The mechanical performance requirements for the lock nut are basically the same as for a normal nut. However, an all-metal lock nut of effective torque type should have a high mechanical performance rating. A nut with a low mechanical performance tends to cause plastic deformation of the non-circular closed portion when screwing into the bolt, and it is difficult to ensure the functional requirements of the elastic locking. The mechanical performance rating of all-metal lock nuts is usually 8-12. The 5th grade nut has lower cost, but its anti-loosening ability and reusability are poor. Generally, it is only used for unimportant use, and the number of repeated assembly and disassembly should be minimized.

A lock nut with good working performance should have the following four basic conditions:

1) Stable and reliable locking torque (also known as effective torque);

2) Good adaptability to bolt tolerances;

3) good reusability;

4) Good twist-pull relationship.

(1) Locking torque

A lock-proof and reliable lock nut should have the tightening torque within the range specified by the standard, and the maximum torque for the first screwing should be kept to a minimum, which is repeated multiple times (usually the 5th or 15th). The minimum torque should be kept to a maximum. The first time the screwing torque is too large, it is difficult to screw people. Reducing assembly efficiency also makes it difficult to maintain the locking torque, reducing the looseness of the nut and the reusability of the fastener. and so. The smaller the first tightening torque, the better, but after a small degree, it may not be possible to guarantee that the torque after multiple times of screwing reaches the standard torque value. The multiple screwing torque of the nut refers to the torque value held by the bolt after repeated screwing 5 times or 15 times and screwing out the 5th or 15th time. The greater the torque, the higher the lockability of the nut. In other words, if the nut is screwed out a number of times, the tightening torque can be stably maintained at a high level, so that the threaded connection has a high reliability against loosening. Factors affecting the stability of the tightening torque include: the structure and size of the non-circular closing part of the nut (refer to the full metal lock nut), the resilience of the locking part, the thread tolerance, the lubrication condition of the thread, and the like. Nylon ring lock nut, due to its structural characteristics and the good performance of nylon material, its locking torque can generally be maintained within a stable and reasonable range under various conditions of use. Therefore, it is currently in various self-locking nuts. A nut with the highest reliability.

(2) Adaptability to bolt tolerances

When the lock nut is screwed with the bolt, the cooperation of the threaded hole of the locking portion and the bolt is an interference fit. When the nut reaches the upper deviation threaded hole (the average diameter of the threaded hole is the largest) and is screwed with the lower deviation bolt (the smallest diameter of the bolt), the amount of interference may be small, and the locking torque generated by the amount of interference may also be small. Conversely, when the lower deviation threaded hole of the nut (the minimum diameter of the threaded hole is the smallest) and the upper deviation bolt (the largest diameter of the bolt are the largest), the amount of interference may be large, and the locking torque generated by the amount of interference may be large. Screw in the maximum torque for the first time specified in the standard. A lock nut with excellent working performance, which should have good adaptability to bolt (thread) tolerances. That is, when it is screwed with a high-limit bolt or a low-limit bolt, the optimum tightening torque value according to the standard can be obtained. Whether the lock nut has good adaptability to the bolt tolerance should be checked by bolt tolerance test (also known as permanent deformation test). This test requires high precision of the thread of the test bolt and the corresponding test cost is also high. Therefore, general-purpose lock nuts do not require this test, and all-metal lock nuts used in important applications such as aerospace must perform this test. Because the nylon material has excellent resilience performance, the nylon ring lock nut has excellent adaptability to the bolt tolerance. Under normal circumstances, the bolt tolerance test may not be performed. The lock nut with good adaptability to bolt tolerances also has good reusability.

(3) Reusability

In many lock nut standards (including international standards) at home and abroad, there is no mention of the reusability of the nut, but generally the nut is required to perform 5 or 15 lock performance tests. Does this mean. After a nut has been removed for 5 or 15 times, it cannot meet the tightening torque requirements specified in the standard. Should it be scrapped? In fact, 5 or 15 times of the locking test is only a test method, it does not mean that the nut only Can be used 5 times or 15 times. Under normal circumstances, after 5 times of screwing in and out, the tightening torque is gradually reduced from a larger value to a smaller value, especially after 15 times of screwing in and out, the minimum torque value of the nut is unscrewed. Always maintain the same balance. However, does this mean that the number of times of repeated loading and unloading of the lock nut can be unrestricted? For a full metal lock nut, the bolt may be screwed out a few times to unscrew the non-circular threaded hole of the nut, which may cause wear of the metal thread. And local plastic deformation, resulting in instability of the value of the locking torque. It may even be below the minimum torque value specified by the standard. Therefore, in important applications, it is recommended to appropriately limit the number of times the nut is repeatedly attached and detached. The American Aerospace Fastener Design Manual recommends that the all-metal lock nut be reused approximately 10 times. The nylon ring lock nut has excellent reusability, and even after being screwed in and out for 1OO times, it can be kept stable even after the minimum torque is unscrewed. During the use, it is not necessary to limit the number of times of assembly and disassembly.

