Patent Document

TECHNICAL FIELD 
       [0001]    The invention concerns a wall plug, in particular chemical, notably for fixing a part to a support material, as well as a fixing kit including a screw and such a wall plug. 
       PRIOR ART 
       [0002]    A chemical wall plug is a wall plug that is fixed to a support material with the aid of a thermosetting resin and a hardener or activator to polymerize the resin. 
         [0003]    Chemical wall plugs exist for solid materials and for hollow materials. 
         [0004]    In a solid material, a hole may be drilled therein, a capsule of resin slid into it in which is housed a capillary tube filled with hardener, before breaking up the combination and mixing the two components. It is also possible to drill a hole and to inject into it resin and a hardener or polymerization activator that mix in it. A stud or a screw may then serve as a fixing element. 
         [0005]    In a hollow material, after drilling a hole in the wall of the material, there may be introduced into it a tubular mesh into which resin and a hardener are then injected, the resin expelled from the screen, once polymerized, fixing the mesh to the rear of the wall. Studs and screws may also be used as fixing elements. 
         [0006]    All the wall plugs referred to above may be used either in a solid material or in a hollow material. 
         [0007]    For a hollow material, there is also known an element including a bearing flange to which is fastened a split skirt, the skirt being adapted i) to be pulled against the rear face of the wall by the action of the tie connecting it to the flange bearing against the front face of the wall and ii) to receive by injection a mixture of resin and hardener for fixing the element to the rear of the wall. 
         [0008]    All the wall plugs referred to above, known for a long time, employ purely chemical fixing. A disadvantage of these chemical fixings is that it is necessary to wait for the mixture of components to polymerize and harden before being able to apply any load to the stud or screw. 
         [0009]    With many chemical wall plugs it is necessary to inject resin and the applicant has attempted to dispense with this relatively fastidious injection process. Moreover, the applicant has attempted to propose a chemical wall plug that not only can be equally suitable for a hollow material and a solid material but also the fixing of which is no longer purely chemical but also mechanical. It would therefore be feasible to apply a load to the screw before polymerization of the components is finished. 
         [0010]    The applicant has therefore proposed, in their previous applications FR-A-2 896 283 and FR-A1-2 903 742, a chemical wall plug including a holed tubular jacket adapted to be compressed by a screw forming a traction element, and including, inside the jacket, a resin component and a hardener component intended to be mixed by virtue of the compression of the jacket and to polymerize to fix the wall plug. 
         [0011]    The jacket of the wall plug defines an internal housing in which the polymerization components are situated. This housing extends the complete length of the jacket. The housing is therefore open at each of the longitudinal ends of the jacket. One of the longitudinal ends of the jacket includes an internal thread with which the screw is intended to cooperate to compress the jacket and to cause a portion of the polymerization components to exit the wall plug. 
         [0012]    The two polymerization components are generally packaged in glass capsules that are intended to break and to release their contents when a screw is engaged in the wall plug. It is equally possible to encapsulate only one of the two components. The capsule containing one of the components is embedded in the other component that is retained inside the jacket by membranes that can be torn and that block the holes in the jacket. These membranes are produced by the same mold as the jacket and are formed in one piece with the latter. The jacket and its membranes are therefore made of the same material. It has already been proposed to produce these membranes by means of an external sock surrounding the jacket. 
         [0013]    The polymerization components are known to degrade rapidly if they are not stored correctly, in particular in a sealed, notably airtight, volume. 
         [0014]    As explained above, the internal housing of the jacket extends axially through this jacket and is open at its two axial ends. Although the polymerization components are prevented by the aforementioned sock from passing through the holes in the jacket, there exist at present no means to retain them and to protect them at the longitudinal ends of the jacket, and notably at the level of its internal thread, through which the components can flow. The polymerization components are therefore exposed to external conditions, such as moisture, at the open longitudinal ends of the jacket of the wall plug. 
