Patent Publication Number: US-2006003038-A1

Title: Injection molding machine shooting pot with integral check valve

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an improved check valve assembly incorporated within the body of a shooting pot cylinder of a coinjection hot runner assembly in an injection molding machine.  
      2. Description of Related Art  
      Coinjection molding is typically used to mold multi-layered plastic packaging articles having a laminated wall structure. Each layer is typically passed through a different annular or circular passageway in a single nozzle structure and each layer is partially, sequentially, injected through the same gate. Some coinjection hot runner systems include shooting pots to meter material of one plastic resin so that each cavity of a multi-cavity mold receives an accurate dose of that resin in the molding cycle. Some design configurations use check valves to prevent backflow of the resin when the shooting pot discharges the resin through the nozzle.  
      U.S. Pat. No. 4,717,324 to Schad discloses an coinjection hot runner assembly, with shooting pots, that does not use check valves. Instead, rotary valves are used to prevent backflow of the resins during injection from the shooting pots. Rotary valves required external actuation mechanisms which increase cost and complication, also rotary valves are prone to leaking resin.  
      U.S. Pat. No. 4,710,118 to Krishnakumar discloses an coinjection hot runner assembly with shooting pots that uses check valves to prevent backflow of resin during injection from the shooting pots. In this patent, the check valves are represented schematically and are shown as enclosed within the manifold, as part of the melt channel. There is no teaching of how the check valves are installed or how they may be serviced, if required. See also:  
      U.S. patent application Ser. No. 10/______ entitled INJECTION MOLDING MACHINE SPIGOTTED SHOOTING POT PISTON (attorney docket number 213201.00213; H-784);  
      U.S. patent application Ser. No. 10/______ entitled APPARATUS AND METHOD FOR SEALING INJECTION UNIT AND SPRUE (attorney docket number 213201.00215; H-785);  
      U.S. patent application Ser. No. 10/______ entitled APPARATUS AND METHOD FOR ACTUATION OF INJECTION MOLDING SHOOTING POTS (attorney docket number 213201.00216; H-781);  
      U.S. patent application Ser. No. 10/______ entitled CONTROL SYSTEM FOR A DYNAMIC FEED COINJECTION PROCESS (attorney docket number 213201.00221; H-786);  
      U.S. patent application Ser. No. 10/_____ entitled HOT RUNNER COINJECTION NOZZLE WITH THERMALLY SEPARATED MELT CHANNELS (attorney docket number 213201.00219; H-788);  
      U.S. patent application Ser. No. 10/______ entitled COINJECTION MOLDING COOLED SHOOTING POT (attorney docket number 213201.00223; H-783); and  
      U.S. patent application Ser. No. 10/______ entitled APPARATUS AND METHOD FOR INJECTION MOLDING SHOOTING POT WEDGE FEATURE (attorney docket number 213201.00220; H-780).  
       FIGS. 1-3  show a known check valve configuration installed in a coinjection hot runner manifold. The installation is remote from the shooting pot assembly and occupies space that could otherwise be saved to decrease the size of the overall assembly.  FIG. 3  shows the detail of the assembly, namely an insert  10 , containing a melt channel  11  in which there is a ball (or other occlusion)  12 , that is retained by a cross dowel  13 . This insert is retained in the manifold by a plate  14 , and oriented to the plate by dowel  15  to ensure the inlet/outlet to the melt channel  11  is aligned with the corresponding channel(s) in the manifold (not shown). There is typically one installation for each shooting pot, consequently in a two material coinjection hot runner for a 48 cavity mold, there would be at least 12 check valve installations.  
      Thus, what is needed is a shooting pot check valve assembly which is easily installed, easily maintained, reliable, and takes up minimal space in the neighborhood of the shooting pot.  
     SUMMARY OF THE INVENTION  
      It is an advantage of the present invention to provide shooting pot check valve method and apparatus whereby injected resin is forcible and reliably prevented from leaking back into the injection melt channel, while making installation and maintenance more efficient and less costly.  
      According to a first aspect of the present invention, a unique combination of structure and/or steps is provided for an injection molding shooting pot assembly check valve configured to be installed in a coinjection hot runner with a coinjection nozzle, where the coinjection nozzle has at least two melt channels ending at the same gate. The check valve preferably includes a valve inlet, and a valve outlet. An check valve occlusion is configured to (i) be disposed integral with or immediately adjacent the shooting pot assembly, and (ii) prevent resin leakage to the valve inlet in response to a melt discharge operation of the shooting pot assembly.  
