Screw for fastening synthetic resin material

Abstract

To provide a synthetic resin material fastening screw having a lock at a bow capable of obtaining large looseness torque.SOLUTION: A synthetic resin material fastening screw has a lock at a bow. A seating face of the bow is formed into an inverted-dish like tapered shape, and serration is formed at least on the outer periphery of the seating face. When fastened to a locking material, the outermost peripheral portion of the seating face of the serration comes into contact with the surface of the locking material, and a portion near the outermost periphery of the seating face of the serration bites into the locking material. Therefore, a torque loss is reduced, so as to obtain large axial force. When the screw is fastened, force is dispersed ton an entire seating face if the seating face has a planar shape. However, if it has a tapered shape, force due to axial force is concentrated only to the ring-like portion of the outermost periphery, and locking force due to serration is improved. Additionally, the ring-like portion is at the outermost peripheral position and has a distance from an axial center, so as to obtain large looseness torque.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a screw for fastening synthetic resin materials. More specifically, it relates to a screw for fastening synthetic resin materials having an anti-loosening feature on the head of the screw.

Background Art

[0002] In recent years, the outer casings of electronic devices and the like have come to be made of synthetic resin materials such as AS (acrylonitrile-styrene) resin and ABS (acrylonitrile-butadiene-styrene) resin. And, while fixing this resin outer casing to a metal frame or the like with a predetermined tightening torque, there has been a demand for a screw for fastening synthetic resin materials such that the screw does not loosen due to vibrations or impacts during transportation of the electronic device or the like, and as a result, the loosening torque does not significantly decrease.

[0003] Conventionally, as such a screw, generally, a washer-embedded screw (or a small screw with SW+PW embedded), which is called a sem screw (registered trademark) and in which a spring washer (SW) and a flat washer (PW) are incorporated into a socket screw, has been used. This washer-embedded screw incorporates washers and the like before rolling the thread so that the washers and the like do not fall off after rolling, and it does not require the labor of incorporating washers and the like manually, improving the work efficiency. And, when the screw is tightened, the spring washer is compressed to prevent loosening, and it is suitable for places where the screw is repeatedly removed. Incidentally, this washer-embedded screw is also defined in JIS (Japanese Industrial Standard JIS B 1188:2017).

[0004] However, in the washer-embedded screw, the spring washer and the flat washer are not fixed to the screw alone, and the flat washer and the like can move within the range incorporated into the screw. Also, the flat washers may overlap each other. Therefore, for example, when trying to align and supply the washer-embedded screw with an auto parts feeder in a factory or the like, there has been the inconvenience that it may get clogged in the auto parts feeder halfway. For such reasons, there has been a demand for a screw having an anti-loosening feature on the head of the screw instead of the washer-embedded screw.

[0005] As such a screw having a locking function on the head of the screw, there is a screw for fixing a resin member disclosed in Patent Document 1. This screw for fixing a resin member is a tapping screw with a cross hole having serrations on the seating surface in the embodiments shown in FIGS. 1 and 3, and is a screw for screwing into a member made of a resin material while cutting a thread to fix the resin member. And it has 18 serrations, and each serration has a locking surface located on the front end side along the tightening direction of the screw and formed substantially parallel to the axis, and an inclined surface formed to incline from the apex of this locking surface toward the rear end side along the tightening direction. If the positional relationship between this locking surface and the inclined surface is configured to be reversed in the same way as a screw having serrations on a general seating surface, there will be little resistance when tightening the screw, and after tightening, the locking surface will bite into the resin material and function as a locking device to prevent loosening.

[0006] Also, as such a screw, there is a bolt and nut disclosed in Patent Document 2. This bolt and nut has a plurality of ridges that curve along the thread groove direction radially provided on the lower surface of the head of the bolt or the upper surface of the nut that mates with it, and these ridges are formed to gradually increase in height from the inner side toward the outer peripheral side. When this bolt and nut is rotated and tightened, the ridges bite into the surface of the mating material. Here, since the cross-sectional shape of the ridge is substantially triangular and the tip is sharp, it bites in with a large force. And since the height of the ridge gradually increases from the inner side toward the outer peripheral side, a large torque acts on the outer peripheral side, a large force is locally applied, and it bites in deeper and is fixed, serving as a locking device to prevent loosening.

[0007] In addition, as a screw having a locking mechanism on the head of such a screw, there is a flange bolt disclosed in Non-Patent Document 1. This flange bolt has a conical collar called a flange on the seating surface side of the hexagonal head with a cross hole. On the seating surface side of this collar, there are serrations, and when these serrations bite into the mating material during fastening, the anti-loosening effect is improved. Also, the collar prevents the seating surface from sinking into the mating material. Note that the height of the peaks of these serrations is higher on the outer peripheral portion than on the inner peripheral portion. Furthermore, although this flange bolt has a conical collar called a flange, the conical shape is only for the upper surface portion of the collar, and the seating surface is flat, and the serrations are formed on this flat portion.

[0008] And, as such a screw, there is a spring-loaded collar screw disclosed in Patent Document 3. This spring-loaded collar screw is formed by integrally forming a reverse-dish-shaped spring-loaded collar on the lower peripheral edge of the head of the screw. And, this collar exhibits spring characteristics by obtaining an appropriate spring constant and deflection amount, and obtains sufficient tightening torque to prevent loosening.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0010]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] However, in the technology with the orientation of Patent Document 1 reversed, since the seating surface of the screw for fixing the resin member is flat, when the protruding height from the seating surface of the serration is the same for both the outer peripheral part and the inner peripheral part, the part from the outer peripheral part to the inner peripheral part of the serration comes into contact with the fastening surface, resulting in a large seating surface friction torque. Also, as the screw is tightened, the serration on the entire seating surface bites into the fastening surface. That is, not only the seating surface friction torque but also the biting torque due to the serration is generated.

[0012] As a result, large torque losses due to friction and biting occur, and since the seating surface friction torque and the biting torque in the total tightening torque increase, the axial force torque decreases, resulting in the disadvantage that the axial force decreases. Also, the serration in the inner peripheral part has the disadvantage that its effect on the loosening torque is low because the distance from the axis is small. Further, when the screw is tightened, since the entire seating surface comes into contact with the fastening surface, there is a disadvantage that the force due to the axial force applied to the seating surface is dispersed. In any case, a screw with serrations that can obtain a larger loosening torque has been demanded.

[0013] By the way, in this screw for fixing the resin member, serrations are provided on the flat seating surface, and the serrations are formed in a substantially radial pattern with respect to the axis. And the circumferential width of each serration is larger at the outer peripheral portion than at the inner peripheral portion. When the serrations are processed, the height of the serration peaks at the outer peripheral portion becomes higher and the depth of the valleys becomes deeper than at the inner peripheral portion. That is, the protrusion height of the serrations from the seating surface at the outer peripheral portion is larger than that at the inner peripheral portion.

