JP2012211678A - Screw fastening structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw fastening structure that can improve screw fastening capability without deteriorating screw fastening work performance.SOLUTION: In the screw fastening structure, a bar ring lower hole 11 is formed at a fastening material 1, a screw 3 is inserted into a through-hole 21 formed at a material 2 to be fastened so that the screw 3 is screwed in to the bar ring lower hole 11, a projecting hole 22 is formed by raising a circumferential edge of the through-hole 21 of the material 2 to be fastened, and when the screw is screwed in to the bar ring lower hole 11, an end 23 of the projecting hole 22 of the through-hole 21 is brought into contact with the circumferential edge 13 of the bar ring lower hole 11.

Description

  The present invention relates to a screw fastening structure for fastening a fastening object and a fastened object with screws.

  For example, as a screw fastening structure between metal plates constituting a box used for gas appliances, etc., a burring pilot hole is formed in a metal plate to be fastened, and a tapping screw is provided in a punch hole provided in the metal plate to be fastened There is a structure that is screwed into the burring pilot hole. In this case, when the tapping screw is tightened, the pulling force of the tapping screw may deform so that the peripheral portion of the burring pilot hole of the fastening object rises, and the screw tightening ability may decrease. In order to eliminate such problems, various screw fastening structures have been proposed.

  For example, as an improvement of the burring pilot hole, the base end of the burring pilot hole is a tapered countersunk, and the rigidity of the peripheral part of the burring pilot hole is increased (Patent Document 1). There is a structure in which a plurality of ribs protruding from the outer peripheral surface are formed at the base portion to prevent deformation of the peripheral portion of the burring pilot hole (Patent Document 2).

  Also, as a modified version of the screw, use a stepped screw so that the peripheral part of the burring pilot hole abuts on the step part of the stepped screw to prevent deformation of the peripheral part of the burring pilot hole (Patent Document 3).

Japanese Patent Publication No.54-27503 JP 2009-293663 A JP-A-62-24011

  However, even if the burring pilot hole is improved, the peripheral edge of the tapered countersink of the burring pilot hole in Patent Document 1 and the peripheral edge of the rib protruding from the outer peripheral surface of the burring pilot hole in Patent Document 2 It was difficult to prevent deformation at the portion due to the lifting force of the screw. In particular, as the fastener for forming the burring pilot hole, when the thickness of the sheet metal constituting the fastener is reduced, the peripheral edge of the burring pilot hole is greatly deformed, and the breaking torque of the female screw of the burring pilot hole is reduced. For this reason, the tightening ability required for screw fastening could not be sufficiently exhibited.

  On the other hand, in the case of using the stepped screw disclosed in Patent Document 3, when the stepped screw is passed through the hole to be fastened, the stepped portion of the stepped screw is caught on the periphery of the hole and obstructing insertion into the hole. In addition, the stepped screw is difficult to see the threaded portion at the tip, and may be troublesome for insertion into the burring pilot hole, which may reduce the workability of screw fastening. In addition, since the hole diameter of the hole to be fastened is increased by adopting the stepped screw, if the object to be fastened is formed of a thin sheet metal, the strength of the peripheral portion of the hole may be reduced. . Moreover, it is uneconomical to use special screws such as stepped screws.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a screw fastening structure capable of improving the screw fastening capability without reducing the screw fastening workability. And

The screw fastening structure according to the present invention includes:
A screw fastening structure in which a burring pilot hole is formed in a fastening object, and a screw is inserted into a burring pilot hole through a screw hole provided in the article to be fastened,
A configuration in which the peripheral edge of the hole to be fastened is raised to form a protrusion, and when the screw is screwed into the burring pilot hole, the tip of the protrusion of the punch hole contacts the peripheral edge of the burring pilot hole; It is a thing.

