DE102021126035B4 - wood screw - Google Patents

Abstract

Wood screw (1), comprising a screw shaft (2) which has a screw head (3) and, on the side opposite the screw head (3), a screw tip (4), wherein at least one threaded section (5, 6, 7, 8) extending to the screw tip (4) is formed on the screw shaft (2), and between the thread flanks (9) of the threaded section (5) of the screw tip (4) there is a thread root (10) which has a concave groove (11) in the longitudinal direction of the screw shaft (2), characterized in that the thread root (10) of the threaded section (5) of the screw tip (4) is composed overall of two regions (11 and 12) which follow one another in the direction of the screw tip (4), so that the concave groove (11) is followed in each case by a region with an inclined surface (12).

Description

The invention relates to a wood screw according to the preamble of patent claim 1.

Wood screws are slightly conical and are primarily screwed into wood, where they cut their own counter-thread. The specific material properties of wood require special attention in the design of such wood screws, as wood tends to splinter due to its fiber structure. Wood screws of the type in question here comprise a screw shaft with a screw head and, on the side opposite the screw head, a screw tip. The screw tip is usually needle- or nail-like, i.e. designed as a tip in the true sense of the word, to enable the screw to penetrate the comparatively softer wood material before screwing in, thus fixing the wood screw in the wood. Wood screws have at least one threaded section on the screw shaft that runs all the way to the screw tip, and thus a thread that reaches all the way to the screw tip. Previously known wood screws can have differently designed threaded sections along the screw shaft, as well as thread-free sections and/or a thread that runs continuously from the screw head to the screw tip.

The EP 2 224 142 B1 discloses a thread-forming screw with a pre-thread at the screw tip. In the area of the pre-thread, several chip pockets are distributed along the circumference, so that the cross-sectional shape of the screw shaft in this area deviates from a circular cylindrical shape. Furthermore, the pre-thread is divided into several thread segments in the area of the chip pockets.

In DE 33 37 534 A1 A universal screw suitable for wood-based materials is described, with a thread extending to the screw tip. The screw tip, viewed in the circumferential direction, has successive, discontinuous, particularly convex and concave shaped sections.

From the DE 93 07 816 U1 A screw for wood materials is produced which has a chip groove on each of two opposite sides of a screw tip section, running in the longitudinal direction of the screw. The chip grooves extend over several thread turns of the thread present in the area of the screw tip section and intersect the thread turns. The chip grooves have a side view, as shown in the 2 shown, a trough-shaped concave shape.

The EP 3 040 563 B1 discloses a wood screw with a thread root between two thread turns. In particular, 6 It can be seen that there is a discontinuity in the area of the thread root in the form of a kink with a beveled section or a stepped groove. Displaced material from the substrate is forced into the discontinuity during screwing.

A self-tapping drilling screw is also available from the EP 0 012 441 A1 The self-drilling screw has a cylindrical base body with threads in the holding part. A constriction is provided between the threads in the thread root, with a conical or roof-shaped bevel extending from the flanks of each thread to form the constriction. The bevels converge at a sharp angle in the area of the constriction.

The DE 699 15 254 T2 Describes a bone screw with a cylindrical shaft and a threaded section that tapers toward the tip. At the base of the thread, i.e., between two adjacent threads, there is a defined profile, which is also conical. This design allows for low specific pressure under load and low torque during screwing.

In the WO 2020/060902 A1 A screw is disclosed in which a screw-shaped recess is provided in the shaft between the threads, which merges with rounded edges into separate, flat edge areas.

Out of US 2008/080953 A1 The result is a screw that is particularly suitable for plastics and has a shaft and a tapered screw tip. The thread runs from the screw tip with its tapered section over the cylindrical shaft to the screw head. Between each thread turn, there is a constriction formed by two converging flanks of the thread root. The constriction is also present in the area of the screw tip.

The DE 10 2017 208 282 A1 shows a wood screw with a thread running along the cylindrical shaft. Only a The area between two thread flanks is concave with a radius R, followed by beveled surfaces on both sides. This is a particularly stretchable screw.

