Abstract:
A check valve assembly for use in a plastic injection molding machine injection unit is disclosed. The check valve utilizes a free-floating poppet member which has tapered angularly spaced-apart tapered flutes on the outer surface thereof and a self-aligning spherical valve seating surface at one end thereof. When a predetermined shot volume in front of the check valve has been filled, forward advancement of the feed screw within the injection unit causes the molten thermoplastic material to grippingly engage the tapered surfaces of the flutes causing the poppet member to move along with the backflow of thermoplastic material closing the check valve.

Description:
[0001]     The present invention relates, in general, to a poppet valve and, more particularly, to an improved poppet valve assembly for use in a plastic injection molding machine where precise shot control is critical.  
       BACKGROUND ART  
       [0002]     The plastic injection molding process typically utilizes two phases or stages—a plasticizing phase or stage followed by an injection phase or stage. Plastic injection molding machines usually utilize a heated barrel in order to plasticize or transform pelletized or granular thermoplastic material into the molten state. The barrel has a reciprocating auger-type feed screw mounted therein which forces the molten thermoplastic material through the outlet end of the barrel for injection into a die. During the plasticizing phase or stage, the feed screw rotates and forces the pelletized or granular thermoplastic material toward the forward end of the screw and barrel. As the pelletized or granular thermoplastic material flows toward the forward end of the feed screw and barrel, it is transformed into the molten state by a combination of frictional heat generated by the movement of the thermoplastic material against the screw and the inner surface of the barrel and conductive heat transferred through the wall of the barrel from electrical resistance heaters mounted on the exterior of the barrel. Continued rotation of the feed screw results in the molten thermoplastic material flowing to the end of the screw where it passes through a check valve into a cavity. As the molten thermoplastic material is received within the cavity, a differential pressure develops across the ends of the feed screw causing the feed screw to move toward the feed end of the barrel while the screw rotates. After a predetermined volume of “shot” of molten thermoplastic material is received within the cavity in front of the check valve, rotation of the feed screw is stopped by associated controls. The injection phase or stage then commences causing the feed screw to move forward toward the end of the barrel whereupon the check valve closes in response to flow of molten thermoplastic material. The “shot” of molten thermoplastic material now remaining in the cavity end of the barrel is then forced through a nozzle and into the die.  
         [0003]     There are a number of commonly used check valves that are responsive to the backflow of molten thermoplastic material in order to close same. These valve types include floating rings, reciprocating balls, and poppets. The poppet styles vary in configuration with some poppets utilizing complicated and failure-prone spring arrangements. Although the valves presently used in the injection molding industry meet with varying degrees of success, there still remains a need for a reliable, fast acting poppet valve in some applications. This is especially true where precise shot control is critical.  
         [0004]     In view of the foregoing limitations associated with presently available check valves for use in plastic injection molding machines, it has become desirable to develop a check valve that utilizes a uniquely responsive poppet member that does not require spring loading and wherein the poppet member is configured so that it is significantly more responsive to the backflow of molten thermoplastic material, thus resulting in the rapid closing of the check valve virtually immediately after the commencement of the injection phase or stage.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention overcomes the problems associated with presently available check valves for plastic injection molding machines, and other problems, by providing a check valve that utilizes a highly responsive, free floating, self-aligning poppet member that is configured so that it is substantially more sensitive to the backflow of molten thermoplastic material than presently available check valves. The poppet member utilized by the check valve of the present invention has angularly spaced-apart tapered flutes on the outer surface thereof permitting molten thermoplastic material to flow through the flutes to fill the cavity in front of the check valve. When the cavity in front of the check valve is full, the commencement of the injection stroke causes the molten thermoplastic material to attempt to backflow through the angularly spaced-apart tapered flutes causing the check valve to close. The thermoplastic material grippingly engages the angularly spaced-apart tapered flutes on the poppet member resulting in virtually no relative movement between the backflow and the poppet member causing the poppet member to move with the backflow into sealing engagement with the check valve seat. A spherical valve seating surface provided on the poppet member allows for precise and repeatable sealing engagement with the check valve seat even if the poppet member is not in longitudinal alignment with same. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a cross-sectional view of a front discharge valve containing the poppet valve assembly of the present invention and illustrates the attachment of the front discharge valve to the end of the feed screw within the outlet portion of a conventional plastic injection molding machine.  
