JPH1137121A - Stud thread structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance fatigue strength by making the root of a stud thread larger than that of a standard thread, and enlarging an inner diameter on the internal thread side. SOLUTION: The root R (R=R1) of a stud thread in relation to a thread pitch P is to be R1=0.108P-0.144P, and the minimum value Dmin of a corresponding internal thread inner diameter is to be Dmin=d2 max-2(H/2-3/2.Rmax), Dmin=d2 max-H+3Rmax, where d2 max is the maximum value of the effective diameter of the stud thread, H is 0.866025P, Rmax is the maximum value (0.144P) of the thread root R, from the geometric relation so as not to interfere with the root of an external thread. With this constitution, in case of fastening the stud thread to the internal thread to fit a mechanical element, stress concentration on the stud thread is relaxed, so that stress applied to the stud thread is reduced. Fatigue strength as stud thread structure is therefore enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stud screw structure, and more particularly to a stud screw structure capable of increasing the fatigue strength of an implantable screw fastening a mechanical element.

[0002]

2. Description of the Related Art A female screw is formed on a machine element to be mounted in order to save time and effort in performing a work when mounting or connecting various machine elements. A method may be adopted in which a stud bolt serving as an implantation-side screw is implanted into the female thread to form a stud screw structure, and an attachment machine element (hereinafter, the machine element is referred to as a “member”) is attached to the attachment member. In a conventional example of such a stud screw structure, a female screw of a general standard is opened on a member to be mounted, and a stud bolt which is also manufactured in accordance with a general standard is screwed to the female screw, and a screw to the member to be mounted is attached. The attachment member is fixedly attached.

[0003]

However, in such a conventional stud screw structure, when a mounting member is mounted on a member to be mounted and a stress is repeatedly applied to the mounting portion, the stud bolt is caused by metal fatigue. May be damaged. In addition to simple tensile and compressive stress, when a mounting member having a temperature difference, such as high-temperature gas piping, is fastened with a stud bolt, the external stress generated at the stud bolt stud portion due to a difference in thermal expansion. Bending stress may be applied, resulting in a more severe use environment.

[0004] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a stud screw structure that can increase the fatigue strength of a stud bolt for fastening a mechanical element.

[0005]

In order to achieve the above object, the present invention provides a stud screw structure comprising a stud bolt (stud bolt) and a female screw (attached member). The gist is that R is made larger than the root R of the thread as specified, and the inner diameter of the female thread is enlarged so that when it is screwed with the male thread, it does not interfere with the root of the thread. I do.

As an example of the root R, the root R (R = R1) of the implanted screw is set to R1 = 0.108P to 0.144P with respect to the screw pitch P, and the minimum diameter of the corresponding internal thread is Value Dmin,
From the geometrical relationship shown in FIG. 1, Dmin = d2max−2 (H / 2−3 / 2 · Rma) so as not to cause interference with the root of the male screw.
x) Dmin = d2max−H + 3Rmax, where d2max: maximum value of effective diameter of implantation side screw H: 0.866025P Rmax: maximum value of thread root R (0.144P)

[0007] With this configuration, when the mechanical element is mounted by tightening the implantable screw on the female screw, the stress concentration on the implantable screw is reduced, and the stress applied to the implantable screw is reduced, so that a stud screw structure is formed. Increases the fatigue strength. In addition, since the stress applied to the implant-side screw is reduced as described above, the difference in the fatigue characteristics between the post-heat treatment rolling and the post-rolling heat treatment during the production of the implant-side screw becomes apparent, and the fatigue strength is synergistic. To increase.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a stud screw structure comprising a stud thread formed by heat treatment on a screw material and a female thread corresponding to the stud thread. The root R of the screw is made larger than the root R of the screw as specified, and the inner diameter of the female thread is enlarged so that it will not interfere with the root of the screw when screwed with a male screw. In addition, when the male screw and the female screw are screwed together and tightened, interference does not occur between them, and stress concentration on the implanted screw is reduced, and the stress applied to the implanted screw is reduced. This has the effect of increasing the fatigue strength of the stud screw structure.

