Abstract:
An injection molding system is disclosed. The system includes a multiple valve gated nozzle. The flow through each valve gate is determined by individually operated valve pins. Each valve pin is independently controlled by a separate actuation unit. In order to achieve a tight pitch between the valve pins, the actuation units are placed in a stacked configuration, with the valve pin controlled by the upper actuation unit passing through the lower actuation unit. The valve pin of the lower actuation unit is offset from a center of the upper actuation unit to allow for the unimpeded passage of the valve pin from the upper actuation unit through the lower actuation unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to injection molding and, more particularly, to a valve gated hot runner injection molding apparatus for tight pitch, single- or multi-material applications. 
     2. Background of the Invention 
     A valve gated injection molding apparatus is well known, as shown and described in U.S. Pat. No. 4,380,426 incorporated herein in its entirety by reference thereto. Usually a valve pin has a cylindrical or tapered front end and reciprocates between a retracted open position and a forward closed position in which the front end is seated in a gate. In some applications, the valve pin functions in the reverse direction and closes in the retracted position. 
     A valve gated injection molding apparatus for coinjecting and/or sequentially injecting two different materials through a single gate with multiple valve pins into a mold cavity is also well known, as shown and described in U.S. Pat. No. 5,238,378 incorporated herein in its entirety by reference thereto. For a greater level of control over the gating process, each individual valve pin may be independently controlled by separate actuation units. 
     Also well-known in the art is a multi-cavity valve gated injection molding apparatus having a plurality of nozzles, wherein each nozzle body is provided with a plurality of equally spaced valve pin bores with a corresponding plurality of valve pins. Such an apparatus in shown and described in U.S. Pat. No. 6,162,044 incorporated herein in its entirety by reference thereto. Each nozzle of the apparatus includes multiple valve pins, but all of the valve pins are controlled by a single actuation unit. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an injection molding system having a single or a plurality of nozzles that include valve gate technology. Each nozzle body is provided with at least two flow channels. In some circumstances one of the flow channel is a dominant flow channel and the other is a secondary flow channel. Each flow channel is fitted with a gating element, such as a valve pin, and each valve pin is independently moved and controlled using an actuation unit, such as a fluid or gas piston. Other actuation means of the valve gating means, such as electrical or mechanical are contemplated in the current invention. Each actuation unit is located for example linearly above its respective flow channel or in some instances in a lateral position with respect to the nozzle. 
     According to one aspect of this invention a primary actuation unit that controls a melt in the dominant flow channel has its valve pin centered on a longitudinal central axis of the actuation system, which is laterally offset from a longitudinal center axis of the nozzle assembly. A secondary actuation unit is located offset from the primary actuation unit with its valve pin alignment offset from the longitudinal central axis of the actuation system. The secondary actuation unit is provided with an opening so that the valve pin of the primary actuation unit can pass through the lower piston arrangement. As a result of this arrangement, the pitch from center to center of each valve pin is minimized. As such, the mold gates facing the nozzle may be arranged in a closer configuration to feed one or several mold cavities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
         FIG. 1  is a sectional view of a dual valve gated injection nozzle with independent actuation of the valve gates in accordance with one aspect of the present invention. 
         FIG. 1A  is a sectional schematic of the injection nozzle of  FIG. 1  showing the machine nozzles for the two materials. 
         FIG. 2  is an enlarged sectional view of the actuation system of  FIG. 1 . 
         FIG. 3A  shows a first step of the operation of the system of  FIG. 1 . 
         FIG. 3B  shows a second step of the operation of the system of  FIG. 1 . 
         FIG. 4  shows a second application of the nozzle system of  FIG. 1 . 
         FIG. 5  shows a third application of the nozzle system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is now described with reference to the figures, where like reference numbers indicate identical or functionally similar elements. 
     Referring now to  FIG. 1 , a valve gated injection molding system  100  is shown. System  100  includes a nozzle assembly  102  and an actuation system  104 . A longitudinal axis  136  of nozzle assembly  102  is shown for reference. 
     Nozzle assembly  102  functions, to a certain extent, similarly to known injection nozzles and includes a nozzle body  138 . Melt is introduced into a first melt channel  105  and a second melt channel  107  of the nozzle body  138  via first and second manifold melt channels  106 ,  108  of a melt distribution manifold  122 . The melt flowing through first melt channel  105  and first manifold melt channel  106  may be the same material as the melt flowing through second melt channel  107  and second manifold melt channel  108 , or two different materials may be flowing through each set of channels. Also, the diameter of first melt and first manifold melt channels  105 ,  106  may be the same as the diameter of second melt and second manifold melt channels  107 ,  108 , or the diameters of the two set of melt channels may be different. Such design considerations are heavily dependent upon the type of product to be produced by system  100  and/or the molding process being implemented. 
