BRIEF DESCRIPTION OF THE DRAWINGS
The drawings show:
FIG. 1 a side view of a fastening element according to the present invention;
FIG. 2 a partial cross-sectional view showing a detail of the fastening element shown in FIG. 1; and
FIG. 3 a schematic cross-sectional view showing a detail of the fastening element shown in FIG. 1 in a set condition.
In the drawings, the same elements are designated with the same reference numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A fastening element 11 according to the present invention for a mineral constructional component 6, which is shown in FIG. 1, is formed as a self-tapping screw having a shaft 12 with a first, setting side end 13 and a second end 16 opposite or remote from the first end 13. At the second end 16, there is provided rotatable application means 17 in form of a hegonal screw head for a setting tool, not shown here. Starting from the first end 13 of the shaft 12, a thread-tapping thread 14 extends regionwise along the shaft 12. From the first end 13 in the direction of the second end 16, regionwise, the shaft 12 is provided with a coating 21 from a polar thermoplast. As a polar thermoplast, ethylenvinylacetate (EVA) is used that has a melting temperature according to DSC of 60° C. and a strength of 4 N/mm2. The polar thermoplast is applied on the fastening element 11, at least in the region of the thread 14 by a whirl sintering process.
As shown in FIG. 2, the coating 21 has a bell-shaped distribution between the threads 15, with a thickness of the coating 21 being greater between the threads 15 than on flanks of the thread 15. The free ends of the thread flanks need not necessarily be provided with the coating 21 because during tapping of the counter-thread in the constructional component 6, the coating 21 is completely removed. The thickness D of the coating 21 between the thread 15 amounts, for compensation of borehole tolerances, to about from 0.005 to 0.10 times of the root diameter A of the shaft 123 in the region of the thread 14.
The functioning of the inventive fastening element 11 will be explained below based on FIG. 3. In the first step, a borehole 5 is formed in the constructional component 6. Then, the fastening element 11 is screwed into the borehole 5. During screwing of the fastening element 11 in the constructional component 6, the thread flanks penetrate into the constructional component, forming a counter-thread 7. Simultaneously, the surplus portion 22 of the coating 21 breaks off as a result of a cohesive peel of the polar thermoplast of the coating 21. Because of a low strength and a strong adhesion to the shaft 12 of the polar thermoplast, the peeling layer 23 flows through the coating 21. Due to the polarity of the polar thermoplast, a portion of the coating 21, which is necessary for a complete sealing of the borehole 5 against a fluid medium, still remains bounded to the shaft 12 even after the breaking off of the surplus portion 22.
During screwing-in, the coating 21 is heated due to friction between the coating 21 and the wall 8 of the borehole 5 in the radial outer melting region 24. The drilling dust, which is produced during tapping and which remains in the borehole 5, becomes spread in the melting region 24 of the coating 21, whereby the coating 21 becomes reinforced after cooling of the melting region 24, at least regionwise. In addition, the coating 21 easily and releasably bonds with the wall 8 of the borehole 5.
Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.
Patent Application
20080019793
