12 kinds of bolt loosening methods, how many do you know?
Time:2024-07-03 15:45:56 / Popularity: / Source:
There are three commonly used anti-loosening methods: frictional anti-loosening, mechanical anti-loosening and permanent anti-loosening. Anti-loose purpose: to work more effectively for a long time; to improve reliability of related workpieces.
01 Double nut
Principle of anti-loosening nuts on the top: when double nuts are locked, two friction surfaces are generated. The first friction surface is between nut and fastened part, second friction surface is between nut and nut. During installation, pretightening force of first friction force surface is 80% of second friction force surface. When impact and vibration loads are applied, friction force on the first friction force surface will decrease and disappear, but at the same time, first nut will be compressed to further increase friction force on second friction force surface. To loosen nut, the first friction force and second friction force must be overcome, because second friction force will increase while first friction force decreases. In this way, anti-loosening effect will be better.![Double nut](/d/file/p/2024/07-03/d4507f2737dce6a0044feb0865976f4c.png)
![Double nut](/d/file/p/2024/07-03/1cfdb6e3311b2822f88b4932ebd920ae.png)
02 30° wedge thread anti-loosening technology
There is a 30° wedge-shaped slope at the bottom of 30° wedge-shaped female thread. When bolt and nut are tightened together, cusp of bolt is tightly pressed against wedge-shaped slope of female thread, thereby generating a large locking force. Due to change in angle of tooth shape, normal force applied to contact between threads is at an angle of 60° to bolt axis instead of 30° angle like ordinary threads. Obviously, normal pressure of 30° wedge thread is far greater than fastening pressure, so resulting anti-loosening friction must be greatly increased. Schematic diagram of Spirax thread structureFrom figure below, it can be seen that force represented by two arrows is Pɑ, normal pressure of traditional 60° angle thread is P=1.15Pɑ; and 30° wedge thread has a 30° wedge-shaped slope at the bottom of tooth. Angle and size of normal pressure are changed, and normal pressure P=2Pɑ. In this way, ratio of normal pressure between 30° wedge thread and traditional 60° thread is ≈12:7, and anti-loosening friction force increases accordingly. Wedge-shaped surface of 30° wedge thread can also eliminate problems of uneven stress on ordinary threads, tripping and seizure.
03 Self-locking nut
Self-locking nuts are generally self-locking by friction, and 30° wedge thread anti-loosening mentioned above should belong to category of self-locking nuts. It is divided into: high-strength self-locking nuts for road construction machinery, mining machinery, vibration machinery and equipment, nylon self-locking nuts for aerospace, aviation, tanks, mining machinery, etc., used for swimming self-locking nuts and spring clip self-locking nuts for products with working pressure not greater than 2atm, working medium of gasoline, kerosene, water or air, and operating temperature of -50~100℃. Insert a wedge between nut and screw to prevent loosening Japan Hadlock eccentric self-locking nut04 Threadlocker
Thread locking adhesive is an adhesive composed of (meth)acrylate, initiator, co-accelerator, stabilizer (inhibitor), dye and filler in a certain proportion.For through-hole conditions: pass bolt through screw hole, apply thread locker to thread of mating part, assemble nut and tighten to specified torque. For working conditions where depth of screw hole is greater than length of bolt: apply locking glue to thread of bolt, assemble and tighten to specified torque. For blind hole working conditions: drop locking glue to bottom of blind hole, then apply locking glue to thread of bolt, assemble and tighten to specified torque; if opening of blind hole is downward, just apply locking glue on thread of bolt, and there is no need to apply glue in blind hole. For stud bolt working condition: locking glue should be dripped into screw hole, then apply locking glue on bolt, assemble stud and tighten it to specified torque; after assembling other parts, apply locking glue to meshing part of stud and nut, assemble nut and tighten it to specified torque; if opening of blind hole is downward, no glue is needed in hole. For pre-assembled threaded fasteners (such as adjustable screws): After assembling and tightening to specified torque, drop locking glue into threaded joints and let glue penetrate by itself.
05 Wedge lock double stack washer
Radial serrations on the outer surface of wedge lock washers engage surface of workpiece they contact. When anti-loosening system encounters a dynamic load, displacement can only occur on inner surface of washer.Expandable distance along thickness direction of wedge lock washer is greater than longitudinal displacement that can be produced by bolt along thread.
![Double nut](/d/file/p/2024/07-03/a9f237f24ef012329857049cf58f8013.png)
120-year-old HEICO-LOCK wedge anti-loosening system products include wedge lock washers, RING-LOCK wedge washers and wedge lock nuts. Main materials are carbon steel coated with Dacromet and 316 Stainless steel, stainless steel materials such as 254SMO, C276 and 718 are also widely used.
06 Split pin, slotted nut
After nut is tightened, insert cotter pin into nut groove and hole at the end of bolt, open tail of cotter pin to prevent relative rotation of nut and bolt.![Double nut](/d/file/p/2024/07-03/1ecf51444370a64ea51e0de2a859e53f.jpg)
![Double nut](/d/file/p/2024/07-03/8fc4de7adbb7216c8591af7df49f91d5.jpg)
07 Series steel wire anti-loosening
Series steel wire anti-loosening is to pass steel wire into hole of bolt head, connect bolts in series, and play role of mutual containment. This loosening method is very reliable, but it is troublesome to disassemble.![Double nut](/d/file/p/2024/07-03/d0782490e5258337c0916f23f4fb1533.jpg)
08 Stop washer
After nut is tightened, single-ear or double-ear stop washer is respectively bent and tightly attached to the side of nut and connecting piece, so that nut can be locked. If the two bolts need to be double locked, a double brake washer can be used to make the two nuts brake each other.![Double nut](/d/file/p/2024/07-03/0fdf04bddab75050be39e121725e014d.jpg)
09 Spring washer
Anti-loosening principle of spring washer is that after spring washer is flattened, spring washer will generate a continuous elastic force, so that threaded connection pair between nut and bolt will continue to maintain a frictional force, generate a resistance torque, and prevent nut from loosening.![Double nut](/d/file/p/2024/07-03/2b1d009f08def6b7d175e6a725e14f72.jpg)
10 Hot melt fastening technology
Hot-melt fastening technology does not require pre-drilling, and can be directly tapped to achieve connection under closed profile, which is widely used in automotive industry. This hot-melt fastening technology is a cold forming process that conducts high-speed rotation of motor through tightening shaft in the center of equipment to plastic deformation of plates to be connected due to friction and heat, then self-tapping and screwing. Hot melt fastening process steps and process include six stages: rotation (heating) → penetration → through hole → tapping → threading → fastening.11 Color changing bolt
Smart color-changing bolts, to be precise, this is an induction bolt called Smartbolt. Bolt head of induction bolt has an induction plate. The tighter you tighten it, the darker its color will be. When intensity reaches 90%, it turns from yellow to green, and when it reaches 100%, it becomes black.12 Preload
High-strength bolt connections generally do not require additional anti-loosening measures, because high-strength bolts generally require a relatively large pre-tightening force, such a large pre-tightening force creates a strong pressure between nut and connected parts, This pressure creates a frictional torque that stops nut from turning, so nut does not loosen.![Double nut](/d/file/p/2024/07-03/82726ca09fb0ba0d2d3583f33e02182c.jpg)
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