Anchor for fixing in a wall

A self-drilling anchor including a screw and an anchor body configured to receive a shank of the screw, the anchor body including: a flange at an end oriented toward a head of the screw, a threaded portion, a deformable expansion portion between the flange and the threaded portion, and a rotation locking mechanism preventing rotation of the anchor body relative to the wall. The threaded portion is configured to engage with the screw thread and advance in a direction of the flange, by deforming the expansion portion, when the screw is screwed into the threaded portion. The anchor body further includes a piercing element at the opposite end from the flange, the anchor including a fastening mechanism between the screw and the anchor body, the fastening mechanism being detachable by a torque, applied between the screw and the anchor body, equal to or greater than a predetermined torque.

The present invention relates to an anchor for fixing in a wall and to a method for manufacturing such an anchor.

It is known to use an expansion anchor bolt to fix a part to a relatively thin wall, such as plasterboard. U.S. Pat. No. 3,316,796 describes a conventional expansion anchor bolt comprising a screw which is received in an anchor body, where the anchor body is provided with a flange at that end of the anchor body oriented toward the head of the screw and, at the opposite end from the head of the screw, a threaded portion which engages with the thread of the screw. In order to fix a part to a wall using such an anchor, several steps are needed. First of all, a hole is made in the wall and the anchor body is inserted therein until the flange comes to press against the wall. The screw is then screwed into the threaded portion which causes the threaded portion to advance toward the head of the screw and causes the anchor body to expand behind the wall. The anchor body is thus immobilized in the wall. The screw is then unscrewed and the part to be fixed is placed against the flange of the anchor body. Finally, the screw is once again inserted into the anchor body through the part, and is screwed there in order to fix the part.

Implementing these successive steps is long and tedious. Moreover, installing the anchor requires several tools, in particular a drilling bit of a suitable size for the anchor body in order to avoid any damage to the wall when the anchor is inserted.

The invention intends more particularly to remedy these drawbacks by proposing a self-drilling anchor which makes it possible to fix a part to a wall simply and quickly, wherein the part can be fixed in a single step and using a conventional screwing tool.

To this end, one subject of the invention is a self-drilling anchor for fixing in a wall, comprising a screw which has a head and a shank bearing a thread, and an anchor body designed to receive the shank of the screw, wherein the anchor body comprises:a flange at that end of the anchor body oriented toward the head of the screw,a threaded portion designed to engage with the thread of the screw,a deformable expansion portion between the flange and the threaded portion,rotation locking means for preventing rotation of the anchor body relative to the wall,
the threaded portion being designed to advance in the direction of the flange, by deforming the expansion portion, when the screw is screwed into the threaded portion, characterized in that the anchor body further comprises a piercing element at its opposite end from the flange, the anchor comprising fastening means between the screw and the anchor body, wherein these fastening means are detachable for a torque, applied between the screw and the anchor body, equal to or greater than a predetermined torque.

Such a self-drilling anchor makes it possible to fix a part to a wall in a single step, by driving the screw in rotation using a conventional screwing tool, in particular an electric screwdriver. In a first step, as long as the torque applied between the screw and the anchor body remains less than the predetermined torque, the screw and the anchor body are connected to each other in terms of movement by the fastening means. By driving the screw in rotation, the piercing element is caused to rotate and, by bringing the piercing element into contact with the wall, a hole is made in the wall, with the anchor body being inserted therein at the same time. It is thus understood that the fastening torque between the screw and the anchor body must be greater than the torque required to pierce the wall. The anchor body is immobilized in the hole in the wall by the rotation locking means, with its flange pressing against the wall or against a part to be fixed to the wall. The screw and the anchor body remain fastened to one another until a torque equal to or greater than the predetermined torque is reached. As the torque on the screw is increased, the screw detaches from the anchor body, causing the screw to be screwed into the threaded portion of the anchor body and causing the threaded portion to advance in the direction of the flange. The result is a deformation of the expansion portion which locks the anchor body in the hole in the wall.

