Abstract:
A shutoff nozzle body and valve assembly operative to reduce molten plastic resin drool when the nozzle body is separated from the mold or runner system. The apparatus includes a porting system that shuts off the flow of resin through the sprue plunger of the valve nozzle body before the valve body seals on the valve seat so as to permit any resin that is within the sprue passages to drain out through the sprue plunger into the mold cavity or runner system before the sprue tip completely withdraws from the mold or runner system thereby eliminating drool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     REFERENCE TO SEQUENCE LISTING 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed generally to an injection nozzle assembly. More particularly, this invention is directed to a heated plastic flow control nozzle assembly for use in plastic molding which significantly reduces drool upon separation of the nozzle assembly from a mold or hot runner. 
     2. Description of the Prior Art 
     The use of plastic products has become widespread in all industries today. A typical molded part is made by filling a mold cavity with pressurized molten plastic, allowing the plastic to cool, and removing the molded article from the mold cavity. It is important in injection molding processes to control the flow of the resinous material in order to avoid the waste of material which increases operating costs and reduces profits. 
     A typical plastic injection machine nozzle engages a mold or a hot runner system associated with the mold. Before the mold halves are separated to permit removal of the molded plastic part, the nozzle must be separated from the hot runner or mold. This separation withdraws the nozzle from its seat in the mold or the runner and the molten plastic in the nozzle is apt to drool out. Such drool results not only in a loss of material but can cause problems in the molding process. For example, the drooling hot plastic is apt to run out into the runner system or into the mold after the part is removed. Such plastic accumulation may adversely affect the operation of the mold by not permitting the mold to close properly or inhibit proper heat exchange during cooling of the mold. Further, such drooling may result in partial voids in the runner system leading to incomplete mold cavity charging. 
     Various controls have been proposed to control the shutoff nozzle to attempt to eliminate drool. In U.S. Pat. No. 2,318,031 issued to Tucker, one type of nozzle shutoff is disclosed. Here, the nozzle utilizes a rotary valve mounted at the output of the nozzle itself. This valve in turn, is rotated by a hydraulic motor which disconnects a passage through the valve body to disconnect the flow of plasticized resin. Another valve method is shown in this patent wherein the opening of the nozzle is accomplished by a pure mechanical means. Here a valve closure has a rod connected to the valve protruding from the end of the nozzle. As the mold is closed, the rod engages the mold surface and opens the valve to allow material to flow into the mold. As the mold is opened the valve will shutoff from the pressure of the resin inside the unit. 
     U.S. Pat. No. 3,231,938 issued to Seymour, shows a spring operated nozzle means wherein the flow of plasticized resin will increase the pressure in the nozzle and cause the shut-off to be pushed against the spring, thus opening the entrance to the mold. Upon completion of the injection step, the pressure of the resin will be reduced and the spring will push the shutoff member back into its original position thereby disconnecting the flow of plasticized resin to the mold. Another U.S. Pat. No. 3,241,191 issued to Nouel, shows a spring-lever type mechanical method for operating the shutoff valve whereby resin under pressure forces the nozzle shutoff to a mid-position acting to regulate the flow of resin through the tip of the nozzle. The valve is double acting and when the mold is filled, the pressure of the resin inside the mold will force back the shutoff through a mechanical arm against a spring which shuts off the flow of resin to the mold. Here the flow of resin and spring biasing means are used to open and return the valve to its shutoff position. 
     U.S. Pat. No. 3,571,856 issued to Voelker, shows a shutoff means whereby the control is by a hydraulic actuator which is connected to a rod inside a ball and socket connected to a manifold means having an orifice opening into the mold. The rod is capable of being moved to open or shutoff the orifice to the mold. The rod operates as a valve to disconnect plasticized resin from flowing through the nozzle means through the orifice into the mold cavity. 
