FR2505946A1 - METHOD FOR MANUFACTURING TUBULAR ANCHORING ELEMENTS FOR SCREWS SAID "ANKLE" AND PRODUCT THUS OBTAINED - Google Patents

Abstract

A tubular screw anchoring member (10) for mounting a screw in a bored hole comprises a number of longitudinally extending, peripherally spaced, flexible ribs or fins (14) projecting radially outwardly from the outer surface of the anchoring member. The anchoring member is of the extruded type having a substantially uniform cross-section along its total length. In order to make it possible to use fins having a relatively big radial extension without substantially increasing the torsional resistance of the anchoring member, the fins or ribs are provided with axially closely spaced notches or indentations (15).

Description

Tubular anchoring device for v said "peg".

The present invention relates to a tubular anchoring device for a so-called "dowel" screw of the type suitable for being inserted into a drilled trc and comprising several flexible ribs or fins extending longitudinally exiled being psriphkerically spaced, said ribs or fins projecting progressively outwardly from the outer peripheral surface of said tubular member.

When a tubular anchor for screws has been inserted into a drilled hole and a screw is viewed in the tubular anchor, the anchor tends to rotate in the hole, especially if the hole was drilled with a diameter slightly larger than the diameter prescribed for the anchor in question. This tendency of the anchoring element to rotate in the drilled hole is counteracted when the external peripheral surface of the anchoring element is provided with flexible ribs or fins which can cooperate with the internal wall of the drilled wheel, even when the diameter of the hole differs to a certain extent from the prescribed diameter.

We know, for example, from the Swedish patent N 99.068 a tubular anchoring element for screws of the type described above provided with ribs and external fins.

The anchor for screws of the type described above can, for example, be mounted in a hole which a - ore or drilled in a solid brick wall or in a hole drilled right through provided in a panel such than a plasterboard. When a screw, for example a wood screw, is screwed into such an anchoring element and tightened, the anchoring element expands inside the hole, not only because the material of the element d the anchor is moved radially outward by the screw, but also because the anchor is compressed axially and also twisted to some extent when the screw is tightened. When the anchor has been mounted in a hole drilled right through in a panel or board having a thickness substantially smaller than the length of the anchor, the part of the anchor protruding from the rear wall of the panel, or of the board, in particular, tends to twist when the screw is tightened (provided that the anchor is made of a suitable material), whereby the projecting part of the anchor can have slightly larger effective diameter opposing removal of the anchor with the screw out of the drilled hole.

To allow the use of a screw anchor having a certain external diameter for a relatively large range of hole diameters, it is desirable to provide the anchor with ribs or fins having a radial dimension or height relatively large.

However, such wide ribs substantially increase the torsional strength of the tubular anchoring element kt, therefore, it is difficult or impossible to sufficiently tighten the screw to obtain satisfactory expansion, and consequently the anchoring of the screw anchor in the hole.

The present invention relates to a tubular anchor for screws of the type described above which can be provided with ribs or external fins having relatively large radial dimensions but which can nevertheless be anchored satisfactorily in a blind hole or a hole drilled right through, even when a relatively low torque is applied to the screw during its tightening. According to the present invention, this is obtained from the fact that each rib or fin is interrupted or weakened from place to place in the axial direction.

These interruptions or weakenings mean that the ribs or fins do not appreciably increase the torsional strength of the tubular anchoring element for screws even when the radial dimensions of the ribs or fins are relatively large. Weaknesses or interruptions can even reduce the torsional strength to an extent that it becomes smaller than the torsional strength of a corresponding screw anchor having no ribs or fins. This decrease results from the fact that the weakening or interruptions of the fins can also cause a notch effect in the underlying material. In addition, these interruptions or weakenings give a certain roughness to the ribs or fins, whereby their ability to increase friction is appreciably improved. Consequently, the anchoring element for screws according to the present invention cannot be pushed by inadvertence too far into the hole drilled in a wall or panel, even if the diameter of the hole exceeds the prescribed diameter. It is therefore not necessary to provide the outer end of the anchoring element for screws according to the invention with a collar or flange extending radially as shown in the Swedish patent mentioned above. Consequently, it is possible to avoid having a space between the surface of the wall in which the anchoring element is mounted and the adjacent internal surface of the object fixed to the wall by means of the element anchor.