      According to a second aspect of the present invention, a unique combination of structure and/or steps is provided for an injection molding shooting pot assembly check valve configured to be installed in a coinjection hot runner with a coinjection nozzle, the coinjection nozzle having at least two melt channels ending at the same gate. Preferably, the check valve includes an inlet melt channel and an outlet melt channel configured to provide melt to the coinjection nozzle. A shooting pot cylinder is disposed between the inlet melt channel and the outlet melt channel. A shooting pot piston is configured to move within the shooting pot cylinder to discharge melt from the shooting pot cylinder to the outlet melt channel. A check valve is disposed integral with or immediately adjacent the shooting pot cylinder and is configured to prevent melt leakage to the melt inlet channel in response to the discharge of melt from the shooting pot cylinder.  
      According to a third aspect of the present invention, a unique combination of structure and/or steps is provided for an injection molding shooting pot assembly check valve configured to be installed in a coinjection hot runner with a coinjection nozzle, the coinjection nozzle having at least two melt channels ending at the same gate. The check valve includes a shooting pot piston, and a shooting pot cylinder that is configured to discharge melt to an outlet melt channel upon activation of the shooting pot piston. A check valve is disposed integral with or immediately adjacent to the shooting pot cylinder, and is configured to reduce leakage of melt from the shooting pot cylinder to an inlet melt channel in response to at least partial discharge of the melt from the shooting pot cylinder upon activation of the shooting pot piston.  
      According to a fourth aspect of the present invention, a unique combination of structure and/or steps is provided for an injection molding shooting pot assembly check valve configured to be installed in a coinjection hot runner with a coinjection nozzle, the coinjection nozzle having at least two melt channels ending at the same gate. The check valve includes a shooting pot cylinder, and means for causing a check valve occlusion to move within a check valve chamber that is disposed integral with or immediately adjacent to the shooting pot cylinder, to cause the melt to at least partially fill the shooting pot cylinder. Means are provided for discharging the melt from the shooting pot cylinder through a melt outlet channel, and through a coinjection nozzle into a mold cavity. The means for discharging causes the check valve occlusion to move within a check valve chamber to substantially reduce melt leakage from said shooting pot cylinder to a melt inlet channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Exemplary embodiments of the presently preferred features of the present invention will now be described with reference to the accompanying drawings.  
       FIG. 1  is a schematic view of a known coinjection hot runner manifold assembly.  
       FIG. 2  is an enlarged view of  FIG. 1  showing a check valve location.  
       FIG. 3  is an enlarged view of  FIG. 2  showing the check valve assembly.  
       FIG. 4  is a schematic view of part of a coinjection hot runner manifold assembly according to a first embodiment of the present invention.  
       FIG. 5  is a schematic view of part of a coinjection hot runner manifold assembly according to a second embodiment of the present invention.  
       FIG. 6  is a schematic view of part of a coinjection hot runner manifold assembly showing a further alternative according to the preferred embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS  
      1. Introduction  
      The present invention will now be described with respect to several embodiments in which an integral check valve is used in the shooting pot of a plastic coinjection molding machine. The coinjection process is partially injecting a first material through the gate followed by partially injecting a second material through the same gate.  
      2. The structure of the First Embodiment  
       FIG. 4  shows a portion of a coinjection hot runner assembly according to the first embodiment according to the present invention. A first manifold  20  has shooting pots and melt channels (not shown) for supplying a first resin “A” to a first melt channel  21  in a nozzle  22 . A second manifold  23  has at least one shooting pot assembly  24  connected via a melt channel  25  for supplying second resin “C” to a second melt channel  26  in the nozzle  22 . The first melt channel  21  and the second melt channel  26  exit the nozzle  22  at the same gate opening. The shooting pot assembly  24  preferably comprises a shooting pot cylinder  27 , a shooting pot piston  28 , and a check valve  29 . The check valve  29  is preferably housed within or partially within (i.e., integral with) the shooting pot cylinder  27 . Alternatively, the check valve  29  could be disposed immediately adjacent to the shooting pot cylinder  27 , in order to conserve space. Also, the preferred embodiment may be adapted for use in nozzles which co-inject three, four, or more resins.  21  Preferably, the shooting pot assembly  24  is set into the second manifold  23  such that the melt channels therein are aligned with an inlet channel  32  and an outlet  33  channel leading to/from the check valve  29  and shooting pot chamber  30 , respectively. With this arrangement, the check valve  29  will act to prevent resin from leaking back into the melt channel when the shooting pot is discharged. Preferably, a check valve  29  is provided for each shooting pot. The check valve  29  may be of any size and shape, depending upon the application.  
