Description Title of Invention: SELF-DRILLING DOWEL

[I] This invention relates to a self-drilling dowel for a crumbly material of the plaster panel type.

[2] Such dowels are used for reinforcing a supporting material area adapted for receiving a part to be secured thereto. After positioning such a dowel, the part is secured by means of a fastening member resulting in the expansion of the dowel, for anchoring it into the material, as well as for fastening the part.

[3] Such a dowel for a crumbly supporting material comprises a drilling end, a supporting collar on the supporting material and, between the drilling end and the collar, an expandable bushing portion arranged for receiving a fastening member adapted to fasten a part to the supporting material while resulting in the expansion of the bushing and the anchoring thereof.

[4] Positioning the dowel into the supporting material is carried out through rotationally driving thereof for using its drilling end like a drill bit. To this end, the part of the bushing portion adjacent to the supporting collar generally comprises a Phillips type fingerprint for being able to drive the dowel, for example by means of a Phillips screwdriver.

[5] Forming such a fingerprint raises some difficulties especially when this is a dowel made from a metal sheet blank, as is the case in the dowel of the present invention.

[6] Now, the aim of the invention is to overcome such difficulties.

[7] To this end, the invention relates a self -drilling dowel for a crumbly supporting material comprising, being made from a metal sheet blank, a collar abutting against the material, a material drilling end and, between the collar and the drilling end, a expandable tubular body, the part of which, being adjacent to the collar, comprises means for rotationally driving the dowel and its drilling end and being arranged for receiving a fastening member for securing a part to the supporting material while resulting in the expansion of the body and the anchoring of the dowel in the supporting material, said dowel being characterized in that the rotationally driving means comprise internal bosses onto which a rotational driving tool is intended to be engaged.

[8] Forming driving bosses is simple to achieve on a metal sheet blank, before rolling it, through stamping, die shaping, punching, etc.

[9] The rotationally driving tool could be a manual tool, of the Phillips type screwdriver, or an electrical or pneumatic tool.

[10] Preferably, the dowel comprises four regularly and angularly spaced apart rotationally driving bosses.

[I I] This invention will be better understood by reading the following description of the

preferred embodiment of the dowel according to this invention, referring to the appended drawing, in which:

[12] - Fig. 1 is a perspective view of the dowel of the invention;

[13] - Fig. 2 is a profile view of the dowel of Fig. 1;

[14] - Fig. 3 is a cross-sectional view of the dowel body in the blank of bosses of the dowel of Fig. 1 ; and

[15] - Fig. 4 is an axial section view of the dowel of Fig. 1.

[16] The dowel will be now described being made from a cut, then folded and rolled metal sheet blank.

[17] Manufacturing the dowel is not essential for understanding this invention. Only matters the fact that it has been manufactured from a metal sheet blank. This is the reason why the process itself for achieving the dowel will be hardly discussed, to the benefit of the description of the dowel. In any event, the man skilled in the art well knows self-drilling dowels made of a folded and rolled metal sheet.

[18] Thus, the dowel according to this invention, with an axis 12, comprises a supporting collar 1, a drilling end 2 and, between the collar and the drilling end, an expandable tubular body 3.

[19] In the periphery of the generally ring-shaped abutting collar 1, anti-rotation studs (4) with a substantially triangular general shape have been folded down, after being cut.

[20] The drilling end 2, after cutting and twisting, conventionally comprises drilling teeth

5, each with a drilling tip 6 and a drilling edge 7. The tubular body 3 comprises three parts, one part 8 adjacent to the collar 1, one part 9 adjacent to the drilling end 2 and one intermediate part 10.

[21] The part 9 adjacent to the drilling end, further to an appropriate cut in the original metal sheet blank, and after rolling, comprises helical threading portions 11 with a section substantially half of that of the body 3 taken as a whole; such threading portions 11 fill a threading function intended for receiving the thread of a fastening and anchoring screw. So, after the dowel has been positioned in a supporting material, and this will be further discussed later, the part to be secured to the supporting material is applied onto the material, while covering the collar 1, then, through the part, a screw is introduced into the dowel and is screwed into the threading portions 11 of the dowel body, until the screw head abuts against the part to be secured or an intermediate washer. While firmly screwing the screw in the part 9 of the dowel body 3, the screw drives said part 9 towards the collar 1, opening the intermediate part 10 of the dowel body 3 for anchoring the dowel into the supporting material.

[22] The intermediate part 10 of the dowel body 3 is split into axial planes for accurately providing for the opening or the expansion of said intermediate part 10.

[23] The opening being considered essentially consists in the slots 13 and the folding

down of the stripes 14 in the dowel body, as being interposed between slots, such a folding down being made easier by the formation of the intermediate part 10 into two frustoconical portions 15, 16 with a larger section in the junction plane 17 thereof. [24] The part 8 adjacent to the collar 1, here being cylindrical tubular, before the metal sheet blank has been rolled, has been punched in four places, so that, once shaped, such a part has four, regularly angularly spaced, internal bosses 18. These are bosses for rotationally driving the dowel body and onto which a driving tool is intended to be engaged, such as a Phillips screwdriver. Such bosses 18 are located slightly near the median transversal plane of the body part 8, for being easily available to the driving tool.