Abstract:
A hot runner nozzle assembly includes a nozzle heater, a hot runner nozzle, a nozzle tip, a nozzle tip seal surrounding the nozzle tip and a connecting element positioned to removably couple the tip seal to the nozzle tip and to create a first contact seal between the nozzle tip and the tip seal and a second annular contact seal between the tip seal and a mold component. The nozzle tip is made or shaped via a sintering process from a metal matrix composite (MMC) material having a first coefficient of thermal expansion. The tip seal is made or shaped from a ceramic based powder material, having a second coefficient of thermal expansion that is different from the first coefficient of thermal expansion. In operation this hot runner nozzle assembly provides an improved heat profile and a reduced leakage at the tip area under a wider operating processing window.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 61/804,602, filed Mar. 22, 2013, the contents of which are incorporated herein by reference in their entirety 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to an injection molding apparatus and more particularly to hot runner injection nozzles made of several cooperating parts. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hot runner injection nozzles are known. These nozzles are made of several parts designed to meet injection molding operating conditions for various materials and for various applications. These parts are made of various materials that need to be manufactured with high accuracy, low tolerances and also configured to be machine-able with available manufacturing equipment. These hot runner nozzles and the associated parts need to be designed and made to be easy to assemble and service in the field. 
         [0004]    An area at the end of the nozzle is the nozzle tip area, which is proximate to the mold gate. In this area the injection pressure is very high. Nozzle tips are known and they are in many cases attached to the body of the nozzle in the nozzle tip area. 
         [0005]    The nozzle tips sometimes have to be made of materials having conflicting properties or characteristics. If they are made of highly conductive materials, these materials are in many cases not very wear resistant. Many of the materials that can be used for the nozzle tips used in hot runner nozzles and that have good wear resistance have low thermal conductivity. 
         [0006]    In many hot runner nozzle applications there is a need to use nozzle tip connectors, nozzle tip seals and nozzle tip insulators that have to cooperate with the nozzle tips and operate and perform together as a unit. 
         [0007]    Because the nozzle tips and the tip seals are made of different materials and because they have a different thermal conductivity and a different coefficient of thermal expansion at the injection molding processing temperatures, there is always a concern with the known tips and seals regarding two types of leakage caused by the injection pressure of a molten material into a mold cavity through the nozzle tips. A first leakage, that sometimes is harder to contain, can appear between an outer surface of the tip and an inner surface of the tip seal. A second more common leakage can appear between an outer surface of the tip seal and a wall of a mold component adjacent the mold gate contacting the outer surface of the tip seal. Other leakage paths can further appear between other cooperating surfaces of the nozzle tip and tip seal that have small gaps caused by manufacturing errors or thermal expansion. 
         [0008]    There is a need to design and manufacture hot runner nozzles and hot runner nozzle tips that have improved features and good thermal and wear resistance properties. 
         [0009]    There is a need to design and manufacture nozzle tips, nozzle tip connectors, nozzle tip seals and nozzle tip insulators that have improved features and characteristics to better cooperate with the nozzle tips and better operate and better perform together as a unit. 
         [0010]    There is a need to design and manufacture nozzle tips, nozzle tip connectors, nozzle tip seals and nozzle tip insulators where the first leakage and the second leakage are contained for long hours of operation of the hot runner nozzle. 
       SUMMARY OF THE INVENTION 
       [0011]    This invention discloses designs and materials to manufacture hot runner nozzles and hot runner nozzle tips with improved operation characteristics. These nozzle tips cooperate with improved nozzle tip connectors, improved nozzle tip seals and improved nozzle tip insulators. 
         [0012]    In one embodiment of the invention, the nozzle tip is shaped or is made by sintering metal matrix composite (MMC) materials. In one embodiment of the invention, the metal matrix composite (MMC) material for the tip is a cemented carbide. In one embodiment of the invention, the cemented carbide material for the tip is Tungsten Carbide (e.g. a carbide that includes tungsten in a proportion exceeding 50%). In one embodiment of the invention the cemented carbide material for the tip is Titanium-Carbide. As a result of the use of the metal matrix composite (MMC) material, the nozzle tip has a first coefficient of thermal expansion at an operating temperature provided by a nozzle heater between about 100 degrees C. and about 400 degrees C. 
