JPS61211510A - Tapping screw - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial application field A type of tapping that is screwed into a screw thread provided in plastic materials, wood, and other plastic materials to form a thread on the inner wall and simultaneously finish tightening. This invention relates to screws, particularly round tapping screws with a relatively large number of flat portions at the bottom (for example, tapping screws of type 1, type 2, and type 4 of the Japanese Industrial Standards).

Conventional Technology Conventionally, in this field, in order to facilitate the formation of female threads in screw threads and increase the holding force after tightening, Reduce the thread angle by 60' to 45 or less (sometimes 30°)
There are also some that have been ranked. ] have been widely used. This is because when a screw with a small thread angle and a coarse pitch is screwed in, the amount of pushing away from the mating material is small, making it easier to tap, but on the other hand, it is difficult to make a relatively large amount of penetration into the material. Because you can. However, when self-tapping screws are manufactured by rolling, the rolling becomes more difficult as the ratio of the pitch to the outer diameter increases and the thread angle decreases. . coarsening the pitch,
In other words, there is a limit to how long the flat part of the valley bottom can be, and it is extremely difficult to freely select the length. For this purpose, the flat part of the valley bottom is appropriately recessed (for example, Japanese Patent Publication No. 59-131014)), and further lower threads are arranged between the threads ( For example, methods such as those described in Japanese Patent Publication No. 53-43625 have been used to make rolling easier and to increase the pitch as much as possible.

Problems to be Solved by the Invention A novel screw thread for a self-tapping screw that allows the flat part of the root to be freely set to a long length, and also enables the thread to be smoothly and easily formed by rolling. This is the problem that the present invention seeks to solve.

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In order to solve the above-mentioned problems, the present invention aims to reduce the amount of deformation due to rolling as much as possible with the following two points as important goals. For most of the length of the flat part, the diameter of the thread rolling blank should be left almost unchanged. As a means to achieve and embody these two goals, the self-tapping screw of the present invention having a special cross-sectional shape was discovered.

In the embodiment shown in FIG. 2, there is a threaded part 2 integrated with the known head 1. The screw provided in the threaded portion 2 is in the shape of a self-tapping screw with a large flat portion at the root. As shown in the enlarged view in Fig. 1, the cross-sectional shape of the threaded portion 2 has threads 6 with a thread angle of approximately 45° arranged at a constant pitch, and the tops 4 of the threads are all aligned with line A. They are aligned to have a constant outer diameter. The top 4 of the mountain is usually provided with a flat portion of the size of a chamfer. Flat portion 5 of the valley bottom which is substantially a cylindrical surface
are all aligned with the B line and have a constant valley diameter d-t, but the spaces between the threads are not all straight lines. A continuous groove 7 is uniformly provided on both sides of the base 6 of the thread 3, and the innermost part 8 of this groove 7 is aligned with the C line. In the drawing, groove 7 is shaped like an inverted trapezoid.
Its base is shown as a straight line parallel to the axis 9, with small rounded corners, and both sides 10.11 of the groove 7
(The side on the thread side is 10, and the side on the opposite side is 11.) is a straight line that matches the flank angle, and the side 10 on the thread 3 side is aligned with the extension line of the flank of thread 6. There is.

This groove 7 is also formed deeper than the line B connecting the flat parts 5,
The diameter of the flat portion, that is, the diameter of the valley 47 is formed to be approximately equal to the diameter of the thread rolling hole 2y of this screw.

When rolling this screw using a round bar material with a thread rolling blank diameter that is approximately equal to the diameter tt, the cross-sectional area should be large enough to effectively roll up one thread 3. thing. In reality, the percentage of the cross-sectional area above the line C of the thread 3 is determined to be approximately equal to the cross-sectional area of the groove 7 below the line B, but the length of the flat part 5 at the bottom of the valley is determined. In connection with this, it is desirable to ultimately determine this by experiment.

The length of the straight portion of the flat portion 5 shortened by the groove 7 is generally larger than the width of the groove 7 on the line 8, and is at least 2.5 times longer than the width of the groove 7 on the line 8.

Another embodiment of the groove 7 is shown in FIG. This has a shape in which a V-shaped groove 7 with a rounded bottom is provided on both sides of the base 60 of the screw thread 3, and the angle θ of the groove 7 is set to be larger than the angle of the thread 3 in any case. It is desirable to form it. In Figure 3, the angle of the thread 6 is approximately 45,
The angle θ of the miso is approximately 90°.

