JPH11336726A - Bolt, nut and connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce stress relax amount after fastening so as to prevent loosening by generating unidirectional setting texture in the axial direction of the main stem part, and generating equi-axed polycrystalline texture in a screw part integrated with the main stem part. SOLUTION: A bolt 11 is formed by the main stem part 12 which has unidirectional setting texture and the setting direction of which agrees with the axial direction of the bolt 11, and a screw part 13 integrally formed on both ends of the main stem part 12, which have equi-axed polycrystalline texture. In manufacturing such bolt 11, first, raw material formed by the part scheduled to form the main stem part 12 and the part scheduled to form the screw part 13 is manufactured by unidirectional casting, then only the part scheduled to form the screw part 13 is subjected to plastic deformation by forging, and the whole is heat-treated. Thus, only the part scheduled to form the screw part 13 is recrystallized to become equi-axed polycrystalline texture. After that, it is machined into a bolt shape. Accordingly, the creep strength of the bolt material can be heightened and the Young's modulus can be made smaller so that the stress relaxation is hard to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt, a nut and a combination of a bolt and a nut which are used particularly at a high temperature.

[0002]

2. Description of the Related Art FIG. 3 shows an example of fastening members using bolts. Numerals 1a and 1b in the figure denote the objects to be fastened, respectively, which are fastened using bolts 2, nuts 3 and washers 4.
By the way, when fastening members such as the bolt 2 and the nut 3 are exposed to a high temperature, each member relaxes the stress by creep, which causes the bolt 2 to loosen. In addition, the tension of the bolt 2 causes stress concentration on the screw bottom, which causes cracking due to creep and fatigue. Conventionally, the bolt 2 is manufactured homogeneously using a bar-shaped drawn or forged material.

FIGS. 4A and 4B are schematic diagrams showing the stress relaxation behavior of the bolt 2 fastened as shown in FIG. 3, respectively.
FIG. 4A shows the relationship between the elongation of the bolt and the bolt stem stress σ, and FIG. 4B shows the relationship between the time and the bolt stem stress σ. Stress relief is caused by the creep of the bolt stem,
The speed dσ / dt is represented by the following equation.

Dσ / dt = −E · (dε / dt) where dε / dt is the creep rate of the material, and E is the Young's modulus of the bolt in the axial direction. That is, as the creep strength of the bolt material is higher and the Young's modulus is smaller, stress relaxation is less likely to occur.

[0005] The Young's modulus in the solidification direction of a directionally solidified alloy is about -1 / 1 / that of an equiaxed polycrystalline material having the same chemical composition.
Since it is 1.5 and the creep strength is equal to or more than that, the amount of stress relaxation is 1 / 1.5 that of the polycrystalline material.

FIG. 5 shows a ratio E of the Young's modulus of the bolt and the nut.
Shows the calculation results of the thread root of the stress concentration factor K _t when changing the _B / E _N. In FIG. 5, the abscissa indicates the number of thread engagement peaks (N), the ordinate indicates the stress concentration coefficient (K _t ), and the curve (A) indicates a curve (E _B / E _N = 1 / 1.5). (B) is for E _B / E _N = 1, and curve (c) is for E _B / E _N = 1.
5 is shown.

When the entire bolt is unidirectionally solidified, the Young's modulus of the thread portion becomes about 1 / 1.5 of that of the polycrystalline body, so that E _B / E _N becomes about 1 / 1.5, and the stress concentration is increased. To E
_{Although B} / E _N is increased more than when 1, the E _B / E _N becomes substantially 1 by making only the threaded portion a polycrystalline structure, so that an increase in stress concentration can be avoided. Further, the effect of E _B / E _N is larger than the effect of reducing the concentration of stress by increasing the number of engaging peaks.

[0008]

SUMMARY OF THE INVENTION The first invention of the present application is directed to a trunk having a unidirectional solidification structure whose solidification direction coincides with the axial direction of the bolt, and a stem formed integrally with the trunk, An object of the present invention is to provide a bolt capable of reducing the amount of stress relaxation and preventing loosening by comprising a screw portion having a crystal structure.

In the second invention of the present application, stress is concentrated on the screw bottom by adopting a configuration in which the nut screwed into the threaded portion of the bolt is unidirectionally solidified along the height direction. An object of the present invention is to provide a nut that can reduce the number of nuts.

Further, the third invention of the present application has a trunk having a unidirectional solidification structure, the solidification direction of which coincides with the axial direction of the bolt, and an integral polycrystalline structure formed integrally with the trunk. A bolt comprising a screw part and a nut screwed to the screw part of the bolt and solidified in one direction along the height direction, so that the screw bottom of the nut is not loosened. It is an object of the present invention to provide a bolt and nut combination that can reduce the concentration of stress on a bolt.

[0011]

According to a first aspect of the present invention, there is provided a bolt having a stem and a screw formed integrally with the stem, wherein the stem has a one-way solidified structure and has a solidified structure. A bolt is characterized in that a direction thereof coincides with an axial direction of the bolt, and the screw portion has an equiaxial polycrystalline structure.

