Abstract:
An injection molding shutoff assembly that includes a chamber containing a movable body movable between rear and forward positions. In the rear position, the movable body provides a seal and prevents flow of molten plastic out the chamber inlet, called drool. When the movable body is in the forward position, one or more passages permit flow of the molten plastic around the movable body and to an exit in the chamber, leading to one or more molds. In an alternate embodiment, the apparatus also includes an elongate stem that maintains the movable body in the forward position allowing the injection molding system to decompress, thereby eliminating drool and decreasing downtime.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to injection molding machines, and in particular, a shutoff device for use in a system that transports molten polymer from the molding machine to at least one stack mold by way of a sprue bar. 
     It is known to provide stack molds in injection molding machines in which there are at least two sets of molding chambers which divide along separate parting lines. One method of delivering molten polymer to all of the molding chambers in a stack mold is by a sprue bar. A sprue bar extends from a sprue of the molding machine, along the axis of the stack mold assembly, to a central manifold located between at least two mold plates in the stack. A plurality of nozzles in turn provide conduits for the molten polymer from the manifold to each of the molding cavities, with some of the nozzles extending forward in an axial direction to those mold cavities which are forward of the manifold, and the rest of the nozzles extending rearward in an opposite axial direction to those mold cavities which are rearward of the manifold. A representative sprue bar-equipped stack mold is illustrated in FIG. 2 of U.S. Pat. No. 7,427,197 to Ciccone et al. 
     After the molten polymer has been injected under pressure into the molding chambers, the system is depressurized, the cavities are cooled, the plates forming the molding chambers are separated, and the molded piece or pieces are ejected. During this process it is necessary to disconnect the sprue from the sprue bar. Upon disconnection, molten polymer or “drool” will often be produced from the orifice of the sprue bar, resulting in the loss of raw material and additional cleanup costs. If enough molten polymer drools from the sprue bar, it may solidify and prevent complete closure of the mold, causing damage to the equipment, expensive repairs, and lost production. At the very least, this drooling effect requires removal by a technician, increasing the time between cycles. Thus, it would be desirable to provide a sprue bar shutoff device that reduces the amount of drool or prevents it completely. 
     SUMMARY OF THE INVENTION 
     The present invention provides, among other things, an improved sprue bar shutoff device that reduces or eliminates drool. According to one aspect of the invention, the shutoff device includes an exterior seat that is sealable to a nozzle of an injection molding machine that is spaced from the assembly when not engaged. The assembly also includes a first opening that provides fluid communication from the exterior seat to a chamber having an entry wall and a first sealing surface surrounding the first opening. The assembly also includes a movable body that is reciprocally movable within the chamber from a rear position proximate to the entry wall to a forward position remote from the entry wall. The movable body has a second sealing surface that seals with the first sealing surface in the entry wall when in the rear position. 
     The chamber includes an exit wall with a second opening providing fluid communication with at least one receiving unit such as a sprue bar. An elongated stem of the injection molding machine nozzle may be inserted through the first opening at or after the time of connecting the injection molding machine to the shutoff assembly. The forward end of the elongate stem contacts the movable body, preventing the movable body from moving to the rear position. 
     One or more passages of the chamber extend from the entry wall to the exit wall and transport molten polymer from the first opening to the second opening when the movable body is in the forward position. The movable body moves to the rear position when the stem is withdrawn from the first opening, which allows the first and second sealing surfaces to contact each other, thereby closing the first opening and reducing or preventing drool. Preferably, the movable body is pushed to the rear position by the molten polymer downstream of the movable body. 
     According to another aspect of the invention, an injection mold shutoff assembly includes an exterior seat that is sealable to a nozzle of an injection molding machine which is spaced from the assembly when not engaged. The assembly also includes a first opening that provides fluid communication from the exterior seat to a chamber having an entry wall and a first sealing surface surrounding the first opening. As above, a movable body is reciprocally movable within the chamber from a rear position proximate to the entry wall to a forward position remote from the entry wall. The movable body has a second sealing surface that seals with the first sealing surface in the entry wall when in the rear position. 
     Additionally, the chamber has an exit wall with a second opening providing fluid communication with at least one mold. One or more passages of the chamber extend from the entry wall to the exit wall and transport molten polymer from the first opening to the second opening when the movable body is in the forward position. The movable body moves to the rear position when the molding machine nozzle is in a nonengaged position, since it is being pushed by molten polymer downstream of the movable body which allows the first and second sealing surfaces to contact each other, thereby closing the first opening. 
