12 super classic bolt locking designs
There are three commonly used locking methods: friction locking, mechanical locking and permanent locking. Mechanical locking and friction locking are called detachable locking, while permanent locking is called non detachable locking. Common permanent locking methods include spot welding, riveting, bonding, etc. this method mostly destroys threaded fasteners during disassembly and cannot be reused. Common friction locking are: using gasket, self-locking nut and double nut, etc. Common mechanical locking methods: use cotter pin, stop gasket and string steel wire rope.
Purpose of prevention: it can work more effectively for a long time and improve the reliability of relevant components.
Today, let’s share 12 more popular or more popular anti loosening designs on the Internet, one better than the other. I hope these designs can provide you with choices or help.
Principle of counter top locknut: two friction surfaces are generated during double nut locking. 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 that of the second friction surface. Under the action of 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 the further increase of the friction of the second friction surface. The first friction force and the second friction force must be overcome when the nut is loosened. As the first friction force decreases, the second friction force will increase. In this way, the anti loosening effect will be better.
Down thread locking principle: down thread fasteners are also locked with double nuts, but the rotation direction of the two nuts is opposite. Under the action of impact and vibration loads, the friction of the first friction surface will decrease and disappear.
The first nut (right-hand rotation in the figure) will have a loosening trend, that is, the nut rotates to the left. However, the rotation direction of the second nut (left-hand rotation in the figure) is opposite to that of the first nut, so the loosening force of the first nut is directly converted into the tightening force of the second nut. In this way, the nut will never loosen.
Locking principle of down screw fastener
30 ° wedge thread locking technology
There is a 30 degree wedge-shaped inclined plane at the tooth bottom of the 30 ° wedge-shaped female thread. When the bolts and nuts are tightened with each other, the tooth tip of the bolt is firmly against the wedge-shaped inclined plane of the female thread, resulting in a great locking force.
Due to the change of the angle of the tooth shape, the normal force generated by the contact between the threads forms an angle of 60 degrees with the bolt axis, rather than 30 degrees like ordinary threads. Obviously, the normal pressure of 30 ° wedge thread is much greater than the fastening pressure. Therefore, the anti loosening friction is bound to increase greatly.
Schematic diagram of screw thread structure of schperot
As can be seen from the figure below, the force represented by the two arrows is pɑ, The normal pressure of traditional 60 degree angle thread is p = 1.15pɑ; The angle and size of normal pressure of 30 ° wedge thread change because there is a wedge inclined plane with an angle of 30 ° at the tooth bottom, and the normal pressure P = 2pɑ.
In this way, the ratio of normal pressure between 30 ° wedge thread and traditional 60 ° thread is ≈ 12 ∶ 7, and the anti loosening friction increases accordingly. The wedge-shaped surface of 30 ° wedge-shaped thread can also eliminate the problems of uneven stress and tripping seizure of ordinary thread.
Self locking nut
Self locking nuts are generally self-locking by friction. The 30 ° wedge thread locking mentioned above should belong to the category of self-locking nuts.
It is divided into: high-strength self-locking nuts for road construction machinery, mining machinery and vibration machinery equipment, nylon self-locking nuts for aerospace, aviation, tank and mining machinery, swimming self-locking nuts for products with working pressure not greater than 2atm, working medium of gasoline, kerosene, water or air and service temperature of – 50 ~ 100 ℃, and spring clip self-locking nuts.
Embedded nylon self-locking nut
A wedge is inserted between the nut and the screw to prevent loosening
Japan hadlock eccentric self-locking nut
Thread locking compound
Thread locking adhesive is an adhesive composed of (meth) acrylate, initiator, promoter, stabilizer (polymerization inhibitor), dye and filler in a certain proportion.
For through-hole working condition: pass the bolt through the screw hole, apply thread locking glue to the thread of the meshing part, assemble the nut and tighten it to the specified torque.
For the working condition that the screw hole depth is greater than the bolt length: apply the locking glue to the bolt thread, assemble and tighten to the specified torque.
For blind hole conditions: drop the locking glue to the bottom of the blind hole, apply the locking glue to the thread of the bolt, assemble and tighten to the specified torque; If the opening of the blind hole is downward, just apply the locking glue to the thread of the bolt, and there is no need to apply glue in the blind hole.
