A double toothed self-tapping screw

Abstract

The utility model discloses a kind of double tooth self-tapping screw, including tail, stem and self-tapping portion sequentially distributed and coaxially integrated connection along axis;Double tooth thread group is provided on stem and self-tapping portion, and double tooth thread group includes the first thread tooth and second thread tooth of equal pitch, interval groove is provided between the two tooth bodies of adjacent in the first thread tooth, the tooth body of second thread tooth is located in the interval groove, and the first thread tooth and second thread tooth are alternately distributed along axis under radial visual angle;Through the structural design of double tooth alternately distributed along axis, the radial change excessive area between stem and self-tapping portion, the cooperation excessive area between tail and stem and conical self-tapping portion, realize the goal of stress dispersion, reduce workpiece damage, improve self-tapping stability and structural durability.

Description

Technical Field

[0001] This utility model belongs to the field of fastener technology, and more specifically, it is a double-threaded self-tapping screw. Background Technology

[0002] Self-tapping screws, as commonly used fasteners, are widely used in fastening workpieces made of soft materials and thin steel plates. While double-threaded self-tapping screws have been developed, they still suffer from several design flaws: In some double-threaded screws, the double threads do not cover the entire length from the shank to the tapping section, but only partially, resulting in poor continuity of the thread-base fit during tapping. This can lead to fluctuations in thread resistance due to thread breakage, affecting fastening efficiency. Furthermore, while some double-threaded screws have double threads throughout, they lack a dedicated transition structure to address the diameter difference between the shank and the tapping section, easily creating a significant diameter abrupt change at the connection point. This leads to stress concentration under load, making these areas prone to damage during long-term use or exposure to vibration and axial forces. Fractures can occur; some double-threaded screws lack optimized inter-thread structure or fail to consider the transition design between the tail and shank. When fastening brittle workpieces such as gypsum board, the concentrated extrusion force of the threads on the substrate can lead to workpiece structural failure, or insufficient gripping force of the double threads can affect connection stability. At the same time, the transition between the tail and shank of traditional double-threaded screws is abrupt, which may not only cause hard contact damage to the threaded hole end due to the short clearance area, but also affect the processing demolding efficiency and the smoothness of tightening during actual use due to the rough surface structure. It is difficult to meet the comprehensive requirements of self-tapping stability, structural durability and workpiece protection. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the existing technology, this utility model provides a double-thread self-tapping screw. Through the structural design of alternating double threads along the entire axis, a diameter transition zone between the shank and the self-tapping part, a fitting transition zone between the tail and the shank, and a tapered self-tapping part, the invention achieves the goals of stress dispersion, reducing workpiece damage, improving self-tapping stability and structural durability.

[0004] Technical solution: To achieve the above objective, this utility model provides a double-threaded self-tapping screw, comprising a tail, a shank, and a self-tapping portion that are sequentially distributed along an axis and integrally connected coaxially; the shank and the self-tapping portion are provided with a double-threaded assembly, the double-threaded assembly comprising a first thread and a second thread with equal pitch, wherein a spacer groove is provided between two adjacent threads in the first thread, and the thread body of the second thread is located in the spacer groove, and the first thread and the second thread are alternately distributed along the axis in a radial view.

[0005] Furthermore, the self-tapping part is tapered, with the tip of the tapered part located on the side away from the shank, and the first thread and the second thread extending from the end of the shank away from the self-tapping part to the tip of the tapered part.

[0006] Furthermore, the tooth height of the first thread is greater than that of the second thread, and the tooth profile angle of the first thread is smaller than that of the second thread.

[0007] Furthermore, the connection between the rod and the self-tapping part constitutes a diameter transition zone, which contains only one turn of the first thread and one turn of the second thread. The first thread in the diameter transition zone is called the first transition thread, and the second thread in the diameter transition zone is called the second transition thread. The maximum outer diameter of the first transition thread and the maximum outer diameter of the second transition thread are equal.

[0008] Furthermore, the tail is flared, and includes a smaller end and a larger end; the smaller end is coaxial with the rod and has the same outer diameter as the rod, the larger end has a larger outer diameter than the rod, and a drive groove is provided at the end of the larger end away from the rod.

[0009] Furthermore, the connection surface between the smaller end and the larger end of the tail is a waist-shaped arc surface; a mating transition area is provided between the smaller end and the rod, and the outer peripheral surface of the mating transition area is a smooth circular surface.

