Abstract:
The technical field of the invention broadly relates to injection molding systems and more particularly to cooling of a core used in a mold of an injection molding machine. Cooling a core involves supplying coolant through a lengthwise supply tube that extends within a hollow bore formed in the core. The coolant flows through the supply tube, exiting as a stream of fluid at an open end of the supply tube where the stream contacts a substantially perpendicular inner surface of the core. The stream of fluid is initially deflected by this inner surface on an axis perpendicular to an axis of the original flow producing a stagnation zone in the stream having zero or relatively low velocity. The stagnation zone is adjacent to a high heat gate area and results in poor cooling of the core tip. The invention solves the problem of stagnation by application of a fluid velocity inducer. The fluid velocity inducer is located in the entry stream path of the fluid inducing a velocity thus reducing or eliminating the stagnation zone and improving the cooling of the core.

Description:
FIELD OF THE INVENTION 
     The present invention relates to injection molding systems and more particularly, the invention relates to cooling of mold cores used in an injection molding machine for forming bottle preforms of polyethylene terephthalate (PET), polyethylene, or other injection moldable materials. 
     BACKGROUND OF THE INVENTION 
     Bottle preforms are molded in large quantities and minimizing the molding cycle time is critical to commercial viability of the system. Formed bottle preforms must be adequately cooled down to a sufficient temperature to allow their release from the mold without surface damage or physical distortion due to warping, or to avoid crystallization of the cooling melt of plastic. The rate of cooling the bottle preform is a major factor in determining overall cycle time. 
     In the field of injection molding, cooling a formed bottle preform located on a core is very well known and commonly used in industry. 
     For example, U.S. Pat. No. 5,571,470 entitled “Method for Fabricating a Thin Inner Barrier Layer within a Preform” issued to the Coca-Cola company on Nov. 5, 1996 and discloses a conventional apparatus for cooling formed bottle preforms. An elongate core rod is shown having an lengthwise inner channel. Cooling fluid circulates in the lengthwise inner channel for cooling the formed preform. 
     U.S. Pat. No. 5,582,788 entitled “Method of Cooling Multilayer Preforms” issued to Contentional PET Technologies Inc. on Dec. 10, 1996 and discloses a conventional apparatus for cooling formed bottle preforms. A cylindrical core is shown inserted within a mold cavity, including a formed bottle preform. The cylindrical core includes a lengthwise bore to receive circulating water within the interior of the core to cool the formed bottle preform during operation. 
     The book entitled “Mold Engineering” published by Hanser/Gardner publications, written by Herbert Rees, copyright 1995, describes bubbler mold cooling and baffle assist mold cooling on page 298. 
     An elongated core having a lengthwise bore is cooled through a bubbler and a conventional cooling medium. The bubbler is essentially a hollow tube having one end extending lengthwise into the lengthwise bore of the elongated core. The other end of the bubbler is connected to a inlet manifold port for supplying the cooling medium. The lengthwise bore forms a mouth at the open end of the core and is connected to a exit manifold port permitting water to exit the core. 
     Water enters the inlet manifold port, travelling through the bubbler into the elongated core and out of the open end of the elongated core into the exit manifold port. Water leaves the open end of the bubbler and contacts an inner surface of the core at a substantially perpendicular angle to the flow of cooling fluid from the bubbler. 
     Baffle assist mold cooling improves cooling by redirecting the flow of water along a differing path for more uniform cooling along the length of the elongated core. The example illustrates a helical path formed on the outer surface of the bubbler for directing the flow of water. 
     U.S. Pat. No. 4,208,177 entitled “Fluid Cooling of Injection Molded Plastic Articles” issued to Logic Devices on Jun. 17, 1980 and discloses an apparatus for cooling an injection molded plastic article. A pair of dies are illustrated, one having a mold cavity, the other having a core. The core includes a hollow chamber, inlet pipe and outlet pipe. The inlet pipe extends lengthwise into the hollow chamber towards an end plug. An outlet pipe is connected at a distant end of a side wall of the chamber. Cooling liquid circulates from the inlet pipe into the chamber and exits the outlet pipe. The cooling liquid streams from the inlet pipe and contacts a surface of the chamber at a substantially perpendicular angle to the flow of cooling fluid. 
     U.S. Pat. No. 5,631,030 entitled “Cooled Injection Core for an Integrated Injection Blow Mold machine” issued to Electraform Incorporated on May 20, 1997 and discloses an apparatus for creating a spiral flow path between the water inlet and the water outlet of a core. The cooling liquid leaves the inlet pipe located within a bore of a core and contacts an inner surface of the bore at a substantially perpendicular angle to the flow of cooling fluid. 
