JPS6231686Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a thread forming screw, particularly a thread forming screw suitable for fastening thin plates.

Conventionally, thread forming screws have been devised in which the cross-sectional shape of the male thread on the distal end side of the leg is approximately triangular, and the cross-sectional shape of the male thread on the base end side of the leg is circular. The female thread forming was performed on the triangular cross section on the distal end of the leg, and the final tightening was performed on the circular cross section on the proximal end of the leg.

However, when tightening this screw, although it is possible to tighten the triangular section with low torque, when the screw enters the prepared hole of the target object and the circular section begins to be screwed in, the tightening torque increases rapidly. In other words, a significantly large internal thread forming torque is required, which causes various problems.

In order to eliminate this drawback,
A screw such as that disclosed in the issue ``Thread-forming screw'' was devised. In this screw, the cross-sectional shape of the male thread on the tapered part on the distal end side of the leg is formed into a substantially polygonal shape with rounded corners, and the cross-sectional shape of the male thread on the straight part on the proximal end side of the leg is formed into a circular shape. Moreover, the external thread cross-sectional shape of the connecting portion between the base end side of the leg and the distal end side of the leg is gradually changed from a triangular shape to a circular shape. In the screw configured as described above, the female thread forming is performed on the triangular cross-section, and the final tightening is performed on the circular cross-section through the shape-changing cross-section of the connecting portion. However, when tightening this screw, not only is the screwing torque large, but also the value is maintained or slightly increased until the time of tightening, resulting in disadvantages such as poor workability.

The present invention aims to eliminate the above-mentioned drawbacks, and embodiments will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a thread forming screw, which consists of a head 2 having a desired driving part and a leg 3 having a thread. The leg portion 3
guides the screw into the pilot hole of the counterpart, and
A first part 4 with a tapered outer diameter of the thread to gradually form a female thread, a second part 5 with a straight outer diameter of the thread to form a female thread, and a female thread with an almost full diameter gradually formed. It consists of a third part 6 to be molded and a fourth part 7 to securely and firmly hold the screw by maintaining a tight fit with the female thread.

The cross-sectional shape of the thread of the first portion 4 is almost triangular in shape in all cross-sections, and as shown in Fig. 4, each vertex has a rounded corner. ing. The corners are smoothly connected by arch-shaped sides. The radius of curvature of the rounded corner is significantly less than half the pitch diameter of the corresponding cross section and less than half the distance from the screw axis to the extreme end of the rounded corner. The radius of curvature of the sides of the arc is greater than half the pitch diameter of the corresponding cross section. The distance from the screw axis to the extreme of the rounded corner and the radius of curvature of the arcuate sides gradually increases as the screw thread approaches the head 2.

As shown in FIG. 3, the cross-sectional shape of the thread of the second portion 5 is connected to the first portion 4 and inherits the substantially triangular shape, and has substantially the same substantially triangular shape.
Also, the distance from the screw axis to the rounded corner and the radius of curvature of the arcuate sides are constant.

As shown in FIG. 2, the cross-sectional shape of the third portion 6 inherits the approximately triangular shape of the second portion 5 at the bottom, but gradually changes to a circular shape as it approaches the head 2. , almost circular in shape at the top. The distance from the screw axis to the extreme end of the rounded corner is constant, but as it approaches the head 2, the radius of curvature of the rounded corner gradually increases; conversely, the radius of curvature of the bow-shaped corner is Decrease gradually.

The cross-sectional shape of the thread of the fourth part 7 inherits that of the third part 6 and is of substantially the same circular shape.

When the tip of the leg 3 of the screw configured as described above is placed in the prepared hole of the mating material and torque is applied, the tapered part of the tip of the leg 3 of the first part 4 gradually deepens the fit with the mating material. In other words, the sides 4a, 4b, 4c
Form a female thread by sequentially screwing in. At this time, since the cross-sectional shape of the tapered part is approximately triangular, the contact area with the mating material is small, and since there is a relief part for the mating material, it is possible to machine a good internal thread with low torque. .

Next, when moving from the tapered part of the first part 4 to the straight part of the second part 5, the sides 5a, 5b,
5c, 5d, 5e, and 5f are screwed in one after another, and the female threads are completely formed. At this time, the screwing torque reaches its peak, and as the straight portion of the second portion 5 is screwed in, the screwing torque continues to decrease, but does not completely reach "zero" due to the spring back of the mating material.

Then, continue from the second part 5 to the third part 6.
, the cross-sectional shape of the external thread gradually changes from a triangle to a circular shape before the sides 6a, 6b, 6c, 6d, and 6e are screwed in. The contact area between the male and female threads increases. Therefore, the screwing torque will increase.

Furthermore, the fourth part 7 is screwed in smoothly following the third part 6, and is securely and firmly tightened. Therefore, the screwing torque that once decreased increases again, and then the screw is screwed in, so that the breaking torque can take a large value. It goes without saying that the breaking torque is maximum when the cross-sectional shape of the external thread is completely circular.

As explained above, the present invention provides the first
Since a second portion having a triangular cross-sectional shape substantially the same as the radius of curvature of the first portion and the third portion is provided between the portion and the third portion, the second portion is provided between the portion and the third portion. By screwing the parts, an internal thread is completely formed, and the third and fourth parts of circular cross-section, which are screwed in following the second part, smoothly enter the mating part. As a result, the screwing torque required until the screw is tightened is reduced, resulting in improved workability and higher work efficiency.

Finally, in the present invention, the screwing torque is Ts, the breaking torque is Tm, and the subscript t is used when the entire thread part is approximately triangular, and the part that connects to the tip tapered part gradually changes from approximately triangular to circular. For Iku type items (Jitko Sho 57-36820), the subscript r
, and in the present invention, by adding a subscript n, Tsr>Tsn=Tst Tmr≧Tmn>Tmt. In other words, the thread-forming screw of the present invention is superior to the one disclosed in Japanese Utility Model Publication No. 57-36820 in terms of the screwing torque targeted by the present invention.

Therefore, the present invention not only has a lower screwing torque than that disclosed in Publication of Utility Model Publication No. 57-36820, but also
It has been found that this method is significantly superior to the conventional example in terms of workability because the value is maintained or slightly reduced until the time of tightening.

[Brief explanation of the drawing]

FIG. 1 is a front view of a thread forming screw according to the present invention, FIG. 2 is a bottom view showing the top position of the thread in the third portion of FIG. 1, and FIG.
a bottom view showing the top position of the thread in the second part of the figure;
FIG. 4 is a bottom view showing the top position of the thread in the first portion of FIG. DESCRIPTION OF SYMBOLS 1... Thread forming screw, 2... Head, 3... Leg, 4... First part, 5... Second
part, 6...the third part, 7...the fourth part.

Claims (1)

[Claims for Utility Model Registration] Consisting of a head portion 2 having a desired driving portion and a leg portion 3 having a screw thread, the leg portion 3 has a cross-sectional shape of the thread having a substantially polygonal shape with rounded corners. A first portion in which the distance from the screw axis to the extreme ends of the rounded corners and the radius of curvature of the bow-shaped side that smoothly connects the rounded corners gradually increase as the distance approaches the head 2; 4
a second portion 5 connected to the first portion 4 and having a constant distance from the screw axis to the rounded corner and a constant radius of curvature of the arcuate side; The distance from the screw axis to the rounded corner is constant, but as it approaches the head 2, the radius of curvature of the rounded corner gradually increases, and conversely, the radius of curvature of the bow-shaped side gradually decreases. Third part 6
A thread forming screw characterized by comprising: