Screw with enlarged core diameter in the reaming portion

Abstract

The invention relates to a wood screw (1), comprising a head (2), a tip (3) and a shank (4) connecting the head (2) to the tip (3), wherein the shank (4) has a first shank portion (4a) with a first thread (5a) and a first core diameter (k1), wherein the shank (4) has a second shank portion (4b) with a second thread (5b) and a second core diameter (k2). The second shank portion (4b) connects the first shank portion (4a) to the tip (3) and the second thread (5b) represents a continuation of the first thread (5a), wherein the second shank portion (4b) has a plurality of projections (6) which extend between at least one pitch of the second thread (5b), wherein the second core diameter (k2) is at least as large as the first core diameter (k1).

Description

[0001] Screw with enlarged core diameter in the reaming section

[0002] The invention relates to a wood screw, comprising a head, a tip and a shank connecting the head to the tip, wherein the shank has a first shank portion with a first thread and a first core diameter, wherein the shank has a second shank portion with a second thread and a second core diameter, wherein the second shank portion connects the first shank portion to the tip and the second thread represents a continuation of the first thread, wherein the second shank portion has a plurality of projections extending between at least one pitch of the second thread.

[0003] Screws are a widely used fastener for creating detachable connections. They usually have a cylindrical body with a thread on the surface consisting of a multitude of thread flanks. A basic distinction is made between self-tapping or self-forming screws and screws with standard threads. With self-tapping or self-forming screws, also called wood screws, the counter thread is cut into a wooden workpiece when screwed in. With screws with standard threads, also called metal or machine screws, the counter thread is cut into a workpiece before screwing. The main methods used to manufacture screws are cold extrusion, which are suitable for large quantities, and hot extrusion, which are suitable for smaller quantities but with larger screw diameters.In the cold extrusion process, the thread is produced using a thread rolling machine without cutting, usually by rolling the thread groove into the surface of the screw shaft. To produce a secondary thread or additional projections on the shaft, the required material is removed from the shaft. Therefore, in the case of a secondary thread or additional projections, the shaft is necessarily thinner compared to a similar screw without such a secondary thread or projections.

[0004] In the prior art, a wood screw mentioned at the outset is known, for example, from US 2020271151 A1. The disclosed wood screw comprises a head, a tip, and a shank connecting the head to the tip. The shank has a first shank portion with a first thread and a first core diameter, and a second shank portion with a second thread and a second core diameter. The second shank portion is provided near the tip and thus connects the first shank portion to the tip. The second thread represents a continuation of the first thread. Between the thread flanks of the second thread, the wood screw has a plurality of projections that extend over several pitches of the second thread. These projections form an additional thread that is designed in the opposite direction to the second thread.To produce the projections, material is transferred from the shank of the second shank section into the projections during rolling, which means that the core diameter of the second shank section is necessarily smaller than the core diameter of the first shank section. However, the smaller core diameter in the second shank section leads to a number of disadvantages. In particular, the friction between the screw and the substrate increases when screwing into the substrate because the reduced core diameter in the second shank section leads to insufficient clearing out or pushing away of substrate material compared to shank sections with a larger core diameter closer to the screw head. As a result, the shank sections with the larger core diameter rest against the drilled hole over their entire length, which massively increases the friction between the screw and the drilled hole. Furthermore, the strength and fracture resistance of the wood screw are compromised due to the smaller core diameter.In very dense wood species, such a wood screw is therefore prone to breaking off in the second shaft section. A thinner core diameter in the second shaft section can also reduce the load-bearing capacity of the wood screw, as the cross-section for load-bearing is smaller. Furthermore, such a wood screw can have a weaker anchorage in the workpiece. If the wood screw has increased flexibility due to the thinner core diameter in the second shaft section, this can also make handling more difficult, especially when inserting the wood screw precisely or when using particularly long wood screws.

[0005] The object of the present invention is to provide a wood screw that overcomes or at least mitigates the described disadvantages of the prior art. This object is achieved by a wood screw having the features of claim 1. Preferred embodiments are specified in the dependent claims, the description, and the drawings.

[0006] The wood screw according to the invention has a second core diameter that is at least as large as the first core diameter. This leads to greater strength, especially in the area of ​​the second shaft section. Thus, the wood screw is less prone to breaking or bending during use and reduces the friction occurring between the drilled hole and the first shaft section. The load-bearing capacity is also increased, since a larger cross-section is available for load bearing. In addition, the wood screw according to the invention can be screwed into a workpiece more easily than wood screws from the prior art, because the at least equally large

[0007] Core diameter in the second shaft section acts as a reamer for the first shaft section.