         [0007]      FIG. 2  is a cross-sectional view of the poppet valve assembly of the present invention.  
         [0008]      FIG. 3  is a perspective view of the poppet member utilized by the poppet valve assembly of the present invention and illustrates the equally angularly spaced-apart tapered flutes and the adjacent angularly spaced-apart ribs on the outer surface of the poppet member.  
         [0009]      FIG. 4  is a top plan view of the poppet member utilized by the poppet valve assembly of the present invention and illustrates a tapered flute on the outer surface of the poppet member.  
         [0010]      FIG. 5  is a right end elevation view of the poppet member utilized by the poppet valve assembly of the present invention and illustrates the spherical surface thereon.  
         [0011]      FIG. 6  is a left end elevation view of the poppet member utilized by the poppet valve assembly of the present invention and illustrates the rounded surface thereon.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring now to the drawings where the illustrations are for the purpose of describing the preferred embodiment of the present invention and are not intended to limit the invention disclosed herein,  FIG. 1  is a cross-sectional view of a front discharge valve  10  containing the poppet valve assembly  12  of the present invention and illustrates the threaded attachment of the front discharge valve  10  to the end of a feed screw  14  within the injection unit  16  of a conventional plastic injection molding machine. The front discharge valve  10  is comprised of a body member  18  having a substantially cylindrical cross-section with a reduced diameter threaded portion  20  adjacent one end thereof and a blind bore  22  within the oppositely disposed end thereof. The reduced diameter threaded portion  20  is threadably received within a threaded blind bore  24  in end  26  of feed screw  14 . The blind bore  22  within body member  18  is sized so as to receive the poppet valve assembly  12  of the present invention and fluidically communicates with the molten thermoplastic material by a plurality of equally angularly spaced-apart cross-bores  28  in body member  18 , each of which joins a longitudinally extending through bore  30  in body member  18 . Body member  18  and feed screw  14  are received within the bore  32  of an outlet barrel  34  in a conventional plastic injection molding machine. A barrel end cap  36  having an inwardly tapered conical surface  38  therein is attached to the outlet end of the outlet barrel  34  and functions to transfer molten thermoplastic material to a die (not shown). A nozzle (not shown) is attached to the outlet of end cap  36 . A plurality of heater bands  40  are mounted around the outer surface of end cap  36  and outlet barrel  34  and are utilized to assist in the melting of the pelletized or granular thermoplastic material and to keep the aforementioned material in the molten state as it is being delivered by the feed screw  14 .  
         [0013]     The poppet valve assembly  12  is comprised of a holder  42 , an insert  44  received within one end of the holder  42  and a poppet member  46  slidingly movable within the holder  42 . The holder  42 , insert  44  and the poppet member  46  are received within blind bore  22  in the outlet end  48  of body member  18  of front discharge valve  10 .  
         [0014]     Referring now to  FIG. 2 , which is a cross-sectional view of the poppet valve assembly  12 , the holder  42  is generally cylindrical in cross-section and has a substantially smooth outer surface  50  that terminates in a threaded outer surface  52 . One end  54  of the holder  42  has a bore  56  therein which communicates with one end of a through bore  58  within holder  42  by means of a substantially continuous tapered surface  60 . The other end of through bore  58  communicates with a blind bore  62  in the oppositely disposed end  64  of holder  42 . A substantially continuous shoulder  66  is provided at the junction of blind bore  62  and through bore  58 . A chamfer  68  is provided on the end  64  of the holder  42  adjacent the threaded outer surface  52  of the holder  42  to assist in the insertion of the holder  42  within the body member  18 . The diameter of bore  56  is less than the diameter of through bore  58  which is less than the diameter of blind bore  62  in holder  42 .  
         [0015]     The insert  44  is generally circular in cross-section and has a bore  80  provided in end  82  thereof. Bore  80  terminates in a substantially continuous tapered valve seating surface  84  which terminates in oppositely disposed end  86  of insert  44 . Chamfers  88 ,  90  are provided on ends  82 ,  86 , respectively, of insert  44 . The outer diameter of insert  44  is slightly less than the diameter of blind bore  62  in holder  42  permitting insert  44  to be received within blind bore  62  in holder  42  and to be positioned therein so that end  86  of insert  44  contacts shoulder  66  in blind bore  62  in holder  42 . It should be noted that insert  44  may be an integral part of body member  18 .  
