Abstract:
A structural assembly device and method for securing together a pair of surfaces of two fusible materials wherein an electrically conductive thermal element is located between the surfaces which will melt, without substantially degrading, when heated. When the thermal element is heated, it is elevated to a temperature sufficient to melt the first and second elements and then is allowed to cool such that the first and second elements are joined to the thermal element and may be joined to each other as well.

Description:
ORIGIN OF THE INVENTION 
     This invention was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method and apparatus for joining structural elements, and more specifically to a method and apparatus for joining plastic elements, such as plastic pipe. 
     2. Prior Art 
     Traditional means of joining two members, such as two pipes, include welding and bolting abutting flanges together. Other methods of joining two members together include the use of adhesives or tape. Still other methods of joining two members together include using interlocking hooks. Other mechanical and chemical connecting means may be known in the art as well. 
     A need exists for an efficient, cost effective way to join two structural members together without requiring the use of mechanical connectors. 
     Another need exists for joining two members together without requiring chemicals such as adhesives. 
     A further need exists for a method of joining two structural members while providing for disassembly at a later date. 
     SUMMARY OF THE INVENTION 
     Consequently, it is a primary object of the present invention to provide a cost effective means to join two structural members together without the use of mechanical connectors or chemicals. 
     It is another object of the present invention to provide a method of joining two structural members while providing for subsequent disassembly. 
     Accordingly, the present invention provides a method and apparatus for joining together two structural members, preferably plastic members, including the use of a thermal element residing between adjoined or conjoined members. The thermal element uses electrical resistance exposed to electrical current to produce sufficient heat for the structured members to attach themselves to each side of the thermal element after melting and subsequent cooling. It is also possible that the two members may attach to each other as well during the cooling process. The thermal element preferably has a plurality of holes to facilitate bonding of the members to the element and/or to each other. The thermal element remains between the elements throughout operation and may be utilized for disassembly at some future date. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded cross-sectional view of a structural assembly device in accordance with the present invention; and 
     FIG. 2 is an exploded perspective view of the structural assembly device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a first member  12  and a second member  14  are illustrated which are intended to be joined together. The first and second members  12 ,  14  as illustrated are pipe sections; however, any appropriate pair of structural elements may be joined. A thermal element such as an annular element  16  is utilized to assist in the joining of the first and second member  12  and  4 . 
     Materials which are suitable for the joining portions of the first and second members  12  and  14  include materials selected from the group of fusible alloys, synthetic, thermoplastic materials and brazing alloys. The joining portions or the entire first and second members  12 ,  14  may be constructed of these materials. Fusible alloys are those alloys which will melt at temperatures below about 250° C. Fusible alloys are usually binary, ternary, quaternary or quinery mixtures of bismuth, lead, tin, cadmium, indium and less frequently other metals. The term “low melting temperature” means a temperature below about 250 ° C. “Non-degradable” thermoplastic materials are those thermoplastic materials which will melt and do not degrade significantly when melted. For higher temperature applications, the joining faces may be brazing alloys. Brazing alloys are well known to those skilled in the art of brazing. 
     Some of the fusible alloys are: 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 EUTECTIC ALLOYS 
               
             
          
           
               
                   
                 Percentage Composition 
               
             
          
           
               
                 Melting Temp. ° C. 
                 Bi 
                 Pb 
                 Sn 
                 Cd 
                 Other  
               
               
                   
               
               
                 248.0 
                  0 
                 82 
                  0 
                 18 
                 0 
               
               
                 221.0 
                  0 
                  0 
                 96 
                  0 
                 Ag 4 
               
               
                 199.0 
                  0 
                  0 
                 91 
                  0 
                 Zn 9 
               
               
                 183.0 
                  0 
                 38 
                 62 
                  0 
                 0 
               
               
                 144.0 
                 60 
                  0 
                  0 
                 40 
                 0 
               
               
                 143.0 
                  0 
                 31 
                 51 
                 18 
                 0 
               
               
                 138.56 1   
                 58 
                  0 
                 42 
                  0 
                 0 
               
               
                 138.5 
                 57 
                  0 
                 43 
                  0 
                 0 
               
               
                 130.0 
                 56 
                  0 
                 40 
                  0 
                 Zn 4 
               
               
                 124.3 2   
                   55.5 
                   44.5 
                  0 
                  0 
                 0 
               
               
                 102.5 
                 54 
                  0 
                 26 
                 20 
                 0 
               
               
                 95.5 
                 52 
                 37 
                 16 
                  0 
                 0 
               
