Abstract:
An expandable fastener provides a fastener having a hollow tube in fluid communication with a flexible membrane forming a bladder around the tube. After the tube is inserted into the panel the bladder is filled with a curable fluid such as an expanding foam, which inflates the bladder against the rear surface of the panel. When the fluid cures it forms a substantially inflexible retaining block that contacts the panel over a large surface area, distributing any longitudinal pulling force applied against the fastener over a broad area of the panel to improve resistance to dislodgment and minimize panel failure.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to fasteners. In particular, this invention relates to an expandable fastener, for example for mounting screws to drywall panels, which provides broad surface contact against the panel to resist dislodgment. 
       BACKGROUND OF THE INVENTION 
       [0002]    Drywall, or plaster wallboard, is cheap and easy to install, making it one of the most popular finishing surfaces for walls and ceilings. Typically drywall panels are nailed or screwed onto a wood or metal frame, and plaster or drywall compound is applied to the seams between panels to finish the wall or ceiling surface. 
         [0003]    Frequently it is desirable to fasten an article or structure to a wall or ceiling, for example when mounting shelves. Drywall is composed of a plaster layer sandwiched between outer paper layers, and as such is relatively weak in the transverse direction, especially when the paper coating has been broken. However, the studs or joists of the wall or ceiling frame may not be aligned to permit the article or structure to be fastened directly to the frame in the desired position. In such cases the article or structure must be fastened to the drywall panel. 
         [0004]    There are two conventional fasteners primarily used for this purpose: a screw set into an anchoring plug embedded in the drywall; and bolt bearing extendible arms that are retracted to allow the fastener to be inserted through a hole in the panel, and extended to bear against the rear surface of the panel when the bolt is tightened. 
         [0005]    Screws cannot be fastened directly to drywall because the threads strip out the plaster when even a slight longitudinal force is applied to the screw. Accordingly, to provide a more secure anchoring force an anchoring plug is lodged in the drywall and the screw is fastened into the anchoring plug. This provides a certain amount of resistance to longitudinal dislodgment of the screw. 
         [0006]    For example, one popular type of anchoring plug consists of a hollow plastic body having a hole for receiving the screw and a ribbed exterior for engaging the plaster surrounding the hole in the drywall. The ribbing provides resistance to longitudinal dislodgment, which is augmented as the screw is driven into the plug and expands the plug, compressing the plug body against the surrounding plaster. However, the resistance of this type of fastener to longitudinal dislodgment remains limited, because it relies solely on an interference fit with a very small surface area, i.e. the layer of plaster immediately surrounding the plug, for resistance to dislodgment. 
         [0007]    Moreover, the anchoring plug tends to cause the plaster surrounding it to crumble when the plug expands as a screw is driven into it, decreasing the integrity of the surrounding drywall and further reducing resistance to dislodgment. If such a plug dislodges it inevitably leaves a larger hole than was initially drilled to hold the plug; thus, once the anchoring plug becomes dislodged it is usually not possible to replace the plug with a plug of the same size without first repairing the damage caused by the dislodged plug. 
         [0008]    A fastener having extendible arms that open after the fastener has been inserted into the drywall panel and bear against the rear surface of the panel has a stronger anchoring force. For example, a so-called “butterfly” fastener comprises a bolt threaded through a pair of extendible arms which can be retracted to insert the fastener through a hole in the drywall, and then spring open so that when the bolt is tightened the arms bear against the rear face of the drywall. 
         [0009]    These types of expanding fasteners provide improved resistance to longitudinal dislodgment, because the retaining wings overlay solid drywall. However, the force of the wings against the drywall is confined to a limited area, and accordingly there is a limit to the amount of longitudinal pulling force that can be exerted on the fastener before the wings shear or break through the panel. Also, once the fastener is installed if the bolt is removed the wings will fall into the wall cavity. 
