Abstract:
An injection molding apparatus comprising a hot runner manifold, a heater coupled to the manifold and a heat dissipation device coupled to said manifold, wherein said heat dissipation device reduces hot spots on said manifold caused by uneven heating.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application No. 60/448,146, filed Feb. 20, 2003, and U.S. provisional patent application No. 60/452,497, filed Mar. 7, 2003. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an injection molding apparatus and, in particular, to a heat dissipation device for and a method of dissipating heat from a manifold. 
     BACKGROUND OF THE INVENTION 
     As is well known in the art, hot runner injection molding systems include a manifold for conveying pressurized melt from an inlet to one or more manifold outlets. Each manifold outlet leads to a nozzle, which, in turn, extends to a gate of an injection mold cavity. Manifolds have various configurations, depending upon the number and arrangement of the nozzles and the corresponding injection mold cavities. 
     It is known to heat the manifold in order to maintain a desired temperature distribution throughout the manifold. Means of heating manifolds include integrally casting or brazing an electrical heating element into the manifold, as described in U.S. Pat. No. 4,688,622 to Gellert and U.S. Pat. No. 4,648,546 to Gellert, respectively. The heating element may also be mechanically joined to the manifold by pressing the element into the manifold to create an interference, friction or deformation fit. Alternatively, thermal spraying techniques may be employed to bond the heating element to the manifold. Further, a cartridge heater may be cast in the manifold, as disclosed in U.S. Pat. No. 4,439,915 to Gellert or a plate heater may be positioned adjacent the manifold to provide heat thereto, as disclosed in U.S. Pat. No. 6,447,283 to Gellert. 
     Referring to  FIG. 1 , a typical prior art manifold is generally indicated at  100 . The manifold  100  includes a manifold channel  102  and an integrated heating element  104 . Heating of the manifold  100  by the heating element  104  is generally not uniform. None of the prior art manifold heating techniques provide an even heat distribution throughout the manifold. Hot spots occur at locations where the watt density is high and there is little or no contact with the surrounding mold plates. It is therefore desirable to remove heat from the manifold at these hot spot locations. As is clear from the layout of the heating element, the watt density varies from one manifold location to the next. Certain locations, near the nozzles for example, receive more heat because there is a greater length of heating element concentrated in those regions. Increasing the amount of heat generated at a particular manifold location by providing additional heating element length is generally not a practical solution. The heating element can only withstand a certain bend radius and must avoid connection points to other injection molding apparatus components such as the nozzles and the manifold backing plate. The hot/cold transition of the heating element, which is located near the entry and exit point of the heating element, is an example of a location where less heat is generated. 
     In an injection molding apparatus, contact between the manifold and the mold plates results in heat loss from the manifold. The location of cooling lines in the mold plates can influence the amount of heat loss from the manifold. Generally, the closer the cooling lines are to the manifold, the greater the heat loss from the manifold. Contact between the manifold and the nozzles may cause the manifold to either lose heat or gain heat depending on the particular application. 
     The temperature of the manifold is further influenced by the melt stream itself. For example, the temperature of the melt tends to be higher at locations where the melt experiences high shear stress, such as at bends in the manifold channel. Different types of melt will also influence the manifold temperature in different ways. 
     An uneven distribution of heat in the manifold causes the temperature of the melt entering the nozzles to vary slightly from one nozzle to the next. Any variation in the temperature of the melt entering each of the nozzles can adversely affect the quality of the molded products being produced by the injection molding process. With the increased use of more difficult to mold plastics materials, the melt must be maintained within narrower and narrower temperature ranges. If the temperature rises too high, degradation of the melt will result, and if the temperature drops too low, the melt will clog in the system and produce an unacceptable product. Both extremes can necessitate the injection molding apparatus being shut down and cleaned out, which can cause a very costly loss of production. 
     An uneven distribution of heat in the manifold has a further disadvantage in that the manifold is subjected to high stress due to continuous cycling between higher and lower temperatures. This can result in a shorter manifold life and increased downtime for the injection molding apparatus. 