     U.S. Pat. No. 4,966,544 entitled “Injection Mold Having Cooling Fins” issued to Fuji Photo Film Company on Oct. 30, 1990 and discloses a series of baffles to direct the flow of coolant in a core. A core and cavity are illustrated within the disclosure. The core includes a supply port, an elongate hollow bore, and a discharge port. An elongate baffle plate is disposed lengthwise from one end of the hollow bore in close proximity of an upper end of the hollow bore. The elongate baffle separates the supply port from the discharge port and defines a flow path in the hollow bore extending between the supply and discharge ports. A pair of heat exchange ribs extend from the side walls of the hollow bore of the core in the direction of coolant flow. The coolant enters through the supply port, flows down one side of the hollow bore defined by the baffle plate, flows around the heat exchange ribs, down the other side defined by the baffle plate and the hollow bore, and out the discharge port. 
     Product literature posted on the internet web site for Choice Mold Components Incorporated on Jul. 12, 1999 illustrates a “Turbo Water Baffle” product for use in a core. The device provides a spiral design or helix to direct and rotate the flow of coolant in a bore of a core. The cooling liquid leaves an inlet pipe and contacts a surface of a bore formed in the core at a substantially perpendicular angle to the flow of cooling fluid before flowing to an exit port. 
     The aforedescribed prior art devices are prone to several problems. 
     It is known in the prior art that a core may be cooled by circulating a coolant such as water through a central bore formed in the core. However, heat removal across the elongate core is not uniform. For example, as a melt of hot plastic travels through the mold gate, it shears, which results in additional heat. During a packing cycle, the gate region is the last area having a melt injected. As such, the hottest area of the core is the semispherical end nearest the mold gate. Crystallization may occur near the mold gate as a result of slow cooling in the crystallization temperature range affecting the quality of the molded part. Conventional prior art approaches to circulating a coolant do not address the high heat gate area of the core which result in relatively long cycle times. 
     It is also known in the prior art that baffles may be applied for re-directing the flow of cooling fluid along a different path to produce a more uniform cooling over the elongate body. Again, the prior art baffles do not teach or provide a solution that addresses cooling the high heat area of the core near the gate. 
     The prior art baffle devices add additional cost and complexities to the core, and require a relatively long cooling cycle time. 
     It is also known in the prior art that an inlet pipe may be centrally located within the bore of the core to deliver the cooling fluid into the bore. The stream of fluid contains a stagnation area at the high heat area of the core where the fluid cannot move and effectively remove heat from the core. This results in slower cooling and a relatively long cycle time. 
     It is also known that if the heat transfer characteristics could be improved by a core cooling device, then the bottle preform molding cycle time could be reduced leading to increased production. 
     Therefore, it is desirable to provide an invention which overcomes the aforedescribed problems of the prior art. 
     SUMMARY OF THE INVENTION 
     There is a need for improving the heat transfer characteristics for cooling a core and for improving an injection molding cycle time. There is also a need to improve the flow of coolant in a stagnation zone near the high heat area of a core tip. 
     The present invention finds particular advantage in improving the convection heat transfer of a coolant by inducing a velocity in the coolant in a stagnation zone. By improving the flow of coolant the convection heat transfer characteristics are improved. 
     The present invention also finds advantage in improving the conduction heat transfer of a core tip by increasing the projected surface area of the core tip in a coolant circulation area. The projected surface area has a primary conductive surface and a secondary conductive surface. The additional surface area also leads to improve the convective heat transfer characteristics. 
     The present invention also finds advantage by improving the cooling of a core tip near a high heat area of a gate. 
     The present invention also finds advantage by reducing or eliminating a coolant stagnation zone formed in a core tip. 
     The present invention also finds advantage by having the capability of being formed during a bore making process. The bore must be formed in a new core and by making the profile of a velocity inducer at the end of a drill bit, the velocity inducer may be made in the same process as the bore. Alternatively, the velocity inducer may be made separately for use in refitting an existing core. 
     In accordance with a primary broad aspect of the present invention, there is provided a core for use in an injection molding system. The core comprises a first channel, a second channel, a circulation area, and a velocity inducer. The circulation area is for receiving an entry flow of coolant from the first channel, circulating the coolant in the circulation area cooling the core, and circulating the coolant to the second channel for directing an exit flow of coolant. The velocity inducer is disposed in a flow path of the entry flow of coolant for inducing a velocity in the coolant for circulating the coolant in the circulation area. 
     The velocity inducer, in the preferred embodiment, is formed on a bore inner tip surface of the core and is in axial alignment with the first channel about a central longitudinal axis. The velocity inducer further comprises a velocity inducing surface that extends outwardly from a bore inner tip surface into a circulation area. 
     The velocity inducing surface further comprises a primary conductive surface for conductive heat transfer through a core material to a coolant. The velocity inducing surface further comprises a secondary conductive surface for conductive heat transfer through the core to the coolant. The secondary conductive surface, in an embodiment of the invention, is a plurality of heat conductive fins extending outwardly from the velocity inducing surface into the circulation area and parallel to the flow of coolant. 
