SCREW FOR WOOD, WOOD-BASED MATERIALS AND WOOD-LIKE MATERIALS

Description

[0001] The invention relates to a screw for wood, wood materials and wood-like materials, having a screw shaft, a screw head with a drive formation at one end of the screw shaft and a screw thread on at least a portion of the screw shaft, wherein an underside of the screw head facing the screw shaft is provided with a plurality of milling teeth spaced apart from one another in the circumferential direction.

[0002] US Patent Application Publication US 2011 / 0164944 A1 discloses a screw for wood, wood-based materials, and wood-like materials, comprising a screw shaft, a screw head with a drive formation at one end of the screw shaft, and a screw thread on at least a portion of the screw shaft. An underside of the screw head facing the screw shaft is provided with a plurality of milling teeth spaced apart from one another in the circumferential direction. The milling teeth each have a straight milling edge. The height of each milling tooth decreases in both circumferential directions starting from the milling edge. The milling teeth each have a diamond-shaped base and are formed symmetrically to the milling edge. The shaft is smooth between a lower end of the milling teeth facing away from the screw head and the beginning of a screw thread on the shaft.

[0003] German utility model DE 298 11 536 U1 discloses a screw for wood materials. It has several circumferentially spaced cutter teeth on the underside of the head facing the screw shaft. Each cutter tooth has a straight cutter edge. A cutter section is arranged on the shaft between the end of the cutter teeth facing the screw shaft and the beginning of a screw thread. The cutter section has helically arranged scraping strips.

[0004] German utility model DE 20 2007 018 179 U1 discloses a screw for wood materials with a screw head with a drive formation at one end of the screw shaft and a screw thread on at least one section of the screw shaft. An underside of the screw head facing the screw shaft is provided with several milling teeth spaced apart from one another in the circumferential direction. A milling section with several helically arranged milling edges is provided between an end of the milling teeth facing the shaft and the beginning of the screw thread.

[0005] British patent GB 15102 discloses a screw for wood materials that has several circumferentially spaced cutter teeth on the underside of the screw head. In one embodiment, the cutter teeth can merge into helical cutter edges arranged between the underside of the screw head and the beginning of the screw thread. The pitch of the helical cutter teeth on the screw shaft is significantly greater than the pitch of the screw thread.

[0006] Japanese Patent Application JP 2002295429 A discloses a screw for wood materials. It has a plurality of circumferentially spaced cutter teeth on the underside of the screw head facing the screw shaft. Between an end of the cutter teeth facing the screw shaft and the beginning of the screw thread, ribs or projections are provided around the screw shaft. The ribs or projections are annular with a zero pitch and can have a rounded outer contour or a triangular or sawtooth-shaped outer contour. In the case of a sawtooth-shaped outer contour, the steeper flanks face the underside of the screw head.

[0007] The invention is intended to provide a screw for wood, wood-based materials and wood-like materials, the screw head of which can be reliably countersunk into the surface of the workpiece when screwed in.

[0008] According to the invention, a screw with the features of claim 1 is provided for this purpose. A screw for wood, wood-based materials and wood-like materials is provided, comprising a screw shaft, a screw head with a drive formation at one end of the screw shaft and a screw thread on at least a portion of the screw shaft, wherein an underside of the screw head facing the screw shaft is provided with a plurality of milling teeth spaced apart from one another in the circumferential direction, wherein the milling teeth have a triangular base area and a rectilinear milling edge, wherein a height of the milling tooth decreases in the circumferential direction starting from the milling edge.

[0009] Milling teeth with a triangular base and a straight milling edge allow even very hard, long-fibered and / or tough materials, especially decking made from tropical hardwoods, to be reliably milled so that the screw head can be countersunk into the surface of the workpiece. In particular, this ensures that the surface of the workpiece surrounding the screw head is not damaged and that the surface of the workpiece surrounding the screw head is not sunk even slightly. Especially with decking boards, the screw heads are in the visible area, so countersinking of the surface of the workpiece surrounding the screw head should be avoided. The straight milling edge of the milling teeth ensures a good milling effect. The triangular base of the milling teeth and the height of the milling teeth, which decreases in the circumferential direction starting from the milling edge, creates space for collecting chips created when the screw head is countersunk.

