Thin-thickness metal plate massage cut screw and structure having the same

Abstract

To secure high fastening rigidity and a retention effect by effectively using a burring part, in a thin-thickness metal plate massage cut screw.SOLUTION: By combining and selecting a relation among a valley diameter D1 (and an outside diameter D2), a shape of a screw thread 5, an inclination angle θ6 of a pursuer flank 9, an inclination angle θ7 of a leading flank, and a pitch P (or a maximum width E2 of the screw thread 5 and a width E1 of a valley part) by making them associated with a plate thickness T of a deck plate 15 (base), a burring part 20 (21a) of the deck plate 15 is stretched to the pursuer flank 9 while pushing the burring part into the valley part 10 without a clearance. Since the burring part 20 (21a) is stretched to the pursuer flank 9 in a non-deformable state in the valley part 12, a high retention effect can be improved while securing high withdrawal resistance (fastening rigidity).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a compression screw for thin metal plates and a structure constructed using the same. Here, the thin metal plate refers to a metal plate (steel plate, stainless steel plate, aluminum plate, etc.) with a thickness of 1.4 mm or less. The structure is equipped with a thin metal plate to which a workpiece is fixed with a compression screw, and includes, for example, the roof, ceiling, and walls of a building, various devices and equipment, etc. [Background technology]

[0002] Many buildings use steel plate substrates with a thickness of about 1 mm as the substrate (base material), and it is common to fasten insulation materials, plywood materials, etc. to the substrate with self-drilling screws. For example, waterproof sheets and insulation materials are fastened to the top surface of the deck plate (folded plate) that constitutes the roof and ceiling of a building with drill screws or welded screws, and insulation materials and interior materials are fastened to pillars and beams made of C-shaped steel or other shaped steel with drill screws or welded screws. It is also common to fasten metal fittings and other components to plate materials with drill screws or welded screws.

[0003] As described above, self-drilling screws that drill pilot holes in a base include drill screws with a drill portion at the tip (e.g., Patent Document 1) and cut-off screws with a tapered tip (e.g., Patent Documents 2 to 4). Cut-off screws penetrate into a base by spreading it, so there is a limit to the thickness of the base that can be used, and generally, they are often used when the plate thickness of the base is 1.2 mm or less.

[0004] Drill screws and cut-off screws are used differently depending on the application and function, but the functional (action) differences are that with drill screws, the generation of swarf is unavoidable as the base material is cut, whereas cut-off screws are less likely to generate swarf, and that while with drill screws it is difficult to form a burred portion in the base material, cut-off screws can form a burred portion with a large protruding dimension.

[0005] The generation of swarf and the function of forming a burred portion are two sides of the same coin. With a milling screw, the base is pushed open by the tapered portion to open the pilot hole, so basically no swarf is generated, and the pushed-out portion remains as a burred portion, so a burred portion with a large protruding dimension can be formed (in the case of a drill screw, if the drill diameter is smaller than the root diameter, the inner edge of the pilot hole will deform into a cylindrical shape, but the degree of this is so slight that it cannot actually be called a burred portion).

[0006] Drill screws and tamper-evident screws are widely used in the construction industry, but when renovating or repairing roofs or ceilings, for example, if the ceiling substrate is exposed inside the room, using drill screws can cause chips to fall into the room, soiling the room or causing the user to step on the chips and injure their feet. For this reason, drill screws are often used in new construction, and tamper-evident screws are used in renovations and repairs (of course, tamper-evident screws are sometimes used in new construction). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7103677 [Patent Document 2] Patent No. 6467319 [Patent Document 3] Patent No. 4204905 [Patent Document 4] JP 2011-256971 A Summary of the Invention [Problem to be solved by the invention]

[0008] One of the features of the compression thread is that it can form a burring part with a large protruding dimension as described above. As for the relationship between the burring part and the thread, it is generally recognized in the screw industry that the greater the engagement of the thread with the burring part, the higher the fastening strength. Therefore, in the case of compression threads for thin metal plates, the thread pitch is narrowed so that the valleys (grooves) between adjacent threads in the axial direction have a triangular cross section, thereby improving the engagement of the thread with the burring part. However, the reality is that narrowing the thread pitch hardly improves the loosening prevention effect.

[0009] Considering this point, it is believed that the burred portion formed on the base by the thread cut-off screw is not a neat cylinder, but is actually cracked, and therefore the thread is screwed in while the burred portion is in a state of elastic deformation (bending deformation), and the frictional resistance between the thread and the burred portion is low. As a result, if the thread loosens even slightly, the frictional resistance drops sharply and the loosening progresses rapidly.

[0010] On the other hand, in Patent Documents 2 to 4, a band-shaped valley surface exists between axially adjacent threads, and therefore the threads with a (triangular) cross-sectional shape and the grooves with a trapezoidal cross-section form a double helix. However, these configurations are not inferior in fastening strength or anti-loosening effect compared to cases where the thread pitch is reduced and the valleys are formed into a triangular cross-sectional shape.

[0011] Considering the current situation, it can be understood that what is necessary to improve the anti-loosening function and fastening strength of a compression thread is to use the burring portion to strongly tension the base material against the threaded portion.

