Abstract:
A shot tube assembly for a die casting process includes a spiral passage for circulating a coolant about a cavity containing the molten metal material. The circulating coolant provides temperature control of the shot tube that improves the casting process and increases shot tube life.

Description:
BACKGROUND 
       [0001]    A die casting process utilizes a mold cavity defined between two mold halves. Molten metal material is fed in to the cavity and held under pressure until the metal has solidified. The mold halves are then separated and the cast part removed. The shot tube is an integral part of the die casting tooling. The shot tube serves as the mechanism that is utilized to hold molten material prior to the initiation of the injection process that introduces the molten metal to the cavity. The shot tube includes an opening for introducing molten material into a bore that leads to the cavity. A plunger moves within the bore to inject and compress the molten material into the cavity. Upon solidification of the alloy, the moving platen retracts from the stationary platen. During this process the plunger continues forward to facilitate the ejection of the biscuit or puck from the end of the shot tube. The plunger is then subsequently withdrawn, the die set closed and additional material is introduced into the plunger for fabricating another part within the same cavity. 
         [0002]    The shot tube experiences very high temperatures as a result of intimate contact with molten metal material and therefore is fabricated of materials compatible with those high temperatures. However, materials that are compatible with the high temperatures encountered during the die casting process can be costly and difficult to machine. Accordingly, it is desirable to design and develop shot tubes that can withstand the high temperatures while reducing cost and easing manufacturing. 
       SUMMARY 
       [0003]    A shot tube assembly for a die casting process according to an exemplary embodiment of this disclosure, among other possible things includes an outer sleeve open at each end including an outer pour opening for receiving molten material. An inner sleeve defines a core for molten material. The inner sleeve is disposed within the outer sleeve and open at each end with an inner pour opening aligned with the outer pour opening. A spiral passage encircles the inner cavity. An inlet communicates a coolant to the spiral passages. An outlet exhausts coolant from the spiral passage. 
         [0004]    In a further embodiment of the foregoing shot tube assembly, the outer sleeve includes an inner surface and the inner sleeve includes an outer surface and the spiral passage is at least partially defined by each of the inner and outer surfaces. 
         [0005]    In a further embodiment of any of the foregoing shot tube assemblies, includes trip strips within the spiral passage for generating a turbulent flow in coolant flowing through the spiral passage. 
         [0006]    In a further embodiment of any of the foregoing shot tube assemblies, the inlet and outlet are disposed on a common end adjacent to the pour opening. 
         [0007]    In a further embodiment of any of the foregoing shot tube assemblies, the inlet and outlet includes a plurality of inlets and a plurality of outlets. 
         [0008]    In a further embodiment of any of the foregoing shot tube assemblies, includes a fluid system for circulating coolant into the inlet and out of the outlet. 
         [0009]    In a further embodiment of any of the foregoing shot tube assemblies, the inner sleeve and the outer sleeve include a common material with a common coefficient of thermal expansion. 
         [0010]    In a further embodiment of any of the foregoing shot tube assemblies, the inner sleeve and the outer sleeve include different materials with different coefficients of thermal expansion. 
         [0011]    A shot tube assembly for a die casting process according to an exemplary embodiment of this disclosure, among other possible things includes an outer sleeve open at each end including an outer pour opening for receiving molten material. An inner sleeve defines a core for molten material. The inner sleeve is disposed within the outer sleeve and open at each end with an inner pour opening aligned with the outer pour opening. A coolant passage is disposed about the inner cavity. A trip strip within the coolant passage generates a turbulent flow in coolant flowing through the coolant passage. An inlet communicates a coolant to the coolant passage. An outlet exhausts coolant from the coolant passage. 
         [0012]    In a further embodiment of the foregoing shot tube assembly, the outer sleeve includes an inner surface and the inner sleeve includes an outer surface and the coolant passage is at least partially defined by each of the inner and outer surfaces. 
         [0013]    A method of casting a cast article according to an exemplary embodiment of this disclosure, among other possible things includes defining a mold cavity between at least two mold parts, mounting a shot tube, maintaining a desired temperature of the shot tube by passing a liquid metal material through passages defined within the shot tube, pouring a quantity of molten material into a core defined within the shot tube through a pour opening in the shot tube, forcing the molten material into the mold cavity, and curing the molten material within the mold cavity. 
         [0014]    In a further embodiment of the foregoing method of casting a cast article, the shot tube includes an inner sleeve disposed within an inner sleeve with the passages defined between the inner sleeve and the outer sleeve and the liquid metal material circulates through the passages to maintain a desired temperature of the shot tube. 
         [0015]    In a further embodiment of any of the foregoing method of casting a cast articles, includes the step of cooling the shot tube with the liquid metal material to maintain the shot tube within a desired temperature range. 
         [0016]    A casting system according to an exemplary embodiment of this disclosure, among other possible things includes a mold including at least one cavity for receiving molten material. A shot tube includes an outer sleeve open at each end including an outer pour opening for receiving molten material. An inner sleeve defines a core for molten material. The inner sleeve is disposed within the outer sleeve and open at each end with an inner pour opening aligned with the outer pour opening. A spiral passage is defined between the inner sleeve and the outer sleeve. An inlet communicates a coolant to the spiral passage. An outlet exhausts coolant from the spiral passage. A plunger is movable through the bore of the shot tube for forcing molten material through the inner cavity and into the at least one cavity. 
