Patent Publication Number: US-6988883-B2

Title: Injection molding apparatus having a nozzle tip and a tip surrounding piece of equal thermal conductivity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 10/817,825 filed Apr. 6, 2004, which is a continuation of U.S. application Ser. No. 10/262,967 filed Oct. 3, 2002 now U.S. Pat. No. 6,869,276, which claims benefit of U.S. Provisional Application No. 60/328,830, filed Oct. 15, 2001, the entire disclosures of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an injection molding apparatus, and more particularly to a nozzle in an injection molding apparatus. 
     2. Background Art 
     A hot runner injection molding apparatus typically includes nozzles that are heated to maintain melt therein at a controlled temperature. The nozzles are typically in contact with a mold component that defines one or more mold cavities. The mold cavities in the mold component are filled with melt that first passes through the nozzles. The mold component is then typically cooled in order to solidify the melt in the mold cavities, thus forming a plurality of molded parts, which are then ejected from the mold cavities. 
     Because the nozzles are typically heated, and the mold component is cooled for at least a portion of an injection molding cycle, it is desirable to have a relatively low heat transfer from the nozzles into the mold component. Many nozzle constructions have been proposed in the past to address this issue. 
     An example of such a nozzle construction is shown in U.S. Pat. No. 5,554,395, to Hume et at. The &#39;395 patent teaches a multi-piece nozzle tip assembly including a tip piece, a tip surrounding piece and a resilient element. The resilient element is provided between the tip piece and the mold component, to inhibit melt leakage therepast. However, heat can be lost from the tip piece through the resilient element and into the mold component. In particular, the heat losses occur near the downstream end of the tip piece, where control over the temperature of the melt is particularly important. 
     Thus, there is a continuing need for new nozzle constructions that have further improved heat transfer efficiency. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided an injection molding apparatus including a manifold, a nozzle, a heat source thermally coupled to the nozzle, and a mold component having a mold cavity for receiving melt from the nozzle through a mold gate. The manifold includes at least one runner that receives melt from a melt source. The nozzle is adapted to be in fluid communication with at least one runner in the manifold. The nozzle includes, a nozzle body having a melt passage therethrough, a nozzle tip having a tip melt passage therethrough, wherein the tip melt passage is in fluid communication with the melt passage of the nozzle body, and a tip surrounding piece that is removably coupled to the nozzle body. At least a portion of the inner surface of the tip surrounding piece is at a distance from the outer surface of the nozzle tip to thereby define a chamber. In one embodiment, the tip surrounding piece is formed of a material that has a thermal conductivity that is substantially equal to that of the nozzle tip. 
     In one embodiment, the nozzle tip includes a retaining surface and the tip surrounding piece includes a support surface. The nozzle tip is aligned such that the support surface of the tip surrounding piece abuts the retaining surface of the nozzle tip to thereby retain the nozzle tip in position with respect to the nozzle body. In one embodiment, the retaining surface of the nozzle tip may take the form of a shoulder, while the support surface of the tip surrounding piece may take the form of a jam surface. The tip surrounding piece may be threadably engaged with the nozzle body. The tip melt passage may take a generally linear path, or may alternatively include an exit that is off-center from the longitudinal axis of the tip melt passage. The nozzle tip and tip surrounding piece are formed of H13. 
     In an embodiment, the injection molding apparatus may also include a heater thermally coupled to the nozzle. The injection molding apparatus may further include a mold plate, wherein the tip surrounding piece touches the mold plate to thereby form a seal. 
     In an embodiment, the nozzle tip is formed of a metallic material and the tip surrounding piece is preferably formed of the same metallic material. 
     In an embodiment, the nozzle tip is formed of a first material and the tip surrounding piece is formed of a second material; wherein the thermal conductivity of the first material is equivalent to the thermal conductivity of the second material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings. 
         FIG. 1  is a sectional view of a portion of a nozzle in accordance with a first embodiment of the present invention. 
         FIG. 2  is a magnified view of a sealing portion of the nozzle shown in  FIG. 1 . 
         FIG. 3   a  is a sectional view of a portion of a nozzle in accordance with a second embodiment of the present invention. 
         FIG. 3   b  is a magnified view of a sealing portion of the nozzle shown in  FIG. 2 . 
         FIG. 3   c  is a sectional view of a portion of a nozzle in accordance with a third embodiment of the present invention. 
