Screws

Abstract

A screw tool capable of improving both the reliability of a tightening operation and the workability of a loosening operation is provided. [Solution] A screw device 1 includes a screw shank 2, a first head 3 located at one end of the screw shank 2 and provided with a first hooking portion 6 for hanging a tool, a second head 4 connected to the first head 3 on the opposite side of the screw shank and provided with a second hooking portion 8 for hanging a tool, and a joint 5 that joins the first head 3 and the second head 4 to each other and breaks when a tightening torque exceeding the allowable amount is applied to the second head 4, in which the first head 3 is provided with a mating hole 6 that opens on the opposite side from the screw shank 2 as the first hooking portion, and the joint 5 is joined to the first head 3 in an area outer than the mating hole 6 of the first head 3.

Description

[Technical Field]

[0001] The present invention relates to a screw tool that allows for reliable tightening operations and can also be loosened after tightening. [Background technology]

[0002] There is known a screw tool that has two head sections connected in the axial direction, and that breaks the joint between the head sections when a tightening torque exceeding the allowable limit is applied to the head section at the tip, thereby optimizing the tightening torque and preventing forgetting to tighten, thereby enabling reliable tightening operations (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-343537 [Patent Document 2] Japanese Patent Application Publication No. 64-26011 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional screw tools are designed to enhance security. Therefore, loosening after tightening is difficult. For example, the screw tools described in Patent Documents 1 and 2 require the head to be partially removed using a grinder or the like, and a new hook portion for hooking a tool must be formed on the outer periphery of the head. However, forcing such work for each screw tool is inefficient. When it is difficult to secure working space for machining the head, it is difficult or impossible to accommodate the loosening operation. It is conceivable to form the outer periphery of the head, which remains on the shank, into a hexagonal prism shape in advance, but if it is difficult to secure working space for hooking a tool such as a wrench on the outer periphery of the head, loosening is also difficult or impossible. When a screw tool is tightly tightened or stuck, a relatively large loosening torque must be applied to loosen the screw. However, it can be difficult to apply such a high torque when hooking a tool such as a wrench on the outer periphery of the head.

[0005] Therefore, an object of the present invention is to provide a screw tool that can improve both the reliability of the tightening operation and the workability of the loosening operation. [Means for solving the problem]

[0006] In one embodiment of the present invention, a screw device comprises a screw shank, a first head located at one end of the screw shank and provided with a first hook for hanging a tool, a second head connected to the first head on the opposite side of the screw shank and provided with a second hook for hanging a tool, and a joint that joins the first head and the second head to each other and breaks when a tightening torque exceeding the allowable amount is applied to the second head, wherein the first head has a fitting hole that opens on the opposite side from the screw shank as the first hook, and the joint is joined to the first head in an area outer than the fitting hole of the first head. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a front view of a bolt according to an embodiment of the present invention. [Figure 2]FIG. 2 is a side view of the bolt as seen from the direction of arrow II in FIG. 1. [Figure 3] Cross-sectional view of the bolt taken along line III-III in Figure 1. [Figure 4] FIG. 2 is a partially exploded perspective view of the bolt of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0008] 1 to 4 show a bolt as an example of a screw device according to the present invention. The bolt 1 comprises a threaded shank 2, a first head 3 located on one end of the threaded shank 2, a second head 4 connected to the first head 3 on the opposite side of the threaded shank 2, and a joint 5 that joins the first head 3 and the second head 4 together. The bolt 1 is made of metal as an example. However, the bolt 1 may be made of resin or various other materials. The threaded shank 2 may be either a right-handed thread or a left-handed thread.

[0009] The first head 3 has a cylindrical shape coaxial with the axis AX of the screw shank 2 and is formed integrally with the screw shank 2. The first head 3 has a first fitting hole 6, an example of a first hook portion for hooking a predetermined tool, formed on the surface side of the first head 3, i.e., the side opposite the screw shank 2. A shallow counterbore 7 is formed on the surface of the first head 3, and the first fitting hole 6 is formed to extend from the bottom of the counterbore 7 toward the screw shank 2. The first fitting hole 6 is an example of a bit hole for fitting a tool and rotating the first head 3. For example, the first fitting hole 6 is formed as a bit hole having a cross-sectional shape of a hexagonal star with each corner of a hexagon bulging outward. The maximum diameter of the first fitting hole 6 is the same as the inner diameter of the counterbore 7. The first fitting hole 6 can be formed by press working or turning. However, the cross-sectional shape of the first fitting hole 6 is not limited to a hexagonal star shape. The first fitting hole 6 may be formed so as to prevent rotation in the circumferential direction of a tool for operating the first head 3. Therefore, the first fitting hole 6 may be formed as a hole having a hexagonal or other cross-sectional shape.