For the working condition of stud bolt: drop the locking glue into the screw hole, apply the locking glue on the bolt, and assemble and tighten the stud to the specified torque; After assembling other parts, apply locking glue to the meshing part of the stud and nut, assemble the nut and tighten it to the specified torque; If the opening of the blind hole is downward, there is no need to drip glue in the hole.
For preassembled threaded fasteners (such as adjustable screws): after assembly and tightening to the specified torque, drop the locking glue into the thread engagement, so that the glue can penetrate by itself.
Wedge lock lock lock double stack washer
Radial serrations on outer surface of the wedge lock washer engage with the workpiece surface it contacts. When the locking system encounters dynamic load, the displacement can only occur on the inner surface of the washer.
The expandable distance of wedge lock washer along the thickness direction is greater than the longitudinal displacement of bolt thread.
It is quite different from other existing locking methods.
Wedged locking bolts are tightened by clamping force rather than friction.
Heico-lock wedge locking system products with a history of 120 years include wedge lock washer, Ring-Lock wedge washer and wedge lock nut. The main materials are carbon steel coated Dacromet and 316 stainless steel. Stainless steel materials such as 254SMO, C276 and 718 are also widely used.
Cotter pin and slotted nut
After the nut is tightened, insert the cotter pin into the nut slot and the bolt tail hole, and pull the cotter pin tail away to prevent the relative rotation of the nut and the bolt.
The installation form of cotter pin is shown as follows:
Slotted nuts are used together with threaded bolts with holes and cotter pins to prevent relative rotation of bolts and nuts.
Series steel wire locking
Series steel wire locking is to thread the steel wire into the hole of the bolt head and connect the bolts in series to restrain each other. This relaxation method is very reliable, but it is troublesome to disassemble.
This locking method is often used in aircraft and rockets.
Single strand steel wire is generally used in small screw groups with close spacing or places that are difficult to reach, as shown in the figure.
After the nut is tightened, bend the single ear or double ear lock washer to the side of the nut and the connector respectively to lock the nut. If two bolts need double interlocking tightening, double brake washers can be used, and the two nuts brake each other.
The anti loosening principle of the spring washer is that after the spring washer is flattened, the spring washer will produce a continuous elastic force, so that the threaded connection pair of the nut and the bolt can maintain a friction force, produce a resistance torque and prevent the nut from loosening.
At the same time, the sharp corners at the opening of the spring washer are respectively embedded in the surface of the bolt and the connected piece, so as to prevent the bolt from rotating relative to the connected piece.
Hot melt fastening technology
Hot melt fastening technology does not need pre opening. It can be directly tapped to realize connection under closed profiles. It is widely used in the automotive industry. This technology is very good. We have a special article discussing in detail the new realm of hot melt fastening technology and screw tightening, which is used by BMW, Mercedes Benz and Audi.
This hot melt fastening technology is a cold forming process of self tapping and bolting after the high-speed rotation of the motor is transmitted to the friction heat of the plate to be connected through the central tightening shaft of the equipment to produce plastic deformation.
The process steps and process of hot melt fastening connection include six stages: rotation (heating) → penetration → through hole → tapping → screwing → fastening.
Intelligent color changing bolt, specifically, this is an induction bolt called Smartbolt. The bolt head of the induction bolt has an induction disk. The tighter you screw it, the darker its color is.
When the strength reaches 90%, it changes from yellow to green. After reaching 100%, it becomes black. We just introduced this kind of bolt some time ago. If you don’t see the article, you can directly critical hit the figure above.
Once the color on the bolt changes, you will know that the bolt is loose.
High strength bolt connection generally does not need additional anti loosening measures, because high strength bolts generally require a relatively large pre tightening force. Such a large pre tightening force will generate strong pressure between the nut and the connected part, which will produce friction torque to prevent the nut from rotating, so the nut will not loosen.
Here is a detailed explanation of the bolt tightening principle.
We shared it before, good.
In addition to the popular anti loosening that we summarized above, that is the permanent anti loosening that we mentioned at the beginning of the article.
Source: China Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading flange manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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