JP2007321930A - Tapping screw for fastening sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tapping screw for fastening a sheet capable of reducing a time for screwing and being screwed into a comparatively thin work without a tilt. <P>SOLUTION: In the tapping screw for fastening a sheet, a thread 10 is formed at a leg 3, the thread 10 at the leg 3 is a double-start thread. The cross section of the leg 3 on the head side is circular, and the cross section on the tip side is approximately triangular. Since a conical recess 20 is formed on the bearing surface 5 of a head 2 from the outside periphery 21 to the center, it is not necessary to form a prepared hole in the work in a burred form. Thus, the crushing of the internal thread or the deformation of the prepared hole does not occur during working. Prescribed torque for screwing can be simply obtained without causing insufficiency in the strength of the internal thread. At the time when the bearing surface of the screw is seated on the part, torque acting on the screw is obtained by the periphery of the head, and thus, the screw hardly causes loosening. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin plate fastening tapping screw for fastening a component to a thin workpiece with a predetermined fastening force.

  In electronic products such as mobile phones, personal computers, and portable music players, and automobile parts that are widely used in recent years, the parts are fixed to relatively thin workpieces because of their weight reduction, thickness reduction, and size reduction. The structure is adopted. In such a component fixing structure, screws are mainly used to fix the components. A screw 101 used in this fixing structure is shown in FIG. In this example, a pilot hole 131 is made in advance in a thin plate-like workpiece 130 and fixed using a single-threaded tapping screw 101. In this case, since the plate thickness of the work 130 is thin, the work fits between the adjacent screw threads 110 and the screw threads 110 without sufficiently forming a female screw in the prepared hole 131 of the plate. Screwing is performed obliquely by the lead angle of the crest 110, and the seating surface 105 of the head 102 is seated diagonally on the component 132 along the lead angle of the screw 101. For this reason, when a high tightening torque is applied, the internal thread of the pilot hole of the work may be crushed or the work or parts may be deformed, and a predetermined fastening force cannot be obtained.

In order to solve such a problem, there is a type in which a burring hole is formed in a prepared hole of a workpiece, and a screw is screwed in while forming a female screw therein. For example, Japanese Laid-Open Patent Publication No. 10-159821 discloses a burring hole formed in a workpiece and a screw is screwed into the burring hole. This is a drilling screw for fixing a gypsum board to a thin metal plate. As shown in FIG. 8, the screw 201 has a stepped shape from the parallel thread portion 210 through the intermediate taper screw portion 211 to the diameter, and from the small diameter parallel thread portion 212 to the tip taper screw portion 213. When driven into a gypsum board and light-weight channel steel by a shape screwing machine (not shown), the tip taper screw portion 213 penetrates the steel plate 230 to form a burring-like protrusion 231 on the steel plate, and a thread on the inner surface thereof. A screw 210 is formed while forming a female screw.
Japanese Patent Laid-Open No. 10-159821

  However, if the thickness of the workpiece is thin, for example, if it is less than the pitch of the screw, the workpiece will fit between the threads during the screwing operation, and the screw will be inclined. The seat is in a so-called one-side floating state in which the seat surface is in contact with only a part of the part, so that the fixing of the part is unstable. Even if a burring hole is formed as a pilot hole in a thin plate-shaped workpiece, the thickness of the workpiece is thin, so even if it is screwed in while forming a female screw with a tapping screw, the female screw is crushed and the screw is idle, The strength of the internal thread is insufficient due to deformation and a predetermined fastening force is not obtained. Furthermore, even if the component can be fixed to the workpiece with an appropriate fastening force, the screw head seating surface is not securely in contact with the component on the outer periphery of the head when it is seated on the component. Is currently in contact around the neck of the screw. For this reason, there is a problem that the screw is loosened and the screw is loosened and the fixed component is displaced with respect to the workpiece.

  An object of the present invention is to obtain a thin plate fastening tapping screw which can eliminate such problems and shorten the screw fastening time and can be screwed into a relatively thin workpiece without inclining.

