CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/346,526, filed Jan. 8, 2002, the entirety of which is hereby incorporated by reference. 


   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to rods for reinforcing ductwork, and more particularly, to a reinforcing rod which is designed to enable a faster and easier installation into ductwork. 
   2. Description of the Related Art 
   Duct work, such as air conditioning ducts, are often made of a metallic material such as galvanized steel. These ducts require reinforcement to provide support to the ducts and to prevent them from bulging or buckling. One way that such reinforcement has been provided has been to surround the outside of the duct with an external reinforcement. 
   Another method that has been developed to reinforce air conditioning ducts and the like has been to position reinforcing rods or conduits on the interior of the ducts. In one previously known method, the length of the rod is threaded, and the rod is inserted into opposing holes in the walls of the duct and secured to these walls using a nut and washer configuration. One problem with this type of reinforcement is that the rods are necessarily longer than the distance between the walls of the duct, making it difficult to install the rods. This becomes especially problematic as the size of the duct decreases. 
   One previously known method to overcome this problem is to provide a conduit having a length corresponding to the distance between the opposing sides of the duct. Each end of the conduit is internally threaded, using an internally threaded nut press fit at each of the conduit. Then, by lining up the conduit with the opposing holes in the duct walls, bolts may be inserted from the outside of the duct through the internally threaded ends to secure the conduit within the ductwork. However, these conduits are difficult to align with the holes for insertion of the bolts. Moreover, these inserts can be pulled out of the conduits with a certain degree of force, thereby making the reinforcement ineffective. 
   Accordingly, what is needed is a method and apparatus for easily and quickly reinforcing an air conditioning duct and the like. 
   SUMMARY OF THE INVENTION 
   In one embodiment, a reinforcement is provided comprising a conduit having a first end and a second end. A pair of plugs is insertable into the first and second ends of the conduit. Each of the plugs has a groove extending along the circumference of the plug, and the plugs are crimped inside the conduit along the grooves. Each of the plugs may have a threaded end extending out of the plug and being retractable into said plug. Alternatively, each of the plugs may have an internally threaded opening extending at least partially through the plug. The reinforcement may then further comprise a bolt insertable into the threaded opening. 
   In another embodiment, a plug for insertion into an end of a conduit is provided. The plug comprises a body portion having a first end and a second end and an opening extending from the first end at least partially through said body portion. A groove extends at least partially along the circumference of the body portion, the groove adapted to receive a crimping force applied to the conduit when the plug is inserted into the end of the conduit. The plug may be internally threaded, or may further comprise a threaded member retractably positioned within the opening. 
   In another embodiment, a reinforced duct work is provided. The duct work has opposing surfaces, each of the surfaces having a hole therein aligned with an opposing hole. A conduit is provided having a first end and a second end, and has a plug inserted into each end thereof. Each plug has a groove extending along at least a portion of the plug, and the conduit is crimped to the plugs along the grooves. The conduit is positioned such that the first and second ends are aligned with the holes and the conduit is secured to the surfaces of the duct work. In one embodiment, the conduit may be secured to the surfaces of the duct work by bolts inserted through the holes in the duct work and into internally threaded holes in each plug at each end of the conduit. In another embodiment, each plug has a retractable threaded end which extends through one of the holes when the conduit is aligned therewith, and the conduit may be secured by nuts tightened over the retractable threaded ends against the surface corresponding to the holes. 
   In another embodiment, a method for reinforcing duct work is provided. The duct work has opposing surfaces, each of the surfaces having a hole therein aligned with an opposing hole. The method comprises providing a conduit having a first end and a second end, wherein the conduit has a plug inserted into each end thereof, each plug having a groove extending along at least a portion of the plug, and wherein the conduit is crimped to the plugs along the grooves. The conduit is positioned such that the first and second ends are aligned with the holes, and the conduit is secured to the duct work. In one embodiment, bolts may be inserted through the holes in the duct work and into internally threaded holes in each plug at each end of the conduit. The bolts are tightened within the plugs to secure the conduit to the duct work. In another embodiment, the plugs each have a retractable threaded end which extend through one of the holes when the conduit is aligned therewith. Nuts are tightened over the retractable threaded ends against the surface corresponding to the hole to secure the conduit to the duct work. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a portion of air conditioning duct. 
       FIG. 2A  is a perspective view of a plug with retractable threads according to one embodiment of the present invention, the threads being shown in their unretracted configuration. 
       FIG. 2B  is a perspective view of a plug with retractable threads according to one embodiment of the present invention, the threads being shown in their retracted configuration. 