[0012] The present invention was made based on such knowledge and consideration, and has as its object to provide a compression cutting screw for thin metal plates that has excellent loosening prevention effect and fastening strength. [Means for solving the problem]

[0013] The present invention includes various configurations, typical examples of which are specified in each claim. The invention of claim 1 relates to a thread cutting screw, "A threaded screw for fixing a workpiece to a thin metal plate substrate with a thickness of 1.4 mm or less, The screw has a shaft portion having a tapered portion formed at the tip end side and a remaining straight portion, a head portion provided at the base end of the shaft portion, and a screw thread rising from the tapered portion and extending to the straight portion, A band-shaped valley surface is exposed between adjacent threads, and the valley portion has a trapezoidal cross section, A burring portion is formed in the base by the expanding action of the tapered portion, and the screw thread is screwed into the inner peripheral portion of the base including the burring portion. This is the basic structure.

[0014] And, in claim 1, in the above basic configuration, "The plate thickness of the base, the pitch, root diameter, and shape of the thread are set so that, with a part of the thread of the straight portion biting into the inner peripheral portion of the base, at least a part of the inner peripheral portion of the base is pressed into the root portion and braced against the following flank of the thread." It has the following characteristics:

[0015] In order for the burred portion of the base to press against the trailing flank of the thread, it is necessary that at least a part of the inner circumference of the base fills the root of the thread, and therefore the volume of the burred portion and the volume of the root are closely related, but while the volume of the burred portion (amount generated) is closely related to the root diameter of the thread, the volume of the root is closely related to the pitch of the thread and the shape of the thread (angle of the trailing flank and angle of the leading flank). Therefore, by selecting the root diameter, pitch, angle of the trailing flank, and angle of the leading flank based on the plate thickness of the base, the burred portion can be pressed against the trailing flank of the thread.

[0016] Regarding the plate thickness of the base and the pitch of the thread, if the pitch P of the thread is smaller than the plate thickness T of the base, the burred portion will protrude from the valley (groove) of the thread, causing a gap between the burred portion and the inner surface of the valley, and the tension of the burred portion against the valley will be reduced. Therefore, it is a necessary condition for the pitch P of the thread to be larger than the plate thickness of the base in order to tension the burred portion against the following flank. On the other hand, if the pitch P of the thread is too large compared to the plate thickness T of the base, the burred portion will have play inside the valley, and the burred portion will not be able to fill the valley. Therefore, there is an upper limit for P in relation to T.

[0017] In addition, since the burred portion is formed by expanding the base, the volume of the burred portion is roughly equal to the planar area of ​​the root portion of the thread multiplied by the plate thickness of the base (in reality, the volume of the threads equal to the plate thickness is also added), but a certain dimension is required for the root diameter to ensure the strength of the shank.

[0018] In light of these circumstances, claim 2 states: "In the straight portion, the root diameter is set to 3.5 times or more the plate thickness of the base, and the pitch of the thread is set in the range of 1.5 to 3.5 times the plate thickness of the base." The following configuration is adopted.

[0019] Since the present invention is mainly aimed at bracing the burred portion of the base against the trailing flank, the angle of the trailing flank is important. In terms of suppressing loosening, the smaller the included angle between the cross section passing through the apex of the crest and the trailing flank, the better. However, if this included angle is too small, a gap will be formed between the valley and the burred portion, and the bracing of the burred portion may be insufficient. In addition, the angle of the crest must be large enough to maintain the necessary strength.

[0020] Taking these circumstances into consideration, claim 3 states the following regarding the thread: "The thread has a ridge angle of 40 to 45°, an included angle between the cut surface passing through the apex of the thread and the trailing flank of 12 to 17°, and an included angle between the cut surface and the leading flank of 25 to 30°." The following configuration is adopted.

[0021] The invention of claim 4 is a specific example of claim 3, "In the straight portion, the maximum axial width of the thread is approximately the same as the width of the root surface." The structure is as follows.

[0022] The invention of claim 5 is also a specific example of claim 3, "At least in the thread of the straight portion, a plurality of groups of notches are formed in the thread, the groups being spaced apart in the circumferential direction and interspersed in the axial direction by cutting the thread." The structure is as follows.

[0023] The invention of claim 6 is also a specific example of claim 3, "By setting the root diameter, pitch and shape of the thread so that the volume of the burred portion of the base is larger than the volume of one revolution of the root portion, the burred portion is allowed to press against the trailing flank of the thread over the entire circumference." The structure is as follows.

[0024] The invention of claim 7 is directed to a structure including a base, a workpiece, and a threaded joint. "A method for manufacturing a thin metal plate cutting screw according to any one of claims 1 to 6, a base having a thickness of 1.4 mm or less into which the cutting screw is screwed, and a workpiece fixed to the base by the cutting screw, The base is formed with a thickened inner peripheral portion that is expanded in the plate thickness direction and includes the burred portion, and at least a portion of the thickened inner peripheral portion is pressed into the valley portion while the thread bites into it, and is pressed against the trailing flank of the thread. The structure is as follows. Effect of the Invention

[0025] As mentioned above, the burred portion formed on the base is not a perfect cylinder, and in reality, cracks exist and it is bent and deformed, so even if a female thread is formed on the burred portion, it does not generate high friction resistance like when a normal bolt and nut are engaged. Therefore, even if multiple threads are engaged with the burred portion, it is difficult to expect high fastening force or anti-loosening effect.