The CN 2 553 163 Y , the US 42 905 A , the US 113 006 A and the US 2 039 368 A each relate to a wood screw with a screw shaft which has a screw head and a screw tip on the side opposite the screw head, wherein at least one threaded section extending to the screw tip is formed on the screw shaft and a thread root is formed between the thread flanks of the threaded section of the screw tip, which has a concave groove in the longitudinal direction of the screw shaft.

Finally, it is from the DE 10 2013 210 566 A1 and from the EP 3 401 557 A1 It is known that the screw head of the wood screw has at least two milling ribs on its underside facing the screw tip, which are arranged symmetrically along the circumference of the screw head.

The invention is based on the object of providing a wood screw whose screwing torque is low, whose screwing behavior is constant and which can be optimally centered at the screwing point, so that the screwing process as a whole is improved and time is saved during the assembly of wooden components.

The invention solves this problem with the features of patent claim 1.

Further embodiments of the invention are the subject of the subsequent subclaims.

A wood screw with a screw shaft which has a screw head and a screw tip on the side opposite the screw head, wherein at least one threaded section extending to the screw tip is formed on the screw shaft, wherein between the thread flanks of the threaded section of the screw tip there is also formed a thread root which has a concave groove in the longitudinal direction of the screw shaft, was further developed according to the invention in such a way that the thread root of the threaded section of the screw tip is composed of two regions which follow one another in the direction of the screw tip, so that the concave groove is followed in each case by a region with an inclined surface.

In other words, the invention is based on the formation of a concave constriction between each of the two thread flanks of the threaded section of the screw tip, which are arranged side by side in the side view of the wood screw. The invention thus relates to the concave, i.e. inwardly curved, core diameter of the screw tip, which decisively facilitates screwing in and centering, also referred to as "biting in," of the wood screw at the screwing point. Since the screwing-in time also depends significantly on the screw's "biting in," the novel design of the screw tip provides an additional corresponding advantage. Wood screws displace the wood material during screwing in. With a wood screw according to the invention, this results in a smaller volume of wood material to be displaced and thus a reduced torque required in the screw-in chamfer. The cutting of the thread flanks and its "screw pull-in force" is optimized, resulting in deeper penetration and continuous and stable screwing in behavior of the wood screw. Due to the concave groove, the increase in the core diameter is accompanied by a reduction in the wedge effect when viewed from the screw tip towards the screw head, so that the wood screw exerts a smaller splitting effect on the wood material. The invention therefore provides a wood screw with a low screwing-in torque, a consistent screwing-in behavior and which can be optimally centered at the screwing-in point, thus improving the overall screwing-in process and saving time when assembling wooden components. A further significant innovation of the invention is that the thread root of the threaded section of the screw tip is made up of two areas that follow one another in the direction of the screw tip, so that the concave groove is followed by an area with an inclined surface. This very special design of the thread root creates a homogeneous transition between the groove and the adjoining inclined surface, which optimizes the material displacement of the wood material during the screwing-in process.

According to a first embodiment of the invention, it is proposed that the concave groove has a radius R for which, based on the nominal diameter d of the thread of the wood screw, the following applies: d / R = 1.2 to 2.0. Preferably, the ratio d / R = 1.714. To give an example, let us assume that the nominal diameter of the screw shaft is 6 mm. For this case study, according to this The proposed solution of the invention therefore involves a radius of 3.5 mm. The radius is the same size at all thread roots of the threaded section of the screw tip.

It is also particularly advantageous if the length (L) of the threaded section of the screw tip is L = 2 x d, i.e., twice the nominal diameter of the wood screw. To stick with the previously mentioned example, where the nominal diameter is 6 mm, this would result in a screw tip length of 12 mm. This already shows that the screw tip is relatively long, which also significantly improves screwing performance.

In addition to the length of the screw tip, the design of the screw tip itself is also important. A further proposal of the invention is for the screw tip to have a tip angle α between α = 15° and α = 25°. A preferred tip angle here is 20°. Thus, the screw tip of a wood screw according to the invention is designed like a needle or nail, allowing it to penetrate the comparatively softer wood material before screwing in. In this way, the fixation of the wood screw in the substrate has been optimized.