According to a second aspect of the present invention, there is provided a stud screw structure comprising a stud screw for forming a thread on an implanted side after heat treatment on a screw material and a female thread corresponding to the stud thread, wherein the root of the thread on the implanted side is formed. R (R = R
1) with respect to the thread pitch P, R1 = 0.108P to 0.144P, and the corresponding minimum value Dmin of the internal diameter of the internal thread is Dmin = d2max-H + 3Rmax, where d2max: maximum value of the effective diameter of the implanted screw H: 0 .8666025P Rmax: The maximum value of the thread root R (0.144P), and the root R of the imperfect thread of the implantation side screw.
(R = R2) is set to R2 = 0.108P or more with respect to the thread pitch P. When the male screw and the female screw are screwed together and tightened, no interference occurs between the inner diameter of the female screw and the root of the male screw. As a result, the stress concentration on the implanted screw is reduced, the stress applied to the implanted screw is reduced, the fatigue strength of the stud screw structure is increased, and the stress applied to the implanted screw is reduced. In addition, the difference in fatigue characteristics between the post-heat treatment rolling and the post-rolling heat treatment during the production of the implantation side screw becomes apparent, and has an effect of synergistically increasing the fatigue strength.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a front view of a stud bolt as a stud-side screw constituting the stud screw structure according to the present invention. In this figure, reference numeral 1 denotes a pilot portion having a role of guiding when a stud bolt is implanted in a member to be mounted, 2 denotes a stud-side screw portion which studs the stud bolt to a member to be mounted, and 3 denotes a nut to be screwed. The nut-side screw portion for fixing and attaching the mounting member to the member to be mounted by 4 is an incomplete screw portion provided between the stud-side screw portion 2 and the shaft portion 6, and 5 is an operation for implanting a stud bolt into the member to be mounted. It is the torque transmitting part with which the tool engages to perform.

FIG. 3 is a cross-sectional view schematically showing the structure of the thread portion 2 on the implantation side. In this figure, the shape represented by the solid line S1 represents the basic angle of the male screw. The shape represented by the dashed-dotted line S2 represents the allowable upper limit of the screw, while the shape represented by the dashed-dotted line S3 represents the allowable lower limit of the screw, and the angle of the screw represents the hatched portion between the line S2 and the line S3. The shape is determined by the range.

In the present embodiment, the root of the stud bolt implantation side screw is set to be larger than the allowable upper limit of the screw as shown by a solid line S4 in FIG. 3, for example. . The valley bottom R has a larger value than the valley bottom R of a male screw (that is, a general stud bolt) according to Japanese Industrial Standards. In FIG. 3, an example of the root R of the thread on the implantation side of the general stud bolt is indicated by a dotted line S5. As is clear from this cross-sectional shape, the stud bolt has a larger root R at the implantation side than a general stud bolt. Then, assuming that the root R is R = R1, R1 is set to R1 = 0.108 to 0.144P P: pitch of screw.

The internal thread (D) of the female screw corresponding to the above-mentioned stud-side screw is adjusted so that when the female screw is screwed with the male screw, no interference occurs with the root of the screw. Is enlarged. That is, in the present embodiment, the inner diameter D of the internal thread is formed, for example, such that the thread of the internal thread matches the solid line S1 in FIG. Is also set large so that it comes to the upper side with a margin. In FIG. 3, the position of the thread of the conventional internal thread is indicated by a dotted line S6. As described above, when the conventional female screw is used as the mating side of the implantable screw of the present embodiment, when the female screw is screwed, interference occurs with the root of the male screw.

In the present embodiment, the minimum value of the inner diameter of the female screw corresponding to the above-mentioned implantation side screw is Dmi.
Assuming that n, Dmin = d2max−H + 3Rmax, where d2max: the maximum effective diameter of the implantation side screw H: 0.866025P Rmax: the root bottom R maximum value of the implantation side screw (0.14
4P).

Further, in the present embodiment, the root R (R = R2) of the imperfect thread portion 4 of the implantation side thread is set to be R2 = 0.108P or more with respect to the thread pitch P.

