JP3109980B2 - Tapping screw - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-tapping screw, and more particularly, to increase the tightening torque by preventing torsional breakage of a shaft body at the time of tightening, preventing seizure of the screw and shear breakage of a female screw formed on a mating member. The present invention relates to a self-tapping screw having a configuration that can be made to work.

[0002]

2. Description of the Related Art In recent years, when assembling a lightweight member such as a thin plate in an apparatus or the like, a tapping screw which can omit a tapping fastening step for forming a female screw on the member in advance is frequently used. The tapping screw does not need to form a female screw in the mating member to be fastened in advance, and is formed so that the tapping screw itself forms a female screw in the prepared hole corresponding to the male screw and simultaneously tightens the female screw.

[0003] However, such a tapping screw is forcibly screwed in while forming a female screw in a pilot hole where no female screw is formed, so that a large torsional load is generated in the screw shaft, and the torsional stress of the shaft increases. As a result, there is a problem that the shaft body is torsionally broken. Therefore, as one measure for eliminating the torsional fracture, it has been considered to increase the shaft diameter of the screw to reinforce the torsional stress.

[0004]

However, in the case of the tapping screw under the above condition, as the female screw is formed on the mating member, the mating member corresponding to the female screw is moved toward the root side along the thread of the tapping screw. When extruded, the gap between the flat portion of the tapping screw and the mating member is narrow, so that the mating member and the flat portion of the tapping screw come into contact with each other. For this reason, a large frictional force is generated in the contact portion, seizure occurs between the two, the strength of the female screw is reduced, the female screw is sheared by the threaded portion of the tapping screw, and the screw flap torque is significantly reduced. And so on.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to prevent seizure of a screw and shear fracture of a female screw formed on a mating member, thereby suppressing a reduction in torque of a screw flap. It is to provide a tapping screw that can be used.

[0006]

In order to achieve the above object, according to the present invention, a helical continuous thread is formed on a peripheral surface of a shaft having a head engaged with a tool. In a tapping screw in which a shaft portion between ridges is formed in a flat portion, a step diameter portion having a larger diameter than the flat portion extends from both bases of the screw thread in parallel with the flat portion. It is characterized by the following. The step between the step diameter portion and the flat portion is 0.0143 to 0.02 of the thread outer diameter.
It is characterized by a factor of 86.

[0007]

According to the above construction, the mating member corresponding to the female screw at the time of forming the female screw is pushed out along the thread slope and tries to abut on the flat portion of the shaft, but is guided in the axial direction by the step diameter portion. Therefore, the flat portion of the tapping screw comes into contact with the mating member and rubs, so that the two do not seize. For this reason, it is possible to prevent the female screw from being shear-ruptured and the screw flap torque being reduced (the screw cannot be screwed) without reducing the strength of the female screw.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A tapping screw according to the present invention will be described with reference to one embodiment of the drawings. 1 is an overall external view of the embodiment, FIG. 2 is an enlarged view of a main part thereof, and FIG. 3 is a diagram for explaining specific numerical ratios of the main part. The embodiment,
A head 1, a shaft 2, a screw thread 3 continuously formed in a spiral shape on a peripheral surface thereof, and a step diameter portion 4 are roughly classified.

The head 1 has a seat surface 1b having a diameter larger than that of the shaft body 2.
For example, it is formed in a round head or a pan head, and the head is provided with an engagement hole 1a (cross hole, hexagonal hole, or the like) that engages with the fastening tool. The shaft body 2 includes the seat surface 1b.
From the reference valley diameter corresponding to the head diameter, and is extended toward the tip of the shaft body 2 by a predetermined length, and a flat portion 2b is formed between the threads of the shaft body 2. The tip 2a is formed in a predetermined taper shape.

The thread 3 is formed by continuous rolling from the base 2c of the shaft 2 to the tip 2a in a triangular cross section at a standard pitch P suitable for the nominal diameter. The thread 3 is a mating member (not shown).
The female screw is screwed into the lower hole 5a and the inner surface of the lower hole 5a is plastically deformed to form a female screw.

The step diameter portion 4 is provided at both bases of the thread 3, and extends in parallel with the step 4 a and the flat portion 2 b having a diameter larger than that of the flat portion 2 b and both side portions of the thread 3. And a flat surface 4b protruding by a predetermined amount from each side in the respective directions. A mating member corresponding to a female screw 5b formed by screwing of a tapping screw (male screw) at the time of fastening is applied to the flat portion 2b of the shaft body 2. It is configured to be guided in the axial direction so as not to touch.