         [0015]    Moreover, the materials used at present to produce the sock of the wall plug are not satisfactory because they are too fragile and breakable and are subject to a risk of premature tearing, before the wall plug is used. Finally, the production of the sock and its mounting on the jacket are not a simple matter and are relatively costly. It is at present not possible to manufacture a thin sock because there would be the risk of it tearing when mounting it on the jacket. There is therefore a tendency to use a thick sock. Using a thick sock is nevertheless risky because there is a risk of it not tearing on compression of the wall plug and therefore preventing some of the polymerization components exiting the wall plug. Using a heat-shrink tubular sock could be envisaged but cannot always provide a good seal between it and the jacket. 
         [0016]    The present invention proposes a simple, effective and economic solution to at least some of the problems of the prior art. 
       SUMMARY OF THE INVENTION 
       [0017]    The invention therefore proposes a wall plug, in particular chemical, comprising: 
         [0000]    i) a holed tubular jacket, this jacket defining an internal housing which emerges at each of the longitudinal ends of the jacket, and
 
ii) an outer sock which surrounds the jacket and covers the holes of the jacket,
 
characterized in that said sock covers said first end of the jacket so as to close said internal housing on the side of this first end.
 
         [0018]    In accordance with the invention, the outer sock does not merely cover the holes of the jacket as in the prior art but also covers the end of the jacket to close its internal housing at this end. The sock therefore forms a sheath all around the jacket and at the level of one end of the jacket. 
         [0019]    The sock can therefore make it possible to transform the inner housing of the jacket into a sealed enclosure on the side of the tubular wall of the jacket and on the side of one of its ends. The other end of the jacket may include an external annular flange. 
         [0020]    The end of the jacket that is closed by the sock preferably comprises on its internal periphery at least one helical rib forming an internal thread. If a screw is intended to be used with the wall plug in accordance with the invention, this helical rib is intended to cooperate with this screw so that screwing the screw into the wall plug leads to compression of the wall plug by movement toward each other of its longitudinal ends. This compression is advantageously intended to cause tearing of the sock at the level of the holes in the jacket. Moreover, on introducing the screw into the wall plug and screwing it in, the screw will come into contact with the portion of the sock covering its longitudinal end and will pierce this end. The sock therefore defines two portions that can be torn, the portion extending around the tubular portion of the jacket and that lying at the end of the jacket including the helical rib. 
         [0021]    The sock is preferably formed in one piece. It is preferably produced by overmolding it onto the jacket. This technique enables precise control of the thickness of the sock. The sock may have a thickness less than or equal to 1 mm, for example between 0.1 and 0.8 mm. It is preferably made of an elastically deformable material. 
         [0022]    The sock is preferably made of a material exhibiting high adhesion to the material of the jacket, so as to avoid the use of glue to join them. Overmolding the sock onto the jacket advantageously suffices to provide this connection by virtue of the adhesion of the material of the sock to that of the jacket. 
         [0023]    The sock may be made of elastomer, such as thermosetting elastomer, thermoplastic elastomer (TPE), or rubber. The thermosetting elastomer is for example PDMS: polydimethylsiloxane. The thermoplastic elastomer may be (i) a styrene block copolymer such as SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene) or SEBS (styrene-ethylene-butylene-styrene), (ii) a mixture of rubber and polyolefin such as olefin-based polypropylene, (iii) a thermoplastic polyurethane, (iv) an ester-ether copolymer, etc. 
         [0024]    In one particular embodiment of the invention, the jacket is made of thermoplastic (such as a polyamide) and the sock is made of thermosetting elastomer or thermoplastic elastomer. The jacket may be produced by injection molding. 