[0014] In this case, when the screw is tightened, the serrations at the outer peripheral portion first bite into the fastening surface, and then the inner peripheral portion abuts against the fastening surface. And as the screw is tightened further, not only the outer peripheral portion but also the inner peripheral portion abuts against and bites into the fastening surface, resulting in a large seating surface friction torque and biting torque. As a result, the axial force torque decreases by the amount that the seating surface friction torque and biting torque in the total tightening torque increase, and there is a problem that the axial force decreases. And if the axial force decreases, there is a problem that the loosening torque also becomes small. Also, when the screw is tightened, since the entire seating surface abuts against the fastening surface, there is a problem that the force due to the axial force applied to the seating surface is dispersed.

[0015] Also, in the technique of Patent Document 2 as well, similar to the case of Patent Document 1, when the screw is tightened, not only the outer peripheral portion but also the inner peripheral portion abuts against and bites into the fastening surface, resulting in a large seating surface friction torque and biting torque, and there is a problem that it is difficult to obtain a large axial force. And if the axial force decreases, there is a problem that the loosening torque also becomes small. Also, when the screw is tightened, since the entire seating surface abuts against the fastening surface, there is a problem that the force due to the axial force applied to the seating surface is dispersed.

[0016] In addition, in the flange bolt of the technique of Non-Patent Document 1, serrations arranged substantially radially with respect to the axis are formed on the seating surface, and the protruding height of the serrations on the outer peripheral portion from the seating surface is larger than that of the inner peripheral portion. That is, similar to the case where the height of the serrations on the outer peripheral portion of Patent Document 1 is higher than that of the inner peripheral portion, when tightening the screw, not only the outer peripheral portion but also the inner peripheral portion comes into contact with and bites into the fastening surface, resulting in a large seating surface friction torque and biting torque, and the axial force decreases, which causes inconvenience. And if the axial force decreases, there is an inconvenience that the loosening torque also becomes small. Further, when the screw is tightened, since the entire seating surface comes into contact with the fastening surface, there is an inconvenience that the force due to the axial force applied to the seating surface is dispersed.

[0017] And in the technique of Patent Document 2, in order for the flange to exhibit spring properties by obtaining an appropriate spring constant and deflection amount, there is an inconvenience that materials and treatments for exhibiting spring properties, such as being formed by carburizing treatment on the surface with a cold heading carbon steel wire, are required. Furthermore, as described in paragraph 0050 of Patent Document 2, in order to obtain spring properties, there is an inconvenience that it is necessary to make the dimensions and size of the screw small or extremely small, such as the screw used in optical devices such as cameras and video cameras.

[0018] Here, consider the case where the shape of the screw described in Patent Document 2 is used, without using a material that exhibits spring properties and without treatment, and the material used is the same as that of a normal screw and the size is also the same as that of a normal screw. When fastening using such a screw, since the flange has no spring properties, it becomes a screw without anti-loosening. That is, it is possible to make a screw with a shape of the screw described in Patent Document 2 using a material without spring properties, but in that case, an inconvenience occurs in that, although it has a complex shape, it becomes a screw without anti-loosening and the loosening torque also becomes small.

[0019] An object of the present invention is to provide a synthetic resin material fastening screw having anti-loosening on the head of the screw, which can obtain a large loosening torque.

Means for Solving the Problems

[0020] In order to solve the above problems, the present invention adopts the following configuration.

[0021] The present invention relates to a screw for fastening a synthetic resin material, which includes a head having a tool engaging portion for rotating a screw, a screw portion integrally formed with the head, and a lock washer on the head. The seating surface of the head is formed in an inverted dish-shaped tapered shape, the seating surface has serrations, and when the serrations are cut in the circumferential direction, the cross-section is substantially in the shape of a saw blade, and the inclination angle is larger on the screw loosening direction side and smaller on the tightening direction side. The locking object is made of a synthetic resin material. When the screw for fastening the synthetic resin material is fastened to the locking object, the outermost peripheral portion of the seating surface of the serrations abuts against the surface of the locking object, and the portion near the outermost peripheral portion of the seating surface of the serrations is configured to bite into the locking object.

[0022] Further, the angle of the seating surface with respect to the plane is characterized in that it is 3 degrees or more and 10 degrees or less.

[0023] Further, the outer diameter of the head is near the outer diameter of a flat washer corresponding to the nominal diameter of the screw.

[0024] Further, the serrations are formed in a shape extending radially with respect to the axis.

[0025] Further, the screw for fastening the synthetic resin material is manufactured by transferring the serrated portion to a product formed by plastic processing.

[0026] Further, the serrations have a locking surface with a large inclination angle on the screw loosening direction side and an inclined surface with a small inclination angle on the tightening direction side, and the angle formed by the intersection of the locking surface and the inclined surface is substantially 90 degrees.

[0027] The inclined surface has an arc surface bulging in the direction of the locking object at least partially.

[0028] Further, it is characterized in that it has a flange in a shape of a substantially pan-shaped small screw.

[0029] And the head is characterized in that it is a head in a truss screw shape or a substantially binding screw shape.

Advantages of the Invention

[0030] According to the present invention, since it has the above-described features, the following can be achieved.

[0031] A screw for fastening a synthetic resin material, comprising a head having a tool engagement portion for rotating the screw, a screw portion integrally formed with the head, and having a lock washer on the head, wherein the seating surface of the head is formed in an inverted dish-shaped tapered shape, the seating surface has serrations, the serrations have a substantially saw blade-shaped cross section when cut in the circumferential direction, the inclination angle is larger on the screw loosening direction side and smaller on the tightening direction side, the locking object is made of a synthetic resin material, and when the screw for fastening the synthetic resin material is fastened to the locking object, the outermost peripheral portion of the seating surface of the serrations abuts against the surface of the locking object, and the portion near the outermost peripheral portion of the seating surface of the serrations is configured to bite into the locking object. Therefore, when the screw is fastened, since the seating surface is in a tapered shape, unlike a flat seating surface, only the ring-shaped portion at the outermost periphery of the seating surface and the serrations of that portion abut against and bite into the locking object, so that a large axial force can be obtained. Also, when the screw is tightened, if the seating surface is flat, the entire seating surface abuts against the locking object and the force is dispersed, but if there is a taper on the seating surface, the force due to the axial force concentrates only on the ring-shaped portion at the outermost periphery, so that the locking force by the serrations at the outermost periphery is improved. Moreover, since the ring-shaped portion is located at the outermost periphery, there is a distance from the axis, and a large loosening torque can be obtained.

[0032] Also, since the angle of the seating surface with respect to the plane is 3 degrees or more and 10 degrees or less, the inclination is gentle and there is little difference from the plane, and by forming the seating surface in an inverted dish shape exceeding 10 degrees, it is possible to prevent the process from becoming difficult or the product from becoming difficult to manufacture.

[0033] In addition, since the outer diameter of the head is near the outer diameter of the flat washer corresponding to the nominal diameter of the screw, it has been possible to easily replace it with a washer-embedded screw.

[0034] In addition, since the serration is formed in a shape extending radially with respect to the axis, it has been possible to make the die for creating the screw easy to manufacture.

[0035] In addition, since the screw for fastening synthetic resin materials is manufactured by transferring the serration portion to the one formed by plastic processing, it has been possible to make it easily manufacturable using the conventional technology.

