Abstract:
A method of forming an end seal on a cable is provided. The method includes providing a curable sealant in a cavity formed in a boot, inserting an end of the cable in to the cavity with the boot extending about the exterior of the cable, forcing the cable in to the curable sealant whilst inhibiting the egress of curable sealant from the boot to force the curable sealant along the interior of the cable, curing the curable sealant to provide a stable load supporting layer of sealant within the cable, and applying a crimping ring to the boot in the area of the load supporting layer to secure the boot to the cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Patent Application No. 62/365,012, filed on Jul. 21, 2016, and titled “End Seal for Heating Cable”, the entire contents of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods of sealing an end of a heating cable and apparatus therefore. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    Heating cables are used to deliver a heating effect at a desired location and thereby prevent low temperatures at those locations. The heating cable has a pair of electrical conductors that extend along its length with a resistive coupling between the conductors. Electrical current passing through the conductors produces a heating effect which can be transmitted to surrounding environments. One such heating cable is available from Pentair under the trade name BTV Self-Regulating Heating Cable. 
         [0004]    One common use of a heating cable is within a conduit that carries a liquid, such as an oil or water. The cable is inserted within the conduit so as to be encompassed in the liquid. Electrical current is applied to the cable to produce heat and maintain the liquid at the required temperature. A typical application is the freeze proofing of a residential water supply line, as exemplified by the product available under the trade name Retro-line from Heat-Line Freeze Protection Systems of Algonquin Highlands, Ontario. 
         [0005]    The immersion of the cable within the liquid requires the end of the cable to be sealed against ingress of liquid. To effect sealing, a boot may be fitted over the end of the cable. Silicon is added to the boot prior to assembly to assist the sealing and the boot is secured to the cable by a crimped ring. In some circumstances however it is found that the body of the cable is unable to withstand the crimping forces and a distortion of the cable or boot may occur. In some cases this can result in damage to the conductors of the cable and in other it can result in leakage of the liquid in to the boot. 
         [0006]    It is therefore an object of the present invention to obviate or mitigate the above disadvantages. 
       SUMMARY OF THE INVENTION 
       [0007]    In general terms, the present invention provides a method of forming an end seal on a cable comprising the steps of providing a curable sealant in a cavity formed in a boot; inserting an end of the cable in to the cavity with the boot extending about the exterior of the cable; forcing the cable in to the curable sealant whilst inhibiting the egress of curable sealant from the boot to force the curable sealant along the interior of the cable; curing the curable sealant to provide a stable load supporting layer of sealant within the cable; and applying a crimping ring to the boot in the area of the load supporting layer to secure the boot to the cable. 
         [0008]    Preferably, the curable sealant is an epoxy adhesive. 
         [0009]    As a further preference, the cable has a conductive core with a protective jacket and a braided protective layer between the core protective jacket and the exterior outer coating of the cable. 
         [0010]    A further aspect of the invention provides an assembly jig having a pair of jaws to grip a cable and a moveable support for a boot, said support being moveable toward said jaws to force said boot on to said cable. 
         [0011]    Preferably, said support encompasses said boot and inhibits radial expansion of said boot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    An embodiment of the invention will now be described with reference to the accompanying drawings wherein: 
           [0013]      FIG. 1  is a perspective representation of a heating cable; 
           [0014]      FIG. 2  is a section on the line II-II of  FIG. 1 ; 
           [0015]      FIG. 3  is a section on the line III-III of  FIG. 1 ; 
           [0016]      FIG. 4  is a perspective view showing components of the heating cable of  FIG. 1  prior to assembly; 
           [0017]      FIG. 5  is a perspective view of the components of  FIG. 4  after assembly; 
           [0018]      FIG. 6  is a plan view of a jig to facilitate assembly of the components of  FIG. 4 ; 
           [0019]      FIG. 7  is a plan view, similar to  FIG. 7  with the components located in the jig; and 
           [0020]      FIG. 8  is a view similar to  FIG. 7  after assembly of the components. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring therefore to  FIGS. 1 to 3 , a heating cable  10  includes a cable  12  and a sealing boot  14 . The boot  14  is secured to the cable  12  by mechanical fasteners, such as crimping rings  16 . The cable  12  has a conductive core  18  with a pair of conductors  20  that extend along the length of the cable  12  embedded in the core  18 . A polyolefin protective jacket  22  is extruded around the core  18  to separate the core  18  from a braided metallic sheath  24  that may also be used to ground the cable electrically. The metallic sheath  24  is encased in a fluoropolymer casing  26  which provides a barrier from liquids and or substances from which the cable is submersed. The cable  12  has a generally oval cross section, as determined by the shape of the core  18 , and is of indeterminate length. It will be appreciated that the cable  12  described above is typical of such cables and the exact arrangement of the cable may vary from manufacturer to manufacturer. 
         [0022]    The sealing boot  14  has a body  30  formed from a thermoplastic vulcanizate (TPV) available under the trade name Santoprene and is generally circular in cross section. A shoulder  32  is formed at one end and a cavity  34  is molded in the body  30  to extend from the end adjacent the shoulder  32 . The cavity  34  is complementary in shape to the cross section of the cable  12  and in its free body state is slightly smaller than the cable  12 . The cable  12  is thus a tight sliding fit in the cavity  34  with the pliancy of the boot  14  allowing sufficient stretch for the cable  12  to be inserted in the cavity  34 . It has been found that an interference fit in the order of the thickness of the exterior plastics casing  26  is satisfactory. 
