Abstract:
A hot runner injection molding apparatus includes a hot runner nozzle and a first heater coupled to the nozzle body of the nozzle. A separate mold gate insert surrounds a nozzle tip area of the nozzle. The mold gate insert is heated by a second heater that is separate and independent from the nozzle body heater. The temperature generated by the first and second heaters is measured by a first thermocouple and a second thermocouple, respectively. A controller is used to adjust at any time the temperature of the first and second heaters independently. The second heater is used to either i) melt, and thus enable a faster removal of, a colder molten material accumulated around the nozzle tip during a color change procedure or ii) to reduce or increase the temperature of the nozzle tip differently from one nozzle to the next.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure relates to hot runner nozzles for injection molding and associated heating devices for controlling the temperature of the hot runner nozzles. 
       BACKGROUND 
       [0002]    Injection molding hot runner systems are known. Depending on the application and other considerations, the hot runner systems can be used as thermal gating nozzles or valve gating nozzles. Reference is made in this regard to U.S. Pat. Nos. 6,609,902 and 6,921,257 showing thermal gating hot runner nozzles. Further reference is made in this regard to U.S. Pat. Nos. 6,921,259 and 8,419,417 showing valve gating hot runner nozzles. 
         [0003]    The known thermal gating nozzles or valve gating nozzles work properly for some moldable parts, for some plastic resins and for some applications. Nevertheless, in many practical applications and instances the known hot runner nozzles are designed differently to ensure an improved control of the heat profile along the nozzle and especially at the areas around the end of the nozzle tip and in the proximity of the mold gate orifice. Reference is made in this regard to U.S. Pat. Nos. 5,061,174, 5,871,786, and 7,914,271 disclosing thermal gating hot runner nozzles. Further reference is made in this regard to U.S. Pat. No. 5,470,219 and to WO 2015/105817 disclosing valve gating hot runner nozzles. 
         [0004]    During injection molding, the nozzle tip area is generally colder than the middle portion of the nozzle, due to heat losses to the mold near the mold cavity orifice, where the nozzle tip is located. As a result, a melt pre-chamber of a nozzle is for example colder than the melt channel. If the temperature in the melt channel is too low in some areas, for example in the area of the contact surface between nozzle tip and mold cavity orifice, several process issues can arise as for example difficulties with the start up or with color changes. In the same way, issues with molded product quality can arise as for example a raised injection gate or inclusions of “chips” of premature solidified melt. 
         [0005]    Based on this, there is a need to further improve the hot runner nozzles mentioned above and similar for applications that require a faster color change between batches of molded articles in order to reduce the waste of material and to improve the productivity. 
         [0006]    There is a need to further improve the hot runner nozzles mentioned above and similar for applications that require highly accurate and visually esthetic molded articles in order to reduce the number of rejected parts and also to meet the demands by an application or a client. 
         [0007]    There is a need to further improve the hot runner nozzles mentioned above and similar for applications that require a more balanced heat profile along the nozzle in order to be able to mold articles of various materials that require a wider operating window of the nozzle. 
       SUMMARY 
       [0008]    An injection molding apparatus according to the present invention may comprise a manifold having a manifold inlet to receive molten plastic material or resin and a plurality of manifold outlets. The injection molding apparatus may comprise a plurality of hot runner nozzles coupled to the manifold outlets and located in individual bores of a mold plate. Each hot runner nozzle may include a nozzle body and a nozzle tip. The hot runner nozzle may further include a first heating element coupled to the nozzle body and a first thermocouple for measuring an amount of heat generated by the first heating element. 
         [0009]    The injection molding apparatus may further comprise a plurality of mold gate inserts located in the bores of the mold plate and in the proximity of the nozzle tips. The mold gate inserts may be separated from the nozzles and from the nozzle tips to prevent direct contact and heat transfer between them and to allow the removal of nozzles via an axial translation relative to the mold gate inserts. The mold gate inserts may have an inner surface an outer surface and a mold cavity surface that forms at least a portion of a mold cavity adjacent to the mold gate orifice. Each mold gate insert may be heated by a second heating element, wherein an amount of heat generated by the second heating element is measured by a second thermocouple. 
         [0010]    The injection molding apparatus may further comprise a plurality of nozzle seals which are coupled to the nozzles. The nozzle seal may make contact with the inner surface of the mold gate insert providing sealing and an alignment of the nozzle with respect to the mold gate orifice. The nozzle seals may further limit a heat transfer from the nozzle to the mold gate insert when the second heating element is activated. The injection molding apparatus may also comprise a controller configured to receive temperature data from the first thermocouple and the second thermocouple for adjusting independently the first heating element and the second heating element. 
         [0011]    In the inventive injection molding machine, the nozzles may be arranged in mold gate inserts which are heated by a second heating element. The mold gate inserts may define the interface between the hot runner nozzles and the mold. The amount of heat of the second heating element may be measured by a second thermocouple independently adjustable via a controller of the injection molding apparatus. Based on at least the data received from the second thermocouple, the heat output of the second heating element may be adjustable by means of the controller for compensating the heat loss to the mold near the mold cavity orifice. 
         [0012]    The manifold inlet may receive molten plastic material or resin. In the following specification there is no distinction between the use of molten plastic material or the use of resin. The advantageous effects of the invention refer to hot runner injection molding apparatuses irrespective of the processing of resin or molten plastic material. 