[0036] In addition, the serration has a locking surface with a large inclination angle on the screw-returning direction side and an inclined surface with a small inclination angle on the tightening direction side, and the angle where the locking surface and the inclined surface intersect is formed at approximately 90 degrees. Therefore, when creating the die for transferring the serration portion, it has been made easier to cut out with a cutting tool or the like, and the creation of this die has been facilitated.

[0037] In addition, since the inclined surface has an arc surface bulging in the direction of the locking object at least partially, it has become possible to make the angle at which the serration abuts on the surface of the locking object a gentle angle close to the horizontal plane or the horizontal plane.

[0038] In addition, since it has a shape with a flange attached to a shape similar to a small pan screw, it has been possible to obtain a screw for fastening synthetic resin materials having a head with a shape similar to a small pan screw and having a flange.

[0039] And since the head is a head in a truss screw shape or a substantially bind screw shape, it has been possible to obtain a screw for fastening synthetic resin materials having a head in a substantially truss screw shape or a substantially bind screw shape.

Brief Description of the Drawings

[0040]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, when the head of the screw for fastening a synthetic resin material is upward and the screw part is downward, it will be referred to as the vertical direction. However, the front-back and up-down directions shown below are for convenience of explanation, and the present technology is not limited to and applied in these directions.

[0042] Here, the screw for fastening a synthetic resin material of the present invention is a screw for fastening a synthetic resin material having anti-loosening on the head of the screw. And the seat surface has an inverted dish-shaped taper shape, and is characterized in that serrations are formed on the taper-shaped seat surface. By making the seat surface taper-shaped, when the screw is tightened to the object to be locked, not the entire seat surface but the outermost peripheral portion of the seat surface and the serrations of that portion come into contact with and bite into the object to be locked.

[0043] That is, when the screw is tightened and the seat surface is flat, the entire seat surface abuts against the fastened object, and due to the serration biting in, a large seat surface frictional torque and biting torque are generated by the entire seat surface. On the other hand, in the screw for fastening synthetic resin materials of the present invention, the seat surface has a tapered shape and is inclined itself. Therefore, unlike the case where the seat surface is flat, only the round ring-shaped portion at the outermost periphery of the seat surface and the serration of that portion come into contact with and bite into the locked object. Therefore, the seat surface frictional torque and biting torque during screw fastening are smaller than those when the seat surface is flat. According to the Motosh formula showing the relationship between the tightening torque and the axial force described later, the decrease in the axial force is reduced, and as a result, a large axial force can be obtained. Also, when the screw is tightened, if the seat surface is flat, the entire seat surface abuts against the locked object and the force is dispersed. However, if there is a taper on the seat surface, the force due to the axial force concentrates only on the outermost peripheral ring-shaped portion, so the surface pressure increases and the locking force due to the serration at the outermost peripheral portion becomes large. That is, the serration in the ring-shaped portion is pressed against the locked object with a strong force and firmly bites and engages with the locked object, generating a large locking force. Moreover, since the ring-shaped portion is located at the outermost periphery, there is a distance from the axis, and a large loosening torque can be obtained. Then, the details of the screw for fastening synthetic resin materials will be described.

[0044] (First Embodiment) With reference to FIGS. 1 to 4, the screw 1 for fastening synthetic resin materials (screw for fastening synthetic resin materials) according to the first embodiment of the present invention will be described in detail.

[0045] FIGS. 1(A), (B), and (C) are perspective views showing the configuration of the head 2 (head) and the screw portion 3 (screw portion) of the screw 1 for fastening synthetic resin materials. FIG. 1(A) is a perspective view seen from the upper surface side, FIG. 1(B) is a perspective view seen from the lower surface side, and FIG. 1(C) is a partial enlarged view of part A in FIG. 1(B). Also, FIGS. 2(A), (B), and (C) are three views of the screw 1 for fastening synthetic resin materials. FIG. 2(A) is a front view, FIG. 2(B) is a top view, and FIG. 2(C) is a bottom view. Also, FIG. 2(D) is a cross-sectional view taken along line BB in FIG. 2(B).

[0046] As shown in FIGS. 1 and 2, at the center of the upper surface of the head 2 of the screw 1 for fastening synthetic resin materials, there is a cross-shaped hole as a screw rotation tool engaging portion 4 (tool engaging portion), and the head 2 has a shape of a substantially truss screw. The outer diameter of the head 2 is 5.3 mm when the screw diameter is M5, and it is formed to be the same as the outer diameter of the corresponding flat washer. In this way, the outer diameter of the head 2 is set to a value near the outer diameter of the corresponding flat washer in order to obtain a large-diameter seating surface and to enable easy replacement with a washer-embedded screw.

[0047] Further, the seating surface 5 (seating surface) of the head 2 is formed in an inverted dish-shaped taper shape with an angle of about 6 degrees with respect to the plane, and the seating surface 5 has 24 serrations 6 extending radially from the center portion. The height of the ridges of the serrations 6 is 0.13 mm when the screw diameter is M5. And each serration 6 has a locking surface 61 (locking surface) located on the rear end side with respect to the tightening direction of the screw on the side of the screw loosening direction and having a large inclination angle. Also, on the tightening direction side, it has an inclined surface 62 (inclined surface) formed at a gentle and small inclination angle from the ridge line of the locking surface 61 toward the front end side with respect to the tightening direction. That is, it is easy to tighten due to the inclined surface 62, and since the locking surface 61 bites in, it is difficult to loosen.

[0048] And the screw 1 for fastening synthetic resin materials is formed by first performing plastic working such as forging on a screw having a shape of a substantially truss screw with a taper-shaped seating surface 5 having an angle of about 6 degrees with respect to the plane. Next, it is formed by transferring the serration 6 portion, and then surface treatment is performed for manufacturing. Also, the material of the screw 1 for fastening synthetic resin materials is formed from the same steel material as ordinary screws, but of course, it may be made of other metals if necessary.

[0049] Here, as shown in FIG. 1(C), the locking surface 61 and the inclined surface 62 of each serration 6 are configured such that the surfaces thereof intersect at an angle of approximately 90 degrees. This is to facilitate the machining, such as cutting with a cutting tool, when creating a mold for transferring the serration 6 portion, thereby facilitating the creation of this mold. Further, when transferring the serration 6 portion, it functions in the same way as a draft angle in so-called injection molding, making it easier to create the locking surface 61. Of course, the angle of the locking surface 61 may be made steeper, for example, an angle parallel to the axis.

[0050] FIG. 3 is a cross-sectional view showing a state in which the screw 1 for fastening a synthetic resin material is fastened to a locking object 100 (locking object) made of a synthetic resin material. That is, the threaded portion 3 of the screw 1 for fastening a synthetic resin material is passed through the fastening hole 110 of the locking object 100 and screwed into the threaded hole 210 with burring provided on the frame 200 made of a metal plate, and is in a fastened state.

