Abstract:
The present invention relates to a system and device which allows the replacement of a damaged thread in an object with a thread identical to the damaged thread by enlarging the original threaded hole and inserting a thread-insert in a newly threaded hole in the object which has an internally threaded hole identical to the original threaded hole. The thread-insert is fastened into the enlarged hole using a thread that securely holds it in place. When the thread-insert is threaded into the enlarged threaded hole, a pocket formed below the drive head of the thread-insert causes metal flow into the pocket to create a seal between the thread-insert and the object.

Description:
FIELD OF THE INVENTION 
     The following invention relates generally to a system and device for replacing damaged screw threads in an object, and in particular to a system and device for replacing damaged screw threads which will replace the threads with a permanently installed insert, the insert also provides a seal between the insert and the object to be repaired. 
     BACKGROUND OF THE INVENTION 
     When internal screw threads cut into an object become damaged, they can sometimes be repaired by chasing the damaged thread with a tap to restore the thread shape. However, if the thread is damaged to such an extent that chasing with a tap will not restore its function, the thread must be replaced. This can be done by boring out the original threads with a drill larger than the major diameter of the thread and rethreading the hole with a larger diameter thread. While this method will provide a usable threaded hole, it will require a fastener of a different size than the original. In an assembly which must be dissembled and reassembled periodically, this method requires that tools with different head sizes are needed. This is, at the very least inconvenient and may result in difficulty for those reassembling the device. 
     In order to replace the damaged thread with the same thread as the original assembly, it is necessary to bore the damaged threads out and replace the original threads with a thread-insert which can be threaded into the larger bored out and threaded hole and which has internal threads the same as the original threads. Such thread inserts are available, however the external threads of the thread-inserts are generally of conventional helical design. A conventional thread-insert has a tendency to become loose when the machine screw is removed for disassembly or, in some cases, the thread-insert will unscrew from the object when removal of the attaching screw is attempted thus complicating the disassembly process. In addition, if the attaching screw must provide a sealed engagement with the object, a conventional thread-insert will not usually provide a seal between its external threads and the wall of the object. 
     The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant&#39;s acknowledged duty to disclose relevant prior art. It is stipulated, however, that none teaches or render obvious the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed. 
     
       
         
               
               
               
             
           
               
                   
               
               
                 PATENT NO. 
                 ISSUE DATE 
                 INVENTOR 
               
               
                   
               
             
             
               
                 5,499,892 
                 March 19, 1996 
                 Reed 
               
               
                   
               
             
          
         
       
     
