Abstract:
A runner cooling block for use in a die casting system comprises a spreader block, a spreader, a bushing block, a sprue bushing and a water jacket. The sprue bushing comprises a sprue channel running through an interior of the sprue bushing and a cooling channel running circumferentially around an exterior surface of the sprue. The sprue bushing, water jacket and bushing block are assembled to allow cooling water to pass through the cooling channel. The spreader block and the bushing block are assembled such that the spreader is centrally located within the sprue channel wherein molten metal is allowed to pass through the sprue channel for passage into the runner system. The cooling channel includes at least one circumferential heat transfer contour to provide increased heat dissipation to enhance cooling of the molten metal passing through the sprue channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     The present application claims the benefit of provisional Application No. 60/578,634, filed Jun. 10, 2004 by Richard L. Dubay, entitled “Cooling Blocks for Molding and Casting Systems” according to 35 U.S.C. § 119(e), which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Die casting is a popular method of forming articles of manufacture from zinc and magnesium alloys, especially for thin walled parts. Zinc and magnesium have relatively low melting points and are suited to both hot chamber die casting and cold chamber die casting. In hot chamber die casting, molten zinc or magnesium is pushed from a crucible, or pot, into a die casting system through a nozzle. The molten metal enters the die casting system through a sprue where it then travels through a runner system before entering the die cavity of a mold. The molten metal flows into the die cavity, where it solidifies and forms an article having a shape matching the die cavity. The solidified articles are then ejected from the mold, so that the process can be repeated. It is advantageous to cycle the molten metal through the runners and die cavity and then cool it down as fast as possible to keep cycle times down, and in turn keep production time and costs down.  
         [0003]     One way to keep cycle times down is to control the temperature of the molten metal so that it enters the die at the optimal temperature to allow it to both flow through the runner system rapidly and cool rapidly. Temperature controlled sprue systems are commonly used to control the temperature and volume of molten metal that enters the runner system and the mold. In a temperature controlled sprue system, cooling fluid, such as water, is circulated through the inside of the die and around the sprue in order to remove heat from the die casting system that has been absorbed from the molten metal at the desired time, rate and location.  
         [0004]     In these types of systems, a runner cooling block in which the sprue is located contains a system of channels for circulating cooling fluids through the runner cooling block very near where the molten metal enters the die at the sprue. This allows for control of the temperature of the molten metal as it enters the die casting system. When cooling fluid is circulated through the runner cooling block, heat from the molten metal is absorbed by the runner cooling block and dissipated by the cooling water. This reduces the time required to solidify the molten metal in the die cavity and the runner system, which in turn keeps cycle times down. However, conventional runner cooling blocks only provide limited levels of thermal dissipation. As such, there is a need for runner cooling blocks with improved thermal dissipation and heat transfer characteristics to reduce cycle times in die casting systems.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     A runner cooling block for use in a die casting system receives molten metal for distribution into a runner system of a die, and cooling fluid for transferring heat away from the molten metal passing through the runner cooling block. The runner cooling block comprises a spreader block having a spreader, a bushing block having a bushing seat and cooling water access holes, and a water jacket comprising a ring having cooling water holes. The runner cooling block also comprises a sprue bushing comprising a sprue channel running through an interior of the sprue bushing, a cooling channel running circumferentially around an exterior surface of the sprue bushing and having at least one circumferential heat transfer contour. The water jacket is positioned over the cooling channel such that the cooling water holes provide access to the cooling channel. The sprue bushing is situated in the bushing seat such that the access holes, the cooling water holes and the cooling channel are lined up to allow cooling water to pass through the cooling channel. The spreader block and the bushing block mate such that the spreader is centrally located within the sprue channel wherein molten metal is allowed to pass through the sprue channel for passage into the runner system.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  shows a sectional view of a die casting system in which the present invention can be used.  
         [0007]      FIG. 2  shows a perspective view of a runner cooling block of the present invention.  
         [0008]      FIG. 3A  shows an exploded sectional view of a runner cooling block taken along section  3 B- 3 B of  FIG. 2 .  
         [0009]      FIG. 3B  shows an assembled sectional view of a runner cooling block taken along section  3 B- 3 B of  FIG. 2 .  
         [0010]      FIG. 4A  shows an exploded sectional view of a runner cooling block taken along section  4 B- 4 B of  FIG. 2 .  
         [0011]      FIG. 4B  shows an assembled sectional view of a runner cooling block taken along section  4 B- 4 B of  FIG. 2 .  