     In another aspect of the invention, a method for connecting and disconnecting an injection molding machine to and from a shutoff assembly includes the steps of mating a nozzle of the injection molding machine to a seat in an exterior wall of a chamber of the shutoff assembly. The seat is in fluid communication with the chamber through a first opening extending from the exterior wall to an interior entry wall of the chamber. The interior entry wall has a first sealing surface around the first opening. 
     An elongate stem of the nozzle is advanced through the first opening into the chamber. Molten polymer then flows through the first opening, to a second opening in an interior exit wall of the chamber, and then to at least one receiving device such as a sprue bar. 
     The injection molding system is then decompressed by stopping the flow of the molten polymer through the first opening. The stem prevents the movable body from reaching a rear position where a second sealing surface of the movable body seals to the first sealing surface. Instead, the movable body is maintained in a forward position where the first and second sealing surfaces are spaced from each other and molten polymer is allowed to flow from the second opening, around the movable body, and through the first opening into the injection molding nozzle  200 . 
     The injection molding machine is disconnected from the assembly by withdrawing the stem of the nozzle from the chamber through the first opening. If there is any pressure left in the system, molten polymer downstream of the movable body will push the second sealing surface of the movable body into sealing engagement with the first sealing surface of the interior entry wall. The nozzle is then disconnected from the seat in the exterior wall of the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further aspects of the invention and their advantages can be discerned in the following detailed description, in which like characters denote like parts and in which: 
         FIG. 1  is an exploded isometric view of a sprue bar shutoff device according to the invention; 
         FIG. 2  is an exploded rear isometric view of the assembly shown in  FIG. 1 ; 
         FIG. 3  is a partial isometric view of a nozzle stem according to the invention; 
         FIG. 4  is an axial sectional view of the sprue bar assembly shown in  FIG. 1 , with a movable body or ball in a rear position; 
         FIG. 5  is an axial sectional view of the sprue bar assembly shown in  FIG. 1 , with a movable body or ball in a forward position; and 
         FIG. 6  is a flow diagram showing a method for connecting and disconnecting an injection molding machine to and from a shutoff assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , in a first embodiment of the invention, an injection mold shutoff apparatus, indicated generally at  100 , includes an exterior seat  102  sealable to a front mating surface  202  of an injection molding machine nozzle  200  that is spaced from the assembly when not engaged. A first opening  104  in an entry wall  204  of a chamber  206  provides fluid communication from the exterior seat  102  of the assembly piece  110  to the chamber  206  in assembly block  109 , which is preferably formed by mating two assembly block halves  110  and  112 . The entry wall  204  has a first sealing surface  208  surrounding the first opening and the chamber  104  includes a movable body  116  that can move within the chamber between a rear position proximate to the entry wall and a forward position remote from the entry wall. See  FIGS. 4 and 5 , respectively. Preferably, the flow of the molten polymer is sufficient to change the position of the movable body  116 . 
     Additionally, the movable body  116  has a second sealing surface  210  that seals with the first sealing surface  208  of the entry wall  204  when in the rear position. The movable body  116  may be selected to be of any shape capable of sealing with the first sealing surface of the entry wall including, but not limited to, an ellipsoid, a sphere, or a wedge. The shapes of the first and second sealing surfaces should be complimentary. 
     The chamber also has an exit wall  120  with a second opening  122  that provides fluid communication with a receiving unit such as a sprue bar. 
     An elongated stem  124  may be fixed relative to the rest of nozzle  200  or, in an alternative embodiment (not shown), may be refracted into and extended from the rest of the nozzle  200  during a process of disconnecting from, or connecting to, the assembly block  109 . As shown in  FIG. 5 , the elongated stem  124  is advanced through the first opening  104  at the time of connecting the injection mold machine nozzle  200  to the shutoff assembly block  109 . Alternatively, an articulated elongated stem (not shown) may be advanced from a refracted position in nozzle  200  through the first opening  104  after the nozzle front surface  202  is sealed to the exterior seat  102 . While it is not required that the stem push the movable body  116  from the rear position to the forward position, it is contemplated that the stem can do so. 
