Abstract:
A coupling system for conduit and pipe for carrying insulated electrical cable, more particularly, a conduit coupling assembly for connecting multiple lengths of conduit in coaxial relationship.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a coupling system for conduit and pipe that contain electrical cable or wiring, more particularly, a conduit coupling assembly for connecting multiple lengths of electrical conduit in coaxial relationship, particularly for carrying insulated electrical cable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a conduit coupling assembly for connecting multiple lengths of conduit in coaxial or end-to-end relationship. It is a conventional practice in many types of pipe or conduit systems, and particularly in electrical systems employing tubular conduits that contain electrical wires or cables, to connect a number of lengths of conduit in end-to-end relation through means of couplings so as to form a continuous conduit system as necessary for a particular application. In the case of thin wall conduit, which is primarily employed for encasing electrical cable or conductor wires in applications where the conduit will not be subjected to large stresses, compression fittings or coupling assemblies may be employed which are swaged or otherwise affixed to adjacent ends of conduit lengths. The conduit is generally available in different lengths and may be quite readily formed to various bend contours and coupled end-to-end through the compression couplings or coupling assemblies. 
     One known technique for connecting lengths of conduit in coaxial or end-to-end relationship is to provide external threads of standard size on the opposite ends of each length of conduit and then connect the lengths of conduit through coupling assemblies. Those coupling assemblies have internal threads, which enable threaded connection with adjacent ends of the conduit lengths to form a structurally sound and electrically sound connection. One known coupling assembly for coupling lengths of conduit is disclosed in commonly assigned U.S. Pat. No. 4,957,314 to Basile et al. 
     The coupling assembly disclosed in the Basile et al. patent requires specially manufactured components, including outer and inner coupling assemblies that must be first installed on each length of conduit before the lengths of conduit can be coupled together. More specifically, the coupling assembly utilizes outer and inner coupling members having threaded ends for threading onto the ends of the lengths of conduit. The outer coupling member is threaded or screwed on to one end of one length of conduit and the inner coupling member is threaded or screwed onto one end of the other length of conduit. The lengths of conduits are then axially aligned and the inner coupling member is inserted into the outer coupling member. The inner coupling member is firmly held in the outer coupling member by set screws disposed on the outer coupling member. 
     Other known coupling assemblies are disclosed in commonly assigned U.S. Pat. No. 4,547,004 to Goldberg and U.S. Pat. No. 4,592,574 to Vollmuth et al. Similar to the coupling assembly disclosed in the Basile et al. patent, the coupling assemblies disclosed in the Goldberg and Vollmuth et al. patents require specially manufactured components, including outer and inner coupling members that must be first installed on one length of conduit before the lengths of conduit can be coupled together. Those outer and inner coupling members have threaded ends and the lengths of conduit are subsequently joined by rotating the outer coupling member to thread or screw it onto the other end length of conduit. 
     Another known technique for connecting lengths of conduit is to provide lengths of conduit with built in set screw assemblies. More specifically, each length of conduit includes a receiving end having an enlarged bell portion or increased diameter that is shaped and configured to receive the insertion end of another length of conduit. In addition, set screws are disposed in apertures located on the bell portion and are used to mechanically hold the insertion end in the bell portion. During installation, the insertion end is positioned in the bell portion and the set screws in the bell portion are advanced or tightened until it engages the insertion end to firmly hold the insertion end in the bell portion. Such a coupling assembly has many advantages over other known techniques for connecting lengths of conduit. For example, such a coupling assembly eliminates the need for multiple components, such as outer and inner coupling members. Thus, the increased cost and time associated with the inventory, shipping, and factory and field installation of the multiple components is eliminated. 
     Even though those built in set screw coupling assemblies have many advantages over other known techniques for connecting lengths of conduit, improvements in those set screw coupling assemblies are needed. For example, a need exists for a built in set screw coupling assembly that (1) reduces the amount of time needed to tighten the screws or bolts during the conduit installation process, (2) reduces or eliminates the amount of offset typically caused when several conduits are assembled and joined together, (3) reduces or eliminates the amount of dimpling or denting that may occur on the insertion end of the length of conduit when the set screws are tightened, (4) reduces or eliminates the possibility that a set screw will vibrate loose from the tightened position, (5) increases the mechanical connection between the lengths of conduit, and (6) increases the safety of the conduit system by eliminating or reducing any damage of the electrical cable at the connection joint between the length of conduit. Those improvements, among others, are found in the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, the present invention is a coupling system for connecting multiple lengths of conduit in coaxial or end-to-end relationship. Each length of conduit includes an insertion end and, at the other end, a bell portion that is shaped and configured to receive the insertion end of another length of conduit. To assemble the lengths of conduit in coaxial relationship, the insertion end of one length of conduit is inserted or positioned into the bell portion of another length of conduit. To provide an improved mechanical connection between the insertion end and the bell portion, the difference between the inner diameter of the bell portion and the outer diameter of the insertion end is less than 0.060 inches and the nominal length of the bell portion is at least 3 inches. Reducing the difference between the inner diameter and the outer diameter results in reduced gap or space between the insertion end and the bell portion when the insertion end is positioned in the bell portion. In turn, the reduced gap or distance substantially reduces or eliminates the amount of offset typically caused when several conduits are assembled and joined together. Thus, several conduits joined together will define a relatively straight line. 