         [0017]    In a further embodiment of any of the foregoing casting system, the outer sleeve includes an inner surface and the inner sleeve includes an outer surface and the spiral passage is at least partially defined by each of the inner and outer surfaces. 
         [0018]    In a further embodiment of any of the foregoing casting systems, includes a trip strip within the spiral passage for generating a turbulent flow in coolant. 
         [0019]    In a further embodiment of any of the foregoing casting systems, includes a fluid system for circulating a coolant through the spiral passage of the shot tube. 
         [0020]    In a further embodiment of any of the foregoing casting systems, the coolant includes a liquid metal material. 
         [0021]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0022]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0023]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic view an example mold assembly. 
           [0025]      FIG. 2  is a cross-section of an example shot tube. 
           [0026]      FIG. 3  is a perspective view of the example shot tube. 
           [0027]      FIG. 4  is a schematic view of trip strips within a passage of the shot tube. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  schematically illustrates an example casting system  10  that includes a mold  12  having a first part  14  and a second part  16  that defines a cavity  18 . The example mold  12  includes an opening  20  that receives a shot tube  22 . The example shot tube  22  defines a bore  34  through which molten material  26  are injected into the cavity  18 . A plunger  24  is movable within the bore  34  to inject the molten material  26  into the cavity  18 . The molten material  26  is of a temperature in excess of 2000° F. (1093° C.). Accordingly, the material comprising the shot tube  22  must be compatible with the excessive temperatures of the molten material  26 . 
         [0029]    The example casting system  10  includes a coolant circuit  52  for circulating a coolant through the shot tube  22 . Coolant flow through the shot tube  22  removes heat to maintain the shot tube  22  within a desired temperature range for the casting process. The example coolant circuit  52  includes a pump  54  that pumps coolant  60  into passages defined within the shot tube  22 . Coolant exhausted form the shot tube  22  flows through a heat exchanger  58  and then back to a reservoir  50 . The circulated coolant  60  removes heat input into the shot tube  22  form the molten metal material  26 . 
         [0030]    In one example the coolant comprise a liquid metal material that is circulated through the coolant circuit  52  and the shot tube  22 . The liquid metal may comprise a gallium based alloy, lead bismuth alloy, indium alloys, tin-indium alloys, tin alloys, zinc alloys, pewter alloys, antimony alloys, aluminum alloys or any other liquid metal alloys and compounds with properties favorable for maintaining the shot tube  22  within a desired temperature range. The use of liquid metal coolant provides increased heat transfer capabilities as compared to non-metal liquid coolants. 
         [0031]    Referring to  FIGS. 2 and 3  with continued reference to  FIG. 1 , the shot tube  22  includes an outer sleeve  28  that circumscribes an inner sleeve  30 . The outer sleeve  28  and the inner sleeve  30  include aligned pour openings  36 ,  38  on a first end  32 . A second end  35  is received within the opening  20  of the mold  12  ( FIG. 1 ). 
         [0032]    The inner sleeve includes an outer surface  48  and the outer sleeve  28  includes an inner surface  50 . A spiral passage  42  is defined between the inner surface  50  and the outer surface  48 . The spiral passage  42  encircles the inner cavity  40  and provides a path for the circulation of coolant  60  for removing heat from the shot tube  22 . 
         [0033]    An inlet  44  and an outlet  46  provide for circulation of coolant through the passages  42 . In this example the inlet  44  is disposed near the pour opening  36  and the outlet  46  is disposed near the second end  35  that is received within the opening  20  of the mold  12 . 
         [0034]    In operation, the second end of the shot tube  22  is received within the opening  20  of the mold  12  and coolant is flowed through the spiral passages  42  to maintain the shot tube  22  at a desired temperature. The coolant  60  is flowed into and out of the shot tube  22  such that heat is removed at a rate that maintains the temperature within a desired range. The molten material  26  is then added to through the pour openings  36 ,  38 . Once the molten material  26  is disposed within the cavity, the plunger  24  drives the molten material into the cavity  18  for fabrication of the desired part. The part is allowed to cure and then is removed from the mold  12 . 
         [0035]    The heat transfer and removal performance of the coolant can be enhanced by the configuration of the spiral passages  42 . The spacing between loops of the spiral passages  42  can prevent the occurrence of hot spots within the shot tube  22 . Moreover, other features can be added to the spiral passages  42  to enhance heat transfer performance. 
         [0036]    Referring to  FIG. 4 , the spiral passage  42  includes flow disrupting features  68  that generate turbulent flows indicated at  64  in the coolant. The turbulent flows  64  mix the coolant  60  and provides for more of the coolant  60  to contact walls of the passage  42 . 
         [0037]    The flow disrupting features  68  can include trip strips  62  and/or pedestals  66  that generate the turbulent flows  64  in the coolant  60 . The flow disrupting features  68  can be all trip strips  64  or all pedestals  66  or a combination of both trip strips  64  and pedestals to provide the desired generation of turbulent flows  64 . Moreover, the specific arrangement of flow disrupting features  68  can include other shapes to provide the desired turbulent flow  64  and improve thermal transfer of heat to the coolant  60 . The trip strips  62  and pedestals  66  increase surface area for heat transfer that further improves the capability of the coolant to maintain the shot tube within a desired temperature range. 
         [0038]    Accordingly, the example shot tube  22 , casting system  10  and method provide greater control of temperatures during casting to reduce wear and increase shot tube life. 
         [0039]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.