         [0013]    A hot runner injection molding apparatus may include a hot runner manifold and several nozzles coupled to the manifold. Each nozzle may include a first heater coupled to the nozzle body. The amount of heat of the first heating element may be measured by a first thermocouple. Based on at least the data received from the first thermocouple, the heat output of the first heating element may be adjustable independently from the heat output of the second heating element by means of the controller for providing a suitable heat profile along the nozzle body and in particular along the melt channel within the nozzle body. 
         [0014]    The nozzle tip may be arranged in a mold gate insert which is heated by the second heater. The second heater may be independent from the first heater and may be placed on an outer surface of the mold gate insert. 
         [0015]    Each nozzle may include a nozzle tip and a nozzle seal. The nozzle seal may make contact with an inner surface of the mold gate insert. The nozzle seal may be arranged at the front portion of the nozzle, in particular at the nozzle tip or at the front end of the nozzle body. The nozzle seal may define the interface between the nozzle and the mold gate insert and may serve in particular—depending on the application—for positioning and sealing the nozzle relative to the mold gate insert and the mold orifice, respectively. 
         [0016]    The temperature generated by the first heater may be measured by the first thermocouple and the temperature generated by the second heater by the second thermocouple. The controller is used to adjust at any time the temperature of the first heater and the temperature of the second heater independently, the second heater being used to either i) heat and melt and thus enable a faster removal of a colder molten material accumulated around the nozzle tip during a color change procedure or for preventing and/or clearing a raised injection gate or ii) to reduce or increase the temperature of the nozzle tip differently from one nozzle to the next or iii) in a startup operation prior to injecting melt into the mold cavity. 
         [0017]    Depending on the application and the processed material the nozzle seal can be manufactured from of a material i) having a lower thermal conductivity than the material of the nozzle tip to provide thermal insulation of the tip relative to the mold gate insert, or ii) having the same thermal conductivity than the material of the nozzle tip to allow a heat transfer from the mold gate insert to the nozzle tip, or iii) having a higher thermal conductivity than the material of the nozzle tip to enhance the heat transfer from the mold gate insert to the nozzle tip. 
         [0018]    In one embodiment the hot runner nozzle is an open gating nozzle. Here, the second heating element is configured to heat up a bubble area defined between the inner surface of the mold gate insert, an outer surface of the nozzle tip, and the nozzle seal, to provide removal of a resin accumulation in the bubble area between subsequent injection steps. 
         [0019]    In another embodiment hot runner nozzle is a valve gating nozzle. Here, the second heating element is configured to heat up the mold gate orifice to a temperature dependent on the resin/the molten material that allows removal of a resin plug formed between injection cycles. 
         [0020]    The invention as described above is applicable with regard to hot runner nozzles in form of open gating nozzles (also known as thermal gate nozzles) or in form of valve gating nozzles (also known as valve gated or valve pin nozzles). The invention is further applicable for an injection molding apparatus comprising hot runner nozzles wherein the nozzle tip is integrally formed with the nozzle body or wherein the nozzle tip is separate from the nozzle body. Advantageous effects of the invention have a positive impact on all such injection molding apparatuses. 
         [0021]    In one embodiment the nozzle tip is made of a different material than the nozzle body material. As different materials have different thermal conductivities, it is possible to influence the heat flow between the nozzle tip and the nozzle body by means of choosing suitable materials for the nozzle body and the nozzle tip. 
         [0022]    In one embodiment the second heating element for heating the mold gate insert is a removable heating element. Removable elements are easier to service and to replace in the case of malfunction or if a different heat output is required for different applications. 
         [0023]    In one embodiment the second heating element for heating the mold gate insert is an embedded heating element. Embedded heating elements are usually arranged in special designed and positioned receiving grooves at the mold gate insert for enhancing the heat flow from the heating element to the mold gate insert. 
         [0024]    One embodiment of the second heating element for heating the mold gate insert includes at least one linear cartridge heater. In another embodiment the second heating element for heating the mold gate insert includes at least one heating element having a coiled heater or a linear cartridge heater. The selection of the type of heating element depends on the application, in particular on the design of the mold and the mold gate insert (for example regarding space requirements) and on the required output of heat for the respective application. 
         [0025]    In one embodiment the mold gate insert includes a cooling device. The cooling device is used after the injection step for cooling at least one portion of the mold gate insert arranged adjacent to the mold gate orifice for allowing a fast solidification of the molded part and thus also to shorten the injection molding cycle. In one embodiment the cooling device is water based and in another embodiment the cooling device is gas based. In particular, the cooling device is an embedded cooling device comprising cooling pipes with a cooling fluid flowing there through. The cooling pipes are in particular formed within or adjacent to the mold gate insert and in particular adjacent to the mold gate orifice. 
         [0026]    In one embodiment a thermal insulation coating is applied on an outer surface of the mold gate insert. By means of a thermal insulation coating the heat transfer from the second heating element to the mold gate insert can be restricted. Depending on the position of the thermal insulation coating on the mold gate insert it is possible to define areas with low heat transfer (coated areas) and areas with high heat transfer (areas without coating). 
         [0027]    It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The following is a description of the examples depicted in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity or conciseness. 