     To secure the length of conduit together, the bell portion of each length of conduit contains a built in set screw or bolt assembly. The bell portion contains threaded rivets for receiving set screws. The threaded rivets are disposed in apertures positioned on the bell portion. Once the insertion end is inserted into the bell portion, the lengths of conduit are secured together by tightening the set screws until the bottom of the set screws contacts the insertion end. The set screws contain thread profiles that measure between 4 and 12 threads per inch and lengths between about 0.5625 and 0.450 inches. Because the present invention incorporates this improved set screw design, only about a ¼ to 1½ turn of the set screw is needed to adequately tighten the set screw. In addition, as a result of the improved set screw design, the head of the set screw fits firmly and securely on the rivet and the contacting surface of the set screw fits firmly and securely on the outer surface of the insertion end of the conduit when the required amount of torque to adequately tighten the set screw is reached. Moreover, the improved design enables an operator to quickly and efficiently tighten the screw against the outer surface of the insertion end of the conduit. In addition, the improved design eliminates the guesswork in determining whether the set screw is in the locked or tightened position and in determining whether enough torque has been applied to adequately tighten the set screw. Furthermore, the improved design substantially reduces or eliminates the possibility of any dimpling or denting that may occur on the insertion end caused by over tightening the set screw and substantially reduces or eliminates the possibility that the set screw will vibrate loose from the tightened position. 
     These and other important features of the present invention may best be understood with reference to the accompanying drawings and in the following detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The foregoing aspects and many of the advantages of the present invention will become readily appreciated by reference to the following detailed description of the preferred embodiment, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  depicts two lengths of conduit in coaxial relationship wherein the insertion end of one length of conduit is positioned in the receiving end of another length of conduit; 
         FIG. 2  depicts a cross-sectional view of the receiving end of one length of conduit; 
         FIG. 3  is a cross-sectional view depicting the insertion end of one length of conduit positioned in and mechanically coupled to the receiving end of another length of conduit; 
         FIG. 4  an enlarged bottom view depicting the inside surface of the rivets and the contacting surface of the set screws utilized in the present invention; and 
         FIG. 5A  depicts an end expander prior to insertion in the length of conduit; 
         FIG. 5B  depicts an end expander inserted in a length of conduit forming a bell portion; 
         FIG. 6  is a schematic of an exemplary embodiment of the multi-task station used to manufacture the length of conduit; and 
         FIG. 7  is a schematic of another exemplary embodiment of the multi-task station used to manufacture the length of conduit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For a better understanding of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings.  FIG. 1  depicts a coupling assembly  10  for connecting a pair of lengths of conduit  12 ,  14  in coaxial relationship. The lengths of conduit  12 ,  14  are preferably of the same outer diameter and have insertion ends  16  and receiving ends  18 . Each receiving end  18  is defined by a bell portion  20 . Referring to  FIG. 2 , the diameter of the insertion end  16  transitions into the diameter of the bell portion  20  at a transition run  22 . 
