Abstract:
An in-line single nozzle valve gate apparatus for injection molding comprises upper and lower matable annular cylinder bodies that house an annular dual sided piston having opposed pressure bearing upper and lower surfaces. The piston has a cross beam to which a valve gate pin is attached for movement therewith. The valve gate pin passes through a sprue bushing flow path to selectively open and close a part cavity gate. An interface is provided to receive molten plastic from the injection machine nozzle and pass it into the sprue bushing flow path. The cylinder bodies reside largely outside of the mold plate architecture to lessen thermal damage too piston seals.

Description:
FIELD OF THE INVENTION 
     This invention in general relates to plastic injection molding technology and, more particularly, to the structure of an in-line single injection molding nozzle having a selectively actuable valve gate to regulate the flow of molten plastic into a mold cavity. 
     BACKGROUND OF THE INVENTION 
     Injection molding is a well-known process for producing parts from both thermoplastic and thermosetting plastic materials. In the process, plastic material is fed into a heated barrel to become molten, mixed, and then forced under pressure via flow paths into a mold cavity whose shape complements the shape of the final part. Afterwards, the cavity is cooled causing the plastic to harden as the final part. The mold is then opened, and the part removed along with any hardened plastic that may remain in the flow channels upstream of the part cavity. 
     Molding architectures generally involve the use of a series of mating plates for delivering and distributing the molten plastic to one or more cavities. The plates are held together against one another by a hydraulic clamping arrangement during the molding cycle. The clamping arrangement typically utilizes a fixed plate on one end of the mold plate stack and a moveable plate that travels between open and closed positions during the mold cycle. The amount of force required to maintain mold plates in contact with one another during the injection portion of the cycle is referred to as the clamping force and can be considerable, usually measured in tons. 
     In many molding architectures, melt flows in a more or less straight line from the injector nozzle to the gate of the part cavity. In such in-line configurations, use is often made of a valve gate pin to open and close the cavity gate to regulate flow into the cavity. 
     Various methods and mechanisms of varying complexity have been used to selectively control the actuation of in-line valve gate pins. All require the application of considerable force to the pin for proper control of the gate. In addition, any design must manage the thermal environment of the mold architecture and be sensitive to the possibility of deleterious effects caused by the presence of high heat generated by components along the flow path, including heat sources found in the various plates typically employed. 
     In many instances, use has been made of pneumatic reciprocating pistons to move the pin between open and closed positions. Such approaches have placed mechanisms proximate the in-line flow path, more or less residing within the plate arrangement, thus resulting in complex architectures and heat management concerns. 
     For example, use has been made of small pistons whose sealing O-rings are in direct contact with heated flow steel. In another approach, a piston was placed in the top clamp plate to keep it more or less cool by placing it remotely from down stream heaters. Another approach placed the entire actuating mechanism above the locating ring and employed a small piston, but subjected O-rings to deleterious heat. 
     Other approaches have located the actuating mechanism out of the direct in-line flow path. For example, external pistons have been used to drive a cam to move the pin. Another has the piston displaced with respect to the in-line path using a rocker arm extending into the in-line path to move the pin. Another out of line approach used a motor driven spline shaft to drive a rack in the pin. 
     While many approaches have been used for in-line valve gate actuators, a need still exists for a solution that addresses various unsolved problems. 
     Consequently, it is a principle object of this invention to provide improved in-line valve gate pin actuation. 
     It is still another object of the present invention to provide high pin force for in-line valve gate actuation. 
     It is yet another object of the present invention to provide in-line valve gate actuation mechanisms that are compact, simple, and reliable. 
     It is another object of the present invention to provide in-line valve gate actuators that can process most highly filled and unfilled commodity resins. 
     It is yet another object of the present invention to provide a pneumatic actuating cylinder within an integrated mold locating ring to lessen deleterious thermal effects on piston seals. 
     It is still another object of the present invention to provide valve gate actuators that move with in-line action to reduce wear. 
     It is yet another object of the present invention to provide in-line valve gate actuation with the ability to easily change nozzles to accommodate a variety of applications. 
     Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter when the following detailed description is read in connection with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     This invention generally relates to injection molding technology, and particularly, to the design of an in-line single nozzle valve gate apparatus. The apparatus comprises upper and lower matable annular cylinder bodies structured to receive an annular dual sided piston having opposed pressure bearing upper and lower surfaces. When mated, the inner surfaces of the upper and lower cylinder bodies define a central through-hole accessible through an annular circumferential slot formed between the inner surfaces of the mated upper and lower annular cylinder bodies. Extending through the annular slot is a cross beam that forms a bridge between the inner surfaces of the piston, approximately midway between its opposed upper and lower pressure bearing surfaces. 
     Extending through the cylinder central through-hole is an injection machine interface. The injection machine interface has the general from of a cylinder. The top of the interface cylinder is provided with a spherical cap sealing surface to mate with the injection machine nozzle from which it receives pressurized molten plastic. The bottom of the interface cylinder is provided with a centrally located groove that extends vertically to provide space for receiving the cross beam so that it can move up and down within the groove. 