[0010] In a further development of the invention, the milling edge is arranged parallel to the central longitudinal axis of the screw.

[0011] In a further development of the invention, the milling teeth are designed as projections on a truncated cone surface with a circular cross-section.

[0012] In a further development of the invention, a height of each milling tooth measured to the truncated cone surface decreases in a direction from the screw head to the screw tip.

[0013] This means that the height of each milling tooth is greatest on the underside of the screw head. The underside of the screw head also requires the most material to be milled off, as this is where the diameter of the screw head of a countersunk head screw is usually already at its largest.

[0014] In a further development of the invention, several surface sections are provided between the milling teeth on the underside of the screw head, which extend radially inward from the outer circumference of the screw head with a main component, wherein the surface sections form an angle of between 95° and 115°, in particular 105°, with the central longitudinal axis. The surface sections are thus arranged at an angle of 5° to 25° to a plane perpendicular to the central longitudinal axis.

[0015] These surface sections fill the spaces between the milling teeth on the underside of the screw head. Because these surface sections are arranged at an angle of more than 90° to the central longitudinal axis, they cause the material of the workpiece to be displaced outwards when the screw is countersunk. This also contributes to reliable countersinking of the screw without adversely affecting the surface of the workpiece surrounding the screw head. In the direction of the screw tip, the surface sections are followed by sections of a truncated cone surface with a significantly steeper angle, in particular between 130° and 150°, in particular 135°, on which the milling teeth are arranged. The head angle or cone angle of this truncated cone surface is then between 100° and 60°, in particular 90°.

[0016] In a further development of the invention, a concave surface with a circular cross-section, a conical surface or a double cone with two adjoining conical surfaces with different cone angles is arranged in the direction from the screw head to the screw tip between the end of the milling teeth and the beginning of a holding section or the beginning of a smooth screw shaft section.

[0017] By means of such a concave, conical or double-conical transition surface, the resulting drill hole can be widened when the screw is screwed in.

[0018] According to the invention, a holding section with a sawtooth-like outer contour is provided between the screw head and the screw thread.

[0019] By means of such a holding section, the holding force of the screw can be increased.

[0020] According to the invention, the sawtooth-like outer contour has steep flanks and flat flanks, wherein the steep flanks, relative to the central longitudinal axis, face the screw tip and the flat flanks face the screw head.

[0021] The holding section therefore has a holding effect on the workpiece that counteracts any movement of the workpiece upwards along the screw shaft towards the screw head. For example, when fastening decking boards to a substructure, the decking boards are pressed downwards towards the substructure when the holding section engages with the decking boards. When fully assembled, the holding section with its sawtooth-like outer contour prevents the decking boards from moving upwards along the screw shaft towards the screw head. This is often observed on outdoor terraces when the decking boards become deformed due to exposure to moisture. The screw according to the invention can remedy this problem.

[0022] In a further development of the invention, the ratio between an outer diameter of the sawtooth-like outer contour and a core diameter of the sawtooth-like outer contour is between 1.05 and 1.2. The ratio between the outer diameter and core diameter is thus significantly smaller in the holding section than in the area of ​​the screw thread, for example, one-quarter to one-third smaller.

[0023] According to the invention, the sawtooth-like outer contour is designed like a thread.

[0024] In this way, the holding section can be moved comparatively easily through a workpiece.

[0025] According to the invention, a pitch of the thread-like sawtooth-like outer contour is the same as the pitch of the screw thread and smaller than a pitch of the screw thread.