         [0016]     Poppet member  46  is slidingly received within through bore  58  in holder  42  and is captured at one end thereof by substantially continuous tapered surface  60  in holder  42  and at the other end thereof by continuous tapered valve seating surface  84  on insert  44 . Poppet member  46  is substantially circular in cross-section and has an outer diameter slightly less than the diameter of through bore  58  in holder  42  permitting poppet member  46  to be slidingly moveable therein. One end  100  of poppet member  46  has a rounded surface  102  defined by a first radius whereas the oppositely disposed end  104  of poppet member  46  has a spherical surface  106  defined by a second radius. The first radius defining rounded surface  102  is greater than the second radius defining spherical surface  106 . End  100  of poppet member  46  defined by rounded surface  102  terminates in a substantially cylindrical surface  108  which, in turn, terminates in a substantially circumferential outwardly tapered surface  110 . Circumferentially outwardly tapered surface  110  terminates in cylindrical outer surface  112  of the poppet member  46 . The cylindrical outer surface  112  of poppet member  46  terminates in a substantially circumferentially inwardly tapered surface  114 . Circumferentially inwardly tapered surface  114  joins cylindrical outer surface  112  with end  104  of poppet member  46  defined by spherical surface  106 . As shown in  FIG. 3 , four equally angularly spaced-apart tapered flutes  120  are provided in the cylindrical outer surface  112  of poppet member  46 . The root diameter of the flutes  120  decreases from end  104  to end  100  of poppet member  46  resulting in the formation of four equally angularly spaced-apart ribs  122  which define the cylindrical outer surface  112  of poppet member  46 . The equally angularly spaced-apart tapered flutes  120  are outwardly tapered from end  104  to end  100  of poppet member  46 . Thus, the transverse width of a flute  120  between two adjacent spaced-apart ribs  122  increases from end  104  to end  100  of poppet member  46  and the transverse width of each rib  122  decreases from end  104  to end  100  of poppet member  46 .  
         [0017]     The front discharge valve  10  containing the poppet valve assembly  12  is installed in a conventional plastic injection molding machine and the poppet valve assembly  12  operates in the same manner as other ball and poppet style check valves in such molding machines. As the feed screw  14  within the injection molding machine turns and advances molten thermoplastic material through the front discharge valve  10 , the flowing thermoplastic material pushes poppet member  46  away from the tapered valve seating surface  84  on insert  44  causing the front discharge valve  10  to open permitting thermoplastic material to flow between flutes  120  on poppet member  46  and the surface defining bore  58  in holder  42 . Once the cavity in front of the front discharge valve  10  is full, the feed screw  14  stops turning and moves toward the end cap  36  causing thermoplastic material to be injected into the die and causing pressure to increase in front of the discharge valve  10  which, in turn, causes the thermoplastic material to start moving in the opposite direction through flutes  120  and the surface defining bore  58  in holder  42 . The “backflowing” thermoplastic material grippingly engages the poppet member  46  causing poppet member  46  to move with the thermoplastic material which, in turn, causes in spherical end  104  of poppet member  46  to sealingly engage the tapered valve seating surface  84  on insert  44 , thus closing the front discharge valve  10 .  
         [0018]     An advantage provided by the poppet valve assembly  12  of the present invention over similar poppet valve assemblies resides in the tapered surfaces of the spaced-apart flutes  120  which grippingly engage the thermoplastic material as the material starts to backflow through the valve. This increased resistance induced by the tapered flutes  120  causes the front discharge valve  10  to close more rapidly than a typical poppet member having straight cut flutes on the surface thereof. In addition, the utilization of a spherical surface  106  on end  104  of poppet member  46  to engage continuous tapered surface  84  on insert  44  in order to close valve  10  makes the poppet member  46  self-aligning, thus allowing the poppet member  46  to freely float within bore  58  without being precisely longitudinally aligned with bore  80  in insert  44 .  
         [0019]     Certain modifications and improvements will occur to those skilled in the art upon reading the foregoing. It is understood that all such modifications and improvements have been deleted herein for the sake of conciseness and brevity, but are properly within the scope of the following claims.