     In an embodiment of the invention, the velocity inducer includes a holder extending outwardly from an apex of the velocity inducing surface and includes a conduction surface for heat conducting engagement with the bore inner tip surface such that the velocity inducer is secured within the circulation area by the holder in contact with an end of the first channel. In another embodiment of the invention, the velocity inducer includes an engagement conduction surface for heat conducting engagement with the bore inner tip surface such that the conduction surface is secured to the bore inner tip surface retaining the velocity inducer within the circulation area. 
     In the preferred embodiment, the velocity inducing surface is a straight sided cone. In an alternative embodiment of the invention, the velocity inducing surface in a concave sided cone. 
     In accordance with a second broad aspect of the present invention, there is provided a mold core plate assembly for use in an injection molding system. The mold core plate assembly comprises a coolant source manifold, a coolant drain manifold, a core, a first channel, a second channel, a circulation area, and a velocity inducer. The first channel is connected to the coolant source manifold , extending into a bore of the core for directing an entry flow of coolant into the core. The second channel is connected to a coolant drain manifold for directing an exit flow of coolant from the core. The circulation area in the core is for circulating the coolant between the first channel and the second channel. The velocity inducer is disposed in a flow path of the entry flow of coolant for inducing a velocity in the coolant for circulating the coolant in the circulation area. In an embodiment of the invention, the first channel for directing an entry flow of coolant is a bubbler having a first opening for connecting with the source manifold for receiving the coolant, and the bubbler having a second opening for streaming the coolant into the circulation area. In an embodiment of the invention, the second channel is formed by an outer surface of the bubbler and a side wall surface of a lengthwise axial ore in the core and the second channel includes a mouth for connecting with the drain manifold. The mold core plate assembly further comprises a plurality of cores. 
     In accordance with a third broad aspect of the present invention, there is provided an injection molding system. The injection molding system comprises an injection unit for plasticising and injecting a melt of plastic, a mold for defining a part, a clamp unit for opening, closing, and clamping the mold, a coolant source manifold, a drain manifold, a core mounted to the mold core plate assembly by a lock ring, a first channel, a second channel, a circulation area, and an velocity inducer. The mold includes a mold core plate assembly and a mold cavity plate assembly. The mold core plate assembly includes a coolant manifold and a coolant drain manifold. The coolant source manifold includes a source connector for connection to a conduit for supplying coolant to the mold core plate assembly. The drain manifold includes a drain connector for connection to another conduit for removing coolant from the mold core plate assembly. The first channel is connected to the coolant source manifold, extending into a bore of the core for directing an entry flow of coolant into the core. The core includes a second channel connected to the coolant drain manifold for directing an exit flow of coolant from the core. The circulation area circulates the coolant between the first channel and the second channel. The core includes a velocity inducer disposed in a flow path of the entry flow of coolant for inducing a velocity in the coolant for circulating the coolant in the circulation area. 
     The injection molding system further comprises a coolant chiller connected to the conduit for supplying coolant to the source manifold and the chiller connected to another conduit for receiving coolant from the drain manifold. 
     While the core described herein is for making a PET bottle preform, it is understood by those skilled in the art that the core shown can be adapted for other types of articles when the mold cavity and core exterior molding surface are changed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the nature and advantages of the present invention reference may be had to the accompanying diagrammatic drawings in which: 
     FIG. 1 is a side view of a preform core, 
     FIG. 2 is a cross sectional view of a preform core taken along the line A—A of FIG. 1 showing a central bore and bubbler, 
     FIG. 3 is a schematic representation of a conventional circulation area illustrating a fluid stagnation zone, 
     FIG. 4 is a schematic representation of a circulation area illustrating a velocity inducer, 
     FIG. 5 is an enlarged cross sectional view showing an end of a conventional elongate preform body area illustrating fluid velocity simulation test results for a stagnation area, 
     FIG. 6 is an enlarged cross sectional view showing an end of an elongate preform body area including a velocity inducer illustrating our fluid velocity simulation test results for the velocity inducer, 
     FIG. 7 is an enlarged cross sectional view taken along line B—B of FIG. 1 showing an end of an elongate preform body area illustrating the preferred embodiment of the velocity inducer, 
     FIG. 8 is an enlarged cross sectional view taken along line B—B of FIG. 1 showing an alternative molding surface having a semispherical core tip separate from an elongate preform body area, 
     FIG. 9 a  is a top view of a bubbler secured velocity inducer, 
     FIG. 9 b  is a side view of a bubbler secured velocity inducer, 
