1, working principle
During the process of twisting the self-tapping locking screw into the pre-made hole (drilling, punching or die-casting optical hole) of the connected part, the screw thread is pressed to form an internal thread in the pre-made hole to achieve the connection and tightness. The purpose of solid.
The structure of self-squeezing screws differs from machine screws, self-cutting screws and ordinary self-tapping screws, and their working principles are also different. The machine screw can only be screwed into the hole with internal thread. Generally speaking, there is a gap between the inner and outer threads, mainly relying on the pre-tightening force to ensure the anti-loose performance between the matching thread and the side surface and the friction of the bearing surface; The tapping screw is to screw the screw into the pre-made hole without thread. Usually, there is interference between the inner and outer threads, mainly relying on the pre-tightening force and the interference between the side of the matching thread and the friction of the bearing surface to ensure the anti-loose. performance. The self-cutting screw's anti-loose principle is between the machine screw and the normal self-tapping screw. In addition to the above-mentioned anti-loosening properties, self-squeezing screws have their own unique features. The screw of the self-extruding screw has a curved triangular section of thread. For ease of analysis, we regard the thread as a ring tooth, see Figure 16-1.
Figure 16-1 Threads in a curved triangular section
Due to the existence of elastic deformation, the diameter of the internal thread outside the three regions of the apex A, B, and C on the annular tooth is smaller than the diameter of the circumcircle of the annular tooth, that is, the three regions A, B, and c on the annular tooth are embedded in the screw hole. In the metal, according to the law of minimum resistance and the law of volume deformation of plastic deformation in the metal pressure processing principle, the metal flows to both sides of the apex. When the ring tooth rotates, in front of the apex movement direction of the ring tooth, on the screw hole Three internal heels are formed and move forward with the rotation of the screw, creating a certain resistance. Therefore, no matter which direction the ring tooth rotates, it is necessary to overcome this resistance. Self-squeezing screws are based on this principle to improve the anti-loosening properties.
2, the main features
(1) Saving internal thread processing
Self-squeezing screws, like ordinary self-tapping screws and self-cutting screws, can save the processing effort of internal threads. For this advantage alone, it has become an important basis for the development of self-tapping screws in the world. It is possible to avoid the tapping process, which does not seem to be taken seriously by people, and generally does not consider its economic value. However, in some advanced industrial countries, such "small things" have been gradually emphasized. For example, Japan published a related article in 1977 that clearly stated that in screw connections, the cost of screws is only 15% of the total cost, while the remaining 85% is used. Equipment, tooling costs, and labor costs for punching, tapping, and anti-loosening devices (gaskets). At the same time, the patents and papers on self-tapping screws in the United States and West Germany are indispensable to demonstrate the economic benefits of eliminating the tapping process. With the opening up of China, especially the introduction of new technologies, this issue has begun to be taken seriously. Self-squeezing screws can save internal thread processing, have low screwing torque, high locking performance, many materials that can be screwed in, and high threading strength. They have been agreed by design, use, production and distribution. The national standard revised by international standards has been more widely adopted and implemented.
(2) Low screwing torque and high locking performance
The self-squeezing screw has a curved triangular section thread, that is, a unique thread shape, which not only makes it superior to ordinary self-tapping screws in mounting screwing torque, but also has much higher reliability than ordinary self-tapping screws and lock washers. Machine screw. In this respect, in recent years, Japan and West Germany have published their own test results, and China has tested conditions.
(3) There are many materials that can be screwed in
The self-squeezing screws are surface hardened and can be screwed into prefabricated holes of black or non-ferrous materials to form threads. The preformed holes can be made by drilling, die cutting or die casting. It can be screwed into all of the malleable materials, that is, it can be screwed into a material with a certain plastic deformation ability. It can be based on the elongation δ of the material. It is generally suitable for materials with δ5 ≥ 8% to 10%, but it is suitable for die-casting alloys with δ5 < 5%, but it should be determined by process verification. The optimal pre-formed hole size and lubrication conditions. Therefore, materials that can be screwed in include non-alloys, low alloys, aluminum and aluminum alloys (common die castings), copper and copper alloys (copper content greater than 63%) and zinc and zinc alloys with tensile strength σb ≤ 60O N/mm2 (commonly used die castings) and so on.
For materials with poor plastic deformation or work hardening, such as stainless steel, gray cast iron and magnesium alloys, such screws can also be used under certain conditions of use.
For materials that are not suitable or when the conditions of use are not appropriate, chipping, seizing (or cold welding) and low roughness of the tapped hole may occur when the screw is screwed in.
(4) High thread connection strength
According to the self-squeezing screw standard, the minimum tensile strength of the screw is 800 N/mm2, which is the same as the high-strength bolt of the 8.8 grade, or the screw. In addition, screwing into the preformed hole to form an internal thread can increase the joint strength of the internal thread by more than 30%. Therefore, the strength of the self-resistance screw connection pair far exceeds that of the machine screw connection pair. Under the same conditions of use, a smaller size self-squeezing screw can be used instead of the machine screw, and it is also possible to reduce the structural size of the main machine. .
I System description:
Heat Shrinkable Sleeve with hot melt adhesive, having properties of excellent insulating, environmental sealing, and resistant to impact and abrasion. It is designed for applications to seal and protect electrical splices, cable terminations and joints where electrical insulation and water proof are required. 3:1 shrink ratio allows it easily fit over irregular shape and large connectors.
II Features
>Resistant to UV-radiation
>High electrical insulation
>Superior mechanical property
>Minimum fully recovery temperature: 120°C
>Standard color: Black
III Techinal Data
Heat Shrinkable Sleeve
Heat Shrinkable Sleeve, Pipe Heat Shrinkable Sleeve, Pvc Heat Shrink Sleeve, Hot Shrink Sleeve, Corrosion Protection Tape
Jining Xunda Pipe Coating Materials Co.,Ltd , http://www.pipe-wrap.com