Fasteners and nuts

Abstract

To provide a fastening tool that enhances corrosion resistance of a joining part of a steel structure and enhances tensile strength.SOLUTION: A bolt 2 of a fastening tool 1 includes a shaft part 21 and a bolt countersunk head part 22. The shaft part 21 has a columnar shape and includes a male screw part 211. The bolt countersunk head part 22 is connected to the shaft part 21, is disposed coaxially with the shaft part 21 and includes a truncated cone part 221 of which diameter increases as separating from the shaft part 21 in the axial direction of the bolt 2. The nut 3 includes a cylindrical part 31, a nut countersunk head part 32, a through hole 33 and a female screw part 34. The cylindrical part 31 has a cylindrical shape. The nut countersunk head part 32 is connected to the cylindrical part 31, is disposed coaxially with the cylindrical part 31 and includes a truncated cone part 321 of which diameter increases as separating from the cylindrical part 31 in the axial direction of the nut 3. The through hole 33 is disposed coaxially with the cylindrical part 31 and the nut countersunk head part 32 and penetrates through the cylindrical part 31 and the nut countersunk head part 32. The female screw part 34 is formed on an inner surface of the through hole 33.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to fasteners and nuts, and more particularly to fasteners including bolts and nuts, and nuts.

Background Art

[0002] Steel structures typified by steel bridges, buildings, towers, chemical plants, etc. are constructed at the site by joining a plurality of steel members with fasteners. The fasteners include bolts and nuts. FIG. 1 is a schematic view of a joint of a steel structure. Referring to FIG. 1, the joint of the steel structure includes, for example, a pair of mother plates 100 and a pair of connecting plates 110. Through holes 140 are formed in the mother plates 100 and the connecting plates 110. A bolt 130 of the fastener 120 is inserted into the through hole 140. With the mother plate 100 sandwiched between the pair of connecting plates 110, they are joined by a plurality of fasteners 120. Specifically, by fastening the bolt 130 and the nut 150 of the fastener 120, the mother plate 100 is joined to the connecting plate 110 by friction joining. Joints as shown in FIG. 1 are formed at multiple locations of the steel structure, and the steel structure is constructed. The fastener 120 used for the joint where the mother plate 100 and the connecting plate 110 are joined by friction joining is required to have high tensile resistance (axial force) capable of realizing friction joining.

[0003] Also, the above-mentioned steel structure is installed outdoors. Therefore, corrosion resistance is required for the joints of the steel structure. Usually, paint is applied to the joints of the steel structure to enhance corrosion resistance, and a paint film is formed. However, as shown in FIG. 1, the joints of the steel structure have irregularities formed by the head of the bolt 130 and the nut 150. It is difficult to paint the surface of the joint where such irregularities are formed, and it is difficult to form a uniform paint film. Therefore, thin portions of the paint film are formed at the joints. The thin portions of the paint film are inferior in corrosion resistance. Furthermore, rainwater tends to stay on the irregularities on the surface of the joint for a long time. As a result, when a certain period of time has passed since the joint was formed, as shown in FIG. 2, the irregular portion (near the nut 150 in FIG. 2) of the joint may corrode.

[0004] To suppress corrosion over time at the joints of such steel structures, Japanese Patent Publication No. 2000-160700 (Patent Document 1) proposes a fastener comprising a so-called countersunk bolt and nut. In this document, when the base plate and connecting plate of the joint are joined with the fastener, the protrusion of the countersunk head of the countersunk bolt from the connecting plate can be suppressed. Therefore, the formation of irregularities at the joint can be suppressed to some extent (see Figure 2 of Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-160700 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, when the base plate and connecting plate of the joint are joined using the fastener disclosed in Patent Document 1, irregularities are still formed on the surface of the connecting plate on the nut side. As a result, it is difficult to form a uniform coating, and sufficient corrosion resistance may not be obtained.

