DE9202650U1 - Countersunk screw - Google Patents

Description

DESCRIPTION Countersunk screw

The invention relates to a countersunk head screw according to the features listed in the preamble of the main claim.

In general, the use of countersunk head screws requires that the hole is countersunk using a countersunk head so far that the screw head of the countersunk head screw used fits completely into this countersunk hole. However, countersunk drilling represents an additional work step, which is why special countersunk head screws, for example in accordance with DE-A-33 34 212, have been developed to avoid this. These known countersunk head screws have countersunk cutting edges that are regularly distributed along the surface lines on the conical underside of their screw head, between which chip-receiving grooves of different depths are arranged, which extend to a cylindrical surface of the screw head just below its front surface.

When screwing such countersunk head screws into simple holes, the countersunk cutting edges are supposed to replace the previously mentioned special countersunk process and work themselves into the material of the workpiece in a self-cutting manner. However, this creates the problem that individual countersunk cutting edges get caught when penetrating the workpiece and therefore cause the edge of the hole to splinter. This defect was unavoidable, although with the previously known countersunk head screws special emphasis was placed on catching the chips that arise when the screw is screwed in.

without them being able to reach the surface of the workpiece. The grooves between the individual countersinking cutting edges are designed to deepen in the opposite direction to the direction of rotation in order to create a sufficiently large storage space for the chips. This led to the countersinking cutting edge being designed at an angle of approx. 90°, starting from the surface of the screw head.

Attempts were then made to arrange the countersunk cutting edges not along a surface line of the screw head but at an angle to it, so that a point on the countersunk cutting edge gradually remains behind against the screwing direction when the point moves outwards, as is clear from DE-A-33 44 048. Apart from the fact that this makes the tool for producing such countersunk head screws even more complicated, the hooking of the countersunk cutting edges and the tearing of the screw points could not be effectively prevented.

The object of the invention is to develop a countersunk head screw that can be produced with a simpler tool and with a long punching time, which enables trouble-free screwing without reducing the quality of the screw point, even with hard workpiece material.

Based on DE-A-33 34 212, the object of the invention is achieved with the features listed in the characterizing part of the main claim.

In practice, it was initially found that increasing the countersinking edges on the screw head enables a better distribution of the screwing forces on the countersinking edges and a more gentle removal of the material chips in the countersinking area. The obtuse-angled transition of the outer surface of the screw head into the

The countersunk cutting edges are prevented from hooking into the flanks of the respective groove between the countersunk cutting edges and a type of scraping process is achieved instead. The screw points formed with the countersunk head screws according to the invention are characterized by high quality and an aesthetic impression that was previously unattainable.

The tool required to produce the countersunk head screws according to the invention has a simpler design than the known tools and is characterized by an increased punching time. This effect is essentially achieved by the fact that the chip-receiving grooves located between the countersunk cutting edges are symmetrical in relation to a surface line running through the groove base. The individual areas of the tool which are specifically intended for forming these grooves and the ribs with the countersunk cutting edges are not subjected to irregular loads during cold forming. In particular, the tool in this sensitive area is not loaded in the circumferential direction of the screw head during the upsetting process, which results in an overall longer punching time for the tool for producing the countersunk head screws according to the invention.

Details of the invention are set out in the subclaims.

In particular, the arrangement of a tapered shoulder between the screw shaft and the screw head has proven to be very useful. This significantly increases the breaking torque of the countersunk head screw and prevents the risk of notch fracture, which is present in the subject of DE-A-33 34 212. This tapered shoulder also helps to increase the punching time of the

the tool required for its manufacture, because the tool's stamping attachment, which is intended to form the attack surfaces for a screwing tool, finds more material during cold forming. The countersunk head screws according to the invention can therefore be provided with deep hexagon socket recesses without any problems.

The other features of the invention listed in the subclaims also contribute to simplifying the tool for producing such countersunk head screws and thus have a significant cost-reducing effect. In addition, the strength of the countersunk head screw according to the invention is improved, which means that it can be used preferably for hard workpiece materials, especially for workpieces made of oak, beech or chipboard.

These and other features of the invention emerge from the drawing. The invention is shown schematically and by way of example. They show:

Fig. 1: a partial side view of a countersunk head screw,

Fig. 2: a section through the countersunk head screw according to Fig. 1 along the line II-II,

Fig. 3: a vertical section through the countersunk head screw according to Fig. 1 and

Fig. 4: a cross-section through the screw head according to Fig. 3 along the line IV-IV.

The countersunk screw (1) shown in the drawing has a conical screw head (2) and a screw shaft (3), between which a conical shoulder (4) is located. While the screw head (2) usually has a full angle of 90°, the full angle of the conical shoulder (4) is 60° in a preferred embodiment.

