Abstract:
A nozzle and gate for a plastic injection mold wherein the gate has a primary sealing surface located adjacent to the vestige and a secondary sealing surface located behind or inwardly of the primary sealing surface. The nozzle has an insert retainer threadably mounted therein to hold a tip or torpedo type insert. The insert retainer has an outer annular primary seal which engages the gate primary sealing sur-face, and an intermediate secondary sealing ring which engages the gate secondary sealing surface.

Description:
FIELD OF THE INVENTION 
     The present invention relates to plastic injection molds, and in particular, to nozzles and gates for the hot runner system of such injection molds. 
     BACKGROUND OF THE ART 
     Injection molds can have gates machined into either the cavity or core portion of the mold, or they can have separate gate inserts that are mounted in the mold cavity or core. The gates or gate inserts contain the nozzles that inject the hot plastic into the mold cavity. The nozzles are fed from manifolds that are part of the hot runner system for the injection mold. 
     In order to prevent the hot plastic being injected into the mold cavity from leaking back behind the nozzles during the injection process, it is necessary to provide a seal between the outlet end of the nozzle and the adjacent portions of the gate or gate insert. If the hot plastic does leak back behind the nozzle, it usually ruins any heating coils used to keep the nozzle hot, or it at least causes a time consuming clean up operation with consequent machine downtime. 
     It is difficult to get a good seal between the nozzle outlet or tip and the adjacent gate surfaces because the surface area of the mating components must be kept small to avoid too much heat loss. Further, the mating components are subject to wear because of thermal expansion and contraction during the molding process. 
     The present invention gives improved sealing by providing a double seal; a primary seal adjacent to the vestige and a secondary seal located behind the primary seal away from the nozzle outlet. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a nozzle for use with a plastic injection mold gate defining a vestige. The nozzle comprises a main body portion including a central bore having an inlet portion, an enlarged threaded outlet portion and an annular shoulder separating the portions. A nozzle insert is located in the outlet portion and the insert includes an annular flange adapted to engage the annular shoulder. A hollow threaded insert retainer is threadably mounted in the outlet portion. The insert retainer has an inner annular shoulder for clamping engagement with the nozzle insert annular flange. An outer annular primary seal is adapted to sealingly engage the mold gate behind the vestige. An intermediate secondary sealing ring is adapted to sealingly engage the mold gate behind the primary seal. 
     According to another aspect of the invention, there is provided a gate insert and nozzle combination which comprises a hollow gate insert body defining a vestige. A first cavity is located behind the vestige and has an annular wall portion defining a primary sealing surface adjacent to the vestige. A second cavity is located behind the first cavity and has an annular wall portion defining a secondary sealing surface. A nozzle is located in the hollow gate insert body. The nozzle has a main body portion including a central bore having an inlet portion, an enlarged threaded outlet portion and an annular shoulder separating the portions. The nozzle also has a nozzle insert located in the outlet portion. The insert includes an annular flange adapted to engage the annular shoulder. The nozzle also includes a hollow threaded insert retainer threadably mounted in the outlet portion. The insert retainer has an inner annular shoulder for clamping engagement with the nozzle insert annular flange. An outer annular primary seal sealingly engages the gate insert primary sealing surface and an intermediate secondary sealing ring sealingly engages the gate insert secondary sealing surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is an elevational view, partly in section, of a preferred embodiment of a gate insert and nozzle combination according to the present invention; 
     FIG. 2 is an exploded perspective view of the nozzle and associated components shown in FIG. 1; 
     FIG. 3 is a vertical sectional view of the nozzle shown in FIG. 1; 
     FIG. 4 is a vertical sectional view similar to FIG. 3, but showing another preferred embodiment of a nozzle having a split flow tip; and 
     FIG. 5 is a vertical sectional view similar to FIG. 3, but showing another preferred embodiment of a nozzle having a torpedo type insert. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring firstly to FIG. 1, a nozzle  10  is shown mounted in an injection mold  12 . Injection mold  12  includes a manifold  14  which is part of the mold hot runner system for delivering hot molten plastic to nozzle  10 . Injection mold  12  includes a cavity portion  16  which is the female portion of the mold defining the shape of an article to be injection molded. A separate hollow gate insert  18  is mounted in cavity  16 , but gate insert  18  could be machined as an integral part of cavity  16 , if desired. Gate insert  18  includes a body  20  which defines a vestige  22  through which hot plastic is injected. Injection mold  12  and cavity  16  can be any configuration desired and are not considered to be part of the present invention, per se. 
