Tapping screw for engineering plastics

Abstract

The invention relates to a tapping screw for engineering plastics, which comprises a screw head and a screw rod, wherein the screw rod is provided with helical threads, an outline of a thread form section comprises an inner incline, an intermediate incline, an outer incline and a thread top surface connected with the outer incline from a screw rod thread bottom to a screw rod thread top; the inner incline, the intermediate incline, the outer incline and the thread top surface are symmetrically arranged along the center and are sequentially connected, the inner incline has a thread angle alpha of 140 DEG+ / -3DEG and an inner thread length L2 of 1 / 5 of the total length of a thread form, the intermediate incline has a thread angle beta of 20DEG + / -3 DEG and an intermediate thread length L2 of 2 / 5 of the total length of the thread form, and the outer incline has a thread angle gamma of 30DEG+ / -3DEG and an outer thread length L3 of 2 / 5 of the total length of the thread form. According to the invention, the stability of multiple connections can be improved and the service life of the tapping screw is prolonged while the connection requirement is met.

Description

technical field [0001] The invention relates to a self-tapping screw for engineering plastics, belonging to the technical field of self-tapping screws. Background technique [0002] The thread on the self-tapping screw used in engineering assembly is helical. When the self-tapping screw is assembled, it uses its own thread structure to tap the matching internal thread in the prefabricated hole to complete the assembly. At present, self-tapping screws mainly use triangular threads. The angle of the triangular thread is usually 50-60°. Compared with other tooth types, it has the characteristics of thick root and high strength, so it is mostly used for connection. However, due to the large tooth angle, when the screw is tapped, there is a large radial force, so that the axial component force is small, which is not conducive to the flow of the connecting material, so there is a large installation torque and it is not easy to tap. At the same time, under certain wall thickness c...

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Problems solved by technology

However, due to the large tooth angle, when the screw is tapped, there is a large radial force, so that the axial component force is small, which is not conducive to the flow of the connecting material, so there is a large installation torque and it is not easy to tap. At the same time, under certain wall thickness conditions, due to its large radial tension, it is easy to cause damage to the connecting material, and it is not easy to reconnect after disassembly, so the self-tapping screw of this structure has relatively low reinstallability. Difference

For the isosceles trapezoidal thread, although the profile angle α=30°, its efficiency is lower than that of the rectangular thread, and it has the advantages of easy processing, good centering, and high root strength, but because it can only bear one-way load, so Widely used in screw transmission, not suitable for connection, so self-tapping screws are usually not used

For the thread profile of the above two structures, the tooth profile slope and the thread bottom diameter are both rounded, and the profile angle is a single angle, so the tooth root width cannot be further increased

Tooth angle is an important structural parameter of self-tapping screws, which directly affects the installation performance, strength and life of self-tapping screws. At present, self-tapping screws use large-angle tooth angles, so the flow of self-tapping screws on the connecting material There are deficiencies in performance, stability of multiple installation performance, tensile and torsional performance, etc.

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