Screw tool

Abstract

To provide a screw tool that can improve both the reliability of tightening operations and the workability of loosening operations. [Solution] A screw tool 1 comprises a screw shaft portion 2, a first head portion 3 located on one end of the screw shaft portion 2 and provided with a first latch portion 6 for latching a tool, a second head portion 4 connected to the first head portion 3 on the opposite side from the screw shaft portion and provided with a second latch portion 8 for latching a tool, and a joint portion 5 that joins the first head portion 3 and the second head portion 4 and breaks when a tightening torque exceeding the permissible amount is applied to the second head portion 4. The first head portion 3 is provided with a fitting hole 6 as the first latch portion, which opens on the opposite side from the screw shaft portion 2, and the joint portion 5 is joined to the first head portion 3 in a region on the outer circumference of the fitting hole 6 of the first head portion 3.

Description

Technical Field

[0001] The present invention relates to a screw tool capable of performing a reliable tightening operation and also corresponding to a loosening operation after tightening.

Background Art

[0002] There is known a screw tool having two-stage heads connected in the axial direction, which enables a reliable tightening operation by breaking the joint portion between the heads when a tightening torque exceeding the allowable amount acts on the head on the tip side, thereby optimizing the tightening torque and preventing forgetting to tighten (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional screw fasteners are designed to enhance security. Therefore, loosening them after tightening is difficult. For example, with the screw fasteners described in Patent Documents 1 and 2, it is necessary to partially remove the head with a grinder or the like and then form a new hooking part on the outer circumference of the head for attaching a tool. However, forcing such work on each individual screw fastener is inefficient. If it is difficult to secure workspace for machining the head, loosening becomes difficult or impossible. It is conceivable to pre-form the outer circumference of the head that remains on the screw shaft side into a hexagonal prism shape, but if it is difficult to secure workspace for attaching a tool such as a wrench to the outer circumference of the head, loosening will also be difficult or impossible. When a screw fastener is tightly tightened or fixed, a relatively large loosening torque is required during the loosening operation, but it can be difficult to apply such high torque when attaching a tool such as a wrench to the outer circumference of the head.

[0005] Therefore, the present invention aims 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 aspect of the present invention, a screw tool comprises a screw shaft portion, a first head portion located on one end of the screw shaft portion and provided with a first latch portion for securing a tool, a second head portion connected to the first head portion on the opposite side from the screw shaft portion and provided with a second latch portion for securing a tool, and a joint portion that connects the first head portion and the second head portion and breaks when a tightening torque exceeding a permissible amount is applied to the second head portion, wherein the first head portion is provided with a fitting hole that opens on the opposite side from the screw shaft portion as the first latch portion, and the joint portion is connected to the first head portion in a region on the outer circumference of the first head portion than the fitting hole. [Brief explanation of the drawing]

[0007] [Figure 1] A front view of a bolt according to one embodiment of the present invention. [Figure 2]A side view of the bolt as seen from the direction of arrow II in Figure 1. [Figure 3] Cross-sectional view of a bolt along line III-III in Figure 1. [Figure 4] Figure 1 shows a partially exploded perspective view of the bolt. [Modes for carrying out the invention]

[0008] Figures 1 to 4 show a bolt as an example of a screw tool according to the present invention. The bolt 1 comprises a threaded shaft portion 2, a first head portion 3 located on one end of the threaded shaft portion 2, a second head portion 4 connected to the first head portion 3 on the opposite side from the threaded shaft portion 2, and a joint portion 5 that connects the first head portion 3 and the second head portion 4 to each other. The bolt 1 is made of metal as an example. However, the bolt 1 may be made of resin or other various materials. The threaded shaft portion 2 may be a right-hand thread or a left-hand thread.