     FIG. 10 is an enlarged cross sectional view taken along line B—B of FIG. 1 showing an end of an elongate preform body area illustrating placement of the bubbler secured velocity inducer, 
     FIG. 11 a  is an top view of a mechanically secured velocity inducer, 
     FIG. 11 b  is a side view of a mechanically secured velocity inducer, 
     FIG. 12 is an enlarged cross sectional view taken along line B—B of FIG. 1 showing an end of an elongate preform body area illustrating placement of the mechanically secured velocity inducer, 
     FIG. 13 is an enlarged top view of a velocity inducing surface showing a plurality of heat conductive fins, 
     FIG. 14 is an enlarged side view taken along the line C—C of FIG. 13 showing profiles for a heat conductive fins, 
     FIG. 15 is an enlarged cross sectional view taken along line B—B of FIG. 1 showing the heat conductive fins disposed upon a velocity inducing surface of a velocity inducer, 
     FIG. 16 is a partial cross sectional view of a core secured to a mold core plate assembly illustrating mold coolant connections for the core, and 
     FIG. 17 is a plan view of an injection molding system including a mold and machine illustrating system coolant connections. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is described with reference to FIG. 1. A core  10  for use in a mold is illustrated having a central longitudinal axis  12 . The core  10  includes an exterior molding surface generally indicated at  14 . The molding surface  14  defines the inside shape of a plastic bottle preform (not shown) manufactured in an injection molding machine. A cylindrical core body is generally indicated at  16 . The exterior molding surface  14  is formed on one end of the cylindrical core body  16  and a core lock  17  is formed on the other end of the core body  16 . The core lock  17  tightly secures the core  10  to a mold (not shown) through a conventional and complimentary lock member (not shown) that bolts to the mold. Formed on the end of the core lock  17  is a coolant connector  18 . The coolant connector provides tight sealing engagement, typically to a manifold located in the mold, and has an opening  20  that allows an entry and exit flow of coolant. 
     It is understood by those skilled in the art that the preferred material for the core  10  is steel. Alternatively, the core  10  may be stainless steel, or tungsten carbide, or beryllium copper, and may include a coating of titanium nitride. 
     It is further understood by those skilled in the art that the preferred coolant is chilled water. Alternatively, a fluid such as water mixed with rust inhibitors, or a gas, or oil, or hot water, may be applied as coolant to cool the core as long as the coolant is supplied at a temperature lower than the hot molded material. 
     Referring now to FIG.  1  and FIG. 2, a cross sectional view is shown in FIG. 2 taken along the line A—A of FIG.  1 . The molding surface  14  includes a neck finish region  22 , an elongate preform body area  26 , and a semispherical core tip  28 . A taper region  24  transitions and extends between the neck finish region  22  and the elongate preform body area  26 . The semispherical core tip  28  is formed on an end of the elongate preform body area  26 . 
     The core  10  includes a central lengthwise bore  30  extending from the opening  20  through the core  10  to a distant end at the core tip  28 . It is understood by those skilled in the art that the bore  30 , neck finish region  22 , taper  24 , body  26  and core tip  28  define a thickness of metal with the bore  30  having suitable strength properties and suitable thermal heat transfer properties for injection molding of a bottle preform. The bore  30  is formed typically in a manufacturing process by a drilling machine. 
     A bubbler  36  extends along the central longitudinal axis  12  from the opening  20  towards the semispherical core tip  28 . The bubbler  36  is a length that extends and ends at a distance above an inner wall of the bore  30  at a circulation area  32  that permits circulation and flow of the coolant over the inner wall of the bore near the semispherical core tip  28 . The bubbler  36  is essentially a hollow tube that provides for a channeled flow of coolant. The bubbler is securely mounted in the mold (not shown) and connected to a manifold located in a mold (not shown). The bubbler  36  and the core  10  are mounted on the mold for central axial placement of the bubbler  36  within the central lengthwise bore  30  of the core  10 . 
     The bore  30  includes a mouth  34  for passing a flow of coolant. The bubbler  36  includes a first opening  40  and a second opening  38 . 
     Preferably, coolant enters the bubbler  36  at the first opening  40 . The coolant travels the length of the bubbler  36  and exits the bubbler at the second opening  38  into the circulation area  32  as a stream of coolant. The coolant circulates in the circulation area  32  and flows down the central lengthwise bore  30  and exits at the mouth  34 . 
     Alternatively, coolant may enter the mouth  34 , flowing down the central lengthwise bore  30  to the circulation area  32  where the coolant circulates and enters the second opening  38  of the bubbler  36 . The coolant travels the length of the bubbler  36  and exits at the first opening  40 . 
     Referring now to FIG.  3  and FIG. 4, an enlarged schematic representation of the circulation area  32  is shown. FIG. 3 illustrates a coolant stagnation zone  48  and FIG. 4 illustrates the velocity inducer  50 . A bubbler  36  delivers a main stream  42  of coolant to the circulation area  32  through the second opening  38  of the bubbler  36 . The main stream  42  contacts the conventional curved surface  52  at a substantially perpendicular angle and deflects the main stream  42  into a circulated stream  46 . 
