A plastic self-tapping threaded part

Abstract

The invention discloses a plastic self-tapping screw, comprising: a threaded rod core, which is cut into two halves by a cylinder through the axis, and then respectively offset in opposite radial directions around the axis, and when the threaded rod core extends downward from the head of the screw, it is initially composed of two half-cylinders of constant diameter, and after extending to the area without thread teeth, it transitions from a cone angle to form a complete cylinder; a plurality of first thread teeth with circular tooth tops, formed at the portion of the threaded rod extending directly below the head of the screw; a plurality of second thread teeth with circular tooth tops, the thread tooth height gradually decreases toward the end face of the rod tail end, and is formed continuously with the first thread teeth; a cutting groove with a certain length extending longitudinally is provided at the end of the screw; a cylindrical guide rod is provided at the end of the threaded rod. When the threaded member of the invention is in the installation hole, the optimal screw-in performance is obtained, while ensuring that the integrity of the formed internal thread shape, the mechanical strength, the load capacity, the anti-deformation ability and the safety of preventing accidental disengagement are optimal.

Description

Technical Field

[0001] The invention relates to a plastic self-tapping threaded part, which cuts an internal thread into the mounting hole of a matching part when the thread is screwed into a plastic matching mounting hole. Background Art

[0002] Since the 1970s, plastic products have been widely used in industry and life. Plastic screws have excellent properties such as insulation, non-magnetic, corrosion-resistant, beautiful, and never rusting, so they are used in many fields.

[0003] The self-tapping quality of self-tapping screws formed by plastic is poor. Generally, the screws used with plastic parts are steel self-tapping screws. According to the type of internal thread of the inner hole of the forming partner, self-tapping screws are divided into extrusion self-tapping screws and cutting self-tapping screws. Common cutting self-tapping screws for plastic are steel self-tapping screws. There is a cutting groove at the tail of the screw, so that the thread teeth at the cutting groove position have a cutting effect. When the thread is selected into the inner hole of the matching part, it plays the role of cutting the inner hole to form the internal thread to complete the assembly and tightening. These threads are not formed by plastic.

[0004] For example, CN101216062B discloses a self-tapping threaded part having a uniquely formed thread profile, which is particularly designed to perform a self-tapping function. However, since the entire threaded rod has the profile shape, the thread bearing area is correspondingly reduced, and the thread bearing capacity is reduced.

[0005] When using self-tapping screws formed from plastic in practice, further improvements are desired. During the formation of the thread, the strength and load capacity of the threaded part and the mating part are adversely affected due to the groove or clamping effect. In addition, the deformation resistance and stability of the threaded part are not always satisfactory. Finally, even if the thread torque is low, maximum safety should be ensured to prevent the threaded part from accidentally disengaging from the mounting hole of the mating part. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to solve the deficiencies in the prior art and to provide a plastic self-tapping threaded part which, when the thread is screwed into the mounting hole of a plastic counterpart and the internal thread is cut into the mounting hole of the counterpart, achieves optimal screw-in performance while ensuring the integrity of the internal thread shape, mechanical strength, load capacity, deformation resistance and safety against accidental disengagement.

[0007] Technical solution: A plastic self-tapping threaded part according to the present invention comprises:

[0008] The threaded rod core is formed by cutting a cylinder into two halves through the axis, and then offsetting them in opposite radial directions around the axis. When the threaded rod core extends downward from the screw head, it is initially composed of two half cylinders of constant diameter, and after extending to the area without thread teeth, it transitions to a complete cylinder through a taper angle;

[0009] A plurality of first thread teeth with rounded tops formed at a portion of the threaded rod extending directly below the threaded member head;

[0010] A plurality of second thread teeth with circular tooth tops, the thread height of which gradually decreases toward the end surface of the rod tail end portion and is formed continuously with the first thread teeth;

[0011] A cutting groove extending longitudinally with a certain length is provided at the end of the threaded member;

[0012] A cylindrical guide rod is provided at the end of the threaded rod.

[0013] Furthermore, each of the plurality of first screw teeth has the same height Z.

[0014] Furthermore, the height of the second screw tooth is smaller than the height of the first screw tooth.

[0015] Furthermore, the axial length of the second thread tooth is 1 to 3 times the length of the spacing P between adjacent thread teeth in the cross section.

[0016] Furthermore, the first thread tooth has a cross-section with a bilinear symmetric shape, and the thread angle β is between 26° and 30°.

[0017] Furthermore, the volume of the spiral gap formed by the thread of the threaded member and the thread teeth is greater than the volume of the thread.

[0018] Furthermore, the screw tooth bottoms and screw tooth side surfaces of the first screw tooth and the second screw tooth are transitionally joined via a circular arc R2.

[0019] Furthermore, the values ​​of P, Z, R1 and R2 are as follows:

[0020] P=1.0 mm / 1.25 mm / 1.5 mm / 1.75 mm / 2.0 mm / 2.5mm

[0021] Z=0.33P

[0022] R1=0.5Z

[0023] R2=0.3Z

[0024] Among them, P is the spacing between adjacent threads in the cross section, Z is the height of the first thread, R1 is the bending radius of the circular tooth top, and R2 is the transition arc radius between the bottom of the thread and the side of the thread.