[0007] The purpose of this disclosure is to provide a fastener that can improve the corrosion resistance of joints formed by joining steel members constituting a steel structure, and increase the tensile strength after fastening. [Means for solving the problem]

[0008] The fastener of this disclosure comprises a bolt and a nut. The bolt includes a shaft and a countersunk head. The shaft is cylindrical in shape and includes a male threaded portion. The countersunk head is connected to the shaft, is coaxially positioned with the shaft, and has a frustoconical portion whose diameter increases as it moves away from the shaft in the axial direction of the bolt. The nut comprises a cylindrical portion, a countersunk nut head, a through hole, and a threaded portion. The cylindrical portion has a cylindrical shape. The countersunk nut head is connected to the cylindrical portion, is coaxially positioned with the cylindrical portion, and has a frustoconical portion whose diameter increases as it moves away from the cylindrical portion in the axial direction of the nut. The through hole is coaxially positioned with the cylindrical portion and the countersunk nut head, and passes through the cylindrical portion and the countersunk nut head. The threaded portion is formed on the inner surface of the through hole.

[0009] The nut of this disclosure includes a cylindrical portion, a nut head, a through hole, and a female thread portion. The cylindrical portion has a cylindrical shape. The nut head is connected to the cylindrical portion, is coaxially positioned with the cylindrical portion, and has a frustoconical portion whose diameter increases as it moves away from the cylindrical portion in the axial direction of the nut. The through hole is coaxially positioned with the cylindrical portion and the nut head, and penetrates the cylindrical portion and the nut head. The female thread portion is formed on the inner surface of the through hole. [Effects of the Invention]

[0010] The fasteners of this disclosure can improve the corrosion resistance of joints formed by joining steel members constituting a steel structure, and can increase the tensile strength after fastening. The nuts of this disclosure are used in the fasteners described above. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram of a conventional steel structure joint. [Figure 2] Figure 2 is a photographic image showing the corrosion of the joint shown in Figure 1. [Figure 3] Figure 3 is a side view of the fastener of this embodiment. [Figure 4] Figure 4 shows the side view and top view of the bolt in Figure 3. [Figure 5] Figure 5 shows a cross-sectional view and a plan view of the nut in Figure 3, parallel to the axial direction. [Figure 6] Figure 6 is a schematic diagram showing the state in which the joint is joined using the fastener of this embodiment. [Figure 7] Figure 7 is a schematic diagram showing a state in which the joint is joined using the fastener of this embodiment, which is different from that shown in Figure 6. [Figure 8] FIG. 8 is a schematic view showing a state in which a joint portion is joined by the fastener of the present embodiment, which is different from FIGS. 6 and 7. [Figure 9] FIG. 9 is a schematic view showing a state in which a joint portion is joined by the fastener of the present embodiment, which is different from FIGS. 6 to 8. [Figure 10] FIG. 10 is a schematic view showing an axially symmetric analysis model of a nut among axially symmetric analysis models of fasteners used for investigating the relationship between the nut shape and the load bearing ratio LSR of the female thread of the nut. [Figure 11] FIG. 11 is a schematic view showing a state in which the axially symmetric analysis model of the nut shown in FIG. 变形后的状态。 [Figure 12] FIG. 12 is a diagram showing the relationship between the female threads of each number and the load bearing ratio LSR of the female thread obtained by the axially symmetric analysis model of the nut in FIG. 10. [Figure 13] FIG. 13 is a side view of a fastener according to a preferred embodiment. [Figure 14] FIG. 14 is a diagram showing the relationship between the rotational torque T (N·m) and the axial force N (kN) during fastening of the fastener. [Figure 15] FIG. 15 is a cross-sectional view and a plan view of a nut of a fastener according to a second embodiment. [Figure 16] FIG. 16 is a plan view of the upper surface of a nut having a bottomed hole with a shape different from that in FIG. 15.