[0026] In contrast, in the present invention, the burring portion is pressed against the trailing flank of the thread by utilizing the elastic restoring force and the tensile force caused by screwing, so a large frictional force can be generated between the inner peripheral portion including the burring portion and the root portion, thereby ensuring a higher fastening strength than conventional friction threads.

[0027] One of the suitable targets for the present invention's welded thread is a deck plate, which is often 0.6 to 1.2 mm thick, and other steel plate substrates are often similar in thickness to the deck plate. The welded thread used for this type of thin metal plate substrate often has a root diameter of about 4 to 6 mm, but by adopting the configuration of claim 2, it is possible to ensure strength while using it on substrates of normal thickness, and the root portion can be made large enough to accommodate the burring portion. Therefore, it is highly practical.

[0028] The workpiece that overlaps the base is often also made of metal plate, but in this case, there are cases where the workpiece has a pilot hole, and cases where the workpiece does not have a pilot hole and is drilled with a thread cutter. In the latter case, the workpiece and base can be drilled even if the layer thickness between the workpiece and base is, for example, about 2 mm, and in this case, since the workpiece and base can be enclosed in the valley, the pitch of the thread is allowed to be up to about 3.5 times the thickness of the base.

[0029] As mentioned above, the shape and angle of the thread are important factors in terms of the bite of the thread into the base material and the effect of preventing loosening. When the numerical values ​​of claim 3 are selected for the thread, first, by setting the thread angle to 40 to 45°, the strength required for the thread can be maintained while maintaining good bite of the thread into the base material.

[0030] Now, if the following flank is leaning too far toward the cut surface, the angle between the following flank and the valley surface becomes too small, and gaps will be created between the burred portion and the following flank and valley surface, which may result in a decrease in the tensioning force of the burred portion. Conversely, if the following flank is raised too far away from the cut surface, the axial component of the frictional force generated by the screwing will decrease, resulting in a problem of reduced loosening prevention function and pull-out resistance.

[0031] In contrast, if the included angle between the cut surface and the following flank is set to 12 to 17° as in claim 3, the burring portion can be filled into the valley portion while preventing the following flank from falling over too much, thereby achieving a high loosening prevention effect and pull-out resistance.

[0032] The present invention aims to achieve a high anti-loosening effect by tensioning the burred portion of the base against the following flank of the thread, but in order to properly achieve this effect, the burred portion that penetrates into the root portion needs to have a certain degree of strength so as to provide strong resistance (tensioning force) against unscrewing, and therefore it is important to strike a balance between the volume of the root portion and the volume of the thread.

[0033] In this regard, if the maximum width of the thread and the width of the root face are set to be approximately the same as in claim 4, the volume of the root part can be made approximately three times the volume of the thread, and the burring part pressed into the root part can be made to have strong resistance against pull-out and unscrewing. Therefore, the effect of preventing loosening and the effect of improving the pull-out strength can be improved.

[0034] Now, when the tapered portion is screwed in, the base deforms to form a burred portion and the thread bites in, but the deformation includes plastic deformation and elastic deformation, and the present invention effectively utilizes elastic deformation to push the burred portion against the following flank. When a notch is formed in the thread as in claim 5, the burred portion enters (escapes) into the notch due to the elastic restoring force, and when the screw is unscrewed, the material that has entered the notch gets caught in the notch, preventing loosening.

[0035] Therefore, by adopting claim 5, the loosening prevention effect can be further improved, which is preferable. In this case, if the notch line is inclined in the opposite direction to the screwing direction (backward), the surface of the notch facing the screwing direction presses the protrusion of the burring part that has entered the notch against the tip side, thereby increasing the resistance to unscrewing. Therefore, the loosening prevention effect can be promoted.

[0036] By adopting the configuration of claim 6, the burring portion braces against the following flank over a wide range without causing a one-sided contact phenomenon, so that the effect of increasing the pull-out resistance and the effect of preventing loosening can be further improved. [Brief description of the drawings]

[0037] [Figure 1] 1A is a cross-sectional view of the first embodiment in use, FIG. 1B is an enlarged view of FIG. 1A, FIG. 1C is a cross-sectional view taken along line CC of FIG. 1B, and FIG. 1D is a view of another example of a notch. [Diagram 2] 2A is an enlarged view of the main parts of FIG. 1A and FIG. 2B, FIG. 2B is a diagram showing a cross section of the thread, FIG. 2C is a diagram showing the state of the notch, and FIG. 2D is an enlarged view of the notch area. [Diagram 3] 1A is a diagram of another example of usage, FIG. 1B is a front view showing the appearance of the burring portion, FIG. 1C and FIG. 1D are partial longitudinal sectional front views of comparative examples, and FIG. 1E is a partial front view of the comparative example. [Figure 4]1A is a partial front view of the screw, FIG. 1B is a schematic cross-sectional view of the burring portion, FIG. 1C is a schematic development of the burring portion, and FIG. 1D to FIG. 1O are bottom views showing the state of the burring portion at the location corresponding to FIG. 1A. [Diagram 5] FIG. 11 is a cross-sectional view showing a state in which thin metal plate workpieces are stacked in use. [Figure 6] FIG. 13 is a diagram showing a second embodiment, in which (A) is an overall view showing a state of use, and (B) is an enlarged view of a main part. [Figure 7] 1 is a graph showing resistance to unscrewing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] (1) Screw structure Next, an embodiment of the present invention will be described with reference to the drawings. A thread cutter (hereinafter, simply referred to as a "thread") is manufactured from a metal bar such as a steel wire or stainless steel wire, and as shown in Figures 1(A) and (B), has a shaft portion 1 with a tapered portion 2 at the tip end and a straight portion 3 at the other portion, and a head 4 integrally formed at the base end (other end) of the shaft portion 1, and a single thread 5 is formed on the shaft 1, which starts from the very end of the tapered portion 2 and continues to the straight portion 3. The tapered portion 2 and the thread 5 are integrally formed by rolling using a die.