  This ensures that the peripheral edge of the burring pilot hole of the fastening object is prevented from rising and deforming due to the lifting force of the screw by the tip of the protrusion of the punch hole coming into contact with the peripheral edge of the burring pilot hole. Can do. Further, the force of the burring pilot hole to increase the diameter by screwing can be suppressed by the tip of the protrusion. Therefore, it is possible to increase the breaking torque, which is the limit torque that the female screw of the burring pilot hole breaks, and to improve the screw tightening ability.

  In addition, the use of a general screw can sufficiently improve the breaking torque of the female screw of the burring pilot hole, and there is no need to use a special screw such as a stepped screw. Therefore, the screw can be smoothly inserted into the punched hole or the burring pilot hole, and the fastening workability of the screw is not deteriorated. Moreover, it is not necessary to increase the hole diameter of the hole to be fastened as in the case of using a stepped screw, and even when the object to be fastened is a thin plate, the strength of the peripheral edge of the hole can be ensured. Moreover, the cost of the screw can be reduced by using a general screw.

In the above-described screw fastening structure, it is preferable that the protrusion is formed in a tapered shape having a small diameter toward the tip.
In this case, the tapered protrusion can exhibit an elastic function, and the burring pilot hole can be suppressed in the reduced diameter direction by the tip of the protrusion. Therefore, the breaking torque of the internal thread of the burring pilot hole can be further increased, and the screw tightening ability can be further improved. Further, since the screw is firmly fixed by the reaction force of the elastic force of the tapered protrusion, the effect of preventing the screw from loosening is improved.

In the above screw fastening structure, the base end portion of the burring pilot hole of the fastening object is formed in a taper shape, and the tip end portion of the piercing hole of the fastening object is in contact with the peripheral portion of the taper portion of the burring pilot hole; It is desirable to do.
In this case, it is possible to increase the rigidity of the peripheral edge of the burring pilot hole by forming the base end part of the burring pilot hole of the fastening object into a taper shape, and to raise the screw by the tip of the protrusion of the punch hole. Deformation of the peripheral edge of the tapered portion of the burring pilot hole due to force can be reliably prevented.

In the above screw fastening structure, the lower surface of the head of the screw is formed as a flat surface, and is configured to press the flat seating surface at the peripheral edge portion of the front side hole that does not form the protrusion of the object to be fastened. Is desirable.
Thereby, the protrusion of the peripheral part of a punching hole can be strongly pressed on the peripheral part of a burring pilot hole by screwing a screw in a burring pilot hole. Therefore, it is possible to more reliably prevent the peripheral edge portion of the burring prepared hole of the fastening product from being pulled up by the screw.

  As described above, according to the screw fastening structure according to the present invention, it is possible to reliably prevent deformation of the peripheral portion of the burring pilot hole of the fastener and increase the breaking torque of the burring pilot hole. Even if the plate thickness is reduced, the tightening ability required for screw fastening can be sufficiently exhibited. Accordingly, the fastening object and the object to be fastened can be thinned to reduce the weight, and the product cost can be reduced. Further, since it is not necessary to use a special screw such as a stepped screw, the workability of screw fastening is not deteriorated.

It is sectional drawing which shows the screw fastening structure by embodiment. It is sectional drawing which shows the state before tightening a tapping screw in the screw fastening structure by embodiment. As other embodiment, it is sectional drawing which shows the screw fastening structure at the time of changing the shape of a protrusion into a taper shape. Moreover, it is sectional drawing which shows the screw fastening structure at the time of changing the shape of a burring pilot hole into a taper shape as other embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
The screw fastening structure of the present embodiment is used for, for example, a connecting portion between a box body that houses a heat exchanger and a box body that houses a burner in a water heater. However, the screw fastening structure of the present invention is not limited to a gas appliance such as a water heater, and can be applied to a screw fastening structure in which a fastening object and a fastening object in various products are fastened with screws.