     It is therefore an object of the present invention to provide a heat dissipation device for a manifold that obviates or mitigates at least one of the above disadvantages. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention there is provided an injection molding apparatus comprising: 
     a hot runner manifold; 
     a heater coupled to said manifold; and 
     a heat dissipation device, having a first end coupled to said manifold between said manifold and a cooler member, said cooler member having a lower temperature than said manifold; 
     wherein said heat dissipation device thermally expands and contacts said cooler member when a temperature of said manifold at said pre-determined location increases above a predetermined temperature. 
     According to another aspect of the present invention there is provided an injection molding apparatus comprising: 
     a manifold; 
     a heater coupled to said manifold; and 
     a heat dissipation device coupled to said manifold, said heat dissipation device having a first orientation when said manifold has a temperature below a predetermined temperature and a second orientation when said manifold has a temperature greater than a predetermined temperature, wherein said first and second orientations differ in that said second orientation contacts an adjacent cooler member. 
     According to another aspect of the present invention there is provided a method of locally cooling a manifold of an injection molding apparatus comprising: 
     measuring the temperature of said manifold; 
     identifying high temperature locations on a surface of said manifold; 
     coupling a first end of a heat dissipation device to said surface of said manifold at said high temperature locations; 
     positioning a second end of said heat dissipation device such that thermal expansion causes said second end to come into contact with a cooler member when the temperature of said surface at said high temperature locations increases to a predetermined temperature; and 
     heating said manifold surface to a temperature greater than said predetermined temperature. 
     According to another aspect of the present invention there is provided a heat dissipation device for use with a hot runner manifold apparatus, comprising: 
     a first end, thermally coupled with a hot runner manifold, a second end and one or more thermally conductive layers, 
     wherein said second end of said heat dissipation device thermally expands and contacts a cooler portion of said manifold apparatus only at temperatures above a predetermined temperature. 
     According to another aspect of the present invention there is provided a method of dissipating heat from a manifold of an injection molding apparatus, comprising: 
     providing an injection molding apparatus including a manifold; 
     providing a manifold backing plate adjacent but not contacting said manifold; 
     providing at least one heat dissipation device having a first end and a second end; 
     coupling said first end to said manifold; 
     directing heat away from said manifold by allowing said heat dissipation device to thermally expand and contact said manifold backing plate when said manifold temperature increases beyond a predetermined temperature. 
     The present invention provides advantages in that the occurrence of hot spots in the manifold is reduced and the temperature distribution throughout the manifold is more even. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which: 
         FIG. 1  is a top view of a prior art manifold; 
         FIG. 2  is a side sectional view an injection molding apparatus in accordance with an embodiment of the present invention; 
         FIG. 3  is a side sectional view of injection molding apparatus in accordance with another embodiment of the present invention; 
         FIG. 4A  is a top view of a heat dissipation device of the present invention; 
         FIG. 4B  is a cross-sectional view taken along line A—A of  FIG. 4A ; 
         FIG. 4C  is a perspective view of the heat dissipation device of  FIG. 4A ; 
         FIG. 5  is alternate cross-sectional view taken along line A—A of the heat dissipation device of  FIG. 4A ; 
         FIG. 6  is an alternate cross-sectional view taken along line A—A of the heat dissipation device of  FIG. 4A ; 
         FIG. 7A  is a top view of an alternate heat dissipation device of the present invention; 
         FIG. 7B  is a cross-sectional view taken along line B—B of  FIG. 7A ; 
         FIG. 7C  is a perspective view of the heat dissipation device of  FIG. 7A ; 
         FIG. 8  is alternate cross-sectional view taken along line B—B of the heat dissipation device of  FIG. 7A ; and 
         FIG. 9  is an alternate cross-sectional view taken along line B—B of the heat dissipation device of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 2 , an injection molding apparatus is generally indicated by reference numeral  10 . The injection molding apparatus  10  comprises a manifold  12  having a manifold channel  14  extending therethrough. A manifold bushing  16  is located at an inlet of the manifold channel  14  to receive a melt stream of moldable material from a machine nozzle (not shown) and to deliver the melt stream to manifold outlets  18 . A heating element  20  is nested in a groove  22  that extends through the manifold  12  to maintain the melt stream at a desired temperature. 