[0025] Furthermore, an angle ε is formed between the bottom surface of the cutting groove and the axis, and the range of ε is between 10° and 20°. The length L of the cutting groove is 3 times to 5 times of the tooth pitch.

[0026] Furthermore, the diameter d of the cylindrical guide rod is the diameter of the inscribed circle of the threaded rod core, and the length l thereof is 0.2 to 0.5 times the nominal diameter D of the thread.

[0027] Beneficial effects: The beneficial effects of the present invention are as follows:

[0028] (1) The present invention uses a relatively small profile angle. When the thread is screwed into the mounting hole of the counterpart, the thread exerts a relatively large axial force and a relatively small radial force. The relatively small radial force and the relatively large radius R1 can ensure that the plastic threaded part is screwed into the mounting hole of the counterpart with minimal slotting effect without applying any harmful screwing pressure.

[0029] (2) According to the profile shape of the thread and the screw of the present invention, the screw is formed by two semi-cylinders radially offset and connected around their axis. When the screw rotates around its axis, a cutting edge and a clearance angle are formed. The surface of the screw is connected to a thread with a constant height, so the overall thread profile also has this feature. The generation of the clearance angle can greatly reduce the friction resistance of the threaded part after entering the inner hole of the mating part, thereby facilitating the threaded part to penetrate into the material of the mating part;

[0030] (3) According to the present invention, due to the coordination between the reduced height external thread with gradually decreasing height and the arcuate surface formed at the thread teeth of the reduced height external thread and the constant height external thread, the stress acting on the mating part in the initial stage of screwing can be released and the internal thread can be smoothly formed; therefore, the screwing torque in the initial stage can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A structural front view of an embodiment of the present invention;

[0032] Figure 2 A cross-sectional view of a first screw tooth of an embodiment of the present invention;

[0033] Figure 3 It is a cross-sectional view of a second screw tooth of an embodiment of the present invention;

[0034] Figure 4 A bottom view of the structure of an embodiment of the present invention;

[0035] Figure 5 It is a schematic diagram of the terminal structure of an embodiment of the present invention;

[0036] Figure 6 It is a schematic diagram of the three-dimensional structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0038] like Figures 1 to 6 As shown, a plastic self-tapping screw member provided by an embodiment of the present invention includes:

[0039] The threaded rod core 1 is formed by a cylinder cut into two halves through the axis 9, and then offset in opposite radial directions around the axis 9. When the threaded rod core extends downward from the screw head, it is initially composed of two half cylinders with constant diameters, and after extending to the area without thread teeth, it transitions to a complete cylindrical guide rod 8 by a taper angle;

[0040] A first thread tooth 4 having a plurality of circular tooth tops with a constant height external thread, each of the plurality of first thread teeth 4 having the same thread tooth height Z and formed at a portion of the threaded rod extending directly below the screw head;

[0041] and a second thread tooth 3 having a plurality of circular tooth tops with external threads of reduced height, the thread tooth height gradually decreasing toward the end surface of the rod tail end portion and being formed continuously with the first thread tooth 4 having a circular tooth top with external threads of constant height;

[0042] The end of the threaded member is provided with a longitudinally extending cutting groove 7 of a certain length, and the number of the cutting grooves 7 is preferably four. The cutting groove 7 provides a cutting edge for the thread teeth at its position, and the internal thread is cut into the mounting hole when the threaded member is screwed into the mounting hole. In addition, the thread provides a special cross-sectional profile shape to reduce the tapping torque used to tap the internal thread.

[0043] A cylindrical guide rod 8 is provided at the end of the threaded rod.

[0044] As a further optimization of the above embodiment:

[0045] Preferably, in this embodiment, each of the plurality of first screw teeth 4 has the same height Z; further, the height of the second screw tooth 3 is smaller than the height of the first screw tooth 4 .

[0046] In this embodiment, preferably, the axial length of the second screw tooth 3 is 1 to 3 times the length of the spacing P between adjacent screw teeth in the cross section.

[0047] In this embodiment, preferably, Figure 2 As shown, the first thread tooth 4 has a cross section with a bilinear symmetrical shape, and the thread angle β is between 26° and 30°, preferably 28°.

[0048] Preferably in this embodiment, the volume of the spiral gap formed by the thread of the threaded member and the thread teeth is greater than the volume of the thread.

[0049] In this embodiment, preferably, the screw tooth bottom 6 and the screw tooth side surface 5 of the first screw tooth 4 and the second screw tooth 3 are transitionally connected through an arc R2.