Wood screws according to the invention can have a thread that runs along the entire screw shaft. However, the special characteristics of the wood material mean that it is advantageous if the wood screw has different thread sections or even thread-free sections, starting from the screw tip and running in the direction of the screw head. Thus, according to one embodiment of the invention, it is proposed that the wood screw have a second thread section, following the thread section of the screw tip in the direction of the screw head, with at least one skiving rib formed between the thread flanks. Such a skiving rib serves in particular to fiberize the wood material. This can effectively counteract unwanted splitting of the wood during screwing.

The peeling rib, formed as a raised structure at the base of the thread, can be designed in different ways. For example, the peeling rib can run helically along the screw shaft of the wood screw. Thus, the peeling rib runs independently of the wood screw's threads, for example, in a direction opposite to the screw's direction.

An alternative embodiment of the skiving rib further comprises the skiving rib running in a straight line along the screw shaft, forming an acute angle β with the central axis of rotation of the wood screw. According to a further proposal of the invention, the angle β can be between β = 10° and β = 40°, but preferably 30°.

If a wood screw according to the invention is divided into several threaded sections, it is the subject of a design measure that the wood screw has a third threaded section following the second threaded section in the direction of the screw head, which third threaded section consists exclusively of a screw thread with thread flanks that are formed along the screw shaft of the wood screw.

Starting from the screw tip and viewed in the direction of the screw head, according to a further development of the invention, it is further proposed that the wood screw have a fourth threaded section following the third threaded section in the direction of the screw head, the thread flanks of which, unlike the thread flanks of the remaining threads of the threaded sections, are designed as skiving cutters. Such a skiving cutter consists of threads arranged helically around the core diameter of the wood screw, the diameter of which is slightly larger than the diameter of the screw shank. The skiving cutter performs a scraping function and is particularly important when, for example, two boards are screwed together. The bore of the upper board is enlarged by the skiving cutter, which subsequently reduces the screwing-in resistance of the wood screw. However, such a skiving cutter is generally only used when wood screws with a partial thread are used. For wood screws with a full thread, the skiving cutter is generally omitted.

According to a further proposal, the wood screw according to the invention is also characterized in that the wood screw has a thread-free section following the fourth threaded section in the direction of the screw head, which extends up to the screw head and has a circular cylindrical diameter. This thread-free section preferably corresponds to the core diameter of the wood screw and also reduces the resistance when screwing the wood screw into the wood material.

The wood screws according to the invention can be equipped with a screw head that is designed as a countersunk head, a flat head, a cylinder head or a pan head. Other Screw head shapes are of course also usable and fall within the scope of the invention. Considering, for example, a wood screw with a countersunk head, it is a particular advantage of the invention if the screw head of the wood screw has at least two milling ribs on its underside facing the screw tip, which are distributed symmetrically around the circumference of the screw head. The milling ribs serve to facilitate the penetration of the screw head into the wood material if there is no pre-drilled hole in the form of a countersunk hole.

Particularly preferably, the screw head has 6 to 8 milling ribs on its underside, evenly distributed along the circumference. This ensures optimal milling of the countersunk head of the wood screw.

In a manner known per se, a wood screw according to the invention is also equipped with a screw head which has a tool engagement surface or a tool attack surface on its screw head top side, which is suitable, for example, for inserting or applying a screwdriver or, in general, a screwing tool.

According to one embodiment of this proposed solution, the tool engagement surface or tool attack surface is a screw slot, a Phillips slot, an external hexagon, an internal wrench surface or an external wrench surface.

The invention is explained in more detail below with reference to the accompanying drawings. The illustrated embodiment does not represent a limitation to the variant shown, but serves merely to explain a principle of the invention.

Identical or similar components are always designated by the same reference numerals. To illustrate the functionality of the invention, the figures show only highly simplified schematic diagrams, omitting components that are not essential to the invention. However, this does not mean that such components are not present in a solution according to the invention.