     Another means of shutting off or disconnecting the flow of plasticized resin through a nozzle is shown in U.S. Pat. No. 3,902,665 issued to Hendry. This patent discloses various nozzle shut-off means being operated by a fluid pressure to stop the flow of plasticized resin from the extruder into the nozzle itself. Here, the opening and closing of the nozzle shut-off means can be by a fluid means or the opening of the shut-off can be caused by the force of plasticized resin against the shut-off rod pushing the valve back to its seated position. The return to a closed position is by a compressed air or fluid means. U.S. Pat. No. 3,649,148 issued to Waltman, shows a means for controlling the orifice of a nozzle which operates using a fluid means to control the wall thickness of plasticized resin as it is extruded from the nozzle in the manufacture of blow molded bottles. 
     Rogers et al., U.S. Pat. No. 5,012,839, discloses a flow control valve intended to be used primarily with a hot runner manifold in a mold of a molding press to prevent plastic drool or seepage when the molten plastic injection nozzle is separated from the mold. The heated plastic flow control valve assembly disclosed utilizes a slide valve which is telescopingly slidable with respect to a valve body to provide positive flow control for molten plastic. The slide valve has a central plastic flow passage whose discharge openings are closed when the discharge end of the slide valve telescopes within the valve body. A coil spring surrounds the slide valve and provides the valve closing force. The body of the valve assembly is surrounded by a band heater while the sprue core portion of the valve assembly, which cooperates with the hot runner manifold in the mold, is provided with a coil heater. These two heaters are individually controllable to ensure that the plastic material in the valve assembly is kept at the proper temperature. 
     As can be seen from the above discussion of the prior art, what is needed is a nozzle assembly which will prevent plastic seepage or drooling of plastic material, thereby avoiding adverse operation of the molding process, reduce down time and loss of costly material. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention is directed towards an improved shutoff nozzle which shuts off the flow of resin without the need to receive or reduce the pressure of the molten plastic resin. The disclosed shutoff nozzle assembly includes a nozzle body, a sprue plunger, a coil spring, a valve body, and a spring guide. In the following description, the words “front” and “rear” are defined according to the flow direction of the molten plastic resin. 
     The nozzle body is generally cylindrical and preferably includes an upstream or front portion threadably connected to a downstream or rear portion. The downstream end of the nozzle rear body is adapted to connect to a mold cavity or runner system while the front end of the nozzle front body is adapted for connection to a conventional injection molding machine, a structural foam process machine, or a gas assist process machine. The nozzle body further includes an internal central passageway that is restricted to form an inlet passage at the front or upstream end and a discharge opening at the rear or downstream end. 
     The downstream portion of the nozzle body includes a valve seat and internal diameter to receive a sprue plunger which includes internal passages to allow the plastic resin to flow through the valve when the valve member is in an open position. The flow of plastic resin through the central internal passageway is controlled by a valve member and spring guide mounted within the central internal passage of the nozzle front and rear bodies. The valve member and spring guide is threadably mounted on the upstream end of the sprue plunger. As the sprue plunger slides within the central internal passage of the nozzle rear body, the valve member is moved from a position in contact with the valve seat to close the flow of plastic resin through the nozzle body to a second position away from the valve seat to allow plastic resin to flow through the internal central passageway of the nozzle body. One end of the valve member acts as a spring guide for a compression spring having one end mounted against a shoulder within the central internal passage of the nozzle front body and an opposite end mounted to the spring guide portion of the valve member which extends in a direction away from the valve seat within the internal central passage of the nozzle rear body. 