       FIG. 2C  is a perspective view of another embodiment of a plug with retractable threads. 
       FIG. 2D  is a cut away side view of the body portion of the plug of FIG.  2 C. 
       FIG. 2E  is a side view of a spring insertable into the plug of FIG.  2 C. 
       FIG. 2F  is a side view of a tube cap for the plug of FIG.  2 C. 
       FIG. 2G  is a side view of an inside bolt for the plug of FIG.  2 C. 
       FIG. 2H  is a top view of the body portion of FIG.  2 D. 
       FIG. 2I  is a bottom view of the body portion of the FIG.  2 D. 
       FIGS. 2J and 2K  are side and top views, respectively, of a rubber washer. 
       FIGS. 2L and 2M  are side and top views, respectively, of an outside nut. 
       FIG. 3  is a side view of a conduit having a plug of with retractable threads inserted into its ends. 
       FIG. 4  is a perspective view of the air conditioning duct of  FIG. 1  reinforced by the conduit of FIG.  3 . 
       FIGS. 5A-5C  are perspective views illustrating the insertion and crimping of grooved plugs into a conduit. 
       FIG. 5D  is a partial cross-sectional view of an end of a conduit having a plug crimped therein. 
       FIG. 5E  is a side view of an end of a conduit having a plug crimped therein. 
       FIG. 6A  is a cross-sectional view of one embodiment of a grooved plug. 
       FIG. 6B  is an end view of the plug of FIG.  6 A. 
       FIG. 7A  is a cross-sectional view of another embodiment of a grooved plug. 
       FIG. 7B  is an end view of the plug of FIG.  6 A. 
       FIG. 8A  is a perspective view of the air conditioning duct of  FIG. 1 , with the conduit of  FIG. 5C  inserted therein. 
       FIG. 8B  is a perspective view of the air conditioning duct of  FIG. 1  reinforced with the conduit of FIG.  5 C. 
       FIGS. 9A-9D  illustrate one preferred sequence for crimping a conduit to a plug. 
       FIG. 10  is a perspective view of another embodiment of a plug having retractable threads. 
       FIG. 11A  is a cross-sectional view of the plug of FIG.  10 . 
       FIG. 11B  is an end view of the plug of FIG.  11 A. 
       FIG. 12  is a perspective view of another embodiment of a plug having retractable threads being inserted into a conduit. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of this invention relate to reinforcement of duct work (e.g., for air conditioning ducts), and more particularly, to conduits used for reinforcing duct work. In particular, certain embodiments describe plugs for insertion into the ends of the conduits in order to provide for easier insertion into the duct work and/or a more secure connection and reinforcement. 
     FIG. 1  illustrates a portion of air conditioning duct  10 . The duct has opposing surfaces  12  and  14 , which include oppositely disposed holes  16 . As described below, these holes  16  are used to reinforce the duct  10  to prevent it from buckling or collapse. 
     FIGS. 2A and 2B  illustrate a plug with retractable threads according to one embodiment of the present invention. The plug  18 , shown in its unretracted configuration in  FIG. 2A , includes a threaded end  20 , which moves into and out of the tubular body portion  24  through head  22 . The threaded end  20  is integrally formed with a shaft  28  which remains internal to the tubular body portion  24 . A spring (not shown) is also positioned within the tubular body portion  24  below the shaft  28 . 
   Provided on the shaft  28  is a pin  30 , which extends into an L-shaped cutout  26  provided in the wall of the body portion. The spring within the body portion presses against the bottom of the shaft  28 , forcing the threaded end  20  outward relative to the head  22 , and correspondingly, positioning the pin at the top of the “L.” Thus, the pin  30 , when contacting the top of the L-shaped cut-out, prevents the threaded end  20  and the shaft  28  from exiting the body portion  24 , and also prevents rotation of the threaded end  20 . 
     FIG. 2B  illustrates that because of the spring within the body portion, the threaded end  20  can be pushed down, compressing the spring and thereafter moving the pin  30  into the bottom-right portion of the L-shaped cut-out. Thus, in this position, the threaded end  20  is in a “locked” or retracted configuration. Preferably, the threaded end  20  will still extend slightly beyond the head  22  in this locked configuration. 
   It will be appreciated that although the plug  18  has been described as containing a locking mechanism  26 , the plug may also be provided without such a locking mechanism. In such an embodiment, the plug  18  is in a relaxed position when the threaded end  20  is fully extending out of the body portion  24 , as shown in FIG.  2 C. Because of the spring inside the body portion  24 , when a force is placed against the threaded end  20 , causing the threaded end to move into the body portion, the threaded end will be biased to move back to its relaxed position unless the force on the threaded end is maintained. 