           [0029]      FIG. 1A  shows an exemplary embodiment of an inventive hot runner apparatus with open nozzles for an injection molding process; 
           [0030]      FIG. 1B  shows a sectional view of an open nozzle of the exemplary embodiment from  FIG. 1A  in more detail; 
           [0031]      FIG. 1C  shows a sectional view of the mold gate area of the exemplary embodiment from  FIG. 1A  in more detail; 
           [0032]      FIGS. 2A-2C  show different views of the mold gate insert with cartridge heaters of the exemplary embodiment from  FIG. 1A ; 
           [0033]      FIGS. 3A-3C  show different views of the mold gate insert with a coiled heater of a further exemplary embodiment of an inventive hot runner apparatus with open nozzles; 
           [0034]      FIGS. 4A-4C  show different views of the mold gate insert with an embedded coiled heater and a cooling device of a further exemplary embodiment of an inventive hot runner apparatus with open nozzles; 
           [0035]      FIG. 5  shows a further exemplary embodiment of an inventive hot runner apparatus with valve pin nozzles for an injection molding process; 
           [0036]      FIGS. 6A-6D  show different views of the mold gate insert with cartridge heaters of the exemplary embodiment from  FIG. 5 ; 
           [0037]      FIGS. 7A-7C  show different views of the mold gate insert with cartridge heaters and a replaceable tip of a further exemplary embodiment of an inventive hot runner apparatus with valve gated nozzles; 
           [0038]      FIGS. 8A-8C  show different views of the mold gate insert with a coiled heater of a further exemplary embodiment of an inventive hot runner apparatus with valve gated nozzles; 
           [0039]      FIGS. 9A-9C  show different views of the mold gate insert with an embedded coiled heater and a cooling device of a further exemplary embodiment of an inventive hot runner apparatus with valve gated nozzles; and 
           [0040]      FIG. 10  shows a schematic illustration of an exemplary embodiment of a hot runner apparatus according to the invention comprising a controller for adjusting at least the heat output of the first and second heating elements. 
       
    
    
       [0041]    The foregoing summary, as well as the following detailed description of certain inventive techniques, will be better understood when read in conjunction with the figures. It should be understood that the claims are not limited to the arrangements and instrumentality shown in the figures. Furthermore, the appearance shown in the figures is one of many ornamental appearances that can be employed to achieve the stated functions of the apparatus. 
       DETAILED DESCRIPTION 
       [0042]    In the following detailed description, specific details may be set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be clear to one skilled in the art when embodiments of the present invention may be practiced without some or all of these specific details. In other instances, well-known features or processes may not be described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals may be used to identify common or similar elements. 
         [0043]      FIG. 1A  shows an exemplary embodiment of an inventive hot runner apparatus  12  with thermal gating/open nozzles for an injection molding process. The hot runner apparatus  12  serves for an injection molding processes and comprises an open nozzle assembly  20  (in the exemplary embodiment having four nozzles; the number of nozzles comprised in an open nozzle assembly depends on the application and may also be two or more than four; 64 or 128 nozzles are also possible) coupled to a hot runner manifold  19  having a manifold inlet  17  to receive molten plastic material and a plurality of manifold outlets (not shown). The hot runner nozzles  20   a  are located in individual bores  30   a  of a mold plate which comprises cavity blocks  30  in the exemplary embodiment of  FIG. 1A . In each cavity block  30  an impression is arranged which forms a part of the mold cavity  32 . 
         [0044]    Each hot runner nozzle  20   a  includes a nozzle body  22  and a nozzle tip  23 , the hot runner nozzle  20   a  further including a first heating element  21  coupled to the nozzle body  22  and a first thermocouple  18  to measure an amount of heat generated by the first heater  21 . The exemplary hot runner apparatus  12  comprises four mold gate inserts  28  located in bores  30   a . In proximity of the nozzle tips  23  the mold gate inserts  28  have an inner surface  28   a  and an outer surface  28   b  and a mold cavity surface  35  that forms a portion of the mold cavity  32 . Each mold gate insert  28  is heated by a second heating element  25 . An amount of heat generated by the second heating element  25  is measured by a second thermocouple  31 . 
         [0045]    The exemplary hot runner apparatus  12  further comprises four nozzle seals  26  each coupled to a nozzle  20   a . The nozzle seal  26  makes contact with the inner surface  28   a  of the mold gate insert  28  and provides sealing and an alignment of the respective nozzle  20   a  with respect to a mold gate orifice  34 . A controller  137  (not shown in  FIG. 1A ) is connected to the hot runner apparatus  12  which is configured to receive temperature data from the first thermocouple  18  and the second thermocouple  31  and for adjusting the heat output of the first heating element  21  and of the second heating element  25  independently from each other. 
         [0046]      FIG. 1B  shows a sectional view of an open nozzle  20   a  of the exemplary embodiment as indicated by a vertical ellipse in  FIG. 1A  in more detail. At the left side of the illustration of the open nozzle  20   a , a diagram plots the level of the temperature T within the melt channel over the length L of the hot runner nozzle  20   a  originating from the flange of the nozzle  20   a  at the manifold  19 . The diagram shows in a broken line the level of the temperature in a situation where the second heating element  25  is not in use. As can be recognized from this diagram, the temperature within the melt channel of the hot runner nozzle  20   a  decreases constantly from the flange of the nozzle to the nozzle tip  23 , wherein the temperature drop is the higher the closer the position is arranged with respect to the nozzle tip  23 , where the temperature is the lowest. The nozzle tip  23  is arranged adjacent to the mold gate orifice  34  and thereby in close proximity to the cavity block  30  which has a lower temperature than the hot runner nozzle  20   a.    