For health reasons, this is very important, for example in the construction of hospitals.

The screw anchoring element according to the present invention may be of the type described in Danish patent NO 125488 and French patent NO 7019457 comprising edge-shaped portions of rods extending longitudinally and spaced apart which are interconnected by flexible and thin wall parts. In said Danish and French patents, the flexible wall parts join the external radial parts of the parts in the form of adjacent rods. In this case, the flexible wall parts substantially increase the torsional strength of the anchoring element. In order to further reduce this torsional strength, the flexible wall parts of the anchoring element for conforming screw to the invention preferably secure the internal radial parts of the adjacent rod-shaped parts and said ribs or fins can then be positioned on the external radial surfaces of the rod-shaped parts and preferably on the external radial edges of the shaped parts of rods The arrangement of the flexible wall parts closer to the axis of the tubular anchoring element for screws not only reduces the torsional strength of the anchoring element but also exposes the external edges of the parts in the form of rods, whereby said edges can cooperate with the internal wall of the borehole and thereby further increase the friction between the anchoring element for screws and the at the borehole wall,
The fins or ribs may be formed by pairs of mutually spaced fins diverging outwardly or substantially parallel, said fins being arranged on the respective rod-shaped parts. It is thus obtained that the ribs on each pair of this type will be bent in opposite perispherical directions when the anchor for screws is pushed inside the borehole. Thus, the fins prevent rotation of the anchor in the drilling in either direction.

In order to allow a high degree of torsion of the anchor element for screws, the spaces between the interruptions or weakening of each of the ribs or fins must be relatively short, for example of the order of one a few millimeters.

In principle, the screw anchoring element according to the invention can be made of any type of deformable material such as rubber, a fiber material and a soft metal.

However, in practice, the anchoring element according to the present invention is normally made of plastic, preferably of a thermoplastic material such as polyvinyl chloride. This material has good heat conductivity so that the heat generated by the friction between the screw and the internal wall of the anchoring element also causes heating and softening of the parts of the external surfaces radially of the element C anchoring in contact with the internal surface of the drilling in LeaSel is mounted the anchor. Such a softening of the portions of the Pxtars surfaces of the anchoring element allows optimal engagement between the anchoring element and the surface of the borehole.

The tubular anchor for screws as defined in the invention can, for example, be manufactured by injection molding.

In this case, the interruptions or weakening of the ribs or fins originate from the shape of the mold cavity and, if desired, the anchoring element for screws can be provided at one end with a collar or a radial flange
However, as explained above, such a flange or flange is not necessary with the anchoring element according to the present invention and, consequently, the anchoring element according to the present invention is capable of be manufactured by extrusion, which is much more economical than by injection molding. Ciisi, the present invention also relates to a process for manufacturing pure screw tubular anchoring elements according to the present invention, said process comprising the extrusion of a fiber, having the desired cross-section and provided with several ribs or preferably flexible fins spaced apart peripherally and extending longitudinally, said ribs or fins projecting radially outward from the surface of said fiber and cutting said fiber into predetermined lengths, said method being characterized in that the fins or ribs are cut transversely at intervals distributed along their length or are provided with teeth or notches distributed along their length. Such cutting or notching can be carried out at any stage of production, before or after cutting to length of the fiber by any suitable means such as by cutting tools.

However, according to a preferred embodiment of the method of the present invention, the fiber is passed through a set of rollers each having on their peripheral surface projections in the form of teeth and the ribs or fins on the fiber come into engagement with the projections of the rollers while that these are rotated so as to produce said teeth or notches before cutting the fiber to predetermined lengths. Such a process in which the cutting or notching of the fins or ribs is carried out at the same time as the extrusion process allows rational and economical production.