         [0023]    The rings  16  are a clearance fit on the boot  14  and are made from stainless steel or similar malleable material. The rings  16  are designed to be crimped on to the boot  14  to provide a compressive force capable of withstanding great external pressures between the boot  14  and cable  12 . 
         [0024]    To secure the boot  14  to the cable, the exterior casing  26  and metallic sheath  24  is first removed from one end of the cable  14 , as shown in  FIG. 4 . Approximately ¾ inch of the polyolefin film  22  and core  18  is exposed. A heat shrink hood  40  is then placed over the film  22  and heat shrunk on to the film to provide a tight fit that prevents entry of moisture and more importantly epoxy adhesive into the core during the assembly process. 
         [0025]    A curable sealant  42  is then placed within the cavity  34  so as to partially fill the cavity  34 . It has been found that between 50% and 75% of the volume of the cavity  34  is sufficient. Sufficient sealant is required to ensure its deployment along the interior of the cable beyond the boot  14 , as explained below, and it is preferred not to completely fill the cavity to avoid sealant  42  from flowing out of the boot  14  during initial assembly. The sealant is preferably a two part epoxy adhesive that is admixed as it is injected in to the cavity  34 . A commercial product sold under the trade name Loctite EA E-90 FL Hysol adhesive has been used successfully. 
         [0026]    With the curable sealant in the cavity  34 , the cable  14  is inserted. The initial insertion is facilitated by the removal of the exterior casing  26  and sheath  24 , which allows the end to be inserted in to the mouth of the cavity  34 . When the exterior casing  26  abuts the end face of the boot  14 , the interference fit seals the cavity  34  and traps the sealant  42 . Further movement of the cable  14  in to the cavity  34  forces the sealant  42  in to the mesh of the braided sheath  24 , which provides a porous layer within the cable  14 . The sealant  42  flows along the cable  12  between the exterior casing  26  and the polyolefin film  22  as it is expelled from the cavity  34  by continued insertion of the cable  12 . The sealant flows within the braided sheath in the voids provided by the braiding and thus effectively fills the free space within the metallic sheath  24 . The extent of its travel will depend on the volume provided initially in the cavity  34  but should extend along the cable  12  beyond the extent of the boot  14 . 
         [0027]    When the cable  12  is fully inserted, the sealant  42  is allowed to cure until a stable load supporting layer of material is provided within the cable  12 . Once cured, the rings  16  are slid on the boot  14  and crimped to hold the boot  14  in place. The cured sealant  42  provides sufficient support for the boot  14  to be compressed without crushing the core  18  or deforming the cable  12  within the cavity  34 . 
         [0028]    With the preferred combination of boot  14  and sealant  42 , the sealant does not adhere to the boot  14  so that if it is necessary to remove the boot  14  for repair of inspection it can be done. The mesh of the metallic sheath  24  provided by the braiding acts as a filamentary support for the sealant  42  to provide a strong structure that can withstand the compressive load of the rings  16 . 
         [0029]    The insertion of the cable  12  in to the cavity  34  requires significant force and therefore a jig is used, as indicated at  50  in  FIG. 6 . The jig  50  consists of a pair of jaws  52 ,  54 , one of which 52 is fixed and the other of which 54 is moveable. The position of the fixed jaw  52  can be adjusted by adjusting screws  56  so the spacing of the jaws can be adjusted. The moveable jaw  54  is mounted on a sliding rod  58  that can be moved by any suitable mechanism such as an air cylinder or an over centre toggle lever. 
         [0030]    The jig  50  also includes a support  60  for the boot  14  which is spaced axially from the jaws  53 ,  54 . The support  60  is cylindrical with an axial recess  62  that conforms to the shape of the boot  14 . The support  60  is mounted on a slidable rod  64  which is driven by a cylinder or toggle lever, or other suitable mechanism. 
         [0031]    To place the boot  34  on the cable  14 , the boot  14  is placed in the recess  62  after the sealant has been inserted in to the cavity  34 . The cable  12  is then positioned between the jaws  52 ,  54  with the free end of the cable aligned with the mouth of the cavity  34 . The moveable jaw  54  is moved toward the fixed jaw  52  to grip the cable and resist axial forces applied to the cable  12 . 
         [0032]    The support  60  is then moved axially toward the jaws  52 ,  54  to push the boot  14  on to the cable  12 . The support  60  inhibits the boot  14  from expanding radially and thus helps to maintain a seal between the boot  14  and cable  12  as the sealant  42  is expelled from the cavity  34 . One the support reaches the limit of its travel, it is reversed to leave the boot  14  on the cable and the jaws  52 ,  54  opened to release the cable  12 . 
         [0033]    Once cured, the ring  16  is crimped in place to provide the completed heating cable  10 . 
         [0034]    Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. The entire disclosures of all references recited above are incorporated herein by reference.