         [0025]    The material of the sock preferably has one or more of the following characteristics:
       a Shore A hardness between 1 and 100, preferably between 30 and 100, more preferably between 50 and 80, even more preferably between 60 and 80, and for example of the order of 60-70;   an elongation at fracture between 100 and 900%, preferably between 200 and 800%, more preferably between 200 and 700%, even more preferably between 200 and 500%, and for example of the order of 200-300%;   a tensile strength between 1 and 10 MPa, preferably between 2 and 6 MPa, more preferably between 3 and 5 MPa, and for example of the order of 4-4.5 MPa;   a resistance to tearing between 5 and 50 MPa, preferably between 10 and 50 MPa, more preferably between 20 and 50 MPa, even more preferably between 20 and 40 MPa, and for example of the order of 30-35 MPa;   an extrusion rate or speed between 10 and 130 g/min, preferably between 30 and 120 g/min, and for example between 50 and 100 g/min; this extrusion rate is notably a function of the viscosity of the material, which is preferably neither too low (material too fluid), which would create risks of infiltration in the mold, nor too high, which could impede its injection.       
 
         [0031]    The invention is particularly but not exclusively suitable for producing a chemical wall plug. The wall plug can therefore include inside said housing a resin component and a hardener component intended to be mixed and to polymerize, for example because of the compression of the jacket, to fix the wall plug. The hardener component is preferably housed in a capsule, for example of glass, which is embedded in the resin component which is directly in contact with the jacket. The sock of the wall plug therefore retains the resin component through the holes of the jacket and through the aforementioned end of the jacket. 
         [0032]    In accordance with a preferred embodiment of the invention, the wall plug comprises a plug which is fitted in a second longitudinal end of the jacket, opposite said first end. This plug is preferably configured to close said end in a sealed manner. The housing of the jacket is thus transformed into a totally sealed enclosure. 
         [0033]    The plug is preferably tubular and defines an internal space which emerges at each of the longitudinal ends of the plug. The plug may comprise on its internal periphery at least one helical rib forming an internal thread. This internal rib is advantageously intended to cooperate with a screw so as to center it upon its introduction into the wall plug. This rib is advantageously similar to that of the jacket. Thus the ribs of the jacket and the plug may be adapted to cooperate with the same screw. The ribs or threads have the same pitch, for example, which is between 1 and 5 mm, preferably between 2 and 4 mm, and for example approximately 3 mm. Rt least one of these ribs (and preferably each of them) is configured to allow the screw to pass only upon screwing it in. This makes it possible to limit the risk of accidental introduction of the screw into the wall plug. 
         [0034]    At least one of the longitudinal ends of the plug is advantageously covered by a transverse membrane so as to close said internal space at this end. This membrane therefore makes it possible to close the internal housing of the jacket at said second end, preferably in a sealed manner. 
         [0035]    The membrane is preferably molded onto the plug. The membrane may have a thickness less than or equal to 1 mm, and for example between 0.1 and 0.8 mm. It is preferably made of elastically deformable material. It may be made of the same material as the aforementioned sock. 
         [0036]    The membrane may be made of elastomer, such as thermosetting elastomer, thermoplastic elastomer (TPE), or rubber. The thermosetting elastomer is for example PDMS: polydimethylsiloxane. The thermoplastic elastomer may be (i) a styrene block copolymer such as SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene) or SEBS (styrene-ethylene-butylene-styrene), (ii) a mixture of rubber and polyolefin such as olefin-based polypropylene, (iii) a thermoplastic polyurethane, (iv) an ester-ether copolymer, etc. 
         [0037]    In one particular embodiment of the invention, the plug is made of thermoplastic (such as a polyamide) and the membrane is made of thermosetting elastomer or thermoplastic elastomer. The plug may be produced by injection molding. 
         [0038]    The present invention further concerns a fixing kit characterized in that it comprises a wall plug as described above and a screw. This screw is advantageously configured to cooperate with the internal rib of the jacket and where appropriate with that of the plug. This screw may include two threaded portions with different pitches. The screw preferably has a pointed longitudinal end to facilitate piercing the sock and where applicable the membrane. 