     FIGS. 2D-2G  illustrate the components of the plug  18  of  FIG. 2C , according to one preferred embodiment The body portion  24 , shown in  FIG. 2D , has a head portion  22  at its proximal end defining an opening  40  through which threaded end  20 , described below, extends. The walls  42  of the body portion  24  are preferably tapered, such that the cavity  46  inside the body portion has a smaller diameter toward the proximal end of the body portion.  FIG. 2H  shows a top view of the body portion  24 . As shown in the bottom view of the body portion  24  of  FIG. 2I , the cavity  46  is preferably hex-shaped to accommodate a bolt having a hex-shaped base, as described below. 
   Provided inside the cavity of the body portion  24  are a spring  48  (shown in  FIG. 2E ) and an inside bolt  52  (shown in FIG.  2 G). The inside bolt  52  includes a threaded end  20  extending from its proximal end, a hex-shaped base  44  at its distal end, and a shaft  28  therebetween. The inside bolt  52  is inserted into the cavity of the body portion  24  through its distal end, with the threaded end  20  entering first. The threaded end  20  is sized to pass through the opening  40 , but the hex-shaped base  44  is sized larger than the opening  40  to prevent the inside bolt from falling out of the body portion  24  at its proximal end. Moreover, the hex-shaped base  44  approximately mates with the hex-shaped cavity  46  to prevent rotation of the bolt within the cavity. The spring  48  is inserted through the distal end of the body portion  24  after the inside bolt  52 . A tube cap  50 , as shown in  FIG. 2F , seals the body portion  24  after the spring and inside bolt  52  have been inserted. The body portion  24  and the tube cap  50  are preferably made of a material such as aluminum or plastic. The other components of the plug are preferably made of a material such as steel and plated to prevent rust. 
     FIG. 3  illustrates that to reinforce an air conditioning duct such as shown in  FIG. 1 , the plugs  18  are placed in the two ends  34 ,  36  of a reinforcing conduit  32 . Preferably, the plugs are press fit into the two ends. The distance between the two ends  34 ,  36  is preferably substantially the same as the distance between the opposing surfaces  12 ,  14  of the air conditioning duct. 
   To install the reinforcing conduit into the duct  10 , the conduit  32  is inserted between the opposing surfaces  12 ,  14  of the duct  10 . The threaded ends  20  of the plugs in the conduit, when pressed against the walls of the duct, are forced into the body portions  24 , thereby shortening the length of the conduit with the plugs. This enables the conduit to be moved around more easily within the duct. The conduit  32  is preferably moved within the duct  10  until the threaded ends  20  encounter the opposing holes  16  of the duct. When the threaded ends  20  are free to unretract from the body portions  24  (i.e., the embodiment of  FIG. 2C , wherein the threaded ends are not locked inside the body portion with a locking mechanism), the threaded ends will pop out once encountering the holes and extend to the outside of the duct  10 . 
   Alternatively, if the threaded ends are locked such as shown in  FIG. 2B  above, because the threaded ends  20  extend slightly beyond the head  22 , the installer can still ascertain when the threaded end encounters a hole  16 . Then, the threaded ends  20  can be activated to their unretracted position simply by moving the pin  30  from the locked to the unlocked position. 
   It will be appreciated that when installing conduit as described above, it is often advantageous to install one end of the conduit  32  first into a hole  16 , with the threaded end  20  at that one end already unretracted, and then simply orienting the conduit such that the other threaded end  20  encounters the opposing hole  16 . In this embodiment, as the other threaded end  20  is brought towards the opposing hole  16 , the end  20  will likely retract into the conduit as the force of the wall nearby the opposing hole  16  presses the threaded end  20  into the body portion  24 . 
   In another embodiment, it will be appreciated that a conduit may be provided in which only one end has a retractable threaded end, while the other end has an threaded end which always extends out of the end of the conduit. 
     FIG. 4  illustrates a partially completed reinforced duct portion  10  with a reinforcing conduit  32  therein. As can be seen, the threaded ends  20  extend to the external surface of the duct, wherein an outside nut  38  is screwed onto the threaded end  20  and against the surface of the duct walls to secure the conduit in place. This nut  38  is shown more particularly in  FIGS. 2L and 2M . When a body portion such as shown in  FIG. 2D  is used, as the outside nut  38  is screwed onto the inside bolt  52  of the body portion, the nut draws the bolt towards the nut. Because the walls  42  of the body portion  24  are tapered, the hex-shaped base  44  of the inside bolt  52  presses against the walls as the bolt  52  is drawn toward the nut  38 . This exerts an additional pressure of the body portion  24  against the inner walls of the conduit  32 , thereby holding the plug  18  more strongly within the conduit. 