[0010] Beneficial effects: Compared with the prior art, the double-thread self-tapping screw of this utility model has the following beneficial effects;

[0011] 1. The first and second transition threads of equal diameter are provided in the diameter transition zone between the shank and the self-tapping part, which can smoothly connect the diameter difference between the shank and the self-tapping part, avoiding the stress concentration phenomenon caused by the abrupt change in diameter of existing double-threaded screws; and the design of only one double thread ensures the transition effect without increasing the structural complexity, taking into account both the convenience of processing and the structural stability, and significantly reducing the probability of screw breakage under stress.

[0012] 2. The transition area between the tail and the shank adopts a smooth circumferential surface design. On the one hand, it extends the clearance fit area between the threaded hole and the smaller end of the tail, avoiding hard contact damage to the threaded hole end caused by the excessive stiffness of the existing screw. On the other hand, the smooth surface facilitates mold release during processing, improves production efficiency, and reduces frictional resistance with the workpiece during use, ensuring smooth screwing.

[0013] 3. The first thread has a higher tooth height than the second thread. The first thread bears the main fastening force, while the second thread helps to enhance stability. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a double-thread self-tapping screw according to the present invention. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] like Figure 1 As shown, a double-threaded self-tapping screw includes a tail portion 1, a shank portion 2, and a self-tapping portion 3 arranged sequentially along an axis. The tail portion 1, shank portion 2, and self-tapping portion 3 are coaxially arranged and integrally connected. The shank portion 2 and self-tapping portion 3 are provided with a double-threaded assembly 4. The double-threaded assembly 4 includes a first thread 5 and a second thread 6 with equal pitch. A spacer groove 7 is provided between two adjacent threads in the first thread 5. The thread body of the second thread 6 is located in the spacer groove 7, and the second thread 6 is located at the center of the spacer groove 7. That is, from a radial perspective, the first thread 5 and the second thread 6 are alternately distributed along the axis.

[0017] During the screw-in process, the double-threaded assembly 4 can simultaneously act on the connected workpiece. Compared with single-threaded screws, screws with double-threaded assemblies 4 have more thread contact points per unit length, which can effectively disperse the stress during self-tapping and tightening, reduce the load on individual thread teeth, extend the screw's service life, and improve the guiding performance during screwing, making the screwing process smoother. The design of equal pitch for the first thread tooth 5 and the second thread tooth 6 in the double-threaded assembly 4 allows the first thread tooth 5 and the second thread tooth 6 to remain synchronized during screwing, preventing interference or sudden changes in screwing resistance due to pitch differences, ensuring the stability of the screwing process, and avoiding screw jumping or jamming due to sudden changes in resistance.

[0018] More specifically, such as Figure 1 As shown, let the pitch of the first thread 5 be D1, and the pitch of the second thread 6 be D2, then D1 = D2; let the width of the second thread 5 be X1, and the width of the second thread 6 be X2, then X1 > X2; let the width of the spacer 7 be S, and the distance between the tooth body of the second thread 6 and the two teeth of the first thread 5 on both sides is P, then P ≤ X1, and X1 + 2P = S.

[0019] The self-tapping part 3 is tapered. The tip of the tapered self-tapping part 3 can easily pierce the workpiece surface in the initial stage of self-tapping. As the screw is screwed in, the tapered structure gradually expands the drilling range, creating conditions for subsequent thread engagement with the workpiece. The tip of the self-tapping part 3 is located away from the shank 2. The first thread 5 and the second thread 6 extend from the end of the shank 2 away from the self-tapping part 3 to the tip of the self-tapping part 3, thus allowing the double-threaded assembly 4 to cover the entire length of the shank to the tip of the self-tapping part. When the tip of the self-tapping part 3 pierces the workpiece surface, the double-threaded assembly 4 can promptly penetrate the pierced hole created by the self-tapping part 3. The entire self-tapping process involves the interaction of the double threads with the workpiece. This component not only improves the self-tapping efficiency of screws but also enables timely and secure fastening through double-threaded construction. In the specific embodiment described in this solution, the taper angle α at the tip of the self-tapping part 3 is 15°~22°. Of course, those skilled in the art can adjust the taper angle α at the tip of the self-tapping part 3 according to actual needs. The smaller the angle α, the higher the self-tapping efficiency, but the lower the pressure it can withstand; the larger the angle α, the lower the self-tapping efficiency, but the higher the pressure it can withstand. By reasonably selecting the taper angle α, a balance can be achieved between self-tapping efficiency and pressure-bearing capacity to meet the needs of different working conditions. For example, a small α can be used for thin workpieces to increase speed, while a large α can be used for heavy workpieces to enhance pressure resistance.