[0009] The first head portion 3 is cylindrical in shape and coaxial with the axis AX of the screw shaft portion 2, and is formed integrally with the screw shaft portion 2. The first head portion 3 is provided with a first fitting hole 6, which is an example of a first hooking portion for securing a predetermined tool, opening on the surface side of the first head portion 3, i.e., on the side opposite to the screw shaft portion 2. A shallow counterbore portion 7 is formed on the surface of the first head portion 3, and the first fitting hole 6 is formed to extend from the bottom of the counterbore portion 7 toward the screw shaft portion 2. The first fitting hole 6 is an example of a bit hole for fitting a tool and rotating the first head portion 3. For example, the first fitting hole 6 is formed as a bit hole having a hexagonal star cross-sectional shape with each corner of the hexagon bulging outward. The maximum diameter of the first fitting hole 6 is the same as the inner diameter of the counterbore portion 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 should be formed in such a way that it prevents a tool for operating the first head 3 from rotating in the circumferential direction. 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 joint 5 are also cylindrical in shape and coaxial with the axis AX of the screw shaft 2. The second head 4 and joint 5 are formed as a single unit. The outer diameter of the second head 4 is larger than the outer diameter of the joint 5. However, the second head 4 and joint 5 may be formed to have equal outer diameters. The second head 4 and joint 5 are formed as separate parts from the screw shaft 2 and the first head 3. Figure 1 shows the second head 4 and joint 5 joined to the first head 3, and Figure 4 shows the second head 4 and joint 5 separated from the first head 3.

[0011] The second head 4 is provided with a second fitting hole 8, which is an example of a second locking portion for securing a predetermined tool, opening on the surface side of the second head 4, i.e., on the side opposite to the screw shaft portion 2. The second fitting hole 8 is an example of a bit hole for fitting a tool and rotating 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 hex wrench, and is different from the special wrench with a hexagonal star cross-section used 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 hexagon. The second fitting hole 8 only needs to be formed so that the tool for operating the second head 4 is prevented 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 other cross-sectional shapes.

[0012] As shown in Figures 1 and 2, the joint 5 has a hollow shape with a through hole 9. The through hole 9 can be formed, for example, by machining a pilot hole for forming the second fitting hole 8 in the second head 4, and machining the pilot hole along the entire length of the joint 5. As shown by dashed lines in Figure 3, the outer diameter of the joint 5 is set to be somewhat smaller than the counterbore 7 of the second head 3, and to overlap with the inward projection 6a of the first fitting hole 6 when viewed from the direction of axis AX. In other words, when an inscribed circle C is drawn so as to be tangent to the projection 6a of the first fitting hole 6, the outer diameter of the joint 5 is set to be larger than the diameter of that inscribed circle C. Therefore, when the joint 5 is abutted coaxially with the first head 3, the joint 5 contacts the projection 6a in the region on the outer circumference of the first fitting hole 6. By welding this contact portion, the joint 5 is joined coaxially with the first head 3 in the region on the outer circumference 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 the 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 such that if a tightening torque exceeding the allowable limit is applied to the second head 4, the welded area will break and the first head 3 and the joint 5 will separate. This allowable limit can be set as an appropriate value for the tightening torque corresponding to the effective thread diameter of the screw shaft 2. The appropriate value may be determined, for example, to allow the application of the largest possible tightening torque without risking the screw shaft 2, or the boundary between the screw shaft 2 and the first head 3, breaking.

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

[0015] To tighten the bolt 1, insert a tool into the second fitting hole 8 of the second head 4 and rotate the entire bolt 1 in the tightening direction until the joint 5 breaks at the joint position with the first head 3, in other words, at the weld point. Upon breakage of the joint 5, the second head 4 and the joint 5 separate from the first head 3, leaving the first head 3 on the screw shaft 2 side. Therefore, the bolt 1 can be loosened by inserting a tool into the first fitting hole 6 of the first head 3. The first fitting hole 6 can also be used to further tighten the bolt 1.

[0016] By tightening the second head 4 until the joint 5 breaks, the tightening torque of the bolt 1 can be brought to approximately its allowable value, thus allowing the tightening torque to be controlled to a generally appropriate constant value. Whether or not the second head 4 and the joint 5 are separated can also be used to check whether or not the bolt 1 has been left untightened. In addition, since the cross-sectional shapes of the first fitting hole 6 and the second fitting hole 8 are different, the shape of the fitting hole exposed on the head of the bolt 1 can be used as a clue to check whether or not the bolt 1 has been left untightened. Thus, it is possible to improve the reliability of the bolt tightening work.