     Nozzles  24  are located between the manifold  12  and respective mold cavities  30 , which are formed in mold cavity plates  34 . Each nozzle  24  includes a nozzle body  26  having a nozzle head  28  and a nozzle tip  32 . A nozzle channel  25  extends through the nozzle  24  for delivering the melt stream from each manifold outlet  18  to the corresponding mold cavity  30 . 
     Mold gates  36  are provided at the entrance to the mold cavities  30 . The mold gates  36  are selectively openable to allow melt to be delivered to the mold cavities  30 . The nozzles  24  may be thermal gated (shown on the left of  FIG. 2 ) or valve gated (shown on the right of  FIG. 2 ). The valve gated nozzles  24  include a valve pin  38  that is driven by a valve piston  40 . Each valve pin  38  is selectively movable to open and close the respective mold gate  36 . 
     Each nozzle  24  is further provided with a heater  42 , which helps to maintain the melt stream at a desired temperature as it passes through the nozzle  24 . The heater  42  is powered through an electrical connector  44  that is in communication with a power source (not shown). Cooling channels  46  are located adjacent the mold cavities  30  in order to cool the melt therein. Heat dissipation devices  50  are coupled to an upper surface  15  of the manifold  12  at the locations shown. 
     Another embodiment of an injection molding apparatus  10   a  is shown in  FIG. 3 . In this embodiment, the manifold is a bridging manifold  12   a , which is comprised of a main manifold  11  and sub-manifolds  13 . The main manifold  11  includes a main manifold channel  48  that is in communication with sub-manifold channels  14   a  of the sub-manifolds  13 . A manifold bushing  16   a  is located at an inlet of the main manifold channel  48  to receive a melt stream of moldable material from a machine nozzle (not shown). The sub-manifolds  13  are coupled to the main manifold  11  by manifold melt links  70 , which allow melt to flow from the main manifold channel  48  into the sub-manifold channels  14   a . The sub-manifolds  13  are positioned in the injection molding apparatus  10   a  relative to mold plate  72  by sub-manifold locating rings  74 . The main manifold  11  is separated from the manifold backing plate  76  by spacers  80  and located relative to the mold plate  72  by a main manifold locating ring  82 . Cooling channels  46   a  extend through the mold plates  72  and  76 . 
     Nozzles  24   a  are coupled to the sub-manifolds  13  by bolts  84 . Each nozzle  24   a  includes a nozzle channel  25   a  that extends therethrough. The nozzles  24   a  are located between the sub-manifold  13  and respective mold cavities (not shown). In operation, the injection molding apparatus  10   a  is heated up from the cold condition, in which all of the components are at generally the same ambient temperature. The manifold  12   a , which includes the main manifold  11  and the sub-manifolds  13 , and the nozzle  24   a  are then maintained at their respective temperatures. Melt is injected from the machine nozzle into the manifold bushing  16   a  of the manifold  12   a . The melt flows through the main manifold channel  48 , through the manifold melt links  70 , through the sub-manifold channels  14   a  and into the nozzle channels  25   a  and is injected into the mold cavities. The melt is then cooled in the mold cavities in order to produce finished molded parts. 
     Heat dissipation devices  50 , similar to those shown in  FIG. 2 , are shown in  FIG. 3 . Heat dissipation devices  50  are secured at a first end  53  to the upper surface  15   a  of the main manifold  12   a , such as by fasteners  51  or another method apparent to one skilled in the art, at one or more hot spots on manifold  12   a . Hot spots are locations on the manifold  12   a  that reach a temperature that is above a desired, pre-determined temperature during operation of the injection molding apparatus  10   a . The hot spots are identified by methods that are well known in the art, such as simulation of an operating manifold using finite element analysis or measurement of the temperature of an operating manifold using an infrared camera. 