[0039] The end of the thread 5 is located halfway through the straight portion 3, but the range in which the thread 5 is provided in the straight portion 3 can be set arbitrarily. The portion of the straight portion 3 where the thread 5 is not formed remains the same as the material diameter.

[0040] The head 4 is a countersunk head with a tapered seating surface that narrows downward, and the top surface is formed with a square, cross or other shaped engagement groove (recess) 6 into which a driver bit (not shown) engages. The head 4 can be selected from a variety of types, such as a hexagonal head, pan head, or flat head, depending on the application.

[0041] As shown in Fig. 2(A), the tapered portion 2 is set to two stages, a first tapered portion 2a located on the tip side and a second tapered portion 2b located on the base end side. The spread angle θ1 of the first tapered portion 2a is set to about 32° (30 to 34°), and the spread angle θ2 of the second tapered portion 2b is set to about 22° (20 to 24°). Therefore, the spread angle θ1 of the tapered portion 2 is larger on the tip side.

[0042] The tip of the tapered portion 2 is a bullet-shaped round tip, but may be a pointed tip or a flat tip. The thread 5 starts from the tip of the tapered portion 2, and naturally, the height gradually increases. The spread angle θ3 of the thread 5 at the first tapered portion 2a is larger than the spread angle θ1 of the first tapered portion 2a, and the spread angle θ4 of the thread 5 at the second tapered portion 2a is larger than the spread angle θ2 of the second tapered portion 2b. Note that it is an essential condition that θ3 is larger than θ1 in order to gradually increase the height of the thread 5, but θ4 and θ2 may be the same.

[0043] In the straight section 3, the thread 5 has a thread surface at the ridge line but is basically triangular (mountain-shaped) in cross section, whereas in the tapered section 2, the height gradually increases, making the cross section trapezoidal.

[0044] 2(B) clearly shows the cross-sectional shape of the thread 5. In the straight portion 3, the angle θ5 of the thread is set to approximately 42° (40 to 45°), the included angle θ6 between the cut surface O2 perpendicular to the axis O1 and the trailing flank 9 is set to approximately 15° (13 to 18°), and the included angle θ7 between the cut surface O2 and the leading flank 10 is set to approximately 27° (25 to 30°).

[0045] In this embodiment, the pitch P of the thread 5 is set to about twice the maximum width E2 of the thread 5 in the axial direction. Therefore, a strip-shaped valley surface (valley bottom surface) 11 exists on the shaft portion 1, and the valley portion (groove) 12 has a trapezoidal cross section. The width E1 of the valley surface 9 and the maximum thickness E2 of the thread 5 are almost the same dimension (strictly speaking, E1 is slightly larger than E2). Therefore, the volume of the valley portion 12 is about three times the volume of the thread 5. Since the thread angle θ5 is about 42° and a thread surface is formed on the ridgeline, the height H of the thread is slightly larger than the maximum width E2 of the thread 5, but if the thread surface is not formed on the ridgeline, the height H of the thread 5 and the maximum width E2 would be almost the same.

[0046] 1(A) and 1(B), the thread 5 has a V-shaped notch (cutout) 13 in a plan view, which is spaced apart from one another in the circumferential direction. In this embodiment, eight notches 13 are formed at equal intervals in the circumferential direction. The notches 13 are arranged in a line that tilts backwards in the screwing direction. The depth of the notches 13 is set to about half the height H of the thread 5.

[0047] As shown in Fig. 1(C), notch 13 has a symmetrical shape in a plan view, but as in the modified example shown in Fig. 1(D), it is possible to set a cut surface including the axis as O3, and make the included angle θ8 between first surface 13a on the front side in the screwing direction and O3 smaller than the angle θ9 between second surface 13b on the rear side in the screwing direction and O3. The included angle θ8 may be 0.

[0048] (2) Usage and basic functions 1(A) and (B), the screw of this embodiment can be used to fasten insulation material 16 to a deck plate 15 that constitutes the roof of a building. The insulation material 16 is held down by the screw head 4 via a circular disk 17. The insulation material 16 is covered with a waterproof sheet 18.