         [0047]    The diagram shows in a solid line the level of the temperature in a situation where the second heating element  25  is in use. As can be recognized from this diagram, the temperature within the melt channel of the nozzle body  22  is generally higher in a situation where the second heating element  25  is in use. In a first area from the flange of the nozzle to the nozzle tip  23 , the temperature is relatively constant. Only in an area closer to the nozzle tip  23  of the hot runner nozzle  20   a , the temperature decreases in a direction to the mold gate orifice  34 , but only to a smaller extent in comparison to a situation without heating from a second heating element  25 . 
         [0048]    The first heating element  21  is arranged at the circumference of the nozzle body  22 . An outflow of heat occurs from the nozzle tip  23  into the cavity block  30 , which leads to decreasing temperatures in the direction to the nozzle tip  23  and also to decreasing temperature of the melt located within the melt channel of the hot runner nozzle  20   a  in these areas. 
         [0049]    In  FIG. 1C  a sectional view of the nozzle end portion  29  as indicated by a horizontal ellipse in  FIG. 1A  is shown in more detail. The illustration shows in particular the area of the nozzle tip  23  with the nozzle seal  26  arranged within the mold gate insert  28  close to the mold gate orifice  34  along with a second heating element  25 . The second heating element for open gated nozzles  25  is configured to heat up a bubble area  39  defined between the inner surface  28   a  of the mold gate insert  28 , an outer surface  23   a  of the nozzle tip  23 , and the nozzle seal  26  to provide removal of a resin accumulation in the bubble area  39  between subsequent injection cycles. 
         [0050]      FIG. 2A  shows a sectional view of a mold gate insert  28  with cartridge heaters  45   a  of the exemplary embodiment of a hot runner apparatus  12  with an open nozzle assembly  20  for an injection molding process from  FIG. 1A . A mold gate insert  28  is arranged in a bore  30   a . The bore  30   a  is arranged in a cavity block  30  which in the exemplary embodiment forms a part of a mold plate. An open hot runner nozzle  20   a  is arranged in the mold gate insert  28  having a first heating element  21  arranged at its nozzle body  22  and with a nozzle seal  26  coupled to the front end of the nozzle  20   a . The nozzle seal  26  is sealingly arranged at the inner surface  28   a  of the mold gate insert  28  thereby positioning the nozzle tip  23  with respect to the mold gate insert  28  and the mold gate orifice  34 , respectively. 
         [0051]    In all the embodiments illustrated in  FIG. 1 a    through  FIG. 9 c   , the mold gate inserts  28  is separated from the hot runner nozzles  20   a ,  27   a  and from the tips  23  to prevent a direct contact and a heat transfer between them and to allow the removal of nozzles  20   a ,  27   a  via an axial translation relative to the mold gate inserts  28 . The mold gate inserts  28  have an inner surface  28   a , an outer surface  28  and a mold cavity surface  35  that forms at least a portion of a mold cavity  32  and an adjacent mold gate orifice  34 . 
         [0052]    Because the mold gate insert  28  is heated and the nozzle seal  26  contacts the mold gate insert  28 , the invention provides new possibilities in the selection of the materials for the nozzle tip  23  and the nozzle seal  26  to use the same geometry for many nozzles and only change the materials for each specific application and for each specific resin to be molded. 
         [0053]    In all the embodiments shown in  FIG. 1A  through  FIG. 9 c    the material of the nozzle seal  28  is adapted to either reduce, maintain or enhance the heat transfer from the mold gate insert  28  heated by all heating elements  25   a ,  45   a  dependent on the resin/molten plastic material to be molded, the required cycle time and other processing factors. Accordingly, the material of the nozzle seal  26  can be the same/similar or an equivalent material as the material of the nozzle tip  23  or a different material. The material of the nozzle seal  26  is, for example, a copper or a copper alloy, a steel such as H 13  or a stainless steel, or a more thermally insulative material such as, for example, titanium and its alloys, ceramics of various compositions, or polyimides (such as Vespel) or high performance plastics (such as PEEK) and defined, for example, in Wikipedia and other resources. The tip nozzle tip  23  is in some embodiments made from a material having both wear resistance and good thermal conductivity such a tungsten carbide or similar/equivalent materials. In this case the nozzle seal  26  is made either of titanium, Vespel, PEEK or a ceramic. These combinations are suitable for bot open gate and valve gated nozzles. 
         [0054]    The material of the mold gate insert also depends on various factors such as the type of the resin/molten plastic material. For example different materials are used for the mold gate insert  28  if Engineering Thermoplastics or Commodity are a subset of plastic materials that are used in applications generally requiring higher performance in the areas of heat resistance, chemical resistance, impact, fire retardancy or mechanical strength. Engineering Thermoplastics are so named as they have properties in one or more areas that exhibit higher performance than commodity materials and are suitable for applications that require engineering to design parts that perform in their intended use. 
