GB2090933A - Anchoring of screw sockets in bores - Google Patents

Abstract

When a screw socket 10 is inserted into the bore 22 by pressing together the smooth resilient arms 15, the arcuate radial projections 18 on the arms 15 slide along the surface of the bore without scraping dust from the bore wall so that there is no likelihood of drilling dust preventing correct positioning of the dowel 10. Upon reaching bore widening 24, arms 15 return to their initial position as projections 18 snap in positive manner into said widening 24. Protrusions 17 prevent twisting of the screw socket 10 in the bore 22 when fastening screws are inserted or when the dowel is subjected to a load. <IMAGE>

Description

SPECIFICATION Dowel for positive insertion The present invention relates to a dowel for positive insertion into a bore, which has a radial widening provided in its interior. The dowel is of the type comprising a dowel sleeve which has an internal thread for a fastening screw and a front portion formed as several segments separated by axial slots, at least part of these segments having, in the rest state, a larger diameter than a rear ring of the dowel sleeve, said diameter being variable in such a way that the segments can be inserted into the bore and can be snapped into the bore widening, said dowel also having the ring and the front portion of the dowel sleeve in one piece, and having the front portion provided with a radial thickening on the outside of each segment and, with a similarly longitudinally-segmented extension adjoining the front end of said frbnt portion in the direction of insertion the outside diameter of said extension corresponding, in the rest state, to that of the ring portion of the dowel sleeve, said dowel also having the internal thread provided in the front portion and the extension of the dowel sleeve with the thread having, in the rest state, substantially the same internal diameter over its entire length.

In the case of a dowel of the said kind, the radial thickening is formed in angular manner, in the insertion direction, in both the front and rear regions. It has become apparent that this form of thickening has considerable disadvantages. To insert the dowel into a base bore in the region of the undercut widening it is necessary to press the segments of the dowel together and then to push same into the bore. In so doing, the segments, because of their inherent resilience, diverge once more and impinge against the sides of the bore, so that in particular the sharp edge which is to the rear in the insertion direction travels along the inner wall of the bore.Thus, during this insertion, the dowel, with its sharp edge, scrapes drilling dust from the wall of the borehole and thereby fills or partially fills the undercut annular groove-like widening with dust and deposits dust along the sides of the bore, so that there is a danger of the dowel not attaining its correct position. If the segments cannot completely spring apart again, then firstly the position of the dowel in the widening is not correct and secondly it is difficult to screw the fastening screw or the like into the dowel. Moreover, it has transpired in vibration tests, i.e. in tests under alternating load, that the rear edge of the dowel cuts up, and thereby destroys, the relevant shoulder of the bore widening, which means that the dowel is able to shift, during such tests, by a relatively large distance within the bore widening.

The object of the present invention is to provide an improved dowel such that the force, occurring under load, in the bore widening can be absorbed more uniformly by the dowel and that the risk of scraping the wall of the bore during introduction of the dowel and destruction of the bore widening during operation are reduced, if not avoided altogether.

With this object in view, the present invention provides a dowel of the kind mentioned at the beginning hereof characterised in that the radial thickening, considered in axial section, has an arcuate outer surface over its entire width.

The result of providing a dowel with the aforesaid feature is that the dowel, upon insertion into the cylindrical bore as far as the bore widening, is practically unable to scrape drilling dust from the inner wall of the bore and bring that dust into the bore widening, so that it is always ensured that the dowel is correctly seated and the springing apart of the segments is not hindered by drilling dust. Moreover, this dowel behaves more favourably than the previously known type when subjected to alternating loads since it cannot cut up, or otherwise destroy, the bore widening. In tests it has been shown that, when subjected to alternating loads the dowel in accordance with the invention does indeed participate in an initial displacement, although this displacement is not as great as with previous dowels.Also subsequent to the initial displacement there is only a minimum further displacement. Furthermore, the dowel having features in accordance with the present invention can be produced just as simply as previous dowels on an automatic lathe.

Further details and developments of the invention will become apparent from the following description, in which the invention is described and explained in more detail with reference to the exemplified embodiment shown in the drawing.

The sole figure shows, partially in elevation and partially in section, a dowel, inserted in positive manner into a cylindrical base bore provided with a widening, in accordance with a preferred exemplified embodiment of the present invention.