The present invention will now be described with reference to the accompanying drawings in which
Figure 1 is a perspective view of a
embodiment of an anchoring element
tubular for screws according to this in
vention; Figures 2 and 3 are views in
end of the anchor shown in
Figure 1 mounted in drilled or drilled holes
in two different diameters in a wall
solid concrete or brick; figure 4 is
an end view corresponding to that shown
in figure 3 but when the screw has been screwed in
the anchoring element; Figures 5 and 6 are
side elevation and partial section views
representing the anchors of the figures
2 and 3 respectively, after tightening the
screw; Figures 7 to 9 are elevational views
side and partial section representing the element
anchor for screw of figure 1 mounted in
a drilled hole through a panel or board,
three different stages of screw tightening
which was screwed into the anchor, the
Figures 10 and 11 are elevational views
side and partial section representing the element
anchor of Figure 1 mounted in a hole
blind drilled or drilled in a solid wall in
aerated concrete or semi-brittle material
biable with the screw respectively in the con
edition not tight and in condition fully
tight; Figure 12 shows the year element
screw hole mounted in a through hole
the wall of a hollow brick with the screw in
the tight condition; figure 13 represents
schematically and on a smaller scale,
an apparatus or installation for producing
anchors for screws conforming to
the present invention and Figure 14 is a
end view partially in section on a scale
enlarged schematically representing the availability
pebbles sition to form interruptions
or teeth spaced in the ribs or fins
of the anchor for screws.

FIG. 1 represents a tubular anchoring element for screws 10 comprising several (in the present case three) parts in the form of rods or massive elongated and solid parts spaced apart and extending longitudinally, each part having a substantially shaped cross-section as a circular ring sector. The solid parts 11 are connected at their internal radial edges by flexible and thin wall parts 12 each having an angular cross-sectional shape so that the internal surfaces of the solid parts II and parts flexible wall 12 together define an axial passage or bore 13 extending over the entire length of the screw anchor element 10 and having a sectional shape which is substantially the shape of an equilateral triangle when the element d the screw anchor is not subject to constraints.

The anchoring element for screws 10 also comprises several fins or radial ribs 14 extending longitudinally, said fins or ribs being formed on the external surfaces of the solid parts 11. In the embodiment shown in the drawings, a fin or rib 14 is formed on each of the external edges of the solid parts 11. The pairs of ribs arranged on each solid part are preferably substantially parallel to one another.

Each fin or rib is interrupted by teeth or notches spaced narrowly along the length. If the cross section of the bottom of these teeth or notches is pointed or acute, the depth of the notches is of less importance due to the notch effect. If, however, the bottoms of the teeth or notches are more rounded, the teeth preferably extend over the entire radial height of the fins or ribs.

The screw anchor 10 shown in Figure 1 can be used to mount a screw in a drilled or drilled hole in a wall or panel, and the same anchor can easily be used in any hole with a diameter included in a relatively large range of diameters corresponding substantially to the radial height of the fins or ribs 14. FIG. 2 represents the situation in which the anchoring element for screws 10 represented
years old firm 1 was sunk in a hole drilled in a
a z. a panel 16 with a diameter lying at the lower limit of the range of diameters in which the anchor element for screws can be used. When the anchor element 10 is pressed into such an undersized hole, the fins or ribs 14 on each of the solid parts are bent in opposite peripheral directions, as shown in FIG. 2, so that the external peripheral surfaces of the solid parts come into close engagement with the internal wall of the hole or borehole in the wall 16 .

If an identical anchor for screw 19 is pressed into a hole drilled with a larger diameter, only the outer radial edge portions of the fins 14 come into engagement with the inner wall of the hole for ~ and are attached. Thus, as shown in FIG. 3, spaces 1 are defined between the external peripheral surfaces of the solid part 11 and the internal wall of the drilled hole.