         [0055]    The mold gate insert  28  is fitted within the bore  30   a  of the cavity block  30  along with cartridge heaters  45   a  for thermal equilibrium in the nozzle end portion  29 . The cartridge heaters  45   a  are embedded in the cavity block  30  within respective cavity block groove  36  which are arranged in the section plane of  FIG. 2A . In the exemplary embodiment shown in  FIG. 2A , both, mold gate insert  28  and nozzle seal  26  are of high thermal conductive material, allowing the flow of heat into the nozzle end portion  29 . The cartridge heaters  45   a  are insulated by means of an insulation element  33  arranged in the respective cavity block groove  36  to restrict the heat flow into the cavity block  30 . A thermal insulation coating  99  is applied on an outer surface of the mold gate insert  28  to restrict the heat transfer to cavity block  30 . 
         [0056]      FIG. 2B  shows a 3-dimensional view of a mold gate insert  28  with the mold gate orifice  34 . In the exemplary embodiment a cartridge heater assembly  45  comprised of three cartridge heaters  45   a  is arranged at the outer surface  28   b  of each of the mold gate inserts  28 .  FIG. 2B  shows the position of the cartridge heaters  45   b  along with the second thermocouple  31  as well as electrical wiring  45   b  of cartridge heaters  45   a . The second thermocouple  31  is arranged near the tip area  29  for measurement of the amount of heat generated by the cartridge heater assembly  45 . 
         [0057]      FIG. 2C  shows a sectional exploded view of the open nozzle  20   a , the mold gate insert  28  with a cartridge heater  45   a  and an insulation element  33  to the right and a second thermocouple  31  to the left and the cavity block  30  of the exemplary embodiment from  FIG. 2A . A cavity block groove  36  is arranged in the bore  30   a  of the cavity block  30  for receiving the insulation element  33  and the cartridge heater  45   a . The elements are shown with an assembly sequence indicated by arrows. 
         [0058]      FIG. 3A  shows a sectional view of a mold gate insert  28  with a coiled heater  55  according to a further exemplary embodiment of a hot runner apparatus  12  with an open nozzle assembly  20  for an injection molding process. A mold gate insert  28  is arranged in a bore  30   a . The bore  30   a  is arranged in a cavity block  30  which in the exemplary embodiment forms part of a mold plate. An open hot runner nozzle  20   a  is arranged in the mold gate insert  28  having a first heating element  21  arranged at its nozzle body  22  and with a nozzle seal  26  coupled to the front end of the nozzle  20   a . The nozzle seal  26  is sealingly arranged at the inner surface  28   a  of the mold gate insert  28  thereby positioning the nozzle tip  23  with respect to the mold gate insert  28  and the mold gate orifice  34 , respectively. 
         [0059]    The open nozzle  20   a  is fitted in the mold gate insert  28  along with a coiled heater  55  for thermal equilibrium in the nozzle end portion  29 . In  FIG. 3A  both mold gate insert  28  and nozzle seal  26  are of high thermal conductive material, allowing the flow of heat into the end portion  29 . Nevertheless, depending on the resin to be molded also different combinations of materials can be used, as already mentioned before. A coil of the coiled heater  55  encircles the outer surface  28   b  of the mold gate insert  28  adjacent to the mold gate orifice  34 . The second thermocouple  31  for measurement of the amount of heat generated by the coiled heater  55  is arranged near the nozzle end portion  29  being also accommodated within a cavity block groove  36  in the bore  30   a  of the cavity block  30 . The bore  30   a  is designed with cavity block grooves  36  for receiving the coiled heater  55  and the second thermocouple  31 , respectively. At the coiled heater  55  an insulation element  33  is arranged for restricting the flow of heat into the cavity block  30 . Also in the embodiment shown in  FIG. 3A , a thermal insulation coating  99  is applied on outer surface of the mold gate insert  28  to restrict the heat transfer in cavity block  30 . The second heating element  25   a  is configured to heat up the bubble area  39  defined between the inner surface  28   a  of the mold gate insert  28 , an outer surface  23   a  of the nozzle tip  23 , and the nozzle seal  26 , to provide removal of a resin accumulation in the bubble area  39  between subsequent injection steps. 
         [0060]      FIG. 3B  shows a 3-dimensional view of a mold gate insert  28  with the mold gate orifice  34 . In the exemplary embodiment of  FIG. 3A , a coiled heater  55  is arranged at the outer surface  28   b  of each of the mold gate inserts  28 . As is shown in  FIG. 3B , the coil of the coiled heater  55  encircles the outer surface  28   b  of the mold gate insert  28  adjacent to the mold gate orifice  34  and touches the mold gate insert  28 . The bore  30   a  of the cavity block  30  is designed with corresponding cavity block grooves  36  for receiving the coiled heater  55  and the second thermocouple, respectively. In  FIG. 3B  the coiled heater  55  along with the second thermocouple  31  as well as the electrical wiring  55   a  of the coiled heater  55  is shown.  FIG. 3B  shows the position of the coiled heater  55  along with the thermocouple  31  which is arranged near the nozzle end portion  29 . 
         [0061]      FIG. 3C  shows a sectional exploded view of the open nozzle  20   a , the mold gate insert  28  with a coiled heater  55  and an insulation element  33 , a second thermocouple  31  and the cavity block  30  of the exemplary embodiment from  FIG. 3A . In the bore  30   a  of the cavity block  30  a cavity block groove  36  is arranged circumferentially to the mold gate orifice  34  for receiving the insulation element  33  and the coiled heater  55 . The elements are shown with an assembly sequence indicated by arrows. 