         [0013]    In another embodiment of the invention the nozzle tip is coated to increase the lifetime, especially the wear resistance, of the nozzle tip. In some embodiments the coating for the nozzle tip is selected for each application. The coatings are selected from one of these materials: TiN (titanium nitride), TiC (titanium carbide), Ti(C)N (titanium carbide-nitride), and TiAIN (titanium aluminum nitride). In other embodiments the coating is made with DLC (Diamond-like carbon). 
         [0014]    In some of the embodiments the coatings are deposited via thermal CVD 
         [0015]    (Chemical Vapour Deposition) and, for certain applications, with the mechanical PVD (Physical Vapour Deposition) method. 
         [0016]    In one embodiment of the invention a nozzle tip seal surrounding the nozzle tip and having an inner surface and an outer surface is shaped or made from a ceramic based powder material, the tip seal having a second coefficient of thermal expansion that is different from (e.g. less than) the first coefficient of thermal expansion at an operating temperature provide by the heater between about 100 degrees C. and about 400 degrees C. 
         [0017]    In one embodiment of the invention a connecting element contacting the nozzle tip and the nozzle tip seal is positioned to removably couple the tip seal to the nozzle tip. This connecting element is also positioned to create a first contact seal (which may be annular) between the nozzle tip and the tip seal. The connecting element may also create a second contact seal between the tip seal and a mold component. In another embodiment of the invention the connecting element is positioned to create third annular contact seal between the nozzle tip and the tip seal. The nozzle tip being adjacent to a mold cavity gate in the mold component. 
         [0018]    In operation this hot runner nozzle assembly provides an improved heat profile, reduced wear of the tip, and reduced leakage at the tip area under a wider operating processing window. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Non-limiting embodiments may be more fully appreciated by reference to the following detailed description when taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a sectional side view of a portion of an injection molding machine that includes a plurality of hot runner injection nozzles in accordance with an embodiment of the present invention; 
           [0021]      FIG. 1   a  is a magnified view of a portion of the injection molding machine shown in  FIG. 1 , showing a mold cavity; 
           [0022]      FIG. 1   b  is a magnified view of a portion of the injection molding machine shown in  FIG. 1 , illustrating heat loss from a nozzle to a mold component proximate the mold cavity; 
           [0023]      FIG. 2  is a sectional side view of one of the hot runner injection nozzles shown in  FIG. 1 ; 
           [0024]      FIG. 2   a  is a sectional side elevation view of a variant of the hot runner injection nozzle shown in  FIG. 1  whereby a tip is connected to a tip retainer by a brazed connection; 
           [0025]      FIG. 3  is a sectional side view of the hot runner injection nozzle shown in  FIG. 2 , with an optional nozzle heater; 
           [0026]      FIG. 4  is a sectional side view of the hot runner injection nozzle shown in  FIG. 2 , with an optional valve pin; 
           [0027]      FIG. 5  is a sectional side view of the hot runner injection nozzle shown in  FIG. 2 , with an optional nozzle heater and valve pin; and 
           [0028]      FIG. 6  is a sectional side view of the hot runner injection nozzle shown in 
           [0029]      FIG. 2 , with an optional nozzle heater and valve pin, and a valve pin alignment member; and 
           [0030]      FIGS. 7-15   b  are sectional side views of portions of additional embodiments of the hot runner injection nozzle shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    In this specification and in the claims, the use of the article “a”, “an”, or “the” in reference to an item is not intended to exclude the possibility of including a plurality of the item in some embodiments. It will be apparent to one skilled in the art in at least some instances in this specification and the attached claims that it would be possible to include a plurality of the item in at least some embodiments. 