         [0039]    The screw may have a diameter between 6 and 20 mm and preferably between 10 and 16 mm. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0040]    The invention will be better understood and other details, features and advantages of the present invention will become more clearly apparent on reading the following description, given by way of nonlimiting example and with reference to the appended drawings, in which: 
           [0041]      FIG. 1  is a diagrammatic part-sectional perspective view of a fixing kit in accordance with the invention including a chemical wall plug and a screw; 
           [0042]      FIG. 2  is a diagrammatic exploded perspective view of the wall plug from  FIG. 1 ; 
           [0043]      FIG. 3  is a diagrammatic exploded view in axial section of the wall plug from  FIG. 1 ; and 
           [0044]      FIG. 4  is a diagrammatic sectional view of a support material into a hole in which is fixed a chemical wall plug in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]      FIGS. 1 to 3  represent one embodiment of the wall plug  10  in accordance with the invention, which here is a chemical wall plug, this wall plug  10  notably being used for the chemical and mechanical fixing of a part to a support material as described in detail with reference to  FIG. 4 . 
         [0046]    The wall plug  10  includes a tubular jacket  12 , here of plastic material, with axis  14 . The jacket  12  is made of thermoplastic, for example, such as polyamide (for example PA6). 
         [0047]    The jacket  12  extends between an end including an annular bearing flange  16  and another end  18  opposite that with the flange  16  and forming a traction nut, as will be explained hereinafter, thanks to an internal thread  20  that may comprise a single projecting rib inside this end  18 . 
         [0048]    The jacket  12  is holed, i.e. its tubular wall includes holes, which here are formed by helical slots  22  extending over a major portion of the axial length of the jacket  12 . 
         [0049]    Each slot  22  extends between two adjacent longitudinal strips  24  of material each of which has a helical general shape. The slots  22  have a width that depends on the spacing between these strips  24  of material, which is typically between 0.2 and 1.5 mm, preferably between 0.5 and 1 mm, and for example of the order 0.8-0.9 mm. 
         [0050]    The strips  24  of material extend between two non-holed annular end portions  26 ,  28  of the jacket  12 . The strips  24  of material are joined to the flange  16  by a first annular end portion  26 . This first end portion  26  has on its outside periphery anti-rotation ribs  30 . 
         [0051]    The second annular end portion  28  has on its inside periphery the aforementioned internal thread  20 . The strips  24  of material are inscribed in a cylinder the outside diameter of which is substantially equal to that of the end portions  26 ,  28 . 
         [0052]    The jacket  12  defines an internal housing  32  that is open at each of its longitudinal ends. Taking the jacket  12  in isolation, its housing  32  in fact communicates with the outside via its internal thread  20  and its end including the flange  16 . 
         [0053]    The wall plug  10  is intended to contain polymerization components and in particular a resin component  36  and a hardener component  38 . In the example shown, the hardener component  38  (for example a peroxide in powder form) is situated in a closed capsule  34 , for example of glass, which has an elongate shape and extends inside the housing  32  coaxially with the wall plug  10  and over substantially all its length. The capsule  32  of hardener  38  is embedded in the resin component  36  which therefore extends around the capsule, between the capsule and the tubular wall of the jacket  12 , as well as between the end  18  of the jacket  12  and the adjacent end of the capsule  34 . 
         [0054]    In accordance with the invention, the housing  32  of the jacket  12  is sealed by a first sock  40  that surrounds the jacket  12  to cover its holes or slots  22  and to cover the end  18 . The sock  40  therefore has two parts, a tubular first part  40   a  that extends around the tubular wall of the jacket  12  over substantially all its axial dimension, i.e. extends beyond the axial ends of the strips  24  of material, as far as the annular end portions  26 ,  28 , which it overlies, and a transverse second part that forms a first membrane  40   b  blocking the end  18  of the jacket  12 . This transverse part or membrane  40   b  of the sock  40  therefore prevents accidental exit of the resin component  36  via the end  18  of the jacket. 