     SUMMARY OF THE INVENTION 
     The present invention has as its objective to provide thread-insert which will avoid the disadvantages noted above. 
     The present invention overcomes the disadvantages of the prior art noted above by first, providing a thread-insert which is fastened into a hole in the object using a thread design on the external surface of the insert and a matching thread formed in the bored out hole. The thread-insert has upwardly slanted thread surfaces that angle upward toward the head which lock the insert securely into the replacement hole of the object. The effect of these threads is to provide a radially inward clamping force as the insert is tightened, due to a clamping reaction of the threads vis-a-vis another part of the insert against the object receiving the insert. Secondly, the thread-insert has an internal thread preferably adapted to receive a desired standard threaded fastener. Thirdly, the thread-insert preferably includes a drive head that can include any of a variety of torque-receiving configurations. For instance, the drive head can have multiple facets dimensioned to be addressed by facets of a wrench. In addition, slots may be formed complementary to a slotted screw driver or other similar structures. Thus, the drive head receives torque and causes the thread repair insert to rotate about a central, long axis thereof. Below the drive head, the insert preferably includes a neck. 
     The thread-insert is provided with a pocket interposed between the neck and the upper surface of the upper most thread on the thread-insert. When the insert is threaded completely into the thread of the bored out hole, the insert deforms the metal of the thread from the object, forcing it into the pocket forming a tight seal between the insert and the wall of the object. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is a primary object of the present invention to provide a thread-insert that upon tightening forms a tight-seal between the insert and the wall of an object. 
     A further object of the present invention is to provide a thread-insert which permits the same thread as the original undamaged threads so as to avoid the complexities of different size fasteners needed to assemble and disassemble an object or objects. 
     Another further object of the present invention is to provide a thread-insert that avoids the tendency to become loose when disassembly is required. 
     Another further object of the present invention is to provide a thread-insert that avoids the tendency to become loose when disassembly is required by providing exterior threads that are upwardly slanted thread surfaces that angle upward toward the head of the thread-insert and lock the insert securely into the replacement hole of the object. 
     A further of object of the present invention is to provide a thread-insert that has a pocket formed between the neck and the upper surface of the upper most thread wherein when the thread-insert is tightened, the metal of the object that constitutes the matching threads flows into the pocket thus creating a seal between the insert and the wall of the object. 
     Another further object of the present invention is to provide a thread-insert which includes having exterior threads and interior threads disposed thereon. 
     Another further object of the present invention is to provide a thread-insert which includes a drive head which is driveable by a commonly available torque-applying instrumentality. 
     Another further object of the present invention is to provide a thread-insert whereby the exterior threads preclude the thread-insert from disengaging from the threaded hole. 
     Another further object of the present invention is to provide a thread-insert which is designed to enter a complementary formed hole a finite distance. 
     Another further object of the present invention is to provide a thread-insert wherein the exterior threads are slightly spaced from each other and maintain a minimum thickness between a root and a crest thereof, providing a durable thread. 
     Another further object of the present invention is to provide a thread-insert which is simple and inexpensive to manufacture and yet durable in construction. 
     Viewed from a first vantage point it is a feature of the present invention to provide a method for providing a seal between a thread-insert and an object the thread-insert is inserted therein, comprising the steps of: boring a hole; cutting the top of the hole to match the shape of the thread-insert; tapping matching threads in the hole; threading the thread-insert into the hole until seated; and further threading the thread-insert into the hole to cause metal flow. 
     Viewed from a second vantage point it is a feature of the present invention to provide a thread-insert that forms a seal between itself and an object within which it is threaded. The thread-insert has a threaded shaft extending from a drive head along a central axis to a distal end; at least one of said shaft threads includes a crest defining a major diameter of said threaded shaft, a root defining a minor diameter of the threaded shaft, and an upper surface extending from a bottom edge of said root to an upper edge of the crest, wherein said upper surface having a portion thereof extending toward the crest at an angle greater that zero from a reference plane perpendicular to the central axis of said threaded shaft; and a pocket interposed between the upper most thread of the threaded shaft and the lower portion of the head. 
     Viewed from a third vantage point it is a feature of the present invention to provide a pocket portion of a thread-insert interposed between an upper most thread and a neck portion located under a drive head of the thread-insert, wherein the upper most thread and said neck portion are in a spaced relationship with a common central axis running therethrough, the neck being formed from an outer cylindrical surface of a diameter d 1 . The pocket portion is defined by surfaces comprising: a relief surface that intersects the neck with the diameter of d 1  at an acute angle and intersects an inner cylindrical surface with a diameter of d 2 , at the acute angle, wherein d 1  is greater than d 2  and the cylindrical surfaces are parallel to said common central axis of the thread-insert and concentric to each other; the inner cylindrical surface; and an upper surface at an angle relative to the common central axis of the upper most thread. 
     These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Ten figures have been selected to demonstrate the present invention. These figures and the following description should be sufficient for those skilled in the art to practice the invention as claimed. 
     FIG. 1 is a sectional view of the thread-insert of the invention threaded into an object and provided with a threaded through hole. 
     FIG. 1A is an enlarged section detailing the pocket. 
     FIG. 2 is an enlarged section detail of the thread-insert. 
     FIG. 3 is a sectional view of an object having damaged threads. 
     FIG. 4 illustrates the first step of the method of using the thread-insert. 
     FIG. 5 illustrates the second step of preparing a hole in an object for using the thread-insert. 
     FIG. 6 illustrates the third step of preparing a hole in an object for using the thread-insert. 