MODE FOR CARRYING OUT THE INVENTION

[0012] The fastener of the first configuration of the present embodiment includes a bolt and a nut. The bolt includes a shaft portion and a bolt dish head portion. The shaft portion has a cylindrical shape and includes a male thread portion. The bolt dish head portion is connected to the shaft portion, is arranged coaxially with the shaft portion, and has a frustum portion whose diameter increases as it moves away from the shaft portion in the axial direction of the bolt. The nut comprises a cylindrical portion, a countersunk nut head, a through hole, and a threaded portion. The cylindrical portion has a cylindrical shape. The countersunk nut head is connected to the cylindrical portion, is coaxially positioned with the cylindrical portion, and has a frustoconical portion whose diameter increases as it moves away from the cylindrical portion in the axial direction of the nut. The through hole is coaxially positioned with the cylindrical portion and the countersunk nut head, and passes through the cylindrical portion and the countersunk nut head. The threaded portion is formed on the inner surface of the through hole.

[0013] In the first configuration of the fastener, the bolt includes a tapered bolt head, and the nut includes a tapered nut head. Therefore, after fastening, the bolt head and nut head are housed in the countersunk holes formed in the steel member. As a result, the fastener can be prevented from protruding from the steel member at the joint of the steel structure, and the surface of the joint can be made smooth. Therefore, it is easier to apply paint uniformly to the surface of the joint, and a uniform coating can be formed. As a result, peeling of the coating can be suppressed, and corrosion resistance can be improved.

[0014] In the first configuration of the fastener, the inclusion of a cylindrical portion in the nut further ensures sufficient threading length. This increases the shear resistance of the threaded portion (male and female threaded portion) and enhances the tensile strength (axial force). As a result, the first configuration of the fastener can withstand friction bonding and can be used in friction joint connections. Furthermore, by forming through holes in the cylindrical portion of the nut and the countersunk head of the nut, it is possible to suppress localized stress concentration in the thin-walled portion of the female thread on the inner surface of the through hole. As a result, resistance to delayed fracture is improved.

[0015] The fastener of the second configuration is the fastener of the first configuration, wherein the cylindrical portion includes a tapered portion at the tip of the inner surface of the cylindrical portion. In the tapered portion, the inner diameter increases toward the opening of the cylindrical portion.

[0016] In the second type of fastener, the tapered portion acts as a guide for the bolt shaft. Therefore, when fastening, the tip of the bolt shaft is easily inserted into the cylindrical portion of the nut. The tapered portion also reduces stress concentration on the first thread of the bolt's male thread during fastening.

[0017] The fastener of the third configuration is a fastener relating to the first or second configuration, wherein the taper angle of the bolt head is greater than the taper angle of the nut head.

[0018] In the third type of fastener, during fastening, the nut head and countersunk socket make surface contact, while the bolt head and countersunk socket make line contact. In this case, localized stress concentration occurs on the bolt head due to the line contact. Therefore, during fastening, the bolt is less likely to rotate around the axis and is fixed securely. As a result, the occurrence of co-rotation is suppressed, and the fastening work becomes easier.

[0019] The fourth configuration fastener is a fastener of any one of the first to third configurations, wherein the nut further has a plurality of blind holes formed around the opening of the through hole on the upper surface of the nut head.

[0020] In the fourth configuration of the fastener, the nut can be easily fastened to the bolt by rotating the nut around its axis using a fastening jig that fits into a bottomed hole.

[0021] The fastener relating to the fifth configuration is the fastener relating to the fourth configuration, wherein the bottomed hole is rectangular when the top surface of the nut is viewed in plan.

[0022] In the fifth configuration of the fastener, the rectangular shape of the bottomed hole makes it easier to transmit the external force of the fastening jig around the axis of the nut. Therefore, the nut can be fastened to the bolt more easily.

[0023] The nut in this embodiment constitutes the fastener described above.

[0024] The fasteners of this embodiment will be described below with reference to the drawings. In each drawing, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0025] <First Embodiment> [Overall configuration of fastener 1] Figure 3 is a side view of the fastener of this embodiment. Referring to Figure 3, the fastener 1 comprises a bolt 2 and a nut 3.

[0026] [Volt 2 Configuration] Figure 4 is a side view and a top view of bolt 2 in Figure 3. Referring to Figure 4, bolt 2 includes a shaft portion 21 and a bolt head portion 22. The shaft portion 21 has a cylindrical shape. The shaft portion 21 includes a male threaded portion 211. The male threaded portion 211 has multiple male threads. The multiple male threads are arranged in the axial direction of the bolt 2.