     It is appreciated by those skilled in the art that the illustrated stream vectors for the main stream  42  and the circulated stream  46  are generalized representations of coolant flow. 
     A stagnation zone  48  exists as shown in FIG. 3. A stagnation zone  48  for the purposes of the present invention is an area wherein the velocity of the coolant is zero, and/or the velocity of the coolant is relatively low compared to the velocity of the coolant within the overall circulation area  32 . 
     The stagnation zone  48  is located in an area of the tip  28  adjacent a gate (not shown). This area of the tip  28  is the hottest area of the core as a result of shearing the plastic through the gate and packing. Shearing the plastic at the gate introduces additional heat. Packing the mold maintains heat and results in prolonging the time for cooling. Coolant requires a movement or velocity to convectively remove heat from the core. The combination of the hottest area of the core and the stagnation zone  48  result in a relatively long cycle time to cool this area of the core. 
     A velocity inducer  50  is shown in FIG.  4 . The velocity inducer  50  removes the stagnation zone  48 . With an increase in the movement or velocity of the coolant, heat may be more effectively removed from the hottest area of the core resulting in an improved and relatively shorter cycle time to cool this area of the core. 
     Referring now to FIG. 5, and FIG. 6, an enlarged cross sectional view of an end section of the elongate preform body area  26  is shown illustrating the results of our computer simulation test in the area of a stagnation zone  48 , before a velocity inducer  50  (FIG. 5) and after a velocity inducer  50  (FIG.  6 ). 
     The bubbler  36  has an inner surface  44  and an outer surface  54 . The inner surface  44  of the bubbler  36  is cylindrical and forms a first channel to direct a flow of coolant. The outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30  form a second channel to direct a second flow of coolant. The side wall surface  31  of the bore  30  transitions into a semispherical bore inner tip surface  60  at the semispherical core tip  28  to define the circulation area  32 . 
     Our computer simulation test was achieved through a software computer program for Computational Fluid Dynamics. The software is known as SASID version 5.4 by Ansys Incorporated. A partial half section of a core  10 , including a circulation area  32 , and a half section of a bubbler  36  including an inner surface  44  and outer surface  54  was simulated to produce a coolant velocity vector profile. 
     The maximum velocity of the entry flow  42  of coolant within the bubbler  36  was 11,009 mm/s. The average velocity of the entry flow  42  was 10,222.5 mm/s. 
     The maximum velocity of the exit flow  47  of coolant between an outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30  was 6291 mm/s. The average velocity of the exit flow  47  of coolant was 4718 mm/s. 
     Referring now to FIG. 5, the stagnation zone  48  contained two velocity profiles. The first velocity profile generally indicated at  62  located the furthest from the second opening  38  of the bubbler  36  and nearest the bore inner tip surface  60  was 0 mm/s. The second velocity profile generally indicated at  64  located nearest the second opening  38  of the bubbler  36  and adjacent the first velocity profile  62  was 1573 mm/s, a relatively low velocity. 
     Referring now to FIG. 6, the velocity profile, as a result of the velocity inducer  50 , over the entire stagnation zone  48  as defined by the first and second velocity profiles was increased to 6291 mm/s. Therefore, the first velocity profile  62  had a velocity increase of 6291 mm/s and the second velocity profile  64  had a velocity increase of 4718 mm/s. 
     Referring now to FIG. 7 the preferred embodiment of the present invention is described. An end portion taken along line B—B of FIG. 1 of an elongate preform body area  26  and semispherical core tip  28  is shown with a bubbler  36  disposed about the central longitudinal axis  12 . The elongate preform body area  26  includes a central lengthwise bore  30 . 
     A velocity inducer  50  is formed at the distant end of the bore  30  in the area of the semispherical core tip  28 . The velocity inducer  50  is substantially conical having a velocity inducing surface  56 . The apex  58  is disposed on the central longitudinal axis  12  at a height above the bore inner tip surface  60  and the velocity inducer is symmetrical about the axis  12 . Alternatively, the velocity inducer may be asymmetrical, for example, in the case of an asymmetrical flow of coolant. The velocity inducer  50  is formed in the same material as the core  10 . The velocity inducer  50  extends outwardly from the bore inner tip surface  60  into the circulation area  32 . 
     Heat transfer from the hot molten material (not shown) in contact with the exterior molding surface  14  (FIG. 1) to the coolant in the core  10  occurs due to a combination of conductive and convective heat transfer. Heat conduction in the solid core material and forced convection in the coolant. Forced convection is coolant motion produced by a mechanical means, for example a coolant pump which circulates coolant through the core. 
     Heat conduction is the transfer of heat through a solid material from a region of higher temperature to a region of lower temperature. Heat conduction in the core  10  is governed by Fourier&#39;s Law Of Conduction which states the rate of change of heat transfer over time is equal to the thermal conductivity of the solid material, multiplied by the area, multiplied by the rate of change of temperature divided by the thickness of the solid material. 