         [0032]    Reference is made to  FIG. 1 , which shows a portion of an injection molding machine  10 . The injection molding machine  10  includes, among other things, a hot runner manifold  100  with a plurality of melt channel network  102  having an inlet  104  and a plurality of outlets  106 . The machine  10  further including a plurality of injection nozzles  11  each of which receive melt from one of the outlets  106  and transport the melt to a gate  24  of a mold cavity  25  (see  FIG. 1   a ) of a mold component  26 . Only a portion of the mold component  26  is shown, however it will be understood that the mold component  26  includes a plurality of elements that mate together to define a plurality of mold cavities  25 . 
         [0033]    The melt that is transported through the hot runner manifold  100  and through the nozzles  11  is heated so as to improve its flow characteristics. Referring to  FIG. 1   a , each mold cavity  25  receives melt from a nozzle  11  and cools the melt to solidify it and thereby form a molded product. Cooling channels shown at  27  are provided in the mold component  26  near the mold cavities  25  to transport coolant for the purpose of cooling the melt. Referring to  FIG. 1   b , the nozzle  11  is located in a space  28  in the mold component  26  and contacts the mold component  26  via a tip seal  18  to seal off the area immediately around the gate  24  in order to contain the melt. Because it is desired to keep the melt hot in the nozzle  11  and to cool the melt in the mold component  26 , there is a temperature difference between the nozzle  11  and the mold component that results in some heat loss from the nozzle  11  into the mold component  26 . It is desirable to reduce this heat loss as it is detrimental to both the flow of melt leaving the nozzle  11  and to the cooling of the melt in the mold cavities  25 . 
         [0034]    Reference is made to  FIG. 2 , which shows a magnified view of a portion of one of the injection nozzles  11 . The injection nozzle  11  includes a nozzle body  12 , which itself includes a nozzle head portion  13 , a nozzle tip  14 , a tip retainer  16  and the aforementioned tip seal  18 . 
         [0035]    The nozzle body  12  has a melt channel  20  therethrough that is positioned to transport melt from one of the hot runner manifold outlets  106  ( FIG. 1 ) to the nozzle tip  14 . The nozzle tip  14  has a melt channel  22  therethrough that is positioned downstream from the melt channel  20  so as to transport the melt to the gate  24  for one of the mold cavities  25  in a mold component  26 . The nozzle tip  14  is preferably made from a suitably hard material and has a first, (preferably high), thermal conductivity and a first coefficient of thermal expansion in the operating temperature window (i.e. temperature range) of about 100 degrees C. to about 400 degrees C. The first coefficient of thermal expansion may be in the range of 4.00-6.00 (×10 −6  K −1 ) at 20-1000 C. An example of a material for the nozzle tip  14  is a sintered metal matrix composite (MMC) powder, such as tungsten carbide in order to resist wear during use from contact with the melt, particularly when the melt is a resin that contains a glass filler or other hard fillers. In some embodiments, such as the embodiments shown in  FIGS. 4 ,  5  and  6 , a tungsten carbide tip is also useful in order to resist wear from friction during movement of a valve pin, as discussed further below. 
         [0036]    Referring to  FIG. 2 , the tip retainer  16  is removably coupled to the nozzle body  12  and has the tip  14  connected thereto, so that the tip  14  is effectively removable from the nozzle body  12  for service. For example, the tip retainer  16  may have an inner threaded portion  30  and may be coupled by the inner threaded portion  30  to an outer threaded portion  32  on the nozzle body  12 . 
         [0037]    The tip  14  may be coupled to the tip retainer  16  by any suitable means. For example, the tip retainer  16  may have a second inner threaded portion  34  and the tip  14  may have an outer surface  35  on which there is an outer threaded portion  36 , through which the tip  14  is coupled to the tip retainer  16 . This structure eliminates the need to provide an inner threaded portion on the tip  14 , which can be relatively difficult to manufacture particularly in embodiments wherein the tip  14  is made from tungsten carbide. The inner threaded portion  30  (which may, for convenience be referred to sometimes as the first inner threaded portion  30 ) and the second inner threaded portion  34  may be separate, distinct portions of the tip retainer  16 , or alternatively they may join to form a continuous threaded portion as shown in  FIG. 2 . 