[0027] The shaft portion 21 may further include a cut-off portion 212 and a tip portion 213. The cut-off portion 212 is located between the male thread portion 211 and the bolt countersunk head 22. The cut-off portion 212 may have an incomplete male thread or no male thread at all. The tip portion 213 is located at the tip of the shaft portion 21. The tip portion 213 may have an incomplete male thread or no male thread at all. The tip of the tip portion 213 is chamfered.

[0028] The bolt head 22 is connected to the shaft 21 and is positioned coaxially with the shaft 21. The bolt head 22 includes a frustoconical portion 221. The frustoconical portion 221 has a frustoconical shape in which the diameter increases as it moves away from the shaft 21 in the axial direction of the bolt 2. The surface of the frustoconical portion 221 comes into contact with the countersunk head of the connecting plate after the fastener 1 is fastened. This stabilizes the tensile strength (axial force) and clamping force of the fastener 1.

[0029] The bolt head 22 may further include a base portion 222 and a surface portion 223. The base portion 222 is connected to the shaft portion 21. The base portion 222 is disc-shaped and has a constant outer diameter. Preferably, the diameter of the base portion 222 is the same as the outer diameter of the cylindrical portion 31 of the nut 3, which will be described later. The base portion 222 and the cylindrical portion 31 resist shear when the fastener 1 fastened at the joint is subjected to shear in a direction perpendicular to the axial direction. To increase the resistance to shear, it is preferable that the outer diameter of the base portion 222 and the cylindrical portion 31 is less than the inner diameter of the through hole formed in the connecting plate, and that the base portion 222 and the cylindrical portion 31 have the maximum diameter into which they can be inserted into the through hole.

[0030] The surface layer 223 is positioned on the larger diameter side of the two base surfaces of the frustoconical portion 221. The surface layer 223 has a taper angle smaller than the taper angle A1 of the frustoconical portion 221. The diameter of the surface layer 223 may be constant. In other words, the surface layer 223 may be disc-shaped. The surface layer 223 prevents the surface shape of the frustoconical portion 221 from changing due to dents or other damage during the transport of the bolt 2.

[0031] [Nut 3 configuration] Figure 5 is a cross-sectional view and a plan view of the nut 3 in Figure 3, parallel to the axial direction. Referring to Figure 3, the nut 3 includes a cylindrical portion 31 and a nut head 32. The cylindrical portion 31 has a cylindrical shape. The nut head 32 is connected to the cylindrical portion 31 and is arranged coaxially with the cylindrical portion 31. The nut head 32 has a frustoconical portion 321. The frustoconical portion 321 has a frustoconical shape in which the diameter increases as it moves away from the cylindrical portion 31 in the axial direction of the nut 3. Of the two base faces of the frustoconical portion 321, the diameter of the base face closer to the cylindrical portion 31 is the same as the outer diameter of the cylindrical portion 31.

[0032] The nut head 32 may further include a surface layer 322. The surface layer 322 is positioned on the larger diameter side of the two bases of the frustoconical portion 321. The surface layer 322 has a taper angle smaller than the taper angle A2 of the frustoconical portion 321. The diameter of the surface layer 322 may be constant. In other words, the surface layer 322 may be disc-shaped. The surface layer 322 prevents the surface shape of the frustoconical portion 321 from changing due to dents or the like when the nut 3 is transported.

[0033] The nut 3 further has a through hole 33. The through hole 33 is coaxially positioned with the cylindrical portion 31 and the nut head 32 and penetrates both the cylindrical portion 31 and the nut head 32. The nut 3 includes a female thread portion 34 on the inner surface of the through hole 33. The female thread portion 34 is formed continuously with the inner surface of the cylindrical portion 31 and the inner surface of the nut head 32 and has multiple female threads. The female thread portion 34 is formed in the axial direction in the through hole 33. Therefore, the screw-in length can be ensured. As a result, the shear resistance of the male thread portion 211 and the female thread portion 34 can be increased, and the tensile strength (axial force) of the fastener 1 can be increased.