     Increasing the overall thickness of the solid material lowers the rate of heat transfer through the material. Although the velocity inducer  50  increases the thickness of the solid material of the semispherical core tip  28  along the central axis  12 , it also increases the heat conductive surface area of the solid material along the velocity inducing surface  56 . As such, the ratio of area to thickness increases, resulting in an increased or improved conductive heat transfer through the solid material. 
     The increased surface area of the velocity inducing surface  56  provides a primary conductive surface for conductive heat transfer from the hot molten material on the exterior molding surface to the coolant metal interface. The coolant metal interface is defined by the side wall surface  31 , bore inner tip surface  60 , and the velocity inducing surface  56  of the core  10 . 
     Heat convection is the transfer of heat in a liquid through a gross motion of the liquid. Heat convection in the coolant is governed by Newton&#39;s Law Of Cooling which states the rate of change of heat transfer over time is equal to the heat transfer coefficient multiplied by the area, multiplied by the temperature differential (the temperature of the solid material minus the temperature of the fluid). The heat transfer coefficient of the fluid depends on properties of the fluid and the velocity of the fluid. 
     The velocity inducer  50  increases the velocity of the coolant, specifically in the area of a stagnation zone. By increasing the velocity of the coolant, the heat transfer coefficient of the fluid increases, resulting in an increased convective heat transfer through the coolant. 
     As a result, the velocity inducer improves the local heat transfer capabilities at the coolant metal interface by improving both the conductive and convective heat transfer rates. 
     It is understood by persons skilled in the art that the opening  38  of the bubbler  36  is disposed at a height above the velocity inducing surface  56  such that a velocity is induced in the coolant in the circulation area. As the distance between the opening  38  and the apex  58  of the velocity inducer  50  is increased, a point is reached where the coolant velocity over the velocity inducer  50  diminishes, reducing convective heat transfer. As the height is decreased by locating the opening  38  closer to the velocity inducer  50  wherein the apex  58  extends well into the opening  38  of the bubbler  36 , there is a point where the mass flow rate becomes restricted impacting the flow rate, reducing convective heat transfer. In a preferred embodiment of the invention, the apex  58  of the velocity inducer  50  extends into the opening  38  of the bubbler  36 , but not to the point where the mass flow rate becomes restricted. 
     It is understood by persons skilled in the art that the ratio of the diameter of the bubbler  36  to the diameter of the bore  30  is such to provide a coolant mass flow rate for convective heat transfer. 
     Preferably, an entry stream of coolant flows within the first channel of the bubbler  36 . The entry stream of coolant exits the bubbler  36  at a second opening  38  located within the circulation area  32 . The coolant contacts the velocity inducing surface  56  and flows towards the bore inner tip surface  60 . The bore inner tip surface  60  generally deflects the flow of coolant back in a direction opposite to the entry flow of coolant as an exit stream of coolant that flows in the second channel defined by the outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30 . 
     It is well understood by those skilled in the art that a bore  30  must be provided in the core  10 . The bore  30  may be manufactured by a manufacturing process and drilling machine. A tip section of a drill bit may be modified to define a profile of a velocity inducer  50 . The velocity inducer  50  may then be manufactured during the same manufacturing process for creating the bore  30 . Alternatively, the velocity inducer  50  may be manufactured after the bore  30  is created by an additional machine and process, such as an electric discharge machine (EDM). 
     Referring to FIG. 8, alternatively, the semispherical core tip  28  and velocity inducer  50  may be manufactured separately from the preform body area  26  of the core  10 . A separate semispherical core tip  28  has an end surface that tightly aligns and engages a complimentary end surface of the preform body area  26  forming a connection joint  59 . The velocity inducer  50  is axially aligned with the bubbler  36  during assembly. The separate semispherical core tip  28  is fastened to the preform body area  26  by conventional means, for example soldered or brazed. 
     Referring now to FIG. 9 a,  FIG. 9 b,  and and FIG. 10, a first alternative embodiment of the present invention is described. The first alternative embodiment may be applied to either a new core, or to refit an existing core. 
     A bubbler secured velocity inducer is generally indicated at  76  and includes a semispherical engagement conduction surface  68  at one end providing a contact area for the bore inner tip surface  60 . A substantially concave conical velocity inducing surface  66  extends upwardly from the semispherical engagement conduction surface  68 . A cylindrical standoff  70  is formed at the apex of the substantially concave conical surface  66  and extends outwardly to a rectangular holder  72 . The rectangular holder extends outwardly from the conical surface  66  and is aligned with the standoff  70  and the velocity inducing surface  66  about a central axis. 