 When a 2 screw 18 is inserted into the external end of the passage or axial bore 13 of the anchor element for screws and tightened, the friction between the fins 14 and the internal wall of the bore prevents rotation of the anchoring element 10 with the screw. Optionally, the screw will radially expand the anchoring element, so that the angular flexible wall parts 12 are tensioned and the external peripheral surfaces of the solid parts 11 are compressed in close engagement with the internal wall of the borehole as shown in the FIG. 4. When, as shown in FIG. 2, anchoring element 10 is mounted in a drilled hole having a relatively small diameter, the radial expansion of the anchoring element caused by the insertion of the screw 18 will be sufficient to bring the anchoring element into close engagement with the wall of the drilled hole and therefore to anchor the anchoring element in the hole. If the hole is a blind hole drilled in a wall of hard material such as a concrete or brick wall, the anchor will not twist or be compressed axially. tightening the screw 18 as shown in Figure 5; however, if the drilled hole is over-slipped, as shown in Figure 6, the anchor member 10 will twist and be compressed axially to such an extent that the radial expansion necessary to obtain an anchoring on is obtained. The fact that the anchoring element 10 is provided with only three solid parts it, ensures self-centering of the anchoring element in the hole when the screw is tightened.

Figure 7 shows the element of> nçrage for screw 10 mounted in a hole drilled right through, drilled in a panel 19 such as a plasterboard. The roughness of the fins 14 provided with teeth or notches 15 and the elastic engagement between the fins 14 and the internal wall of the hole gives rise to substantial friction forces between the anchoring element for screws 10 and the internal wall of the hole , even when the diameter of the hole is relatively large.

This eliminates the risk that the screw anchor 10 will be inadvertently pushed entirely through the hole and will be lost.

When a screw 18 is screwed into the anchoring element 10, the axial section 20 of the anchoring element 10 positioned in the drilled hole cannot rotate with the screw 18 as explained previously. However, the axial section 21 of the anchoring element for screws 10 extending beyond the internal side of the panel 19 may, when the screw 18 is tightened, rotate to a certain extent with the screw so that the section 21 spin. Because the solid parts 11 are positioned radially outside the walls defining the axial passage 13 of the anchoring element 10, and that the fins or ribs 14 are provided with teeth or notches 15 with a small spacing, these massive parts and the fins will contribute little to the torsional strength of the screw anchor element 10 and, consequently, this resistance will be relatively low. Therefore, when the screw 18 is tightened so that the head 22 of the screw engages tightly with a washer 23 or other element section 21 of the screw anchor 10 which lies beyond the wall will not only be compressed axially but will also be significantly twisted as shown in FIG. 9, so that the effective external diameter of the twisted section 21 substantially exceeds the diameter of the borehole in the panel 19, which effectively prevents the withdrawal of screw anchor element 10 from the borehole made in ns the panel 19. Figure 8 shows an intermediate stage of tightening the screw and clearly shows how the teeth or notches 15 can be widened and shortened in order to facilitate the twisting of the anchoring element. Thus, the teeth or notches communicate a kind of channel effect to the fins 14 and the massive parts 11.

Figures 10 and 11 show a similar situation, in which the screw anchor 10 has been mounted in a blind hole 24 in a wall 25 of aerated concrete or similar breaking material. FIG. 10 represents the situation in which the screw 18 has just been inserted in the anchoring element for screws 10 mounted in the borehole 24 and FIG. 11 represents the situation after the tightening of the screw 18. As shown, anchor is expanded to such an extent that it displaces a little of the wall material surrounding the drilled hole, which improves anchoring.

 FIG. 12 shows the anchoring element 10 mounted in a hole drilled in a hollow brick 38 or in another element of hollow construction. In this case, the anchoring element functions in substantially the same way as in the case shown and described with reference to FIGS. 7 to 9.