         [0062]      FIG. 4A  shows a sectional view of a mold gate insert  28  with an embedded coiled heater  55  and a cooling device  37  according to a further exemplary embodiment of a hot runner apparatus  12  with an open nozzle assembly  20  for an injection molding process. A mold gate insert  28  is fitted in a bore  30   a  along with the embedded coiled heater  55  and the cooling device  37  in form of cooling pipes  37   a  for thermal equilibrium in the nozzle end portion  29  of the mold gate insert  28 . The bore  30   a  is arranged in a cavity block  30  which in the exemplary embodiment forms part of a mold plate. An open hot runner nozzle  20   a  is arranged in the mold gate insert  28  having a first heating element  21  arranged at its nozzle body  22  and with a nozzle seal  26  coupled to the front end of the nozzle  20   a . The nozzle seal  26  is sealingly arranged at the inner surface  28   a  of the mold gate insert  28  thereby positioning the nozzle tip  23  with respect to the mold gate insert  28  and the mold gate orifice  34 , respectively. 
         [0063]    The open nozzle  20   a  is fitted in the mold gate insert  28 . In  FIG. 4A  both mold gate insert  28  and nozzle seal  26  are of high thermal conductive material, allowing the flow of heat into the nozzle end portion  29 . Nevertheless, depending on the resin to be molded different combinations of materials can be used, as already mentioned before. Several coils of the coiled heater  55  are helically arranged within corresponding recesses formed at the tapered outer surface  28   b  of the mold gate insert  28  adjacent to the mold gate orifice  34 . Cooling pipes  37   a  are helically arranged between the coils of the coiled heater  55  at the tapered outer surface  28   b  of the mold gate insert  28  adjacent to the mold gate orifice  34 . Also the cooling pipes  37   a  are embedded within the outer surface  28   a  of the mold gate insert  28 . A cooling gas is provided through the inlet  38  of the cooling device. 
         [0064]    The second thermocouple  31  for measurement of the amount of heat generated by the coiled heater  55  is arranged near the nozzle end portion  29  being accommodated within a cavity block groove  36  in the bore  30   a  of the cavity block  30 . The bore  30   a  is also designed with cavity block grooves  36  for receiving the second thermocouple  31 . At the coiled heater  55  an insulation element  33  is arranged for restricting the flow of heat into the cavity block  30 . 
         [0065]      FIG. 4B  shows a 3-dimensional view of a mold gate insert  28  with the mold gate orifice  34 . In the exemplary embodiment of  FIG. 3A , a coiled heater  55  and cooling pipes  37   a  are embedded in the outer surface  28   b  of each mold gate insert  28 . Coils of the coiled heater  55  and heat pipes  37  of the cooling device are embedded in the outer surface  28   b  of the mold gate insert  28  adjacent to the mold gate orifice  34 . The bore  30   a  of the cavity block  30  is designed with a corresponding cavity block groove  36  for receiving the second thermocouple  31 . In  FIG. 4B  the coiled heater  55  along with the second thermocouple  31  as well as the electrical wiring  55   a  of the coiled heater  55  is shown.  FIG. 4B  shows the position of the coiled heater  55  along with the thermocouple  31  which is arranged near the nozzle end portion  29 . 
         [0066]      FIG. 4C  shows a sectional exploded view of the open nozzle  20   a , the mold gate insert  28  with a coiled heater  55  and a second thermocouple  31  and the cavity block  30  of the exemplary embodiment from  FIG. 4A . An insulation element  33  is arranged within the grooves for the coiled heater  55  at the tapered front portion of the mold gate insert. A cavity block groove  36  is arranged in the bore  30   a  of the cavity block  30  for receiving the second thermocouple  31 . The elements are shown with an assembly sequence indicated by arrows. 
         [0067]      FIG. 5  shows a further exemplary embodiment of an inventive hot runner apparatus  14  with valve gated nozzles  27   a  (also known as valve pin nozzles or valve gating nozzles) for an injection molding process. In the same way as the hot runner apparatus  12  as shown in  FIGS. 1A to 4C , the hot runner apparatus  14  serves for an injection molding processes and comprises a valve gated nozzle assembly  27  (in the exemplary embodiment four nozzles; the number of nozzles comprised in a valve gated nozzle assembly depends on the application and may be two or more than four, up to 64 or 128 nozzles are also possible) coupled to a hot runner manifold  62  having a manifold inlet  67  to receive molten plastic material and a plurality of manifold outlets (not shown). The hot runner nozzles  27   a  are located in individual bores  30   a  of a mold plate which comprises cavity blocks  30  in the exemplary embodiment of  FIG. 5 . In each cavity block  30  an impression is arranged which forms a part of the mold cavity  32 . The valve pins  24  of the valve gated nozzles  27   a  are actuated by means of a pneumatic system  61  for controlling the flow of melt into the impression and thereby into the mold cavity  32 . 