[0051] As shown in FIG. 3, when the screw 1 for fastening a synthetic resin material is rotated and tightened, since the seating surface 5 is formed in a tapered shape, only the outermost peripheral portion of the seating surface 5 abuts against the locking object surface 120 which is the surface of the locking object 100. Then, the ring-shaped portion near the outermost peripheral portion of the seating surface 5 of the serration 6 bites into the locking object surface 120, and the outermost periphery of the seating surface 6 abuts against the surface of the locking object 100. Here, the portion of the serration 6 at the outermost periphery of the seating surface 5 bites deepest into the locking object 100.

[0052] FIG. 4 is a photograph of the fastening mark 130 on the locking object surface 120 when the locking object 100 is an ABS (acrylonitrile-butadiene-styrene) resin plate with a thickness of 6 mm, the screw 1 for fastening a synthetic resin material is screwed with a predetermined torque using a nut, and then the nut is loosened and removed. As shown in the photograph of FIG. 4, the fastening mark 130 has an annular mark 140 which is a circular groove formed by the outermost peripheral portion of the seating surface 5 and recessed marks 150 which are 24 recesses formed by the serrations 6 at the outermost peripheral portion.

[0053] Thus, since the seat surface 5 is formed in an inverted dish-shaped taper, as shown in the photograph of FIG. 4, only the outermost peripheral portion of the seat surface 5 and the serration 6 of the outermost peripheral portion are pressed against and bite into the surface of the locking object 100 when tightening the screw. On the other hand, when the seat surface is formed in a flat planar shape, the entire seat surface and its serration will be pressed against the surface 120 of the locking object. Then, compared with the serration screw with a flat seat surface, when tightening the screw, the frictional torque of the seat surface 5 against the locking object and the biting torque by the serration 6 of the synthetic resin material fastening screw 1 are reduced. And when the frictional torque of the seat surface and the screw tightening torque are reduced during screw tightening, as will be described later, the axial force torque is improved.

[0054] Also, when the screw is tightened, if the seat surface 5 is planar, the entire seat surface 5 abuts against the locking object 100 and the force is dispersed. However, if there is a taper on the seat surface 5, the force due to the axial force concentrates only on the outermost peripheral ring-shaped portion. Therefore, the locking force by the serration 6 is improved. That is, the serration 6 at the outermost peripheral portion is pressed against the locking object 100 with a strong force, and the serration 6 firmly bites into the locking object 100, generating a large locking force. Moreover, since the ring-shaped portion is located at the outermost peripheral position, there is a distance from the axis. As a result, by using the synthetic resin material fastening screw 1 of the present embodiment, a large loosening torque can be obtained.

[0055] Incidentally, there may be a consideration that the effect of the outer peripheral portion biting deeply is the same as that of providing serrations 6 on the tapered seat surface 5 and that of providing serrations on the flat seat surface such that the ridges on the outer peripheral portion are higher than those on the inner peripheral portion. Here, in the case of the tapered one, since the seat surface itself has an angle, the serrations near the outer peripheral portion bite in at a large angle, and the ring-shaped portion at the outermost periphery of the seat surface 5 abuts against the surface of the locking object 100. On the other hand, in the case of the flat one, although it surely bites in from the serrations on the outer peripheral portion, eventually the entire seat surface abuts against and bites into the locking object, so as described above, a large difference occurs in the loosening torque. Also, there is a limit to forming the serrations of the flat one high. Note that a structure in which a tapered surface is provided on a part of the flat seat surface and serrations are provided thereon is also included in the present invention.

[0056] In addition, in the present embodiment, the angle of the seat surface 5 with respect to the plane is set to about 6 degrees, but it may be 3 degrees or more and 10 degrees or less. If it is less than 3 degrees, since the inclination is gentle, there is no difference from the plane, and if it exceeds 10 degrees, the process becomes difficult because the seat surface 5 is formed in an inverted dish shape, making it difficult to manufacture. Also, the angle of the seat surface 5 with respect to the plane may be 4 degrees or more and 8 degrees or less. If it is 4 degrees or more, the effect of the taper is further enhanced, and if it is 8 degrees or less, it becomes easier to manufacture.

[0057] In addition, the screw 1 for fastening the synthetic resin material is first formed by plastic working such as forging, and then the serration 6 portion is formed by transfer. This is to enable easy manufacturing using conventional techniques. Also, it is not limited to this. For example, when performing plastic working, it is of course possible to restrain the outermost peripheral portion of the head 2 and form it in a shape such that the outermost peripheral portion is cut with a cylindrical surface. And in this case, by providing the serration 6 up to the end of the seat surface 5, a larger loosening torque can be obtained.

[0058] In addition, in the above-described embodiment, the head 2 has a cross recess, but it goes without saying that it may have a minus-shaped grooved shape, a hexagonal recess, or a star-shaped hexagonal hexalobular recess, etc. Also, although the shape of the head is substantially that of a carriage bolt, it goes without saying that it may be shaped like a saucepan screw with a flange, a binding screw, a round screw, or a hexagonal flange bolt, etc.

[0059] Furthermore, the thread portion 3 of this embodiment shows the form of a normal screw, but it goes without saying that it is not limited to this and may be a tapping screw or the like. Also, it goes without saying that the length of the thread portion 3 may be made longer or shorter.

[0060] Moreover, the threads 6 in these embodiments are provided with 24 threads, but it goes without saying that this number may be changed, for example, to 16 threads, increased, or decreased. Also, for large screws, the number of threads 6 may be decreased, and for small screws, the number may be decreased to make it easier to manufacture.

[0061] Moreover, in this embodiment, the threads 6 extend radially from the center of the seating surface 5. The reason the bulging portion 7 extends from the center is that when fastening a locking object 100 made of a soft material such as a rubber sheet-like elastic body, for example, the seating surface 5 will deeply bite into the locking object 100. At this time, the bulging portion 7 near the center also bites into the locking object 100, and a greater anti-loosening effect can be obtained. However, it goes without saying that the threads 6 may not extend from the center, and no threads 6 may be provided at the center of the seating surface 5, but they may be provided starting from the middle or only near the outermost periphery of the seating surface 5. This is because when the locking object 100 is made of resin, a sufficient effect can be obtained.

[0062] Furthermore, the head 2 is a headed head, and the outer diameter of the flange portion 22 is set to be near the outer diameter of a flat washer corresponding to the screw diameter, but this flange may be made larger and wider. The wider flange not only prevents the seating surface from sinking into the locking object 100, but in the case of the present invention, the position where the bulging portion 7 bites in becomes farther from the axis of the screw, and a greater anti-loosening effect can be obtained. It is also effective in improving the axial force.

[0063] Also, in the case of this embodiment, although there is only one type of height of the serration 6, a second screw 1 for fastening a synthetic resin material with a higher height of the serration may be prepared. When there is a serration 6 on the seating surface 5, if the screw 1 for fastening the synthetic resin material is loosened after tightening and then removed, the surface of the locking object 100 is scraped off by the serration 6. Then, even if the same screw 1 for fastening the synthetic resin material is tightened again, since the surface of the locking object 100 has been scraped off, the serration 6 does not bite into the locking object 100, and sufficient loosening torque cannot be obtained. In such a case, when the second screw 1 for fastening the synthetic resin material is used, the serration 6 bites deeper into the surface of the locking object 100, so that sufficient loosening torque can be obtained again.