The screw anchors 10 of the type shown in Figure 1 can be produced very rationally by extrusion. Figures 13 and 14 show an apparatus or system for producing such anchors. The apparatus shown in FIG. 13 comprises an extrusion die 26 extruding a tubular fiber 27 having a cross section corresponding to that of the anchoring element shown in FIG. 1. The extruded fiber 27 passes along d a support element 28 and is held in contact with a guide surface by a roller 29 subjected to the action of a spring. After having been sufficiently cooled, the fiber 27 passes through a set of notching rollers 30 comprising a frame 31 on which is rotatably mounted a pair of small notching rollers 32 having projections 33 in the form of teeth formed on their peripheral surfaces and a larger notching roller 34 which is driven by a drive motor 35 with a peripheral speed corresponding substantially to the speed of extrusion of the fiber 27. As best represented in FIG. 14 the notching rollers 32 and 34 are arranged so that their projections or teeth 33 engage with and form teeth with a small spacing in the fins or ribs 14 of the fiber 27. While the notching roller 34 is entralée by the motor 35, the notching rollers 32 are driven by the displacement of the fiber 27. As better represented in FIG. 14, the adjacent fins 14 on the adjacent solid parts extend substantially parallel to one another towards the outside so that the fins of a pair can be notched by a single roller. The fiber 27 after passage through the roller assembly 30 can be sent to a cutting device 36 to cut the fiber 27 to the desired length in order to form the anchoring elements for screws 10. These anchoring elements for screws can be collected in a storage container 37.

The screw anchor 10 is preferably made of a plastic material of the type normally used for screw anchors such as polyvinyl chloride. It will be understood that without departing from the scope of the present invention, the anchoring element for screws 10 may have any suitable cross-section other than that shown in the drawings and be provided with notched external fins or ribs. By way of example, a section can be used like that described in the Danish patent N5 12 '# 8 and the French patent N 7019457. It will be understood that in the present description the term fins or ribs "must be interpreted very Thus, the massive external parts 11 shown in the drawings can be considered in themselves as fins or ribs and be provided with teeth or notches spaced axially to facilitate the twisting of the anchoring element for screws.

Claims (9)

Claims 1. A tubular screw anchor (10) of the type adapted to be inserted into a drilled hole and comprising several ribs or fins (14) preferably flexible, spaced apart peripherally and extending longitudinally, the fins or ribs projecting radially outwards from the external peripheral surface of the tubular element, characterized in that each rib or fin (14) is interrupted or weakened from place to place in the axial direction. 2. An anchoring element for screws according to claim 1 of the type comprising protruding parts in the form of rods (11) longitudinally and spaced apart peripherally which are secured by flexible and thin wall parts (1?), Characterized in that that the flexible wall parts (12) connect the internal radial parts of the massive parts in the form of adjacent rods (11) and in that the fins or ribs (14) are positioned on the external radial surfaces of the form parts (11) chopsticks 3. An anchor for screws according to claim 2, characterized in that the fins or ribs (14) are positioned on the outermost edges radially of the rod-shaped parts (11). 4. An anchor for screws according to any one of claims 2 and 3, characterized in that the fins or ribs (14) comprise a pair of fins spaced from one another diverging outwardly or substantially parallel, the fins being positioned on the respective rod-shaped parts (11).  5 An anchoring element for screws according to any one of claims 1 to 4, characterized in that the spacings of the interruptions or weakening have dimensions of the order of one to a few millimeters. 6. An anchor for screws according to any one of claims 1 to 5, characterized in that it is made of plastic, preferably polyvinyl chloride.  7 An anchor for screws according to any one of claims 2 to 6, characterized in that the internal sides of the massive parts in the form of rods (11) delimit a passage (13) having a section in section having substantially the form of an equilateral triangle, the vertices of the triangle being defined by said flexible wall portions (12).  8. A method of manufacturing tubular anchors for screws according to any one of claims 1 and 7, the method consisting in extruding a tubular fiber (27) having the desired section and provided with several ribs or fins preferably. flexible (14) spaced apart peripherally and extending longitudinally the ribs or fins projecting radially outward from the outer surface of the fiber and cutting the fiber to predetermined lengths, characterized in that the ribs or fins ( 14) are cut transversely at axial intervals or provided with axially spaced teeth or notches (15).  9. A method according to claim 8, characterized in that the fiber (27) is passed between a set of rollers (32, 34) each having on its peripheral surface projections (33) in the form of teeth and engaging the fins or ribs of the fiber with the projections of the rollers while these are rotated so as to provide the fins or ribs with teeth or notches (15) before cutting the fiber to predetermined lengths.