         [0010]    A variation of the butterfly fastener is described and illustrated in U.S. Pat. No. 5,725,341 issued Mar. 10, 1998 to Hofmeister, which is incorporated herein by reference. This fastener has a main tube divided into flexible radial segments and a nut at its base. Tightening a bolt disposed through the tube draws the nut toward the neck of the tube, compressing the tube lengthwise and forcing the segments to collapse onto the back of the panel as retaining wings. The wings lay flush against the rear face of the panel to resist longitudinal dislodgment of the fastener. The tube contains an epoxy packet which is punctured as the bolt is driven into the tube, and the epoxy secures or fuses the plug components together. 
         [0011]    The Hofmeister device still relies largely upon engagement between the plug and the drywall to resist dislodgment, and the use of an expensive epoxy compound in combination with the mechanical means achieves only relatively minor enhancement in performance. Further, having a size limited to the tube interior diameter the epoxy packet can contain only a very limited amount of epoxy, and the epoxy is prone to falling into the wall cavity as the packet is punctured. 
         [0012]    It would accordingly be advantageous to provide a fastener which contacts the panel over a broad surface area, to maximize resistance to longitudinal dislodgment, and retain its engagement with the drywall when the screw or bolt is removed. 
         [0013]    It would also be advantageous to provide such a fastener with a retaining structure that is flexible during installation, to permit the plug to be inserted through a relatively small hole in the drywall, but becomes substantially inflexible after installation. 
         [0014]    It would further be advantageous to provide a fastener which repairs damage to the drywall from drilling or from prior dislodgment of a conventional anchoring plug. 
         [0015]    In the preferred embodiments the present invention provides these advantages by providing a fastener having a hollow tube in fluid communication with a flexible membrane forming a bladder around the tube. After the tube is inserted into the panel the bladder is filled with a curable fluid such as an expanding foam, which inflates the bladder and adheres it to the rear surface of the panel. When the fluid cures it forms a substantially inflexible retaining block that contacts the panel over a broad surface area, distributing a pulling force over a larger area of the panel to improve resistance to dislodgment. In the preferred embodiment a compressing member, for example a bolt extending through the tube into a nut, draws the retaining block against the panel to compressively engage the fastener to the panel. 
         [0016]    In one preferred embodiment the fluid is injected into the fastener through the neck of the tube. In a further embodiment the fluid may be contained in a pressurized capsule within the tube, which may be pierced by the tip of the bolt as the bolt is driven into the tube. 
         [0017]    The present invention thus provides a fastener, comprising a hollow tube having an outer end and an inner end, the outer end being provided with a stop for preventing the passage of the outer end of the tube through a hole in a wall, at least one opening through a wall of the tube, and a flexible bladder disposed over the tube and anchored thereto, the opening in the tube being in fluid communication with an interior of the bladder, wherein when the fastener is disposed through a panel and a curable fluid is injected into the tube the fluid inflates the bladder, such that the fluid cures to form a substantially inflexible retaining block to retain the tube against longitudinal dislodgment from the panel. 
         [0018]    In a preferred embodiment a compressing member for drawing the bladder toward the outer end of the tube comprises a bolt cooperating with a nut. 
         [0019]    The present invention further provides a method of affixing a fastener to a panel, comprising the steps of a) inserting a hollow tube and a bladder anchored to an inner end thereof and disposed over the tube into a hole in the panel, until a stop about an outer end of the tube contacts the panel, and b) inflating the bladder by injecting a curable fluid into the tube and through at least one opening in a wall of the tube in fluid communication with an interior of the bladder. 