[0049] In the figure, the waterproof sheet 18 is overlaid on the disk 17, but in this case, a resin layer is formed on the upper surface of the disk 17, and the waterproof sheet 18 is welded to the disk 17. There are also cases where the disk 17 is overlaid on the waterproof sheet 18 from above, in which case the disk 17 is covered from above with a resin patch material that is welded to the waterproof sheet 18.

[0050] As described above, the thickness T of the deck plate 15 is often in the range of about 0.6 to 1.2 mm. Therefore, the dimensions of each part of the screw in this embodiment are set to accommodate this plate thickness. As an example of specific dimensions, the root diameter D1 is set to about 4.6 mm, the outer diameter of the crest is set to 6.8 mm (nominal diameter is 7 mm), the root width E1 is set to about 1.1 mm, and the maximum width E2 of the crest is set to about 1.0 mm. In the drawing, the thickness T of the deck plate 15 is shown as 1.0 mm.

[0051] In installation, when the screw is rotated with a driver tool and pressed against the installation location, first the shank of the screw enters the insulation material 16, then the tip of the screw reaches the deck plate 15 and the tip of the tapered portion 2 bites into the deck plate 15, and the deck plate 15 is then spread apart by the tapered portion 2, causing the thread 5 to be screwed into the pilot hole formed in the deck plate 15 by the tapered portion 2. Then, when the head 4 hits the disk 17, resistance increases and the screwing (fastening operation) ends.

[0052] The expanding action of the tapered portion 2 forms a burring portion 20 in the deck plate 15. The state in which the burring portion 20 is generated is shown diagrammatically in Figures 4(D) to (O). In Figure 4(B), the burring portion 20 is shown as being formed as a complete cylinder, however, since the burring portion 20 is formed by expanding a circular plate of the deck plate 15 with an outer diameter of the root diameter D1, it is not a complete cylinder, and has an uneven shape as shown diagrammatically in Figure 4(C) when expanded.

[0053] Therefore, as shown as a comparative example in Figure 3 (E) , in the case where the burring portion 20 merely protrudes below the deck plate 15, even if multiple threads 5 are embedded in the burring portion 20, the burring portion 20 will easily collapse outward and deform as shown by arrow 21, so that high frictional force between the threads 5 and the burring portion 20 cannot be expected and the fastening strength is low. Furthermore, when an external force for unscrewing the screw is applied due to vibration or the like, the screw will easily rotate, and in reality there is almost no anti-loosening effect.

[0054] Therefore, even if the pitch of the threads 5 is reduced to increase the grip of the threads 5 on the burring portion 20, no anti-loosening effect can be expected. Furthermore, since the pilot hole has a continuous closed inner circumference within the thickness of the deck plate 15, if multiple stages of the threads 5 bite into the pilot hole within the thickness of the deck plate 15, a reasonable level of fastening strength (pull-out resistance) and anti-loosening effect can be achieved, but in this case it is difficult to say that the burring portion 20 can be effectively used.

[0055] As described above, the burring portion 20 is formed by expanding a disk having the same outer diameter as the root diameter D1. Therefore, the volume of the burring portion 20 is theoretically the volume of a disk having the same outer diameter as the root diameter D1 [π×(D3 / 2) 2 × T]. Also, if it is assumed that it is formed into a perfect cylinder, the volume of the burred portion 20 is the value obtained by multiplying the circumference of the wall thickness center D3 of the cylinder by the plate thickness T and the protruding dimension, but as described above, the burred portion 20 does not become a perfect cylinder.

[0056] And because the burring portion 20 is formed by the tapered portion 2 of the thread, it basically protrudes in the screwing direction, but because the deck plate 15 is also pushed towards the head 4 by the pressing action of the threads 5, the entire burring portion 20 does not necessarily protrude towards the tip side, and depending on the resistance of the threads 5, it may bulge towards the head side as well, as shown in Figure 2(A). In other words, the burring portion 20 may be a composite of a tip side protruding portion 20a and a head side protruding portion 20b.

[0057] Fig. 3(A) shows the state where the entire burred portion 20 protrudes toward the tip. When the insulation material 16 is fixed as in the construction example of the embodiment, the material of the deck plate 15 does not resist escaping upward, so it can be said that the burred portion 20 is likely to swell upward. There is variation in the way the burred portion 20 is generated, but it is self-evident that it protrudes significantly toward the tip.

[0058] In this embodiment, the pitch P is set to about twice the plate thickness T, so that the burring portion 20 fits snugly into at least a portion of the valley portion and is set to press against the following flank 9. In other words, the dimensions of each portion are selected so that the volume of the burring portion 20 formed in the deck plate 15 is larger than the volume of one revolution of the valley portion 12 in the thread, and the burring portion 20 is set so that almost the entire circumference is pressed into the valley portion 12 with no gaps.

[0059] More specifically, when the tapered portion 2 pushes the deck plate 15 apart, the deck plate 15 undergoes a combined deformation of plastic and elastic deformation, forming a burring portion 20 and drilling a pilot hole. First, due to the elastic restoring force of the deck plate 15, the valley portion 12 is embraced by the inner periphery of the deck plate 15, including the burring portion 20.

