JP2001032812A - Self-tapping screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-tapping screw to be screwed into a resin material hardly generating a crack on the resin workpiece. SOLUTION: This self-tapping screw has a foot part 3 on which a thread part 10 having a relatively large lead angle, a high height, and a relatively small included angle is formed, and a round surface part 12 comprising flank surfaces 11 on both sides ranging from neighborhood of the pitch diameter to the major diameter sagging toward the crest side on the thread part 10. This constitution reduces a generation of stress relaxation caused by aging effect. The large lead angle and the relatively high height prevent a female thread from breaking during wrenching, thereby eliminating a generation of a damaged thread. Since only a relatively small component force f1 in the horizontal direction with respect to a wrenching force F is generated on the flank surface of the tread, a generation of a crack on a workpiece made of a resin material is reduced extremely, thereby eliminating a generation of defects such as incapability of fixing a part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In recent years, resin materials have been actively used in recent years to reduce the weight and ease of assembly of assembled products, and are particularly suitable for fixing such resin parts to each other as works. Related to self-tapping screws.

[0002]

2. Description of the Related Art Recently, the development of resin materials has progressed, and various resins have been widely used in various fields as works. Along with this, the use of relatively hard resin materials that maintain high strength by mixing glass fibers into the resin to improve the strength of the resin material as a work is increasing. Are also spreading rapidly. Further, the use of such a resin material in a high-temperature environment and in a bad environment in which a temperature change repeatedly occurs is increasing. Under such a bad environment, due to the nature of the resin material, it is a viscoelastic body at room temperature,
It exhibits properties intermediate between rubber and metal, but undergoes significant deformation at higher ambient temperatures, and subsequently reduces its volume when ambient temperature falls. Therefore, when fastening a work made of this kind of resin material with a self-tapping screw, in addition to stress relaxation due to aging, the resin material is plastically deformed due to thermal expansion and contraction of the resin, and the axial force of the screw is reduced. Even when a slight external force is applied in the loosening direction of the screw, the self-tapping screw may rotate in the loosening direction and loosen the screw. In order to solve this, as shown in FIG. 4, there is a self-tapping screw in which the thread crest angle is made slightly smaller than a normal thread crest angle so as to reduce biting of the thread portion 110 into the work 120 made of resin material. .

[0003]

However, even if this self-tapping screw is used, the above problem is only slightly solved, and stress relaxation due to aging still occurs. Even if the head is hexagonal and a relatively large screwing force is transmitted as in this conventional example, a large tightening force can be obtained at the time of tightening and a large locking force can be obtained, but when the time is long, In addition, since the stress relaxation is caused by the deformation of the resin material, the loosening prevention force is reduced. Further, as shown in FIG. 4, the tightening force generated at the end of the screwing is such that the head seating surface is seated on the work and fixed between the work and the screw thread.
A relatively large horizontal component force f1 with respect to the tightening force F is generated on the flank surface of the screw thread, so that a work made of a resin material is cracked, and defects such as inability to fix parts are generated. ing. In order to solve this, there is a method of drilling a hole in the resin, inserting a metal bush into this hole, and screwing it into the hole, but there are many problems such as an increase in the number of parts and an increase in assembly cost. have.

[0004] A first object of the present invention is to provide a self-tapping screw which solves such a problem and hardly causes cracks in a work even when screwed into a resin material as a work.

A second object of the present invention is to provide a self-tapping screw capable of obtaining a relatively large locking force.

A third object of the present invention is to provide a self-tapping screw which has a relatively low screwing force and a reliable locking force.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to:
In a self-tapping screw composed of a head 2 having an engagement portion with a screw tightening tool and a leg 3 integrally formed with the head 2 and having a thread 10, the leg 3 has a relatively large lead angle and a screw. A thread portion 10 having a high crest height and a relatively small crest angle is formed, and both side flanks 11 are formed on the thread portion 10 from near its effective diameter to the outside diameter of the thread.
Is achieved by providing a self-tapping screw having a curved portion 12 bent toward the head side.

[0008] The second object of the present invention is achieved by providing a self-tapping screw in which the curved surface portion is formed over the entire length of the thread portion 10 of the leg 3.

The third object of the present invention is achieved by providing a self-tapping screw in which the curved surface is formed on a part of the thread portion 10 of the leg 3.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention.
3 through FIG. 1 and 2, 1
Is a self-tapping screw, and the self-tapping screw 1 has a hexagonal head 2 as an engaging portion that engages with a screw tightening tool (not shown) and transmits a screwing force. It is composed of legs 3 that are integrally connected. The leg 3 has a substantially circular cross section from the neck 4 located at the lower part of the head 2 to the tip, and the leg 3 has a thread portion 10 forming an external thread. The thread 10 at the tip of the leg 3 is slightly tapered.
In this embodiment, the cross section of the leg 3 is substantially circular, but may be substantially triangular.

As shown in FIGS. 1 and 3, the thread portion 10 is formed such that the outer diameter top portion of the thread portion 10 has a sharp edge of 40 ° or less in a longitudinal sectional shape along the axis of the leg portion 3.
The flank surfaces 11 on both sides forming the top side are inclined at the same angle on the base side. The flank 11 is usually formed with an apex angle at an equal angle equally divided by a straight line perpendicular to the leg 3, but the angle forming one flank 11 is larger than the angle forming the other flank 11. Alternatively, a small unequal angle thread may be used.