[0010] The second head 4 and the joint portion 5 also have a cylindrical shape coaxial with the axis AX of the screw shank 2. The second head 4 and the joint portion 5 are integrally formed. The outer diameter of the second head 4 is larger than the outer diameter of the joint portion 5. However, the second head 4 and the joint portion 5 may be formed to have the same outer diameter. The second head 4 and the joint portion 5 are formed as separate parts from the screw shank 2 and the first head 3. Figure 1 shows the second head 4 and the joint portion 5 joined to the first head 3 side, and Figure 4 shows the second head 4 and the joint portion 5 separated from the first head 3 side.

[0011] The second head 4 has a second fitting hole 8, an example of a second hook portion for hooking a predetermined tool, that opens on the surface side of the second head 4, i.e., the side opposite the screw shank 2. The second fitting hole 8 is an example of a bit hole for fitting a tool to rotate the second head 4. The second fitting hole 8 may also be formed by press working or turning. The tool to be fitted into the second fitting hole 8 does not necessarily have to be the same as the tool to be fitted into the first fitting hole 6. In the illustrated example, the second fitting hole 8 is formed as a bit hole with a hexagonal cross-sectional shape. Therefore, the tool to be fitted into the second fitting hole 8 is a general-purpose hexagonal wrench, which differs from the dedicated wrench with a hexagonal star cross-section to be fitted into the first fitting hole 6. However, the cross-sectional shape of the second fitting hole 8 is not limited to a hexagonal shape. The second fitting hole 8 may be formed so as to prevent the tool to operate the second head 4 from rotating in the circumferential direction. Therefore, the second fitting hole 8 may be formed as a hole having a hexagonal star shape similar to the first fitting hole 6, or another cross-sectional shape.

[0012] As shown in FIGS. 1 and 2 , the joint 5 has a hollow shape with a through hole 9. For example, the through hole 9 can be formed by drilling a pilot hole for forming the second fitting hole 8 in the second head 4, and drilling the pilot hole over the entire length of the joint 5. As shown by the imaginary line in FIG. 3 , the outer diameter of the joint 5 is slightly smaller than the counterbore 7 of the second head 3 and is set within a range that overlaps with the inward protrusion 6a of the first fitting hole 6 when viewed from the direction of the axis AX. In other words, when an inscribed circle C is drawn tangent to the protrusion 6a of the first fitting hole 6, the outer diameter of the joint 5 is set to be larger than the diameter of the inscribed circle C. Therefore, when the joint 5 is butted coaxially with the first head 3, the joint 5 contacts the protrusion 6a in a region radially outward of the first fitting hole 6. By welding the contacting portion, the joint 5 is joined coaxially to the first head 3 in a region radially outward of the first fitting hole 6. By setting the outer diameter of the joint portion 5 as described above, it is possible to join the first head portion 3 and the joint portion 5 even if a first fitting hole 6 is formed on the surface side of the first head portion 3.

[0013] The joint strength between the joint 5 and the first head 3 is set so that when a tightening torque exceeding the allowable amount is applied to the second head 4, the welded portion breaks and the first head 3 and the joint 5 are separated. The allowable amount can be set as an appropriate tightening torque value according to the effective thread diameter of the screw shank 2. The appropriate value may be determined, for example, so that as large a tightening torque as possible can be applied within a range that does not cause the screw shank 2 or the boundary portion between the screw shank 2 and the first head 3 to break.

[0014] Various welding methods such as spot welding, groove welding, and fillet welding may be used to weld the joint 5 and the first head 3. The weld strength can be set by appropriately adjusting the welding conditions. For example, in the case of spot welding, various parameters related to the weld strength, such as the pitch of the welded points, the welding current value, the current application time, and the electrode pressure, may be appropriately set and adjusted. In the case of groove welding, the welding conditions, such as the groove shape and the weld area, may be appropriately set and adjusted. In the case of fillet welding, the weld strength can be set by adjusting the welding conditions in the same way.

[0015] To tighten the above-described bolt 1, a tool is fitted into the second fitting hole 8 of the second head 4, and the entire bolt 1 is rotated in the tightening direction until the joint 5 breaks at the joint position with the first head 3, in other words, at the welded location. When the joint 5 breaks, the second head 4 and joint 5 are separated from the first head 3, leaving the first head 3 on the threaded shank 2 side. Therefore, by fitting a tool into the first fitting hole 6 of the first head 3, the bolt 1 can be operated in the loosening direction. The first fitting hole 6 can also be used to retighten the bolt 1.