      In the  FIG. 4  embodiment, the check ball has a ball diameter of about 6.0 mm, a shooting pot piston diameter of about 10.0 mm, and a shooting pot cylinder overall length of about 83.0 mm. However, these dimensions can vary tremendously in size depending on the application.  
      3. The Method of the First Embodiment  
      In operation, resin supplied from the injection unit (not shown) via the inlet channel  32  of the second manifold  23  flows past the check valve  29  to fill the shooting pot chamber  30 , thereby displacing the shooting pot piston  28  upward until the predetermined shot size for the chamber  30  is made. The forward (downward) actuation of the shooting pot piston  28  by an actuator  31  causes the “C” resin in the shooting pot chamber  30  to be moved out along channels  25  and  26  to enter the mold cavity (not shown). The movement of the “C” resin by the piston  28  also causes the check valve to block the inlet channel  32  in shooting pot cylinder  27 , thereby preventing backflow of the “C” resin towards the injection unit. By including the check valve within, partially within, or adjacent to the shooting pot cylinder, the costs of manufacture, assembly, and maintenance are reduced, and space is saved in the hot runner assembly.  
      4. The Structure of the Second Embodiment  
       FIG. 5  shows a second embodiment of the present invention in which shooting pots are shown in both manifolds of a coinjection hot runner assembly. A first manifold  40  has at least one first shooting pot  41  assembly, and a melt channel  42  for supplying the first resin “A” to a melt channel  43  in the nozzle  44 . A first check valve  51  is disposed within the first shooting pot assembly  41 . Both the inlet channel  50  and the outlet channel  49  of the check valve  51  are aligned transverse to the centerline of the shooting pot  41 .  
      A second manifold  45  has at least one second shooting pot assembly  46  connected via a melt channel  47  for supplying second resin “C” to a melt channel  48  in the nozzle  44 . A second check valve  52  is disposed within the second shooting pot assembly  46 . Again, both the inlet channel  53  and the outlet channel  54  of the check valve  52  are aligned transverse to the centerline of the shooting pot  46 . The compact configuration of each shooting pot assembly containing its respective check valve allows the shooting pots in the two manifolds to be aligned coaxially, That is, shooting pot  46  is directly beneath shooting pot  41 , thereby optimizing the transverse space requirement for housing the shooting pots in their respective manifolds.  
      5. The Method of the Second Embodiment  
      In operation, the shooting pots are actuated simultaneously or sequentially according the to the coinjection molding process being employed, and their check valves operate to prevent backflow, as described above with respect to the first embodiment.  
      6. The Structure of a Further Alternative  
       FIG. 6  shows the preferred embodiments of the invention in which the inlet channel  70  is aligned coaxially with the centerline of the shooting pot  72 , and the outlet channel  71  is transverse to the centerline of the shooting pot  72 . This configuration allows the check valve chamber  73  to be extended to allow more travel for the ball, thereby enhancing decompression and/or suckback of the shooting pot. See, for example, U.S. patent application Ser. No. 10/______ entitled “CONTROL SYSTEM FOR DYNAMIC FEED COINJECTION PROCESS” (attorney docket no. 213201,00221; H-786). For example, the check valve chamber my be equal to or greater than twice the diameter of the check valve ball  74 . The previously-described embodiments aligned the check valve chamber transverse to the shooting pot centerline and consequently were limited in chamber length by the diameter of the shooting pot cylinder. In the  FIG. 7   6  embodiment, the length of the chamber faces no such restriction.  
      8. Conclusion  
      Advantageous features according to the present invention may include: 
          In a coinjection hot runner assembly, a shooting pot cylinder containing its own check valve and the associated inlet and outlet channels.     Aligning the check valve within the shooting pot cylinder so that the inlet and/or outlet channels can be oriented either coaxial to the shooting pot centerline or transverse thereto.     Aligning the inlet channel coaxially with the shooting pot centerline provides space to extend the check valve chamber thereby providing a decompression/suckback capability in the configuration.        

      Thus, what has been described is a method and apparatus for efficiently disposing a check valve within, partially within, or adjacent to the shooting pot assembly to provide enhanced sealing, reduced space requirements, and lower assembly and maintenance costs.  
      The individual components shown in outline or designated by blocks in the attached Drawings are all well-known in the injection molding arts, and their specific construction and operation are not critical to the operation or best mode for carrying out the invention.  
      While the present invention has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.  
      All U.S. patent documents discussed above are hereby incorporated by reference into the Detailed Description of the Preferred Embodiment.