Abstract:
A co-injected fitting has a core made of recycled or reground PVC and ABS, which is less expensive and to which, in some embodiments, a blowing agent, such as azo and/or sodium bicarbonate, can be added to lower the weight. The fitting includes a skin on opposite sides of the core forming the internal side of the fitting and the external side of the fitting, respectively, in concentric relationship to the inner core. Such fittings may also include a strengthening core material, such as polycarbonate, to provide a stronger pipe fitting which likewise can be co-injection molded.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119(e) on U.S. Provisional Application No. 60/677,036 entitled C O -I NJECTED  P IPE  F ITTING , filed on May 3, 2005, by Earl H. Sexton, et al. +the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to pipe fittings and particularly pipe fittings which can be injection molded utilizing co-injection of different polymeric materials.  
         [0003]     Pipe fittings include elbows, T-s, couplings, and the like, which are employed for transmitting fluids in conduits and coupling conduits in flow systems. The use of thermoplastic materials to injection mold such fittings is well known. The conventional methods of producing composite pipe joints include the use of thermoset materials and multiple production steps resulting in a composite pipe fitting or pipe section comprised of multiple layers of thermoset and/or thermoplastic materials. The cost of pipe fittings utilizing polymeric materials, such as PVS and ABS, and particularly pipe fittings which are 1-  1 / 2 ″ or larger in diameter can be somewhat expensive due to the cost of virgin raw materials. Additionally, relatively large fittings can be somewhat bulky and heavy.  
       SUMMARY OF THE INVENTION  
       [0004]     There is a need, therefore, for pipe fittings which can be injection molded and which can employ an inner core which is either inexpensive, lighter in weight, or which has characteristics which improve the structural characteristics of the fittings. Such inner cores can be surrounded by a skin of conventional polymeric material, such as PVC and/or ABS.  
         [0005]     The system of the present invention provides such a product by the process of co-injection molding a core made of recycled or reground PVC and ABS, which is less expensive and to which, in some embodiments, a blowing agent, such as azo and/or sodium bicarbonate, can be added to lower the weight. The fitting includes a skin on opposite sides of the core forming the internal side of the fitting and the external side of the fitting, respectively, in concentric relationship to the inner core. Such fittings may also include a strengthening core material, such as polycarbonate, to provide a stronger pipe fitting which likewise can be co-injection molded.  
         [0006]     This invention discloses a composite pipe joint comprised of three layers of thermoplastic material and produced by co-injection molding in a single mold in a single operation. This invention resolves issues with earlier technologies including scrap reclaim issues associated with the use of thermoset materials, elimination of resin cure time, the ability to use existing production tooling and production of composite pipe joints without the need of secondary operations.  
         [0007]     These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic view of a co-injection machine and die which provide the structure and process for manufacturing fittings according to this invention;  
         [0009]      FIG. 2  is a cross-sectional view of a T-pipe fitting embodying the present invention;  
         [0010]      FIG. 3  is an enlarged, fragmentary, cross-sectional view of a pipe fitting incorporating a first embodiment of the present invention;  
         [0011]      FIG. 4  is an enlarged, fragmentary, cross-sectional view of a pipe fitting incorporating a second embodiment of the present invention; and  
         [0012]      FIG. 5  is an enlarged, fragmentary, cross-sectional view of a pipe fitting incorporating a third embodiment of the present invention; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     Referring initially to  FIG. 1 , there is shown a, schematic view of an injection molding machine  10  which is employed in the co-injection of pipe fittings according to the present invention. The machine is commercially available and manufactured by Spirex Corporation and identified as a Twinshot co-injection design barrel and screw. In  FIG. 1 , there is shown a schematic diagram of such a machine  10  which includes a barrel  12  with a first feed hopper  14  and a second feed hopper  16 . The first feed hopper  14  carries the material which is employed to inject the skin layers of a fitting according to the present invention, while the second feed hopper  16  includes the material which forms the core of the fittings.  
