Metal dowel for anchorage in thin wall panels

A metal anchor for mounting screws in thin wall boards made of plasterboard, pressed wood or similar building material includes a body (1) formed from a sheet metal plate and provided with semi circular retention ridges (2) projecting alternately to each side, which are matched in width and pitch to the thread shape of the screw (13) to be tightened such that the retention ridges (2) engage into the latter's thread grooves (19). The entire body (1) is formed of three sections, of which the first section (4), situated on the outer end, bears the retention ridges (2), the second section (5), situated in the middle, has two axially running outer bending ridges (7) and two inner bending ridges (8) which are mutually separated by slits (12) and can be bent off in opposing directions, and the third section (6), situated at the head end, is provided with semi circular guide shells (9) extending in opposed directions for inserting the screw (13.).

BACKGROUND OF THE INVENTION 
The invention pertains to a metal dowel to be anchored in thin wall boards 
made of plasterboard, pressed wood or similar building material, wherein 
the dowel shaft is formed from a sheet metal plate and provided with semi 
circular retention ridges punched out of the shaft and projecting 
alternately to each side, which are matched in width and pitch to the 
thread shape of the screw to be tightened such that the retention ridges 
engage into the thread grooves of the latter. 
DESCRIPTION OF THE PRIOR 
U.S. Pat. No. 5,443,343 discloses such a metal dowel, in which two 
spreadable shaft sections are connected in one piece at their tips by a 
thin ridge and are bent apart. The semi circular retention ridges for 
tightening the screw are located in this case in the head area of the 
shaft. When tightening the screw into the thread ridges, the tip of the 
screw pushes between the two shaft sections and spreads them apart such 
that they find support on the back side of the wall board. 
This metal dowel can indeed be driven easily into the plasterboard sheets 
and also offers enormous retention power. It has the difficulty, however, 
that double the length of sheet metal material is consumed for 
manufacturing the shaft, due to the two folded-apart shaft halves. The 
problem of the invention is to design this metal dowel such that less 
material is needed for the same functionality and equally good retention 
power. 
SUMMARY OF THE INVENTION 
This problem is solved in that the entire shaft is formed of three 
sections, of which the first section, situated on the outer end, bears the 
retention ridges, the second section, situated in the middle, is formed of 
two axially running outer bending ridges and two inner bending ridges, 
which are mutually separated by slits and can be bent off in opposing 
directions, and the third section, situated at the head end, is provided 
with semi circular guide shells pointing to both sides for inserting the 
screw. Because of this shaft design, it is now possible to stamp the metal 
dowel out of a sheet metal plate and to form it such that, due to the 
lower material consumption, the manufacturing costs are considerably lower 
than for the known two-ply metal dowel. 
If appropriately hardened spring steel is used, the formed dowel can be 
driven into the aforementioned wall boards without difficulty. By 
tightening the screw into the retention ridges at the dowel tip, the tip 
is pulled towards the wall board from the rear. In the process the outer 
ridges of the middle section bend off to one side and the two inner ridges 
to the other side, and support themselves on the back side of the wall 
over half the width of the bending ridges. 
Additional beneficial characteristics for constructing the invention are 
disclosed as follows. The bending ridges of the middle section are bent 
over exactly at the specified bending lines. The connection of the two 
half-round inner cross-ridges has the effect of strengthening the bending 
ridges and thus the middle section of the shaft and insures that the dowel 
keeps its shape when being driven into the wall board. An additional 
reinforcing effect is achieved by bending away the axial shaft edges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
The metal dowel shown in the figures serves for anchoring in thin wall 
boards of plasterboard, pressed wood or similar building material. An 
elongated body 1, is, as is shown in FIG. 5, punched in one ply out of a 
sheet metal plate and stamped, and consists of three sections. A first 
lower section 4 has two tips 3 at its outer end and is provided with 
several retention ridges 2 stamped out of the central strip and formed to 
project outwardly alternately to each side and which match the width and 
pitch of the thread shape of the screw 13 to be inserted such that the 
retention ridges 2 engage into its thread grooves 19. 
A middle section 5 serves for the actual anchoring and is formed by two 
outer bending ridges 7 running parallel to the axis and two inner bending 
ridges 8, which are separated from the outer bending ridges 7 by slits 12. 
The two outer ridges 7 are bent off slightly to one side out of the shaft 
plane at the bending lines K1, K2 and K3, while the two inner ridges 8 are 
bent slightly away to the opposite side at the bending lines at the same 
height and as is evident from FIG. 2, they form a narrow rhombus in cross 
section with the outer ridges 7. The inner bending ridges 8 are connected 
together by two cross ridges 10, which span the free space needed for the 
introduction of the screw 13 in a semi circular shape on the side provided 
for bending outwards. 
A head section 6 is provided with semi circular guide shells 9 for the 
screw 13, which are formed pointing alternately outwards to each side, the 
head end, possesses flaps 14 projecting outwards on each side intended to 
make contact with the wall board 15 when driving in the dowel as shown in 
FIG. 4 the cross-section of the shaft 1 is, moreover, strengthened at both 
sides of the retention ridges 2 of the lower section 4 by edges 11 bent 
away parallel to the axis. 
The functioning of the metal dowel is illustrated graphically in FIG. 6. In 
order to fasten a flat object, such as a plate 15 on the wall board 16, 
the metal dowel is driven via the flaps 14 into the wall board 16 until 
the flaps 14 lie against the wall board surface. Then the screw 13 is 
introduced through a hole 17 in the plate 15 and the guide shells 9 of the 
head section 6, until the screw tip 18 has reached the screw area of the 
lower shaft section 4 and the retention ridges 2 engage in the thread 
grooves 19. 
Upon further tightening of the screw 13, the lower shaft section 4 is 
pulled upwards, i.e., in the direction of the head section 6, with the 
ridges 7 and 8 bending outwardly in opposite directions at the designated 
bending lines K1, K2 and K3 and supporting themselves on the back side of 
the wall board 15 over half the width of the bent ridges 7 and 8. 
In case the screw 13 must be loosened later, the metal dowel remains behind 
in its anchoring position and can be used again at any time for inserting 
the screw 13.