However, in the above embodiment, as shown in FIG. 3, specific main parameters of the thread 3 are set at the following numerical ratios. That is, when the outer diameter of the thread 3 is D, the height H of the thread 3 protruding from the flat portion 2b is H = Dx0.12.
9 Step F = Dx0.0 from flat portion 2b to step diameter portion 4
The length W of the 143 to 0.0286 step difference diameter portion 4 protruding in the side direction of the screw thread 3 is set to W = Dx0.0143 to 0.0214.

Incidentally, for example, the thread dimensions of D = φ1.4 mm formed based on the above ratio are as follows: H = 0.18 mm F = 0.02-0.04 mm W = 0.02-0.03 mm Become.

In this case, it is preferable that the step F is within the range of the set value. If the step F is less than the set value, the bulging portion of the formed female screw 5b is effectively separated from the flat portion 2b of the shaft body 2. If it is more than that, the biting amount of the female screw is reduced, and the screwing torque is significantly reduced at the time of fastening. The length W of the step diameter portion 4 is
It is preferable to be within the range of the set value. If it is less than the above value, the effect of guiding the bulging portion of the formed female screw 5b in the axial direction is small, and if it is more than that, the thread pitch P is almost continuous. Therefore, seizure may occur between the counterpart member and the step diameter portion 4.

Next, the operation of the embodiment constructed as described above will be described. The tapping screw shown in the above embodiment is
It is used to easily fasten a member to be fastened (not shown) to a mating member serving as a main body. Specifically, the member to be fastened, which has a through hole through which the thread 3 of the tapping screw can be inserted, and the member to be fastened, which passes only through the lower hole into which the thread 3 of the tapping screw is screwed.

In this case, after the two members are arranged in an overlapping manner, a tapping screw is inserted into the through hole of the member to be fastened so that the tip 2a faces the lower hole of the mating member.
Rotate in the tightening direction while engaging and pressing the tightening tool with a. As a result, the thread 3 of the tapping screw bites into the lower hole of the mating member, and the inner surface of the lower hole is plastically deformed and screwed while forming the female screw 5b. When 1b contacts the member to be fastened, the member to be fastened is fastened to the mating member.

In this case, since the thread 3 of the tapping screw is forcibly screwed into the prepared hole in which the female screw 5b is not formed while forming the female screw, torsional stress increases in the shaft 2 of the tapping screw due to the resistance. However, since the diameter of the shaft body 2 is increased, it is possible to cope with the stress, and the shaft body 2 does not generate torsional breakage. Further, by forming the step diameter portion 4 in the thread 3, it is possible to effectively disperse the concentrated stress in the torsional fracture direction acting on the thread base when the load imposed on the shaft 2 increases. While you can
The stepped diameter portion 4 prevents the mating member for the female screw 5b formed on the inner surface of the pilot hole from coming into contact with the flat portion 2b of the shaft body 2 along the slope of the screw thread 3 in the axial direction. Can be guided. For this reason, seizure of the screw caused by the contact of the formed female screw 5b with the flat portion 2b can be avoided, and the shear fracture of the female screw 5b can be prevented without reducing the strength of the female screw. At the same time, it is possible to suppress a decrease in the screw flap torque, and it is possible to significantly improve the guaranteed tightening torque of the tapping screw.

Incidentally, it has been confirmed that the improvement rate of the tightening torque in the embodiment is 16 to 20% as compared with the conventional case.

[0019]

As described above, according to the present invention, since the stepped diameter portion is provided in the thread base, the concentrated stress in the twist direction acting on the thread base can be dispersed when the tapping screw is fastened. In addition to being able to prevent torsional breakage of the shaft body, it is possible to effectively prevent the bulged portion of the formed female screw from abutting on the flat portion by guiding it in the axial direction, and to prevent the tapping screw and the mating member from coming into contact with each other. This has the effect of preventing seizure and shear fracture of the internal thread, and suppressing the reduction of the screw flap torque to remarkably improve the fastening assurance torque.

[Brief description of the drawings]

FIG. 1 is an external view showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a diagram for explaining main specifications of a screw thread;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Head part 2 Shaft body 2b Flat part 3 Screw thread 4 Step diameter part

Claims (2)

(57) [Claims] A helical continuous thread is formed on a peripheral surface of a shaft having a head engaged with a tool.
In a tapping screw in which a shaft portion between the screw threads is formed in a flat portion, a step diameter portion having a larger diameter than the flat portion has a stepped diameter portion.
A tapping screw extending from both bases in parallel with the flat part . 2. The method according to claim 1, wherein the step between the step diameter portion and the flat portion is a screw.
It is 0.0143 to 0.0286 times the outer diameter of the mountain.
The self-tapping screw according to claim 1.