         FIG. 4  is a sectional view of a portion of a nozzle in accordance with a fourth embodiment of the present invention. 
         FIG. 5  is a sectional view of a portion of a nozzle in accordance with a fifth embodiment of the present invention. 
         FIG. 6  is a sectional view of a portion of a nozzle in accordance with a sixth embodiment of the present invention. 
         FIG. 7  is a side view of a nozzle in accordance with a seventh embodiment of the present invention. 
         FIG. 8  is a sectional view of a portion of the nozzle shown in  FIG. 7 . 
         FIG. 9  is a sectional view of a portion of a nozzle in accordance with an eighth embodiment of the present invention. 
         FIG. 10  is a sectional view of a portion of a nozzle in accordance with a ninth embodiment of the present invention. 
         FIG. 11  is a sectional view of a portion of a nozzle in accordance with a tenth embodiment of the present invention. 
         FIG. 12  is a sectional view of an injection molding apparatus incorporating a nozzle in accordance with an eleventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to  FIG. 1 , which shows a nozzle  10 , in accordance with a first embodiment of the present invention. Nozzle  10  is for transferring melt from a runner in a manifold in a hot runner injection molding apparatus to a mold cavity  11  in a mold component  12 . Mold cavity cooling channels  13  may optionally be included in mold component  12 . 
     Nozzle  10  includes a nozzle body  14 , a tip  16 , and a heater  17  and may include a tip surrounding piece  18 , an alignment piece  20  and a thermocouple  26 . The nozzle body  14  has a body melt passage  28  that passes therethrough. 
     The heater  17  may be any suitable kind of heater, such as a resistive wire heater, or a sleeve heater, as long as it is thermally connected to the nozzle body  14 , i.e. the heater  17  is connected such that heat is transferable from the heater  17  to the nozzle body  14 . For example, the heater  17  may wrap around the nozzle body  14  in a groove on the outer surface of the nozzle body  14 . 
     The tip  16  may be removably connected to the nozzle body  14 . The tip  16  defines a tip melt passage  30  therethrough that is downstream from, and in fluid communication with, the body melt passage  28 . The tip melt passage  30  may exit from tip  16  into a chamber  32 . A gate  34  transfers melt from the chamber  32  into the mold cavity  11 . 
     Melt passes from a melt source, through one or more runners in a runner component such as a manifold, through the nozzle body melt passage  28 , through the tip melt passage  30 , through the chamber  32 , through the gate  34  and finally into the mold cavity  11 . The center of the gate  34  defines an axis  35 , which is parallel to the direction of flow of melt through gate  34 , into the mold cavity  11 . 
     The exit from the tip melt passage into the chamber  32  is shown at  36 . Exit  36  may be concentric with respect to axis  35 , as shown in  FIG. 1 . 
     Because the melt flows through the tip  16 , the tip  16  can be used to transfer heat from the heater  17  to the melt. To facilitate the heat transfer, the tip  16  is preferably made from a thermally conductive material, such as Beryllium-Copper. 
     Because of the melt flow through tip  16 , the tip  16  may be exposed to a highly abrasive environment, and it may be desirable to make the tip  16  from a wear resistant material. An example of a material that is both thermally conductive and wear resistant is Tungsten Carbide. The tip  16  may be made in accordance with the teachings in U.S. Pat. No. 5,658,604 (Gellert et al.), which is hereby incorporated by reference and which discloses the construction of a nozzle tip using Tungsten Carbide. 
     The tip  16  may be positioned within a bore  37  in the nozzle body  14 . Depending on the material selected for the tip  16 , a threaded portion can be relatively difficult to machine. Furthermore, such a threaded portion can be brittle and subject to premature failure, depending on the material of manufacture for the tip  16 . Thus, by making the tip  16  threadless, a greater number of materials are available for its manufacture. 
     Furthermore, by making the tip  16  threadless, some cost of manufacture is saved for the tip  16  and correspondingly for the nozzle body  14 , relative to a threaded tip. 
     The tip surrounding piece  18  may retain the tip  16  in place in the nozzle body  14 . The tip surrounding piece  18  may include a jam surface  38  which abuts a shoulder  39  on the tip  16  to retain the tip  16  in place. The jam surface  38  and the shoulder  39  may cooperate to form a mechanical seal. 