(4) Twist-pull relationship

The twist-pull relationship refers to the relationship between the applied torque and the pre-tightening force generated in the fastening system due to tightening when tightening the threaded fastener. The pre-tension is also called the pre-tension of the bolt, the axial force or the clamping force of the fastening system. The reliability of threaded fastener fastening depends to a large extent on this force. Practice has proved that one of the main reasons for the looseness and fatigue damage of threaded fasteners is due to the lack of reasonable preload. The so-called reasonable preload. Generally speaking, the fastener and the connected member should have a sufficiently high pre-tightening force without being damaged by the tightening. A sufficiently high preload can greatly reduce the applied stress amplitude, thereby increasing the reliability of anti-loose and anti-fatigue.

The use of a torque wrench to tighten the fastener is a method that has been widely used in the assembly process for a long time at home and abroad. The preload force obtained by this method is very inaccurate. Under normal circumstances, for a non-locking ordinary nut, the unit torque loss caused by the friction on the bearing surface accounts for about 50% of the total torque, and the unit torque loss caused by the friction on the thread contact surface accounts for the total torque. 40%. The torsional moment that produces the preload is only about 10% of the total torque. Therefore, when the nut is tightened, even if the same tightening torque is applied to the same nut, the deviation of the preload force may be as high as ±25%. For safety reasons, only tighten the nut to a lower preload value to avoid excessive preload and damage the threaded connection. Compared with ordinary nuts, the lock nut that obtains the locking performance by increasing the friction of the thread or the bearing surface will have a greater uncertainty in the twist-and-pull relationship. For the free-rotation type lock nut with toothed surface, due to the change of the friction state of the bearing surface and the scratch of the joint surface, the twist-and-pull relationship will produce a nonlinear change, that is, when the same torque is applied, the pre-acquisition is obtained. The dispersion of the tightening force will be greater. For effective torque type lock nut. The change of the locking torque will affect the stability of the twist-pull relationship. In general, the torque applied to the nut should be equal to the torque applied to the normal nut plus the tightening torque (see Figure 19-14). The locking torque of the all-metal lock nut tends to vary greatly during use, and the dispersion of the pre-tightening force value also increases.

A good performance lock nut should have a good twist-pull relationship. A good twist-pull relationship means that the relationship between the torsional moment and the pre-tightening force is a stable linear relationship for the fasteners of the same condition, and a stable pre-tightening force can be obtained when the same torque is applied. Only a good twist-pull relationship, the fastening system can obtain a high enough pre-tightening force for the full metal lock nut, improve the thread precision, improve the adaptability to the bolt tolerance can stabilize the tightening torque, so that it has a good twist A pull relationship. For the nylon ring lock nut, because its locking torque is very stable, its twist-pull relationship is better than the full metal lock nut.

As with ordinary nuts, lubrication of the threads and bearing surfaces of the lock nut can significantly improve the twist-pull relationship, because lubrication can improve the friction of the thread and the bearing surface, while also stabilizing the locking torque and reducing friction against stable preload. The adverse effects of force. Therefore, lock nuts used in important applications are often nuts with a dry film lubrication layer or a sizing agent during assembly.

Pipe Cutting Machine mainly fit for metal pipe cutting requirements.

1. 3 axis Pipe Plasma Cutting Machine mainly be used for round pipe cutting.

2. 4 aixs pipe Cutting Machine mainly be used for square pipe continuous cutting special shape. 

3. Also as multifunction cutting machine use together with Plasma Cutting Table.

4. Accept OEM for any pipe cutting diameter and working length. ( Normally from 100x100mm up to 600x600mm dia. )

5. Accept any materials cutting: Iron plate, Stainless steel plate, Titanium plate, Galvanized sheet, Aluminum plate, High speed steel, etc

Pipe Cutting Machine

Pipe Cutting Machine,Pipe Cutter,Automatic Pipe Cutting Machine,Customized Pipe Cutting Machine

Jinan Huaxia Machinery Equipment CO.,Ltd , https://www.cnformingmachine.com