     Referring to  FIG. 3 , the elongated stem  124  preferably includes at least one channel  302  that permits flow of the polymer through the nozzle  200  and into the chamber  206  and even more preferably has a plurality of such channels (such as three) distributed around and parallel to the nozzle axis. Alternatively, the molten polymer may flow around the stem into the chamber. The stem also includes a preferably concave forward end  304  that contacts the movable body  116  when inserted through the first opening to prevent it from moving back to the rear position when under pressure by the molten polymer. 
     Referring to  FIGS. 4 and 5 , one or more passages  402  of the chamber formed into the halves  110  and  112  extend from the entry wall  204  to the exit wall  120 . This provides fluid communication between the first opening  104  and the second opening  122 , thereby transporting molten polymer when the movable body  116  is in the forward position. The passages  402  are sealed by the movable body  116  when the movable body  116  is in the rear position. 
     The chamber may further include a plurality of ridges  404  in the chamber that extend from the entry wall  204  to the exit wall  120  so as to constrain the movement of the movable body along a path of motion, preferably a straight, axial path. More preferably, the passages  402  and ridges  404  are placed circumferentially around an axis defined by the path of motion and the passages are spaced from each other by the ridges. 
     When the stem  124  is withdrawn from the first opening  104 , the movable body  116  moves to the rear position, allowing the first and second sealing surfaces  208 ,  210  to contact each other, thereby closing the first opening  104 . In a preferred embodiment, the movable body  116  is pushed to the rear position by the molten polymer downstream of the movable body  116  and no spring, incline, or decline is used to bias the movable body  116  to either the forward of rear position. 
     Referring to  FIG. 6 , in another aspect of the invention, a method for connecting and disconnecting an injection molding machine to and from a shutoff assembly includes the steps of mating ( 602 ) a nozzle of the injection molding machine to a seat in an exterior wall of a chamber of a shutoff assembly. The seat is in fluid communication with the chamber through a first opening extending from the exterior wall to an interior entry wall of the chamber. The interior entry wall has a first sealing surface around the first opening. 
     An elongate stem of the nozzle is advanced ( 604 ) through the first opening into the chamber. The stem may be fixed to the nozzle or may be retracted to and from an advanced position as desired by the user. Thus, the stem may be advanced into the first opening after or concurrently with the step of mating the nozzle to the seat. Similarly, the stem may be removed from the first opening before or concurrently with the step of disconnecting the nozzle from the seat. 
     Molten polymer then flows ( 606 ) through the first opening through channels  402  to the second opening in an interior exit wall of the chamber and then to one or more sprue bars or molds in fluid communication with the second opening. The molten polymer may flow around a small-diameter stem into the chamber or, alternatively, through one or more channels in the stem such as channels  302 . Preferably, the molten polymer then flows around the movable body through one or more channels  402  that provide fluid communication between the first and second openings when the movable body is in the forward position. 
     At the conclusion of injecting polymer into a mold cavity, the injection molding system is then decompressed by stopping ( 608 ) the flow of the molten polymer through the first opening. The movable body is prevented ( 610 ) by the stem  124  from reaching a rear position where a second sealing surface of the movable body  116  seals to the first sealing surface of the chamber wall. Instead, the movable body is maintained in a forward position where the first and second sealing surfaces are spaced from each other and molten polymer is allowed ( 612 ) to flow in the direction from the second opening, around the movable body, and toward the first opening. 
     The injection molding machine is disconnected from the assembly by withdrawing ( 614 ) the stem of the nozzle from the chamber through the first opening. Molten polymer downstream of the movable body is allowed ( 616 ) to push the second sealing surface of the movable body  116  into sealing engagement with the first sealing surface formed in the interior entry wall. Preferably, no spring, incline, or decline is used to bias the movable body in either the forward or rear positions. The nozzle is then disconnected ( 618 ) from the seat in the exterior wall of the chamber. As discussed previously, the stem may be removed from the first opening before or concurrently with the step of disconnecting the nozzle from the seat. 
     In summary, the method and assemblies described herein decrease material loss due to drooling, increase reliability, and lower maintenance costs. They may be used anywhere a shutoff for molten polymer is required including, but not limited to sprue bars, hot runners, cold runners, and plates. 
     While illustrated embodiments of the present invention have been described and illustrated in the appended drawings, the present invention is not limited thereto but only by the scope and spirit of the appended claims.