[0020] The maximum outer diameter of the first thread tooth 5 is greater than the maximum outer diameter of the second thread tooth 6. For ease of description, the thread height is used to represent the maximum outer diameter difference between different thread teeth. The thread height is the difference between the outer contour of the thread tooth and the axis of the rod 2 and the difference between the outer circumferential surface of the rod 2 and the axis of the rod 2 from a radial perspective. The thread height of the first thread tooth 5 is greater than the thread height of the second thread tooth 6. Let the thread height of the first thread tooth 5 be H1 and the thread height of the second thread tooth 6 be H2, and H1>H2. The higher thread height of the first thread tooth 5 allows it to bear the main fastening force when mating with the workpiece, while the lower thread height of the second thread tooth 6 helps to enhance the connection stability. At the same time, since the second thread tooth 6 is located in the spacer groove 7 of the first thread tooth 5, the higher first thread tooth 5 can also protect the second thread tooth 6, reducing its direct wear during the self-tapping process and extending the overall service life of the double thread group 4. In the specific embodiment described in this scheme, the value range of H1 is 1.23~1.63, and the value range of H2 is 0.52~0.92.

[0021] The connection between the rod portion 2 and the self-tapping portion 3 forms a diameter transition zone 13. This transition zone 13 contains only one turn of the first thread 5 and one turn of the second thread 6. The first thread 5 in the transition zone 13 is designated as the first transition thread 5a, and the second thread 6 in the transition zone 13 is designated as the second transition thread 6a. The maximum outer diameter of the first transition thread 5a and the maximum outer diameter of the second transition thread 6a are equal. Figure 1As shown, the maximum outer contour of the first transition thread 5a and the maximum outer contour of the second transition thread 6a are both on the same horizontal schematic line Z. That is, the distance between the maximum outer contour of the first transition thread 5a and the axis of the shank 2 and the distance between the maximum outer contour of the second transition thread 6a and the axis of the shank 2 are equal, so that the double thread group 4 forms a short-term smooth transition structure in the diameter transition zone. During the self-tapping process, the screw is continuously subjected to the extrusion force and screwing torque of the workpiece. The smooth transition structure of the diameter transition zone 13 allows the force to be transmitted more evenly from the shank 2 to the self-tapping part 3, avoiding stress concentration at a certain position due to the abrupt change in the diameter of the shank and the self-tapping part, preventing the screw from breaking at this point, and significantly improving the structural strength of the screw and the reliability of the self-tapping process.

[0022] The tooth profile angle of the first thread 5 is smaller than that of the second thread 6. Let the tooth profile angle of the first thread 5 be the first tooth profile angle θ1, and the tooth profile angle of the second thread 6 be the second tooth profile angle θ2. In the specific embodiment described in this scheme, the angle of the first tooth profile angle θ1 is 45°, and the angle of the second tooth profile angle θ2 is 60°. The smaller first tooth profile angle θ1 makes the tooth flank of the first thread 5 steeper, which can provide a larger axial component force when bearing axial force and enhance the fastening effect. The larger second tooth profile angle θ2 makes the tooth flank of the second thread 6 relatively gentle, which helps to reduce the frictional resistance during screwing. The combination of the two tooth profile angles can not only increase the fastening force of the screw, but also increase the convenience of screwing during the screwing process.

[0023] It is important to emphasize that the angles of the first tooth profile angle θ1 and the second tooth profile angle θ2 can be arbitrary and can be adjusted according to actual needs, as long as θ1 < θ2. It is not necessary to use the data provided by this party. By flexibly adjusting the size of the tooth profile angle, it can be adapted to workpieces of different materials.

[0024] The tail portion 1 is shaped like a trapezoidal trumpet, comprising a smaller end 8 and a larger end 9. The smaller end 8 is coaxially integrated with one end of the rod portion 2, and its outer diameter is equal to that of the rod portion 2. The larger end 9 has a much larger outer diameter than the rod portion 2, and a driving groove 10 is formed at the end of the larger end 9 furthest from the rod portion 2. The driving groove 10 can be cross-shaped, slotted, hexagonal, etc. When the screw is tightened, the larger end 9 can make more full contact with the workpiece surface, increasing the contact area, dispersing pressure, and preventing the workpiece surface from being dented or damaged due to excessive local pressure.

[0025] Furthermore, in the specific embodiment described in this solution, the outer diameter of the larger end 9 is greater than three times the outer diameter of the rod portion 2, and the connection surface between the smaller end 8 and the larger end 9 is a waist-shaped arc surface, thus the tail portion 1 has a sudden change in diameter from the small end to the large end; a mating transition area 11 is also provided between the smaller end 8 and the rod portion 2, and the outer circumferential surface of the mating transition area 11 is a smooth circular surface, making the transition between the smaller end 8 and the rod portion 2 smoother; during screw manufacturing, the smooth circular surface of the mating transition area 11 facilitates mold demolding and improves processing convenience; when the screw is used, the smooth circular surface of the mating transition area 11 can reduce friction with or between the screw and the workpiece, avoiding wear or resistance caused by friction that affects screw tightening.