     The velocity inducer  76  is inserted into the second opening  38  of the bubbler  36 . A pair of securing surfaces  74  engage the bubbler inner surface  44  for securing the velocity inducer  76  with the bubbler  36 . It is understood by those skilled in the art that the holder  72  may be press fit or brazed, or soldered to axially align and retain the velocity inducer  76  with the bubbler. 
     The bubbler  36  and mounted velocity inducer  76  are disposed in the bore  30  about the central longitudinal axis  12 . The semispherical engagement conduction surface  68  of the velocity inducer  76  is a heat conducting surface and tightly engages the complimentary bore inner tip surface  60  for heat conducting engagement. The holder  72  shape and dimensions must secure the velocity inducer  76  to the bubbler  36  and permit a flow of coolant to exit the bubbler  36  at the second opening  38 . 
     Alternatively, the end of the bubbler may rest on the holder  72  to secure the velocity inducer  76  with the bore inner tip surface  60 . 
     Preferably, an entry stream of coolant flows within the first channel of the bubbler  36 . The entry stream of coolant flows around the holder  72  and exits the bubbler  36  at a second opening  38  located within the circulation area  32 . The coolant flows around the standoff  70  and contacts the velocity inducing surface  66  and flows towards the exposed section of the bore inner tip surface  60 . The bore inner tip surface  60  generally deflects the flow of coolant back in a direction opposite to the entry flow of coolant as an exit stream of coolant that flows in the second channel defined by the outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30 . 
     Preferably, the bubbler secured velocity inducer  76  is manufactured out of a metal having both good heat conductive properties and good corrosion resist properties, for example copper. Alternatively, the velocity inducer  76  could be aluminum, marine brass, or steel. The velocity inducer  76  may be manufactured by grinding, machining, or casting. 
     Referring now to FIG. 11 a,  FIG. 11 b,  and FIG. 12, a second alternative embodiment of the present invention is described. The second alternative embodiment may be applied to either a new core, or to refit an existing core. 
     A mechanically secured velocity inducer is generally indicated at  78  and includes a semispherical engagement conduction surface  68  at one end providing a contact area for the bore inner tip surface  60 . A groove  82  is formed about a central axis of the semispherical engagement conduction surface  68 . A substantially concave conical velocity inducing surface  80  extends outwardly from the semispherical engagement conduction surface  68  to an apex  58 . The semispherical engagement conduction surface  68  is a heat conducting surface for heat conducting engagement with a complimentary bore inner tip surface  60 . 
     A second groove  86  is axially formed in the bore inner tip surface  60 . 
     The mechanically secured velocity inducer  78  is mounted and secured in the bore  30  by the fastener  84  pressed into tight engagement with the groove  86  and tight engagement with the groove  82  in the semispherical engagement conduction surface  68 . 
     Preferably, the mechanically secured velocity inducer  78  is manufactured out of a metal having both good heat conductive properties and good corrosion resist properties, for example copper. Alternatively, the velocity inducer  78  could be aluminum, marine brass, or steel. The velocity inducer  78  may be manufactured by grinding or machining. 
     Preferably, an entry stream of coolant flows within the first channel of the bubbler  36 . The entry stream of coolant exits the bubbler  36  at the second opening  38  located within the circulation area  32 . The coolant contacts the velocity inducing surface  80  and flows towards the bore inner tip surface  60 . The bore inner tip surface  60  deflects the flow of coolant back in a direction opposite to the entry flow of coolant as an exit stream of coolant that flows in the second channel defined by the outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30 . 
     While the preferred embodiment of the velocity inducer  50  is shown as a substantially straight sided cone and the alternative embodiments are shown as substantially concave sided cones, it is also understood that other geometric shapes such as a parabolic shape, or semi circular shape may be used to induce a fluid velocity. The selected shape of the velocity inducer must improve the velocity of a coolant in a stagnation zone and as a result, improve the cooling profile along the coolant metal interface in the circulation area. 
     It is also understood that the semispherical engagement conduction surface  68  of the alternative embodiments and the complimentary semispherical shape of the bore inner tip surface  60  may include other complimentary shapes that provide a good contact area and tight engagement preventing a flow of fluid between the two surfaces and providing heat conduction. 
     Referring to FIG. 13, alternatively, the velocity inducing surface  56  may include a plurality of outwardly extending heat conductive fins  61 . Each heat conductive fin extends from the apex  58  of the velocity inducing surface  56  towards a distant end of the velocity inducing surface  56 . The heat conductive fin  61  provide a secondary conductive surface for conduction heat transfer in the circulation area. 
     In a preferred embodiment, each conductive fin is equally spaced about the velocity inducing surface  56 , for example 45 degrees, and are parallel to the flow of coolant. The conductive fin  61  effectively increase the surface area of the velocity inducer  50  in the flow of coolant further improving the conductive heat transfer at the core tip. 