         [0020]    In a further preferred embodiment the method comprises the additional steps of c) allowing the curable fluid to cure, and d) compressively drawing the bladder toward the outer end of the tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In drawings which illustrate by way of example only a preferred embodiment of the invention, 
           [0022]      FIG. 1  is an exploded cross-section of a preferred embodiment of a fastener according to the invention, 
           [0023]      FIG. 2  is a cross-section of a fastener of the invention lodged in a hole in a wall panel, and 
           [0024]      FIG. 3  is a cross-section of the fastener of  FIG. 2  after inflation of the bladder and compression of the tube to draw the bladder toward the panel. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]      FIGS. 1 to 3  illustrate a first preferred embodiment of a fastener  10  according to the invention. The fastener  10  is particularly suitable for fastening an article or structure to a panel, such as a drywall panel  4  in a hollow wall  2  having a wooden or metal frame  6 . However, the fastener may be used in other applications, and the invention is not intended to be so limited. 
         [0026]    In the preferred embodiment the fastener  10  comprises a tube  20 , for example a metal or plastic cylinder, having a stop, for example a flange  22 , disposed about its outer end. The flange  22  may formed in a separate bushing or sleeve  26  adapted to fit into the outer end of the tube  20 , as shown, or may be integrally formed with the tube  20 . Optionally the flange  22  may be provided with teeth  26   a  (as shown in  FIG. 1 ) to prevent rotation and thus facilitate installation of the fastener  10 . 
         [0027]    A flexible bladder  30 , which may be formed from plastic, paper, or any other suitable flexible material, is in fluid communication with the tube  20 . One example of a suitable material for the bladder  30  is Tyvec (trademark) manufactured by DuPont (trademark). The tube  20  extends through an opening  31   a  in the bladder  30 , preferably in sliding relation so that the opening  31  a can slide along the tube  20  as the bladder  30  expands. The bladder  30  in the preferred embodiment is provided with perforations  33  through a proximal portion  30   a  of the bladder  30  that faces the panel  4  when the fastener  10  is inserted, for reasons described below. A distal portion  30   b  of the bladder  30  opposite to the proximal portion  30   a  is anchored to the tube  20  in the manner described below. 
         [0028]    After the fastener  10  has been inserted through a hole  8  in the panel  4 , the bladder  30  will be inflated by injecting a curable fluid, for example an expanding foam, through the hollow tube  20 . Openings  41  in the wall of the tube  20  allow the curable fluid to egress into the bladder  30 , which inflates the bladder  30  so that when the foam cures it forms a substantially inflexible retaining block  32 , shown in  FIG. 3 , which secures the inner end of the tube  20  and bears against the rear surface of the panel  4  to retain the fastener  10  in the panel  4  and resist longitudinal pulling forces. The bladder  30  contains the spread of the curable fluid and prevents the curable fluid from falling into the wall cavity. 
         [0029]    In the preferred embodiment the curable fluid also has adhesive properties, as many commercially available expandable foams do, and is thus permitted to seep out of the bladder  30  in the direction of the panel  4 , for example through small perforations  33  through the proximal portion  30   a  of the bladder  30  (which faces the panel  4 ). This both retains the fastener  10  in position in the panel  4  and bonds any damaged portions of the panel  4  about the hole  8  to restore structural integrity to the panel  4 . 
         [0030]    In the preferred embodiment a compressing member is provided to draw the retaining block  32  against the rear surface of the panel  4 , which compressively anchors the fastener  10  in the panel  4 . In the embodiment shown, the portions of the wall of the tube  20  about the openings  41  form radial segments  28 , which collapse and fold into wings  42  (see  FIG. 3 ) when the tube  20  is compressed longitudinally by the compressing member. 
         [0031]    In the preferred embodiment the compressing member comprises a threaded bolt  12  having a length sufficient to extend through the tube  20  and a head  12   a  that is too large to pass through the inner end of the tube  20 , cooperating with a nut  24  abutting the inner end of the tube  20 . The nut  24  may be affixed to or formed integrally with the tube  20 , or may be separate from the tube  20  as shown, in which case the nut  24  is preferably formed with a neck  24   a  dimensioned to be press-fitted into the inner end of the tube  20 , to prevent separation of the nut  24  from the tube  20  during installation. The nut  24  extends through an opening  31   b  in the distal portion  30   b  of the bladder  30 , and is provided with a flange  24   b  that anchors the distal portion  30   b  of the bladder  30  to the tube  20 . The bolt  12  is threaded through the nut  24  and tightened to draw the nut  24  toward the outer end of the tube  20  and tension the membrane  30 , to thus compressively engage the retaining block  32  against the rear surface of the panel  4 . 
