초록

A screw anchor includes a roughly cylindrical body (1) with a drilling portion (3) provided, at its free end, with drilling teeth (14-16), at the other end of the body, a bearing flange (5) and an external screw thread (7). The drilling portion (3) is configured as a portion of a drill bit.

대표청구항 ▼

The invention claimed is: 1. A screw anchor for friable material, said anchor comprising a roughly cylindrical body; a drilling portion provided at a first free end of the body with drilling teeth; a bearing flange at a second end of the body; and an external screw thread extending around the body

The invention claimed is: 1. A screw anchor for friable material, said anchor comprising a roughly cylindrical body; a drilling portion provided at a first free end of the body with drilling teeth; a bearing flange at a second end of the body; and an external screw thread extending around the body in a first direction; the drilling portion being configured as a portion of a drill bit, wherein the drill bit portion has two helical flutes which extend in the first direction, each of said flutes opening onto a respective flat surface forming walls of both a central drilling tooth and one of two lateral drilling teeth. 2. The anchor according to claim 1, further comprising a threaded shank portion that extends the body beyond the bearing flange. 3. The anchor according to claim 1, wherein the body is hollow and pierced with a bore. 4. The anchor according to claim 1, wherein said drilling portion further comprises two drill bit ribs bordering said flutes, each of said ribs forming one of said lateral drilling teeth. 5. The anchor according to claim 1, wherein an angle between said walls is zero. 6. The anchor according to claim 4, further comprising a threaded shank portion that extends the body beyond the bearing flange. 7. The anchor according to claim 4, wherein the body is hollow and pierced with a bore. 8. A screw anchor, comprising: a shank; a head formed at an upper end of said shank; a drilling portion formed at a lower end of said shank; and a plurality of external threads which helically extend in a first direction about said shank between said head and said drilling portion; wherein said drilling portion comprises: a central drilling tooth having opposing flat surfaces; and two helical flutes helically extending in the first direction, each of said flutes ending at one of said flat surfaces of said central drilling tooth; and wherein said drilling portion further comprises two lateral drilling teeth on opposite sides of said central drilling tooth, each of said lateral drilling teeth having a flat surface which is coplanar with one of the flat surfaces of said central drilling tooth. 9. The anchor of claim 8, wherein said drilling portion further comprises two drill bit ribs bordering said flutes, each of said ribs forming one of said lateral drilling teeth. 10. The anchor of claim 9, wherein each of said flat surfaces of the central drilling tooth extends laterally to define the flat surface of a first of said lateral drilling teeth, and the rib that forms a second of said lateral drilling teeth, defines a raised border of said central drilling tooth on said flat surface. 11. The anchor of claim 10, wherein each of said flat surfaces of the central drilling tooth extends laterally to define a flat surface of only one of said lateral drilling teeth. 12. The anchor of claim 11, wherein each of said flat surfaces of the central drilling tooth extends downwardly to an pointed end of said central drilling tooth which pointed end is a lowermost point of said anchor. 13. The anchor of claim 12, wherein each of said flutes ends abruptly at a respective flat surface of the central drilling tooth. 14. The anchor of claim 13, wherein said flat surfaces of the central drilling tooth define four cutting edges. 15. The anchor of claim 14, wherein the four cutting edges are essentially straight edges. 16. The anchor of claim 12, further comprising a threaded shank portion located above said head. 17. The anchor of claim 12, wherein said shank is hollow and has a bore. 18. A screw anchor, comprising: a shank; a head formed at an upper end of said shank; a drilling portion formed at a lower end of said shank; and a plurality of external threads which helically extend in a first direction about said shank between said head and said drilling portion; wherein said drilling portion comprises: a central drilling tooth having opposing flat surfaces; and two helical flutes helically extending in the first direction, each of said flutes ending at one of said flat surfaces of said central drilling tooth; and wherein said drilling portion further comprises two lateral drilling teeth on opposite sides of said central drilling tooth, each of said lateral drilling teeth having a flat surface which is a continuous extension of one of the flat surfaces of said central drilling tooth, and which extends seamlessly without interruption into said one of the flat surfaces of said central drilling tooth. 19. The anchor of claim 18, wherein each of said flat surfaces of the central drilling tooth extends downwardly to an pointed end of said central drilling tooth which pointed end is a lowermost point of said anchor. 20. The anchor of claim 18, wherein each of said flutes ends abruptly at a respective flat surface of the central drilling tooth. 21. The anchor of claim 18, wherein said flat surfaces of the central drilling tooth define four cutting edges. 22. The anchor of claim 21, wherein the four cutting edges are essentially straight edges.