[0064] (Second Embodiment) Referring to FIGS. 5 and 6, a second embodiment of the present invention will be described. In this second embodiment, the shapes of the upper part of the head 2 and the seating surface 5 of the first embodiment are changed. Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted, and only the different parts will be described.

[0065] FIGS. 5(A), (B), and (C) are perspective views showing the configuration of the head 2 and the screw portion 3 of the screw 1 for fastening a synthetic resin material. FIG. 5(A) is a perspective view seen from the upper surface side, FIG. 5(B) is a perspective view seen from the lower surface side, and FIG. 5(C) is a partially enlarged view of part C in FIG. 5(B). Also, FIGS. 6(A), (B), and (C) are three views of the screw 1 for fastening a synthetic resin material. FIG. 6(A) is a front view, FIG. 6(B) is a top view, and FIG. 6(C) is a bottom view. Also, FIG. 6(D) is a cross-sectional view taken along line DD in FIG. 2(B).

[0066] As shown in FIGS. 5 and 6, the upper part of the head 2 has the same cross-shaped hole as in the first embodiment, but in this embodiment, it has the shape of a headed portion composed of a screw head 21 having a shape of a substantially pot-shaped small screw and a flange portion 22. The outer diameter of the head 2 is formed to be substantially the same as the outer diameter of the flat washer corresponding to the screw diameter. In any case, it is preferable that the outer diameter of the head 2 is in the vicinity of the outer diameter of the flat washer corresponding to the screw diameter. This is because it becomes possible to easily replace it with a washer-embedded screw.

[0067] Further, the seating surface 5 of the head 2 is formed in an inverted dish-shaped taper shape with an angle of about 6 degrees with respect to the plane, and the seating surface 5 has 16 serrations 6 extending radially from the center portion. The height of the serration 6 is 0.13 mm when the screw diameter is M5. And each serration 6 has a locking surface 61 located on the rear end side with respect to the tightening direction of the screw and formed substantially parallel to the axis, and an inclined surface 62 formed to incline at a gentle angle from the ridge line of this locking surface toward the front end side with respect to the tightening direction.

[0068] Here, since the serration 6 of this embodiment has 16 teeth, the number is reduced compared to the 24 teeth of the first embodiment, but the basic effects and the like are the same as those of the 24-tooth one. Also, in the case of 24 teeth, it becomes difficult to create a mold for forming the transfer of the serration 6 portion, especially for small screws such as M2, because the number of teeth is large, but in the case of 16 teeth, it becomes possible to easily create a mold from small screws such as M2 to relatively large screws such as M5. In any case, it becomes substantially the same as that of the first embodiment, and the state when fastened to the mating member 100 shown in FIG. 3 and the fastening mark 120 when removed shown in FIG. 4 are also the same, and the same effects will be exhibited, so the drawings and explanations thereof are omitted.

[0069] (Third Embodiment) Referring to FIGS. 7 and 8, a third embodiment of the present invention will be described. In this third embodiment, the shapes of the upper part of the head 2 and the seat surface 5 in the first embodiment are changed. In particular, the inclined surface 62 of the serration on the seat surface is changed from a planar shape to a substantially arc-shaped curved surface. Hereinafter, the same parts as those in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted, and only the different parts will be described.

[0070] Figs. 7(A), (B), and (C) are perspective views showing the configuration of the head 2 (head) and the screw portion 3 (screw portion) of the screw 1 for fastening synthetic resin materials. Fig. 7(A) is a perspective view seen from the upper surface side, Fig. 7(B) is a perspective view seen from the lower surface side, and Fig. 7(C) is a partially enlarged view of the E portion in Fig. 5(B). Also, Figs. 8(A), (B), and (C) are three views of the screw 1 for fastening synthetic resin materials. Fig. 8(A) is a front view, Fig. 6(B) is a top view, and Fig. 8(C) is a bottom view. Also, Fig. 8(D) is a sectional view taken along the line FF in Fig. 8(B), and Fig. 8(E) is a partially enlarged view of the G portion in Fig. 8(A).

[0071] As shown in Figs. 7 and 8, the upper part of the head 2 has a cross recess similar to that in the first embodiment. In this embodiment, however, it has a substantially hemispherical shape and is similar in shape to a button head screw or a truss head screw. The outer diameter of the head 2 is formed to be substantially the same as the outer diameter of a flat washer corresponding to the screw diameter. This is because it can be easily replaced with a screw with a built-in washer.

[0072] As shown in Figs. 7(B), (C) and Figs. 8(D), (E), the surface at the position connecting the valleys of the serrations 6 of the head 2 is formed in an inverted dish-shaped taper shape with an angle of about 6 degrees with respect to the plane. On the seat surface 5, 16 ridges extending radially from the center are formed, and the height of the ridges is 0.2 mm. Each serration 6 is formed with a locking surface 61 having a large angle located on the rear end side with respect to the tightening direction of the screw, and an inclined surface 62 having a substantially arc-shaped curved surface located on the front end side. In this embodiment, the surface at the position connecting the valleys will be referred to as the seat surface 5.

[0073] As shown in Fig. 8(E), when each serration 6 is viewed from the outer peripheral side of the screw head 21, a locking surface 61 having an angle of approximately 70 degrees with respect to the seating surface 5 indicated by the two-dot chain line, and an inclined surface 62 having a substantially arc-shaped surface formed so as to bulge from the top of the ridge toward the locking object side are formed. That is, this inclined surface 62 is an example of a surface having an arc-shaped surface that bulges at least partially in the direction of the locking object.

[0074] Here, since the inclined surface 62 near the top of the ridge of the serration 6 is a horizontal plane or a gently sloping surface close to the horizontal plane, there is no angle, so the locking force decreases. However, the seating surface 5 has a taper, and the outermost peripheral portion of the serration 6 bites into the surface 120 of the locking object at the taper angle, so a predetermined locking force is ensured. Also, because there is a gentle surface, it becomes easier to slide, and the seating surface friction torque and biting torque during screw fastening are further reduced, the decrease in axial force is less, and the effect of improving the axial force occurs.

[0075] Although the locking surface 61 has been described as having an angle of approximately 70 degrees with respect to the seating surface 5, it is not limited to this, and it goes without saying that the angle of the locking surface 61 can be made steeper, for example, an angle parallel to the axis.

[0076] Incidentally, products fastened with the screw 1 for fastening synthetic resin materials are transported, stored, unloaded, and used in hot places to cold places, inside automobiles, containers, etc. Also, at that time, they are subjected to many vibrations and impacts. Under such severe conditions, an experiment and measurement were conducted to see if the screw 1 for fastening synthetic resin materials has sufficient loosening torque or slackening torque and can be used, and the results are reported below.