     As shown in  FIG. 1 , first manifold melt channel  106  is located closer to an outlet surface  109  of manifold  122  than second manifold melt channel  108 . While not necessary for the operation of the present invention, offsetting the manifold melt channels  106 ,  108  allows for the later inclusion of additional melt channels or the modular addition of separate manifolds. Separate manifolds may be necessary if two different materials are used that have substantially different melt characteristics that require maintaining the melt at different temperatures. 
     Connecting manifold  122  to nozzle assembly  102  is a melt connector  121 . Melt connector  121  includes a first connection melt channel  123  and a second connection melt channel  125 . Melt connector  121  is a bushing used to connect manifold melt channels  106 ,  108  to nozzle melt channel  105 ,  107 . Manifold melt channels  106 ,  108  are disposed in this embodiment towards the exterior perimeter of manifold  122 . Nozzle melt channels  105 ,  107  are disposed closer to longitudinal axis  136  than manifold melt channels  106 ,  108 . As such, first connection melt channel  123  is disposed diagonally through melt connector  121  so that first connection melt channel  123  fluidly connects first manifold melt channel  106  to first nozzle melt channel  105 . Similarly, second connection melt channel  125  is disposed diagonally through melt connector  121  so that second connection melt channel  125  fluidly connects second manifold melt channel  108  to second nozzle melt channel  107 . 
     As the melt flows through the first and second melt channels  105 ,  107  of the nozzle body  138 , the temperature of the melt is maintained by heating element  124 . Heating element  124  may be coiled, embedded, clamped, and/or cast to nozzle body  138 . Further, heating element  124  may be comprised of a thin or thick film heating element. The melt flows through first and second valve gates  114 ,  116  into a mold cavity (not shown). The flow of the melt through each valve gate  114 ,  116  is independently controlled. First valve gate  114  is open when first valve pin  110  is not seated within first valve gate  114 . Similarly, second valve gate  116  is open when second valve pin  112  is not seated within second valve gate  116 .  FIG. 1A  shows first valve gate  114  in the open position and second valve gate  116  in the closed position. 
     The flow of the melt through first and second valve gates  114 ,  116  is controlled by actuation system  104 . Actuation system  104  is located on the opposite side of the manifold  122  as the nozzle assembly  102 . First and second valve pins  110 ,  112  extend through manifold  122  into actuation system  104 . 
     With reference now to  FIG. 2 , movement of the first valve pin  110  is controlled by a first actuation unit  118 . First actuation unit  118  includes a first piston driving mechanism  204  and a first piston  208 , which is slidable within a cylinder  217 . First valve pin  110  is axially movable through a first valve pin channel  212 . First valve pin channel  212  extends through a second actuation unit  120 , manifold  122 , and melt connector  121 . 
     First piston driving mechanism  204  may be any of several mechanisms known in the art, for example, pneumatic or hydraulic systems, bladder pistons, or cam and lever systems. A pneumatic driving system operates by hooking an external air source to the piston driving mechanism with valves controlled by a timing circuit which applies and releases the pressure in a repetitive timed sequence in conjunction with the application of pressure to the melt from the molding system. A hydraulic driving system operates in the same manner as the pneumatic system, only hydraulic fluid is substituted for air. 
     In another embodiment, first piston driving mechanism  204  may be a bladder piston, as shown and described in the copending U.S. Appl. No. 60/363891 filed on Mar. 14, 2002 by the same assignee which is incorporated herein in its entirety by reference thereto. A bladder piston is an expandable and elongated bag which shortens in length when filled with a pressurized fluid like air, water or oil. One end of the bladder is affixed to a valve pin such that as the bladder is pressurized it contracts in length the valve pin is unseated from the valve gate allowing the melt to flow into the mold cavity. Similarly, depressurizing the bladder causes the bladder to increase in length, which seats the valve pin in the valve gate and stops the flow of the melt into the mold cavity. 
     As first piston driving mechanism  204  cycles through the sequence, first piston  208  is driven up and down. This causes first valve pin  110  to be driven downwards and upwards, thereby seating and unseating first valve pin  110  within first valve gate  114 . 