  As shown in FIG. 1, in the screw fastening structure of the embodiment, a second plate material 2 to be fastened is superposed on a first plate material 1 to be fastened with a seal packing 4 interposed therebetween. In this structure, the first plate member 1 and the second plate member 2 are fastened with a tapping screw 3. The 1st board | plate material 1 and the 2nd board | plate material 2 are formed with a sheet metal, and the packing 4 is formed with the foaming resin material etc. As the tapping screw 3, a general tapping screw including a head portion 31 and a screw shaft 33 is used, and a lower surface 32 of the head portion 31 is formed in a flat surface.

  The first plate 1 is formed with a burring pilot hole 11 having a cylindrical portion 12 that rises at approximately 90 degrees by burring at a screw tightening position. The inner diameter of the cylindrical portion 12 of the burring pilot hole 11 is smaller than the crest diameter of the screw shaft 33 of the tapping screw 3, and the tapping screw 3 is screwed into the burring pilot hole 11.

  In the second plate member 2, a punched hole 21 having a diameter larger than that of the burring pilot hole 11 is formed at a position corresponding to the burring pilot hole 11 of the first plate member 1. The inner diameter of the punch hole 21 is larger than the crest diameter of the screw shaft 33 of the tapping screw 3 and smaller than the outer diameter of the head 31 of the tapping screw 3. The tapping screw 3 is inserted into the punched hole 21.

  Further, the peripheral edge portion of the punched hole 21 of the second plate member 2 is a cylindrical protrusion 22 that is raised at about 90 degrees by burring on the back side of the second plate member 2. When the tapping screw 3 is screwed into the burring pilot hole 11 through the hole 21, the tip 23 of the protrusion 22 comes into contact with the peripheral edge 13 of the burring pilot hole 11. A peripheral edge portion of the punched hole 21 on the front side of the second plate member 2 is a flat seat surface 24, and the flat lower surface 32 of the head portion 31 of the tapping screw 3 is brought into contact with the flat seat surface 24. . Note that a washer may be interposed between the head 31 of the tapping screw 3 and the seating surface 24 of the second plate member 2 in the punched hole 21. The packing 4 is formed with a hole 41 having a size into which the protrusion 22 of the punched hole 21 in the second plate member 2 is fitted.

Next, the operation of screwing the first plate material 1 and the second plate material 2 with the tapping screw 3 will be described.
The first plate member 1 and the second plate member 2 are combined with the packing 4 so that the burring pilot hole 11 of the first plate member 1, the hole 41 of the packing 4, and the punched hole 21 of the second plate member 2 coincide with each other. Overlay with intervening. At this time, the protrusion 22 of the punched hole 21 of the second plate member 2 is fitted into the hole 41 of the packing 4. Then, the tapping screw 3 is inserted from the front side of the second plate 2 into the hole 21 and the hole 41 of the packing 4, and the tip of the screw shaft 33 of the tapping screw 3 is inserted into the burring pilot hole of the first plate 1. 11, the head 31 of the tapping screw 3 is tightened with a tool such as a screwdriver. Then, as shown in FIG. 2, the screw shaft 33 of the tapping screw 3 is screwed in while engraving the female screw on the inner peripheral surface of the cylindrical portion 12 of the burring pilot hole 11. After the lower surface 32 of the head portion 31 of the tapping screw 3 abuts against the seating surface 24 of the second plate member 2, when the tapping screw 3 is further screwed, the second plate member 2 is moved to the first portion 31 by the head portion 31 of the tapping screw 3. The packing 4 is finally compressed between the first plate 1 and the second plate 2 so that the tip 23 of the protrusion 22 of the hole 21 in the second plate 2 is pressed. Tightening is completed in a state where the first plate 1 is in contact with the peripheral edge 13 of the burring pilot hole 11 (see FIG. 1).