Example

[0077] Vibration was applied in a vibration test after a heat cycle test, and then the loosening torque was measured, and the results are reported. That is, we examined whether the screw 1 for fastening synthetic resin materials according to the first embodiment of the present invention can correspond to a washer-incorporated screw (or a small screw with SW+PW incorporated), which is called a Sems screw and is a small pot screw with a spring washer and a flat washer incorporated. Also, for comparison, a small pot screw and a screw with only a taper (Comparative Example 1), and a tapered screw with a bulging portion (Second Invention Product) were added, and actual experiments and measurements were conducted. Note that as the screw 1 for fastening synthetic resin materials, which is the product of the present invention, a tapered screw with 24 threads according to the first embodiment was used, which has a head portion 21 with a shape of a small pot screw and a washer-attached head shape composed of a flange portion 22.

[0078] As the screw with only a taper (Comparative Example 1), a screw having a tapered seating surface 5 formed by plastic working was used without transferring the serration 6 portion, and a tapered screw without serration 6 was created for the screw 1 for fastening synthetic resin materials and used in this test. Also, as the tapered screw with a bulging portion (Second Invention Product), it was filed as Japanese Patent Application No. 2022-206497 by the applicant of the present application, or its domestic priority application Japanese Patent Application No. 2023-134986, and a screw having a plurality of bulging portions provided on the seating surface of the tapered screw was used. This Second Invention Product is characterized in that when the screw is tightened and then loosened, it does not scrape or whiten the surface of the locking object 100 like a serration. Details of the Second Invention Product will be described later.

[0079] First, five pieces each of a small pot screw, a washer-incorporated screw (SW+PW incorporated small screw), the Comparative Example 1 which is a tapered screw without serration 6, the Second Invention Product, and the screw 1 for fastening synthetic resin materials which is the product of the present invention, all of M5×12, were prepared. Then, these screws were fixed to a 6-mm-thick ABS resin plate with a drilled pilot hole using an M5 hex nut with a tightening torque of 15 kgf·cm to prepare test pieces for this experiment.

[0080] Then, as a heat cycle test, these test pieces were placed in an environment of -20°C over 10 minutes from room temperature, held for 60 minutes, placed in an environment of 80°C over 25 minutes, and held for 60 minutes, and then left at room temperature for 24 hours or more. Next, as a vibration test, vibration was applied to each of the XYZ axes by a vibration testing machine. That is, vibration was applied for 3 hours in the X-axis direction (vertical direction), and for 1.5 hours each in the Y-axis direction (left-right direction) and the Z-axis direction (front-back direction). Then, a loosening test was conducted. For this loosening test, a PC torque analyzer (registered trademark) manufactured by Vectorix Co., Ltd. and a screw torque graphic analysis system were used. Incidentally, the subsequent tightening tests and loosening tests were also conducted using the same equipment.

[0081] The data of the results of the loosening test involving this vibration test are shown in Table 1 of Fig. 9. As shown in Table 1 of Fig. 9, first, in the case of the small flange screw, compared with the washer-inserted screw, the loosening torque (TL) is small and the loosening work amount (EL) is also small. This is presumably because the diameter of the head of the screw is small and the seating surface is flat, so the frictional force between the seating surface of the screw and the surface of the locking object 100 becomes small, resulting in the screw being loosened significantly by vibration. In any case, it is inappropriate to use the small flange screw as an alternative to the washer-inserted screw.

[0082] Next, when the locking screw is the washer-inserted screw, the loosening torque (TL) is larger than that in the case of the small flange screw. This is presumably because the diameter and area of the flat washer in contact with the surface of the test piece are large, and the frictional force with the surface of the test piece is large. However, the loosening torque with respect to the tightening torque is small. Incidentally, the reason why the loosening work amount (EL) is very large is presumably that due to the spring force of the spring washer, after the screw is loosened once, the work amount is increased to prevent the screw from loosening further and falling off. And in order to be used as an alternative to the set screw, it is necessary to be at least larger than this loosening torque (TL).

[0083] In the case of the tapered screw of Comparative Example 1, the loosening torque (TL) is better than that of the pot small screw, but less than half that of the washer-embedded screw. This is because although the outer diameter of the tapered screw is larger than that of the pot small screw, due to the taper on the seating surface 5, only the portion near the outermost periphery is in contact with the surface of the locking object 100, resulting in a small frictional force. Therefore, it is considered that this is the reason why the screw loosened significantly due to vibration. In any case, it is inappropriate to use the tapered screw as an alternative to the washer-embedded screw.

[0084] In the case of the tapered screw with a bulging portion of the second invention product and the serrated tapered screw of the present invention product, the loosening torque (TL) is very large, more than twice in Comparative Example 2 and about four times in the present invention product, compared with the washer-embedded screw. Also, for the loosening torque with respect to the tightening torque, in the second invention product, approximately half or more of the torque remains, and in the present invention product, it only slightly decreases. That is, from this experiment, the second invention product and the present invention product can be used as alternatives to the washer-embedded screw. Also, as data after applying heat cycle and vibration, it is considered that they have sufficient values.

Example

[0085] In Example 1, vibration was applied by a vibration test after the heat cycle test. In Example 2, after the same heat cycle test, instead of the vibration test, an impact was applied by an impact resistance test, and the results are reported. This time, the pot small screw was not measured, and experiments and measurements were actually conducted using a washer-embedded screw (or a small screw embedded with SW+PW), a screw with only a taper (Comparative Example 1), a tapered screw with a bulging portion (second invention product), and the screw 1 for fastening synthetic resin materials of the present invention.

[0086] First, five pieces each of M5×12 of the washer-embedded screw (or a small screw embedded with SW+PW), Comparative Example 1, the second invention product, and the present invention product were prepared. Then, these screws were fastened and fixed to a 6-mm-thick ABS resin plate with a drilled pilot hole using an M5 hexagonal nut with a tightening torque of 15 kgf·cm to prepare test pieces for this experiment.

[0087] First, as a heat cycle test, in the same manner as in Example 1, these test pieces were placed in a -20°C environment over 10 minutes from room temperature, held for 60 minutes, placed in an 80°C environment over 25 minutes, and held for 60 minutes, and then left at room temperature for 24 hours or more. Next, as an impact resistance test, impacts of 50G, 100G, and 500G were applied to the test pieces in the X-axis, Y-axis, and Z-axis directions of the screw, that is, in the up-down, left-right, and front-back directions, respectively, using an impact tester. Then, a loosening test was conducted thereafter. The data of the results of this loosening test are shown in Table 2 of FIG. 10. Here, the maximum torque required to loosen the screw was compared with the tightening torque during tightening, and how much it loosened as a result of the test was expressed as a loosening rate.

[0088] As shown in Table 2 of FIG. 10, first, in the case of the locking screw being a washer-embedded screw (or a small screw with SW+PW embedded), the loosening torque with respect to the tightening torque is small, and the loosening rate is large. This is considered to be the influence of the impact test. In order to replace the washer-embedded screw, at least, it is necessary to be smaller than the loosening rate of this loosening torque (TL) and have less loosening.

[0089] In the case of the screw with only a taper in Comparative Example 1, although the loosening rate drops significantly from -41% to -28%, it shows a good value compared to the washer-embedded screw. The screw with only a taper showed a bad value in the test involving the vibration test of Example 1, but showed relatively good results in the test involving the impact test.