The piercing element advantageously comprises an internal bore designed for the shank of the screw to pass through freely. The piercing element, which is secured to the threaded portion, can thus advance with the latter in the direction of the flange as the screw is screwed into the threaded portion. As a result, the anchor body takes up less space behind the wall when in the mounted configuration.

The predetermined torque, above which the screw and the anchor body are no longer fastened to one another, is adjusted depending on the mechanical properties of the wall and of the elements making up the anchor body. In particular, the predetermined torque must be greater than the torque needed for piercing the wall and less than the torque above which the rotation locking means of the anchor body are no longer effective.

Within the scope of the invention, the detachable fastening means are active between the screw and the anchor body independently of a contact force between the head of the screw and the flange of the anchor body. In particular, there can be a space between the head of the screw and the flange of the anchor body when piercing the wall. The presence of such fastening means which act independently of a contact force between the head of the screw and the flange of the anchor body is particularly advantageous when the torque to be applied in order to achieve the deformation of the expansion portion is less than the piercing torque. According to an advantageous feature, the detachable fastening means ensure a fastening between the shank of the screw and the anchor body.

According to other advantageous features of an anchor according to the invention, considered in isolation or according to all technically possible combinations:the piercing element comprises, at its opposite end from the flange, a plurality of teeth distributed circumferentially around the bore; in particular, the piercing element can be a hole saw;the opposite end of the shank of the screw from the head forms a center punch for the piercing element;the radial dimensions of the piercing element are equal to or greater than the radial dimensions of the threaded portion and of the expansion portion in the non-deformed state, and are strictly smaller than the radial dimensions of the flange;the expansion portion is made of plastic;the piercing element is made of metal;the threaded portion is made of metal;the threaded portion and the piercing element are a single metal part;the anchor body is obtained by injection molding a plastic material around the or each metal part formed by the threaded portion and/or the piercing element;the expansion portion, the threaded portion and the piercing element are made of plastic;the threaded portion and the piercing element are made of a plastic material which is more rigid than the plastic material of the expansion portion;the anchor body is obtained by injection molding in a single part;the detachable fastening means comprise a layer of adhesive between the screw and the anchor body, which is designed to break when the predetermined torque is exceeded;the detachable fastening means comprise a frangible connection between the screw and the anchor body, which is designed to break when the predetermined torque is exceeded;the detachable fastening means comprise a prestress connection between the screw and the anchor body, which is designed to break when the predetermined torque is exceeded;the rotation locking means for preventing rotation of the anchor body relative to the wall comprise at least one fin for anchoring in the wall near the flange;the expansion portion comprises a plurality of longitudinal slits which are distributed circumferentially and are inclined relative to a longitudinal axis of the expansion portion, which define a plurality of strips which are helically deformable when the screw is screwed into the threaded portion.

Another subject of the invention is also a method for manufacturing an anchor as described hereinabove, the threaded portion and/or the piercing element of which is made of metal, wherein the or each metal part formed by the threaded portion and/or the piercing element is placed in a mold and a plastic material is injected into the mold around the or each metal part.

Another subject of the invention is also a method for manufacturing an anchor as described hereinabove, the expansion portion, the threaded portion and the piercing element of which are made of plastic, by injecting a plastic material or several compatible plastic materials in a mold.

Another subject of the invention is also the use of an anchor as described hereinabove for fixing in a thin wall, in particular a construction panel, such as a plasterboard, including a fiber reinforced plasterboard or a fiber clad plasterboard, in particular using glass fibers (glass mat); a cement board; a chipboard; a wooden panel; a hollow clay block. Such construction panels can be used in conjunction with an insulating panel, in particular the invention can be implemented for fixing in a composite panel formed, for example, by assembling a plasterboard panel and an expanded polystyrene panel or by assembling a plasterboard panel and a polyurethane foam panel.

A final subject of the invention is the use of an anchor as described hereinabove for fixing in a solid material, in particular cellular concrete.