• 1: eine Holzschraube in der Seitenansicht,
• 2: einen vergrößerten Ausschnitt des Gewindeabschnittes der Schraubenspitze der Holzschraube aus 1 und
• 3: den Schnittverlauf III-III aus 1.

It shows:

• 1 : a wood screw in side view,
• 2 : an enlarged section of the threaded section of the screw tip of the wood screw from 1 and
• 3 : the section III-III from 1 .

The exemplary in the 1 The wood screw 1 shown essentially consists of the screw shaft 2, which has a screw head 3 on one side and a screw tip 4 on the side opposite the screw head 3. Viewed in the longitudinal direction of the screw shaft 2, this has different threaded sections 5, 6, 7, 8 and a thread-free section 16. The threaded section 5 relevant according to the invention ends in the thread tip 4, which in the present case is designed to be needle-like or nail-like and to taper to a point, so that the wood screw 1 can first be pierced into the wood material with the screw tip 4 before screwing in and can thus be loosely fixed at the screwing point before the actual screwing in process begins. The special features of the threaded section 5 with the screw tip 4 according to the invention will be described in more detail below in connection with the description of the 2 received.

The threaded section 5 is followed, starting from the screw tip 4 and moving towards the screw head 3, by a threaded section 6, between the thread flanks 9 of which skiving ribs 13 are formed, which in the example shown have a straight line at an angle β to the rotational center axis 14 of the wood screw 1. The angle β in the example shown is approximately 20°. However, such skiving ribs 13 can be formed not only in sections, as in the example shown in 1 shown wood screw 1, but also over the entire length of the screw shaft 2. The peeling ribs 13 have the task of defibringing the wood material in order to prevent the wood from splitting when screwing in the wood screw 1.

If one follows the screw shaft 2 further in the direction of the screw head 3, the previously described threaded section 6 is followed by a further threaded section 7, which only has a conventional screw thread of a wood screw 1.

Following the threaded section 7 there follows a differently designed threaded section 8, the thread flanks 15 of which form a skiving cutter, the thread flanks 15 having a larger diameter than the shaft diameter of the screw shaft 2. When screwing two boards together, the bore of the upper board is enlarged with the skiving cutter, so that the overall screwing resistance of the wooden hood 1 is reduced.

In the direction of the screw head 3, the threaded section 8 is followed by a thread-free section 16.

On the underside 17 of the screw head 3 facing the thread-free section 16, a plurality of milling ribs 18 are arranged along the circumference. These milling ribs, in the case of a countersunk screw, enable the formation of a countersunk hole in the wood material when screwing in, provided such a countersunk hole has not been previously introduced into the wood surface. In a conventional manner, the screw head 3 has a tool engagement surface 20 on its upper side 19, which serves to couple the screw head 3 to a suitable screwing tool. The tool engagement surface 20 can be, for example, a Phillips head.

From the 2 shows an enlarged section of the threaded section 5, which contains the screw tip 4. This is shown in a more improved manner than in connection with the description of the 1 was possible, clearly showing the special features of the threaded section 5 of the screw tip 4 according to the invention. Between each individual thread flank 9, a thread root 10 is formed, which has a concave, i.e., rounded groove 11. The grooves 11 have a ratio of the nominal diameter d of the thread to the radius, which in this case is 1.714. A further special feature of the thread root 10 can be seen in the fact that, viewed in the direction of the screw tip 4, an inclined surface 12 adjoins each concave groove 11, the width of which, viewed in the direction of the screw tip 4, increases with each thread turn. With constant dimensions of the thread root 10 between two adjacent thread flanks 9, the length of the concave groove 11 is consequently reduced. The illustration in the 2 also the threaded section 6 adjoining the threaded section 5 with the peeling ribs 13 formed thereon.

The 3 finally shows the section III-III from 1 through the screw shaft 2 of the wood screw 1. The cut runs through the thread-free section 16, which in this design corresponds to the shaft diameter of the wood screw 1 and allows a view of the underside 17 of the screw head 3. Several milling ribs 18 are formed along the circumferential surface, which are distributed symmetrically over the circumference of the underside 17 of the screw head 3.