[0008] In a preferred embodiment, the second core diameter is larger than the first core diameter. In this embodiment, the second core diameter is not just the same as the first core diameter, but larger. This leads to even more pronounced advantages compared to the case where the two core diameters are the same.

[0009] In a preferred embodiment, both the first shaft section and the second shaft section have a volume of material measured over an axial length unit, from which the first shaft section and the second shaft section, respectively, are formed, wherein the two volumes are of equal size. In other words, the material length density, i.e. the material density per axial length unit, is of equal size in the first shaft section and in the second shaft section. If, for example, the first core diameter and the second core diameter are of equal size, this means that the material density of the first thread per axial length unit is of equal size to the material density of the second thread and the plurality of projections in the second shaft section per axial length unit.If the second core diameter is larger than the first core diameter, the material density of the second thread and the plurality of projections in the second shaft portion together is smaller than the material density of the first thread, each per unit axial length.

[0010] In a preferred embodiment, the outer diameter of the second thread is smaller than the outer diameter of the first thread. In this embodiment, the second thread continues to be a continuation of the first thread, but the outer diameter of the thread decreases at the transition from the first to the second shank section. In other words, the second thread has a smaller thread depth than the first thread. The thread depth generally refers to the distance between the thread crest and the core diameter of the wood screw, i.e., the difference between the flank or outer diameter and the core diameter.

[0011] In a preferred embodiment, the flank angle of the second thread is smaller than the flank angle of the first thread. The flank angle of a thread is measured between the facing flanks of two adjacent thread turns and is a measure of the width of a thread flank in the axial direction of the wood screw. A small flank angle results in a pointed thread, in which a thread flank has less material per unit axial length than a thread flank with a large flank angle.

[0012] In a preferred embodiment, the pitch of the second thread is greater than the pitch of the first thread. For metric threads (as opposed to inch threads), the pitch or thread pitch refers to the axial path of the wood screw along the thread in one revolution. In other words, the pitch is the distance between two thread crests. The pitch determines the axial path the wood screw travels in the workpiece in one revolution.

[0013] In a preferred embodiment, the head is a countersunk head or a flat head and preferably has milling ribs and / or milling pockets on the side facing the shaft. A countersunk head is completely sunk into the material. With wood, the wood screw can penetrate the soft material with its head. Since this displaces wood fibers, cracks and splits in the material can occur. To simplify displacement and ensure clean fastening, the head of the wood screw preferably has milling ribs and / or milling pockets on the side facing the shaft. In this case, it is also referred to as a countersunk head or countersunk pocket head. The side of a screw head facing the shaft is also called the chin. The milling ribs and / or milling pockets mill away the wood fibers and the head can sink flush into the material without damaging the surface.Fraying around the head, which is sunk into the material, is also avoided, which is particularly advantageous for wood with a brittle coating.

[0014] The washer or flat head has the advantage that a washer is not required, as this function is performed by the head. It thus distributes the applied force over a larger area. While a countersunk head, for example, can penetrate deep into soft wood if too much force is applied, a flat head protects the wood surface. This not only increases the holding power but also protects the material. Other screw head shapes are also possible, which are well known to experts. These include a truss head (also called a pan head, lens head, round head, UFO head, or mushroom head), a hexagon head, a trumpet head, a raised countersunk head, or a cylinder head.

[0015] In a preferred embodiment, the shaft further comprises a third shaft section which is arranged between the first shaft section and the head, wherein the third shaft section is threadless. This is generally referred to as a screw with a partial thread. With a full thread, the thread usually extends below the head of the screw. Partial threads, on the other hand, are particularly suitable for screwing squared timber or panels to beams. The unthreaded section should preferably be at least as long as the thickness of the panel or beam. This allows the thread to anchor itself firmly in the lower piece of wood, while the upper piece of wood is pulled tightly towards the lower piece via the head of the wood screw. This enables particularly good fastening by the wood screw. In a further embodiment, the third shaft section has a diameter which is larger than the first core diameter of the first shaft section.In a preferred embodiment, the shaft further comprises a fourth shaft section arranged between the first shaft section and the third shaft section, wherein the fourth shaft section is provided with ribs, preferably in the form of threads, wherein the outer diameter of the fourth shaft section is preferably larger than the diameter of the third shaft section. Ribs designed in this way are also referred to as end mills or friction shanks. The ribs enable minimal wood destruction through a displacing, milling effect. Due to a high breaking torque and a low screw-in torque, the fourth shaft section with ribs leads to a low risk of screw breakage, especially with long wood screws. Furthermore, the fourth shaft section with ribs leads to a reduced splitting effect when the shaft is inserted into the workpiece.