         [0055]    This sock  40  is preferably overmolded onto the jacket  12 . To this end, the jacket  12  may be held by a spindle (not shown) engaged axially in the jacket  12  that is housed in a mold (not shown) for the overmolding operation. To ensure correct positioning of the jacket  12  in the mold, the latter may include radial fingers (radial relative to the axis  14  of the wall plug  10 ) intended to bear on the jacket  12 . In the example shown, four fingers bear on the annular end portion  28  of the jacket  12 . Because of this bearing engagement, which is maintained during the overmolding operation, the jacket  12  will clearly not be covered with the material of the sock  40  at the level of the bearing areas. In the example shown, these bearing areas  42  are generally T-shaped. 
         [0056]    The wall plug  10  in accordance with the invention further includes a plug  44  that is configured to be mounted in the end of the jacket  12  including the flange  16  and to block the internal housing  32  of the jacket at this end. 
         [0057]    The plug  44  has a tubular shape with axis  14 . Here it is made of plastic material. The plug  44  is for example made of thermoplastic, such as polyamide (for example PA6). It includes at one of its ends an internal thread  46  that may comprise a single rib projecting inside this end. 
         [0058]    The plug  44  defines an internal space  48  that is open at each of its longitudinal ends. Taking the plug  44  in isolation, its space  48  in fact communicates with the outside via its internal thread  46  and its opposite end. 
         [0059]    In accordance with the invention, the housing  32  of the jacket  12  is sealed by a second sock  50  that surrounds the plug  44  to cover its tubular wall and to cover the end of the plug including the internal thread  46 . The sock  50  therefore has two parts, a tubular first part  50   a  that extends around the tubular wall of the plug  44  over substantially all its axial dimension and a transverse second part that forms a second membrane  50   b  for blocking the end of the plug  44 . This transverse part or membrane  50   b  of the second sock  50  therefore prevents accidental exit of resin component  36  via the end of the jacket  12  including the flange  16 . 
         [0060]    This sock  50  is preferably overmolded onto the plug  44 . To this end, the plug  44  may be held by a spindle engaged axially in the plug  44  that is housed in a mold for the overmolding operation. To ensure correct positioning of the plug  44  in the mold, the mold may include radial fingers (radial relative to the axis  14  of the plug) intended to bear on the plug, as explained above. In the example shown, these bearing areas are referenced  52 . 
         [0061]    The plug  44  may be inserted or force-fitted into the end of the jacket  12 . It may have a diameter substantially equal to or slightly greater than the inside diameter of the end portion  26  or the strips  24  of material of the jacket  12 . The tubular portion  50   a  of the sock  50  may be designed to deform slightly through compression on mounting the plug  44  and/or to take up any play caused by manufacturing tolerances. 
         [0062]    The plug  44  may include at its end opposite the membrane  50   b  an annular external rim  54  the external periphery of which is intended to cooperate with a cylindrical internal entry surface  56  of the jacket  12 , and in particular the end portion  26  thereof, and is able to come to bear axially on the ends of the strips  24  of material to define a correct position upon mounting the plug  44  in the jacket  12 . 
         [0063]    The rim  54  of the plug  44  is covered by the sock  50  which forms around this rim an additional thickness or an annular bead  60 . This bead  60  is intended to be compressed between the rim  54  and the surface  56  in the mounted position of the plug  44  in the jacket and to provide a seal between the plug  44  and the jacket  12 . 
         [0064]    The wall plug  10  is intended to be compressed by a traction screw  70  which here is also a fixing screw, intended to engage the threads  46 ,  20  of the wall plug (the thread  46  of the plug  44  and the thread  20  of the jacket  12 ). 
         [0065]    The screw  70  includes two axial threaded portions  72 ,  74  separated from one another by an annular external flange  76 . The first threaded portion  72  is intended to lie outside the wall plug  10 , after fitting, and to receive a part to be fixed to the screw  70  by a nut to be screwed onto this threaded portion  72 . 