LIST OF REFERENCE SYMBOLS:

1

wood screw

2

screw shaft

3

screw head

4

screw tip

5

Threaded section (tip)

6

threaded section

7

threaded section

8

threaded section

9

Thread flank

10

Thread root

11

concave groove

12

inclined surface

13

peeling rib

14

Rotation center axis

15

Thread flank

16

threadless section

17

bottom

18

milling rib

19

Screw head top

20

Tool engagement surface

Claims (16)

Wood screw (1), comprising a screw shaft (2) which has a screw head (3) and, on the side opposite the screw head (3), a screw tip (4), wherein at least one threaded section (5, 6, 7, 8) extending to the screw tip (4) is formed on the screw shaft (2), and between the thread flanks (9) of the threaded section (5) of the screw tip (4) there is a thread root (10) which has a concave groove (11) in the longitudinal direction of the screw shaft (2), characterized in that the thread root (10) of the threaded section (5) of the screw tip (4) is composed overall of two regions (11 and 12) which follow one another in the direction of the screw tip (4), so that the concave groove (11) is followed in each case by a region with an inclined surface (12). Wood screw (1) after Claim 1 , characterized in that the concave groove (11) has a radius (R) for which, based on the nominal diameter (d) of the thread of the wood screw (1), the following applies: d / R = 1.2 to 2.0. Wood screw (1) according to one of the preceding claims, characterized in that that the length (L) of the threaded section (5) of the screw tip (4) is L = 2 xd. Wood screw (1) according to one of the preceding claims, characterized in that the screw tip (4) has a tip angle α between α = 15° and α = 25°. Wood screw (1) according to one of the preceding claims, characterized in that the wood screw (1) has a second threaded section (6) following the threaded section (5) of the screw tip (4) in the direction of the screw head (3) and having at least one skiving rib (13) which is formed between the thread flanks (9). Wood screw (1) after Claim 5 , characterized in that the peeling rib (13) runs helically along the screw shaft (2) of the wood screw (1). Wood screw (1) after Claim 5 , characterized in that the peeling rib (13) runs straight along the screw shaft (2), forming an acute angle β with the center axis of rotation (14) of the wood screw (1). Wood screw (1) after Claim 7 , characterized in that the angle β is between β = 10° and β = 40°. Wood screw (1) according to one of the preceding claims, characterized in that the wood screw (1) has a third threaded section (7) following the second threaded section (6) in the direction of the screw head (3), which third threaded section consists exclusively of a screw thread with thread flanks (9) which are formed along the screw shaft (2) of the wood screw (1). Wood screw (1) according to one of the preceding claims, characterized in that the wood screw (1) has a fourth threaded section (8) following the third threaded section (7) in the direction of the screw head (3), the thread flanks (15) of which, in contrast to the thread flanks (9) of the remaining threads of the threaded sections (5 to 7), are designed as skiving cutters. Wood screw (1) according to one of the preceding claims, characterized in that the wood screw (1) has a thread-free section (16) which follows the fourth threaded section (8) in the direction of the screw head (3), which is formed up to the screw head (3) and has a circular cylindrical diameter. Wood screw (1) according to one of the preceding claims, characterized in that the screw head (3) of the wood screw (1) has at least two milling ribs (18) on its underside (17) facing the screw tip (4), which are arranged distributed symmetrically along the circumference of the screw head (3). Wood screw (1) after Claim 12 , characterized in that the screw head (3) has 6 to 8 milling ribs (18) on its underside (17). Wood screw (1) according to one of the preceding claims, characterized in that the screw head (3) of the wood screw (1) has a tool engagement surface (20) or a tool attack surface on its screw head top side (19). Wood screw (1) after Claim 14 , characterized in that the tool engagement surface (20) or the tool engagement surface is a screw slot, a Phillips slot, an external hexagon, an internal key surface or an external key surface. Wood screw (1) according to one of the preceding claims, characterized in that the screw head (3) is designed as a countersunk head, a plate head, a cylinder head or a pan head.

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