[0016] In a preferred embodiment, the projections on the second shaft section are arranged linearly or obliquely along the longitudinal direction of the second shaft section and are optionally spaced from one another in the circumferential direction of the shaft or in the longitudinal direction of the shaft. The projections thus serve as an end mill integrated into the second thread and reduce the force required when screwing in the wood screw.

[0017] In a preferred embodiment, the projections on the second shaft section form a third thread along the longitudinal direction of the second shaft section, which extends over several pitches of the second thread, wherein the direction of rotation of the third thread is optionally opposite to the direction of rotation of the second thread. If the direction of rotation of the third thread is the same as the direction of rotation of the second thread, the second shaft section is referred to as a double-start thread, as opposed to a single-start or even multi-start thread. In general, the advantage of a multi-start thread is that better force distribution can be achieved due to the increased number of thread flanks engaging with the workpiece. With a multi-start thread, the thread with a larger outer diameter is usually given a larger thread pitch orA pitch is provided so that a slight rotational movement when screwing in the wood screw results in the greatest possible axial movement into the workpiece. In this case, it is also referred to as a helix thread. If the direction of rotation of the third thread is opposite to the direction of rotation of the second thread, the third thread acts as an end mill.

[0018] In a preferred embodiment, both the second thread and the projections have a height measured radially from the second core diameter, with the height of the projections being smaller than the height of the second thread. This ensures that the projections do not impede screwing in the wood screw, but rather, as end mills, facilitate screwing in.

[0019] Advantageous and non-limiting embodiments of the invention set out in the claims are explained in more detail below with reference to the drawings.

[0020] Fig. 1a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is the same as the first core diameter and the second thread has a smaller outer diameter than the first thread.

[0021] Fig. 1b shows an enlarged partial view of the wood screw from Fig. 1a.

[0022] Fig. 1c shows a cross-section of the view in Fig. 1b.

[0023] Fig. 2a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is larger than the first core diameter and the second thread has a smaller outer diameter than the first thread.

[0024] Fig. 2b shows an enlarged partial view of the wood screw from Fig. 2a.

[0025] Fig. 2c shows a cross-section of the view in Fig. 2b.

[0026] Fig. 3a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is the same as the first core diameter and the second thread has a smaller flank angle than the first thread.

[0027] Fig. 3b shows an enlarged partial view of the wood screw from Fig. 3a.

[0028] Fig. 3c shows a cross-section of the view in Fig. 3b.

[0029] Fig. 4a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is larger than the first core diameter and the second thread has a smaller flank angle than the first thread.

[0030] Fig. 4b shows an enlarged partial view of the wood screw from Fig. 4a.

[0031] Fig. 4c shows a cross-section of the view from Fig. 4b. Fig. 5a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is the same size as the first core diameter and the second thread has a larger pitch than the first thread.

[0032] Fig. 5b shows an enlarged partial view of the wood screw from Fig. 5a.

[0033] Fig. 5c shows a cross-section of the view in Fig. 5b.

[0034] Fig. 6a shows an embodiment of the wood screw according to the invention, wherein the second core diameter is larger than the first core diameter and the second thread has a larger pitch than the first thread.

[0035] Fig. 6b shows an enlarged partial view of the wood screw from Fig. 6a.

[0036] Fig. 6c shows a cross-section of the view in Fig. 6b.

[0037] Fig. 7 shows a shaft of the wood screw according to the invention, wherein the projections are oriented parallel to the screw axis.