     As shown in  FIG. 3 , the bell portion  20  has an inner diameter slightly larger than the outer diameter of the insertion end  16 , and the bell portion  20  is shaped and sized to receive the insertion end  16  during assembly of the lengths of conduit  12 ,  14 . The transition run  22  serves as an abutment for limiting the extent that the insertion end  16  can be inserted into the bell portion  20 . Preferably, the insertion end  16  and the bell portion  20  are sized such that when the insertion end  16  is inserted into the bell portion  20 , the gap or distance between an outer surface  24  of the insertion end  16  and an inner surface  26  of the bell portion  20  is minimized or reduced. To minimize that gap or distance between the outer surface  24  and the inner surface  26 , the difference or tolerance between the inner diameter of the bell portion  20  and the outer diameter of the insertion end  16  should be less than 0.060 inches. More preferably, the distance between the two diameters is about 0.025 inches. The reduced gap or distance between the outer surface  24  of the insertion end  16  and the inner surface  26  of the bell portion  20  provides for an improved mechanical fit between the two lengths of conduit  12 ,  14 . Moreover, the reduced gap or distance reduces or eliminates the dimpling that may occur on the insertion end  16  when the lengths of conduit  12 ,  14  are coupled (as explained in detail below). In addition, the reduced gap or distance provides better overall geometry that reduces the amount of time needed to tighten the screws or bolts during the conduit assembly process (as explained in detail below). Furthermore, the reduced gap or distance between the outer surface  24  of the insertion end  16  and the inner surface  26  of the bell portion  20  reduces or eliminates the amount of offset typically caused when several conduits are assembled and joined together. As a result, the several conduits joined together will be substantially aligned in co-axial relationship and the central axes of the several conduits will define a relatively straight line. 
     Referring back to  FIG. 2 , the bell portion  20  has at least one aperture  30  formed therethrough. If the bell portion  20  has more than one aperture  30 , the apertures  30  may be radially and/or longitudinally aligned on the bell portion  20 . In the preferred embodiment, the bell portion  20  has two regularly spaced apertures  30  which are longitudinally aligned on the bell portion  20 . Rivets  32  are fixedly secured within the apertures  30 . Each aperture  30  may be located on a raised boss or crest  34  so that when the rivets  32  are disposed or seated within the apertures  30 , the inside surface  36  of the rivets  32  sit substantially flush with the inner surface  26  of the bell portion  20  (depending on the gap existing between the outer surface  24  of the insertion end  16  and the inner surface  26  of the bell portion  20 ). Each rivet  32  is threaded to receive a set screw  38 . The set screws  38  may be of the type which can be advanced using an Allen wrench or may have any other suitable extending head for engagement by a suitable wrench, screwdriver, or the like. As shown in  FIG. 4 , the inside surface  36 A of the rivets  32  and/or a contacting surface  40 A of the sets screw(s)  38  may contain a serrated pattern or other suitable pattern to provide frictional engagement between the rivets  32  and/or the set screw(s)  38  with the outer surface  24  (not shown) of the insertion end  16 . In addition, the outside surface of the rivets  32  and the underside surface of the head of the set screw(s)  38  may also contain a serrated pattern or other suitable pattern to provide enhanced frictional engagement between the outside surface of the rivets  32  and the underside surface of the head of the set screws  38 . Such a construction provides a positive locking between the rivets  32  and the set screws  38  when the set screws  32  are in a tightened position and further avoids the set screws  38  from vibrating loose from that tightened position during vibration of the interconnected lengths of conduits  12 ,  14 . 
     During assembly of multiple lengths of conduit  12 ,  14 , as shown in  FIG. 3 , the insertion end  16  is positioned into the bell portion  20  until the insertion end  16  abuts the transition run  22 . The set screws  38  are then tightened to mechanically couple the lengths of conduit  12 ,  14  together. The apertures  30  containing the set screws  38  should be located a sufficient distance from the transition run  22  and the edge  23  of the length of conduit so that when the set screws  38  are tightened, any dimpling that may occur on the insertion end  16  will be reduced or eliminated. Preferably, the center of the apertures  30  containing the set screws  28  are located at least 0.8125 inches from the end  39  of the transition run  22 , preferably between about 1.3125 and 1.8125 inches from the transition run  22 . In addition, center of the apertures containing the set screws  28  are located at least 0.8125 inches from the edge  23  of the length of conduit. 
     Preferably, each set screw  38  is a 5/16 set screw with a double or triple lead thread, or any suitable broad thread design. In addition, the set screw  38  preferably contains a thread profile  41  that measures between 4 and 12 threads per inch and a length  42  between about 0.5625 and 0.450 inches, preferably 0.450 inches. The thread profile 41 and the length 42 of each set screw  38  should be dimensioned such that only about a ¼ to 1½ turn of the set screw  38  is needed to adequately tighten the set screw  38 .In addition, the length  42  should be sized so that when the required amount of torque to adequately tighten the set screw  38  is reached, the head of the set screw  38  fits firmly and securely on the rivet  32  and the contacting surface  40  of the set screw  38  fits firmly and securely on the outer surface  24  of the insertion rod  16 . Accordingly, only about ¼ to 1½ turn of the set screw  38  is needed before the set screw  38  fits firmly and securely on the outer surface  24  of the insertion rod  16 . Preferably, the torque required to adequately tighten the set screw  38  is between about 50 to 130 in-lb. Such a construction enables an operator to quickly and efficiently tighten the screw  38  against the outer surface  24 . Moreover, such a construction substantially eliminates the guesswork in determining whether the set screw  38  is in the locked or tightened position and in determining whether enough torque has been applied to adequately tighten the set screw  38 . Furthemore, such a construction reduces or eliminates the possibility that any dimpling may occur on the insertion end  16  caused by over tightening the set screw  38  and reduces or eliminates the possibility that the set screw  38  will vibrate loose from the tightened position. 