     The nozzle and valve assembly of the present invention utilizes the spring load to maintain the valve in a closed position. Further, direct plastic resin pressure acts in conjunction with the spring force to maintain the valve body onto the valve seat to terminate resin flow through the central internal passage. To initiate resin flow through the central internal passage, the complete nozzle body is moved towards a mold or runner system until a sprue tip mounted in the sprue plunger makes contact therewith. The movement is continued until there is sufficient force on the sprue plunger to overcome the combined biasing force of the compression spring as well as the force of the plastic resin pressure to lift the valve body off the valve seat. At this point there is still no resin flow. The plastic resin will begin to flow through the central internal passage after the sprue plunger has traveled a sufficient distance to move the internal passages within the plunger past the valve seat such that the plastic resin can flow into these internal passages and through the internal passages in the sprue plunger and the sprue tip, past the sprue tip and into the mold or runner system. To terminate the flow of plastic resin, the nozzle body is moved in a direction away from the mold or runner system, allowing the spring to decompress and thereby move the valve body and spring guide towards the valve seat in the nozzle rear body. At the same time, the sprue plunger and its internal passages under the force of the compression spring travel across the valve seat into the internal diameter of the nozzle rear body and terminate communication of resin flow past the valve seat, allowing the plastic resin within the sprue plunger to run into the mold or runner system. Thereafter, the valve body and spring guide are forced onto the valve seat to seal the shutoff valve and insure complete termination of plastic resin flow past the valve seat so that drooling of plastic resin from the valve sprue is completely eliminated. The force of the high-pressure plastic resin acts on the backside of the valve body to create an effective force that assists the compression spring in maintaining the valve body on the valve seat to maintain the valve in a closed position. 
     Accordingly, it is an object of the present invention to provide a flow control valve to stop plastic resin drool. 
     Another object of the present invention is to provide a self-actuating nozzle assembly that shuts off the flow of plastic resin and permits the resin in the sprue plunger to run into the mold or runner system, after the shutoff valve has stopped the flow of resin through the internal passages of the sliding sprue plunger. As the sprue plunger is further moved away from the mold, the valve body seats on the valve seat and completely stops the flow of plastic resin into the sprue plunger to thereby completely eliminate drool of plastic resin from the sprue plunger. 
     It is yet a further object of the present invention to provide a nozzle assembly that is of simple construction with few moving parts. 
     It is yet a further object of the present invention to provide a nozzle body assembly that is reliable and requires minimal operator attention. 
     It is yet a further object of the present invention to provide a self-actuating nozzle assembly that is economical, easy to manufacture and assemble, and that is safe and effective in releasing pressure from the molded article. 
     For a more complete understanding of the nozzle apparatus of the present invention, reference is made to the following detailed description and accompanying drawings in which the presently preferred embodiment of the invention is shown by way of example. As the invention may be embodied in many forms without departing from the spirit of essential characteristics thereof, it is expressly understood that the drawings are for purposes of illustration and description only, and are not intended as a definition of the limits of the invention. Throughout the description, like reference numbers refer to the same component throughout the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of the preferred embodiment of the nozzle assembly of the present invention; 
         FIG. 2  is a cross-sectional view of the nozzle assembly of  FIG. 1 ; 
         FIG. 3  is a sectional view of the downstream nozzle rear body of the invention; 
         FIG. 4  is a sectional view of the upstream nozzle front body of the invention; 
         FIG. 5  is a sectional view of the sprue plunger of the invention; 
         FIG. 6  is an isometric view of the sprue plunger of the invention; 
         FIG. 7  is an isometric view of the valve body and spring guide of the invention; 
         FIG. 8  is a sectional view of the nozzle body of  FIG. 1  illustrating the plastic resin within the nozzle body when the valve is in a closed position; and 
         FIG. 9  is a sectional view of the nozzle body of  FIG. 1  illustrating the plastic resin flow through the nozzle body when the valve is in an open position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is shown in  FIGS. 1-9  a preferred embodiment of a shutoff nozzle body and valve assembly which eliminates drool according to the present invention. The drool eliminator shutoff nozzle body and valve assembly includes a front  14  and rear  16  nozzle body, a shutoff valve body and spring guide  54 , a helical spring  56 , and a sprue plunger  36  attached to the rear nozzle body  16 . In the following description, the words “front” and “rear” are defined according to the flow direction of the molten resin. 
     The nozzle body  12  is generally cylindrical and preferably includes a front nozzle body  14  or upstream portion detachably threadably connected to a rear nozzle body  16  or downstream portion. The front nozzle body  14  or upstream portion is preferably a male threaded portion  15  which is threaded into a female rear nozzle body  16  or downstream portion having a female interior thread  17 . The nozzle body  12  includes a central passageway  18  having an inlet passage  20  and a discharge opening  22 . 