         [0012]      FIG. 5A  shows a runner cooling block spreader with baffle type cooling.  
         [0013]      FIG. 5B  shows a runner cooling block spreader with cascade type cooling. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  shows a sectional view of die casting system  10  in which the present invention is used. The invention is typically used in zinc or magnesium hot chamber die casting operations, and can also be used in cold chamber die casting operations. Die casting system  10  includes stationary die half  12  and moving die half  14 . Stationary die half  12  and moving die half  14  together comprise mold cavity  16 , which has the shape of an object that can be molded with die casting system  10 . Die casting system  10  also includes runner cooling block  18 , which is used to control the flow of molten metal into die cavity  16 . Molten metal from crucible  20  is injected with piston  22  into die casting system  10  through nozzle  24  and sprue  26  of runner cooling block  18 . As molten metal enters runner cooling block  18  through sprue  26 , sprue post  28  directs the flow of the molten metal into runner  30 A. Runner  30 A directs flow of molten metal to outlet  32 , into die runner  34  and into mold cavity  16 . Runner cooling block  18 , movable die half  14  and stationary die half  12  also include additional channels (not shown) for circulating cooling fluid, such as water, through runner cooling block  18  in order to control the temperature of the molten metal and, hence, its flow and cooling characteristics. Runner cooling block  18  provides improved heat dissipation for the injected metal as it enters die cavity  16 , which accordingly reduces the cycle time required to cool the injected molten metal when creating articles of manufacture in die cavity  16 . Once the molten metal is fully injected into die cavity  16  and properly cooled, movable die half  14  is pulled away from stationary die half  12  so that the cooled molten metal having the shape of die cavity  16  can be removed using ejectors  36 .  
         [0015]      FIG. 2  shows a perspective view of runner cooling block  18 . Runner cooling block  18  includes bushing block  38  and spreader block  40 . Sprue  26  is located inside sprue bushing  42  of bushing block  38 . Molten metal enters runner cooling block  18  at sprue  26  through runner  30 A and exits at outlet  32 . Bushing block  38  includes bushing block water channel  44 A, and spreader block  40  includes spreader block water channel  46 A. Bushing block water channel  44 A and spreader block water channel  46 A are used to circulate temperature controlled cooling fluid such as water through runner cooling block  18  in order to regulate the temperature of molten metal flowing through sprue  26  and runner  30 A. Bushing block mounting holes  48 A- 48 D are used to couple bushing block  38  to stationary die half  12  with threaded fasteners.  FIG. 2  shows cutting plane lines  3 B and  4 B for sectional views of runner cooling block used in  FIGS. 3A, 3B ,  4 A and  4 B, in which the features of the present invention are best described.  
         [0016]      FIG. 3A  shows an exploded sectional view of runner cooling block  18  taken along section  3 B- 3 B of  FIG. 2 . Runner cooling block  18  includes spreader block  40 , spreader  50 , bushing block  38 , sprue bushing  42  and water jacket  52 .  
         [0017]     Spreader block  40  includes runner  30 B, which is a small channel that is machined out of spreader block  40 . Runner  30 B includes outlet  32  at one end and connects with runner  30 A at a second end. Molten metal flows through runner  30 B on its way to die cavity  16 . Spreader block  40  includes spreader block water channels  46 A and  46 B, and spreader block base water channel  54 . Spreader block water channels  46 A and  46 B, and spreader block base water channel  54  are used to circulate cooling water through spreader  50  in order to control heat transfer between spreader post  28  and the molten metal. Spreader block also includes spreader seat  56 , which receives spreader  50  when runner cooling block  18  is assembled.  
         [0018]     Spreader  50  includes sprue post  28  and runner  30 A. Sprue post  28  is a conventional sprue post type and is used to direct molten metal into the runner system of die casting system  10 . Spreader  50  also includes spreader water channels  58 A and  58 B, spreader base water channel  60  and baffle channel  62 . Spreader water channels  58 A and  58 B, spreader base water channel  60  and baffle channel  62  allow cooling water to be circulated through spreader  50  in order to control heat transfer between spreader post  28  and molten metal flowing through sprue  26 .  
         [0019]     Bushing block  38  includes bushing block water channels  44 A and  44 B. Bushing block water channels  44 A and  44 B are used to circulate cooling water around sprue bushing  42 . Bushing block  38  also includes sprue bushing seat  64 . Sprue bushing seat  64  receives sprue bushing  42  when runner cooling block  18  is assembled.  