         [0038]    In another embodiment shown in  FIG. 2   a , the tip  14  may be brazed to the tip retainer  16 . In  FIG. 1   a , the brazed joint a shown at  38 . Brazing the tip  14  to the tip retainer  16  provides several advantages. One advantage is that it eliminates the need to provide the outer threaded portion  36  on the tip  14 , which can be difficult when the tip  14  is made from a material such as tungsten carbide. In yet another embodiment, the tip  14  may be connected to the tip retainer  16  by a press-fit connection. 
         [0039]    The tip  14  may be sealingly engaged with the nozzle body  12  via engagement of tip engagement surface  47  on the nozzle body  12  with a body engagement surface  49  on the tip  14 , so as to permit melt to flow from the nozzle body  12  into the tip  14  without leaking out of the nozzle  11 . 
         [0040]    The tip seal  18  is positioned around the tip  14  and has an outer surface  37  is positioned to engage a sealing surface  39  on the mold component  26  to form a seal therewith so as to inhibit the flow of melt therepast. The tip seal  18  may be made from a material that has a second thermal conductivity that is preferably lower than that of the tip  14  so as to inhibit heat transfer from the tip  14  into the mold component  26 . The tip seal  18  also has a second coefficient of thermal expansion in the operating temperature window of about 100 degrees C. to about 400 degrees C. The second coefficient of thermal expansion may be lower than that of the tip  14 . The tip seal  18  is preferably made from an insulative material. An example of a suitable insulative material is a sintered ceramic based powder material. The tip seal  18  further includes a radially inner surface  41  that faces a portion of the outer surface  35  of the tip  14 . The tip seal  18  further includes a first annular surface  43  and a second annular surface  45 . 
         [0041]    It will be noted that it can be difficult to directly join a ceramic component to a component made from a metal matrix composite such as tungsten carbide. To overcome this difficulty, a seal retainer  40  (which may also be referred to as a seal and connector element  40 ) may be used to retain the tip seal  18  on the tip  14 . The seal retainer  40  is a unitary component which contacts both the tip  14  and the tip seal  18 . The seal retainer  40  removably connects to the tip  14  by any suitable means, so that the seal  18  is held between a retainer surface  42  on the seal retainer  40  and a retaining surface  44  on the tip  14 , such that first annular surface  43  on the tip seal  18  faces retaining surface  44  and second annular surface  45  on the tip seal  18  faces retainer surface  42 . The seal retainer  40  may connect to the tip  14  by an inner threaded portion  46  on the seal retainer  40  that engages an outer threaded seal retainer engagement portion  48  on the tip  14 . In other words the seal retainer  40  may be threaded onto the tip  14  and removably couples the tip seal  18  to the tip  14 . 
         [0042]    Optionally, the seal retainer  40  may be welded to the tip  14 , however, in preferred embodiments it is not welded. In yet another alternative, the seal and/or the seal retainer  40  may be connected to the tip  14  by an adhesive such as a suitable type of Loctite (provided by Henkel Corporation of Rocky Hill, Conn., USA). In yet another alternative, the seal retainer  40  may be shrink fit (i.e. an interference fit formed by mounting the seal retainer  40  the tip  14  when either the seal retainer  40  is heated to temporarily expand its inner diameter and/or the tip  14  is cooled to temporarily reduce its outer diameter, and then to return them to a temperature where the inner diameter of the seal retainer  40  is smaller than the outer diameter of the tip  14 ). 
         [0043]    It has been found that, due to the materials used for one or both of the tip  14  and the tip seal  18  it can be difficult to manufacture the tip  14  and the tip seal  18  to tight tolerances. This can be because the manufacturing processes used for both are inherently difficult to provide tight tolerances. This can also be because of the different coefficients of thermal expansion between the tip  14  and the tip seal  18 . As a result, it has been found that there can be a leakage path between the tip  14  and the tip seal  18 . There can also be a leakage path between the tip seal  18  and the mold component  26 , however, it has been found that this is relatively easier to address and to arrive at a suitable seal between the outer surface  37  of the tip seal  18  and the sealing surface  39  of the mold component  26 . 