     As shown in  FIG. 4A  a heat dissipation device  50  is a generally rectangular plate. However, heat dissipation device  50  may be a plate that is shaped other than generally rectangular. For example, heat dissipation device  50  may be oval, arcuate shaped, or another polygonal or non-polygonal shape.  FIG. 4B  is a cross section taken along line A—A of  FIG. 4A . As seen in  FIG. 4B  heat dissipation device  50  is made from a single piece of a highly thermally conductive material, with a high coefficient of thermal expansion. These materials may be copper, copper alloys, aluminum, and aluminum alloys. 
     Preferably, heat dissipation device  50  has a second end  55  that is curved, as shown in  FIG. 4C . Once positioned between a manifold backing plate  76  and a manifold  12 , second end  55  is curved toward manifold backing plate  76  just enough that it is close to but does not contact manifold backing plate  76 , when cool. As heat dissipation device  50  draws heat from manifold  12 , heat dissipation device  50  begins to expand due to thermal expansion, as shown in shadow in  FIG. 4C . Based on the coefficient of thermal expansion, one skilled in the art may select the correct material, size and length of heat dissipation device  50 , such that it will expand to bring second end  55  into contact with manifold backing plate  76  when the temperature of manifold  12  reaches a desired temperature. Once second end  55  contacts the cold manifold backing plate  76 , heat will be transferred to manifold backing plate  76  and away from the hot spot of manifold  12 , cooling and lowering the temperature of manifold  12  at the location opposite first end  53  of heat dissipation device  50 . 
     Once the temperature at the hot spot falls below the pre-determined temperature, heat dissipation device  50  will cool and shrink away from manifold backing plate  76 . If the hot spot regenerates, heat dissipation device  50  will again thermally expand and the cycle will repeat, creating a temperature actuating heat dissipation device  50 . 
     In another embodiment of the present invention, heat dissipation device  50  may require no contact to the manifold backing plate  76 . Instead, the excessive heat at hot spots on manifold  12  can be transferred to the air between manifold backing plate  76  and manifold  12 . However, second end  55  of heat dissipation device  50  must be positioned so that even with thermal expansion the second end  55  does not contact manifold backing plate  76 . 
       FIG. 5  shows an alternative cross section along line A—A of heat dissipation device  50  from  FIG. 4A . In this case, heat dissipation device  50   a  of  FIG. 5  includes a first layer  56 , which contacts the upper surface  15   a  of manifold  12 , and a second layer  58  adjacent to first lay  56 . First layer  56  and second layer  58  are coupled to one another by brazing, welding, soldering or a high temperature adhesive. First layer  56  is comprised of a material having a high coefficient of expansion and second layer  58  is comprised of a material having a low coefficient of expansion. 
     Suitable materials for first layer  56  include copper, copper alloys, aluminum, and aluminum alloys. Suitable materials for second layer  58  include titanium, titanium alloys, stainless steels, iron alloys, ceramics and fiberglass. In a preferred embodiment, heat dissipation device  50   a  is bi-metallic with a copper or copper alloy first layer  56  and a nickel second layer  58 . It will be appreciated by persons skilled in the art that any combination of materials can be used for heat dissipation device  50   a , provided that first layer  56  has a higher coefficient of thermal expansion than second layer  58 . 
     The thickness of both first and second layers  56 ,  58  is selected based on the desired thermal response characteristics for a particular application. The thickness of the layers  56 ,  58  is generally in the range of 0.01 inches to 0.125 inches. 