     Referring to  FIG. 4 , the front nozzle body  14  or upstream portion of the nozzle body  12  has in inlet end  24  and outlet end  26 . The outlet end  26  is open defining a portion of the central passageway  18 . The inlet end  24  is restricted thereby forming an inlet passage  28 , the internal diameter of the inlet passage  28  being smaller than the internal diameter of the central passageway  18 . An internal shoulder  30  connects the central passageway  18  with the inlet passage  28 . The inlet end  24  of the front nozzle body  14  or upstream portion of the nozzle body  12  is adapted to establish a connection between the inlet passage  28  and a conventional molding machine (not shown). 
     Referring to  FIG. 3 , the rear nozzle body  16  or downstream portion of the nozzle body  12  has an inlet end  32  and an outlet end  34 . The inlet end  32  of the rear nozzle body  16  or upstream portion of the nozzle body  12  is open defining a portion of the central passageway  18 . The outlet end  34  of the rear nozzle body  16  or upstream portion of the nozzle body  12  is restricted to receive the sprue plunger  36  (shown in  FIG. 5 ) having internal passages  38  which communicate with a discharge opening  40  in the sprue plunger  36 , the internal diameter of the discharge opening  40  being smaller than the internal diameter of the central passageway  18 . A valve seat  42  created by an internal shoulder  44  in the rear nozzle body  16  separates the central passageway  18  and the discharge opening  40 . The downstream portion of the rear nozzle body  16  of the nozzle body  12  includes an internal diameter  46  that receives the outer diameter  48  of the sprue plunger  36  shown in  FIG. 5 . The sprue plunger  36  includes an upstream end having a male threaded end portion  50  for receiving a shutoff valve body and spring guide  54  as will hereinafter be discussed. As shown in  FIG. 5 , the downstream end portion  52  of the sprue plunger  36  has an outer diameter  48  that mates with the internal diameter  46  of the rear nozzle body  16  utilizing a slip fit. Between the male threaded end portion  50  and the discharge opening  40  are a plurality of internal passages  38  which are machined at an acute angle with respect to the central axis of the sprue plunger  36  to permit molten resin to flow through the nozzle body  12 . When the mold is being filled, the resin flows through the central passageway  18  past the open valve seat  42  and into the plurality of internal passages  38  towards the discharge opening  40  of the sprue plunger  36  as illustrated in  FIG. 9 . Fluid communication of the molten resin is terminated by the shutoff valve body and spring guide  54  seating on the valve seat  42  when the molding machine has completed its injection of the molten resin into the mold or runner system, as shown in  FIG. 8  and will be discussed hereinafter. In  FIG. 6 , the shutoff valve body and spring guide  54  with a helical spring  56  (not shown) are mounted in the central passageway  18  to complete the shutoff nozzle body and valve assembly. The shutoff valve body and spring guide  54  has an internal threaded hole  58  which is threaded onto the male threaded end portion  50  of the sprue plunger  36 . One end of the shutoff valve body and spring guide  54  supports the helical spring  56  that is mounted within the central passageway  18  as shown in  FIG. 2 . One end of the helical spring  56  abuts the internal shoulder  30  of the front nozzle body  14  while the opposite end of the helical spring  56  abuts the backside or one end of the outer flange  60  of the shutoff valve body and spring guide  54 . The front face  62  of the shutoff valve body and spring guide  54  is a valve surface that seats on the complimentary valve seat  42  of the rear nozzle body  16 . 
     Although not essential for the operation of the invention, the helical spring  56  (shown in  FIG. 2 ) will be described in the context of the preferred embodiment. Other embodiments implementing alternative means for biasing the shutoff valve body and spring guide  54  against the valve seat  42  of the rear nozzle body  16  to shutoff the central passageway  18  can be envisioned. The helical spring  56  is configured to bias the shutoff valve body and spring guide  54  rearwards toward the valve seat  42  of the rear nozzle body  16 . Since the shutoff valve body and spring guide  54  is mounted to the male threaded end portion  50  of the sprue plunger  36 , the helical spring  56  also biases the sprue plunger  36  in the downstream direction. 