               
                 91.5 
                 52 
                 40 
                  0 
                  8 
                 0 
               
               
                 78.8 
                 57 
                 17 
                  0 
                 26 
                 0 
               
               
                 70.0 3   
                 50 
                   26.7 
                   13.3 
                 10 
                 0 
               
               
                 70.0 4   
                 50 
                 27 
                 13 
                 10 
                 0 
               
               
                 58.0 5   
                 49 
                 18 
                 12 
                  0 
                 In 2 
               
               
                 46.9 6   
                   44.7 
                   22.6 
                   8.3 
                   5.3 
                 In 19.1  
               
               
                   
               
             
          
           
               
                 NON-EUTECTIC ALLOYS 
               
             
          
           
               
                 Yield Temp. 
                 Melt Range, 
                 Percentage Composition 
               
             
          
           
               
                 ° C. 
                 ° C. 
                 Bi 
                 Pb 
                 Sn 
                 Other  
               
               
                   
               
               
                 159 
                 145-176 
                   12.6 
                   47.5 
                   39.9 
                 0 
               
               
                 154 
                 143-163 
                 14 
                 43 
                 43 
                 0 
               
               
                 145 
                 130-173 
                 20 
                 50 
                 30 
                 0 
               
               
                 142 
                 120-152 
                 21 
                 42 
                 37 
                 0 
               
               
                 135 
                 129-132 
                  5 
                 32 
                 45 
                 Cd 18 
               
               
                 127 
                 124-130 
                 56 
                  2 
                   40.9 
                 In 0.4 Cd 0.7 
               
               
                 116 
                 103-227 
                 48 
                   28.5 
                   14.5 
                 Sb 9 
               
               
                 111 
                  95-143 
                   33.3 
                   33.4 
                   33.3 
                 0 
               
               
                 100 
                  95-114 
                   59.4 
                   14.8 
                   25.8 
                 0 
               
               
                 96 
                  95-104 
                 56 
                 22 
                 22 
                 0 
               
               
                 89 
                 83-92 
                 52 
                   31.7 
                   15.3 
                 Cd 1.0 
               
               
                 72.5 
                 70-90 
                   42.5 
                   37.7 
                   11.3 
                 Cd 8.5 
               
               
                 64.0 
                 61-65 
                 48 
                   25.6 
                   12.8 
                 Cd 9.6 In 4.0  
               
               
                   
               
             
          
           
               
                 Fusible Alloy Examples 
               
             
          
           
               
                   
                 Approx. 
                   
                   
                   
                   
               
               
                 Material 
                 M.P. ° C. 
                 Bi 
                 Pb 
                 Sn 
                 Cd  
               
               
                   
               
               
                 Material A 
                   138.6 
                 58 
                 0 
                 42 
                 0 
               
               
                 Material B 
                   123.8 
                   55.5 
                   44.5 
                  0 
                 0 
               
               
                 Material C 
                 100  
                 50 
                 28 
                 22 
                 0 
               
               
                 Material D 
                 95 
                 50 
                 31 
                 19 
                 0 
               
               
                 Material E 
                 93 
                 50 
                 25 
                 25 
                 0 
               
               
                 Material F 
                 71 
                 50 
                 24 
                 14 
                 12  
               
               
                 Material G 
                 71 
                 50 
                 25 
                   12.5 
                  12.5 
               
               
                 Material H 
                 70 
                 50 
                 27 
                 13 
                 10  
               
               
                 Material I 
                 70 
                 50 
                   26.7 
                   13.3 
                 10   
               
               
                   
               
               
                   1 Cerrotru;  2 Cerrobase;  3 Cerrobend;  4 Lipowitz&#39;s metal;  5 Cerrolow-136;  6 Cerrolow-117  
               
             
          
         
       
     
     Synthetic, thermoplastic materials joinable by this invention are those materials which will melt, without degrading, at temperatures below about 250° C. and will, preferably, wet the surfaces to be sealed to opposite sides of the thermal element. Such materials include hot melt adhesives, nylon, polyethylene and other plastics including polyvinyl chloride that are well known to those skilled in the art. It can readily be seen that the adjoining surfaces  18 ,  20 ,  22 ,  24  may be made of different materials. For example, the adjoining surfaces  18  and  22  may be made of a fusible alloy while the adjoining surfaces  20 ,  24  of the other member may be a synthetic, thermoplastic material. In the preferred embodiment, the layers on opposite sides of the thermal element melt at about the same temperature range. 
     This structural assembly device  10  and method could also be used in high temperature applications including the brazed-joining of lightweight components to each other using a thermal element about 60 ms thick coated with a bronze alloy which melts about 1,125° F. with a braze flux type B-(1000-1700° F.). This application is particularly suited to vacuuming systems, catalytic converters and refrigeration systems. 
     There are many brazing alloys. Some of the most common are: 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Brazing Alloy Examples 
               
             
          
           
               
                 Composition A 
                 Cu 
                 Ag 
                 Zn 
                 Cd 
                 P 
                 Melting Range, ° C.  
               