[0017] Furthermore, due to the fracture of the joint 5, 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 troublesome work such as machining the head for loosening operations, nor is there any need to secure space around the bolt 1 for such work. Since the first fitting hole 6 is a bit hole, there is no need to secure space to hook a tool such as a wrench onto the outer circumference of the first head 3. Thus, even when the bolt 1 is installed in a relatively narrow place, loosening operations can be performed without any problems. Moreover, bit holes with a hexagonal or hexagonal star-shaped cross-section have the advantage of being able to easily apply high torque, so even when the bolt 1 is tightened with a relatively large torque or when the bolt 1 is stuck, the bolt 1 can be loosened relatively easily. Combined with the above effects, the above-described form of bolt 1 makes it possible to improve workability during loosening operations.

[0018] In this embodiment of bolt 1, the presence of an inward projection 6a in the first fitting hole 6 is utilized, and the joint 5 is welded using this projection 6a. This configuration allows for a moderately limited welding area, ensuring that the welded joint between the joint 5 and the first head 3 breaks reliably when tightening torque is applied. Even if the cross-sectional shape of the first fitting hole 6 is not a hexagonal star shape, for example, a hexagon, corners for gripping a tool are formed in the first fitting hole 6, and inward projections are created between these corners. Therefore, it is possible to weld the joint 5 to the first head 3 using these projections. When welding the joint 5 using the projection 6a, the joint 5 can be formed relatively larger compared to when the first fitting hole 6 is provided within a range that does not exceed the inner diameter of the joint 5. This makes it possible to apply a greater torque to the first fitting hole 6. However, the joint 5 does not necessarily need to be provided in contact with the projection 6a. The joint 5 may be joined to the first head 3 in a region exceeding the maximum diameter of the first fitting hole 6.

[0019] The present invention is not limited to the embodiments described above, and may be implemented in forms that are appropriately modified or altered. For example, the joint portion 5 is not limited to a cylindrical shape, but may be formed in various shapes such as a frustoconical or drum-shaped form. The joint portion 5 does not necessarily have to be joined to the first head portion 3 by welding. For example, the first head portion 3, the joint portion 5, and the second head portion 4 may be formed integrally, and the first fitting hole 6 may be formed by pressing or turning using the through hole 9. In that case, the thickness of the joint portion 5 should be set so that the joint portion 5 breaks when the tightening torque acting on the second head portion 4 exceeds the allowable amount. In other words, the concept of joining in the present invention is not limited to cases where separate parts are connected in a later process, but also includes cases where they are formed to be connected integrally using various processing methods such as cutting.

[0020] It is not always necessary for the latching portion of the second head 4 to be formed as the second fitting hole 8. For example, by forming the second head 4 into a hexagonal column shape that can be operated by a tool such as a wrench, its outer circumference may function as the second latching portion. Even in such a case, by tightening the second head 4 until the joint portion 5 breaks, it is possible to improve the certainty of the tightening operation. However, when the second latching portion is a fitting hole, there is no need for a space to place a tool such as a wrench around the second head even during the tightening operation, and the workability of the tightening operation can be improved because the work can be performed even in a narrow space. Also, a relatively large torque can be applied to the second head even during tightening.

[0021] In the above embodiment, the joint portion 5 was broken at the joint location with respect to the first head 3, but the break location of the joint portion 5 is not limited to such a position. For example, a constricted portion with a reduced wall thickness may be formed in a part of the joint portion 5, and the joint portion 5 may be broken at the constricted portion. Alternatively, the joint portion 5 may be broken at the joint location between the second head 4 and the joint portion 5. In any case, the break of the joint portion 5 may occur at an 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 as an example of a threaded fastener was illustrated, but the threaded fastener of the present invention is not limited to a bolt and may be configured as a screw with a relatively small diameter. That is, the threaded fastener of the present invention is a concept that includes various threaded parts including a threaded shaft portion and a head, regardless of the names such as bolt and screw.

