Abstract:
In an injection molding system providing a supply of flowable material to a mold cavity, a hot runner system comprising a sealing member located between two manifolds that concentrates the sealing pressure adjacent the melt channels.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to injection molding machines and more particuarly relates to a sealing member inserted in an injection molding machine for substantial reduction or elimination of leakage of a molten material.  
           [0003]    2. Summary of the Prior Art  
           [0004]    Hot runner assemblies are previously known and are used for molds having a plurality of mold cavities for injection molding of articles of relatively large surface dimensions. The advantage of hot runner molds is that the material is maintained in the molten state in the channels during the interval between each injection operation and the following one.  
           [0005]    Prior art hot runner molds may be divided into two groups, i.e. hot runner manifolds that are one piece and have all the melt channels formed therein and multi-piece manifolds that are connected together with “bridge” manifolds. In the multi-piece arrangement, a “bridge” manifold connects at least two sub-manifolds. Melt channels in the bridge manifold align with melt channels in the sub-manifolds. Typically, the bridge manifold is connected to a supply of pressurized molten material.  
           [0006]    The melt channels in the “bridge” manifold must align with the melt channels in the sub-manifolds when they are at a predetermined elevated temperature. The sub-manifolds typically communicate with at least one injection nozzle for the transfer of the molten material to a mold cavity. Due to thermal expansion during heat up of the various hot runner manifolds, relative motion between the “bridge” manifold and the sub-manifolds will occur. In accordance with the prior art, the flat surface of the sub-manifold will rub across the flat surface of the “bridge” manifold during heat up, and when the desired temperature is reached, the interface between the respective melt channels will align and seal off by virtue of compressive forces that build up during the heat up process. The reliability and repeatability of this seal off has proven to be problematic and leakage of the molten material between the “bridge” manifold and the sub-manifold is a recurrent problem.  
           [0007]    Therefore there is a need for an improved hot runner system that increases the reliability and repeatability of the seal between separate manifold melt channels.  
         SUMMARY OF THE INVENTION  
         [0008]    The primary objective of the present invention is to provide a means for reliably sealing the melt channel interface between a bridge manifold and a sub-manifold.  
           [0009]    Another object of the present invention is to reduce the compressive forces generated in a hot runner subsystem during heat up thereby allowing the use of fewer fasteners.  
           [0010]    Yet another object of the present invention is to reduce or eliminate the occurrence of galling and/or fretting between plates as they move during heat up.  
           [0011]    The foregoing objects are achieved by providing a sealing member or compression disk at the interface of the melt channels between the two manifolds. The sealing member preferably has at least one non-flat surface for concentrating the sealing pressure adjacent the melt channels thereby reducing the forces required to create a reliable seal therebetween.  
           [0012]    Further objects and advantages of the present invention will appear hereinbelow.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a simplified cross-sectional view of a hot runner system in accordance with the present invention;  
         [0014]    [0014]FIG. 2 is an enlarged view of the sealing member in accordance with the present invention;  
         [0015]    [0015]FIG. 3 is a cross-sectional view of the sealing member with a graph showing the sealing pressure distribution along the sealing member;  
         [0016]    [0016]FIG. 4 a - 4   g  are cross-sectional views of alternate embodiments of the sealing member in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Referring first to FIGS. 1 and 2, a hot runner subsystem in accordance with the present invention is generally shown. A sealing member  10  having a top surface  12   a  and a bottom surface  12   b  is inserted in a recess  11  of a sub-manifold  44 . A melt duct  14  in sealing member  10  is aligned with a first melt channel  48  and second melt channel  46  located in a bridge manifold  50  and sub-manifold  44  respectively. Bridge manifold  50  is located in a manifold cavity  53  formed in backing plate  30 . A plunger  51 , preferably comprised of a plunger bushing  52  and a spring means  54 , is located in pocket  64  and maintains a gap between bridge manifold  50  and backing plate  30  to reduce thermal communication therebetween. In the preferred embodiment, the spring means  50  is comprised of a series of stacked belleville springs to create a resilient spacer to adjust to thermal expansion of the various components.  
         [0018]    A plurality of fasteners  55  rigidly affixes a manifold plate  32  to backing plate  30 . Sub-manifold  44  is located in a cavity  57  formed in manifold plate  32 . A spacer  56  is located between sub-manifold  44  and backing plate  30  to reduce thermal communication therebetween. In a preferred embodiment, spacer  56  is rigidly affixed to sub-manifold  44  and is allowed to slide along a surface of backing plate  30  thereby allowing thermal expansion. However, spacer  56  could also be rigidly affixed to backing plate  30  and allowed to slide along a surface of sub-manifold  44 .  
