screw

Abstract

The invention relates to a screw (1), in particular a wood screw, which has a countersunk head (4) with two truncated conical shapes. It is proposed that the edge (9) in front along the direction of rotation during screwing, which forms the milling groove (7), is configured with a curvature along the direction of rotation during screwing, whereby the milling groove (7) is lengthened in the circumferential direction, whereby the engagement of the cutting edge (8) into, for example, wood is improved.

Description

Technical Field

[0001] The present invention relates to a screw, and in particular to a wood screw, that is, a screw with a wood screw thread. Background Art

[0002] Many wood screws have a countersunk head, ie a screw head with a truncated conical underside, which, when the screw is driven in with an electric screwdriver, is embedded in the wood and forms a complementary countersunk hole in the wood.

[0003] Utility model DE 20 2007 018 179 U1 discloses a wood screw with a countersunk head. This countersunk head has a recess in the underside of the head, which is a milled groove. This recess is delimited by two radial and two arc-shaped edges extending in the circumferential direction. The rear edge of the milled groove forms a cutting edge that separates chips from the wood when the screw head is inserted into the wood during screwing. This cutting edge creates a countersunk hole for the screw head, or at least makes it easier to create the countersunk hole. The term "rear" refers to the direction of rotation of the wood screw when it is driven into wood or other material. Summary of the Invention

[0004] The object of the present invention is to improve the machining effect of a milled groove on the underside of the countersunk head of a screw inserted into wood, plastic, etc. and / or to reduce the weakening of the screw in the region of the screw head and / or the transition from the screw head to the screw shank. "Etc." refers to materials with similar machining properties to wood or plastic, so that the milled groove on the underside of the screw head forms a countersunk hole.

[0005] The screw according to the present invention is, in particular, a wood screw with a wood screw thread. The wood screw has a countersunk head as a screw head with a head underside. The head underside can be designed, for example, in a truncated cone shape or in a concave shape (i.e., in a concave rounded shape). Therefore, the generatrix of the head underside can be a straight or curved line. In particular, the screw head has the shape of two axially adjacent truncated cones with different cone angles that taper in the same direction. The generatrix of the head underside has a bend in the axial plane, and the side surface of the head underside has a circumferential inner edge. In addition to a concave rounded shape, "concave" can also be understood to mean a head underside with one or more circumferential inner edges.

[0006] The term "side face" refers to a surface that is rotationally symmetrical about the longitudinal axis of the screw and circumscribes the underside of the head. At least one milled groove is cut out of this rotationally symmetrical surface, preferably a plurality of geometrically identical milled grooves, and in particular, the plurality of milled grooves are arranged rotationally symmetrically about the longitudinal axis. The at least one milled groove forms a depression in the underside of the head. This depression is bounded at the transition to the side face by an intersection line, which, relative to the direction of rotation of the screw during installation, is formed by a front and a rear edge. The front and rear edges together form the intersection line. The rear edge forms a cutting edge that separates chips when the screw is installed and the screw head is embedded in wood, plastic, etc., thereby creating a countersink for the screw head, or at least facilitating its creation. The terms "rear" and "front" always refer to the direction of rotation of the screw during installation. The "rear" edge follows the "front" edge in the direction of rotation. The rear edge (or the cutting edge) can consist of a plurality of line segments that merge into one another, in particular when the underside of the head has a bend.