         [0044]    The seal retainer  40  controls a first seal between the tip seal  18  and the tip  14 , which is the seal formed between annular surface  43  on the tip seal  18  and the associated annular surface  44  on the tip  14 . This seal may be referred to as a first “tip seal-nozzle tip” seal. The seal retainer  40  may control this first tip seal-nozzle tip seal by, for example, controlling the force with which the surface  43  on the tip seal  18  engages the surface  44  on the tip  14  (i.e. driving the annular surface  43  into engagement with the annular surface  44  with a selected force). If a sufficient force is not used, there will not be an effective seal between the tip  14  and the tip seal  18 . Where the term ‘seal’ is used in the context of this patent application, it is intended to mean that substantially no leakage occurs therepast during normal operation of the associated components. Thus, simple contact between the surfaces  43  and  44  may not provide a seal. Thus it can be seen that the seal retainer  40  may do more than just hold the tip seal  18  on the tip  14 . By controlling the first seal between the nozzle tip  14  and the tip seal  18  (in particular by controlling the seal between annular surfaces  43  and  44 ) the seal retainer  40  compensates to some extent for the difference in thermal expansion in operation between the tip  14  and the seal  18  and more broadly compensates for the poor seal that may be provided between radially inner and outer surfaces  41  and  51  and between surfaces  43  and  44 , which results from manufacturing tolerances and differences in amounts of thermal expansion. 
         [0045]    The seal between surfaces  41  and  51  may be referred to as a second “tip seal-nozzle tip” seal between the tip seal  18  and the nozzle tip  14 . The seal retainer  40  may also control the second “tip seal-nozzle tip” seal in one or more of several ways. For example, a seal may be formed between surfaces  42  and  45  thereby preventing leakage of melt therepast. A seal may be formed between the inner surface  46  of the seal retainer  40  and the corresponding outer surface  48  (which his part of outer surface  35 ) on the tip  14 . 
         [0046]    Referring to  FIG. 3 , the nozzle  11  may further include a nozzle heater  50  that may include a heater body  52  and an electric heating element  54  that is positioned in a groove  56  in the heater body  52 . The nozzle heater  50  is engaged with the nozzle body  12  and is configured for heating melt in the nozzle  11 . The nozzle heater  50  provides an operating temperature window for the nozzle  11  of between about 100 degrees C. and about 400 degrees C. 
         [0047]    Referring to  FIG. 4 , the nozzle  11  may further include a valve pin  58 , that is movable between a closed position (shown in  FIG. 3 ) in which the valve pin  58  prevents the flow of melt through the gate  24 , and an open position to permit the flow of melt through the gate  24 . A tip portion  60  of the valve pin  58  is aligned with the gate  24  by a wall  61  of the nozzle tip  14 . Thus there may be frictional contact between the valve pin  58  and the nozzle tip  14  during movement of the valve pin  14 . Making the nozzle tip  14  from a hard material such as tungsten carbide reduces the amount of wear that results from such frictional contact. 
         [0048]    Referring to  FIG. 5 , the nozzle  11  may further include both the valve pin  58  and the nozzle heater  50 . 
         [0049]    Referring to  FIG. 6 , the nozzle  11  is shown including both the valve pin  58  and the nozzle heater  50 , and also a valve pin alignment member  62  that is positioned between the nozzle tip  14  and the nozzle body  12  (and that is held in place by the tip retainer  16 ). The valve pin alignment member  62  is configured for aligning a portion  64  of the valve pin  58  upstream from the tip portion  60  of the valve pin. 