     Referring to FIG. 14, a sectional view taken along the line C—C from FIG. 13 illustrates different profiles for the heat conductive fins  61 . For example, the profile may be rectangular  63 , semi-cylindrical  65 , or triangular  67 , such that the surface area of the velocity inducing surface  56  increases. The heat conductive fins  61  extend outwardly into the circulation area while permitting a flow of coolant in the circulation area. 
     Referring to FIG. 15, a cross sectional view taken along the line B—B from FIG. 1 illustrates a rectangular  63  profile of the heat conductive fins  61  formed on the velocity inducing surface  56  of the preferred embodiment. The heat conductive fins  61  extend outwardly from the velocity inducing surface  56  into the flow path of coolant increasing the surface area of the metal at the semispherical core tip  28 . 
     Referring now to FIG. 16, a partial sectional view of a preform stack assembly for use in a mold is generally indicated at  88 . The stack includes a mold cavity plate assembly  92  and a mold core plate assembly  94 . 
     A cavity  96  is formed in the cavity plate  92  by the gate insert  98 , cavity insert  97 , and neck ring  103  which collectively define the outside shape of the bottle preform. The gate insert  98  is located at an end of the cavity plate  92  for controlling the flow of hot plastic material into the cavity. 
     A bubbler  36  is mounted to the core plate  94  with the first opening  40  engaged and sealed with an opening in a coolant source manifold  100 . The coolant source manifold  100  and bubbler  36  direct an entry flow of coolant to the core  10 . 
     The core  10  is mounted to the core plate  94  by a lock ring  102 . The bubbler  36  is axially aligned with the bore  30  of the core  10 . The coolant connector  18  engages and seals with an opening in a coolant drain manifold  104 . The coolant connector  18  and drain manifold direct an exit flow of coolant from the core  10 . 
     Referring now to FIG. 17, an injection molding system is generally indicated at  106 . The injection molding system includes a base  108 , an injection unit  110 , a clamp mechanism  112 , controls (not shown), and a mold  90 . Optionally, the injection molding system  106  includes a chiller (not shown) to lower the temperature of a coolant. The base  106  typically houses the controls and electrics. The base  106  supports the injection unit  110  and the clamp mechanism  112 . 
     The injection unit  106  receives a plastic material, for example PET, through a hopper  114 . A rotating feed screw plasticizes the plastic material. The injection unit  110  also injects a melt of plastic into the mold  90 . 
     The clamp mechanism  112  includes a stationary platen  116  and a moving platen  118 . A mold core plate assembly, generally indicated at  94  (including a stripper plate, not shown) is typically mounted to the moving platen  118 . A mold cavity plate assembly generally indicated at  92 , (including a manifold plate, and backing plate, not shown) is typically mounted to the stationary platen  116 . The mold  90  may be opened, closed, and clamped by the clamp mechanism  112 . 
     The mold  90  includes a plurality of preform stack assemblies  88  (not shown). Each core  10  has a bubbler  36  and coolant connector  18  (as shown in FIG.  2 ). The mold  90  also includes a main coolant source connector  120  and a main coolant drain connector  122 . 
     The coolant source connector  120  connects to a source conduit  124  for receiving an entry flow of coolant from a coolant supply. The coolant source connector  120  also extends into the mold through a source channel and source manifold (not shown). 
     The coolant drain connector  122  connects to a drain conduit  126  for directing an exit flow of coolant for heat exchange. The coolant drain connector  122  also extends into the mold through a drain channel and drain manifold (not shown). The conduits are flexible to accommodate movement of the core plate  94 . 
     The source manifold connects to each bubbler  36  of each core  10  (see FIG.  12 ). The drain manifold connects to each coolant connector  18  of each core  10  (see FIG.  16 ). 
     Referring now to FIGS. 2,  7 ,  16 , and  17 , operation of the preferred embodiment is described for a single machine cycle. 
     The mold  90  is closed and clamped by the clamp mechanism  112 . Plastic material enters the injection unit  110  through the hopper  114 . The plastic material is plasticized producing a shot of hot plastic which is subsequently injected into the mold. The injection molding machine then enters a pack cycle. 
     Coolant enters the source conduit  124  and flows to the coolant source connector  12 , into the source manifold  100 , through the first channel of the bubbler  36  into the circulation area  32 , onto the velocity inducer  50 , through the second channel formed by the outer surface  54  of the bubbler  36  and the side wall surface  31  of the bore  30  to the drain manifold  104 , to the coolant drain connector  122 , and through the drain conduit  126  for heat exchange. 
     When the formed part is sufficiently cooled, the mold  90  is opened by the clamp mechanism  112  and the part is ejected. The machine cycle then repeats. 
     It is to be understood by those skilled in the art that the present invention is not limited to the illustrations described and shown herein, which are deemed to be illustrative of the preferred and alternative embodiments of the invention and may be modified without departing from the scope and spirit of the invention. The invention is intended to encompass all modifications, which are within its scope and spirit as defined by the attached claims.