[0007] The front edge of the milled groove, in the direction of rotation when the screw is inserted, at the transition to the side surface of the underside of the head, consists of two line segments, and the first line segment, located radially further outward with respect to the longitudinal axis of the screw, has a curvature in the direction of rotation when the screw is inserted. "Curvature in the direction of rotation" means that the arched structure is oriented in the same direction as the direction of rotation, i.e., away from the cutting edge. In particular, the maximum distance of an imaginary chord of the line segment from the front edge is at least 5 percent of the chord length. The second line segment of the front edge of the milled groove, in the transition to the side surface of the underside of the head, located radially further inward with respect to the longitudinal axis of the screw, is straight or nearly straight. Hereinafter, "inner" and "outer" are always understood to mean in a radial direction relative to the longitudinal axis of the screw, that is, "inner" is understood to mean "near the longitudinal axis of the screw." If the head underside has the shape of two axially adjacent truncated cones, the curved line segment of the front edge of the milled groove lies on the truncated cone with the larger radius and, in particular, adjoins the surrounding inner edge on the outside, at which the two truncated cones merge into one another. The straight, almost straight, or at least slightly curved line segment of the front edge of the milled groove lies on the truncated cone with the smaller diameter. In particular, the first line segment of the front edge merges into the second line segment at the surrounding inner edge.

[0008] Due to the curvature of the front edge of the milling groove on the transition to the side surface of the lower side of the head in the outer line segment, the milling groove has a longer length in the circumferential direction, thereby also extending the back cutting surface of the milling groove in the circumferential direction. The back cutting surface is the following surface of the milling groove: in the direction of rotation when the screw is screwed in, this surface is located in front of the cutting edge. The milling groove can have a relatively large volume at a small depth, thereby improving the milling effect without excessively weakening the head. Therefore, extending the milling groove and the back cutting surface in the circumferential direction improves the pressing of the cutting edge of the milling groove into the workpiece and thus improves the cutting effect of the milling groove and the cutting edge.

[0009] Because the front edge of the milled groove is straight or nearly straight in the second, innermost segment compared to the outermost segment, the milled groove is shorter in the circumferential direction in the second, innermost segment compared to the first segment. This weakens the screw head less in the second, innermost segment than if the entire front edge of the screw head were bent or more strongly curved. The mechanical stresses on the screw head caused by the torque applied during screw insertion are greater radially closer to the longitudinal axis, so weakening of the screw head caused by the milled groove there should be minimized. Furthermore, tool mating surfaces (e.g., hexagonal, torx, etc.) in the screw head for the rotating tool used to drive the screw further weaken the screw head, particularly in the second, innermost segment.

[0010] In the technical solution of the present invention, the front edge of the milled groove in the second, more inner line segment is the intersection of an imaginary plane and the side surface of the underside of the head of the screw head. This intersection line is a straight line only when the plane is an axial plane. However, the plane is preferably a secant plane. "Almost straight" refers in particular to this intersection line of the secant plane and the side surface of the underside of the head.

[0011] The technical solution of the present invention is that the edge of the milling groove in the front along the rotation direction when the screw is screwed in extends obliquely from the inside to the outside along the rotation direction when the screw is screwed in in a second, more inner line segment.

[0012] The cutting edges preferably extend obliquely from the inside outward, counter to the direction of rotation when the screw is screwed in. Compared to a straight arrangement of the cutting edges, the oblique arrangement improves the milling behavior. A so-called "pulling" cut occurs, as is known from planing.

[0013] In particular, the inner second line segment of the front edge and the cutting edge each extend obliquely in different directions, ie one in the direction of rotation and one opposite to the direction of rotation.

[0014] The technical solution of the present invention provides a concave base surface for the milling flute. As mentioned above, "concave" refers to a two-dimensional, concave, arched structure. The base surface is the surface adjacent to the front edge of the milling flute in the direction of rotation during screwing. As explained above, the base surface is the flank, and the concave structure improves the cutting effect and increases the chip holding capacity of the milling flute.

