Patent Publication Number: US-2002003199-A1

Title: Core for injection molding tools

Description:
TECHNICAL FIELD  
       [0001] This is a utility application based upon provisional U.S. Application No. 60/169,165 filed Dec. 6, 2000.  
       [0002] This invention relates to molding apparatus and more particularly to molding apparatus having water-cooled core and cavity assemblies that cooperate to form hollow molded parts. The apparatus is an improvement on the molding apparatus shown in U.S. Pat. No. 5,498,150 issued to me on Mar. 12, 1996 and incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0003] To decrease cycle time and to insure good molding of either metal casting or injection molded plastic parts, it is advantageous to provide coolant flow passages within a mold apparatus. When cooling fluid is passed through such passages during the molding process, it removes heat from the apparatus. Where a molding apparatus includes a mold cavity part that has a plurality of female cavities formed within it, and where those female cavities are configured to receive core parts that cooperate with the female cavities to form the surfaces of a molded part, apparatus for cooling has included a round cooling tube that is formed by the interior surface of the core part.  
       [0004] An example of such cooling apparatus is set forth in U.S. Pat. No. 4,655,280.  
       [0005] One problem with such arrangements is that molded parts having an elongated configuration must be formed, in part, by a core that has a length to width ratio large enough to allow the core to deflect when impacted by material that is injected against the core under high pressure conditions. Since many materials are best shaped and densified under such high-pressure conditions, one problem with prior art apparatus is how to provide a low cost, elongated core that will not deflect or warp under high temperature and high-pressure operation.  
       [0006] Another problem with such molding apparatus is that the coolant flow is restricted to an annular surface in such a way as to limit the removal of heat from each of the mold cavities.  
       [0007] U.S. Pat. No. 5,498,150 issued to me on Mar. 12, 1996 addresses these problems by disclosing a mold assembly having a mold part that forms the outer wall of a molded part. The mold part has a plurality of elongated cavities within it. A fluid cooled core is inserted within each of the elongated cavities before injecting material into the mold assembly. Each fluid cooled core has an outer surface that forms an inner wall of a tubular portion of the molded part. Each fluid cooled core includes a plurality of circumferentially spaced, longitudinal ribs or fins that extend integrally and radially inward from around an inner circumferential surface of the core. The ribs reinforce each fluid cooled core radially inwardly of their respective elongated cavities and along the length of each fluid cooled core. The cooling channels defined therein increase the surface area or wetting area of the mold assembly so as to increase the cooling efficiency. This construction controls core deflection that results from high-pressure injection of a material to be molded. A separate fluid inlet pipe is disposed coaxially within each core and is radially spaced from the inner circumferential surface of each core. An outer end of each fluid inlet pipe is adapted to be connected to a source of coolant and an inner end is in communication with a plurality of circumferentially spaced passages defined by the ribs within each core. Each of these passages returns the flow of cooling fluid to an elongated annular passage that extends along the length of the core between the fluid inlet pipe and the inner surface. Radially inner edges of the ribs are configured to slidably receive an inner length of the fluid inlet pipe during core assembly.  
       [0008] After assembly, each fluid inlet pipe lies in contact with or in close proximity to the rib inner edges. While this design is more resistant to warping and deformation during injection than prior art assemblies, the fluid inlet pipe still has some freedom to rotate, flex, warp and otherwise deform under the force of pressurized injections of molten material during molding. In addition, while the temperature of the core can be controlled using the fluid cooling system, the cavity portion of the mold cannot.  