[0034] Preferably, the nut 3 further includes a tapered portion 35 at the tip of the inner surface of the through hole 33 of the cylindrical portion 31. The tapered portion 35 has a tapered shape, and its inner diameter increases towards the opening 36 of the cylindrical portion 31. If the cylindrical portion 31 has a tapered portion 35, the tapered portion 35 acts as a guide for the shaft portion 21 of the bolt 2. Therefore, when fastening, the tip of the shaft portion 21 of the bolt 2 is easily inserted into the cylindrical portion 31 of the nut 3. The tapered portion 35 further alleviates stress concentration on the first thread of the male thread portion 211 of the bolt 2 when fastening.

[0035] [Function of fastener 1] [Function due to the provision of a bolt countersunk head 22 and a nut countersunk head 32] In the fastener 1 having the above configuration, the bolt 2 includes a tapered bolt head 22, and the nut 3 also includes a tapered nut head 32. As shown in Figure 6, after fastening, the bolt head 22 and the nut head 32 are housed in countersunk holes 111 formed in the steel member, represented by the connecting plate 110. As a result, it is possible to suppress the fastener 1 from protruding from the joint at the joint of the steel structure. Specifically, it is possible to suppress the bolt head 22 and the nut head 32 from protruding from the surface of the connecting plate 110. In this way, by joining steel members (base plate 100 and connecting plate 110) using the fastener 1, the surface of the joint can be made smooth. Therefore, it is easy to apply paint uniformly to the surface of the joint and to make the paint film uniform. As a result, peeling of the paint film can be suppressed and corrosion resistance can be improved.

[0036] [Effects of having the cylindrical portion 31] In this embodiment, the fastener 1 further has a cylindrical portion 31 in the nut 3. Female threads 34 are formed on the inner surface of the cylindrical portion 31 and the inner surface of the nut head 32. As a result, the male thread portion 211 of the bolt 2 and the female thread portion 34 are fastened over a long axial range. In other words, the threading length is increased in this case. This increases the tensile strength (axial force) of the fastener 1. As a result, the fastener 1 can withstand frictional joining sufficiently. In particular, when a tensile load or repeated load is applied to the fastened fastener 1, the fatigue strength of the fastener 1 increases. Furthermore, because the threading length is long, loosening can be suppressed.

[0037] Furthermore, the fastener 1 can increase its shear strength when the joint changes from a friction joint to a bearing state. As described above, the joints of the steel structure are friction-jointed by the fastener 1. However, when the transmission of load by friction exceeds its limit, the joint changes from a friction joint to a bearing state. In the bearing state, a shear force is applied to the fastener 1. Here, the shear strength is affected by the diameter of the fastener 1. In the fastener 1, the shaft portion 21 of the bolt 2 is inserted into and fitted into the cylindrical portion 31 of the nut 3. Therefore, the diameter of the cylindrical portion 31 corresponds to the diameter of the fastener 1. The diameter of the cylindrical portion 31 is larger than the diameter of the shaft portion 21. Therefore, the shear strength of the fastener 1 can be increased by the cylindrical portion 31.

[0038] Furthermore, the fastener 1, by having a cylindrical portion 31, can accommodate variations in the thickness of the fastening plate. For example, as shown in Figures 7 to 9, even if the thickness T2 of the base plate 100 is thicker than the thickness T1 of the base plate 100 in Figure 6, the fastener 1 can still be fastened because the cylindrical portion 31 ensures sufficient screw-in length.

[0039] Specifically, compared to the case in Figure 6, it is sufficient to extend a part of the bolt 2 or a part of the nut 3. For example, it is sufficient to extend one or more of the base portion 222, the shaft portion 21 of the bolt 2, and the cylindrical portion 31 of the nut 3. In Figure 7, the base portion 222 of the bolt 2 is extended. In Figure 8, the shaft portion 21 of the bolt 2 is extended. In Figure 9, the cylindrical portion 31 of the nut 3 is extended. In the fastener 1, the cylindrical portion 31 ensures sufficient threading length. Therefore, even if one or more of the base portion 222, the shaft portion 21, and the cylindrical portion 31 are extended, sufficient threading length can be ensured. As a result, the fastener 1 can ensure sufficient tensile strength (axial force).

