Countersunk head screw

1. A countersunk head screw comprising a cylindrical shaft ( 2 ) and an essentially conical countersunk head ( 4 ) comprising at least two edges ( 15 ) on the lower side, wherein the edges ( 15 ) each mark an end of a partial surface ( 10 ) located on the lower side, each of the partial surfaces lying on a non-concave surface of rotation, characterised in that each partial surface ( 10 ) has a separate axis ( 12 ) which does not coincide with the shaft axis ( 6 ), and which is inclined with respect to the shaft axis at an inclination angle α; wherein an arc defined by an intersection of the partial surface with a plane normal to the shaft axis is not circular in nature.

2. The countersunk head screw according to claim 1 , characterised in that each surface of rotation is a cone envelope surface forming the partial surface ( 10 ).

3. The countersunk head screw according to claim 1 , characterised in that the cone angle β of the partial surfaces ( 10 ) is β≦180°.

4. The countersunk head screw according to claim 1 , characterised in that the inclination angle α is in the range 0<α≦15° or 25°≦α≦35°.

5. The countersunk head screw according to claim 1 , characterised in that the axes ( 12 ) of the conical partial surfaces ( 10 ) do not intersect with the shaft axis ( 6 ).

6. The countersunk head screw according to claim 5 , characterised in that for the cone angle β and the inclination angle α, the relationship 2*α+β<180° applies.

7. The countersunk head screw according to claim 6 , characterised in that 90°≦2*α+β≦160°.

8. The countersunk head screw according to claim 6 , characterised in that 2*α+β≅120°.

9. The countersunk head screw according to claim 1 , characterised in that the transition of the partial surfaces ( 10 ) from the countersunk head ( 4 ) to the shaft ( 2 ) is formed by an angular surface ( 30 ).

10. The countersunk head screw according to claim 1 , characterised in that each conical partial surface ( 10 ) has a common surface line ( 16 ) with an imaginary surface of rotation, which has an axis which is common with the shaft axis ( 6 ), and that beginning from this surface line ( 16 ), each partial surface ( 10 ), with respect to the imaginary surface of rotation, is gradually radially curved inwards in circumferential direction.

11. The countersunk head screw according to claim 10 , characterised in that the surface of rotation is a conical surface, wherein the common surface line ( 16 ) lies in an axial section plane A-A containing the shaft axis.

12. The countersunk head screw according to claim 10 , characterised in that the common surface line ( 16 ) coincides with one of the two approximately radial edges ( 15 ) of the respective partial surface ( 10 ), or is located between these edges ( 15 ).

13. The countersunk head screw according to claim 10 , characterised in that the common surface line ( 16 ) in a right-hand configuration forms a leading cutting edge ( 15 ) of the respective partial surface ( 10 ).

14. The countersunk head screw according to claim 10 , characterised in that the common surface line ( 16 ) in a left-hand configuration forms a trailing locking edge ( 15 ) of the respective partial surface ( 10 ).

15. The countersunk head screw according to claim 1 , characterised in that the partial surfaces ( 10 ) are uniformly distributed in a number of 2≦T≦24 around the circumference of the countersunk head ( 4 ) wherein T is the number of partial surfaces.

16. The countersunk head screw according to claim 15 , characterised in that the number T of the partial surfaces is 2, 3, 4, 6, 8, 12, or 24.

17. A countersunk head screw comprising a cylindrical shaft ( 2 ) and an essentially conical countersunk head ( 4 ) comprising at least two edges ( 15 ) on the lower side, wherein the edges ( 15 ) each mark an end of a partial surface ( 10 ) located on the lower side, each of the partial surfaces lying on a non-concave surface of rotation, characterised in that each partial surface ( 10 ) has a separate axis ( 12 ) which does not coincide with the shaft axis ( 6 ), and which is inclined with respect to the shaft axis at an inclination angle α; wherein each surface of rotation is a cone envelope surface forming the partial surface ( 10 ); the cone angle β of the partial surfaces ( 10 ) is β≦180° and the inclination angle α is in the range 0<α≦15° or 25°≦α≦35°; wherein an arc defined by an intersection of the partial surface with a plane normal to the shaft axis is not circular in nature.

18. The countersunk head screw according to claim 17 , characterised in that the transition of the partial surfaces ( 10 ) from the countersunk head ( 4 ) to the shaft ( 2 ) is formed by an angular surface ( 30 ).

19. The countersunk head screw according to claim 17 , characterised in that in that each conical partial surface ( 10 ) has a common surface line ( 16 ) with an imaginary surface of rotation, which has an axis which is common with the shaft axis ( 6 ), and that beginning from this surface line ( 16 ), each partial surface ( 10 ), with respect to the imaginary surface of rotation, is gradually radially curved inwards in circumferential direction.

20. A countersunk head screw comprising a cylindrical shaft ( 2 ) and an essentially conical countersunk head ( 4 ) comprising at least two edges ( 15 ) on the lower side of the countersunk head, wherein the edges ( 15 ) each mark an end of a partial surface ( 10 ) located on the lower side, each of the partial surfaces lying on a non-concave surface of rotation, characterised in that each partial surface ( 10 ) is defined by a separate axis ( 12 ) and wherein the separate axis ( 12 ) does not coincide with the shaft axis ( 6 ), and which is inclined with respect to the shaft axis at an inclination angle α; wherein an arc defined by an intersection of the partial surface with a plane normal to the shaft axis is not circular in nature.

21. The countersunk head screw according to claim 20 wherein in each surface of rotation is a cone envelope surface forming the partial surface ( 10 ), the cone angle β of the partial surfaces ( 10 ) is β≦180° and the inclination angle α is in the range 0<α≦15° or 25°≦α≦35°.