[0090] In the case of the tapered screw with a bulging portion of the second invention product, the loosening rate is about -10%, which is an extremely good value without even comparing it with the value of the washer-embedded screw. As a result of the impact test, it was found that the bulging portion of the seating surface of the second invention product effectively acts against the loosening of the screw.

[0091] In the serrated tapered screw of the product of the present invention, the loosening rate is from 18% to 34%, and the loosening torque when the screw is loosened is greater than the tightening torque when the screw is tightened. Moreover, the ratio is larger when it is 500G. It is considered that by applying an impact, the serration bites deeper into the surface of the locking object and results in such values. That is, from the results of this experiment, it is considered that the second invention product and the product of the present invention can be substituted for the washer-embedded screw. Also, it is considered that the value is sufficient for use in fastening products.

[0092] Thus, in the screws for fastening synthetic resin materials of the second invention product and the product of the present invention, a much larger loosening torque (TL) is obtained than that of the washer-embedded screw, and it is difficult to loosen. Furthermore, it eliminates the problems in the production site of the washer-embedded screw. Therefore, it was confirmed that the screw for fastening synthetic resin materials of the product of the present invention can replace the washer-embedded screw.

[0093] The tapered screw with a bulging part of the second invention product and the serrated tapered screw of the product of the present invention are provided with a plurality of bulging parts, serrations, that is, protruding parts at least on the outermost peripheral part of the seating surface of the tapered screw. It can be seen that the unevenness on the outermost peripheral part has a long distance from the axis of the screw, and it is easy to obtain a large torque. However, considering that this large loosening torque (TL) is obtained, it is thought that it may be related to the axial force when the screw is tightened, and an experiment was conducted in Example 3 next.

Example

[0094] As Comparative Example 2, a commercially available screw with serrations and a flat seating surface described in Non-Patent Document 1 was obtained, and an experiment was conducted to compare it with the serrated tapered screw of the product of the present invention and is reported. The height of the serration peaks is 0.3 mm for the commercially available screw of Comparative Example 2, which is larger than 0.13 mm for the product of the present invention. Also, the height of the serration peaks is higher on the outer peripheral part than on the inner peripheral part. First, as an axial force test, the tightening axial force when these screws were tightened with a predetermined torque was measured, and the results were summarized in Table 3 of Fig. 11. Then, the loosening torque was measured and summarized in Table 4 of Fig. 12.

[0095] As shown in Table 3 of Fig. 11, the tightening axial force when tightened with a predetermined tightening torque was measured. As a result, the tightening axial force of a commercially available screw with a serration and a flat seat surface in Comparative Example 2 was about 0.65 kN, while that of the tapered screw with a serration of the present invention was about 1.1 kN. The product of the present invention obtained a tightening axial force about 70% larger.

[0096] Also, as shown in Table 4 of Fig. 12, when the loosening torque was measured, a larger value was obtained for the loosening torque than the tightening torque for both screws. The loosening torque of a commercially available screw with a serration and a flat seat surface in Comparative Example 2 was about 19.4 kgf·cm, while that of the tapered screw with a serration of the present invention was about 29.6 kgf·cm. The product of the present invention obtained a loosening torque about 50% larger. That is, the product of the present invention had a tightening axial force about 70% larger and a loosening torque about 50% larger than that of Comparative Example 2.

[0097] Generally, in the case of a screw with a serration and a flat seat surface, since the seat surface is flat, many serrations can be installed on both the outer peripheral part and the inner peripheral part, and the serrations can bite deeply into the fastening surface. Therefore, it is considered that a large loosening torque can be obtained. On the other hand, in the tapered screw with a serration of the present invention, since the seat surface is tapered, only the outermost peripheral part of the seat surface contacts the fastening surface in a circular ring shape with a predetermined width, and only the serrations in this part bite into the fastening surface. At first glance, it seems that the number of serrations biting into the seat surface also decreases, so the loosening torque also decreases. However, as a result of the experiment, the screw of the present invention with fewer serrations biting in obtained a larger loosening torque.

[0098] First, consider why the axial force of Comparative Example 2 is lower than that of the product of the present invention. First, in Comparative Example 2, as the screw is tightened, since the seating surface is flat, not only the outer peripheral portion but also the inner peripheral portion comes into contact with and bites into the fastening surface, so it is considered that a large seating surface frictional torque and biting torque are generated over the entire seating surface. On the other hand, in the product of the present invention, as the screw is tightened, since the seating surface is tapered, it comes into contact with and bites into the surface of the locking object only at the outermost peripheral portion of the seating surface and the round ring-shaped portion of the serration at that portion, rather than the entire seating surface. Therefore, it is considered that the frictional torque and biting torque of the seating surface are reduced.

[0099] Then, it is considered that the seating surface frictional torque and biting torque of Comparative Example 2 are larger than those of the product of the present invention. Here, there is an equation called the Motosh's equation that shows the relationship between the tightening torque and the axial force. According to this equation, the total tightening torque applied from the outside can be decomposed into three components: the frictional torque on the seating surface, the frictional torque on the screw surface, and the axial force torque. Among these three torques, the frictional torque on the screw surface is considered to be constant. Then, when the seating surface frictional torque increases, the axial force torque decreases, and as a result, the axial force decreases. Conversely, when the seating surface frictional torque decreases, the axial force torque increases, and as a result, the axial force increases. And when there is serration on the seating surface, in addition to the seating surface frictional torque, the torque reduction due to the serration biting into the fastening surface is also added. So, the torque reduction by the seating surface is the combined action of these seating surface resistance torques. And in this case, in Comparative Example 2, it is considered that this seating surface resistance torque acts greatly and the axial force decreases.

[0100] Next, consider the relationship between the axial force and the loosening torque. In Comparative Example 2, when the screw is tightened, since the seating surface 5 is flat, the entire seating surface 5 comes into contact with the locking object 100 and the force is dispersed, so the force pressing the serration 6 on the entire seating surface 5 against the locking object 100 becomes weak. On the one hand, in the product of the present invention, since the seating surface 5 has a taper, the force due to the axial force is concentrated only on the outermost peripheral ring-shaped portion, and the locking force by the serration 6 is improved. That is, the serration 6 in the ring-shaped portion is pressed against the locking object 100 with a strong force, and the serration 6 bites firmly into the locking object 100, generating a large locking force. Moreover, since the ring-shaped portion is located at the outermost periphery, there is a distance from the axis, and it is considered that a large loosening torque can be obtained.

[0101] (Second invention product) Here, the tapered screw with a bulging portion, which is the second invention product used in this experiment, will be described with reference to FIG. 13. In this second invention product, the shape of the seating surface 5 of the first embodiment is changed, and the shape of the head 2 is made into the shape of the second embodiment. Hereinafter, the same parts as those in the first embodiment or the second embodiment are denoted by the same reference numerals, and the description thereof is omitted, and only the different parts will be described.

[0102] As shown in FIG. 11(A), the upper part of the head 2 has a cross hole similar to that of the first embodiment, but has a shape of a headed portion composed of a screw head 21 having a shape of a substantially pot-shaped small screw and a flange portion 22 similar to that of the second embodiment. The outer diameter of the head 2 is formed to be substantially the same as the outer diameter of the flat washer corresponding to the screw diameter. This is because it can be easily replaced with a washer-embedded screw.