[0040] [Effect of nut 3 having a through hole 33] In this embodiment, the fastener 1 further has a through hole 33 in the nut 3, and a female thread portion 34 is formed not only on the inner surface of the cylindrical portion 31 but also on the inner surface of the nut head 32. This makes it possible to suppress the occurrence of localized stress concentration in a part of the female thread portion 34 formed on the cylindrical portion 31. As a result, the delayed fracture resistance and tensile strength of the fastener 1 can be increased. Consequently, the fastener 1 can be used as a fastener for friction joints. This point will be explained below.

[0041] Assuming the analysis cases of the two nuts 3 shown in Figures 10(A) and (B), an axisymmetric analysis simulating the tightening of the fastener 1 was performed.

[0042] The analysis solver used was Dassault Systèmes' Abaqus / Standard. The elements and boundary conditions used were as follows: In the analysis model, the base plate 100 was an 8-node quadrilateral reduced integral quadratic element with a minimum element side length of 1 mm. The bolts 2 and nuts 3 and the connecting plate 110 were 6-node triangular quadratic elements with a minimum element side length of 0.05 mm.

[0043] For the screw engagement, the contact between the bolt head 22 and the countersunk 111 of the connecting plate 110, and the contact between the nut head 32 and the countersunk 111 of the connecting plate 110, Coulomb's law of friction was applied, and the coefficient of friction of the contact surfaces was set to 0.1. The stress-strain relationship of the fastener 1, base plate 100, and connecting plate 110 was given by setting the elastic modulus E to 2.0 × 10⁻⁶. 5 N / mm 2 A bilinear type was used, with a Poisson's ratio ν of 0.3 and a work hardening coefficient H = E / 100. The yield point σy of fastener 1 was set to 1260 N / mm². 2 , tensile strength σt is 1400 N / mm 2 The yield point σy of the base plate 100 and the connecting plate 110 was set to 355 N / mm². 2 , tensile strength σt is 490 N / mm 2 That's what I decided.

[0044] The nuts in Figures 10(A) and (B) were both based on axisymmetric analysis models. In Figure 10(A), the nut does not have a through hole and has a non-through hole and a cover portion. On the other hand, in Figure 10(B), the fastener 1 of this embodiment is assumed, and the nut has a through hole. Here, the female threads in Figures 10(A) and 10(B) are numbered sequentially from the opening of the cylindrical portion of the nut. Specifically, in the nut of Figure 10(A), since it has a cover portion, there are 16 female threads from P1 to P16. On the other hand, in Figure 10(B), since the nut has a through hole and female threads are formed along the entire length of the inner surface, there are 19 female threads from P1 to P19.

[0045] Based on the above conditions, an axisymmetric analysis was performed to determine the load sharing ratio (LSR) (%) for each numbered female thread. Figure 11 is a schematic diagram showing the axisymmetric analysis model of the nut after the axisymmetric analysis of the nut shown in Figure 10. Figure 12 is a diagram showing the relationship between each numbered female thread and the load sharing ratio LSR of that female thread, obtained from the axisymmetric analysis model of the nut in Figure 10.

[0046] Graph G10A in Figure 12 shows the results of the analysis model for the nut in Figure 10(A). Graph G10B shows the results of the analysis model for the nut in Figure 10(B). Referring to Figure 12, in the nut in Figure 10(A), the load bearing ratio LSR is high for the female thread P15 near the nut head, among the female threads of the cylindrical part. The wall thickness of the cylindrical part is thinner than the wall thickness of the nut head. Therefore, if a high localized stress is applied to this part, delayed fracture may occur.

[0047] On the other hand, in the nut shown in Figure 10(B), which corresponds to fastener 1 of this embodiment, the load bearing ratio LSR is kept low in the female thread P15 near the nut head of the cylindrical part. Therefore, it is possible to suppress the application of high localized stress to this thin-walled part. The load bearing ratio LSR is high in the female thread P17 inside the nut head. However, the part where the female thread P17 is formed is inside the nut head and has sufficient wall thickness. Therefore, even if the load bearing ratio of the female thread P17 is high, delayed fracture is unlikely to occur.