[0015] The features and feature combinations, designs and technical solutions of the present invention mentioned above in the description, as well as the features and feature combinations mentioned later in the description of the drawings and / or drawn in the drawings, can be used not only in the respectively given or drawn combination, but also in basically any other combination, or alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawings. The single drawing shows a screw according to the invention. DETAILED DESCRIPTION

[0017] The screw 1 according to the present invention shown in the accompanying drawings is a wood screw having a shank 3 with a wood screw thread 2. The screw 1 has a countersunk head 4 as a screw head. The screw head, or the underside of the head of the screw head, has the shape of two axially adjacent truncated cones. The two truncated cones forming the countersunk head 4 taper in the same direction (i.e., away from the shank 3) and merge into each other at a circumferentially circular inner edge 5. The shape of the underside of the head can also be understood as concave due to the circumferential inner edge 5. The smaller diameter of the two truncated cones has a more acute cone angle.

[0018] A milled groove 7 is cut out of the side surface 6 of the head underside. The side surface 6 is a rotationally symmetrical, conical portion of the surface of the head underside. Without the milled groove 7, the side surface 6 would form the entire head underside. The milled groove 7 is surrounded at the transition to the side surface by a rear edge and a front edge in the direction of rotation when the screw 1 is inserted, and the front and rear edges merge into each other.

[0019] The rear edge of the milled groove 7 forms a cutting edge 8 at the transition to the side surface 6 of the underside of the head. When the screw 1 is screwed into a workpiece (not shown), such as wood or plastic, this cutting edge separates chips from the workpiece and thereby creates a countersunk hole for the screw head 4 of the screw 1, or at least simplifies its creation. The cutting edge 8 extends obliquely from the inside to the outside, counter to the direction of rotation during screwing. Because the cutting edge 8 intersects the inner edge 5, it has two transitional segments that are essentially straight and inclined relative to each other. "Inside" and "outside" refer to the distance from the longitudinal axis L of the screw 1, with the distance from the longitudinal axis L being smaller than the distance from the longitudinal axis L.

[0020] The front edge 9 of the milled groove 7 at the transition to the side surface 6 of the head underside, in the direction of rotation when the screw 1 is screwed in, consists of two segments: a first outer segment 11 and a second inner segment 12. The first outer segment 11 of the front edge 9, which is arranged within the larger diameter truncated cone of the screw head, which is configured as a countersunk head 4, has a curvature in the direction of rotation when the screw 1 is screwed in. In this embodiment, the radius of curvature of the first outer segment 11 of the front edge 9 of the milled groove 7 is initially constant outward from the inner edge 5 at the transition between the two truncated cones of the countersunk head 4, then decreases and increases as the front edge 9 approaches the rear edge of the milled groove 7, which forms the cutting edge 8, all the way to the outer end of the first outer segment. In other words, the outer segment 11 transitions abruptly with the cutting edge 8. The cutting edge 8 also extends from the inside outward as two segments, but each of the two segments is straight.

[0021] The inner line section 12 of the front edge 9 of the milled groove 7 at the transition to the side surface 6 of the underside of the head, in the direction of rotation when the screw 1 is screwed in, is straight in the region of the smaller diameter truncated cone of the countersunk head 4, or more precisely, is the intersection of an imaginary, flat, axially parallel secant plane with the smaller diameter truncated cone of the countersunk head 4, which can be described as "almost straight". In the region of the smaller diameter truncated cone of the countersunk head 4, the inner line section 12 of the front edge 9 of the milled groove 7 runs obliquely from the inside to the outside in the direction of rotation when the screw 1 is screwed in.

[0022] In summary, the front edge 9 of the milled groove 7, which is located in the direction of rotation when the screw 1 is screwed in, has a smaller curvature in a line segment 12 that is located further inward relative to the longitudinal axis of the screw 1 than in an outwardly adjacent, radially outer line segment 11. In the present embodiment, the curvature of the front edge 9 of the milled groove 7, which is located in the direction of rotation when the screw 1 is screwed in, begins at the inner edge 5. The inner line segment 12 transitions into the outer line segment 11 at the inner edge 5. The curvature of the front edge 9 of the milled groove 7 initially remains constant from the inner edge 5 outward, or then increases, while in the region of the second inner line segment, the curvature runs almost straight inward from the inner edge 5.