     Heat dissipation device  50   a  need not be initially curved like heat dissipation device  50  of  FIG. 4C . Instead, heat dissipation device  50   a  moves between a generally flat position, shown at  50   a  in  FIG. 3 , in which the heat dissipation device  50   a  lies against upper surface  15   a  of manifold  12 , and a curved position, similar to that shown at  50  in  FIG. 3 , in which a second end  55   a  of heat dissipation device  50   a  curves away from manifold  12 . As injection molding apparatus  10   a  is heated up from a cold condition, the temperature of manifold  12  increases, particularly at the previously identified hot spots, and first layer  56  and second layer  58  of heat dissipation device  50   a  expand due to thermal expansion. However, second layer  58  expands at a slower rate than first layer  56 . The difference in rates of expansion between first layer  56  and second layer  58 , makes heat dissipation device  50   a  curl. 
     As it curls, second end  55   a  of heat dissipation device  50   a  curves away from manifold upper surface  15   a . When the temperature of the hot spots has increased beyond a pre-determined value, the curved heat dissipation device  50   a  contacts manifold backing plate  76 . Heat is then transferred from manifold  12  to manifold backing plate  76  via heat dissipation device  50   a . The temperature at the hot spots reduces in response to the heat lost to manifold backing plate  76 . As the temperature reduces, first layer  56  and second layer  58  shrink, also at different rates. Once the temperature falls below a pre-determined temperature, second end  55  shrinks enough to lose contact with manifold backing plate  76 , and heat dissipation device  50   a  falls back to a generally flat position. The heat dissipation device  50   a  cycles between a generally flat position and a curved position to regulate the temperature of manifold hot spots. 
       FIG. 6  shows an alternative cross section along line A—A of heat dissipation device  50  from  FIG. 4A . In this case, heat dissipation device  50   b  includes an outer layer  60  located adjacent second layer  58  of heat dissipation device  50   a  of  FIG. 5 . Outer layer  60  is secured to second layer  58  by brazing, soldering, welding or a high temperature adhesive. Outer layer  60  is generally thinner than heat dissipation device  50   a  so as not to hinder the curving motion discussed above created by the thermal expansion rate difference between first layer  56  and second layer  58 . Outer layer  60  is comprised of a material having a high rate of thermal conductivity. Suitable outer layer  60  materials include copper, copper alloys, aluminum, and aluminum alloys. Outer layer  60  and first layer  56  may be the same material. Outer layer  60  may, alternatively, be a material completely separate from heat dissipation device  50   a.    
     In operation, heat dissipation device  50   b  operates as previously described for heat dissipation device  50   a . As heat dissipation device  50   a  moves away from upper surface  15   a  of manifold  12 , outer layer  60  moves with it. Both heat dissipation device  50   a  and outer layer  60  continue to curve away from manifold  12  until second end  55   b  of outer layer  60  contacts manifold backing plate  76 . When in contact, second layer  58  acts as insulation between first layer  56  and outer layer  60 , thus operating as a damper so that heat loss from manifold  12  via heat dissipation device  50   b  is gradual. This ensures that heat dissipation device  50   b  does not oscillate too rapidly between the curved and generally flat positions. 
     Referring to  FIG. 7A , another embodiment of a heat dissipation device  62  is shown. The construction and operation of heat dissipation device  62  is similar to that of heat dissipation device  50 . However, instead of being a generally rectangular plate, heat dissipation device  62  includes a plurality of fins  52  extending from a base  54 .  FIG. 7B  is a cross section taken along line B—B of  FIG. 7A . As seen in  FIG. 7B , heat dissipation device  62  is made from a single piece of a highly thermally conductive material, with a high coefficient of thermal expansion. These materials may be copper, copper alloys, aluminum, and aluminum alloys. 
     Heat dissipation device  62  operates identically to heat dissipation device  50 . Fins  52  of heat dissipation device  62  are curved, as shown in  FIG. 7C  and positioned so that fins  52  are close to but do not contact manifold backing plate  76 , when cool. When heated, thermal expansion causes fins  52  to expand to contact manifold backing plate  76 , as shown in shadow in  FIG. 7C . When enough heat has transferred from manifold  12  to manifold backing plate  76  to reduce the temperature of manifold  12 , heat dissipation device  62  has cooled enough that fins  52  shrink away from manifold backing plate  76 . The distance that the fins  52  move can be controlled based on selection of materials and selection of a fin length. 