     The tip surrounding piece  18  may be removably attachable to the nozzle body  14 . For example, the tip surrounding piece  18  may include a tip surrounding piece threaded portion  40  for mating with a corresponding nozzle body threaded portion  41  on the nozzle body  14 . The threaded portion  40 , as shown in  FIG. 1 , is an external thread; however, it is alternatively possible for the tip surrounding piece to include an internal thread to mate with an external thread on the nozzle body  14 . 
     The tip surrounding piece  18  may also include a tool engagement portion  42 , for receiving a tool (not shown), for the installation and removal of the tip surrounding piece  18  with respect to the nozzle body. 
     A gap seal  48  may be formed by the tip surrounding piece  18  in cooperation with the mold component  12 , as shown more clearly in  FIG. 2 . More specifically, a tip surrounding piece sealing surface  50  on the tip surrounding piece  18  may cooperate with a mold component sealing surface  52  on the mold component  12  to form the gap seal  48 . The tip surrounding piece sealing surface  50  may be an outer surface on the tip surrounding piece  18 , and the mold component sealing surface  52  may be the wall of the nozzle well, which is shown at  53 . The tip surrounding piece sealing surface  50  and the mold component sealing surface  52  are separated from each other by a gap G. The tip surrounding piece sealing surface  50  may be referred to as the first gap seal surface  50 , and the mold component sealing surface  52  may be referred to as the second gap seal surface  52 . 
     Due to the viscosity of the melt in the chamber  32 , the proximity of the first tip surrounding piece sealing surface  50  and the mold component sealing surface  52  inhibits melt from flowing between the first tip surrounding piece sealing surface  50  and the tip sealing surface  52 . Thus, the gap G, in conjunction with the viscosity of the melt, acts as a seal. 
     The Gap G may be less than approximately 0.07 mm if it is the only intended seal and is therefore not combined with a mechanical seal. If the gap seal  48  is used in combination with a mechanical seal, the gap G may optimally be between approximately 0.15 mm and approximately 0.25 mm. It will be noted that the gap G required to inhibit the flow of melt is dependent on the specific molding application. The rheological properties of the melt at the injection temperature, such as its viscosity, determine the maximum gap G that provides the desired seal. 
     An advantage to including the gap seal  48  is that the manufacturing tolerances for sealing surfaces  50  and  52  are less demanding, relative to a typical mechanical sealing portion. A further advantage is that because melt does not pass through the gap seal  48 , an air space  54  is maintained between the tip surrounding piece  18  and the mold component  12 . The air space  54  provides an insulative layer to reduce heat transfer between the tip surrounding piece  18 , and from the entire nozzle  10  in general, into the mold component  12 . 
     To further reduce heat losses from the tip surrounding piece  18 , and the nozzle  10 , into the mold component  12 , the tip surrounding piece  18  may be made from a material that has a thermal conductivity that is lower than that of the material for the tip  16 , depending on the specific requirements of the molding application. 
     The tip surrounding piece  18  may alternatively be made from a material that has a thermal conductivity that is similar to that of the nozzle tip  16 . Because the tip surrounding piece  18  may be positioned between a portion of the heater  17  and the tip melt passage  30 , as shown in  FIG. 1 , it may be advantageous to make the tip surrounding piece  18  from a material that has a thermal conductivity that is generally equal to that of the tip  16 , to improve heat transfer between the heater  17  and the tip melt passage  30 . 
     Because the melt that contacts the tip surrounding piece  18  is generally slower moving than the melt flowing through the tip  16 , the tip surrounding piece  18  may be made from a material that is less wear resistant than that of the tip  16 . Accordingly, the tip surrounding piece  18  may be made from a material that is relatively easily machined with threads. 
     Referring to  FIG. 1 , the alignment piece  20  may be included to align the nozzle  10  with respect to the gate  34  in molding applications where such alignment is important. The alignment piece  20  may be positioned between the nozzle body  14  and a bore  56  in the mold component  12 . The bore  56  includes therein, the nozzle well  53 . The alignment piece  20  may be positioned between the mold component  12  and any other suitable component of the nozzle  10 , instead of the nozzle body  10 . 
     The alignment piece  20  may be made from a material that has a lower thermal conductivity than that of the nozzle portion with which it is in contact, which is in this case, the nozzle body  14 . For example, the alignment piece  20  may be made from tool steel, titanium, H13, or any other suitable material. It is alternatively possible for the alignment piece  20  to be integrally formed into the nozzle body  14 , or into any other suitable portion of the nozzle  10 , such as the tip surrounding piece  18 . 