[0048] As shown in Figure 12, in the fastener 1, the nut 3 includes a cylindrical portion 31 and a through hole 33 is formed, which further enhances resistance to delayed fracture. In addition, it can further improve corrosion resistance at the joint of steel structures.

[0049] As described above, in the fastener 1 of this embodiment, both the bolt 2 and the nut 3 have countersunk heads (bolt countersunk head 22 and nut countersunk head 32). Therefore, it is possible to suppress the protrusion of a part of the fastener from the surface of the joint at the joint of a steel structure. As a result, it is easier to form a uniform coating on the surface of the joint, and corrosion resistance can be improved. In addition, the fastener 1 includes a cylindrical portion 31 in the nut 3. Therefore, the screw-in length can be increased. As a result, the shear resistance of the threaded portion (male threaded portion and female threaded portion) can be increased, and the tensile strength (axial force) can be increased. As a result, the fastener of the first configuration can withstand friction joints sufficiently. Furthermore, the strength of the fastener 1 can be increased, and loosening can be suppressed. In addition, the nut 3 has a through hole that penetrates the cylindrical portion 31 and the nut countersunk head 32, and a female threaded portion 34 is formed on the inner surface of the through hole. This makes it possible to suppress localized high stress on the thin-walled portion of the female threaded portion 34, and delayed fracture resistance and tensile strength can be improved.

[0050] [Preferred form of fastener 1] Preferably, as shown in Figure 13, the taper angle A1 of the countersunk head 22 of the bolt 2 of the fastener 1 is larger than the taper angle A2 of the countersunk head 32 of the nut 3. In this case, during fastening, the countersunk head 32 of the nut makes surface contact with the countersunk 111 formed on the steel member such as the connecting plate 110, while the countersunk head 22 of the bolt makes line contact with the countersunk 111 at the larger diameter portion of the frustoconical section 221. Therefore, localized stress concentration occurs at the frustoconical section 221. As a result, during fastening, the rotational resistance of the bolt 2 becomes greater than that of the nut 3. Consequently, the bolt 2 is less likely to rotate and is fixed when fastened by the rotation of the nut 3. Therefore, the occurrence of co-rotation is suppressed, and fastening work becomes easier.

[0051] The angle is not particularly limited as long as the taper angle A1 is greater than the taper angle A2. Preferably, the taper angle A2 is 90° and the taper angle A1 is 1 to 3° greater than the taper angle A2.

[0052] Figure 14 shows the relationship between rotational torque T (N·m) and axial force N (kN) when fastening a fastener. In Figure 14(A), fastening is performed using fastener 1 shown in Figure 13, where the taper angle A1 is 92° and the taper angle A2 is 90°. Figure 14(B) shows the relationship between rotational torque T (N·m) and axial force N (kN) when the taper angles A1 and A2 are the same. In Figure 14(B), both the taper angles A1 and A2 are 92°.

[0053] Referring to Figure 14, in Figure 14(A), where the taper angle A1 is larger than the taper angle A2, the tensile strength (axial force) per unit rotational torque can be increased compared to Figure 14(B), where the taper angle A1 is the same as the taper angle A2. Therefore, by making the taper angle A1 larger than the taper angle A2 in the fastener 1, the occurrence of co-rotation can be suppressed, and the tensile strength (axial force) per unit rotational torque can also be increased.

[0054] <Second Embodiment> Figure 15 shows a cross-sectional view and a plan view of the nut 3 of the fastener 1 in the second embodiment. Referring to Figure 15, the nut 3 has a plurality of blind holes 38 in the nut upper surface 37 of the nut head 32. The plurality of blind holes 38 are formed around the opening 39 of the through hole 33. Preferably, the plurality of blind holes 38 are arranged at equal intervals around the opening 39. The blind holes 38 are non-through holes with bottoms. The nut 3 can be easily fastened to the bolt 2 by rotating the nut 3 around its axis using a fastening jig that fits into the blind holes 38.