       [0009] In my copending U.S. patent application Ser. No. 09/153,956 filed Sep. 16, 1998, incorporated herein by reference a further improvement is provided that defines a fluid cooled core that is stronger, more rigid and therefore more resistant to deflection and warping under high temperature and high-pressure operation and a configuration that is able to cool both inner and outer walls of a tubular portion of a molded part. A mold assembly is provided that includes spaced, moveable mold parts, one mold part including a hollow cavity having a cavity inner surface configured to form an outer wall of an elongated, generally annular molded part and the other mold part including a corresponding core element having a core outer surface configured to form an inner wall of the molded part. The core element is at least partially disposed within the cavity and the core outer surface is spaced from the cavity inner surface defining a generally annular mold chamber for receiving molten material to be molded to the shape of the molded part. The core element has an open end and a closed end that defines a hemispherical portion of the core outer surface. The shape of the closed end can vary according to the application and could be flat. The core element further includes a generally tubular core inner surface and a plurality of circumferentially spaced longitudinal ribs that integrally extend radially inward from the core inner surface. The ribs define a plurality of elongated coolant passages. The core element is at least partially disposed within the cavity and the core outer surface is spaced from the cavity inner surface defining a generally annular mold chamber for receiving molten material to be molded to the shape of the molded part. The core element further includes a first portion of a high strength material defining generally tubular core inner surface and a plurality of circumferentially spaced longitudinal ribs that integrally extend radially inward from the core inner surface through part of the length of the core element. The ribs define a plurality of elongated coolant passages that receive return coolant flow from an annular space formed between a second reduced diameter hollow tip portion of the core element formed by a high heat transfer material that can be impact resistant; a fluid inlet pipe is coaxially disposed within the core element. The fluid inlet pipe has an outer surface spaced from the core inner surface, one end of the fluid inlet pipe configured to connect to a source of coolant and a second end of the pipe being in fluid communication with the plurality of coolant passages.  
       [0010] In my copending Application 90/526,626 filed Mar. 16,2000 a core element and fluid inlet pipe are integrally connected together to further reinforce the core element radially inwardly of the mold chamber and along the length of the core element against core deflection that results from high pressure injection of a material to be molded while providing increased cooling efficiency. This design is more resistant to warping and deformation during injection than prior art designs. The arrangement further comprises the use of bimetal materials in the core body so that a first lower portion can be formed of relatively high strength lower heat transfer material such as stainless steel and the molding surface on the core body can be formed of a high strength alloy composite material such as a nickel copper tungsten material that will resist impact damage and that will provide increased thermal diffusivity and increased thermal conductivity at an inlet opening for flow of molten material into the mold cavity formed between the hollow mold part and the core part. The fluid inlet pipe is a single element that can be assembled axially within preformed first and second portions of differing heat transfer characteristics. Furthermore, the first and second portions can be connected by suitable bonding techniques so that the preexisting core elements of the type shown in copending United States Patent Application can be can be upgraded to have improved heat transfer characteristics by a method that includes the steps of cutting the end of a core end with integral fluid inlet pipe and replacing the inlet pipe with a inlet pipe extending from the first portion of the preexisting core; providing a hollow tip of higher thermal conductivity than the first portion and placing it over the heat pipe extension and thereafter bonding an end of the hollow tip to the cutoff end of the first portion by suitable techniques including but not limited to diffusion bonding.  
       INVENTION SUMMARY  
       [0011] In one embodiment a core is provided as a solid metal tip of high thermal conductivity material. In another embodiment a core is configured to have a shaped inner wall suitable for forming a preform for a non-round plastic bottle.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
     [0013]FIG. 1 is an exploded sectional view of the first embodiment prior to assembly;  
     [0014]FIG. 2 is a sectional view of the embodiment in FIG. 1 following assembly;  
     [0015]FIG. 3 is a sectional view of another embodiment;  
     [0016]FIG. 4 is an enlarged fragmentary sectional view of a part of the embodiment in FIG. 3; and  
     [0017]FIG. 5 is a sectional view of a non-round bottle formed by the embodiment in FIGS. 3 and 4. 
    
    
     PREFERRED EMBODIMENT DESCRIPTION  
     [0018] An integral bubbler type water-cooled core element or core assembly  10  is shown in FIG. 1 as having a core support member  12 , and a core part  14 . The support member  12  is configured to be supported within a known mold apparatus of the type shown in U.S. Pat. No. 5,498,150 issued to me on Mar. 12, 1996. Such apparatus includes separable mold parts one of which carries the core support member and includes cooling passages for connection to an inlet segment  16 . An extension segment  18  locates the core  14  within a mold part cavity that will receive plastic or other material to be cooled by fluid flow through the interior of the member  12 .  