With the above-described configuration, when a mechanical element is mounted by fastening the implanted screw to the female screw, the stress concentration due to the tightening of the screw can be reduced, and the stress applied to the implanted screw can be reduced. Therefore, the fatigue strength of the implant-side screw when repeatedly loaded is increased.

In addition, since the stress applied to the thread on the implantation side is reduced as described above, a difference in the fatigue characteristics between the post-heat treatment rolling and the post-rolling heat treatment during the production of the implantation side screw becomes apparent, Strength increases synergistically. This will be described below. FIG. 4 divides the bolts (including the implant-side screws of the present invention) produced by rolling after heat treatment and those produced by heat treatment after rolling, and repeats the bolts belonging to these two sections respectively. It is the result of an experiment in which a load was applied and the state of fatigue was examined in a graph. Here, the types of bolts corresponding to the respective graphs in FIG. 4 are selected as shown in the following (Table 1). That is, (Table 1) Mark on the diagram Bolt type Diagram White circle: M12 × 1.5, 12T; Bolt L1 blackened after heat treatment Black: M12 × 1.5, 12T; Bolt for heat treatment after forming L4 White triangle: M11 × 1.5, 12T; Bolt for rolling after heat treatment L2 Black triangle: M11 × 1.5, 12T; Bolt for heat treatment after rolling L5 White square : M12 × 1.75, 12T; bolt L3 of rolled after heat treatment Black-marked square mark: M12 × 1.75, 12T; bolt of heat treated after roll L6 was selected and used.

In the experimental results, the horizontal axis of the graph indicates the average stress value (Kgf / mm ² ) applied to the bolt,
The vertical axis represents the value of the amplitude stress (Kgf / mm ² ) obtained from the maximum value of the load that does not cause fatigue failure even when the bolt is repeatedly received.
(Ie, a value representing fatigue fracture strength). From this graph, for example, the average stress when bolting is 30K
In the case of gf / mm ² , M12 × 1.5, 12T; the value of the amplitude stress representing the fatigue fracture strength is approximately 15 kgf / mm ² in the rolled bolts (open circles) after heat treatment. . On the other hand, when the average stress when bolting is also 30 kgf / mm ² , M
12 × 1.5, 12T: The value of the amplitude stress representing the fatigue fracture strength is approximately 8K for bolts (black solid circles) subjected to post-rolling heat treatment.
gf / mm ² . As a whole, the average stress when bolted is 30 kgf / m
In the case of m ² (indicated by an arrow A in FIG. 4), the value of the amplitude stress representing the fatigue fracture strength of a bolt formed by heat treatment and rolling (open mark) is approximately 17 kgf / mm ² , For the bolts subjected to post-rolling heat treatment (filled black marks), the value of the amplitude stress representing the fatigue fracture strength is approximately 8 kgf / mm ^2.
It is. This is because the average stress when bolted is 3
When it is 0 Kgf / mm ² , it means that the value of the amplitude stress representing the fatigue fracture strength of the bolt after heat treatment and rolling after heat treatment is about 10 kgf / mm ² larger than that of the bolt after heat treatment and is advantageous in use. .

Next, in the graph of FIG. 4, the stress when the bolt is tightened is 100 kgf / mm ^{2 to} 120 kg.
In the case of f / mm ² (indicated by an arrow B in FIG. 4), the amplitude stress of the bolt after heat treatment and the bolt after heat treatment after rolling are the same, and the amplitude representing the fatigue fracture strength. It can be seen that the stress values are comparable. In a use environment in which a bending stress is applied to the stud bolt stud due to a temperature difference (difference in thermal expansion) as described in the above description, it is necessary to use a rolled bolt after heat treatment for the above-described reason. Also, even if a bolt for heat treatment after rolling was used, the magnitude (advantage or disadvantage) of the fatigue fracture strength due to the difference between the heat treatment and the rolling was not surfaced.

However, as described above, in the present embodiment, such a structure for alleviating stress concentration on the stud-side screw of the stud bolt allows such a 100-120 kgf / m.
The average stress applied to the implant side screw near m ² will be smaller. Thereby, the difference in fatigue characteristics between post-heat treatment rolling and post-rolling heat treatment during the production of the implantation side screw became apparent, and the stress was reduced. The fatigue strength of the bolt is synergistically increased due to both effects of the fact that the difference in the fatigue characteristics between the two becomes apparent.