     Similar to heat dissipation device  50 , it may be desirable to dissipate heat from the manifold  12  without heat dissipation device  62  having direct contact with manifold backing plate  76 . In this case, particular characteristic of the material and fin length are selected so that the fins  52  do not contact manifold backing plate  76  even with thermal expansion. In this case, more heat will be dissipated from heat dissipation device  62  than heat dissipation device  50  due to the increased surface area created by fins  52  of heat dissipation device  62 . 
       FIG. 8  shows an alternative cross section along line B—B of heat dissipation device  62  from  FIG. 7A . In this case, heat dissipation device  62   a  of  FIG. 8  includes a first layer  64 , which contacts upper surface  15   a  of manifold  12 , and a second layer  66  adjacent to first layer  64 . First layer  64  is comprised of a material having a higher coefficient of expansion than the material of second layer  65 . Heat dissipation device  62   a  of  FIG. 8  operates in the same manner as heat dissipation device  50   a  of  FIG. 5 . Fins  52  curl away from manifold  12  due to the difference in thermal expansion rates of first and second layers  64 ,  66  until fins  52  contact manifold backing plate  76  at a predetermined temperature. When the temperature of manifold  12  falls to below the predetermined temperature, the fins uncurl and move back towards a relatively flat position. The cycle continues as the temperature of manifold  12  fluctuates above and below the predetermined temperature. 
       FIG. 9  shows an alternative cross section along line B—B of heat dissipation device  62  from  FIG. 7A . In this case, heat dissipation device  62   b  includes an outer layer  68  located adjacent second layer  66  of heat dissipation device  62   a  of  FIG. 8 . Outer layer  68  operates identically to outer layer  60  of heat dissipation device  50   b . As heat dissipation device  62   a  curls due to the different thermal expansion rates of first and second layers  64 ,  66 , outer layer  68  contacts manifold backing plate  76 . Thus, second layer  66  acts as insulation between the higher thermal conductive materials of first layer  64  and outer layer  68 . In another embodiment, fins  52  of outer layer  68 , may be corrugated. 
     Because each heat dissipation device operates independently and is heat-actuating, a heat dissipation device is useful for regulating hot spots of any temperature based on the particular selection of materials and construction. Further, several heat dissipation devices may be used at different locations on manifold  12  to regulate the temperature of different hot spots. For example, if one hot spot is at a higher temperature than another, a heat dissipation device at that spot will curve away from the surface more quickly to contact manifold backing plate  76  and remain in contact with the manifold backing plate  76  for a longer period of time than a heat dissipation device positioned adjacent a lower temperature hot spot, which will dissipate a larger amount of heat from the higher temperature spot. The heat-actuating behavior of a heat dissipation device of the present invention allows it to perform differently in response to each hot spot. 
     It will be appreciated that any heat dissipation device of the present invention may be sized to cover any area on manifold  12 . In addition, a heat dissipation device is not limited to being coupled to upper surface  15   a  of manifold  12 . A heat dissipation device may be coupled to manifold  12  at any location where it is desirable to dissipate heat. In a bridging manifold, such as that of  FIG. 3 , a heat dissipation device of the present invention may be coupled to the main manifold  11 , the sub-manifolds  13 , or both. A heat dissipation device may further be coupled to any location in an injection molding apparatus where local heat dissipation is desired. It will further be appreciated by a person skilled in the art that a heat dissipation device may be used with any type of manifold that is heated by any type of manifold heating arrangement. 
     The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will be readily apparent to one skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described by the text, figures or claims herein, and all suitable modifications and equivalents are to be considered to fall within the scope of the invention.