[0026] When the screw is driven through a workpiece to be fastened and into a substructure, for example, when screwing into a decking board, the workpiece is pressed against the substructure during screwing. This ensures secure and reliable installation of the workpiece against the substructure.

[0027] In a further development of the invention, the ratio of the pitch of the thread-like sawtooth-like outer contour and the pitch of the screw thread is between 0.75 and 0.9.

[0028] For example, the pitch of the sawtooth-like outer contour is 1.8 and the pitch of the screw thread is 2.2. A pitch ratio between 0.75 and 0.9 achieves a reliable pressing effect of a workpiece against a substructure when screwing in the screw according to the invention.

[0029] Further features and advantages of the invention emerge from the claims and the following description of preferred embodiments of the invention in conjunction with the drawings. Individual features of the various illustrated and / or described embodiments can be combined in any way without exceeding the scope of the invention. This also applies to the combination of individual features without other individual features with which they are illustrated and / or described in connection. In the drawings: Fig. 1a side view of a screw according to the invention, Fig. 2a side view of the screw according to the invention of the Fig. 1 , whereby the screw was rotated a little around its longitudinal axis, Fig. 3 a view of the screw of the Fig. 1 from above, Fig. 4 a view of the screw of the Fig. 1 from below, Fig. 5 a sectioned side view of the screw of the Fig. 1 , Fig. 6 a sectional view of the screw of the Fig. 1 , wherein the cutting plane is slightly offset from the central longitudinal axis, Fig. 7 an enlarged view of a section of the sectional view of the Fig. 6 , Fig. 8the screw of the Fig. 1 from below, Fig. 9a partial view of the screw of the Fig. 1 from obliquely below onto the underside of the screw head, Fig. 10 a further partial view of the screw according to the invention onto the underside of the screw head, Fig. 11 a side view of the section of the screw according to the invention with the screw head, Fig. 12 a further section-wise side view of the section of the screw according to the invention with the screw head, wherein the screw compared to the view of the Fig. 11 was slightly rotated about its central longitudinal axis, and Fig. 13 a sectional view of the screw head of the screw according to the invention, wherein the sectional plane is slightly offset from the central longitudinal axis.

[0030] Fig. 1 shows a screw 10 according to the invention in a side view. The screw 10 has a screw shaft 12 and a screw head 14, wherein the screw head 14 is provided with a drive formation 16, which in Fig. 1 is barely visible. A screw tip 18 is arranged at the opposite end of the screw shaft 12 opposite the screw head 14. In the illustrated embodiment of the screw 10, the screw tip 18 is designed as a drill tip. Within the scope of the invention, however, the screw tip 18 can also be designed as a simple, tapered tip.

[0031] On an underside of the screw head 14 facing the screw shaft 12, a plurality of milling teeth 20 are provided, spaced apart from one another in the circumferential direction. A total of six milling teeth 20 are provided on the underside of the screw head, see. Fig. 8 . In the presentation of the Fig. 1 Only four milling teeth are visible. The milling teeth 20 each have a triangular base. This is already evident in the illustration of the Fig. 1 It can be seen that the height of the milling teeth in the circumferential direction and against the intended screwing direction, in Fig. 1 to the right. The Fig. 1 The left end of each milling tooth 20 is defined by a straight milling edge 22. Within the scope of the invention, 4 to 10 milling teeth can be provided.

[0032] In the direction toward the screw tip 18, a concave surface 24 with a circular cross-section adjoins the milling teeth 20. This concave surface 24 then transitions into a holding section 26, which has a thread-like, sawtooth-like outer contour.

[0033] Adjoining the holding section 26 in the direction of the screw tip 18 is a tapered truncated cone surface 28. The truncated cone surface 28 is then followed by a section of the screw shaft with a screw thread 30. In the illustrated embodiment, the screw thread 30 ends in the upper region of the drill tip 18. If the screw is provided with a conically tapered tip, for example, the screw thread 30 can also extend to the end of the tip.