[0060] Then, when the head 4 of the screw presses the disk 17 and fastening is completed, the shank 1 (thread 5) is pulled upward as shown by the white arrow in Fig. 2(A), so that the leading flank 9 of the thread 5 and the leading end protrusion 20a of the burring portion 20 push against each other strongly. That is, the leading end protrusion 20a of the burring portion 20 is pressed into the valley portion 12 and cannot escape to the outside, and the leading end protrusion 20a of the burring portion 20 pushes against each other strongly.

[0061] As a result, a strong frictional force is generated between the tip end protrusion 20a of the burring portion 20 and the trailing flank 9, providing high fastening strength (pull-out resistance). Also, since the tip end protrusion 20a of the burring portion 20 and the valley portion 12 are confined in an undeformable state, even if an external force in the return direction acts on the thread due to vibration or the like, the frictional resistance is not reduced by that level of external force, providing a high anti-loosening effect.

[0062] Since the burring portion 20 is formed by expanding the tapered portion 2, basically no cutting chips are generated. This is an advantage that drill screws do not have.

[0063] In Figure 2 (A), the state in which the deck plate 15 has a thickness of 1.2 mm is shown by a dotted line. If the deck plate 15 has a thickness T of 1.2 mm, the thickened inner circumferential portion including the burring portion 20 can be pressed tightly into the two-stage valley portion 10 and braced against the following flank 9, thereby significantly increasing the fastening strength (pull-out resistance) and the anti-loosening effect.

[0064] The graph in Fig. 7 shows the results of an unscrewing resistance test of the embodiment when used on steel plates having thicknesses T of 0.6 mm, 0.8 mm, 1.0 mm, and 1.2 mm. In other words, the relationship between the unscrewing angle and the resistance (back torque) is shown. The comparative example is an example in which the tip-side protrusion 20a of the burring portion 20 enters the valley portion but does not protrude into the following flank 9, and the thickness of the steel plate was 0.8 mm.

[0065] Even with a thickness of 0.6 mm, the product of this embodiment has a higher resistance to unscrewing than the conventional product that is used with a thickness of 0.8 mm, and this shows the anti-loosening performance of this embodiment.Moreover, it can be seen from Figure 7 that the product of this embodiment has a higher initial resistance to an external force when unscrewing than the conventional product, which means that the product is less likely to start loosening even when an external force such as vibration is applied to unscrewing, and has a high function of continuing to maintain the fastened state, and can be highly evaluated at construction sites.

[0066] (3) Features of Usage and Embodiment As described above, the burring portion 20 is not formed into a neat cylinder but has projections and recesses, but in this embodiment, as shown in Fig. 3(B) as a schematic, the tip-side protrusion 20a of the burring portion 20 has a crack 22 and is pressed into the valley portion 12 as a whole (confined with no escape route), so that the tip-side protrusion 20a of the burring portion 20 does not collapse outward (in the radial direction) and deforms, but remains braced against the following flank 9. Therefore, loosening is prevented and high fastening strength can be maintained.

[0067] 3(C) shows, as a comparative example, a state in which the included angle θ6 between the cut surface O2 of the shaft portion 1 and the following flank 9 is several degrees (10 degrees or less). In this way, when the following flank 9 is tilted significantly toward the cut surface O2, it contributes to increasing the pull-out resistance, but because the angle between the following flank 9 and the valley surface 11 becomes too close to an acute angle, the tip-side protrusion 20a of the burred portion 20 cannot be entirely pressed against the following flank 9 and the valley surface 11, and a gap 23 is likely to be formed between the inner surface of the valley portion 12 and the burred portion 20.

[0068] Then, the frictional resistance between the valley portion 12 and the burring portion 20 decreases, and the material of the tip side protrusion 20a constituting the burring portion 20 escapes into the gap 23 and deforms, so that the fastening strength (pull-out resistance) decreases and the resistance to the external force of unscrewing decreases. In other words, the tip side protrusion 20a of the burring portion 20 is deformed and pressed into the valley portion by the pressing action caused by screwing in the screw, but if the following flank 9 is inclined too far toward the cross-section surface O2, the tip side protrusion 20a cannot be deformed to fit closely to the corner of the valley portion 12, and the gap 23 is formed, so that high fastening strength and anti-loosening effect cannot be achieved.

[0069] On the other hand, in the comparative example shown in Fig. 3(D), the included angle θ6 between the cut surface O2 and the trailing flank 9 is set to about 30°, and in this case, the angle between the valley surface 11 and the trailing flank 9 is a large obtuse angle, so that the tip end protrusion 20a of the burring portion 20 can be firmly deformed and brought into close contact with the corner of the valley portion 10. However, in this case, the trailing flank 9 is raised too much, so that the axial component F2 of the pulling force F1 caused by the screwing is reduced, and the pull-out resistance is reduced and the anti-loosening effect is also reduced. In addition, the tip end protrusion 20a of the burring portion 20 is easily released outward (radially), which also reduces the anti-loosening effect.

[0070] In contrast, when θ6 is set to 12 to 17° as in the embodiment, the tip side protrusion 20a of the burring portion 20 is firmly deformed to fill the corner of the valley portion 10, while maintaining a high axial resistance, thereby ensuring high pull-out resistance and anti-loosening effect.