     Referring next to FIGS. 1 to  3 , nozzle  10  includes a main body portion  24  which includes a central bore  26 . Central bore  26  has an inlet portion  28  (see FIG.  3 ), an enlarged, threaded outlet portion  30 , and an annular shoulder  32  separating the inlet portion  28  and outlet portion  30 . A heating coil  33  (omitted from FIGS. 3 to  5  for clarity) is mounted on main body portion  24 . Heating coil  33  is held in place by retainers  35 . An adapter ring  37  helps position nozzle  10  in mold  12 . Heating coil  33 , retainers  35  and adaptor ring  37  can be configured differently, if desired. 
     Referring in particular to FIG. 3, a nozzle insert  34  is located in outlet portion  30  of main body central bore  26 . Nozzle insert  34  is in the form of a direct sprue nozzle tip and it has a central passage  36  communicating with the central bore inlet portion  28 , and an outlet opening  38  at its tip through which the hot plastic is actually injected. Nozzle insert  34  also has an annular flange  40  that is adapted to engage annular shoulder  32 . Nozzle insert  34  is normally made of beryllium copper. 
     A hollow threaded insert retainer  42  is threadably mounted in the central bore threaded outlet portion  30 . Insert retainer  42  has an inner annular shoulder  44  for clamping engagement with the nozzle insert annular flange  40 . Insert retainer  42  also has an outer, annular primary seal  46  adapted to sealingly engage the mold gate body  20  behind vestige  22 . Actually, mold gate body  20  has a first cavity  48  which defines an annular wall portion defining a primary sealing surface  50  located behind and adjacent to vestige  22 . The insert retainer annular primary seal  46  engages the insert annular, primary sealing surface  50  to prevent hot plastic from passing backward behind nozzle  10 . 
     Gate insert  18  also has a second cavity  52  located behind first cavity  48 . Second cavity  52  also has an annular wall portion which defines a secondary sealing surface  54 . Insert retainer  42  is formed with an intermediate, secondary sealing ring  56  adapted to sealingly engage the mold gate behind the primary seal  46 . Actually, secondary sealing ring  56  engages secondary sealing surface  54 . This secondary sealing ring  56  ensures that even if some plastic gets behind primary seal  46 , that it will not pass behind secondary sealing ring  56  and contact heating coil  33 . 
     It should also be noted that when nozzle  10  is assembled in gate insert  18 , the secondary sealing ring  56  engages secondary sealing surface  54  before the primary seal  46  engages primary sealing surface  50 . The secondary sealing ring  56  thus guides the primary seal  46  into position, thus protecting it from damage during assembly and disassembly of mold  12 , especially if thermal expansion and/or contraction affect the fit between primary seal  46  and primary sealing surface  50 . 
     Insert retainer  42  also has a gripping flange  58  located between the annular primary seal  46  and the secondary sealing ring  56 . Gripping flange  58  is in the form of a star type, hexagonal or octagonal bolt head, so that a wrench can be used to tighten insert retainer  42  in main body portion  24  and tightly clamp nozzle insert  34  in place. 
     Referring next to FIG. 4, another preferred embodiment of the invention is shown which is substantially the same as the embodiment of FIGS. 1 to  3 , except that the FIG. 4 embodiment employs a split flow nozzle insert or tip  60 . Like reference numerals are used in FIG. 4 to indicate components that are the same as in the embodiment of FIGS. 1 to  3 . Nozzle tip  60  has a plurality (usually two or three) of radially disposed outlet channels or outlets  62  that communicate with the nozzle tip central passage  36 . Hot plastic passing through outlets  62  passes through first: cavity  48  and out through vestige  22 . 
     Referring next to FIG. 5, another preferred embodiment of the invention is shown which again is similar to the previous embodiments, except that the FIG. 5 embodiment employs a torpedo type nozzle insert  64 . Also in this embodiment, like reference numerals are used to indicate components that are the same as in the previous embodiments. Torpedo type insert or tip  64  has an annular flange  65  that has axial flow openings  66  therethrough to permit hot plastic to flow through flange  65 . In this embodiment, insert retainer  68  has a distal end portion  70  that defines the sprue or vestige  72  and also forms the primary seal  74  with an adjacent annular first cavity  76  in gate insert  78 . In other words, primary seal  74  also defines the nozzle outlet  72 . 
     Having described preferred embodiments of the invention, it will be appreciated that various modifications can be made to the structures described above. For example, other types of nozzle inserts or tips can be employed in the present invention. Other types of heating coils can be used as well. Main body portion  24  can be configured and mounted differently. As mentioned above, gate inserts  18  and  78  can be formed integrally as part of either the mold cavity or the mold core, where the injection nozzles are mounted in the core portion of the mold. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. The foregoing description is of the preferred embodiments by way of example only, and is not to limit the scope of the invention.