  An object of the present invention is a screw having a head 2 having a drive hole 4 and a leg 3 integral therewith, and a screw thread 10 formed on the leg 3. Further, the cross section of the leg portion 3 on the head side is a circular shape, and the cross section on the distal end side of the leg portion 3 is formed in a substantially triangular shape. On the other hand, the sheet surface 5 of the head 2 is provided with a thin plate fastening tapping screw in which a conical recess 20 inclined from the outer peripheral edge 21 to the center of the seat 2 in the direction of the apex of the head 2 is formed. To be achieved.

  In addition to the above-described configuration, the object of the present invention is such that the trajectory circle connecting the three apexes of the substantially triangular shape fits into the pilot hole 31 in which the female screw is formed. Therefore, the screw tip can be easily positioned, and the biting of the screw at the beginning of screwing becomes smooth. Further, in addition to these configurations, the thread is a flank angle (α), (β) composed of a follower flank surface 11 and an advancing flank surface 12 with respect to a perpendicular perpendicular to the axis of the leg 3. Is an asymmetric thread in which the flank angle (α) on the head side is an unequal angle smaller than the flank angle (β) on the leg tip side, the axial force after screw tightening becomes large.

  According to the present invention, it is not necessary to make the pilot hole of the workpiece into a burring hole shape as in the prior art, so that the female screw is crushed during the screwing operation and the screw is idled until the screw reaches a predetermined tightening torque, The pilot hole will not be deformed. Further, the strength of the female screw is not insufficient, and a predetermined tightening torque can be easily obtained. Furthermore, the head seating surface is a conical recess formed in a conical taper shape inclined toward the top of the head from the outer periphery to the center of the head, so that when the seating surface of the screw is seated on a part, Since the torque acting on the head is obtained at the outer periphery of the head, even if a predetermined maximum tightening torque of the screw is applied, the torque acting on the female screw is less than that, so that the female screw is not crushed and is not easily loosened. Moreover, even if the workpiece thickness is equal to or less than the pitch of the thread, since the thread is two-threaded, the thread valleys facing each other across the center of the leg are in the same position. The workpiece fits in between the screw and the screw, and the screw can be screwed almost perpendicularly to the workpiece without following the lead angle of the screw thread. can do. As a result, a specific effect such as stabilization of the fixing of the component to the workpiece can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2, reference numeral 1 denotes a screw having a tapping function as an example of a screw with a female screw forming function, which is composed of a head 2 and a leg 3 formed integrally therewith. A drive hole 4 through which a screw driving force is transmitted from a driver bit (not shown) is formed. Two threads 10 are formed on the leg 3 integral with the head 2 from the vicinity of the seating surface 5 of the head 2 to the tip of the leg 3, and about 1 on the head side of the leg 3. / 3 has a circular cross section of the leg 3, and the cross section is substantially triangular from the tip of the leg 3 to the circular shape on the head side, and gradually becomes substantially triangular as it approaches the head side. The shape is set to be circular. Moreover, the tip portion of the leg 3 is slightly but gradually narrowed, and the tip of the leg 3 has a locus circle connecting three apexes of a substantially triangular shape in the pilot hole 31 of the work 30 forming the female screw. It is configured to fit. On the other hand, as shown in FIG. 3, each thread 10 has a flank angle (α) composed of a follower flank surface 11 and an advancing flank surface 12 with respect to a perpendicular perpendicular to the axis of the leg 3. (Β) is an asymmetric thread in which the flank angle (α) on the head side is made smaller than the flank angle (β) on the tip side of the leg and becomes an unequal angle.

  Further, the two threads 10 formed on the leg 3 have an equal pitch, and the threads 10 and the valleys 13 facing each other across the center line of the leg 3 are the head 2. The screw thread 10 and the valley 13 are positioned at the same distance from the seating surface 5. As a result, as shown in FIG. 4, when screwed into the pilot hole 31 formed in the thin plate-like workpiece 30, the workpiece 30 fits between the threads 10 and 10 of the screw 1 as shown in FIG. 3. It is like that. The width between the screw threads 10 and 10 may be set according to the width of the work 30 to be fastened, that is, the pitch of the screws 1 may be made rough or fine.