     FIG. 4  also illustrates the use of a rubber washer  54 , illustrated more particularly in  FIGS. 2J and 2K . Prior to installation, rubber washers  54  can be placed against the heads  22  of the plugs  18  at each end of the conduit  32 , with the threaded ends  20  extending through the holes  56  in the washers. Then, once the plugs  18  are aligned in the duct  10  and the threaded ends  20  extend through the holes  16 , the rubber washers  54  abut against the surfaces  12 ,  14  of the duct to protect the duct from damage. 
   The embodiments described also improve over the prior art in which threaded reinforcement rods are used in that reinforcing conduits as described herein are stronger than threaded rods and therefore are more resistant to buckling. 
     FIGS. 5A-5C  illustrate another embodiment of a system for reinforcing air conditioning ducts and the like. In this embodiment, a conduit  32  such as described above is provided. Plugs  58  and  60  having an outer diameter corresponding to the inner diameter of the conduit are inserted into ends  34  and  36  of the conduit, respectively, until the outer ends of the plugs are flush with the ends of the conduit, as shown in FIG.  5 B. As described in further detail below, the plugs  58  and  60  each have a groove  62  extending around the circumference of the plug and have an internally threaded opening  64  extending through the central axis of the plug. After the plugs are inserted into the conduit, a crimping device, such as described below, can be used to crimp the conduit at the location of the grooves  62 , shown by the arrows in FIG.  5 B. As shown in the resulting conduit in  FIG. 5C , the crimping of the conduit locks the plugs  58  and  60  within the conduit at crimped locations  62 A and  62 B to prevent the plugs from being pulled out.  FIG. 5D  illustrates in cross-section one preferred plug crimped inside an end of a conduit, with a bolt screwed into the threaded opening  64  through a washer.  FIG. 5E  illustrates an end view of the crimped conduit. 
     FIGS. 6A and 6B  illustrate one preferred design for the plugs  58  and  60 . In this embodiment, the threaded opening  64  preferably has a diameter of about ¼″ and extends entirely through the plug. The plug in one embodiment has a diameter of about 0.605″ and a length of about 0.69″, with the groove located about 0.33″ from the outer end of the plug (i.e., the end that is flush with the end of the conduit) and about 0.15″ from the inner end of the plug. The groove  62  in this embodiment preferably has a length of about 0.21 inches. As shown in  FIG. 6B , the groove preferably has a depth of about 0.07 inches. 
     FIGS. 7A and 7B  illustrate another preferred design for the plugs  58  and  60 . In this embodiment, the threaded opening  64  also has a diameter of about ¼″, and the length and location of the groove are the same. However, the plug of  FIGS. 7A and 7B  has a diameter of about 0.81″. It will be appreciated that plugs of various sizes may be used to accommodate different sized conduits. 
     FIG. 8A  illustrate that after the plugs are inserted and crimped into the conduit as shown in  FIG. 5C , the conduit can be aligned with holes  16  in the duct  10 . As shown in  FIG. 8B , from the outside of the duct, a washer  66  is positioned over the hole  16  and a bolt  68  is inserted through the washer, through the hole  16 , and threadedly inserted into the opening  64  to secure the conduit within the duct. This process is repeated for each end of the conduit and for each conduit positioned in the duct. 
   It will be appreciated that the plugs  58  and  60  can be made from a variety of suitable materials. For example, certain preferred materials include, but are not limited to, nylon, steel and aluminum. Desired materials may be selected based on the superior pull out strength offered by the crimped plugs. For example, a nylon plug which has been injection molded desirably provides a pull out strength of about 800 to 1200 lbs. A steel plug desirably provides a pull out strength of about 3200 to 5000 lbs. An aluminum plug desirably provides a pull out strength of about 1500 to 2500 lbs. It will also be appreciated that to provide increased pull out strength, more than one groove  62  may be provided on the plugs. 
   Crimping of the plugs  58  and  60  to the conduit can preferably be accomplished using any suitable crimping device. One such device is shown in  FIGS. 9A-9D . As shown in  FIG. 9A , a pneumatic fixture is bench mounted, with a peg extending vertically from the bench. A plug is slipped over the peg, as shown in FIG.  9 B. The plug is covered with a conduit, shown in  FIG. 9C , which preferably has a ½″ or ¾″ diameter. Using the pneumatic crimping device, the conduit is crimped, preferably in only about one second, onto the plug, as shown in FIG.  9 D. It will be appreciated that various crimping mechanisms can be used, and therefore, the plug need not be crimped by the device or methods shown in  FIGS. 9A-9D . 