         [0066]    The flange  76  of the screw  70  is intended to come to bear against the flange  16  of the wall plug  10  which is itself intended to bear against a support material in a hole in which the wall plug  10  is engaged. 
         [0067]    The second threaded portion  74  of the screw  70  is configured to cooperate with the threads  46 ,  20  of the wall plug  10  and is therefore sized accordingly. The threaded portion  74  therefore includes at least one external helical rib the pitch of which is substantially equal to that of the threads  46 ,  20 , which is preferably between 1 and 5 mm, and is approximately 3 mm in the example shown. The screw  70  forms a traction element because it is configured to cooperate with the thread  20  of the wall plug to pull the end  18  toward the flange  16 , i.e. to compress the wall plug  10  axially. 
         [0068]    The end  78  of the screw  70  opposite its threaded part  72  is in the form of a spike to facilitate piercing of the membranes  50   b ,  40   b  upon introduction of the screw into the wall plug  10 . It is clear that the axial distance L between the flange  76  and the tip of the screw  70  must be greater than the length of the wall plug  10  so that the screw has already pierced the membrane  40   b  of the wall plug when its flange  76  bears on the flange  16  of the wall plug  10 . It is also clear that the axial distance L′ between the flange  76  and the end of the threaded portion  7  situated on the side opposite the flange  76  must be greater than the distance between the flange  16  of the wall plug and its thread  20  so that the screw can cooperate with this thread before its flange  76  comes to bear on that of the wall plug  10 . 
         [0069]    The combination comprising the wall plug  10  and the screw  70  forms a fixing kit in accordance with the invention. 
         [0070]    Refer from now on to  FIG. 4 , which shows diagrammatically the kit after its use to fix a part to a support material  80 . 
         [0071]    Here the support material  80  is a hollow material an exterior wall  81  of which is pierced by a hole  82  having a diameter slightly greater than the outside diameter of the jacket  12  of the wall plug  10 . The wall plug  10  is introduced into the hole  82  until its flange  16  is pressed against the exterior surface  84  of the wall  81 . Then, using a tool and an appropriate screw-driving bit  86 , the screw  70  is driven in rotation. 
         [0072]    The screw  70  is firstly introduced into the plug  44  of the wall plug  10  until its tip pierces the membrane  50   b . The end of the threaded portion  74  opposite the flange  76  is then able to cooperate with the thread  20  of the plug  44 . As explained above, the screw cannot be introduced into the wall plug by simple movement in axial translation of the screw  70  in the wall plug  10  because the thread  20  of the plug forms retaining means cooperating in axial abutment engagement with the aforementioned end of the threaded portion  74  of the screw to prevent this movement in translation. The screw  70  can be introduced into the wall plug only by rotating the screw to screw it into the plug. During screwing, the screw  70  advances in the wall plug and breaks the capsule  34  of hardener component  38 , which mixes with the resin component  36 . The threaded portion  74  of the screw may therefore be viewed as similar to a lead screw for mixing the polymerization components. This effect is accentuated by the fact that a plurality of turns of the screw are necessary for it to pass axially through the wall plug. Rotation of the screw  70  is maintained until its tip pierces the membrane  40   b  and the end of the threaded portion  74  opposite the flange  76  cooperates with the thread  20  of the wall plug. Continued screwing leads to movement of the end portion  28  of the wall plug, which moves along the screw and approaches the other end portion  26  that is held immobile by virtue of the flange  16  pressing on the exterior surface  84  of the support material  80 . This causes compression and radial expansion of the wall plug  10  to form a knot behind the wall  81  so that the wall plug  10  is already fixed mechanically to the wall  81 . The compression of the wall plug causes tearing of the sock  40  at the level of the slots  22  of the jacket  12 . The mixture of polymerization components is then partly expelled through these slots  22  to form behind the wall  81  a mass that polymerizes to compete by chemical means the fixing of the wall plug to the wall  81 .

Technology Category: 2