     Reference is made to  FIG. 3   a , which shows a nozzle  60  in accordance with a second embodiment of the present invention, in combination with a mold component  61 . 
     Nozzle  60  is similar to nozzle  10  ( FIG. 1 ), and includes the nozzle body  14 , the tip  16 , and the heater  17 , and may include a tip surrounding piece  62  and a thermocouple  26 . The tip surrounding piece  62  may be similar to the tip surrounding piece  18  ( FIG. 1 ), and may have a jam surface  63  thereon which cooperates with the shoulder  39  on the tip  16  to retain the tip  16  in place in the nozzle body  14 . 
     The tip surrounding piece  62  may include a tip surrounding piece threaded portion  64  that cooperates with the threaded portion  41  on the nozzle body  14 , so that the tip surrounding piece  62  is removably attached to the nozzle body  14 . 
     The tip surrounding piece  62  cooperates with the mold component  61  to form a multi-portion seal  65  therebetween. The multi-portion seal  65  includes a gap seal  66  and also includes a second seal  68 , which may be, for example, a mechanical seal, that is adjacent the gap seal  66 . The gap seal  66  may be similar to the gap seal  48  ( FIG. 1 ), and is formed by the cooperation of a first tip surrounding piece sealing surface  70  on the tip surrounding piece  62 , with a first mold component sealing surface  72  on the mold component  61 . The first tip surrounding piece sealing surface  70  and the first mold component sealing surface  72  are separated by the gap G, as shown more clearly in  FIG. 3   b . The first tip surrounding piece sealing surface  70  and the first mold component sealing surface  72  may be referred to as the first gap seal surface  70  and the second gap seal surface  72 , respectively. 
     Because of the presence of the second seal  68 , the gap G, in the embodiment shown in  FIG. 3   a  may optimally be approximately 0.15 mm, and may be less than approximately 0.25 mm. 
     The second seal  68  may also be referred to as a supplementary seal  68 , and is formed by the cooperation of a second tip surrounding piece sealing surface  74  on the tip surrounding piece  62 , with a second mold component sealing surface  76  on the mold component  61 . The sealing surfaces  74  and  76  may contact each other, as shown in  FIG. 3   a . The second tip surrounding piece sealing surface  74  and a second mold component sealing surface  76  may be referred to as the first supplementary seal surface  74  and the second supplementary seal surface  76  respectively. 
     The second seal  68  may be positioned behind the gap seal  66  with respect to the chamber  32 , so that melt is exposed to the gap seal  66  before the second seal  68 . 
     Because of the presence of the gap seal  66 , the surface area of contact between the tip surrounding piece  62  and the mold component  61  along the sealing surfaces  74  and  76 , is smaller than would be required if the second seal  68  acted alone to seal against melt leakage therepast. Thus, the heat transfer from the tip surrounding piece  62  and from the nozzle  60  in general, into the mold component  61  is reduced accordingly. 
     In addition to forming the second seal  68 , the second sealing surfaces  74  and  76  may cooperate to align the nozzle  10  with respect to the gate, which is shown at  78 . This applies particularly in the case, as shown in  FIG. 3   a , where the sealing surfaces  74  and  76  are substantially vertical surfaces. However, the second sealing surfaces  74  and  76  may be inclined instead of being vertical, and may still be adapted to align the nozzle  60  with respect to the gate  78 . 
     Referring to  FIG. 3   a , the mold component  61  may be similar to the mold component  12  ( FIG. 1 ), and defines a plurality of mold cavities  80 , each of which has at least one gate  78  leading thereto. The mold component  61  may include cooling channels  82  for cooling of melt in the mold cavities  80 . 
     Reference is made to  FIG. 3   c , which shows a variant  60 ′ of the embodiment shown in  FIG. 3   a . In the nozzle  60 ′, a tip  84  replaces the tip  16  ( FIG. 3   a ). The tip  84  may be similar to the tip  16  ( FIG. 3   a ) and may define a tip melt passage  86  therethrough. However, the tip  84  includes a torpedo portion  87 , and the tip melt passage  86  may have an exit  88  that is off-center from the axis of the gate  78 , which is shown at  90 . 