[0055] When the top surface 37 of the nut is viewed from above, the bottomed hole 38 is preferably rectangular. Because the bottomed hole 38 is rectangular, the external force of the fastening jig is easily transmitted around the axis of the nut 3. Therefore, the nut 3 can be fastened to the bolt 2 more easily.

[0056] As shown in Figure 16, when the top surface 37 of the nut is viewed from above, the bottomed hole 38 may be circular in shape.

[0057] [Fastener 1 configuration] The male threaded portion 211 of the bolt 2 of the fastener 1 may include a loose threaded portion having one or more male threads that are not inserted into the cylindrical portion 31 when the bolt 2 is fastened with the nut 3 and the tip of the shaft portion 21 reaches the upper surface 37 of the nut 3. The loose threaded portion homogenizes the stress applied to each male thread of the male threaded portion. Preferably, the loose threaded portion includes two or more male threads. In this case, the stress applied to each male thread can be further homogenized.

[0058] [Regarding the shape of the rounded-off section 212] Preferably, the cut-off portion 212 of the shaft portion 21 of the bolt 2 may be curved in a concave shape. That is, the cut-off portion 212 may have a fillet radius. In this case, it is possible to alleviate localized stress on the male and female threads after fastening and to homogenize the stress.

[0059] The embodiments of this disclosure have been described above. However, the embodiments described above are merely examples for implementing this disclosure. Therefore, this disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of this disclosure. [Explanation of symbols]

[0060] 1 Fasteners 2 bolts 3 nuts 21 Shaft 22 Bolt countersunk head 31 Cylindrical section 32 Nut countersunk head 33 Through hole 34 Female thread section 211 Male threaded section 221, 321 Truncated cone section

Claims

1. Bolt and, Equipped with a nut, The aforementioned bolt is It has a cylindrical shape, and a shaft portion including a male threaded portion, The bolt head is connected to the shaft portion, is arranged coaxially with the shaft portion, and has a frustoconical portion whose diameter increases as it moves away from the shaft portion in the axial direction of the bolt, The aforementioned nut is A cylindrical part having a cylindrical shape, A nut head is connected to the cylindrical portion, is arranged coaxially with the cylindrical portion, and has a frustoconical portion whose diameter increases as it moves away from the cylindrical portion in the axial direction of the nut, The cylindrical portion and the nut head are arranged coaxially, and the through hole penetrates the cylindrical portion and the nut head, The female thread portion formed on the inner surface of the through hole, The female thread portion is formed continuously with the inner surface of the cylindrical portion and the inner surface of the nut head. Fasteners.

2. A fastener according to claim 1, The cylindrical portion includes a tapered portion at the tip of the inner surface of the cylindrical portion. In the tapered portion, the inner diameter increases towards the opening of the cylindrical portion. Fasteners.

3. A fastener according to claim 1, The taper angle of the bolt head is greater than the taper angle of the nut head. Fasteners.

4. A fastener according to claim 1, The aforementioned nut further, The nut top surface of the nut head has a plurality of bottomed holes formed around the opening of the through hole, Fasteners.

5. A fastener according to claim 4, When the upper surface of the nut is viewed from above, the bottomed hole is rectangular. Fasteners.

6. It is a nut, A cylindrical part having a cylindrical shape, A nut head is connected to the cylindrical portion, is arranged coaxially with the cylindrical portion, and has a frustoconical portion whose diameter increases as it moves away from the cylindrical portion in the axial direction of the nut, The cylindrical portion and the nut head are arranged coaxially, and the through hole penetrates the cylindrical portion and the nut head, The female thread portion formed on the inner surface of the through hole, The female thread portion is formed continuously with the inner surface of the cylindrical portion and the inner surface of the nut head. nut.

7. The nut according to claim 6, further, The nut top surface of the nut head has a plurality of bottomed holes formed around the opening of the through hole, nut.

8. The nut according to claim 7, When the upper surface of the nut is viewed from above, the bottomed hole is rectangular. nut.

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