It has been previously understood that the shape of the groove 7 is not limited to those of these two embodiments, and may be any other shape as long as it satisfies the conditions shown above. This will be understood from the explanation. That is, in the case of FIGS. 1 and 3, the bottom of the groove 7 may be a curved line, or may be a sharp V-shape with no roundness at the bottom.

Functions and Effects of the Invention The present invention is used by inserting and screwing the screw through the guide portion 12 at the tip, which has a smaller diameter than that configured as shown in the embodiment. In this case, the cylindrical surface of the flat part 5 of the root is always in surface contact with the inner wall of the screw pilot hole and acts as a tapping guide, and since the contact area is very large, the center of the screw pilot hole and the screw It always aligns with the center and never gets bent or screwed. Furthermore, when the thread 3 pushes apart the mating material and bites into it, the flat part 5 completely suppresses the deformation of this part of the mating material, and the deformation occurs only in the thread 3 part. All the deformed parts of the material will be forced into the space of the groove 7 along the seven ranks of the screw 6 and will be accommodated therein. Therefore, the frictional resistance increases overall, and the return torque of this screw is much stronger than the tightening torque, making it extremely effective in preventing loosening.

It's similar to pressing a key in and tightening it, so it's less likely to loosen due to external force. Even when used on hard and brittle materials such as concrete, the torsion will enter the scraped and partially compressed material, and the crushed powder will be pushed into the groove 7, making it a good product. I know it can be used.

Next, when manufacturing this screw by rolling, the corresponding part of the rolling die is first pushed into the groove 7 to raise the thread 3, but the flat part 5
Naturally, material buildup also occurs on the side of the machine. The amount of increase in the diameter J of the valley due to the heaping of this material in the flat part 5 is:
Although it depends on the length of the flat part 5, the amount of increase in the outer diameter d of the thread 6 may be less), and by pressing and smoothing this part with a rolling die, the flat part 5 at the bottom of the root can be almost flattened. It can be finished uniformly. The longer the length of the flat part 5,
The difference between the diameter of the thread rolling blank and the diameter d of the flat portion 5 at the root becomes small. According to experiments, the amount of deformation due to rolling is almost equal to the diameter of the thread rolling blank over most of the length of the flat part 5, and tends to be slightly larger near both ends, but the overall dimension is almost uniform. I found out that it ended up being . These facts indicate that in the screw of the present invention having this cross section, plastic deformation due to rolling occurs in a very locally limited state.

In addition, the rolling circle of the blank during rolling has very little fluctuation throughout the process compared to conventional screws, and remains stable at a nearly constant value, making rolling work extremely smooth and easy. .

Furthermore, the shapes of the grooves 7 as shown in Figures 1 and 3 indicate that the threaded surface of the rolling die, which is the opposite surface, has a flat portion or a portion with large ridges. As shown, such a shape means that the rolling die has very good durability.

The present invention is based on prior patent No. 579893 (Japanese Patent Publication No. 43-2
6'/43, a wave-shaped thread die for rolling non-circular threads], it can also be applied to non-circular tapping screws that can be used for plastic metals.

[Brief explanation of the drawing]

FIG. 2 is a side view of the self-tapping screw of the present invention, FIG. 1 is an enlarged explanatory view of the cross-sectional shape of the threaded portion in FIG. 2, and FIG. 3 is an enlarged explanatory view of the cross-sectional shape of the threaded portion in another embodiment. 1000 heads, 200. Threaded portion, 601. screw thread, 40
0. The top of the mountain, 5. ,, flat part of the valley floor, 600. Base of thread, 760. Groove, 810. Bottom of groove 9, 910.
Axis, 10.0. Thread side of groove, 11. ,, the side opposite the thread of the groove, 12. ,, Information Department. Aoo, line connecting the tops of the threads, B80. A line connecting the flat part of the valley floor, C06, a line connecting the lowest part of the groove. C90, outer diameter, i, ..., valley diameter, C0,. Only the angle of the figure 7.

Claims (1)

[Scope of Claims] 1. In a screw having a shape with a large flat portion at the root, the base of the screw thread is uniformly deeper on both sides than the flat portion and has a thickness of about 1 of the cross-sectional area of the thread. A continuous groove with a cross-sectional area of A tapping screw characterized in that its diameter d_1 is formed to be approximately equal to the diameter of a thread rolling blank. 2 Groove 7 has the shape of an inverted trapezoid, and both sides 10,
The tapping screw according to claim 1, wherein 11 is a straight line that matches the flank angle, and the side 10 on the thread side is made to match the extension line of the flank. 3. The tapping screw according to claim 1, wherein the groove 7 has a V-shape, and the angle θ thereof is always larger than the angle of the thread 3.