  According to the screw fastening structure of the present embodiment described above, the tip 23 of the protrusion 22 of the punch hole 21 is in contact with the peripheral portion 13 of the burring pilot hole 11, so that the tapping screw 3 is placed in the burring pilot hole 11. It is possible to reliably prevent the peripheral edge portion 13 of the burring pilot hole 11 of the first plate 1 from rising and deforming to the second plate 2 side by the pulling force of the tapping screw 3 when screwed. Further, the lower surface 32 of the head portion 31 of the tapping screw 3 is formed as a flat surface and presses the flat seating surface 24 at the peripheral portion of the through hole 21 on the front side of the second plate member 2. The mouth 22 can strongly press the peripheral portion 13 of the burring prepared hole 11 of the first plate 1. Thereby, it can prevent more reliably that the peripheral part 13 of the burring pilot hole 11 of the 1st board | plate material 1 swells and deform | transforms into the 2nd board | plate material 2 side by the drawing-in force of the tapping screw 3. FIG. Furthermore, the burring pilot hole 11 can suppress the force of expanding the diameter of the burring prepared hole 11 by screwing the tapping screw 3 by the tip portion 23 of the protrusion 22.

  As a result, the breaking torque, which is the limit torque that the female screw of the burring pilot hole 11 breaks, can be increased, and the screw tightening ability required for screw fastening can be improved. Therefore, even if the plate thickness of the first plate 1 is made thin, the tightening ability required for screw fastening can be sufficiently exerted. Therefore, the first plate 1 and the second plate 2 are made thin. The weight can be reduced, and the product cost can be reduced. Further, the tapping screw 3 is firmly fixed by the reaction force of the force that the protrusion 22 of the punching hole 21 strongly presses the peripheral edge portion 13 of the burring lower hole 11, and the loosening prevention effect is exhibited.

  The tapping screw 3 can sufficiently improve the breaking torque of the internal thread of the burring pilot hole 11 by using a general screw without using a special screw such as a stepped tapping screw. Therefore, compared with the case where the stepped tapping screw is used, the tapping screw 3 can be smoothly inserted into the through hole 21 of the second plate member 2 or the burring pilot hole 11 of the first plate member 1. The fastening workability is not reduced. Further, when the stepped tapping screw is used, the hole diameter of the punched hole 21 of the second plate member 2 is increased, and the strength of the peripheral portion 13 of the punched hole 21 can be reduced. However, the general tapping screw 3 is used. As in the case of using a stepped tapping screw, it is not necessary to increase the diameter of the punched hole 21 of the second plate member 2, and the peripheral portion 13 of the punched hole 21 even when the second plate member 2 is thin. The strength of the can be ensured. In addition, by using a general tapping screw 3, the cost of the screw can be reduced as compared with the stepped tapping screw.

Incidentally, in the screw fastening structure in which the first plate member 1 and the second plate member 2 are fastened with the tapping screw 3, when the breaking torque of the female screw of the burring pilot hole 11 is measured, the hole 21 of the second plate member 2 is measured. When the protrusion 22 was not formed, the breaking torque was 1.7 N · m. On the other hand, in the case where the protrusion 22 is formed in the peripheral portion of the punched hole 21 of the second plate member 2 as in the embodiment shown in FIG. 1, the breaking torque is increased to 2.6 N · m. Therefore, the screw tightening ability is remarkably improved by forming the protrusion 22 that contacts the peripheral portion 13 of the burring lower hole 11 of the first plate member 1 at the peripheral portion of the punching hole 21 of the second plate member 2. Confirmed to do.
In addition, each conditions of the board | plate materials 1 and 2, the packing 4, and the tapping screw 3 which were used by this breaking torque test are as follows.
First plate material 1: stainless steel, plate thickness 0.4 mm, inner diameter of burring pilot hole 11 3.2 mm, length of cylindrical portion 12 1.1 mm
Second plate material 2: stainless steel, plate thickness 0.6 mm, inner diameter 4.5 mm of the punched hole 21, and length of the protrusion 22 0.5 mm (the protrusion 22 is an embodiment)
Packing 4: Foamed resin material, thickness 2 mm (compressed to 0.5 mm after screw tightening), inner diameter 6 mm of hole 41
Tapping screw 3: Stainless steel, outer diameter of head 31 is 8 mm, height of head 31 is 3.5 mm, crest diameter of screw shaft 33 is 3.8 mm, trough diameter of screw shaft 33 is 3.2 mm, screw shaft 33 Screw pitch 1.6mm, screw shaft 33 length 10mm