Further, the flank surfaces 11 on both sides are slightly curved toward the head side of the screw 1 on the outer diameter top portion over the entire length of the thread portion 10, and are curved in this way. The curved surface portion 12 is continuous with the flank surface 11 on the base side of the thread portion 10. In this embodiment, the position curved from the straight flank surface 11 is substantially a position close to the effective diameter of the thread, and the curved surface portion 12 has the self-tapping screw 1.
The screwing force acts strongly between the seating surface of the head 2 and the flank 11 on the head side of the threaded portion 10 as it becomes parallel to the line perpendicular to the axis of the leg 3. However, the horizontal component force f1 of the tightening force F is reduced, and cracking of the work 20 at the time of forming the internal thread and at the time of tightening can be prevented. The curved surface portion 12 does not necessarily need to be formed over the entire length of the thread portion 10 of the leg portion 3, but may be formed as necessary.
May be formed at the front end, the middle, or the head side.

The lead angle of the thread portion 10 is formed relatively large, and the height of the thread is formed relatively higher than the standard screw with respect to the shaft diameter. Thereby, the female screw 21 can be formed relatively coarsely with respect to the work 20 made of resin material, and the decrease in the contact area with the female screw 21 formed on the work 20 due to the relatively large lead angle reduces the thread. By increasing the height, this contact area is equal to or larger than a normal thread.

A screw tightening tool is fitted to the head 2 of the self-tapping screw 1 thus configured to apply a screw tightening force, and the self-tapping screw 1 is previously drilled to a work 20 by a predetermined dimension. When screwing into a hole (not shown), the thread 10 provided at the tip of the leg 3 bites into the peripheral wall of the pilot hole, and the female screw 21 is formed smoothly.
In this manner, as shown in FIG. 3, the thread portion 10 is screwed into the prepared hole of the work 20 while forming the female screw 21. As a result, the resin material in the prepared hole is gradually pushed away and the thread portion 10 is formed. Swells at the portion close to both flank surfaces 11 on the base side of the slab.

Therefore, the raised resin comes into contact with the flank surface 11. On the other hand, since the top side of the thread portion 10 is curved toward the bearing surface side of the head 2, the work 20
When the seating surface of the head 2 is seated on the screw head, a tightening force of the screw acts, and only a small horizontal component f1 of the tightening force F acts on the flank surface 11 on the head side of the thread portion 10. The work 20 hardly cracks. For this reason,
Since a reliable tightening force can be obtained for a long time, the self-tapping screw 1 is prevented from loosening even when the work 20 is deformed or vibrated by the temperature.

[0016]

According to the present invention, as is apparent from the above-described embodiment, the head 2 having the engagement portion with the screw tightening tool is provided.
And a self-tapping screw comprising a head 3 and a leg 3 having a thread portion 10 integral with the head portion 2, the leg portion 3 has a relatively large lead angle, a high thread height and a relatively small thread crest angle. Since the thread portion 10 is a self-tapping screw having a curved surface portion 12 in which both flank surfaces 11 are bent toward the head from the vicinity of the effective diameter of the thread portion 10 to the outer diameter of the thread portion, This reduces the occurrence of stress relaxation. In addition, since the lead angle is large and the screw thread is relatively high, the female screw is not broken at the time of tightening, and so-called screw stutter does not occur. Further, at the time of tightening, a large tightening force is obtained and a large locking force is obtained. Even if the time is long, stress relaxation is reduced due to deformation of the resin, so that a reduction in the locking force is reduced. In addition, the tightening force generated at the end of screwing is generated when the head seating surface is seated on the work and fixed between the curved flank of the thread and the flank of the thread. Since only a relatively small horizontal component force f1 is generated with respect to F, the occurrence of cracks is extremely reduced in a work made of a resin material, and defects such as inability to fix parts are not generated. In addition, this makes it unnecessary to form a hole in the resin, insert a metal bush into this hole, and screw it into the bush to assemble, thereby reducing the number of parts and the assembly cost.

Further, since the curved surface portion 12 is formed over the entire length of the thread portion 10 of the leg portion 3, a relatively large locking force can be obtained. By forming a part of the thread portion 3 of No. 3, the screwing torque can be reduced and a secure locking force can be obtained, so that a specific effect such as a decrease in quality as a product does not occur.

[Brief description of the drawings]

FIG. 1 is a front view of a self-tapping screw according to an embodiment of the present invention.

FIG. 2 is a bottom view of FIG.

FIG. 3 is an enlarged vertical sectional view of a main part showing a screwed state.

FIG. 4 is an enlarged longitudinal sectional view of a main part showing a conventional example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Self-tapping screw 2 Head 3 Leg 4 Neck 10 Thread part 11 Frank surface 12 Curved surface part 20 Work 21 Female screw

Claims (3)

[Claims] 1. A head 2 having an engagement portion with a screw tightening tool.
A self-tapping screw comprising a head portion 2 and a leg portion 3 having a thread portion 10 integrally with the head portion 2. The leg portion 3 has a relatively large lead angle, a high thread height, and a relatively small thread crest angle. A thread portion 10 is formed, and the thread portion 10 has a curved surface portion 12 in which both flanks 11 are bent toward the head from the vicinity of the effective diameter to the outer diameter of the thread. Self-tapping screw. 2. The self-tapping screw according to claim 1, wherein the curved surface portion is formed over the entire length of the thread portion of the leg portion. 3. The self-tapping screw according to claim 1, wherein the curved surface portion is formed on a part of the thread portion of the leg portion.