     It will be noted that the tip  84  may also replace the tip  16  in the embodiment shown in  FIGS. 1 and 2 . 
     Reference is made to  FIG. 4 , which shows another variant  60 ″ of the embodiment shown in  FIG. 3   a . In the variant shown in  FIG. 4 , the tip  84  replaces the tip  16  ( FIG. 3   a ). The items shown in  FIG. 4  are similar to those in  FIG. 3   a , except as follows. A gap seal  66 ′ is formed which is similar to the gap seal  66  ( FIG. 3   a ), except that the gap seal  66 ″ is formed between a first tip surrounding piece sealing surface  70 ″ on a tip surrounding piece  62 ″, and a first mold component sealing surface  72 ″ on a mold component  61 ″. The first sealing surfaces  70 ″ and  72 ″ may be entirely inclined surfaces in the embodiment shown in  FIG. 4 , whereas they are shown as including an inclined portion and a substantially vertical portion in the embodiment shown in  FIG. 3   a . The first sealing surfaces  70 ″ and  72 ″ may also be referred to as the first and second gap seal surfaces  70 ″ and  72 ″ respectively. 
     Reference is made to  FIG. 5 , which shows yet another variant  60 ″ of the embodiment shown in  FIG. 3   a . In the variant shown in  FIG. 5 , the tip  84  replaces the tip  16  ( FIG. 3   a ). The items shown in  FIG. 5  are similar to those in  FIG. 3   a , except as follows. A gap seal  66 ″ is formed which is similar to the gap seal  66  ( FIG. 3   a ), except that the gap seal  66 ″ is formed between a first tip surrounding piece sealing surface  70 ″ on a tip surrounding piece  62 ″, and a first mold component sealing surface  72 ″ on a mold component  61 ″. The first sealing surfaces  70 ″ and  72 ″ may be substantially vertical surfaces in the embodiment shown in  FIG. 5 , whereas they are shown as including an inclined portion and a substantially vertical portion in the embodiment shown in  FIG. 3   a . The first sealing surfaces  70 ″ and  72 ″ may also be referred to as the first and second gap seal surfaces  70 ″ and  72 ″ respectively. 
     Reference is made to  FIG. 6 , in which a nozzle  100  is shown in accordance with an alternative embodiment of the present invention. The nozzle  100  may be similar to the nozzle  60  ( FIG. 3   a ), and may include a multi-portion seal  101  between a tip surrounding piece  102  and a mold component  103 . 
     The multi-portion seal  101  includes a gap seal  104  and a second seal  105 . The gap seal  101  is made by a first tip surrounding piece sealing surface  106  on the tip surrounding piece  102  cooperating with a first mold component sealing surface  107  on the mold component  103 . 
     In this embodiment, the sealing surfaces  106  and  107  may be substantially horizontal as shown, and are separated by the gap G. The sealing surfaces  106  and  107  may also be referred to as the first and second gap seal surfaces  106  and  107  respectively. In this embodiment, a separate alignment means (not shown) may be included if desired. 
     It will be noted that the nozzle  100  may optionally not include the second seal  105 , and have only the gap seal  101  with the mold component  103 . 
     Reference is made to  FIGS. 7 and 8 , which show a nozzle  200 . Nozzle  200  is similar to nozzle  10 , but is an edge-gated nozzle. Nozzle  200  includes a nozzle body  201  having a nozzle melt passage  202 , which divides into a plurality of the melt passage portions  204  ( FIG. 8 ). Nozzle  200  is for feeding melt through a plurality of gates  205  into a plurality of mold cavities  206 , in a mold component  208 . Nozzle  200  has an end  210 , which may be positioned in a bore  212  in the mold component  208 , for transferring melt into the mold cavities  206 . On the end  210 , is mounted a guide piece  214 . The guide piece  214  fits within a guide aperture  215  for aligning the end  210  of nozzle  200  in the bore  212 . The nozzle  200  may include a heater  216  and a thermocouple  218  ( FIG. 7 ). 