[0016] By tightening the second head 4 until the joint 5 breaks, the tightening torque of the bolt 1 can be made to roughly match its allowable amount, making it possible to control the tightening torque at a roughly appropriate constant value. Whether the second head 4 and the joint 5 are separated can also be used to check whether the bolt 1 has been incompletely tightened. In addition, because the cross-sectional shapes of the first fitting hole 6 and the second fitting hole 8 are different from each other, it is possible to check whether the bolt 1 has been incompletely tightened by using the shape of the fitting hole exposed in the head of the bolt 1 as a clue. This makes it possible to improve the reliability of the bolt 1 tightening operation.

[0017] Furthermore, when the joint portion 5 is broken, the first fitting hole 6, which is an example of a bit hole, is exposed on the surface side of the first head 3, similar to a general-purpose bolt. Therefore, there is no need to perform the tedious task of machining the head for loosening, and there is no need to secure space around the bolt 1 for such work. Because the first fitting hole 6 is a bit hole, there is no need to secure space for hooking a tool such as a wrench onto the outer periphery of the first head 3. Therefore, the bolt 1 can be loosened without any problems even when installed in a relatively narrow space. Furthermore, bit holes with a hexagonal or hexagonal star cross-section have the advantage of being easy to apply high torque. Therefore, even if the bolt 1 is tightened with a relatively large torque or is stuck, the bolt 1 can be loosened relatively easily. The above-mentioned effects combined together make it possible for the bolt 1 of the above-described form to improve the ease of loosening.

[0018] In the bolt 1 of this embodiment, the presence of an inward protrusion 6a in the first fitting hole 6 is utilized, and the joint 5 is welded at the protrusion 6a. This appropriately limits the welding area, ensuring that the welded portion between the joint 5 and the first head 3 is reliably fractured when a tightening torque is applied. Even if the cross-sectional shape of the first fitting hole 6 is a shape other than a six-pointed star, such as a hexagon, corners for hooking a tool are formed in the first fitting hole 6, and inward protrusions are formed between those corners. This makes it possible to weld the joint 5 to the first head 3 using the protrusions 6a. When the joint 5 is welded using the protrusions 6a, the joint 5 can be formed relatively larger than when the first fitting hole 6 is formed within a range that does not exceed the inner diameter of the joint 5. This allows for a greater torque to be applied to the first fitting hole 6. However, the joint 5 does not necessarily need to be formed so as to contact the protrusions 6a. The joint 5 may be joined to the first head 3 in an area exceeding the maximum diameter of the first fitting hole 6.

[0019] The present invention is not limited to the above-described embodiment and may be embodied in various modified or altered forms. For example, the joint 5 is not limited to a cylindrical shape and may be formed into various shapes, such as a truncated cone shape, a hand drum shape, or the like. The joint 5 does not necessarily have to be joined to the first head 3 by welding. For example, the first head 3, the joint 5, and the second head 4 may be integrally formed, and the first fitting hole 6 may be formed by pressing or turning using the through hole 9. In this case, the thickness of the joint 5 may be set so that the joint 5 breaks when the tightening torque acting on the second head 4 exceeds the allowable limit. In other words, the joining in the present invention is not limited to an example in which separate parts are connected in a subsequent process, but also includes a concept in which the parts are formed into an integral, continuous structure using various processing methods, such as cutting.

[0020] The hooking portion of the second head 4 does not necessarily have to be formed as the second fitting hole 8. For example, the second head 4 may be formed as a hexagonal prism that can be manipulated with a tool such as a wrench, with its outer periphery functioning as the second hooking portion. Even in this case, the reliability of the tightening operation can be improved by tightening the second head 4 until the joint 5 breaks. However, if the second hooking portion is a fitting hole, no space is required around the second head to place a tool such as a wrench during the tightening operation, making it possible to work in narrow spaces and improving the workability of the tightening operation. Furthermore, a relatively large torque can be applied to the second head during tightening.

[0021] In the above embodiment, the joint 5 is broken at the joint location with the first head 3, but the location at which the joint 5 breaks is not limited to such a position. For example, a constricted portion with a thinner wall thickness may be formed in part of the joint 5, and the joint 5 may be broken at that constricted portion. Alternatively, the joint 5 may be broken at the joint location between the second head 4 and the joint 5. In either case, the joint 5 may break at any appropriate position within the range from the end on the first head 3 side to the end on the second head 4 side.

[0022] In the above embodiment, a bolt is used as an example of a screw tool, but the screw tool of the present invention is not limited to a bolt and may be configured as a relatively small diameter screw. In other words, the screw tool of the present invention is a concept that encompasses various screw parts including a screw shank and a head, regardless of whether they are called bolts or screws.

[0023] Various aspects of the present invention derived from the above-described embodiments and modifications will be described below. In the following description, corresponding components shown in the accompanying drawings will be written in parentheses to facilitate understanding of each aspect of the present invention, but the present invention is not limited to the illustrated forms.