         [0068]    Each valve gated hot runner nozzle  27   a  includes a nozzle body  22  with a nozzle tip  23  formed integrally with the nozzle body  22 . Corresponding to the open nozzles  20   a  shown in the exemplary embodiments of  FIGS. 1A to 4C , each valve gated hot runner nozzle  27   a  further includes a first heating element  21  coupled to the nozzle body  22  and a first thermocouple  18  to measure an amount of heat generated by the first heater  21 . The exemplary hot runner apparatus  14  comprises four mold gate inserts  28  located in bores  30   a  of cavity blocks  30 . The cavity blocks  30  as well as the mold gate inserts  28  of the hot runner apparatus  14  are designed corresponding to hot runner apparatus  12  shown in  FIGS. 1A to 4C . The front end of the nozzle  27   a  is arranged in proximity to an inner surface  28   a  of the mold gate insert  28 . Each mold gate insert  28  is heated by a second heating element  25 . An amount of heat generated by the second heating element  25  is measured by a second thermocouple  31 . 
         [0069]    The exemplary hot runner apparatus  14  further comprises four nozzle seals  26  each coupled to a valve gated nozzle  27   a . The nozzle seal  26  makes contact with the inner surface  28   a  of the mold gate insert  28  and provides sealing and an alignment of the respective nozzle  20   a  with respect to the mold gate orifice  34  and limits the heat transfer from the nozzle  27   a  to the mold gate insert  28 . A controller  137  (not shown in  FIG. 5 ) is connected to the hot runner apparatus  12  which is configured to receive temperature data from the first thermocouple  18  and the second thermocouple  31  and for adjusting the first heating element  21  and the second heating element  25  independently from each other. 
         [0070]      FIGS. 6A to 6D  show different views of the mold gate insert  28  with cartridge heaters  45   a  of the exemplary embodiment from  FIG. 5 . The design and functions of the elements shown in  FIGS. 6A to 6D  correspond to a large extent to the design and functions of the elements shown in  FIGS. 2A to 2C . Therefore, in the following the description will focus on the differences between these two embodiments. 
         [0071]      FIGS. 6A and 6B  show sectional views of a mold gate insert  28  with cartridge heaters  45   a  of the exemplary embodiment of a hot runner apparatus  14  with a valve gated nozzle assembly  27  for an injection molding process from  FIG. 5 .  FIGS. 6A and 6B  correspond to each other except that  FIG. 6A  shows the valve pin  24  in a closed position where the flow of melt into the mold cavity  32  is interrupted while  FIG. 6B  shows the valve pin  24  in an open position where melt can flow into the mold cavity  32 . 
         [0072]    A mold gate insert  28  is arranged in a bore  30   a  of a cavity block  30  forming a part of a mold plate. A first heating element  21  and a first thermocouple  18  are arranged at the nozzle body  22 . A nozzle seal  26  is coupled to the nozzle tip  23 , sealingly arranged at the inner surface  28   a  of the mold gate insert  28  thereby positioning the nozzle tip  23 . 
         [0073]    For thermal equilibrium in the nozzle end portion  29  the mold gate insert  28  is fitted within the cavity block  30  along with cartridge heaters  45   a  which are embedded in the cavity block  30 . Both, mold gate insert  28  and nozzle seal  26  are of high thermal conductive material, allowing the flow of heat into the nozzle end portion  29 . The cartridge heaters  45   a  are insulated by means of an insulation element  33  which restricts the heat flow into the cavity block  30 . A thermal insulation coating  99  is applied on an outer surface  28   b  of the mold gate insert  28  to restrict the heat transfer to cavity block  30 . Nevertheless, depending on the resin to be molded different combinations of materials can be used, as already mentioned before. The second heating element  45   a  is configured to heat up the mold gate orifice  34  to a temperature dependent on the resin that allows removal of a resin plug formed between injection cycles. 
         [0074]      FIG. 6C  shows a sectional exploded view of the valve gated nozzle  27   a , the mold gate insert  28  with a cartridge heater  45   a  and an insulation element  33  to the left and a second thermocouple  31  to the right and the cavity block  30  of the exemplary embodiment from  FIG. 6A to 6C . A cavity block groove  36  is arranged in the bore  30   a  for receiving the insulation element  33  and the cartridge heater  45   a . The elements are shown with an assembly sequence indicated by arrows. 
         [0075]      FIG. 6D  shows a 3-dimensional view of a mold gate insert  28 . A cartridge heater assembly  45  comprised of three cartridge heaters  45   a  is arranged at the outer surface  28   b  along with a second thermocouple  31 . The second thermocouple  31  is arranged near the nozzle end portion  29  for measurement of the amount of heat generated by the cartridge heater assembly  45 . 
         [0076]      FIGS. 7A to 7C  show different views of the mold gate insert  28  with cartridge heaters  45   a  and a replaceable nozzle tip  23  of a further exemplary embodiment of an inventive hot runner apparatus  14  with valve gated nozzles  27   a . The design and functions of the elements shown in  FIGS. 7A to 7C  correspond to the design and functions of the elements shown in  FIGS. 6A to 6C  with the exception that a valve gated nozzle  27   a  comprises a nozzle body  22  and a separate nozzle tip  23  mounted to the nozzle body  22 . Compared with the embodiment of  FIGS. 6A to 6C , the nozzle tip  23  may be manufactured from a material having a different thermal conductivity than the nozzle body. This allows one to increase or decrease the heat flow within the nozzle tip  23  and between the nozzle tip  23  and the nozzle body  22 . 
