DE29812947U1 - Screw-in dowels for soft building materials - Google Patents

Description

fischerwerke

Artur Fischer GmbH & Co. KG

72178 Waldachtal

M1919

16.07.1998
JU/SQ

Screw-in anchors for soft building materials

The invention relates to a screw-in anchor for soft building materials, in particular rigid foam boards according to the preamble of claim 1.

Atis" of DE 40 41 765 A1 is a generic screw-in anchor with a

^/ pointed and an external thread shaft is known, which has an internal cavity for receiving a fastening element. The external thread of the known screw-in anchor is a pointed thread, the flank angle of which is flatter in the front area of the screw-in anchor than in the rear area. The flank angle increasing towards the rear area is intended to ensure that the material is compressed in the thread area with increasing screw-in depth of the anchor, increasing the holding value.

Due to the pointed thread with a tip angle in the rear area of approximately 90°, only a small thread height is required on the known screw-in anchor

which creates a small undercut in the building material to be anchored. Furthermore, the building material is only compacted in the area of the threaded base, which, despite the high screwing-in torque, only allows low extraction forces with the known screw-in anchor.
30

The invention is based on the object of achieving an increase in the pull-out value of a screw-in anchor for soft building materials such as rigid foam boards.

This object is achieved by the features specified in claim 1.

With a trapezoidal thread, which usually has a flatter flank angle than a tapered thread, a considerably higher flank height of the thread and thus a deeper cut of the thread into the building material is possible. Since the screw-in anchor according to the invention thus engages more material, higher holding forces are inevitably also achieved. Furthermore, the increase in the width of the thread ridge from the front end to the rear end of the anchor on the entire engagement surface of the thread results in a compaction of the building material, which contributes to a further increase in the pull-out force of the screw-in anchor. With the design that the thread starts from the taper and reaches its full flank height in one thread turn, almost the entire length of the thread with its full cross-section is engaged.

It has proven to be particularly advantageous for the screwing-in torque on the one hand and the holding value on the other hand if the flank height of the thread is approximately three quarters of the shaft diameter and the pitch of the thread approximately corresponds to the shaft diameter.

A flank angle of the thread of between 5° and 10° is advisable, at least in the front area. In order to achieve a somewhat stronger compression in the area of the thread root, in another practical embodiment the flank angle can increase towards the rear end of the shaft to a flank angle of between 15° and 20°.

For applications of the screw-in anchor according to the invention with soft building materials on which a thin layer of plaster is still applied, it is advantageous to form the tapered portion in a pyramid shape. The square cross-section of the tapered portion results in reaming edges that make it possible to ream a hole in the harder building material gypsum that corresponds to the shaft diameter of the screw-in anchor.

The invention and further embodiments of the screw-in dowel are explained in more detail below using the embodiment shown in the drawings. They show:

Figure 1 is a side view of the screw-in anchor according to the invention;

• *·

Figure 2 a front view of the screw-in anchor and

Figure 3 shows the screw anchor anchored in a building material with fastening

element

The screw-in dowel 1 according to the invention has a shaft 2 and a pyramid-shaped tapered portion 3 at the front end of the shaft 2. A trapezoidal thread 4 is arranged on the shaft 2, starting from the tapered portion 3 and extending to the flange 5 arranged at the rear end of the shaft 2. The flank height h of the thread is approximately three quarters of the shaft diameter d, with the full flank height h being reached after approximately one thread turn. The pitch s of the thread 4 also corresponds approximately to the shaft diameter.

In order to achieve compaction of the building material over the entire engagement surface of the thread 4, the thread is designed in such a way that the width of the thread ridge 6 increases from the front end to the rear end of the screw-in dowel. In order to achieve even greater compaction in the area of the thread base, in the embodiment shown the flank angle α increases from 5° to 10° at the front end to 15° to 20° at the rear end. The screw-in dowel 1 has an inner cavity 7 for receiving a fastening element. In alignment with the inner cavity 7, a hexagon socket 8 for attaching a turning tool is incorporated in the rear area of the screw-in dowel 1 (see Figure 2).

In Figure 3, the screw-in dowel 1 is screwed into a rigid foam board 10, on which there is still a thin layer of plaster 11. The plaster layer is screwed into the building material 10 by pushing and simultaneously turning the dowel 1 with the pyramid-shaped tip 3 of the screw-in dowel 1 using a turning tool that engages the hexagon socket 8 until the flange 5 sits on the outer surface of the plaster layer 11. A fastening element 12 - a hook in the embodiment shown - can now be screwed into the inner cavity 7 of the screw-in dowel 1 anchored in the building material 10.

Claims (8)

1. Screw-in dowel with a shaft having a tapered portion and a thread, which has an internal cavity for receiving a fastening element, characterized in that the thread ( 4 ) is a trapezoidal thread which starts from the tapered portion ( 3 ) and reaches its full flank height (h) in one thread turn, and that the width of the thread ridge ( 6 ) increases from the front end to the rear end of the screw-in dowel ( 1 ). 2. Screw-in dowel according to claim 1, characterized in that the flank angle (α) at the front end of the thread ( 4 ) is between 5° and 10°, and increases towards the rear end to a flank angle (α) between 15° and 20°. 3. Screw-in dowel according to claim 1, characterized in that the flank height (h) of the thread ( 4 ) is approximately three quarters of the shaft diameter (d). 4. Screw-in dowel according to claim 1, characterized in that the pitch (s) of the thread ( 4 ) approximately corresponds to the shaft diameter (d). 5. Screw-in dowel according to claim 1, characterized in that the tapered portion ( 3 ) is pyramid-shaped. 6. Screw-in dowel according to claim 1, characterized in that a thin-walled flange ( 5 ) is arranged at the rear end of the shaft ( 2 ), the outer diameter of which corresponds to the outer thread diameter. 7. Screw-in dowel according to claim 1, characterized in that a hexagon socket ( 8 ) aligned with the inner cavity ( 7 ) for attaching a turning tool is incorporated at the rear end of the shaft ( 2 ). 8. Screw-in dowel according to claim 1, characterized in that it consists of a fiber-reinforced plastic.