     The machine interface sealing surface has at least one, but preferably two, flow paths that are angled so as to simultaneously extend outwardly and downwardly to travel around the cross beam groove where they terminate as spaced apart holes in the bottom surface of the interface. 
     The apparatus also has a heated sprue bushing having an elongated body provided with a central flow path. The body has a head section that has two angled flow paths that mate with the two flow paths in the bottom surface of the injection machine interface. Molten pressurized plastic is received in the sprue bushing flow paths to enter the sprue bushing&#39;s central flow path at the end of which is a removable tip having a flow aperture that mates with the cavity gate. 
     Extending vertically trough the sprue bushing central flow path is a valve gate pin having an upper end connected to the piston cross beam and a lower end configured to open and close the cavity gate to regulate the flow of molten plastic to the part cavity. 
     The annular piston and upper and lower annular cylinder bodies are configured and arranged with respect to another so that head spaces are formed between the piston&#39;s upper and lower pressure bearing surfaces and corresponding upper and lower internal pressure bearing surfaces located, respectively, in the upper and lower annular cylinder bodies. The head spaces are provided with seals in the form of o-rings. Ports connected to pressurized air sources (or other suitable fluid) are provided to controllably cause the annular piston to move up and down so that the valve gate pin opens and closes the cavity gate. 
     The geometry of the upper cylinder body is shaped to act as the locating ring for the system to align its various parts with the nozzle of the injection molding machine while also permitting the annular dual sided piston to travel within a space that is largely outside of the mold plates. This allows the piston seals to operate in lower thermal environments than they might otherwise experience because they are more remote from thermal sources in other mold parts thus lessening damaging high temperature effects. 
     Throughout the system, judicious use of air gaps is made to provide thermal barriers to isolate thermally sensitive features from high temperature sources and their damaging effects. 
     The geometry of the dual sided annular piston is preferably minimized in overall height while maximizing the size of its overall pressure surfaces to optimize the force to drive the gate pin while still residing within the industry standards for the size of a locating ring. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
       The structure, operation, and methodology of the invention, together with other objects and advantages thereof, may best be understood by reading the detailed description to follow in connection with the drawings in which each part has an assigned label and/or numeral that identifies it wherever it appears throughout the various figures where: 
         FIG. 1  is a diagrammatic partially sectional elevational view showing an in-line single nozzle valve gate in accordance with the invention utilized within various plates of a mold; 
         FIG. 2  is a diagrammatic exploded perspective view of the single nozzle valve gate of  FIG. 1 ; 
         FIG. 3  is a diagrammatic exploded perspective view of the single nozzle valve gate of  FIG. 2  from a different perspective and sectioned in half; and 
         FIG. 4  is a diagrammatic perspective sectioned elevational view of the single nozzle valve gate of  FIG. 1  along with various mold plates which are also shown in section. 
     
    
    
     DETAILED DESCRIPTION 
     This invention generally relates to injection molding technology and, more particularly, to the design of an in-line single nozzle valve gate apparatus. 
     Referring now to  FIG. 1 , there is shown a plastic injection mold system designated generally at  10 . Injection molding system  10  is used to manufacture parts from plastic in a well-known manner. During the manufacturing process, plastic pellets are placed in a large hopper which then feeds the pellets into a heated chamber where the pellets are melted into a flowable state. Afterwards, the melted plastic is injected into a molding system. Injection is achieved via an injection machine screw that is advanced by a drive unit and injection cylinder through an injection machine nozzle  12 . Then, the melted plastic travels to a single nozzle valve gate apparatus generally designated at  14 . The single nozzle valve gate apparatus  14  is in accordance with the invention. The pressurized plastic melt travels through the nozzle apparatus  14  in a manner to be described, eventually exiting it, to fill a gated part cavity  16  formed in the mold “B” plate, here designated at  18 . 
     As seen in  FIG. 1 , apparatus  14  resides in the various mold plates comprising an injection machine platen, an “A” plate  24 , and the “B” plate  18  already mentioned. The major parts of apparatus  14 , as seen in  FIG. 1 , comprise an upper annular cylinder body  20 , a lower annular cylinder body  22 , a hot sprue bushing  28 , and an injection nozzle interface  26 . 
     Referring now to  FIGS. 2, 3, and 4 , upper and lower annular cylinder bodies,  20  and  22 , respectively, are configured to mate together (See  FIG. 4 ) to receive between them an annular dual sided piston  40  having opposed pressure bearing upper and lower surfaces,  42  and  44 , respectively ( FIG. 3 ). When mated, the inner circumferential surfaces of upper and lower cylinder bodies,  20  and  22 , designated at  70  and  72 , respectively (See  FIGS. 2 and 3 ) define a through hole  74  (See  FIGS. 2  and  4 ) that is bridged by a cross beam  50  that extends from one side to another of an inner circumferential surface  43  ( FIG. 3 ) of piston  40  at a height approximately midway between its opposed upper and lower pressure bearing surfaces,  42  and  44 . 