         [0050]    Referring to  FIG. 7 , the tip seal  18  may be retained on the nozzle tip  14  by a seal retainer  40  (which may be made from steel for example), however, an insulator member  66  may be provided between the seal retainer  40  and the tip seal  18  so as to inhibit heat transfer from the seal retainer  40  into the tip seal  18 . The seal retainer  40  is shown in  FIG. 7  as being welded to the nozzle tip  14 , wherein the weld is represented by a circle  68 . It will be noted that the circular shape identified at  68  is provided only to identify that a weld is there. The weld  68  need not be circular in cross-section and may have any suitable shape, such as a fillet weld. It will be further noted that the weld is entirely optional may be omitted and the seal retainer  40  may be connected to the nozzle tip  14  any other suitable way. 
         [0051]    Referring to  FIG. 8 , the tip seal  18  is retained on the nozzle tip  14  by a seal retainer  40  that is itself also an insulator member  66   a  so as to inhibit heat transfer from the nozzle tip  14  to the tip seal  18  through the seal retainer  40 . Additionally, a second insulator member  66   b  is provided between the inner diameter surface (shown at  70 ) of the tip seal  18  and the nozzle tip  14  so as to reduce heat transfer from the nozzle tip  14  into the tip seal  18  (and ultimately into the mold component  26  ( FIG. 1 )). The insulator member  66   b  also acts as a seal to prevent leakage of melt therepast where it mates with other elements. In  FIG. 8 , the first insulator member and seal retainer  40 ,  66   a  is shown as being welded to the tip seal  18  via weld  68 . An optional weld  68  or some other connecting means such as a threaded connection, holds the first insulator member and seal retainer  40 ,  66   a,  the second insulator member  66   b  and the tip seal  18  in place in a groove shown at  71  in the nozzle tip  14 . 
         [0052]    Referring to  FIG. 9 , the tip seal  18  is retained on the nozzle tip  14  by the seal retainer  40 , which may be joined to the nozzle tip in any suitable way. An insulator member  66  is provided between the inner diameter surface  70  of the tip seal  18  and the nozzle tip  14  to inhibit heat transfer from the nozzle tip  14  into the tip seal  18  through surface  70 . 
         [0053]    Referring to  FIG. 10 , an insulator member  66  is provided between axial end face  43  of the tip seal  18  and the nozzle tip  14  so as to reduce heat transfer from the nozzle tip  14  into the tip seal  18  through end face  43 . Also shown in  FIG. 10 , the seal retainer  40  is threaded onto to the nozzle tip  14 . 
         [0054]    The embodiment in  FIG. 10   a  is the same as the embodiment in  FIG. 10 , except that there is no insulator member  66 ; instead the tip seal  18  abuts the shoulder  44  on the tip  14 . 
         [0055]    Referring to  FIG. 11 , an insulator member  74 , which may be, for example, an o-ring, is provided between the end face  43  of the tip seal  18  and the retaining surface  44  of the nozzle tip  14 . A groove for the o-ring may be provided in one or both surfaces  43  and  44 . The insulator member  74  may also act as a seal member that prevents the leakage of melt therepast. In a preferred embodiment the o-ring acts to space the surface  43  from the surface  44 , thereby increasing its effectiveness to inhibit heat transfer into the tip seal  18 . Even if the two surfaces  43  and  44  contact each other, however, the insulator member  74  preferably still has sufficient resiliency to act as a seal to prevent melt leakage therepast. The seal retainer  40  may be welded to the nozzle tip  14  or connected to the nozzle tip  14  by any other suitable means (e.g. a threaded connection). 
         [0056]    Referring to  FIG. 12 , a first insulator member  74   a  (which may be, for example, an o-ring) is provided between the end face  43  of the tip seal  18  and the retaining surface  44  of the nozzle tip  14 , and a second seal member  74   b  (which may be, for example, an o-ring) is provided between the inner diameter surface  70  of the tip seal  18  and the nozzle tip  14 . One or both of the insulator members  74   a  and  74   b  may act as seal members to prevent the leakage of melt therepast. In a preferred embodiment the o-rings act to space the surface  43  from the surface  44  and the inner diameter surface  70  from the corresponding surface on the tip seal  18 , thereby increasing their effectiveness to inhibit heat transfer into the tip seal  18 . The seal retainer  40  may be welded to the nozzle tip  14  or connected to the nozzle tip  14  by any other suitable means (e.g. a threaded connection). It is possible to have an embodiment wherein only member  74   b  is provided and not insulator member  74   a.    