[0050] In this embodiment, preferably, P, Z, R1 and R2 are taken as follows:

[0051] P=1.0 mm / 1.25 mm / 1.5 mm / 1.75 mm / 2.0 mm / 2.5mm

[0052] Z=0.33P

[0053] R1=0.5Z

[0054] R2=0.3Z

[0055] Among them, P is the distance between adjacent screw teeth in the cross section, Z is the height of the first screw tooth 4, R1 is the bending radius of the circular tooth top, and R2 is the transition arc radius between the screw tooth bottom 6 and the screw tooth side 5.

[0056] Using a relatively small profile angle, the thread exerts a relatively large axial force and a relatively small radial force when screwed into the mounting hole of the counterpart. The relatively small radial force and relatively large radius R1 can ensure that the plastic threaded part is screwed into the mounting hole of the counterpart with minimal slotting without applying any harmful screwing pressure.

[0057] In this embodiment, preferably, Figure 1 As shown, there is an angle ε between the bottom surface of the cutting groove 7 and the axis, and the range of ε is between 10° and 20°. The length L of the cutting groove 7 is 3 times to 5 times the tooth pitch.

[0058] In this embodiment, preferably, Figure 4 As shown, the diameter d of the cylindrical guide rod 8 is the inscribed circle diameter of the threaded rod core, and the length l thereof is 0.2 to 0.5 times the nominal diameter D of the thread.

[0059] According to the thread and screw profile of the present invention, the screw is formed by two semi-cylinders radially offset and connected around their axis. When the screw rotates around the axis, a cutting edge and a clearance angle are formed. The surface is connected to a highly constant thread, so the overall thread profile also has this feature. The generation of the clearance angle can greatly reduce the friction resistance of the threaded member after entering the inner hole of the mating member, thereby facilitating the threaded member to penetrate into the material of the mating member. The cutting geometry of the thread profile is shown in the figure.

[0060] According to the present invention, due to the coordination between the reduced height external thread with gradually decreasing height and the arc surface formed at the thread teeth of the reduced height external thread and the constant height external thread, the stress acting on the counterpart in the initial stage of screwing can be released and the internal thread can be smoothly formed. Therefore, the screwing torque in the initial stage can be reduced.

[0061] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A plastic self-tapping screw part, characterized in that: include: A threaded rod core (1), the threaded rod core is formed by cutting a cylinder through an axis (9) into two halves, and then offsetting the two halves in opposite radial directions around the axis (9). When the threaded rod core extends downward from the threaded part head, it is initially composed of two half cylinders with constant diameters, and after extending to a region without thread teeth, it transitions to a complete cylinder through a taper angle; A plurality of first thread teeth (4) with circular tooth tops are formed at a portion of the threaded rod extending directly below the threaded member head; A plurality of second thread teeth (3) with circular tooth tops, the thread tooth height gradually decreasing toward the end surface of the rod tail end portion, and being formed continuously with the first thread teeth (4); A cutting groove (7) extending longitudinally with a certain length is provided at the end of the threaded member; A cylindrical guide rod (8) is provided at the end of the threaded rod.

2. A plastic self-tapping screw member according to claim 1, characterized in that: The plurality of first screw teeth (4) each have the same height Z.

3. A plastic self-tapping screw member according to claim 1, characterized in that: The height of the second screw tooth (3) is smaller than the height of the first screw tooth (4).

4. A plastic self-tapping screw member according to claim 1, characterized in that: The axial length of the second thread tooth (3) is 1 to 3 times the length of the spacing P between adjacent thread teeth in the cross section.

5. The plastic self-tapping screw member according to claim 1, characterized in that: The first thread tooth (4) has a cross-section with a bilinear symmetric shape, and the thread angle β is between 26° and 30°.

6. A plastic self-tapping screw member according to claim 1, characterized in that: The spiral gap formed by the thread of the threaded part and the thread teeth has a volume greater than the volume of the thread.

7. The plastic self-tapping screw member according to claim 1, characterized in that: The screw tooth bottom (6) and the screw tooth side surface (5) of the first screw tooth (4) and the second screw tooth (3) are transitionally joined via a circular arc R2.

8. The plastic self-tapping screw member according to claim 1, characterized in that: The values ​​of P, Z, R1 and R2 are as follows: P=1.0 mm / 1.25 mm / 1.5 mm / 1.75 mm / 2.0 mm / 2.5mm Z=0.33P R1=0.5Z R2=0.3Z Wherein, P is the distance between adjacent thread teeth in the cross section, Z is the height of the first thread tooth (4), R1 is the bending radius of the circular tooth top, and R2 is the transition arc radius between the thread tooth bottom (6) and the thread tooth side surface (5).

9. The plastic self-tapping screw member according to claim 1, characterized in that: There is an angle ε between the bottom surface of the cutting groove (7) and the axis, and the range of ε is between 10° and 20°. The length L of the cutting groove (7) is 3 to 5 times the tooth pitch.

10. The plastic self-tapping screw member according to claim 1, characterized in that: The diameter d of the cylindrical guide rod (8) is the diameter of the inscribed circle of the threaded rod core, and its length l is 0.2 to 0.5 times the nominal diameter D of the thread.

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