[0034] Fig. 2 shows the screw 10 in a further side view, where the screw 10 is opposite to the illustration of the Fig. 1 was slightly twisted around its central longitudinal axis. This is visible at the drill bit 18 in Fig. 2 The drill bit 18 has two halves with a triangular cross-section, cf. Fig. 8 , which taper toward the central longitudinal axis. This creates two cutting edges at the drill tip. The two triangular halves create sufficient space in the area of ​​the drill tip 18 to accommodate chips generated during drilling.

[0035] Fig. 3 shows a view of the screw 10 from an angled top view. In this view, the drive formation 16 in the screw head 14 is clearly visible. In the illustrated embodiment, the drive formation 16 is designed as an internal drive with cylindrical, curved surfaces. Within the scope of the invention, however, the drive formation 16 can also be designed, for example, as a hexagon socket, a raised hexagon, a Phillips head, or in any other manner.

[0036] Fig. 4 shows the screw 10 in a view from below. The formation of the screw tip 18 can be seen and the milling teeth 20 on the underside of the screw head 14 can also be seen. In this view and in the view of the Fig. 8 It is clearly visible that the milling teeth 20 have a triangular base with a straight base. A boundary line of each milling tooth 20 facing the outer circumference is convex. A boundary of each milling tooth 20 facing the central longitudinal axis is concave. This gives the milling teeth 20 a triangular base in the shape of a shark fin, see also Fig. 8 .

[0037] Fig. 5 shows a partially enlarged view of the screw 10 of the Fig. 1 The screw head 14 has a convex upper surface 32 in which the drive formation 16 is arranged centrally. The upper surface can, for example, also be flat. An outer circumference of the screw head 14 is formed by a circular cylindrical surface 34. Starting from the outer circumference, the underside of the screw head 40 is formed in sections by surface pieces 36, which extend radially inwards from the outer circumference with a main component. The surface pieces 36 fill the spaces between the milling teeth 20 on the underside of the screw head 14. The surface pieces 36 are part of an imaginary, circumferential truncated cone surface, which is aligned with the central longitudinal axis, in the illustration of the Fig. 5 measured downwards, forms an angle of more than 90°, see also Fig. 7 and Fig. 13 . The milling teeth 20 are separated below the surface pieces 36 by sections of a truncated cone surface with a significantly steeper angle to the central longitudinal axis, in particular 135°, for example between 130° and 140°.

[0038] It can be seen in Fig. 5 the sawtooth-like outer contour of the holding section 26. The sawtooth-like outer contour has steep flanks 38 and flat flanks 40. The steep flanks 38 face the screw tip 18, in Fig. 5 The flat flanks 40 are facing the screw head 14, Fig. 5 i.e. facing upwards. In the illustrated embodiment, the flat flanks form an angle of approximately 10° with the central longitudinal axis. The steep flanks 38 form an angle of approximately 105° with the central longitudinal axis, in the illustrated embodiment, each measured in the right half of the Fig. 5 and clockwise.

[0039] Fig. 6 shows a sectional view of the screw according to the invention. The sawtooth-like outer contour in the holding section 26 can be seen. The sawtooth-like outer contour in the holding section 26 is, cf. Fig. 5 , thread-like. The ratio of the pitch of the thread-like, sawtooth-like outer contour 26 to the pitch of the screw thread 30 is between 0.75 and 0.9. In the illustrated embodiment, the pitch of the sawtooth-like outer contour is 1.8, and the pitch of the screw thread 30 is 2.2. The sawtooth-like outer contour 26 has a significantly smaller profile depth than the screw thread.

[0040] Fig. 7 shows an enlarged sectional view of the holding section 26 of the screw 10. In this enlarged view, the steep flanks 38 and the flat flanks 40 of the sawtooth-like outer contour are clearly visible.