     Referring to  FIG. 8 , each nozzle melt passage portion  204  has therewith a nozzle tip  220  and a tip surrounding piece  222 . The tip  220  and the tip surrounding piece  222  may mount to the nozzle body  201 , in a similar manner to tip  16  and tip surrounding piece  18  to nozzle body  14  ( FIG. 1 ). The tip  220  includes a tip melt passage  224  in communication with a nozzle melt passage portion  204 , and has an exit  226 . The tip surrounding piece  222  may include a tip surrounding piece sealing surface  228  that surrounds exit  226  and gate  205 , and is positioned at a gap G from a mold component sealing surface  230  on the mold component  208 , forming a gap seal  232  therewith. A chamber  234  is defined between the tip  220  and the gate  205 . The tip surrounding piece sealing surface  228  and the mold component sealing surface  230  may be referred to as the first and second gap seal surfaces  228  and  230  respectively. 
     Melt passes through nozzle melt passage  202 , melt passage portions  204 , tip melt passages  224 , out from exits  226  into chambers  234 , through gates  205  and into mold cavities  206 . Melt is inhibited from escaping from chamber  234  by the gap seal  232 . 
     Nozzle  200  may include an alternative tip  240  and tip surrounding piece  242  which are integrally joined, forming a single piece, instead of tip  220  and tip surrounding piece  222 , or may include some of each type of tip and tip surrounding piece. 
     Reference is made to  FIG. 9 , which shows a nozzle  300  in accordance with another embodiment of the present invention, in combination with a mold component  301 . The nozzle  300  may be similar to nozzle  10  ( FIG. 1 ), and includes a nozzle body  302 , the heater  17 , a tip  304  and may optionally include the thermocouple  26 . The nozzle body  302  defines a nozzle body melt passage  306  therethrough. The heater  17  may be positioned on the nozzle body  302  in any suitable way, for heating melt in the nozzle body melt passage  306 . 
     The tip  304  may be similar to the tip  16  ( FIG. 1 ) and defines a tip melt passage  308  therethrough. The tip  304  may be removably connected to the nozzle body  302  in any suitable way, so that the tip melt passage  308  is in fluid communication with and downstream from the nozzle body melt passage  306 . The tip  304  may, for example, have a tip threaded portion  310  for mating with a nozzle body threaded portion  312  on the nozzle body  302 . The tip may further include a tip tool engagement portion  314  for receiving a tool (not shown), for the installation and removal of the tip  304  with respect to the nozzle body  302 . 
     The mold component  301  defines a plurality of melt cavities  316 , each of which has at least one gate  318  leading thereto. A plurality of cooling channels  320  may be included in the mold component  301  to cool melt in the mold cavities  316 . 
     A gap seal  322  may be formed by the cooperation of the tip sealing surface  324  and a mold component sealing surface  326 , which are separated by the gap G. The tip sealing surface  324  and the mold component sealing surface  326  may also be referred to as the first and second gap seal surfaces  324  and  326  respectively. 
     The tip can be manufactured by any of the materials that are used for the tip  16  ( FIG. 1 ), however, it may be advantageous to use a material other than Tungsten Carbide, due to the existence of the threaded portion  310  on the tip  304 . 
     Reference is made to  FIG. 10 , which shows a nozzle  400  in accordance with another embodiment of the present invention, in combination with the mold component  301 . The nozzle  400  may be similar to the nozzle  300  and includes a nozzle body  402 , the heater  17 , a tip  404 , a tip surrounding piece  406  and may optionally include the thermocouple  26 . The nozzle body  402  may be similar to the nozzle body  302  ( FIG. 9 ), and defines a nozzle body melt passage  408  therethrough. The nozzle body  402  also includes a first nozzle body threaded portion  410  for mating with a tip threaded portion  412  on the tip  404 . The nozzle body  402  also includes a second nozzle body threaded portion  414  for mating with a tip surrounding piece threaded portion  416  on the tip surrounding piece  406 . The tip  404  may be similar to the tip  304  and defines a melt passage  418  therethrough. The tip  404  may also include a tip tool engagement portion  420  for receiving a tool (not shown). In the embodiment shown in  FIG. 10 , the tip  404  is removably connected to the nozzle body  402  by means of the cooperation of threaded portions  416  and  410 . 
     The tip surrounding piece  406  may be similar to the tip surrounding piece  18  ( FIG. 1 ), except that the threaded portion  414  on the tip surrounding piece  406  may be an internally threaded portion, instead of an externally threaded portion, and except that the tip surrounding piece  406  does not retain the tip  404  in place. 
     The tip surrounding piece  406  may include a tip surrounding piece tool engagement portion  422  for receiving a tool (not shown). 