[0024] A screw device (1) according to one embodiment of the present invention comprises a screw shank (2), a first head (3) located at one end of the screw shank and provided with a first hooking portion (6) for hanging a tool, a second head (4) connected to the first head on the opposite side of the screw shank and provided with a second hooking portion (8) for hanging a tool, and a joint (5) that joins the first head and the second head to each other and breaks when a tightening torque exceeding the allowable amount is applied to the second head, wherein the first head has a fitting hole that opens on the opposite side from the screw shank as the first hooking portion, and the joint is joined to the first head in an area outer than the fitting hole of the first head.

[0025] According to the screw device of the above aspect, the tightening torque of the screw device can be maintained at a generally appropriate constant value by tightening the second head until the joint breaks. Whether the second head and the joint break from the first head can also be used to check whether the screw device has been inadvertently tightened. This improves the reliability of the tightening operation. When the joint breaks, the first fitting hole is exposed on the surface side of the first head. Therefore, there is no need to perform the tedious task of machining the head for loosening, nor is there a need to secure space around the screw device for such work. There is also no need to secure space around the first head for hooking a tool. Therefore, loosening can be performed without problems even when the screw device is installed in a relatively narrow space. When a tool is hooked to the first fitting hole, it is easy to apply a relatively high torque. Therefore, even if the screw device is tightened with a relatively large torque or is stuck, it can be loosened relatively easily. The above effects combine to improve the ease of loosening.

[0026] In the above-described embodiment, the following items can be further added. The following various items may be applied in appropriate combinations as long as they are not mutually contradictory.

[0027] In the screw device of the above aspect, the joint may be welded to the second head, and the weld between the joint and the second head may break if a tightening torque exceeding the allowable amount is applied to the second head. In this way, the screw device of the above aspect can be manufactured by first forming a mating hole in the first head and then welding the joint to the first head. By appropriately adjusting the welding conditions, the allowable amount of tightening torque that serves as the criterion for breaking the joint can be set to a desired level.

[0028] In a mode using welding, an inward protrusion (6a) may be present around the fitting hole of the first head, and the joint may be welded at the protrusion. Since the fitting hole for latching a tool has an inward protrusion, welding the joint using the protrusion allows the weld area to be appropriately limited, ensuring that the weld between the joint and the first head breaks when tightening torque is applied. Compared to a case where the first fitting hole is provided within a range that does not exceed the inner diameter of the joint, the joint is formed relatively larger, which allows a greater torque to be applied to the first fitting hole.

[0029] In the above-described embodiment, the second head may be provided with a fitting hole (8) that opens on the opposite side of the joint as the second engaging portion. If the second engaging portion is also a fitting hole, no space is required around the second head to place a tool such as a wrench during tightening, and the screw can be tightened reliably even in a relatively narrow space. Furthermore, it is possible to apply a relatively large tightening torque by using the fitting hole. This also improves workability during tightening.

[0030] In the above-described embodiment, the cross-sectional shape of the fitting hole in the first head portion and the cross-sectional shape of the fitting hole in the second head portion may be different from each other. This allows the user to check whether the screw has been left untightened by using the shape of the fitting hole exposed in the head portion of the screw. This further improves the reliability of the screw tightening operation. [Explanation of symbols]

[0031] 1 volt 2 Screw shaft 3 First head 4 Second head 5 Joint 6 First fitting hole 6a Protrusion 8 Second fitting hole

Claims

1. a screw shaft portion; a first head portion located on one end side of the screw shaft portion and provided with a first hook portion for hooking a tool; a second head portion connected to the first head portion on the opposite side of the screw shaft portion and provided with a second hook portion for hooking a tool; a joint portion that joins the first head and the second head together and that breaks when a tightening torque exceeding an allowable amount is applied to the second head, The first head portion is provided with a fitting hole that opens to the opposite side to the screw shaft portion as the first hook portion, The joint portion is joined to the first head in an area radially outward of the fitting hole of the first head.

2. 2. The screw device according to claim 1, wherein the joint is welded to the second head, and when a tightening torque exceeding the allowable amount is applied to the second head, the welded portion between the joint and the second head breaks.

3. 3. The screw device according to claim 2, wherein an inward protrusion is present around the fitting hole of the first head, and the joint is welded at the protrusion.

4. The screw device according to any one of claims 1 to 3, wherein the second head is provided with a fitting hole that opens on the opposite side to the joint portion as the second engaging portion.

5. The screw device according to claim 4, wherein the cross-sectional shape of the fitting hole in the first head and the cross-sectional shape of the fitting hole in the second head are different from each other.

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