         [0020]     Sprue bushing  42  includes sprue  26  and cooling channel  66 . Sprue  26  is a channel running through the center of sprue bushing  42  through which molten metal from crucible  20  flows en route to entering die cavity  16 . Cooling channel  66  runs circumferentially along the exterior surface of sprue bushing  42  and encircles sprue  26 . Cooling water is circulated through cooling channel  66  in order to transfer heat away from sprue bushing  42 . Nozzle seat  68  is comprised of a beveled ring surrounding the entrance to sprue  26 . Nozzle seat  68  is used to facilitate connection of runner cooling block  18  with nozzle  24  of die casting system  10  or another source of molten metal. Sprue bushing  42  also includes flange  70  for securing sprue bushing  42  inside sprue bushing seat  64 .  
         [0021]     Cooling channel  66  is shown as a groove cut into the exterior surface of sprue bushing  42 . Cooling channel  66  includes circumferential heat transfer contours, such as circumferential fins  72  and circumferential grooves  73 . Cooling channel  66  includes a plurality of circumferential fins  72  and a plurality of circumferential grooves  73 , which increase the surface area of cooling channel  66 . In one embodiment, as shown in  FIG. 3A , the plurality of circumferential fins  72  comprises three fins, and the plurality of circumferential grooves  73  comprise four grooves. In other embodiments, circumferential fins  72  comprise a plurality of ribs or projections that run circumferentially around the exterior surface of sprue bushing  42  inside cooling channel  66 . The number of circumferential fins  72  and circumferential grooves  73  may vary as needed depending on the particular design requirements of the article to be cast in die chamber  16 . In other embodiments, as few as one fin or one channel is used. For each die having a particular die chamber  16 , different flow and cooling characteristics of the molten metal are required. Thus, the amount of heat transfer between the molten metal materials and the cooling water is a design requirement and can be controlled using additional or fewer circumferential fins  72  or circumferential grooves  73  to increase the surface area of cooling channel  66 . Circumferential fins  72  and circumferential grooves  73  of sprue bushing  42  may be formed with a computer numerical controlled machining system, which accepts digital models of sprue bushing  42 , and machines cooling channel  66  and circumferential fins  72  and circumferential grooves  73  directly out of the raw materials used to form sprue bushing  42 . Computer numerical controlled systems allow for highly accurate machining of circumferential fins  72  and circumferential grooves  73 , which helps control the exact surface area of cooling channel  66 .  
         [0022]     Preferably, the surface area of cooling channel  66  with circumferential fins  72  and circumferential grooves  73  is at least about 25% greater than a surface area of cooling channel  66  with a substantially smooth surface. More preferably, the surface area of the cooling channel  66  with circumferential fins  72  and circumferential grooves  73  is at least about 50% greater than a surface area of cooling channel  66  with a substantially smooth surface. Even more preferably, the surface area of cooling channel  66  with circumferential fins  72  and circumferential grooves  73  is at least about 100% greater than a surface area of cooling channel  66  with a substantially smooth surface. The increase in surface area of cooling channel  66  improves the heat transfer rate of heated molten metal materials located inside sprue  26  to cooling water circulating inside cooling channel  66  through sprue bushing  42 .  
         [0023]     Water jacket  52  includes openings  74 A and  74 B which allow for passage of cooling water from bushing block water channels  44 A and  44 B to cooling channel  66 . Water jacket  52  forms a sealed surface over cooling channel  66  and completely defines the volume of cooling channel  66 .  
         [0024]     The components of runner cooling block  18 , including spreader block  40 , bushing block  38 , sprue bushing  42 , water jacket  52  and spreader  50 , can be manufactured from materials with high thermal conductivities, such as tool steels, heat-treated steels, copper, beryllium and/or beryllium-free materials, and combinations thereof. In one embodiment, sprue bushing  42 , water jacket  52  and spreader  50  are made of heat treated AISI H-13 steel.  
         [0025]      FIG. 3B  shows an assembled sectional view of runner cooling block  18  taken along section  3 B- 3 B of  FIG. 2 . During operation of die casting system  10 , bushing block  38  and spreader block  40  open and close along interface  76 . When closed, molten metal enters runner cooling block  18  through sprue  26 . The molten metal then fills runners  30 A and  30 B. The molten metal exits runner cooling block  18  through outlet  32  and enters die runner  34  of die casting system  10 . After a die cast article is molded in die chamber  16 , spreader block  40  is pulled away from bushing block  38  along interface  76  when movable die half  14  is pulled away from stationary die half  12 . Ejectors  36  (not shown) remove the molded article from die cavity  16  and hardened molten metal remaining in runners  30 A and  30 B and die runner  34 .  
