[Steel Structure · Technology] 12 classic bolt locking designs

There are three commonly used methods of locking:

1. Friction locking；
2. Mechanical locking ;
3. Permanent locking.

Mechanical locking and friction locking are called removable locking, while permanent locking is called non-removable locking. Commonly used permanent locking methods include spot welding, riveting, bonding, etc. This method will mostly destroy threaded fasteners during disassembly and cannot be reused. Common friction locking devices include gasket, self-locking nut and double nut. Common mechanical locking methods: use cotter pin, stop washer and string wire rope.

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The key point of such anti-loosening inspection is that the relevant parts cannot be missing or damaged

Today, we share 12 more anti-loose designs than popular ones or online ones. I hope these designs can provide you with choices or help.

1 Double nut

The principle of the counter-top locknut: two friction surfaces are generated when the double nut is loosened. 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 the impact and vibration loads, the friction force of the first friction surface will decrease and disappear, but at the same time, the first nut will be compressed and the friction force of the second friction surface will further increase. Nut loosening must overcome the first friction and the second friction, because the first friction will decrease while the second friction will increase. In this way, the anti-loosening effect will be better.

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Tang's thread locking principle: Tang's thread fasteners also use double nuts to prevent loosening, but the rotation direction of the two nuts is opposite. Under the impact and vibration loads, the friction force of the first friction surface will decrease and disappear.

The first nut (right rotation in the figure) will have a loosening trend, that is, the nut will rotate to the left. However, the rotation direction of the second nut (left 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.

2. 30 ° wedge thread locking technology

There is a 30-degree wedge bevel at the tooth base of the 30 ° wedge female thread. When the bolts and nuts are tightened, the tooth tip of the bolt tightly presses against the wedge bevel of the female thread, thus producing 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 and the bolt axis form an angle of 60 degrees, rather than a 30 degree angle like the common thread. Obviously, the normal pressure of the 30 ° wedge thread is far greater than the fastening pressure, so the generated anti-loosening friction force is bound to increase greatly.

From the figure below, we can see that the forces indicated by the two arrows are P ɑ， Normal pressure of traditional 60 ° thread P=1.15P ɑ； However, the angle and size of normal pressure of 30 ° wedge thread have changed due to a wedge bevel with a 30 ° angle at the tooth base, and the normal pressure P=2P ɑ。

In this way, the ratio of normal pressure between 30 ° wedge thread and traditional 60 ° thread is ≈ 12 ∶ 7, and the anti-loosening friction is correspondingly increased. The wedge surface of the 30 ° wedge thread can also eliminate the problems of uneven stress on the common thread, tripping and seizure.

3. Self-locking nut

Self-locking nuts are generally self-locking by friction. The 30 ° wedge thread locking we 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, vibration machinery and equipment, nylon self-locking nuts for aerospace, aviation, tanks, mining machinery, etc., movable self-locking nuts for products with working pressure not greater than 2 atm and working medium of gasoline, kerosene, water or air with working temperature of - 50~100 ℃, and spring clip self-locking nuts. Embedded nylon self-locking nut

4 .Thread locking compound

Thread locking adhesive is an adhesive composed of (methyl) acrylate, initiator, promoter, stabilizer (polymerization inhibitor), dye and filler in a certain proportion.

For through-hole working condition: put the bolt through the screw hole, apply the thread locking adhesive to the thread of the engagement part, assemble the nut and tighten it to the specified torque.

For the working condition that the depth of the screw hole is greater than the length of the bolt: it is necessary to apply the locking adhesive to the bolt thread, assemble and tighten to the specified torque.

For the working condition of blind hole: drop the locking adhesive to the bottom of the blind hole, then apply the locking adhesive to the bolt thread, assemble and tighten to the specified torque; If the blind hole opening is downward, it is only necessary to apply locking glue to the bolt thread, and there is no need to apply glue in the blind hole.

For the working condition of stud bolts: drop the locking glue into the screw hole, then apply the locking glue on the bolt, assemble and tighten the stud to the specified torque; After assembling other parts, apply the locking glue to the engagement part of the stud and nut, assemble the nut and tighten it to the specified torque; If the blind hole opening is downward, there is no need to drop glue in the hole.

For pre-assembled threaded fasteners (such as adjustable screws): after assembly and tightening to the specified torque, drop the locking glue into the thread engagement, and allow the glue to penetrate by itself.

5 .Wedge-type lock lock double lock washer

The radial sawtooth on the outer surface of the wedge lock washer engages with the surface of the workpiece 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 the wedge lock washer along the thickness direction is greater than the longitudinal displacement of the bolt along the thread.

Different from other existing locking methods, wedge-type locking uses clamping force instead of friction to fasten bolts

HEICO-LOCK wedge lock 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, and stainless steel materials such as 254SMO, C276 and 718 are also widely used.

6 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 to prevent the relative rotation of the nut and the bolt.

The installation form of cotter pin is as follows:

The slotted nut is used together with the threaded bolt with hole and the split pin to prevent the bolt from rotating relative to the nut.

7 Series steel wire locking

The series steel wire anti-loose is to penetrate the steel wire into the hole of the bolt head, and connect the bolts in series to play a role of mutual restraint. This relaxation method is very reliable, but it is troublesome to disassemble.

This anti-loosening method is often used in aircraft and rockets.

Single-strand steel wire is usually used in small screw groups with close distribution intervals or places where it is difficult to reach, as shown in the figure.

8 Stop washer

After the nut is tightened, bend the single-lug or double-lug lock washer to the side of the nut and the connecting piece respectively, and then lock the nut. If two bolts need double interlocking, double brake washers can be used to brake each other.

9 Spring washer

The anti-loosening principle of the spring washer is that after the spring washer is pressed flat, the spring washer will produce a continuous elastic force, which will keep a constant friction force between the nut and the threaded connection pair of the bolt, and produce a resistance torque to prevent the nut from loosening.

At the same time, the sharp corners at the opening of the spring washer are embedded into the bolt and the surface of the connected part respectively, so as to prevent the bolt from rotating relative to the connected part.

10 Hot melt fastening technology

The hot-melt fastening technology does not require pre-opening, and can be directly tapped to realize connection under closed profiles, which is widely used in the automobile industry.

This hot melt fastening technology is a cold forming process of self-tapping and screwing after the high-speed rotation of the motor is transmitted to the plate to be connected through the central tightening shaft of the equipment to generate plastic deformation due to friction heat.

The process steps and process of fastening connection include six stages: rotation (heating) → penetration → through-hole → tapping → screwing → fastening.

11 Color change bolt

Smart color-changing bolt, to be exact, is a kind of sensing bolt called Smartbolt. The bolt head of the sensing bolt has a sensing disc. The tighter you screw it, the darker its color is.

When the strength reaches 90%, it changes from yellow to green, and then it becomes black. We have just introduced this kind of bolt some time ago, and we can just hit the above picture directly without seeing the article.

Once the color on the bolt changes, you will know that the bolt is loose.

12 Pre-tightening

High-strength bolt connections generally do not require additional anti-loosening measures, because high-strength bolts generally require a relatively large preload. Such a large preload creates a strong pressure between the nut and the connected part. This pressure will produce friction torque that prevents the nut from rotating, so the nut will not loosen. Let's share a detailed explanation of bolt tightening principle

In addition to some of the more popular anti-looseness we summarized above, that is the permanent anti-looseness we mentioned at the beginning of the article.

Fastener locking is not only a small matter, but also a major event, and it is also a matter full of wisdom.

???【Guangzheng holds that the last development is the true development】??

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