[0071] The inner circumference of the deck plate 15 is thickened due to the presence of the burred portion 20, and therefore the deck plate 15 has a thickened inner circumference including the burred portion 20 (20a, 20b). In this embodiment, the thread 5 bites into the thickened inner circumference, while a portion of the thickened inner circumference is pressed into the valley portion 12 and braces against the following flank 9. The biting action of the thread 5 and the bracing action of the thickened inner circumference provide high fastening strength (pull-out resistance) and an anti-loosening effect.

[0072] When a notch 13 is formed in the thread 5 as in this embodiment, a part of the tip side protrusion 20a enters the notch 13 in the fully screwed state, as shown in Figures 2(C) and (D). That is, a protrusion 20c that enters the notch 13 is generated in the tip side protrusion 20a of the burring portion 20. It can be said that the generation of the protrusion 20c is performed by the elastic restoring force of the tip side protrusion 20a and the pressing of the tip side protrusion 20a by the following flank 9. And, because the protrusion 20c of the burring portion 20 enters the notch 13, the notch 13 acts as a resistance against the external force of unscrewing, thereby promoting the anti-loosening effect.

[0073] In this case, when the notch 13 is tilted to the opposite side to the screwing direction as in the embodiment, as shown by arrow 24 in Fig. 2(D), the perpendicular line of the first surface 13a facing the unscrewing direction faces the tip side of the lead line of the thread 5, so that when the first surface 13a tries to rotate in the unscrewing direction, the first surface 13a presses the protrusion 20c of the burring portion 20 downward (towards the tip side), which acts to promote the meshing of the notch 13 and the protrusion 20c. This increases the resistance to unscrewing and promotes the anti-loosening effect.

[0074] Since the thread 5 is inclined with respect to the axis, even if the line of the notches 13 is formed parallel to the axis, the perpendicular line 24 of the first surface 13a faces downward with respect to the lead line of the thread 5, but by inclining it backward with respect to the screwing direction as in the embodiment, the inclination of the first surface 13a can be made larger, and the anti-loosening effect can be increased. As shown in Fig. 1(D), by reducing the included angle θ8 between the first surface 13a of the notch 13 and O3, the hooking ability of the burring portion 20 with the protrusion 20c can be improved, further promoting the anti-loosening effect.

[0075] In Figures 4(D) to (O), the generation status of the burring portion 20 is shown in plot form, and by comparing these (D) to (O), it can be seen that the resistance per unit cross-sectional area (or unit volume) of the tapered portion 2 increases the closer it is to the tip.

[0076] That is, the ratio of the cross-sectional area of ​​the tapered portion 2 to the volume (or bottom area) of the burring portion 20 increases toward the tip of the tapered portion 2. Therefore, if the angle of the tapered portion 2 is too small, the tapered portion 2 will be torn off due to resistance. On the other hand, if the taper angle is too large, the amount of deformation per unit length becomes too large, which increases the burden on the worker.

[0077] Therefore, when designing the tapered portion 2, it is necessary to provide a strength that allows the tapered portion 2 to penetrate into a substrate of the maximum expected thickness without tearing, and to minimize the resistance to penetration. In this regard, as in this embodiment, by configuring the tapered portion 2 with a first tapered portion 2a and a second tapered portion 2b, and setting the spread angle θ1 of the first tapered portion 2a to be larger than the spread angle θ2 of the second tapered portion 2b, and setting θ1 to approximately 32° (30 to 34°), it is possible to prevent the tapered portion 2 from breaking during the initial to middle stages of penetration, while making the length of the tapered portion 2 as long as possible and minimizing the screw-in resistance.

[0078] (4) Other examples and embodiments In the example of use in Fig. 5, a lower plate 25 made of a thin steel plate is placed on the deck plate 15, and a heat insulating material 16 is placed on the upper surface of the lower plate 25. Therefore, the lower plate 25 is the workpiece, but the heat insulating material 16 is fixed to a laminate consisting of the lower plate 25 and the deck plate 15. Then, since both the burred portion 26 of the lower plate 25 and the burred portion 20 of the deck plate 15 can be braced against the following flank 9 while filling the root portion 12 of the thread, extremely high fastening strength and anti-loosening effect can be enjoyed.

[0079] In this case, since the burred portion 26 is also formed in the lower plate 25, there is a limit to the overall plate thickness of the lower plate 25 and the deck plate 15 in order to form an appropriate burred portion 20 in the deck plate 15. That is, firstly, there is a limit to the thickness of the laminate in terms of the force required to press a screw against the laminate and break through it to push it apart.

[0080] Considering this point, the lower plate 25 and the deck plate 15 are not integrated, and in reality, it is normal for there to be a gap between the two during the drilling process, so the process is such that the lower plate 25 is slightly drilled before drilling the deck plate 15 begins, and drilling of the deck plate 15 usually begins after the drilling torque for the lower plate 25 has decreased, so that even if the overall thickness is greater than about 1.4 mm, it is possible to drill both. Even in the case of steel plate, if the overall thickness is about 2 mm, it is estimated that the fastening work can be done by hand.

[0081] Another problem is that the burred portion 20 of the deck plate 15 is also pushed out by the burred portion 25 of the lower plate 25, and therefore there is a limit to the overall plate thickness of the laminate in order to keep the burred portion 20 of the deck plate 15 pressed into the valley portion 10 without spreading it outward; however, this can be addressed by increasing the pitch of the threads 5.