In accordance with a preferred exemplified embodiment of the present invention a dowel 10, which is preferably made of metal, serves for positive insertion into a bore 22, appropriately shaped or respectively provided with a radial widening 24, which is trapezoidal in cross-section, in a concrete wall or the like. The dowel 10 consists of a single part, namely a dowel sleeve 11. The dowel sleeve 11, shown in the rest position in the figure, is, save for a ring 12 arranged at the rear end, multiply longitudinally slotted, i.e. in the case of the exemplified embodiment provided with six longitudinal slots 13.This results in the formation, in the case of the exemplified embodiment, of six segment arms 1 5 which are distributed uniformly around the circumference of the dowel sleeve 11, which extend lengthwise and which can be pressed together by virtue of the identical longitudinal slots 13, which are of the same width over their entire length, and by virtue of the resiliently-elastic material and overall design of the dowel 1 0. Part of these segment arms 1 5 form a front portion 14 which is connected by way of a connection web 1 6 to the ring 12. Whilst the segment arms 1 5 are smooth on the surface, the ring 12 is provided with several elongate protrusions 1 7 which are distributed uniformly over its circumference.For example, in the preferred embodiment these protrusions 1 7 extend axially, projecting beyond the outer circumferential surface of the ring 12, and are pressed in, or respectively forced out, from the inside of the bore into the surrounding material.

The segment arms 1 5 each possess, in the front portion 14, a radial thickening 1 8 which, considered as a whole, with interruptions by the longitudinal slots 13, acts like an annular thickening on the dowel sleeve 11. The thickenings 1 8 are, considered in axial longitudinal section, provided with an arcuate outer surface 26 which corresponds exactly to an arc of a circle.

The radius of the aforesaid circle is preferably such that the outer surface 26 forms approximately an arc of the inscribed circle of the trapezoidal cross section of the widening 24.

At the opposite end of the dowel 10 to the ring 12, a longitudinally-segmented extension 1 9 is connected to the thickening region 1 8. The extension 1 9 has, in the rest state, a cylindrical circumference and an outside diameter similar to that of the ring 12.

The dowel sleeve 11 is provided with an internal thread 21 which extends from the free end of the extension 1 9 through the entire portion 14 as far as the connection webs 1 6. The core radius of the internal thread 21 is smaller than the inner radius of the ring 12, by an amount which corresponds approximately to the thread depth. As the aforesaid region of the dowel sleeve 11 which has the internal thread 21 is segmented, the internal thread 21 is, of course, itself interrupted, in the circumferential direction, by the longitudinal slots 13.

To introduce the dowel sleeve 11 into the front region 23a of the cylindrical base bore 22 it is necessary to press together the segment arms 1 5, which are elastically and resiiiently yielding, to such an extent that the maximum outer circumference of the thickening 1 8 is at least equal to the inside diameter of this bore region 23a. The dowel sleeve 11 can then be pushed into the bore region 23a, in which respect the circular thickening 1 8 slides along the inner surface without scraping drilling dust from the inner wall of the bore. Upon reaching the trapezoidal bore widening 24, the segment arms 1 5 return to their initial position, since the circular thickening 1 8 can snap, in a substantially positive manner, into the trapezoidal bore widening 24. In this position the extension 1 9 lies in the inner bore region 23b of the base bore 22.

Since this positive insertion can be effected, without hindrance by drilling dust or the like, it is also possible to screw the fastening screw or the fastening bolt in by hand without any problems.

Moreover, theoutwardly-projecting protrusions 1 7 on the ring 12 prevent torsion of the dowel sleeve 11 in the bore 22.

Claims (5)

1. A dowel for positive insertion into a bore, which has a radial widening provided in its interior, said dowel comprising a dowel sleeve which has an internal thread for a fastening screw and a front portion formed as several segments separated by axial slots, at least part of these segments having, in the rest state, a larger diameter than a rear ring of the dowel sleeve, said diameter being variable in such a way that the segments can be inserted into the bore and can be snapped into the bore widening, said dowel also having the ring and the front portion of the dowel sleeve in one piece, and having the front portion provided with a radial thickening on the outside of each segment and, with a similarly longitudinallysegmented extension adjoining the front end of said front portion in the direction of insertion, the outside diameter of said extension corresponding in the rest state, to that of the ring portion of the dowel sleeve, said dowel also having the internal thread provided in the front portion and the extension of the dowel sleeve, with the thread having, in the rest state, substantially the same internal diameter over its entire length, characterised in that the radial thickening, considered in axial section, has an arcuate outer surface over its entire width.

2. A dowel as claimed in claim 1 , characterised in that the arcuate outer surface of the radial thickening corresponds exactly to an arc of a circle the radius of which is so selected that it is at the most the same as, but preferably smaller than, the radius of the inscribed circle of the widening in the interior of the bore, which latter widening is channel-shaped in axial section.

3. A dowel as claimed in claim 1 or 2, characterised in that the outer surface of the segments is smooth.

4. A dowel as claimed in any of claims 1 to 3, characterised in that the ring is provided with protrusions which project beyond its outer circumferential surface.

5. A dowel substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.