         [0032]    In the construction of the preferred embodiment, the inner end of the tube  20  is inserted into the opening  31  a in the bladder  30 , the neck  24   a  of the nut  24  is disposed through the opening  31   b,  and the nut  24  is then pressed into the inner end of the tube  20 . These components can be preassembled for sale to the consumer. 
         [0033]    To install the fastener  10 , a hole  8  sufficiently large to allow the nut  24  to pass through is drilled in the panel  4 . The bladder  30  is pleated or folded around the tube  20  and the tube  20  is inserted through the hole in the panel  4  until the sleeve  26  contacts the front (exposed) surface of the panel  4 , as shown in  FIG. 2 . A curable fluid, such as a commercially available expandable fast-curing foam  40 , is injected through the tube  20  and flows through the openings  41  into the bladder  30 , causing the bladder  30  to inflate. The foam  40  also seeps out of the perforations  33  in the proximal portion  30   a  of the bladder  30  to contact the panel  4  and form a base for the retaining block  32  that closely conforms to the panel surface and adheres the bladder to the panel  4 , as shown in  FIG. 3 . 
         [0034]    A check valve or flap  27  is preferably provided near the outer end of the tube  20 , to prevent the expanding foam  40  from seeping out of the tube  20 . In the embodiment shown the flap  27  is hingedly affixed to the sleeve  26 , allowing foam  40  to be injected into the outer end of the tube  20 , but closing off the tube  20  as the foam expands within the tube  20  and bladder  30 . This ensures that the foam  40  expands into the bladder  30  with sufficient pressure to fully inflate the bladder  30 , and prevents soiling or staining of the exposed surfaces of the panel  4 . The flap  27  may tear away or fold back when the bolt  12  is inserted into the tube  20 . 
         [0035]    After the foam  40  cures to form a retaining block  32 , the bolt  12  is pushed through the tube  20  and threaded into the nut  24 . A typical expandable foam  40  will readily yield to the force of the bolt  12  being inserted into the tube  20  (if an epoxy, plaster, cement or some other hard curable material is used, it may be necessary to thread the bolt  12  to the nut  24  before the material has cured). The bolt  12  is rotated to draw the nut  24 , and thus the cured retaining block  32 , toward the outer end of the tube  20 . In the embodiment shown this compresses the tube  20  and causes the radial segments  28  to collapse into wings  42 , as shown in  FIG. 3 , as the panel  4  is compressively engaged between the retaining block  32  and the flange  26 . 
         [0036]    In this embodiment the bolt  12  can also be used to secure the article or structure (not shown) to the panel  4 . In an alternative embodiment (not shown), the compressing member may be a pin (not shown) extending through the inner end of the tube  20  and projecting out of the neck  22 , which compresses the tube  20  and then breaks away like a pop-rivet. In this case the installed tube  20  serves as a reinforced anchoring plug, and a separate screw or like fastener is used to fasten the article or structure to the tube  20 . 
         [0037]    Preferred embodiments of the invention having been thus described by way of example only, it will be apparent to those skilled in the art that certain modifications and adaptations may be made without departing from the scope of the invention. For example, without limiting the foregoing, although it is desirable to compressively engage the retaining block  32  against the pane  14 , it may not always be necessary. The compressing member may comprise other structures that function to draw the retaining block  32  toward the outer end of the tube  20 . Also, while use of an expandable foam  40  has been found to be advantageous other curable fluids (expanding or otherwise) can be used to inflate the bladder  30 . The invention is intended to include all such modifications and adaptations as fall within the scope of the appended claims.