     [0019] More particularly, the member  12  has a bore  20  at one end thereof adapted to be connected to a coolant source. The member  12  includes a bore  22  at the opposite end for supporting the core  14 . The core  14  is configured as a solid metal piece of high heat conductivity material and includes a large diameter end  24  thereon with a flat planar end surface  26 . The large diameter end  24  is adapted to be bonded to the member  12  at surfaces there between including but not limited to at a tubular annular planar surface  22   a  within the bore  22  and at a flat planar end surface portion  26   a.    
     [0020] The member  12  has a elongated tube  28  therein through which coolant is directed to flow against a flat end surface  26  of the core  14  at the bore  22 . The bonded configuration prevents fluid leakage of the coolant and furthermore precisely locates the solid metal core  14  so as to precisely center a tapered cylindrical outer surface  31  and a hemispherical end  33  within a mold cavity that with the core defines the shape of a part to be molded. The mold apparatus is of the type shown in the &#39;150 patent including a cavity in the mold apparatus. In the present example the outer surface  31  can be configured to define a hollow preform suitable for blowing molding a bottle. The shape of the outer surface of the core  14  thus depends on the shape of the part to be injection molded about the core. In some cases the portions surface  31  can be almost the same diameter with a small taper when, for example, the part being formed is a preform for hollow cylinder disposable syringes. In the illustrated embodiment, the solid core  14  is formed of a high heat transfer material such as Copper, Aluminum, Tungsten Carbide Cobalt, Silicon Carbide, Beryllium Cooper but is preferably formed of a high impact resistance material that does not have materials therein that are incompatible with applications for molding medical parts or the like. One example of such material is an alloy of nickel copper and tungsten.  
     [0021] The embodiment shown in FIG. 3 includes a bubbler  30  comprising tube  32  for supplying coolant from a inlet of the type shown in my earlier patent and provisional applications as referenced herein. The bubbler  30  directs coolant against a return surface  34  shown in FIG. 4 and into a coolant return passage  36  formed between the bubbler  30  and a core member  40 . As best seen in FIG. 3, the core member  40  has an irregular inner surface  42  and a cylindrical outer surface  44 , shown round with it being understood that other shapes are contemplated within the scope of the invention. The irregular inner surface  42  is configured so that the wall thickness at regions  40   a  of the core member  40  are relatively thinner than regions  40   b  of the core member  40 . More specifically the irregular inner surface is  42  formed as a flattened diamond shape with diverging walls  42   a ,  42   b ,  42   c ,  42   d . The walls  42   a ,  42   b  join at an apex  42   e  and the walls  42   c ,  42   d  join at an apex  42   f  The walls  42   a  and  42   c  are joined by a curved segment  42   g  and the walls  42   b  and  42   d  are joined by a curved segment  42   h . The irregular shape can be varied to produce a desired variation in the thickness of the core wall so that more or less cooling can be produced within the injection molded material directed into a mold cavity  46  formed between the core member  40  and a mold cavity member  48  of known mold apparatus. As a consequence, a preform results that has plastic that will remain hotter in the regions where the core wall thickness is greatest, e.g., at  40   b  and the plastic will be cooler adjacent the thin wall thicknesses, e.g., at  40   a . Such preforms, when processed in a one stage system will remain heated so as to when placed at a blow molding station will be better suited for shaping with uniform all thickness into a non round bottle having a hollow cylindrical shape and a generally oval outline as shown at reference numeral  50  in FIG. 5.  
     [0022] By virtue of the bimetal construction described above, the mold cavity is more effectively cooled at the inlet flow passage of molten material into the mold cavity than if it were to rely solely on cooling provided by a water cooled core assembly of the type shown in the prior art.