     Extending through the central hole  74  is the injection machine interface  26  ( FIG. 4 ). The injection machine interface  26  has the general from of a cylinder. The top of the cylindrical injection machine interface  26  is provided with a curved seal  27  in the form of a concave spherical cap to mate with the corresponding shape of the injection machine nozzle  12  from which it receives pressurized molten plastic from the injection machine. The bottom of the cylindrical interface  26  is provided with a centrally located clearance groove  60  that extends vertically to provide space for receiving the cross beam  50  so that it can freely move up and down within groove  60 . Injection machine interface  26  is also heated via preferably by four heater cartridges two of which are designated generally at  29 . 
     As best seen in  FIG. 3 , the machine interface seal  27  has at least one, but preferably two, flow paths  80  and  82  that are angled so as to extend outwardly and downwardly to travel around the cross beam groove  60  ( FIG. 2 ) where they terminate as spaced apart holes  84  and  86 , respectively, in the bottom surface of interface  27 . 
     Apparatus  14  also includes an elongated heated sprue bushing  28  having a body  34  and a head  36 . Elongated heated sprue bushing  28  is provided with a central flow path  35  extending vertically from head to tip. Head  36  sits atop the body  34  and has two angled flow paths  37  and  39  that communicate, respectively, with the two flow paths  80  and  82  via the holes  84  and  86  located in the bottom surface of the injection machine interface  26 . Molten pressurized plastic is received in the hot sprue bushing flow paths  37  and  39  to enter the sprue bushing&#39;s central flow path  35  at the end of which is a removable tip  30  having a flow aperture that mates with the cavity gate  17 . Tip  30  is held in place via a retention nut  31 . 
     Extending vertically trough the hot sprue bushing central flow path  35  is a valve gate pin  32  having an upper end connected to the piston cross beam  50  and a lower end configured to open and close the cavity gate  17  to regulate the flow of molten plastic to the part cavity  16 . A heater  45  surrounds body  34  to assure that plastic remains in a flowable state so that it can proceed to the cavity  16 . 
     As best seen in  FIGS. 3 and 4 , piston  40  and upper and lower cylinder bodies,  20  and  22 , respectively, are configured and arranged with respect to another so that head spaces.  73  and  75 , respectively, are formed between the piston upper and lower pressure bearing surfaces,  42  and  44 , respectively, and corresponding upper lower internal pressure bearing surfaces.  57  and  59 , located, respectively, in the upper and lower cylinder bodies  20  and  22 . The head spaces,  73  and  75 , are provided with seals in the form of O-rings  46  and  48 , respectively. 
     Ports  100  and  102  ( FIG. 4 ) are connected to pressurized air sources (or other suitable fluid) to controllably cause the piston  40  to move up and down so that the gate pin  32  in turn opens and closes the cavity gate  17 . 
     The geometry of the upper cylinder body  20  is shaped to act as the locating ring for the apparatus  14  to align its various parts with the nozzle  12  of the injection molding machine while also permitting the annular dual sided piston  40  to travel within a space that is largely outside of the mold plates thus distancing the piston  40  from thermal sources in other mold parts whereby the piston seals (“O” rings  46  and  48 ) operate in lower thermal environments that might otherwise not exist. In this manner, the piston seals are protected from damaging high temperature effects. 
     Throughout the system, judicious use of air gaps is made to provide thermal barriers to isolate thermally sensitive features from high temperature effects. The air gaps are designated generally at  200  in  FIG. 4  and are made wide enough to effectively act as thermal insulators, keeping heat where it is needed while preventing it from traveling to parts that might be damaged from otherwise higher temperatures. 
     The geometry of the dual sided annular piston  40  is preferably minimized in overall height while the size of its overall pressure bearing surfaces  42  and  44  are maximized to optimize the available force to drive gate pin  32  while still residing within the industry standards for the size of a locating ring. With this arrangement, pin forces of 400 pounds are possible, but it will be recognized that this geometry can be appropriately scaled as needed. 
     It should also be noted that the inner circumferential surfaces  70  and  72  of upper and lower cylindrical bodies  20  and  22  are of different heights so that an annular clearance groove  51  is provided to allow cross beam  50  to travel up and down. 
     To assemble apparatus  14 , piston  40  is first placed between upper and lower cylindrical bodies  20  and  22  which are guided with locating pins  52  and  106  ( FIG. 2 ). Afterwards, interface  26  is placed in the apparatus  14  to that its groove  60  travels around cross beam  50  and seats against the top surface of heated sprue bushing head  36 . Afterward, bolts  110  are used to hold all of the parts of apparatus  12  together. 
     As can be appreciated, the inventive single nozzle valve gate apparatus is compact and mechanically reliable because it uses but few components and confines activation within the mold locating ring. Also, all components move in an in-line action which greatly reduces wear. Changing nozzles is also easy to that the apparatus can be used for a variety of applications. 
     Having set forth the invention by describing specific embodiments, others variants will be apparent to those skilled in the relevant art given the teachings of the and such other variants are intended to be within the scope of its teachings and claims.