     As viewed in  FIGS. 8 and 9 , the drool eliminator shutoff nozzle body and valve assembly of the present invention in operation uses direct resin pressure in addition to the biasing spring force of the helical spring  56  to keep the shutoff valve body and spring guide  54  on the valve seat  42  of the rear nozzle body  16  in a closed position to prevent flow of molten plastic resin  100  through the shutoff nozzle body and valve assembly. 
     The molding cycle begins by the molding machine (not shown) advancing the shutoff nozzle body and valve assembly towards the mold or runner system inlet (not shown) as the sprue tip (not shown), mounted in the threaded passage of the discharge opening  40  of the sprue plunger  36 , advances towards the mold or runner system and upon contact, the sprue plunger  36  can no longer advance but the front and rear nozzle body  14 ,  16  continues to advance toward the mold. The relative movement of the valve seat  42  of the rear nozzle body  16  with respect to the front face  62  of the shutoff valve body and spring guide  54  lifts the front face  62  off the valve seat  42  and compresses the helical spring  56 . Resin flow into the internal passages  38  of the sprue plunger  36  does not begin until the shutoff valve body and spring guide  54  has traveled a sufficient distance to allow the inlet of the internal passages  38  to slide past the valve seat  42  of the rear nozzle body  16 . As the helical spring  56  continues to be compressed by the relative movement of the front and rear nozzle bodies  14 ,  16  with respect to the stationary sprue plunger  36 . Molten plastic resin  100  begins to flow past the valve seat  42  into the internal passages  38  of the sprue plunger  36  and along the discharge opening outer diameter  48  past the sprue tip (not shown) and into the mold or runner system, until the complete shot of molten plastic resin  100  is injected into the mold. Upon completing the injection shot, the molding machine is programmed to begin withdrawal of the shutoff nozzle body and valve assembly. As the nozzle body  12  retracts in a direction away from the mold or runner system, the sprue plunger  36  remains in contact with the mold or runner system under the influence of the helical spring  56  bias. The relative motion between the rear and front nozzle bodies  14 ,  16  and the shutoff valve body and spring guide  54  screwed to the male threaded end portion  50  of the sprue plunger  36 , results in the inlets to the internal passages  38  to slide past the valve seat  42  and shutoff the flow of molten plastic resin  100  as the internal passages  38  travel past the valve seat  42  of the rear nozzle body  16  before the front face  62  of the shutoff valve seat and spring guide  54  seats on the valve seat  42  of the rear nozzle body  16 . As the molten resin flow  100  is shutoff, the portion remaining in the internal passages  38  and discharge opening  40  of the sprue plunger  36  continues to flow into the mold or runner system. As the shutoff nozzle body and valve assembly continues to travel away from the mold or runner system, the front face  62  of the shutoff valve body and spring guide  54  will come into contact with valve seat  42  of the rear nozzle body  16  to completely seal the passage of molten plastic resin  100  through the central passageway  18  and withdraw the sprue plunger  36  and sprue tip from contacting the mold or sprue system inlet. Since all of the molten plastic resin  100  in the internal passages  38  and discharge opening  40  of the sprue plunger  36  has already emptied into the mold or runner system, there is practically no molten plastic resin  100  that is able to drool out of the sprue plunger  36  and sprue tip as it withdraws from the mold or runner system. 
     It is evident that many alternatives, modifications, and variations of the nozzle assembly and method of the present invention will be apparent to those skilled in the art in light of the disclosure herein. It is intended that the metes and bounds of the present invention be determined by the appended claims rather than by the language of the above specification, and that all such alternatives, modifications, and variations which form a conjointly cooperative equivalent are intended to be included within the spirit and scope of these claims.