[0026] The shank 2, self-tapping part 3, and double thread set 4 together constitute the threaded area. During the tapping process, the threaded area forms a corresponding threaded hole on the workpiece. When the screw is tightened, the threaded area and the threaded hole are in a threaded fit state. At this time, the end of the threaded hole near the tail 1 and the smaller end 8 are in clearance fit, and the port is limited to contact the curved surface of the waist. The setting of the fit transition area 11 can increase the range of clearance fit, so that the port of the threaded hole has a longer smooth section for transition before contacting the curved surface of the waist. When the screw is subjected to vibration or axial force, this clearance fit area can provide a certain buffer space to avoid the port of the threaded hole directly contacting the diameter change of the tail and generating local stress.

[0027] Furthermore, the design of the mating transition zone 11, combined with the smooth transition structure of the diameter change transition zone 13, forms a multi-level stress dispersion structure from the self-tapping part 3 to the shank 2 and then to the tail 1 during the screw's self-tapping locking process on the workpiece. This structure prevents stress concentration at the connection between the tail 1 and the shank 2 due to hard contact under force, and also avoids stress concentration at the diameter change point between the shank 2 and the self-tapping part 3 due to abrupt diameter changes. This comprehensively improves the screw's fatigue resistance and fracture resistance, making the screw more durable under repeated disassembly and assembly or long-term load conditions.

[0028] In addition, wear-resistant protrusions 12 can be provided on the end surface of the larger end 9 away from the rod 2, or it can be provided as a smooth surface. When wear-resistant protrusions 12 are provided, the friction between the tail 1 and the driving tool can be increased to prevent slippage during screwing and improve the reliability and efficiency of screwing. Smooth surfaces are suitable for occasions where appearance requirements are high or no additional friction is required, to meet different usage needs.

[0029] The above are the preferred embodiments described in this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the scope of protection of this utility model.

Claims

1. A double-thread self-tapping screw, characterized in that: It includes a tail (1), a rod (2) and a self-tapping part (3) that are distributed sequentially along the axis and are integrally connected along the axis; the rod (2) and the self-tapping part (3) are provided with a double thread group (4), the double thread group (4) includes a first thread (5) and a second thread (6) with equal pitch, a spacer groove (7) is provided between two adjacent teeth in the first thread (5), the tooth body of the second thread (6) is located in the spacer groove (7), and the first thread (5) and the second thread (6) are alternately distributed along the axis in a radial view.

2. The double-threaded self-tapping screw according to claim 1, characterized in that: The self-tapping part (3) is tapered, with the tip of the tapered part (3) located away from the rod (2), and the first thread (5) and the second thread (6) extend from the end of the rod (2) away from the self-tapping part (3) to the tip of the tapered part (3).

3. A double-thread self-tapping screw according to claim 2, characterized in that: The tooth height of the first thread (5) is greater than the tooth height of the second thread (6), and the tooth profile angle of the first thread (5) is less than the tooth profile angle of the second thread (6).

4. A double-thread self-tapping screw according to claim 2, characterized in that: The connection between the rod (2) and the self-tapping part (3) forms a diameter transition zone (13). The diameter transition zone (13) contains only one turn of the first thread (5) and one turn of the second thread (6). The first thread (5) in the diameter transition zone (13) is called the first transition thread (5a), and the second thread (6) in the diameter transition zone (13) is called the second transition thread (6a). The maximum outer diameter of the first transition thread (5a) and the maximum outer diameter of the second transition thread (6a) are equal.

5. A double-thread self-tapping screw according to claim 1, characterized in that: The tail (1) is horn-shaped and includes a smaller end (8) and a larger end (9). The smaller end (8) is coaxial with the rod (2) and the outer diameter of the smaller end (8) is equal to the outer diameter of the rod (2). The outer diameter of the larger end (9) is greater than the outer diameter of the rod (2), and a drive groove (10) is provided at the end of the larger end (9) away from the rod (2).

6. A double-thread self-tapping screw according to claim 5, characterized in that: The connection surface between the smaller end (8) and the larger end (9) of the tail (1) is a waist-shaped arc surface; a mating transition area (11) is provided between the smaller end (8) and the rod (2), and the outer peripheral surface of the mating transition area (11) is a smooth circular surface.

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