[0041] On the underside of the screw head 14 in the right half of the illustration the Fig. 7 a milling edge 44 of a milling tooth 20 can be seen. The milling edge 44 closes in the side view of the Fig. 7 with the central longitudinal axis an angle of approximately 125° to 135°, especially 130°. In the left half of the illustration of the Fig. 7 one of the surface pieces 36 can be seen. As explained, the surface piece 36 is aligned with the central longitudinal axis, in Fig. 7 Measured counterclockwise downwards, it forms an angle of approximately 105°. The surface pieces 36 thus exert a displacement effect on the material of the workpiece with a radially outward component.

[0042] Fig. 8 shows the screw 10 of the Fig. 1 from below. In this view, the drill bit 18 is clearly visible. On the underside of the screw head 14, the flat pieces 36 can be seen, as well as a total of six milling teeth 20. Each milling tooth 20 has a triangular base, with a base 46 of the base being straight. In the view of the Fig. 8 the base 46 coincides with the straight milling edge 44. A radially outer boundary 48 is convexly curved. A radially inner boundary 50 of each milling tooth 20 is convexly curved. The two boundaries 48, 50 converge at a tip 52 of the triangular base surface. The triangular base surface has, in the view of the Fig. 8 The shape of a shark fin is thus created. The next cutting tooth 20 follows in the circumferential direction at a short distance from the tip 52 of a cutting tooth. In order to achieve a cutting effect with the cutting teeth 20, the screw 10 would have to be Fig. 8 counterclockwise. The screw 10 is therefore designed as a right-hand screw, see also Fig. 1 .

[0043] Fig. 9 shows a section-wise view of the screw 10 from below onto the screw head 14. In this view, it can be seen that the milling teeth rise from a truncated cone-shaped surface with a circular cross-section 56, which merges into the milling teeth 20 or the surface pieces or surface sections 36 in the direction of the underside of the screw head 14. In the view of the Fig. 9 Both the straight milling edge 44 and the base 46 of the triangular base surface can be seen on two of the milling teeth 20. The milling edge 44 extends to the outer circumference of the screw head 14, i.e., to the circular cylindrical surface 34, which defines the outer circumference of the screw head 14.

[0044] Fig. 9 It can also be seen that the height of each milling tooth 20 in the circumferential direction, in Fig. 9 i.e., clockwise, to zero. This creates the flat pieces 36 on the underside of the screw head 40. Within the scope of the invention, the height of the milling teeth does not necessarily have to be reduced to zero in the circumferential direction.

[0045] Fig. 10 shows another view of the screw head 14 from its underside. It can be seen that the decreasing height of the milling teeth 20 in the circumferential direction provides space for accommodating chips generated when the screw head 14 is countersunk.

[0046] Fig. 11 shows a sectioned side view of the screw head 14. In this view it is clearly visible that the surface pieces 36 form an angle of more than 90° with the central longitudinal axis, in Fig. 11 Measured clockwise from the right. As explained, this angle is 105° in the illustrated embodiment.

[0047] Fig. 12 shows a further sectioned side view of the screw head 14, with the screw opposite to the illustration of the Fig. 11 was rotated a little around the central longitudinal axis. Fig. 12 milling tooth 20 facing the viewer, it can be seen that the straight milling edge 44 in the view of the Fig. 12 runs parallel to the central longitudinal axis of the screw 10. Fig. 7 and Fig. 12 It can therefore be seen that a milling edge 44 and the central longitudinal axis lie in a common plane. If the view is perpendicular to this plane, see Fig. 7 , the milling edge 44 forms an angle of approximately 125° to 135°, in particular 130°, with the central longitudinal axis. If the view is parallel to this plane, see Fig. 12 , the milling edge 44 and the central longitudinal axis are aligned.

[0048] The concave transition surface 24 between the lower end of the milling teeth 20 and the beginning of the holding section 26 can also be seen. Within the scope of the invention, the transition surface 24 can also be designed as a conical surface or as a double cone with two adjacent conical surfaces with different cone angles. The cone angle is then larger toward the milling teeth 20 than toward the holding section 26.