     FIG. 10  illustrates another design of a plug  70  having a retractable threads similar to the embodiment of FIG.  2 C. The plug includes a threaded end  72 , which moves into and out of the tubular body portion  74 . The threaded end  72  is integrally formed with a shaft  76  (not shown) which remains internal to the tubular body portion  74  in an opening  88  (described below). A spring  78  (shown in  FIG. 11A ) is also positioned within the opening  88  of the tubular body portion  74  below the shaft  76 . 
   Provided on the shaft  76  is a pin  80 , which extends into a slot  82  provided in the wall of the body portion. The spring within the body portion presses against the bottom of the shaft  76 , forcing the threaded end  72  outward, and correspondingly, positioning the pin at the top of the slot  82 . Thus, the pin  80 , when contacting the top of the slot, prevents the threaded end  72  and the shaft  76  from exiting the body portion  74 , and also prevents rotation of the threaded end  72 . 
   Near the top of the slot  82 , a passageway  84  is provided to allow the threaded end  72  and the shaft  76  to exit the tubular body portion  74 . An operator can remove the threaded end from the body portion  74  by pressing slightly down on the threaded end  72 , and turning the threaded end (in the embodiment shown, counter-clockwise) such that the pin  80  follows the passageway  84 . The passageway  84  turns up toward the top end of the body portion  74 , which allows the threaded end to be removed. 
   The tubular body portion further includes a groove  86  near the end of the plug opposite the threaded end  72 . This groove, as with the embodiments of  FIGS. 5A-5C  described above, enables the plug to be inserted into a conduit and crimped therein to provide excellent pull out strength. Once the plug is inserted and crimped at each end of the conduit, a duct can be reinforced such as shown in  FIG. 4  above. 
     FIGS. 11A and 11B  illustrate one preferred design for the plug  70 . In this embodiment, the opening  88  in which the spring  78  and the shaft  76  are inserted preferably has a diameter of about {fraction (5/16)}″ and a depth of about 1.4″. The overall length of the plug is about 1.5″, with the groove  86  located about 1.14″ from the outer end of the plug (i.e., the end that is flush with the end of the conduit) and about 0.15″ from the inner end of the plug. The groove  86  in this embodiment preferably has a length of about 0.21 inches and a depth of about 0.07″. The slot  82  and passageway  84  preferably have a width of about {fraction (3/16)}″, with the bottom of the slot located about 1.09″ from the outside end of the plug. The plug can have a variety of diameters, and in two preferred embodiments, has a diameter of about 0.81″ or about 0.605″. 
     FIG. 12  illustrates an alternative embodiment of a plug having retractable threads being inserted into a conduit. This plug design is similar to the design of  FIG. 2C , except that the walls  42  of the tubular body portion  24  have slots extending longitudinally therein from the inner end of the plug (i.e., the end adapted to be positioned away from the end of the conduit) and partially toward the head  22 . Like the embodiment of  FIG. 2C , the walls  42  are tapered such that the cavity  46  inside the body portion has a smaller diameter toward the proximal end or top end of the body portion. 
   Although the embodiments described herein relate to reinforcement of air conditioning ducts, it will be appreciated that the preferred embodiments of the present invention may be used in other applications as well. It will be appreciated that the plugs  18  described above may be used in applications with and without the conduit  32 . For example, a conduit having plugs with retractable threads may be used for inserting shower curtain rods. In another example, plugs with retractable threads may be used for furniture legs. In such an embodiment, in fact, the retractable portion of the plug need not be threaded. Other possible uses include hangers between doors and inside closets, and clothes hangers in automobiles. 
   It should be understood that certain variations and modifications of this invention will suggest themselves to one of ordinary skill in the art. The scope of the present invention is not to be limited by the illustrations or the foregoing descriptions thereof, but rather solely by the appended claims.
A method and apparatus for reinforcing duct work is provided. In one embodiment, a reinforcement comprises a conduit having a first end and a second end. A pair of plugs is insertable into the first and second ends of the conduit. Each of the plugs has a groove extending along the circumference of the plug, and the plugs are crimped inside the conduit along the grooves. Each of the plugs may have a threaded end extending out of the plug and being retractable into said plug. Alternatively, each of the plugs may have an internally threaded opening extending at least partially through the plug. In this embodiment, the conduit can be secured to duct work by aligning the conduit with holes in the duct work, and inserting a bolt through the holes and into the internally threaded openings of the plugs.