         [0057]    Referring to  FIG. 13 , an insulator member  74  which may be an o-ring is provided in a corner groove  75  between surfaces  43  and  41 , and a corner groove  77  between surfaces  51  and  44  on the nozzle tip  14 . Generally speaking, melt may infiltrate between the nozzle tip  14  and the tip seal  18  until it is stopped by whatever seals exist between the two surfaces. The melt itself can act as a seal and furthermore can act as an insulator. 
         [0058]    Referring to  FIG. 14 , the tip seal  18  may be connected to the nozzle tip  14  via one or more set screws  78  or dowels  78 . The set screws or dowels  78  may be considered to the seal retainers and may act to provide the surfaces  43  and  44  by virtue of driving the tip seal axially into surface  44  when they are in place in both the apertures shown at  79  and  81  in the tip seal  18  and the tip  14  respectively. The set screws or dowels  78  may also seal against the tip and tip seal to prevent melt leakage out through the apertures  79 . Alternatively they may not seal the apertures  79 , however the seals formed between the outer surface of the tip seal  18  and the mold component  26  and between the surfaces  43  and  44  will prevent melt leakage outwards. 
         [0059]    Referring to  FIG. 15   a , the tip seal  18  may have a groove  80  therein that receives an insulator member  82 , which may also be a seal member, as with the embodiments shown in  FIGS. 10-14 . The insulator member  82  may be C-shaped. A corresponding groove  84  is provided in the nozzle tip  14 . As shown in  FIGS. 15   a  and  15   b , the tip seal  18  may slide into place on the nozzle tip  14 . As the seal  18  is slid onto the nozzle tip  14 , the clearance between the two is sufficiently small to force the insulator member  82  to compress. As the seal  18  is slid into place such that the grooves  80  and  84  line up, the insulator member  82  expands into the groove  84  thereby providing an insulation function, a seal function providing the first “tip seal-nozzle tip” seal, and acting as a seal retainer to retain the tip seal  18  on the nozzle tip  14 . 
         [0060]    In  FIGS. 15   a  and  15   ab  member  82  controls and provides a first annular sealing. When the tip seal  18  is slid over the member  82 , the curvature of the ring  82  becomes flatter and may enter the corners of the inner grooves  84  and  80 . By positioning the outer groove of the tip  14  closer to the shoulder we need to seal, the member  82  will apply a sealing force. If resin under pressure enters the chamber formed by grooves  84  and  80 , more pressure will be applied on the seal ring  82  to generate the first annular seal. 
         [0061]    In the embodiments shown herein, the tip seal  18  is provided on the nozzle tip  14  instead of being on the tip retainer  16 . This is advantageous for several reasons. By providing the seal  18  on a smaller diameter element (i.e. the tip  14  as opposed to the larger diameter tip retainer  16 ) the reliability of the seal increases because there is a generally smaller area being sealed. Additionally, the overall diameter of the nozzle  11  is kept relatively smaller by mounting the seal  18  on the tip  14  instead of being on the tip retainer  16 , which permits the pitch between nozzles  11  to be smaller, thereby permitting a greater number of articles to be molded on a machine, in some instances where the nozzle pitch is a limiting factor on the production capacity of the machine. 
         [0062]    While the element  18  is referred to as a tip seal, it may be more broadly referred to as a mold component contacting piece. 
         [0063]    In  FIG. 1 , two nozzles  11  are shown, one with a valve pin and one without. It will be noted that the two different nozzles are provided for illustrative purposes only, and that in practice, an injection molding machine may have all its nozzles including valve pins, or may have all of its nozzles without valve pins. 
         [0064]    In any embodiments where a weld is provided between the seal retainer and the tip the weld is optional and may be a continuous weld or a point weld or a plurality of point welds. 
         [0065]    The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.