The anchor10, seen inFIGS. 1 to 4, is a self-drilling anchor designed to fix a part, not shown in these figures, to a thin support wall40. As a nonlimiting example, the wall40is a plasterboard.

The anchor10comprises a screw1and an anchor body4. The screw1, having a longitudinal axis X1, comprises a head2and a shank3bearing a thread31. The head2is provided with a recess21for receiving a screwing tool on its face oriented away from the shank3. The anchor body4has a tubular overall shape and comprises an internal bore having a circular cross section, centered on an axis X4, which is designed to receive the shank3of the screw. When the shank3is received in the bore of the anchor body4, the axes X1and X4coincide.

At that end oriented toward the head2of the screw, the anchor body4comprises a flange5of external diameter D5which is designed to come to press against the wall40. The flange5is connected to an expansion portion6of external diameter D6smaller than that of the flange. The flange5and the expansion portion6are made of the same plastic material. The side wall of the expansion portion6has longitudinal slits61which are distributed circumferentially and are inclined relative to the axis X4. The slits61define, between them, strips63which can be deformed plastically. The anchor body4also comprises rotation locking fins9located at the junction of the flange5and the expansion portion6.

At its other end, the anchor body4comprises a piercing element8in the form of a hole saw. The hole saw8comprises an internal bore81, through which the shank3of the screw can pass freely, and a series of teeth83distributed circumferentially around the bore81. Advantageously, the opposite end33of the shank3of the screw from the head2is tapered so as to form a center punch for the hole saw8.

The hole saw8and the expansion portion6are connected to one another by a threaded portion7, wherein the external diameters D7and D8of the threaded portion7and of the hole saw8are substantially equal to that of the expansion portion6. The threaded portion7has an internal thread71designed to engage with the thread31of the screw such that it forms a nut on the shank3of the screw. When the shank3is screwed into the threaded portion7, the latter advances in the direction of the flange5, helically deforming the expansion portion6as shown inFIGS. 2 and 3. When the expansion portion6is in the deformed state, the anchor10is immobilized with respect to the wall40.

In this first embodiment, the threaded portion7and the hole saw8are made of metal, in particular steel, in one piece. The anchor body4is advantageously manufactured by injection molding the plastic material of the flange5and the expansion portion6around the metal part formed by the threaded portion7and the hole saw8. In accordance with the invention, the screw1and the anchor body4are fastened to one another by a layer of adhesive12interposed between the thread71of the threaded portion7and the thread31of the screw, this layer of adhesive12being designed to break when a predetermined torque T0is exceeded.

Installing the anchor10in the wall40is done by driving the screw1in rotation in the conventional screwing direction, by using a tool in the recess21provided for this purpose in the head2of the screw. In a first step, the torque applied between the screw1and the anchor body4is less than the predetermined torque T0, such that the screw and the anchor body are connected to each other in terms of movement by the layer of adhesive12. Rotating the screw1causes the hole saw8to rotate and, by putting the hole saw8in contact with the wall40, a hole41is made in the wall, with the anchor body4being inserted therein at the same time. When the flange5comes to press against the wall40, the rotation locking fins9are in engagement with the material of the wall40, such that the anchor body4is prevented from rotating relative to the wall. The screw1and the anchor body4remain fastened to one another until a torque equal to or greater than the predetermined torque T0is reached. By continuing to drive the screw1in rotation, and thus increasing the torque, the screw1detaches from the anchor body4, causing the screw to be screwed into the threaded portion7and causing the threaded portion7to advance in the direction of the flange5. This results in deformation of the expansion portion6, which locks the anchor body4in the hole41in the wall.

In the second embodiment shown inFIG. 5, those elements which are analogous to those of the first embodiment bear identical reference signs. The anchor shown inFIG. 5differs from that of the first embodiment in that all of the anchor body4is made of plastic, including the threaded portion7and the hole saw8. The anchor body4is then advantageously manufactured as a single part by injection molding. The threaded portion7and the hole saw8are preferably made of the same plastic material, which is more rigid than the plastic material from which the flange5and the expansion portion6are made.