In the embodiment, twelve ribs (5) are evenly distributed on the underside of the screw head (5), between which chip-receiving grooves (6) are provided. As Fig. 4 clearly shows, the flanks (10) delimiting the grooves (6) and the outer surface (11) of the ribs (5) form countersunk cutting edges (7) that run along the surface lines of the screw head (2). The angle between these flanks (10) and the tangent of the outer surface (11) is an obtuse angle. In the example in Fig. 4, it is shown that the flanks (10) of a rib (5) form an angle gamma with each other, which in the embodiment is 30°.

The grooves (6) are symmetrical in relation to a surface line (14) running through the groove base (see Fig. 1). However, the depth of the groove is not constant, as shown in Fig. 3. At the upper end, the individual groove (6) is delimited by a circumferential line (12) which extends parallel to the edge of the front face (8) of the screw head (2). At the lower end, the individual groove (6) is provided with a groove-shaped run-out (13). The depth of the groove increases steadily from the groove-shaped run-out (13) in the direction of the circumferential line (12). As shown in Fig. 3 in particular, smooth transitions into the associated surface areas are provided at both ends of the groove. The lower transition of the individual groove (6) extends into the surface area of the conical shoulder (4), with the beginning

of the concave-shaped outlet (13) is approximately at the height of the transition of the conical shoulder (4) into the screw head (2).

Fig. 4 also shows in section that the groove base is formed in the shape of a circular arc and merges into the oblique flanks (10). The radius of this circular arc remains the same over the length of the groove. The angle ( oC 1) between a surface line running through the groove base and the adjacent surface line through the surface area of the screw head is approximately 5° in the embodiment. The transition angle ( σ<^) from the groove base to the surface area of the screw head (2) is approximately 30°.

When the countersunk head screw (1) shown in the drawing is screwed into a hole in a workpiece, the ribs (5) with their countersunk cutting edges (7) hit the edge of the hole and scrape it parallel to the outer surface of the screw head (2). Because the angle between the outer surface (11) of the rib (5) and the flanks (10) of the groove (6) is blunt, the material of the workpiece is subjected to a scraping process which prevents the countersunk cutting edges (11) from hooking into the material. In this way, splintering of the material in the area of the screw point is reliably avoided. The countersunk hole created when the countersunk head screw according to the invention is screwed in looks as if it had been created by a special countersunk process.

Of course, the countersunk head screw has the usual recesses for the attack of a screwing tool, for example in the form of a Phillips head, screw slot or hexagon socket profile.
The invention is not limited to the drawing

illustrated embodiment. It also extends to designs that are immediately apparent to the average person skilled in the art from knowledge of the invention.

10 PARTS LIST

1 countersunk screw

2 screw head

3 Screw shaft

4 Cone attachment

5 Rib

6 grooves

7 Countersinking blade

8 Front face

9 cylindrical surface

10 flank

11 Surface of the rib

12 Circumference line

13 coved spout

14 Mantle line

11

Claims (8)

PROTECTION CLAIMS 1) Countersunk head screw (1) with ribs (5) arranged regularly on the conical underside of its screw head (2), running along surface lines and having countersunk cutting edges (7), between which chip-receiving grooves (6) of different depths are arranged, which extend to a cylindrical surface (9) of the screw head (2) just below its front surface (8), characterized in that more than eight, preferably twelve ribs (5) are provided, between which the grooves (6) are formed symmetrically with respect to a surface line (14) running through the groove base, the individual countersunk cutting edge (7) being formed by an obtuse-angled transition of the surface (11) of the screw head (2) into the flank (10) of the associated groove (6). 2) Countersunk head screw according to claim 1, characterized in that the transition of the screw shaft (3) into the screw head (2) is formed by a conical extension (4) whose full angle ( fi ) is smaller than the full angle ( c?<C ) of the screw head (2). 3) Countersunk head screw according to claim 2, characterized in that the full angle ( β) of the conical extension (4) is approximately 60°. 4) Countersunk head screw according to claim 1 or one of the following, characterized in that the individual groove (6) extends to the transition between the conical shoulder (4) and the screw head (2) and then gently into the outer surface of the conical shoulder (4) transforms. 5) Countersunk head screw according to claim 1 or one of the following, characterized in that the grooves (6) have a depth that increases from the conical shoulder (4) in the direction of the cylindrical outer surface (9) of the screw head (2). 6) Countersunk head screw according to claim 1 or one of the following, characterized in that the grooves (6) have a radius in their base that remains constant along the groove (6). 7) Countersunk head screw according to claim 1 or one of the following, characterized in that the transition of the individual groove (6) into the cylindrical surface (9) takes place along a circumferential line (12) running parallel to the upper edge of the screw head (8). 8) Countersunk head screw according to claim 1 or one of the following, characterized in that the transition of the individual groove (6) into the outer surface of the conical shoulder (4) is designed as a groove-shaped outlet (13).