[0103] As shown in FIG. 11(B), the seating surface 5 of the head 2 is formed in an inverted dish-shaped taper, and the seating surface 5 has six bulging portions 7 with a predetermined width that bulge downward and extend radially from the center portion. The circumferential cross-section of the portion with the predetermined width of the bulging portion 7 is formed in a substantially arc shape continuous with the seating surface 5, and the tip portion at the outer peripheral portion also has an arc surface.

[0104] Here, the angle of the reverse dish-shaped tapered seating surface 5 with respect to the plane is approximately 6 degrees. Also, when the diameter of the threaded portion 3 is 5 mm, the bulging surface of the portion with a predetermined width is a large arc surface with a radius of approximately 5 mm, and it is a substantially arc-shaped surface that bulges with a large radius.

[0105] As shown in FIG. 11(C), the foremost end portion of the outer peripheral portion of the bulging portion 7 is shaped as if it is cut by the outermost peripheral surface continuous from the upper surface of the head 2. And at the outermost peripheral portion of the bulging portion 7, a bulging tip portion 8 that bulges downward from the seating surface 5 is formed.

[0106] Thus, since the seating surface 5 is formed in a reverse dish-shaped tapered shape, the six bulging portions 7 at the outer peripheral portion far from the axis of the screw bite into the locking object 100, so it serves as a loosening prevention with a large torque. And the outermost peripheral portion of the seating surface 5 is brought into contact with the surface of the locking object, and the axial force is firmly held. In this way, a screw for fastening a synthetic resin material capable of obtaining an axial force while preventing loosening of the screw was obtained.

[0107] Also, since the portion of the bulging portion 7 facing the locking object 100 is formed in a substantially arc shape, the loosening prevention force is weaker than that of serration with claws, but by forming the seating surface 5 in a reverse dish shape, sufficient loosening prevention could be achieved. Also, since the portion biting into the surface of the locking object 100 when the screw is fastened is formed in a substantially arc shape, it is possible to prevent the surface of the locking object from being scraped and whitened when the screw is loosened.

[0108] Here, in the bulging portion 7 of the second invention product, it is the shape of six bulging portions 7 with a predetermined width that bulge downward and extend radially from the central portion, and the circumferential cross-section of the portion with the predetermined width is formed in a substantially arc shape continuous from the seating surface 5, and the tip portion at the outer peripheral portion also has an arc surface. However, since only the outer peripheral portion of the bulging portion 7 actually contacts and bites into the locking object 100, for example, it may be in the shape of a substantially elliptical bulging portion 7 or the number of bulging portions 7 may be increased further.

[0109] Then, regarding the product of the present invention and the second invention product, as a higher-level concept combining the two, it can also be expressed as follows. A screw for fastening synthetic resin materials, comprising a head having a tool engaging portion for rotating the screw, a screw portion integrally formed with the head, and having a lock washer on the head. The seating surface of the head is formed in an inverted dish-shaped taper, and at least the outermost peripheral portion of the seating surface has a protruding portion. The locking member is made of a synthetic resin material. When the screw for fastening synthetic resin materials is fastened to the locking member, the portion near the outermost periphery of the seating surface abuts and bites into the surface of the locking member, and the outermost peripheral portion of the seating surface abuts against the surface of the locking member so that an axial force can be obtained. The protruding portion is configured to be locked by biting into the locking member.

[0110] With such a configuration, when the screw is fastened, since the seating surface has a tapered shape, not the entire seating surface but only the outermost peripheral portion of the seating surface and the uneven portions in the vicinity thereof abut and bite into the locking member. The seating surface friction torque and biting torque during screw fastening are smaller than those of a flat seating surface, and the decrease in axial force is reduced. As a result, a large axial force can be obtained. Due to this large axial force, the serration at the outermost periphery of the seating surface, which is at a large distance from the axis, bites into the abutting object, and a large loosening torque can be obtained by this synergistic effect.

[0111] The screw for fastening synthetic resin materials of the present invention is not limited to the embodiments described above and shown in the drawings, and various modifications can be made without departing from the gist thereof. For example, in the above description, the locking member is made of a synthetic resin material. However, for example, it can also be used for laminated steel plates or vinyl steel plates in which resin is coated on the surface of a zinc-plated steel plate or the like, which are used in outdoor units of air conditioners and the like. Also, for example, it can of course be used for those made of soft metals such as aluminum or copper.

Explanation of Reference Numerals

[0112] 1 Screw for fastening synthetic resin materials 2 Head 21 Screw head 22 Flange part 3 Thread part 4 Screw rotation tool engagement part 5 Seat surface 6 Serrations 61 Locking surface 62 Inclined surface 7 Bulge part 100 Locking object 110 Fastening hole 120 Locking surface 130 Fastening mark 140 Annular mark 150 Recessed part mark 200 Frame 210 Screw hole

Claims

1. A screw for fastening synthetic resin materials, comprising a head portion having a tool engagement portion for rotating the screw, and a threaded portion formed integrally with the head portion, the head portion having a locking mechanism, The seat surface of the head is formed in an inverted dish-like tapered shape, At least an outer periphery of the seat is formed with serrations protruding toward the fastener. The serration has a generally sawtooth cross section when cut in the circumferential direction, and is formed with an inclination angle that is larger on the screw return direction side and smaller on the screw tightening direction side, The fastener is made of a synthetic resin material, When the synthetic resin fastening screw is fastened to the fastening object, the outermost periphery of the seating surface of the serration is brought into contact with the surface of the fastening object, and the portion of the serration near the outermost periphery of the seating surface is configured to bite into the fastening object. A synthetic resin fastening screw characterized by:

2. The angle of the seat surface with respect to the plane is 3 degrees or more and 10 degrees or less.

2. The screw for fastening synthetic resin materials according to claim 1.

3. The outer diameter of the head is close to the outer diameter of the flat washer that corresponds to the nominal diameter of the screw.

3. The screw for fastening synthetic resin materials according to claim 2.

4. The serrations are formed in a shape extending radially from the axis.

4. The screw for fastening synthetic resin materials according to claim 3.

5. Synthetic resin fastening screws are manufactured by transferring the serrations onto a piece formed by plastic processing.

5. The screw for fastening synthetic resin materials according to claim 4.

6. The serration has a locking surface with a large inclination angle on the screw return direction side and an inclined surface with a small inclination angle on the screw fastening direction side, and the angle at which the locking surface and the inclined surface intersect is formed at approximately 90 degrees.

6. The screw for fastening synthetic resin materials according to claim 1.

7. The inclined surface has at least a part of an arcuate surface that bulges toward the fastener.

6. The screw for fastening synthetic resin materials according to claim 1.

8. The head is substantially in the shape of a pan head screw with a flange.

6. The screw for fastening synthetic resin materials according to claim 1.

9. The head is a truss screw-shaped or substantially bind screw-shaped head.

6. The screw for fastening synthetic resin materials according to claim 1.

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