In the third embodiment shown inFIG. 6, those elements which are analogous to those of the first embodiment bear identical reference signs. The anchor shown inFIG. 6differs from that of the first embodiment in that the threaded portion7is made of plastic whereas the hole saw8is still made of metal. The threaded portion7is preferably made of a plastic material which is more rigid than the plastic material from which the flange5and the expansion portion6are made. As in the first embodiment, the anchor body4is advantageously manufactured by injection molding the plastic materials of the flange5, the expansion portion6and the threaded portion7around the metal part formed by the hole saw8.

In the fourth embodiment shown inFIGS. 7 to 10, those elements which are analogous to those of the first embodiment bear identical reference signs. The anchor10shown inFIG. 7differs from that of the first embodiment in that the detachable fastening means between the screw1and the anchor body4are no longer formed by a layer of adhesive12, but by frangible tabs13. As shown inFIGS. 7 to 10, the threaded portion7and the hole saw8are formed by a single metal part, while the flange5and the expansion portion6are obtained by injection molding a plastic material around this metal part. During injection molding, the plastic material from which the flange5and the expansion portion6are made passes into holes14in the metal part. This forms the frangible tabs13as well as a platform65positioned pressing against a shoulder75of the metal part located at the junction of the threaded portion7and the piercing element8. The platform65receives, in abutment, the opposite end33of the shank3of the screw from the head2, such that the screw1and the anchor body4are fastened to one another. The frangible tabs13are designed to break when the predetermined torque T0is exceeded, so as to detach the platform65from the rest of the expansion portion6and to make it possible to screw the screw1into the thread71of the threaded portion7and thus to deform the expansion portion6. In this embodiment, as the end33of the screw is in abutment against the platform65, it cannot be used as a centering element when the wall40is pierced using the hole saw8. A center punch67made of plastic, produced in one piece with the platform65and projecting therefrom away from the end33of the screw, can then be formed during the injection molding.

In the fifth embodiment shown inFIGS. 11 to 15, those elements which are analogous to those of the first embodiment bear identical reference signs. The anchor10shown inFIG. 11differs from that of the first embodiment in that the rotation locking means for preventing the anchor body4from rotating relative to the wall40are not fins9for anchoring in the material of the wall, but raised patterns52provided on that face5B of the flange5which is oriented away from the head2of the screw and which are designed to engage with complementary raised patterns152provided on a part150to be fixed to the wall. In the example shown inFIGS. 11 to 15, the part to be fixed to the wall40is a bracket150, one leg154of which is intended to come to press against the wall. The leg154of the bracket150comprises two openings151, the rotation locking patterns152being provided around each opening151on a face150A of the leg154intended to be oriented toward the face5B of the flange5. The leg154advantageously comprises, on its face150B which presses against the wall40, studs153for provisionally immobilizing the bracket with respect to the wall40. The openings151can then be used as centering elements when piercing the wall40using the hole saw8. In this case, it is not necessary for the end33of the screw to form a center punch.

The invention is not restricted to the examples described and shown. In particular, a frangible connection, in particular by means of frangible tabs13as above, can be implemented in the case of an all-plastic plastic anchor body4, or when only the piercing element8is made of metal. Moreover, the detachable fastening between the screw1and the anchor body4can be obtained by a prestress connection between the thread of the screw and the thread of the threaded portion, instead of by means of a layer of adhesive or frangible tabs as described in the preceding examples. The piercing element can also be of any form other than a hole saw, provided it comprises an internal bore through which the shank of the screw can pass freely. Finally, the expansion portion may differ from that described and shown, in particular it may comprise deformation modes other than a helical deformation; it may in particular be an expansion body comprising a plurality of elongate metal legs which are designed to bend and fold flat against the rear face of the wall, spread out in a star shape.