A second invention of the present application is a nut characterized in that it is unidirectionally solidified along a height direction. The third invention of the present application comprises a stem having a unidirectional solidification structure, the solidification direction of which coincides with the axial direction of the bolt, and a screw portion formed integrally with the stem and having an equiaxial polycrystalline structure. A bolt-nut combination comprising: a bolt; and a nut which is screwed to a threaded portion of the bolt and solidified in one direction along a height direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing a metal structure state of the bolt 11 according to the present invention. The bolt is made of hexagonal metal. Reference numeral 12 in the figure denotes a trunk having a unidirectional solidification structure, the solidification direction of which corresponds to the axial direction of the bolt 11. At both ends of the stem 12, screw portions 13 having an equiaxed polycrystalline structure are formed integrally with the stem 12.

The bolt 11 having the structure shown in FIG.
It is manufactured as shown in FIG. That is, first, FIG.
As shown in FIG. 2A, after a forging material 14 composed of a portion 14a for forming a trunk portion and a portion 14b for forming a screw portion is manufactured by one-way solidification casting, only the portion 14a for forming a trunk portion is formed as shown in FIG. Plastic deformation was applied by forging, and the whole was heat-treated. As a result, only the trunk portion 14a is recrystallized to have an equiaxed polycrystalline structure. Then, it was formed into a bolt shape by machining.

According to the bolt 11 shown in FIG. 1, the trunk 12 has a unidirectional solidification structure, and the solidification direction coincides with the axial direction of the bolt 11.
And a screw portion 13 having an equiaxed polycrystalline structure integrally formed at both ends of the stem portion 12, so that stress relaxation due to creep can be prevented even when exposed to high temperatures.

FIG. 6 shows a bolt / nut assembly in which nuts 21 according to the present invention are screwed to both ends of the bolt 11 of FIG. Here, the nut 21 is in the height direction (A direction in the figure).
The alloy is made of a directionally solidified alloy.

Here, the Young's modulus E in the height direction of the nut 21 is shown.
_{Since N} becomes approximately 1 / 1.5 of the equiaxed crystal due to the unidirectional solidification, the stress concentration can be reduced as shown by the curve (C) of E _B / E _N = 1.5 in FIG. In addition, in the method of manufacturing a bolt according to the present invention, forging and heat treatment of a bolt screw portion are required, so that the method of manufacturing a nut according to the present invention requires only one-way solidification of the nut (the bolt is usually a bolt material). ), The cost is quite advantageous.

[0018]

As described above in detail, according to the present invention, a stem having a unidirectional solidification structure, the solidification direction of which coincides with the axial direction of the bolt, and a stem formed integrally with the stem and having the same axis By using a screw portion having a polycrystalline structure, it is possible to provide a bolt capable of reducing the amount of stress relaxation and preventing loosening.

Further, by unidirectional solidification along the height direction, it is possible to provide a nut capable of reducing concentration of stress on the screw bottom. Further, a bolt having a unidirectional solidification structure, a solidification direction coinciding with the axial direction of the bolt, and a bolt comprising a screw portion formed integrally with the trunk and having an equiaxed polycrystalline structure; and Screwed into
By providing a nut that is solidified in one direction along the height direction, it is possible to provide a bolt-nut combination that can reduce the concentration of stress on the screw bottom of the nut without loosening the bolt.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a metal structure state of a bolt according to one embodiment of the present invention.

FIG. 2 is an explanatory view showing a method of manufacturing the bolt of FIG. 1 in the order of steps.

FIG. 3 is an explanatory view showing a fastening state using bolts and nuts.

FIG. 4 is a schematic view of a stress relaxation behavior of a bolt.

[5] when changing the bolt and the ratio E _B / E _N Young's modulus of the nut, characteristic diagram showing the relationship between the number of ridges mesh with the stress concentration factor K _t of the thread root.

FIG. 6 is a partial explanatory view of a bolt and nut combination body in which a bolt and a nut according to the present invention are screwed.

[Explanation of symbols]

 11 ... bolt, 12 ... trunk, 13 ... thread, 14 a ... trunk formation scheduled part, 14 b ... thread formation scheduled part, 21 ... nut.

Claims (3)

[Claims] 1. A bolt having a stem and a screw formed integrally with the stem, wherein the stem has a one-way solidification structure, and the solidification direction thereof coincides with the axial direction of the bolt. A bolt having a thread portion having an equiaxed polycrystalline structure. 2. A nut screwed into a threaded portion of a bolt according to claim 1, wherein the nut is unidirectionally solidified along a height direction. 3. A bolt comprising a stem having a unidirectional solidification structure, the solidification direction of which coincides with the axial direction of the bolt, and a screw portion formed integrally with the stem and having an equiaxial polycrystalline structure. And a nut which is screwed to the threaded portion of the bolt and is solidified in one direction along the height direction.