         [0019]    An insulator  42  is located between manifold plate  32  and sub-manifold  44  to maintain a space therebetween and reduce thermal communication. In the preferred embodiment, insulator  42  is inserted into a first hole  66  located in sub-manifold  44  and extends into a second hole  68  located in manifold plate  32  such that it inhibits relative motion between the sub-manifold  44  and manifold plate  32  in the area of sealing member  10 .  
         [0020]    A nozzle assembly  40  well known in the art is in fluid communication with second melt channel  46  for the communication of fluid to a cavity  38 . In the preferred embodiment, the nozzle assembly  40  has a heater  41  as well known in the art to maintain the material therein in a flowable state. In the preferred embodiment, the nozzle assembly  40  is located in manifold plate  32  and extends through a cavity plate  34  to cavity  38 . Cavity plate  34  is aligned with manifold plate  32  by at least one alignment pin  58  as well known in the art. A core plate  36  is located in alignment with cavity plate  34  to form cavity  38  which defines the shape of the molded article to be produced.  
         [0021]    Operation of the preferred embodiment hot runner subsystem with regard to the present invention will now be described. Before an injection molding operation begins, the various components that comprise the hot runner subsystem are at room temperature. At room temperature, or in its cold condition, first melt channel  48  and melt duct  14  are purposely designed to be misaligned so that when heat is applied by heaters  60  and  62 , the components will grow due to thermal expansion and move into an aligned configuration. As bridge manifold  50  is heated by heater  62 , it will expand in a direction as shown by arrow A. Plunger  51  will allow bridge manifold  50  to slide and align first melt channel  48  with melt duct  14  in sealing member  10 . This requires that the bottom surface of bridge manifold  50  slide along the top surface  12   a  of sealing member  10 .  
         [0022]    In the prior art, this sliding would occur on the top surface of sub-manifold  44 , requiring the entire surface to be precision ground to reduce galling between the sliding surfaces. In addition, since the prior art required sealing between first melt channel  48  and second melt channel  46  to occur between these two large surfaces, extremely high pressures between the two plates were required to ensure a reliable seal. In accordance with the present invention, the sealing member  10  concentrates the sealing force directly adjacent the melt channels and also allows for reduced pressure between the plates to create a reliable seal. In addition, a reduction in the sliding surface area substantially reduces the chance of galling as the plates grow and slide due to thermal expansion.  
         [0023]    Referring now to FIG. 3, an enlarged cross-sectional view of the sealing member  10  with a sealing pressure distribution graph  16  is shown. As shown in the figure, top surface  12   a  and bottom surface  12   b  are non-flat or conical. This configuration concentrates the sealing pressure  18  along the periphery of the melt duct  14  and creates a highly reliable seal. By concentrating the sealing pressure, the force required to ensure a reliable seal is reduced, and this reduces the chance of galling as the plates move. It also reduces the number of fasteners  55  required to hold the backing plate  30  to the manifold plate  32  and further reduces the amount of bowing by the various plates during an injection cycle.  
         [0024]    Referring now to FIGS. 4 a - 4   g , an array of alternative embodiments for sealing member  10  is shown. FIG. 4 a  shows a sealing member where top surface  12   a  is angled or conical and bottom surface  12   b  is substantially flat. FIG. 4 b  shows a spherical or radiused top and bottom surface. FIG. 4 c  shows a flat bottom with a spherical or radiused top surface. FIG. 4 d  shows a top surface  12   a  that has a raised annular area that concentrates the sealing pressure along the melt duct  14  and FIG. 4 e  also shows this raised annular area on both the bottom and the top surface. FIG. 4 f  shows another alternative embodiment where the top and bottom surface have a flat portion and then a spherical or radiused portion to concentrate the sealing pressure. FIG. 4 g  shows yet another alternative embodiment where the top and bottom surface have a raised flat portion  20  that is designed to limit the amount of load transmitted to the sealing interface. As the sealing member is compressed from the sealing force, the flat portions  20  will make contact with the respective manifold surface and distribute the load over a larger surface area, thereby reducing the compressive stresses at the sealing interface.  
         [0025]    It is to be understood that the invention is not limited to the illustrations described herein, which are deemed to illustrate the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts and details of operation. The invention is intended to encompass all such modifications, which are within its spirit and scope as defined by the claims.