         [0014]     The injector  10  includes a dual feed screw  18  with a first thread flight  20  and a second thread flight  22  for carrying polymeric material from feed hoppers  14  and  16  inside barrel  12  to convert it to a fluid form. A conduit  24  (shown in phantom in  FIG. 1 ) allows the material from hopper  14  to exit the injector nozzle  40  while a second conduit  26  allows the material from hopper  16  to coaxially exit injector nozzle  40 . Check valve  28  prevents material from reentering the threaded sections  20 ,  22 . The screw  18  conveys material from the first hopper in a first plasticizing zone past the second threaded section  22  of screw  18  through the conduit  24  and into opening  29  at the center of the injector  40 . Simultaneously, the second screw section  22 , which plasticizes material in hopper  16  in the plasticizing zone along its length, conveys the second melt through opening  26  behind and to the periphery of the melt from conduit  24 . Screw  18  is rotatably driven by a motor  42  coupled by a longitudinally movable platen  44  to the screw  18 . Motor  42  is a high torque and relatively low rotational speed motor. The injection platen is controlled by a hydraulic cylinder  46  to inject the two different materials into a die  50  with the nozzle  40  in engagement with the gate of the die or mold  50 . In the embodiment shown, the die is in the form of a pipe fitting to be co-injected.  
         [0015]     The co-injection process advances screw  28  as seen in  FIG. 1  with the molten skin material from hopper  14  first being injected into the mold  50  to coat the inner surfaces of the mold with the polymeric skin. As the screw is further advanced in a direction indicated by arrow A in  FIG. 1 , the core material is injected into mold  50  in the remaining open space forming the core area of the fitting being molded. The injector  10  and its operation is disclosed in greater detail in U.S. Pat. No. 7,004,739, the disclosure of which is incorporated herein by reference.  
         [0016]     In summarizing, the steps for producing a composite thermoplastic pipe joint using this co-injection molding process include: 
        a) The skin layers material is loaded into the molding machine rear hopper  14 .     b) The rear section  20  of the processing screw  18  melts and processes this skin material. The material is pushed down the screw where a dam located at the mid-point of the screw forces the material to flow into a hollow section  24  running along the interior of the screw to the material accumulation chamber  26  located at the screw tip.     c) Simultaneously, the core layer material is loaded into the molding machine forward hopper  16 .     d) The forward section  22  of the processing screw  18  melts and processes the core material and pushes it to the material accumulation chamber  26  located at the screw tip or nozzle  40 . At this time, the accumulation chamber contains pools of both skin and core materials with the skin material closer to the nozzle.     e) Both skin and core materials are then subsequently injected into the mold  50  forming the part  60  by the actuation of cylinder  46 , which advances screw  18  to the position shown in  FIG. 1 . Laminar flow of the two materials assures that the skin material flows to and forms the skin layers  62  and  64  of the composite pipe fitting  60  and the core material flows to the core layer  63  of the fitting.        
 
         [0022]     Mold  50  includes a die cavity  52  which defines the inner and outer shape of a fitting  60  to be co-injected within the mold. Mold  50  may be a single cavity mold for relatively large parts or, as indicated by the dotted lines  51 , may be extended for up to 12 to 16 cavities for smaller parts. The mold itself is of conventional construction including a gate which mates with nozzle  40  and suitable mold inserts, such as  54  and  56 , which define the interior walls of the fitting to be molded. During the injection process, the skin material from hopper  14  first coats the inner surfaces of mold cavity  62  and the outer surfaces of the inserts  54  and  56  with a thickness as described below, leaving an open area in the mold between the skin surfaces so defined. As screw  18  is further advanced, the now molten core material from hopper  16  is then injected into the mold cavity to fill the core area between the skins.  
         [0023]     Referring now to  FIG. 2 , there is shown a composite pipe fitting  60  comprised of three distinct layers. The outer and inner skin layers  62  and  64  are comprised of the same thermoplastic material acceptable for use in drainage, flow control, or potable water applications including polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), chlorinated polyvinyl chloride (CPVC), polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), or nylon (PA). The core layer  63  can be any thermoplastic material compatible with the skin layer material and capable of bonding to it through cohesion.  
         [0024]     The preferred embodiment is that the skin layers  62  and  64  material be of the same family of thermoplastic material used in an adjoining pipe to which the fitting may be attached, allowing use of existing and proven joining technologies. The core layer  63  is any thermoplastic material compatible with the skin layers  62  and  64  material and which is capable of bonding to it through cohesion without the use of adhesives. The core layer  63  material can be selected to reduce the cost of the resulting fitting or to enhance its performance properties.  
         [0025]     The preferred embodiment is that the core layer  63  material can be of any of a family of cellular (foam) thermoplastic materials. These cellular materials can be produced through the use of chemical blowing agents or the direct addition of gas to the thermoplastic melt in the injection molding machine. These cellular materials can be of the same thermoplastic family as the skin layers material or any thermoplastic material compatible with the skin layers material and capable of bonding to it through cohesion.  