     FIG. 7A illustrates the first step in installing the thread-insert. 
     FIG. 7B illustrates the second step in installing the thread-insert. 
     FIG. 7C illustrates the final step in installing the thread-insert. 
     FIGS. 8A and 8B show a variation of FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Considering the drawings, wherein like reference numerals denote like parts throughout the various drawing figures, reference numeral  10  is directed to the preferred embodiment according to the present invention. 
     Referring to FIG. 1, there is illustrated one preferred embodiment of the thread-insert  10  after it has been fully installed in an object  12  to replace damaged threads  32  (FIG. 3) in a hole in the object. The object  12  can be any device which requires threaded holes for assembly with a second part or for attaching other devices to the object. A hole  18  (FIG. 4) has been bored with a drill  34  into the object  12  and matching threads  19  (FIG. 6) have been cut into the wall of the hole  18 . 
     The thread-insert  10  may be rotated into the threaded hole of the object until the top surface  21  of the thread-insert  10  is substantially flush with the upper surface of the object  12 . If the top surface  21  projects above the object  12 , it may be left as is or ground flush. As can be seen in FIG. 1A, a pocket  11  is defined by a neck  13  shaped as an outer cylindrical surface having a diameter d 1 ; a relief surface  15  that intersects neck  13  at a cusp  17  and at an angle delta (Δ). Cusp  17  is an active surface which causes deformation by crimping the object&#39;s material. In effect, cusp  17  reforms a top thread  26  of the hole  18  to be transformed into a locking ring  26 ′. Relief surface  15  intersects an inner cylindrical surface  29  having a diameter d 2 . The angle between surface  15  and surface  29  is β, preferably an acute angle and preferably 80°. Note d 1  is greater than d 2 . Neck  13  and inner cylinder surface  29  are parallel and concentric. The uppermost thread surface  68  intersects the inner cylindrical surface  29  at an angle epsilon (ε), preferably 90°. The pocket  11  formed by acute angle Δ, relief surface  15 , inner cylindrical surface  29  and thread surface  68  forces the metal that forms the top thread  26  of the hole  18  to flow. This metal flow forms a locking ring seal  26 ′ at the top of the threads of the thread-insert. The seal  26 ′ forms a permanent fluid tight joint between the object  12  and the thread-insert  10 . 
     An internal thread  16  preferably is of conventional design and is centrally formed in the body of the thread-insert  10  to replace the original damaged thread. The internal thread  16  preferably is centered about a long axis of the insert  10 . The steps of this process are described in detail below in connection with the discussion of FIGS. 2 through 6. 
     Referring now to FIG. 2, there is shown an enlarged detail of the thread  20  on the exterior of the thread-insert  10 . The threads are helically wound and include a crest  64  defining a major diameter  62  and a root  66  defining a minor diameter  60 . The threads have an upper surface  68  which extends from the bottom edge  67  of the root  66  to the upper edge  69  of the crest  64 . The threads  20  also include lower surface  70  which extends from the top edge  74  of the root  66  to the lower edge  76  of the crest  64 . Both the upper surface  68  and the lower surface  70  angle upwards toward the top of the thread-insert. The crest  64  and the root  66  exhibit a constant distance from the central axis  63 . The upper surface  68  extends from the root  66  at an upper surface angle alpha (α) diverging from a reference plane  65  orthogonal to the central axis  63 . The upper surface angle α is preferably 20° but could be any angle between 0° and 90°. The lower surface  70  extends from the root  66  to the crest  64  at a lower surface angle beta (β) such that the thickness of the threads at the crests  64  is less than the thickness of the threads between adjacent roots. Thus the threads are provided with a greater thickness and hence greater strength adjacent the minor diameter  60  and are therefore capable of bearing the loads required to form the seal shown in FIG.  1 . 
     Referring now to FIGS. 3 through 7, the following is detailed description of the process of using the device of this invention. In FIG. 3, the object  12  is illustrated with its original threaded hole  30  in which the threads have been damaged as shown at  32 . To replace this damaged thread with a threaded hole of the same size as the original thread, a new larger hole  18  is bored into the object  12  with drill  34  as shown in FIG.  4 . In this illustration, the threaded hole is a through hole. The next step of the process is illustrated in FIG.  5 . Here, the top of the hole  18  has been shaped by the cutter  42 , to match the shape of the head of the thread-insert  10  as shown first in FIG.  1 . The diameter  50  of the cutter  42  fits the diameter of the hole  18  and serves to center the cutter  42  in the hole  18 . The cutting surface  44  forms the upper diameter  36  of the hole which matches the outer diameter of the head of the thread-insert  10 . Surface  46  forms the stop surface  38  in the hole; surface  48  of the cutter forms the point  40  of the hole. FIG. 6 illustrates the tap  58  used to form the matching threads  19  in the hole  18 . The tap  58  forms a matching thread  19  in the hole  18  having a major diameter  56  and a minor diameter  54  which respectively clear with the major diameter  62  and minor diameter  60  of the insert  10 . 
     Referring now to FIGS. 7A,  7 B and  7 C where the assembly of the thread replacement apparatus is illustrated. The hole  18  has been prepared as described above to accept the head  14  of the thread-insert  10  in the head receiving opening and the threaded portion  20  into the threads  19  of the hole  18 . In FIG. 7A the thread-insert  10  is positioned above and centered on the hole  18 . In FIG. 7B, the thread-insert  10  has been threaded part way into the hole  18  until the point  17  contacts the upper thread surface  68  of the top thread  26 . As the thread-insert  10  is threaded further into the hole  18 , the point  17  deforms the thread  26  causing metal flow into the pocket  11  of the thread-insert  10 . The thread-insert  10  is further turned into the hole  18  until the top surface  21  of the thread-insert  10  is substantially flush with the upper surface  22  of the object  12 . When the thread-insert  10  is fully threaded into the hole  18 , the seal  26 ′ is fully formed in the pocket  11  by distorting the top thread  26  as shown in FIGS. 1 and 1A. The thread-insert  10  is now permanently installed in the object. 
     FIGS. 8A and 8B show a variation from FIGS. 1,  1 A where the insert&#39;s included angle Δ is about 70° whereas in FIG. 1 and 1A it was 80°. The object includes an active surface having an included angle Δ preferably of 55°. When relief surface  15 ′, surface  29 ′ and topmost thread surface  68 ′ are mated as shown in FIG.  8 B. The metal flow makes a very good seal. Diameter d′ of the surface  29 ′ is preferable greater than the root  66  of the thread. 
     Moreover, having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.