  Further, as shown in FIG. 5, a tapered conical recess 20 inclined at an angle θ in the apex direction of the head 2 from the outer peripheral edge 21 of the head 2 to the center is provided on the seating surface 5 of the head 2 of the screw 1. Thus, when the seating surface 5 of the head 2 is seated by being screwed in, the outer peripheral edge 21 of the head 2 is seated first. Due to the action of the outer peripheral edge 21 of the head 2, a predetermined axial force after screwing continues to act on the screw 1.

  As shown in FIG. 4, when the screw 1 configured in this manner is screwed into a prepared hole 31 formed in advance in the work 30 in a state where the component 32 is placed on the work 30, the pitch 1 is substantially equal to the pitch of the thread 10. The workpiece 30 having a thickness is fitted between the threads 10 and 10 as shown in FIG. When the screw tightening operation is performed in this state, the screw 1 is screwed in while maintaining a state substantially perpendicular to the workpiece 30.

  In this way, the screw 1 is screwed in, and the outer peripheral edge 21 of the head 2 is seated on the seating surface of the component 32. At this time, the head outer peripheral edge 21 of the seat surface 5 comes into contact with the component 32 first, and a screwing force is applied until a predetermined tightening torque is reached in this state. On the other hand, the part of the pilot hole 31 of the workpiece 30 is fitted between the screw threads 10 and 10, and the female screw is prevented from being crushed.

  In this embodiment, the thickness of the work 30 is set to be substantially equal to the pitch of the screw 1, but the present invention is not limited to this, and the same effect occurs even if the thickness is smaller than this. In addition, when the workpiece 30 is thick, on the contrary, the internal thread can be accurately formed in the prepared hole 31, and the work as the screw 1 is maintained without being easily crushed.

  FIG. 6 is an example showing the tightening torque when the screw 1 having a nominal screw M3 is screwed into a resin plate or a steel plate as the workpiece 30. In this figure, A is the minimum tightening torque, and B Indicates the maximum tightening torque. Further, the steel plate having a thickness (t) of 0.5 mm, 0.8 mm, 1.0 mm, and 1.6 mm is used, while the diameter of the prepared hole is 2.5 mm for the resin plate and the steel plate for each. Depending on the thickness, 2.0 mm, 2.7 mm, 2.8 mm, and 2.9 mm were adopted and measured. As is clear from this, until now, the tightening torque has been adjusted and changed to an appropriate torque each time due to differences in the type and thickness of the workpiece 30. It is also possible to make the operating torque of 30 the same, that is, the torque range between the dotted lines in FIG. 6, so that it is not necessary to change the torque adjustment each time the workpiece changes, and the usage range of the screw 1 is wide and the screw Fastening work efficiency is also improved.

It is a front view which shows embodiment of this invention. It is a right view of FIG. It is a principal part cross-sectional enlarged view which shows the screwing state of this invention. It is a principal part cross-sectional enlarged view which shows the screwing start state of this invention. It is a partial cross-section enlarged view of the present invention. It is a figure which shows the relationship of the fastening torque of a workpiece | work and this invention. It is a front view which shows the screwed state by the prior art example of this invention. It is principal part sectional drawing which shows the screwed state by another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw 2 Head 3 Leg 4 Drive hole 5 Seat surface 10 Screw thread 11 Follow side flank surface 12 Advance side flank surface 13 Valley 20 Conical recessed part 21 Outer peripheral edge 30 Work piece 31 Pilot hole 32 Parts

Claims (3)

In a screw composed of a head (2) having a drive hole (4) and a leg (3) integral with the head (2), and a thread (10) formed on the leg,
The thread of the leg is a double thread, and the cross section of the leg on the head side is a circular shape, and the cross section on the tip side of the leg is formed in a substantially triangular shape. On the other hand, the seat surface (5) of the head is formed with a conical recess (20) inclined in the direction of the apex of the head from the outer periphery (21) to the center. A tapping screw for thin plate fastening.   The thin plate fastening tapping screw according to claim 1, wherein the tip of the leg portion is configured such that a locus circle connecting three vertices of a substantially triangular shape is fitted into a pilot hole (31) in which a female screw is formed. The thread is perpendicular to the axis perpendicular to the axis of the leg, and the flank angle (α) and (β) formed by the follower flank surface (11) and the advancing flank surface (12) are unequal angles. 3. The thin plate fastening tapping screw according to claim 1, wherein the tapping screw is an asymmetric screw thread.

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