     Referring back to  FIG. 3 , the nominal length  39  of the bell portion  20  (i.e., the distance from the edge of the length of conduit on the receiving end to the transition run  22 ) should measure greater than 3.0 inches, and preferably measures between 3.5 and 4.0 inches to provide the most efficient mechanical fit. Increasing the length  39  of the bell portion  20  results in an increase in the amount of surface area of the bell portion  20  in contact with the insertion end  16 . In turn, an increase in surface area contact provides an improved mechanical connection between the insertion end  16  and the bell portion  20 . 
     In the preferred embodiment, the bell portion  20  is manufactured using a conduit end expander  44 . The end expander  44  is inserted into an unexpanded conduit length  45  ( FIG. 5A ) until a bell portion  20  having a desired length is formed ( FIG. 5B ). Preferably, the end expander  44  is sized and configured to form a bell portion  20  having a nominal length of at least three inches. After the bell expansion step, the conduit is loaded or transferred to a multitask station  46 . At the multi-task station  46 , the conduit is fixedly held while the multi-task station  46  performs the following tasks on the conduit: forming the apertures  30  and the raised crests  34  in bell portion  20 ; placing and clinching the rivets  32  into the apertures  30 ; and placing and tightening the set screws  38  into the rivets  32 . Preferably, the conduit is fixedly held in front of the multi-task station  46  by electromagnets or other suitable methods. 
     As illustrated in  FIG. 6 , the multi-task station  46  is preferably a rotating table  48 . With such a construction, the three aforementioned tasks can be performed on the conduit without having to move or reposition the conduit. For instance, in Step  1 , a punch machine  50  located on the rotating table  48  is positioned in front of the conduit. The punch machine  50  forms or punches the apertures  30  in the bell portion  20  and forms the raised crests  34  in the bell portion. In Step  2 , the rotating table  48  rotates 120° until a rivet machine  52  is positioned in front of the conduit. The rivet machine  52  places and clinches the rivets  32  into the apertures  30 . In Step  3 , the rotating table  48  rotates 120° until a set screw machine  54  is positioned in front of the conduit. The set screw machine  54  places the set screws  38  into the rivets  32  and tightens the set screws  38  such that the set screws  38  will not vibrate loose during the shipping of the conduit. After the above tasks are performed on the conduit, the conduit is transferred to a finishing station where the conduit is prepared for shipping to end-users in the field. 
     In another embodiment, the multi-task station  46  may also be configured to perform the bell expansion step. With such a construction, all four aforementioned tasks can be performed on the conduit without having to move or reposition the conduit. For instance, as illustrated in  FIG. 7 , in Step  1 , end expander machine  56  located on the rotating table  48  is positioned in front of the conduit. The end expander machine  56  forms a bell portion  20  having a desired length and shape in the conduit. In Step  2 , the rotating table  48  rotates 90° until the punch machine  50  is positioned in front of the conduit. The punch machine  50  forms or punches the apertures  30  in the bell portion  20  and forms the raised crests  34  in the bell portion. In Step  3 , the rotating table  48  rotates 90° until the rivet machine  52  is positioned in front of the conduit. The rivet machine  52  places and clinches the rivets  32  into the apertures  30 . In Step  4 , the rotating table  48  rotates 90° until the set screw machine  54  is positioned in front of the conduit. The set screw machine  54  places the set screws  38  into the rivets  32  and tightens the set screws  38  such that the set screws  38  will not vibrate loose during the shipping of the conduit. After the above tasks are performed on the conduit, the conduit is transferred to a finishing station where the conduit is prepared for shipping to end-users in the field. 
     In the foregoing specification, the present invention has been described with reference to specific exemplary embodiments thereof. It will be apparent to those skilled in the art, that a person understanding this invention may conceive of changes or other embodiments or variations, which utilize the principles of this invention without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than restrictive sense.