[0038] Figures 1a to 1c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3, and a shank 4 connecting the head 2 to the tip 3. Fig. 1a shows an overall view of the wood screw 1, Fig. 1b shows a detailed view from Fig. 1a, and Fig. 1c shows a cross-section of the view from Fig. 1b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1, and a second shank section 4b with a second thread 5b and a second core diameter k2. In the embodiment shown, the first core diameter k1 is the same size as the second core diameter k2, so that only the first core diameter k1 is shown in Fig. 1c. The second shank section 4b connects the first shank section 4a to the tip 3, and the second thread 5b represents a continuation of the first thread 5a.Furthermore, the second shaft section 4b has a plurality of projections 6 that extend between at least one pitch of the second thread 5b. The projections 6 are arranged obliquely on the second shaft section 4b along the longitudinal direction of the second shaft section 4b and spaced from one another in the circumferential direction of the shaft 4. However, the projections 6 can also be arranged linearly, i.e., parallel to the longitudinal direction of the shaft 4 (see Fig. 7). In the embodiment shown, the projections 6 form a third thread that extends over several pitches of the second thread 5b and whose direction of rotation is opposite to the direction of rotation of the second thread 5b. However, it is also possible for the direction of rotation of the third thread to be the same as the direction of rotation of the second thread 5b.Furthermore, it is conceivable that the projections 6 are spaced from one another in the longitudinal direction of the shaft 4, so that the projections 6 do not form a continuous third thread. In Fig. 1c it can be seen that the outer diameter a2 of the second thread 5b is smaller than the outer diameter a1 of the first thread 5a. In the embodiment shown, the head 2 of the wood screw 1 is designed as a countersunk head and has milling ribs and / or milling pockets 7 on its chin, i.e. the side facing the shaft 4. The wood screw 1 also has a third shaft section 4c on its shaft 4, which is arranged between the first shaft section 4a and the head 2, wherein the third shaft section 4c is designed without a thread. In the embodiment shown, the third shaft section 4c has a diameter that is larger than the first core diameter kl of the first shaft section 4a.Finally, the shaft 4 further comprises a fourth shaft section 4d, which is arranged between the first shaft section 4a and the third shaft section 4c, wherein the fourth shaft section 4d is provided with ribs 8 designed as threads. These ribs 8 act as end mills and enable minimal wood destruction through a displacing, milling effect. The double arrows in Fig. 1a mark the axial direction of the wood screw 1, which also corresponds to the longitudinal direction of the shaft 4. Viewed in this axial direction, both the first shaft section 4a and the second shaft section 4b of the embodiment shown have a volume of material measured over an axial length unit, from which the first shaft section 4a and the second shaft section 4b, respectively, are formed, wherein the two volumes are of equal size.

[0039] Figures 2a to 2c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3 and a shank 4 connecting the head 2 to the tip 3. Fig. 2a shows an overall view of the wood screw 1, Fig. 2b shows a detailed view from Fig. 2a and Fig. 2c shows a cross-section of the view from Fig. 2b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1 and a second shank section 4b with a second thread 5b and a second core diameter k2. In this embodiment, the second core diameter k2 is larger than the first core diameter k1 and the second thread 5b has a smaller outer diameter a2 than the first thread 5a. For a further description of the other features, reference is made to the description of Figures 1a to 1c.

[0040] Figures 3a to 3c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3, and a shank 4 connecting the head 2 to the tip 3. Fig. 3a shows an overall view of the wood screw 1, Fig. 3b shows a detailed view from Fig. 3a, and Fig. 3c shows a cross-section of the view from Fig. 3b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1, and a second shank section 4b with a second thread 5b and a second core diameter k2. In this embodiment, the second core diameter k2 is the same size as the first core diameter k1, and the flank angle f2 of the second thread 5b is smaller than the flank angle f1 of the first thread 5a. For a further description of the other features, reference is made to the description of Figures 1a to 1c.

[0041] Figures 4a to 4c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3, and a shank 4 connecting the head 2 to the tip 3. Fig. 4a shows an overall view of the wood screw 1, Fig. 4b shows a detailed view from Fig. 4a, and Fig. 4c shows a cross-section of the view from Fig. 4b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1, and a second shank section 4b with a second thread 5b and a second core diameter k2. In this embodiment, the second core diameter k2 is larger than the first core diameter k1, and the flank angle f2 of the second thread 5b is smaller than the flank angle f1 of the first thread 5a. For a further description of the other features, reference is made to the description of Figures 1a to 1c.

[0042] Figures 5a to 5c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3, and a shank 4 connecting the head 2 to the tip 3. Fig. 5a shows an overall view of the wood screw 1, Fig. 5b shows a detailed view from Fig. 5a, and Fig. 5c shows a cross-section of the view from Fig. 5b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1, and a second shank section 4b with a second thread 5b and a second core diameter k2. In this embodiment, the second core diameter k2 is the same size as the first core diameter k1, and the pitch g2 of the second thread 5b is greater than the pitch g1 of the first thread 5a. For a further description of the other features, reference is made to the description of Figures 1a to 1c.