               
                   
               
               
                 Composition B 
                   99+ 
                   
                   
                   
                   
                 1083 
               
               
                 Composition C 
                 50 
                 50 
                   
                   
                   
                 778-850 
               
               
                 Composition D 
                   15.5 
                 50 
                   16.5 
                 18 
                   
                 627-734 
               
               
                 Composition E 
                 93 
                   
                   
                   
                 7 
                 704-800 
               
               
                 Composition F 
                 28 
                 72 
                   
                   
                   
                  778 
               
               
                 Composition G 
                 34 
                 50 
                 16 
                   
                   
                 695-775  
               
               
                   
               
             
          
         
       
     
     Various brazing fluxes may be used with these brazing alloys. Those skilled in the art of brazing will be familiar with brazing alloys and the brazing fluxes which will work best with each alloy. The brazing flux may be brushed onto the brazing alloy and protected by a thin layer of paper or plastic until the thermal element is to be used. Or, the flux may be brushed onto the brazing alloy at the point of use. 
     In operation, the structural assembly device is arranged with the opposed joining faces  18 ,  20 ,  22 ,  24  disposed with the thermal element  16  therebetween. Although the surfaces  18  and  22  and also the surfaces  20  and  24  are respectively the same surface in the embodiment illustrated, i.e., top and bottom portions of a pipe-like element, if the embodiment were, for example, a square end shape instead of circular, then these surfaces would be different. Adhesives, bolts or other mechanisms may, or may not, be utilized to assist in holding the first and second members together such as to create a preassembly. Preferably, an electric current is then passed through the thermal element  16  to melt at least portions of the opposed joining faces  18 ,  20 ,  22 ,  24 . One or more detents or aligners, illustrated as notch  26 , may be utilized as a self aligning feature of the thermal element. The notch, or notches  26 , may fit within recessed portions  28 . Additionally, protrusions  30  may assist in aligning the aligners  26  into the recesses  28  in order to provide the proper fit between the opposing joining faces  18  through  24  .Other aligners may also be utilized. 
     A Vee type indention for the notch  26  has been found effective to locate the notch  26  in the recesses  28 . The Vee type indention also assists the protrusion  30  in cooperating with the notch  26  in the thermal element  16  to properly fit together with the recesses  28  in the first member  12 . FIG. 2 illustrates the notch  26  extending radially around a portion of the thermal element  16 . Other cooperating arrangements may also be utilized to assist in the fitting together of the first and second members with the thermal element. 
     The thermal element  16  is illustrated as comprising a ring or annular member  32  in FIG. 2 having an inner diameter and an outer diameter. The ring member  32  may fit within the inner and outer diameters of the opposed flanges  34 ,  36 . The opposed faces of the flanges  34 ,  36  are illustrated in FIG. 1 as joining surfaces  18 - 24 . Alternatively, the inner diameter of the ring member  32  may correspond to the inner diameter of the flange member or members  34 ,  36  as illustrated in FIG.  1 . The thermal element  16  may employ tabs  38 ,  40  to act as conductors to assist in heating the thermal element  16  by conducting or communicating electricity from one tab  38  to another tab  40 . Other methods of heating the thermal element  16  may also be utilized. 
     The thermal element  16  may also have one or more orifices, illustrated as holes  42  which may facilitate bonding between the first and second members  12  and  14 . The holes  42  may be of any geometric configuration so long as they are capable of communicating melted portions of the first and second members  12  and  14  with one another. 
     After a joint has been created, the assembly  10  may be utilized and later disassembled. If disassembly is desirable, a current may be introduced into the thermal element  16  to locally remelt the exterior surface portions  18 - 24 . Once the surfaces  18 - 24  are no longer joined to the thermal element  16  or to each other, the two members  12 ,  14  may be separated. 
     This joining technology has many applications. One application is the commercial sign industry wherein the elements may have any geometrical configuration conventional for signs. Additionally, the joining of plastic pipe and subsequent disassembly is another practical application of the structural assembly method and apparatus taught herein. Furthermore, a portable enclosure support structure may be constructed utilizing the technology taught herein. 
     Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.