     A longitudinal axis  216  of actuation system  104  is slightly offset from longitudinal axis  136  of nozzle assembly  102 . However, first valve pin  110  of first actuation unit  118  is centered on longitudinal axis  216 . 
     In order to minimize the space required to control movement of the valve pins  110 ,  112  independently, the second actuation unit  120  is disposed between first actuation unit  118  and manifold  122 . Second actuation unit  120  includes a second piston driving mechanism  206  and a second piston  210 , which is movable within a second cylinder  219 . Second valve pin  112  is axially movable through a second valve pin channel  214 . Second valve pin channel  214  extends through manifold  122  and melt connector  121 . 
     First valve pin channel  212  passes through second actuation unit  120  to allow first valve pin  110  to reach nozzle assembly  102  unimpeded. A length of second valve pin  112  and second valve pin channel  214  are offset from longitudinal axis  216  in order to provide for the disposition of first valve pin channel  212  through second actuation unit  120 . As shown in  FIG. 1A , a rod  140  is disposed on second piston  210  in order to balance the operation of second piston  210  due to the offset positioning of second valve pin  112 . Rod  140  may also be a dowel or other similar component. 
     Second piston driving mechanism  206  may be any of the various driving mechanisms as mentioned above with reference to first piston driving mechanism  204 . As second piston driving mechanism  206  cycles through the sequence, second piston  210  is driven up and down. This causes second valve pin  112  to be driven downwards and upwards, thereby seating and unseating second valve pin  112  within second valve gate  116 . 
     This arrangement of first and second actuation units  118 ,  120  permits the minimization of a pitch  202  between the longitudinal center axis of first valve pin  110  and second valve pin  112 . Pitch  202  may be as small as less than 7 mm. This tight pitch configuration of the valve pins  110 ,  112  makes possible the close setting of valve gates  114 ,  116  of nozzle assembly  102  while maintaining independent actuation of valve gates  114 ,  116 . 
     If a greater number of valve gates are desired with independent control from first and second valve gates  114 ,  116 , additional actuation units can be stacked upon the existing actuation units. Additional offset valve pin channels would be provided through first and second actuation units  118 ,  120 . Rod  140  could be eliminated as the additional valve pins would provide the necessary balancing of the piston action. 
     A bladder piston actuation unit may be employed for each valve pin of a multiple valve pin arrangement which may or may not require stacking or a lateral offset of each actuation unit 
       FIGS. 3A and 3B  show one possible application of a tight pitch dual valve gate configuration, the overmolding of a small part. A mold cavity  302  is shaped to mold a dual material small part, such as a cap. A mold core  304  is disposed within mold cavity  302  in order to form a secondary mold cavity  306 . Secondary mold cavity  306  is filled with a first material through second valve gate  116 , which is in the open position. To prevent a second material from entering secondary mold cavity  306 , first valve gate  114  is in the closed position. 
       FIG. 3B  shows the second step of the overmolding process in which a mold core  304  has been moved axially away from the valve gates  114 ,  116 . A second material is injected into mold cavity  302  through first valve gate  114 , which is in an open configuration to permit the flow of the second material. Second valve gate  116  is in the closed configuration to prevent further injection of the first material in to mold cavity  302 . The second material covers a first molded material piece  306   a  to form a single dual material cap. 
       FIG. 4  shows another application of the present invention. The valve gated injection molding apparatus of the present invention is shown with a mold having two separate mold cavities  440 ,  442  of the same size and shape in close proximity. In this application, two similar articles of a different color or different material may be simultaneously molded. If for some reasons there is a need to mold more parts of one color than the other, the fact that two valve pins  410 ,  412  are independently movable allows one to inject only one kind of part for any number of cycles. Also of the two materials have different molding characteristics, such as the viscosity, the parts can be still molded by reciprocating valve pins  410 ,  412  at different times. Furthermore, one can either shuttle or rotate mold cavities  440 ,  442  to provide an overmolding solution where a second color/material is injected into each cavity. 
       FIG. 5  shows another application of the present invention. The valve gated injection molding apparatus of the present invention is shown with a mold having two separate cavities  540 ,  542  of different size and shape in close proximity. In this application, two articles of the same or different color and/or same or different material may be simultaneously molded. Pressure sensors  502  are shown in the nozzle and or in the manifold that are used to control the movement of the valve pins in each melt channel, as well as the temperature of each nozzle based on the pressure readings. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.