     The tip surrounding piece  406  has a tip surrounding piece sealing surface  424 , which cooperates with the mold component sealing surface  326  to form a gap seal  428  therewith. The sealing surfaces  424  and  326  are separated by the gap G, which inhibits melt leakage therebetween. The sealing surfaces  424  and  326  may also be referred to as the first and second gap seal surfaces  424  and  326  respectively. 
     Reference is made to  FIG. 11 , which shows a nozzle  60 ″, in combination with a mold component  61 ″, in accordance with a variant of the nozzle  60 ″ and mold component  61 ″ shown in  FIG. 5 . The nozzle  60 ″ may be similar to the nozzle  60 ″ with the exception that a tip surrounding piece  62 ″ on the nozzle  60 ″ includes a seal piece  450  thereon. The seal piece  450  may be a band that surrounds the outer surface of the tip surrounding piece  62 ″, and forms a gap seal  452  with the mold component  61 ″. The seal piece  450  has a sealing surface before that mates with mold component sealing surface  72 ″ to form the gap seal  452 . The sealing surfaces  454  and  72 ″ are separated by the gap G, which inhibits melt leakage therepast. The sealing surfaces  454  and  72 ″ may also referred to as the first and second gap seal surfaces  454  and  72 ″ respectively. 
     The seal piece  450  may be made from a material that has a lower thermal conductivity than that of the tip surrounding piece  62 ″. The seal piece  450  may, for example, be made from titanium, H13, stainless steel, mold steel or chrome steel. Other alternative materials include ceramics and plastics. The seal piece  450  may, instead of being a separate piece that is joined to the tip surrounding piece  62 ″, be a coating or layer that is applied to a portion of the outside surface of the tip surrounding piece  62 ″. 
     The tip surrounding piece  62 ″ may be positioned, at least in part, between the heater and the tip melt passage  86 . It may be advantageous in the case shown in  FIG. 11 , for the tip surrounding piece  62 ″ to be made from a material that is generally equally thermally conductive as the material of the tip  84 . The seal piece  450  reduces the heat transfer between the tip surrounding piece  62 ″ and the mold component  61 ″, by being made from a material that has a lower thermal conductivity than that of the tip surrounding piece  62 ″. 
     Reference is made to  FIG. 12 , which shows an injection molding apparatus  500 , that includes a runner component  502 , the mold component  12  and a plurality of nozzles  504  in accordance with the present invention. 
     The runner component  502  includes a plurality of runners  506  which transfer melt from a main runner inlet  508  to the nozzles  504 . The runner component  502  may be heated by a heater  510 . 
     The nozzles  504  transfer melt from the runner component  502  to the mold component  12 . The nozzles  504  may be any of the nozzle embodiments and variants described above and shown in  FIGS. 1–11 , and include a nozzle sealing surface  512  that is separated from a mold component sealing surface  514  by the gap G to form a gap seal  516  therewith. The nozzle sealing surface  512  and the mold component sealing surface  514  may also be referred to as the first and second gap seal surfaces  512  and  514  respectively. The nozzle sealing surface  512  may be positioned on any suitable portion or component of the nozzle  504 . 
     A particular example of an injection molding apparatus is shown in  FIG. 12 . It will be appreciated that the injection molding apparatus that incorporates the gap seal of the present invention may be any suitable type of injection molding apparatus and is not limited to the example shown. 
     It will be appreciated that the first and second gap seal surfaces that make up the gap seal of the present invention, may be surfaces on any component of the nozzle and mold component respectively, and are not limited to the examples shown and described herein. For greater certainty, the first gap seal surface may be positioned on any suitable structure that is part of the nozzle, and is therefore connected at least indirectly to the nozzle body. 
     Thermal expansion and contraction during a molding cycle must be considered during the construction of the nozzles described above, so that the gap G is within the ranges given above when the nozzle feeds melt into the gate. 
     It will be appreciated that it may be advantageous to size the gap G so as to reduce to a desired level, the amount of heat lost from the nozzle. 
     It will be appreciated that the particular configuration of the gap seal portion may be selected depending on the specific molding application, including the Theological properties of the melt, such as its viscosity at the injection temperature. It is contemplated that the invention can be applied to nozzles with types of melt other than those types of melt specifically disclosed herein. 
     While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the accompanying claims.