[0023] The various aspects of the present invention derived from each of the above-described embodiments and modification examples are described below. In the following description, corresponding components illustrated in the accompanying drawings are appended in parentheses to facilitate understanding of each aspect of the present invention, but the present invention is not limited to the illustrated forms by this.

[0024] A screw tool (1) according to one aspect of the present invention comprises a screw shaft portion (2), a first head portion (3) located on one end of the screw shaft portion and provided with a first locking portion (6) for locking a tool, a second head portion (4) connected to the first head portion on the side opposite to the screw shaft portion and provided with a second locking portion (8) for locking a tool, and a joint portion (5) that joins the first head portion and the second head portion to each other and breaks when a tightening torque exceeding a permissible amount is applied to the second head portion, wherein the first head portion is provided with a fitting hole that opens on the side opposite to the screw shaft portion as the first locking portion, and the joint portion is joined to the first head portion in a region on the outer circumference side of the fitting hole of the first head portion.

[0025] With the above-described screw tool, the tightening torque of the screw tool can be controlled to a generally appropriate constant value by tightening the second head until the joint breaks. It is also possible to check whether the screw tool has been left untightened by checking whether the second head and the joint have separated from the first head. Therefore, it is possible to improve the reliability of the tightening work. 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 troublesome work such as machining the head for loosening, and there is no need to secure space around the screw tool for such work. There is also no need to secure space on the outer circumference of the first head for hooking a tool. Therefore, even when the screw tool is installed in a relatively narrow place, it is possible to loosen it without any problems. When hooking a tool onto the first fitting hole, it is easy to apply a relatively high torque. Therefore, even if the screw tool is tightened with a relatively large torque, or if the screw tool is stuck, it can be loosened relatively easily. The above effects combined make it possible to improve the workability during loosening operations.

[0026] In the above embodiment, the following matters may be further added. These various matters may be applied in appropriate combinations, provided they do not conflict with each other.

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

[0028] In embodiments utilizing welding, an inward projection (6a) exists around the fitting hole of the first head, and the joint may be welded at the projection. Since an inward projection is generated in the fitting hole for securing a tool, welding the joint using this projection allows for a moderate limitation of the welding area, ensuring that the welded joint between the joint and the first head breaks when a tightening torque is applied. Compared to the case where the first fitting hole is provided within a range not exceeding the inner diameter of the joint, the joint can be formed relatively larger, thereby enabling a greater torque to be applied to the first fitting hole.

[0029] In the above embodiment, the second head may be provided with a fitting hole (8) that opens on the opposite side from the joint, serving as the second latching portion. When the second latching portion is also a fitting hole, there is no need to place a tool such as a wrench around the second head during tightening, and the screw can be securely tightened even in a relatively narrow space. Furthermore, it is possible to apply a relatively large tightening torque by utilizing the fitting hole. This improves the workability during tightening.

[0030] In the above embodiment, 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 may be different from each other. This allows for confirmation of whether or not the screw has been left untightened by using the shape of the fitting hole exposed on the head of the screw as a clue. Therefore, it is possible to further improve the reliability of the screw tightening work. [Explanation of symbols]

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

Claims

1. The screw shaft and, A first head portion is located on one end of the screw shaft portion and is provided with a first hooking portion for attaching a tool, A second head is provided with a second latching portion for attaching a tool, which is connected to the first head on the side opposite to the screw shaft portion, The first head and the second head are joined together, and the joint portion is designed to break if a tightening torque exceeding a permissible amount is applied to the second head, The first head portion is provided with a fitting hole that opens on the opposite side from the screw shaft portion, which serves as the first latching portion. The joint portion is a screw that is joined to the first head in a region of the first head that is on the outer circumference side of the fitting hole of the first head.

2. The screw tool according to claim 1, wherein the joint is welded to the second head, and if 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. The screw tool according to claim 2, wherein an inward projection exists around the fitting hole of the first head, and the joint is welded at the projection.

4. The screw tool 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 from the joint, serving as the second latching portion.

5. The screw tool 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.

Images