By the way, M8 × 1.25, 9T; a stud bolt obtained by applying the present invention to the same stud bolt (conventional product) as this stud bolt (conventional product) and a stud bolt subjected to post-rolling heat treatment. Fig. 5 shows the results of a comparative test of the bending fatigue fracture strength of the improved product).
You. In FIG. 5, a line L11 is a fatigue fracture diagram of the above-mentioned conventional stud bolt, and a line L12 is a stud bolt obtained by improving the conventional stud bolt by merely increasing the root R of the stud bolt (improved product 1). L13 is a stud bolt diagram (improved product 2, improved stud bolt) in which the root R of the stud bolt is made larger than the conventional stud bolt, and further improved by rolling after heat treatment.
It is a fatigue fracture diagram of the improved product 3). As is clear from this graph, the improved product 1 has a larger amplitude stress than the conventional product.
0 Kgf / mm ² -15 Kgf / mm ^{2 is} improved,
Improved product 2 and improved product 3 are 2
It can be seen that the improvement is about 5 kgf / mm ^{2 to} 30 kgf / mm ² .

[0022]

As described above, according to the present invention,
In a stud screw structure composed of an implanted screw and a female screw corresponding to the implanted screw which are rolled after heat treatment on the screw material, the root R of the implanted screw is made larger than the root R of the screw as specified. Since the inner diameter of the female thread has been increased, when mounting the machine element by tightening the implantable screw on the female thread, the stress concentration on the implanted screw is reduced and the stress applied to the implanted screw decreases. The fatigue strength of the stud screw structure increases. In addition, since the stress applied to the implant-side screw is reduced as described above, the difference in the fatigue characteristics between the post-heat treatment rolling and the post-rolling heat treatment during the production of the implant-side screw becomes apparent, and the fatigue strength is synergistic. Is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an inner diameter value of a female screw which does not cause interference with a root of a male screw in fastening a male screw and a female screw.

FIG. 2 is a front view showing an embodiment of a stud bolt as a stud-side screw constituting the stud screw structure of the present invention.

FIG. 3 is a cross-sectional view schematically illustrating a structure of a stud-side thread portion of the stud bolt according to the embodiment.

FIG. 4 divides the stud bolt according to the embodiment into a bolt manufactured after heat treatment and rolling, and a bolt manufactured by heat treatment after rolling, and repeatedly applies a load to each of the bolts belonging to these two sections. In addition, it is a graph showing an experimental result of examining the state of fatigue.

FIG. 5 shows a comparison test of fatigue fracture strength between a conventional stud bolt and a stud bolt (improved product 1, improved product 2, improved product 3) obtained by applying the present invention to the same stud bolt. It is a graph which shows the result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pilot part 2 Implantation side screw part 3 Nut side screw part 4 Incomplete screw part 5 Torque transmission 6 Shaft part

Claims (2)

[Claims] 1. A stud screw structure comprising an implanted screw which is rolled after heat treatment on a screw material and a female thread corresponding to the implanted screw, wherein a root R of the implanted screw is formed.
And the root R of the imperfect thread to the root R
A stud screw structure characterized in that the inner diameter of the stud screw is made larger than that of the female screw, and the inner diameter of the female screw is enlarged so that no interference occurs when the female screw is screwed. 2. A stud screw structure comprising a stud screw for heat-treating a thread on a screw material and a female thread corresponding to the stud screw, wherein a root R (R = R1) of the thread on the thread is set to a thread pitch. For P, R1 = 0.108P to 0.144P, and the corresponding minimum value Dmin of the internal diameter of the female screw is Dmin = d2max-H + 3Rmax, where d2max: maximum effective diameter of the implanted screw H: 0.866025P Rmax: screw root R maximum value (0.144P), and the root R of the imperfect thread of the implantation side screw
A stud screw structure, wherein (R = R2) is set to R2 = 0.108P or more with respect to a screw pitch P.