         [0026]     Another option for the core layer material  63  is to use post-industrial and/or post-consumer thermoplastic recycle materials. These recycle materials may be of the same family of thermoplastic material as the skin layers material or any thermoplastic material compatible with the skin layers material and capable of bonding to it through cohesion.  
         [0027]     A third option for the core layer material  63  is to use a modified and/or reinforced thermoplastic material. These materials may be of the same family of thermoplastic material used in the skin layers or any thermoplastic material compatible with the skin layers material and capable of bonding to it through cohesion. Examples of modified and/or reinforced materials include: 
        a) A thermoplastic material having increased heat distortion temperature. Use of this type of material in the core layer would form a composite pipe fitting having increased temperature resistance.     b) A thermoplastic material reinforced to have increased strength and/or stiffness. Use of this type of material in the core layer would form a composite pipe joint having increased strength allowing a reduction in the pipe fitting wall thickness without sacrificing performance. Reinforcing agents include any of the mineral, glass or natural or manmade fiber fillers known to increase the strength and stiffness of thermoplastic materials.        
 
         [0030]     Thus, this invention envisions a composite pipe fitting, such as  60  in  FIG. 2 , which is comprised of three thermoplastic layers as described above formed through co-injection molding. Co-injection molding of thermoplastic materials offers many advantages over existing known technologies of producing composite fittings using thermoset materials. These advantages include the ability to reuse scrap from the co-injection process, reduction of manufacturing time through the elimination of the cure time necessary with thermoset materials and reduction of manufacturing costs through the elimination of secondary operations.  
         [0031]     Referring now to  FIG. 3 , there is shown a pipe fitting  70  which can be a T, an elbow, a coupling, a conduit, or any other form of a pipe fitting designed to conduct a fluid therethrough. In each of the examples of  FIGS. 3-5 , a pipe fitting fragmentary cross section is shown, it being understood that the actual fitting will be a standard coupling, elbow, T, pipe section, or the like. The pipe fitting of  FIG. 3  has a central, generally cylindrical opening  72  and is co-injection molded with a central core  74  surrounded by an outer skin  76  and an inner skin  78 . In the embodiment shown, the outer and inner skins,  76  and  78  respectively, are made of a virgin polymeric material, as described above including PVC or ABS, while the inner core  74  can be made of recycled, reground PVC or ABS, which is significantly less expensive. The fitting  70  can be molded utilizing co-injection equipment and method described above. This manufacturing process provides the following benefits: 
        Reduce resin costs by 25 percent or more;     Make use of off-spec and regrind materials;     Encapsulate a lower-cost resin within a higher-cost UV stabilized resin;     Use less energy;     Enjoy simpler set-up and lower operational complexity;     Reduce maintenance costs;     Use less floor space;     Use a nozzle configuration that is completely standard; and     Easily convert back to single-material mode (supply the same material to both feed hoppers).        
 
         [0041]     In the embodiment of  FIG. 4 , a pipe fitting  80  is provided which includes a central conduit  82  defined by an inner skin  88  of a polymeric material, such as virgin PVC or ABS or the like, a core  114 , which also can be made of recycled, reground ABS and/or PVC or other suitable material, to which a foaming or blowing agent has been added, such as azo and/or sodium bicarbonate to provide a lighter weight and yet significantly strong inner core which is surrounded during the co-injection process by an outer skin  86  also made of a virgin PVC or ABS material. The relative thickness of the inner core  74  of  FIG. 3  and  84  of  FIG. 4 , is about four times that of the inner and outer skins and, for a  2  inch diameter fitting, for example, the inner core  74 ,  84  may have a thickness of about 0.080″ while the skins  76 ,  78 ,  86  and  88 , respectively, have a thickness of about 0.020″. For different sized pipes, these dimensions will vary with, for example, in a four inch pipe, the inner core may have a thickness of about 0.140″ while the skin&#39;s thickness may be increased to about 0.030 inches.  
         [0042]      FIG. 5  shows yet another embodiment of the invention in which a pipe fitting  90  includes an inner conduit  92  having an inner skin  98 , a central core  94 , and an outer skin  96 . The inner core  94  of this embodiment of the invention is also a co-injection polymeric material but one which adds a structural characteristic different than that of the first and second embodiments. Thus, the polymeric material used for inner core  94  may be polycarbonate or some other co-injectable material which adds greater strength to the fitting for more rigorous applications.  
         [0043]     It will become apparent to those skilled in the art that various modifications to the preferred embodiments of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.