         [0077]      FIGS. 8A to 8C  show different views of the mold gate insert  28  with a coiled heater  25   a  of a further exemplary embodiment of an inventive hot runner apparatus  14  with valve gated nozzles  27   a . The design and functions of the elements shown in  FIGS. 8A to 8C  correspond to a large extent to the design and functions of the elements shown in  FIGS. 3A and 3C . Therefore, in the following the description will focus on the differences between these two embodiments. 
         [0078]    Compared with the embodiment of  FIGS. 3A and 3C , the embodiment of  FIGS. 8A to 8C  comprises a valve gated hot runner nozzle assembly  27  with valve gated nozzles  27   a  having a nozzle tip  23  formed integrally with the nozzle body  22 .  FIGS. 8A and 8B  show sectional views of a mold gate insert  28  with a coiled heater  25   a  of the exemplary embodiment of a hot runner apparatus  14  with a valve gated nozzle assembly  27  for an injection molding process from  FIG. 5 .  FIGS. 8A and 8B  correspond to each other except that  FIG. 8A  shows the valve pin  24  in a closed position where the flow of melt into the mold cavity  32  is interrupted while  FIG. 8B  shows the valve pin  24  in an open position where melt can flow into the mold cavity  32 . 
         [0079]      FIG. 8C  shows a sectional exploded view of the valve gated nozzle  27   a , the mold gate insert  28  with a coiled heater  55  and an insulation element  33 , a second thermocouple  31  and the cavity block  30  of the exemplary embodiment from  FIGS. 8A and 8B . In the bore  30   a  of the cavity block  30  a cavity block groove  36  is arranged circumferentially to the mold gate orifice  34  for receiving the insulation element  33  and the coiled heater  55 . The elements are shown with an assembly sequence indicated by arrows. 
         [0080]      FIGS. 9A to 9C  show different views of the mold gate insert  28  with an embedded coiled heater  55  and a cooling device  37  of a further exemplary embodiment of an inventive hot runner apparatus  14  with valve pin nozzles. The design and functions of the elements shown in  FIGS. 9A to 9C  correspond to a large extent to the design and functions of the elements shown in  FIGS. 4A and 4C . Therefore, in the following the description will focus on the differences between these two embodiments. 
         [0081]    Compared with the embodiment of  FIGS. 4A and 4C , the embodiment of  FIGS. 9A to 9C  comprises a valve gated hot runner nozzle assembly  27  with valve gated nozzles  27   a  having a nozzle tip  23  formed integrally with the nozzle body  22 .  FIGS. 9A and 9B  show sectional views of a mold gate insert  28  with a coiled heater  55  of the exemplary embodiment of a hot runner apparatus  14  with a valve gated nozzle assembly  27  for an injection molding process from  FIG. 5 .  FIGS. 9A and 9B  correspond to each other except that  FIG. 9A  shows the valve pin  24  in a closed position where the flow of melt into the mold cavity  32  is interrupted while  FIG. 9B  shows the valve pin  24  in an open position where melt can flow into the mold cavity  32 . 
         [0082]      FIG. 9C  shows a sectional exploded view of the valve gated nozzle  27   a , the mold gate insert  28  with a coiled heater  55  and a second thermocouple  31  and the cavity block  30  of the exemplary embodiment from  FIGS. 9A and 9B . An insulation element  33  is arranged within the grooves for the coiled heater  55  at the tapered front portion of the mold gate insert. The elements are shown with an assembly sequence indicated by arrows. 
         [0083]      FIG. 10  shows a schematic illustration of an exemplary embodiment of an inventive hot runner apparatus comprising a controller for adjusting at least the heat output of the first and second heating elements. 
         [0084]      FIG. 10  shows a hot runner injection molding system  10 . The injection molding system  10  includes an injection molding machine  102 , comprising a mold plate  104 . The injection molding machine  102  includes an injection unit  108  and a clamping unit  110 . The clamping unit  110  may include a plurality of hydraulic rams  114  that bring a first platen  116  and a second platen  118  towards and away from each other. A hot runner apparatus  12  or  14  of one of the exemplary embodiments can be arranged at the first platen  116 . The hot runner apparatus  12 ,  14  further comprises a controller  137  configured to receive temperature data from the first thermocouple  18  and the second thermocouple  31  from each nozzle  20   a ,  27   a , serving to adjust the first heating element  21  and the second heating element  25  independently from each other. The first and second thermocouples  18 ,  31  are arranged at the nozzles  20   a ,  27   a  and are connected to the controller  137 . The controller  137  may be integrated in the general controller of the hot runner injection molding system  10 . Also a plurality of processing sensors  120  may be provided to detect, among other things, the pressure of the molten material, motor current draw on the motors and any other suitable processing information. The sensors  120  are examples for further injection molding machine sensors and any other type of sensor may additionally or alternatively be provided for controlling the hot runner injection molding system  10  and the heat output of the first and second heating elements  21 ,  25 . 
         [0085]    Some of the elements described herein are identified explicitly as being optional, while other elements are not identified in this way. Even if not identified as such, it will be noted that, in some embodiments, some of these other elements are not intended to be interpreted as being necessary, and would be understood by one skilled in the art as being optional. 
         [0086]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.