In addition, this invention is not limited only to the said embodiment, A various change is possible within the range of the summary of this invention.
For example, as shown in FIG. 3, the protrusion 22 </ b> A may be formed in a tapered shape having a smaller diameter toward the tip end portion 23. In this case, the tapered protrusion 22A exhibits an elastic function, and the burring pilot hole 11 can be suppressed in the reduced diameter direction by the tip 23 of the protrusion 22A. Therefore, the breaking torque of the internal thread of the burring pilot hole 11 can be further increased, and the screw tightening ability can be further improved. Further, since the screw is firmly fixed by the reaction force of the elastic force of the tapered protrusion 22A, the effect of preventing the loosening of the tapping screw 3 is improved.

  As shown in FIG. 4, the base end portion of the burring pilot hole 11A of the first plate member 1 is formed in a taper shape, and the distal end portion 23 of the protrusion 22 of the punched hole 21 of the second plate member 2 is the burring pilot hole 11A. It is good also as a structure contact | abutted to the peripheral part 13a of the taper part 5 of this. In this case, the rigidity of the peripheral portion 13a of the burring pilot hole 11A can be increased by forming the base end of the burring pilot hole 11A of the first plate 1 in a tapered shape, and the protrusion of the punch hole 21 22 is in contact with the peripheral portion 13a of the tapered portion 5 of the burring pilot hole 11, so that the pulling force of the tapping screw 3 more reliably prevents the peripheral portion 13a of the tapered portion 5 of the burring pilot hole 11A from being deformed. be able to. Therefore, the breaking torque of the female screw of the burring pilot hole 11A can be further increased, and the screw tightening ability can be further improved.

Moreover, you may make it fasten the 1st board | plate material 1 and the 2nd board | plate material 2 with a screw | thread, without interposing the packing 4. FIG.
Moreover, a fastening object and / or a to-be-fastened part are not only board | plate materials, such as sheet metal, but structures, such as resin, may be sufficient.
Further, a female screw is engraved in the cylindrical portion 12 of the burring pilot hole 11 in advance, and a screw that can be screwed into the female screw of the burring pilot hole 11 is used instead of the tapping screw 3. Good.

1 First plate (fastened)
2 Second plate (fastened object)
3 Tapping screw 4 Packing 5 Tapered part 11 Burring pilot hole 12 Cylindrical part 13 Peripheral part 21 Perforated hole 22 Protrusion 23 Tip part 24 Seating surface 31 Head surface 32 Lower surface 33 Screw shaft 41 Hole

Claims (4)

A screw fastening structure in which a burring pilot hole is formed in a fastening object, and a screw is inserted into a burring pilot hole through a screw hole provided in the article to be fastened,
When the peripheral edge of the hole to be fastened is raised to form a protrusion, and the screw is screwed into the burring pilot hole, the tip of the punch hole is in contact with the peripheral part of the burring pilot hole. Screw fastening structure. The screw fastening structure according to claim 1,
The protrusion is a screw fastening structure formed in a tapered shape having a small diameter toward the tip. The screw fastening structure according to claim 1 or 2,
A screw fastening structure in which a base end portion of a burring pilot hole of a fastening object is formed in a tapered shape, and a tip end portion of a protruding hole of a fastening object comes into contact with a peripheral portion of a tapered portion of the burring pilot hole. In the screw fastening structure according to any one of claims 1 to 3,
A screw fastening structure in which a lower surface of a screw head is formed as a flat surface and presses a flat seating surface at a peripheral portion of a front-side punch hole that does not form a protrusion of a fastening object.

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