[0043] Figures 6a to 6c show a preferred embodiment of the wood screw 1 according to the invention, which has a head 2, a tip 3 and a shank 4 connecting the head 2 to the tip 3. Fig. 6a shows an overall view of the wood screw 1, Fig. 6b shows a detailed view from Fig. 6a and Fig. 6c shows a cross-section of the view from Fig. 6b. The shank 4 has a first shank section 4a with a first thread 5a and a first core diameter k1 and a second shank section 4b with a second thread 5b and a second core diameter k2. In this embodiment, the second core diameter k2 is larger than the first core diameter k1 and the pitch g2 of the second thread 5b is larger than the pitch g1 of the first thread 5a. For the further description of the other features, reference is made to the description of Figures 1a to 1c.

[0044] Fig. 7 shows the shaft 4 of a wood screw 1 according to the invention, wherein the projections 6 in the embodiment shown are oriented parallel to the longitudinal direction of the shaft 4, i.e., parallel to the axial direction of the wood screw 1, and wherein the projections 6 are spaced apart from one another in the longitudinal direction of the shaft 4. The projections 6 can be positioned between the second thread 5b, or a flank of the second thread 5b can extend through one of the projections 6. Projections 6 in this orientation are known as TENZ® Stairs and specifically create a smaller friction surface between the screw and the wood, thereby significantly reducing screw-in resistance.

Claims

Patent claims 1. Wood screw (1), comprising a head (2), a tip (3) and a shank (4) connecting the head (2) to the tip (3), wherein the shank (4) has a first shank section (4a) with a first thread (5a) and a first core diameter (k1), wherein the shank (4) has a second shank section (4b) with a second thread (5b) and a second core diameter (k2), wherein the second shank section (4b) connects the first shank section (4a) to the tip (3) and the second thread (5b) represents a continuation of the first thread (5a), wherein the second shank section (4b) has a plurality of projections (6) extending between at least one pitch of the second thread (5b), characterized in that the second core diameter (k2) is at least as large as the first core diameter (k1).

2. Wood screw according to claim 1, characterized in that the second core diameter (k2) is larger than the first core diameter (kl).

3. Wood screw according to one of claims 1 or 2, characterized in that both the first shaft section (4a) and the second shaft section (4b) have a volume of material measured over an axial length unit, from which the first shaft section (4a) and the second shaft section (4b) are formed, respectively, the two volumes being of equal size.

4. Wood screw according to one of claims 1 to 3, characterized in that the outer diameter (a2) of the second thread (5b) is smaller than the outer diameter (a1) of the first thread (5a).

5. Wood screw according to one of claims 1 to 4, characterized in that the flank angle (f2) of the second thread (5b) is smaller than the flank angle (fl) of the first thread (5a).

6. Wood screw according to one of claims 1 to 5, characterized in that the pitch (g2) of the second thread (5b) is greater than the pitch (gl) of the first thread (5a).

7. Wood screw according to one of claims 1 to 6, characterized in that the head (2) is a countersunk head or a plate head and preferably has milling ribs and / or milling pockets (7) on its side facing the shaft (4).

8. Wood screw according to one of claims 1 to 7, characterized in that the shaft (4) further comprises a third shaft portion (4c) which is arranged between the first shaft portion (4a) and the head (2), wherein the third shaft portion (4c) is designed without a thread.

9. Wood screw according to claim 8, characterized in that the third shaft section (4c) has a diameter which is larger than the first core diameter (kl) of the first shaft section (4a).

10. Wood screw according to one of claims 8 or 9, characterized in that the shaft (4) further comprises a fourth shaft section (4d) which is arranged between the first shaft section (4a) and the third shaft section (4c), wherein the fourth shaft section (4d) is provided with ribs (8), preferably designed as threads, wherein preferably the outer diameter of the fourth shaft section (4d) is larger than the diameter of the third shaft section (4c).

11. Wood screw according to one of claims 1 to 10, characterized in that the projections (6) on the second shaft portion (4b) are arranged linearly or obliquely along the longitudinal direction of the second shaft portion (4b) and are optionally spaced from one another in the circumferential direction of the shaft (4) or in the longitudinal direction of the shaft (4).

12. Wood screw according to one of claims 1 to 11, characterized in that the projections (6) on the second shaft section (4b) form a third thread along the longitudinal direction of the second shaft section (4b), which extends over several pitches of the second thread (5b), wherein optionally the direction of rotation of the third thread is opposite to the direction of rotation of the second thread (5b).

13. Wood screw according to one of claims 1 to 12, characterized in that both the second thread (5b) and the projections (6) have a height measured in the radial direction from the second core diameter (k2), the height of the projections (6) being smaller than the height of the second thread (5b).

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