction anti-loosening, mechanical anti-loosening and permanent anti-loosening.
- Double bolt
Principle of anti-loosening nut on top: there are two friction surfaces when double nuts are anti-loosening. The first friction surface is between the nut and the fastener, and the second friction surface is between the nut and the nut. During installation, the preload of the first friction surface is 80% of the second friction surface. Under impact and vibration loads, the friction of the first friction surface will decrease and disappear, but at the same time, the first nut will be compressed, resulting in further increase of the friction of the second friction surface. The first and second frictions must be overcome when the nut is loosened, since the second frictional force increases as the first frictional force decreases. In this way, the anti-loosening effect will be better.
Down thread anti-loosening principle: Down thread fasteners also use double nuts to prevent loosening, but the two nuts rotate in opposite directions. Under impact and vibration loads, the friction of the first friction surface will decrease and disappear.
- 30° wedge thread anti loose technology
There is a 30° wedge bevel at the base of the tooth of the 30° wedge female thread. When the bolt nuts are tightened together, the tooth tips of the bolt are tightly pressed against the wedge bevel of the female thread, resulting in a large locking force.
Due to the change in Angle of the conformal, the normal force applied to the contact between the threads is at an Angle of 60° to the bolt shaft, rather than 30° as with normal threads. It is obvious that the normal pressure of the 30° wedge thread is much greater than the clamping pressure, so the resulting anti-loosening friction must be greatly increased.
- Since the lock nut
It is divided into: used for road construction machinery, mining machinery, mechanical equipment vibration of high-strength self-locking nuts, used in aerospace, aircraft, tanks, mining machinery, such as nylon self-locking nuts, used to working pressure is not greater than 2 ATM for gasoline, kerosene, water or air as the working medium used for – 50 ~ 100 ℃ temperature winding self-locking nut on the product, and the spring clamp locking nut.
- Thread locking glue
Thread locking glue is (methyl) acrylic ester, initiator, promoter, stabilizer (polymer inhibitor), dye and filler together in a certain proportion of the adhesive.
For through-hole condition: pass the bolt through the screw hole, apply the thread locking glue to the thread of the meshing part, assemble the nut and tighten it to the specified torque.
For the condition where the screw hole depth is greater than the bolt length, it is necessary to apply the locking glue to the bolt thread, assemble and tighten to the specified torque.
For the blind hole condition: drop the locking glue to the bottom of the blind hole, then apply the locking glue to the thread of the bolt, assemble and tighten to the specified torque; If the blind hole is opened downward, only the locking glue is applied to the thread of the bolt, and no glue is needed in the blind hole.
For the double-head bolt working condition: the locking glue should be dropped into the screw hole, and then the locking glue is coated on the bolt, and the stud is assembled and tightened to the specified torque; After assembling other parts, apply the locking glue to the meshing part of the stud and the nut, assemble the nut and tighten it to the specified torque; If the blind hole is open downward, there is no glue drop in the hole.
For pre-assembled threaded fasteners (such as adjustable screws) : after assembling and tightening to the specified torque, drop the locking glue into the meshing place of the thread to allow the glue to penetrate by itself.
- Wedge-in locking anti-loose double pack washer
The radial saw tooth on the outer surface of wedged lock washer is occluded with the workpiece surface it contacts. When the anti-loosening system encounters dynamic load, displacement can only occur on the inner surface of the gasket.
The extensibility distance of wedge lock washer in the direction of extensibility thickness is greater than the longitudinal displacement of bolt extensibility thread.
- Split pin and slotted nut
After the nut is tightened, insert the cotter pin into the nut slot and the tail hole of the bolt, and open the tail of the cotter pin to prevent the relative rotation of the nut and the bolt.
- Series steel wire loose
The anti-loosening of series steel wire is to put the steel wire into the hole of the bolt head, and connect the bolts in series to contain each other. It’s a very reliable way to relax, but it’s tricky to disassemble.
- Stop gasket
After the nut is tightened, bend the single-lug or double-lug stop washer to the side of the nut and connector to lock the nut. If two bolts need double interlocking, double brake washers can be used to make the two nuts brake each other.
- Spring washer
The anti-loosening principle of the spring washer is that after the spring washer is flattened, the spring washer will produce a continuous elasticity, so that the nut and bolt thread connection pair continue to maintain a friction force, produce a resistance moment, to prevent the nut loose.
- Hot melt fastening technology
Hot melt fastening technology, without the need for pre-opening, in the closed profile can be directly tapped to achieve connection, in the automotive industry used a lot.
This hot melt fastening technology is a cold forming process of self-tapping and screw joint after the high-speed rotation of the motor is conducted to the sheet material to be connected through tightening shaft in the center of the equipment and plastic deformation is generated by friction heat.
- preloaded
High strength bolt connection is generally do not need additional anti-loosening measures, because high strength bolts generally require a relatively large pre-tightening force, such a large pre-tightening force between the nut and the connector to produce a strong pressure, this pressure will prevent the rotation of the nut friction torque, so the nut will not loose.
Post time: Mar-04-2022