[0082] In the second embodiment shown in Fig. 6, the head 4 of the screw is formed in a hexagonal shape with a flange, and is used to fasten a workpiece 27 made of a plate material such as a steel plate to a deck plate 15 (or other substrate). Therefore, the length of the screw is shorter than that of the first embodiment, and the thread 5 extends to below the neck. A recess 28 is formed in the bearing surface of the head 4.

[0083] In this embodiment, no pilot holes are drilled in the workpiece 27, and the screw threads 5 are screwed into the laminate consisting of the workpiece 27 and the deck plate 15, and the deck plate 15 is pulled upward by the screw, thereby fixing the workpiece 27 to the deck plate 15.

[0084] 6, by forming recess 28 in the seating surface, the deformed portion of workpiece 27 can be allowed to escape into recess 28, thereby preventing burring portion 29 of workpiece 27 from protruding downward and preventing burring portion 20 of deck plate 15 from spreading outward too much. This ensures that burring portion 20 of deck plate 15 is pressed into valley portion 12, maintaining high fastening strength and anti-loosening effect.

[0085] Pilot holes may be pre-drilled in the work 27. If the work 27 is a metal fitting, it is generally the case that pilot holes are pre-drilled from the beginning. In this case, since no burring portion is formed in the work 27, even if the deck plate 15 is relatively thick, the burring portion 20 can be pressed into the valley portion 10 to maintain high fastening strength and anti-loosening effect.

[0086] Although the embodiment of the present invention has been described above, the present invention can be embodied in various other ways. For example, in the embodiment, the screw dimensions are set to correspond to thicknesses of 0.6 to 1.2, but it is also possible to prepare a plurality of screw threads with different dimensions corresponding to various plate thicknesses. As already mentioned, it can be used for various purposes. The number of notches can be selected arbitrarily according to the outer diameter of the thread, etc. It is also possible to form the notches in a posture that leans forward in the screwing direction. The tapered portion can also be formed into a rounded bullet shape as a whole. [Industrial Applicability]

[0087] The present invention can be embodied in a cutter screw and a structure using the same, and therefore can be used industrially. [Explanation of symbols]

[0088] O1 axis center O2 cross section 1-axis 2 Tapered section 2a First tapered section 2b Second taper section 3 Straight section 4 head 5 Threads 9 Thread follower flank 10 Thread Lead Flank 11 Valley face 12 Valley 13 Notches 13a 1st page 15 Deck plate as an example of a base 16 Insulation as a workpiece 17 Disks constituting the work and structure 18 Tarpaulin 20 Burring part of deck plate 20a Tip side protrusion 20b Proximal protrusion

Claims

1. A threaded screw for fixing a workpiece to a thin metal plate substrate having a thickness of 1.4 mm or less, The screw has a shaft portion having a tapered portion formed at the tip end side and a remaining straight portion, a head portion provided at the base end of the shaft portion, and a screw thread rising from the tapered portion and extending to the straight portion, A band-shaped valley surface is exposed between adjacent threads, and the valley portion has a trapezoidal cross section, A burring portion is formed in the base by the expanding action of the tapered portion, and the thread is screwed into the inner peripheral portion of the base including the burring portion. The plate thickness of the base, the pitch, the root diameter, and the shape of the thread are set so that, in a state where a part of the thread of the straight portion is biting into the inner peripheral portion of the base, at least a part of the inner peripheral portion of the base is pressed into the root portion and braced against the following flank of the thread. Cutting screw for thin metal plates.

2. In the straight portion, the root diameter is 3.5 times or more the thickness of the base material, and the pitch of the thread is set in the range of 1.5 to 3.5 times the thickness of the base material.

3. A compression cutting screw for thin metal plates according to claim 1 or 2.

3. The thread has a ridge angle of 40 to 45°, an included angle between a cut surface passing through the apex of the thread and a trailing flank of 12 to 17°, and an included angle between the cut surface and a leading flank of 25 to 30°.

3. A compression cutting screw for thin metal plates according to claim 1 or 2.

4. In the straight portion, the maximum width in the axial direction of the thread is approximately the same as the width of the valley surface. The threaded cutting screw for thin metal plates according to claim 3.

5. At least the thread of the straight portion has a plurality of notches cut into the thread, the notches being scattered in the axial direction and spaced apart from each other in the circumferential direction. The threaded cutting screw for thin metal plates according to claim 3.

6. The root diameter, pitch, and shape of the thread are set so that the volume of the burred portion of the base is larger than the volume of one revolution of the root portion, thereby allowing the burred portion to be pressed against the trailing flank of the thread over the entire circumference. The threaded cutting screw for thin metal plates according to claim 3.

7. A method for manufacturing a thin metal plate having a workpiece, comprising: a thin metal plate cutting screw according to any one of claims 1 to 6; a base having a thickness of 1.4 mm or less into which the cutting screw is screwed; and a workpiece fixed to the base by the cutting screw; A thickened inner peripheral portion including the burring portion and expanding in the plate thickness direction is formed on the base, and at least a part of the thickened inner peripheral portion is pressed into the valley portion while the thread bites into it, and is pressed against the following flank of the thread. structure.

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