[0023] The curvature of the front edge 9 of the milled groove 7, which lies in the direction of rotation when the screw 1 is screwed in, extends the milled groove 7 and its clearance face 10 in the circumferential direction. The clearance face 10 is the surface of the milled groove 7 adjoining the front edge 9 and can also be understood as the base surface of the milled groove 7. Unlike the side surface of the underside of the head, the clearance face 10 does not rest against the workpiece when the countersunk head 4 is lowered into the workpiece, at least if the workpiece is not partially elastic. Therefore, the clearance face 10 improves the engagement of the cutting edge 8 in the workpiece and the stress effect on the cutting edge 8.

[0024] By making this flank concave, that is to say two-dimensionally concave, the effect of the flank 10 as the base of the milling flute 7 is improved. This not only improves the engagement of the cutting edge 8 in the workpiece, but also increases the volume of the milling flute 7 and thus the chip space for accommodating the chips.

[0025] Reference Signs List

[0026] screws

[0027] 1 screw

[0028] 2 wood screw threads

[0029] 3 screw rods

[0030] 4 countersunk head

[0031] 5 Inner edge

[0032] 6 Side

[0033] 7 Milling slots

[0034] 8 cutting edges

[0035] 9 on the front edge

[0036] 10 Flank

[0037] 11 The first segment of edge 9

[0038] 12 The second line segment of edge 9

[0039] L Longitudinal axis.

Claims

1. A screw with a countersunk head (4) having a head underside as a screw head, wherein: At least one milling groove (7) is excavated from the side surface of the lower side of the head, and a cutting edge (8) is formed on the transition portion to the side surface of the lower side of the head, which is used to produce a countersink in the workpiece when the screw (1) is screwed into the workpiece, wherein the edge (9) of the milling groove (7) on the transition portion to the side surface (6) of the lower side of the head, which is in the direction of rotation when the screw (1) is screwed in, is composed of two line segments (11, 12), the edge in the front having a curvature in the direction of rotation when the screw (1) is screwed in in a first line segment (11) radially more outward with respect to the longitudinal axis of the screw (1), and the edge in the front having a curvature in the direction of rotation when the screw (1) is screwed in in a second line segment (12) radially more inward. is straight, wherein the screw head has the shape of two axially adjacent truncated cones with different cone angles, wherein the truncated cones taper in the same direction and transition into each other at the surrounding inner edge (5) of the side surface, characterized in that the first line segment (11) of the front edge (9) of the milling groove (7) with the curvature is located on the truncated cone with a larger diameter and adjoins the surrounding inner edge (5) on the outside, on which the two truncated cones transition into each other; the straight second line segment (12) of the front edge (9) of the milling groove (7) is located on the truncated cone with a smaller diameter; and the first line segment (11) of the front edge (9) transitions into the second line segment (12) at the surrounding inner edge (5).

2. The screw according to claim 1, characterized in that The front edge (9) of the milling groove (7) along the rotation direction when the screw (1) is screwed in is an intersection line of a plane and the side surface of the lower side of the head in a second line segment (12) that is radially more inward.

3. The screw according to claim 1 or 2, characterized in that The front edge (9) of the milled groove (7) in the direction of rotation when the screw (1) is screwed in extends obliquely from the inside to the outside in the second radially inner line segment (12) in the direction of rotation when the screw (1) is screwed in.

4. The screw according to claim 1 or 2, characterized in that The cutting edge (8) extends obliquely from the inside to the outside in a direction opposite to the direction of rotation when the screw (1) is screwed in.

5. The screw according to claim 1 or 2, characterized in that The head underside of the screw head has the shape of two truncated cones that are axially adjacent to each other and taper in the same direction and have different cone angles.

6. The screw according to claim 1 or 2, characterized in that The base surface of the milled groove (7) which is adjacent to the front edge (9) of the milled groove (7) in the direction of rotation when the screw (1) is screwed in is concavely arched.

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