[0049] Fig. 13 shows a sectioned sectional view of the screw 10 in the area of ​​the screw head 14. In this view it is also clearly visible that the Fig. 13 The milling edge 44 of a milling tooth 20, visible on the right, extends straight from the transition surface 24 to the outer circumference of the screw head 14, i.e. to the edge surface 34. The edge surface 34 is also referred to as the pressing contour and is created by pressing the blank between a die and a punch. The outer surface 36 is in Fig. 13 cylindrical, but the finished screw is usually slightly curved outwards. Fig. 13 In the left half it can be seen that the surface pieces form 36 sections of an imaginary truncated cone surface around the central longitudinal axis and, in Fig. 13 measured counterclockwise downwards, form an angle of approximately 105° with the central longitudinal axis and thereby have a displacement effect on the material of the workpiece radially outwards and downwards.

Claims

1. Screw for wood, wood-based materials and wood-like materials, having a screw shank, having a screw head (14) with a driving formation (16) at one end of the screw shank, and having a screw thread (30) on at least one portion of the screw shank, wherein a bottom side, facing towards the screw shank, of the screw head (14) is provided with multiple milling teeth (20) which are spaced apart from one another in a circumferential direction, wherein the milling teeth (20) have a rectilinear milling edge (44), wherein, proceeding from the milling edge (44), a height of each milling tooth (20) decreases in the circumferential direction, characterized in that the milling teeth (20) have a triangle-like base surface, characterized in that a holding portion (26) with a sawtooth-like outer contour is provided between the screw head (14) and the screw thread (30), in that the sawtooth-like outer contour has steep flanks (38) and shallow flanks (40) in relation to the central longitudinal axis, wherein the steep flanks (38) face towards the screw tip (18) and the shallow flanks (40) face towards the screw head (14), in that the sawtooth-like outer contour is of thread-like design, and in that a thread gradient of the sawtooth-like outer contour of thread-like design is co-directional in relation to the thread gradient of the screw thread (30) and is smaller than a thread gradient of the screw thread (30).

2. Screw according to Claim 1, characterized in that the milling edge (44) is arranged parallel to the central longitudinal axis.

3. Screw according to Claim 1 or 2, characterized in that the milling teeth (20) are in the form of projections on a frustoconical surface (56) with a circular cross section.

4. Screw according to Claim 3, characterized in that a height of each milling tooth (20) measured from the frustoconical surface (56) decreases in a direction from the screw head (14) to the screw tip (18).

5. Screw according to at least one of the preceding claims, characterized in that the milling edge (44) extends as far as an outer circumference of the screw head (14) at the bottom side of the screw head.

6. Screw according to at least one of the preceding claims, characterized in that, at the bottom side of the screw head (14), there are provided between the milling teeth (20) multiple surface pieces (36) which, proceeding from the outer circumference of the screw head (14), extend with a main component radially inwards, wherein the surface pieces (36) include with the central longitudinal axis an angle of between 95 degrees and 115 degrees, in particular 105 degrees.

7. Screw according to at least one of the preceding claims, characterized in that a concave surface (24) with a circular cross section, a cone lateral surface or two mutually adjoining cone lateral surfaces with different cone angles is / are arranged between the end of the milling teeth (20) and the beginning of a holding portion (26), or the beginning of a smooth screw-shank portion, in the direction from the screw head (14) to the screw tip (18).

8. Screw according to one of the preceding claims, characterized in that a ratio between an outer diameter of the sawtooth-like outer contour and a core diameter of the sawtooth-like outer contour is between 1.05 and 1.2.

9. Screw according to one of the preceding claims, characterized in that a ratio of the thread gradient of the sawtooth-like outer contour of thread-like design and the thread gradient of the screw thread (30) is between 0.75 and 0.9.