         [0026]     Spreader  50  is positioned in spreader seat  56  of spreader block  40 . Water jacket  52  is seated on flange  70  of sprue bushing  42 . Water jacket  52  is seated against the top of flange  70  such that openings  74 A and  74 B line up with cooling channel  58 . The top of water jacket  54  lines up flush with the top of sprue bushing  52 . Cooling channel  66  is thus completely defines by the inner wall of water jacket  52  and the exterior surface of sprue bushing  42 .  
         [0027]     Sprue bushing  42  and water jacket  52  are bonded together to form a water-tight seal between the two pieces. In one embodiment, sprue bushing  42  and water jacket  52  are bonded together using copper brazing. Copper brazing involves placing copper rings along the interface of sprue bushing  42  and water jacket  52 . Sprue bushing  42  and water jacket  52  are then heated to melt the copper, creating a seal at the interface when the copper cools. In one embodiment, the interface between sprue bushing  42  and water jacket  52  may include grooves in which the copper rings are placed. When the copper is heated, it melts and fills in the interface between opposing grooves, thereby improving the water-tight seal when cooled. The brazing between sprue bushing  42  and water jacket  52  is leak tested to ensure the seal can withstand 1800 pounds-per-square-inch of pressure. Once assembled, sprue bushing  42  and water jacket  52  are inserted into sprue bushing seat  64  of bushing block  38 . The bottom of flange  70  of sprue bushing  42  sits flush against sprue bushing seat  64 .  
         [0028]     When sprue bushing  42  and water jacket  52  are positioned in sprue bushing seat  64 , sprue bushing water channel  44 A and  44 B, openings  74 A and  74 B and cooling channel  66  are aligned to allow for passage of cooling fluid through cooling channel  66  in order to transfer heat from molten metal flowing through sprue  26 . In one embodiment, cooling water is circulated through bushing block  38  in a unidirectional manner. In one embodiment, cooling water enters runner cooling block  18  through bushing block water channel  44 A, passes through opening  74 A, flows into cooling channel  66 , flows around sprue  26 , enters opening  74 B and exits runner cooling block  18  at bushing block water channel  44 B.  
         [0029]     Sprue bushing  42  absorbs heat from the molten metal flowing through sprue  26 . This heat is then absorbed by cooling water circulating through cooling channel  66 . The rate of heat transfer between sprue bushing  42 , and the circulating cooling water is proportional to the product of the temperature difference and the exposed surface area. Because circumferential fins  72  and grooves  73  of cooling channel  66  increase the surface area of sprue bushing  42  that is exposed to the circulating cooling water, the rate of heat that is transferred from sprue bushing  42  to the circulating cooling water is significantly increased compared to a substantially smooth cooling channel  66 . This effectively allows sprue bushing  42  to dissipate a greater amount of heat from the injected metal to the circulating water.  
         [0030]     Runner cooling block  18  with circumferential heat transfer contours, such as circumferential fins  72  and circumferential grooves  73 , allow for improved heat transfer between molten metal materials entering sprue  26  and cooling water flowing through cooling channel  66 . Injected molten metal flowing out of runner cooling block  18  through outlet  32  can then be set to an optimal temperature for flowing through die runner  34 , and then rapidly cooling inside die cavity  16 . This accordingly reduces the time required for the injected metal to solidify in die cavity  16 , which increases efficiency in the die casting system.  
         [0031]     Spreader  50  is positioned in runner spreader seat  56  of spreader block  40 . When spreader  50  is inserted into seat  56  of spreader block  40 , spreader water channels  58 A and  58 B, spreader base water channel  60  and baffle channel  62  align with spreader block water channels  46 A and  46 B, and spreader base water channel  54 . This allows cooling water to circulate through sprue post  28  in a cascade type, baffle type or other type of cooling manner. The cooling of spreader  50  also assists in dissipating heat from the injected molten metal flowing through sprue  26 .  
         [0032]     When spreader block  40  is coupled with bushing block  38  inside die casting system  10 , sprue post  28  is concentrically located inside sprue  26 . There is a small gap between sprue post  28  and sprue  26  of sprue bushing  42 , which is not visible in  FIGS. 3A-5B . In one embodiment, the gap is approximately 0.030 inches. Additionally, there is also an approximately a 0.030 inch gap between spreader block  40  and bushing block  38 . Runner  30 A is machined into sprue post  28  and runner  30 B is machined into spreader block  40 . Runners  30 A and  30 B are used to connect molten metal flowing from runner sprue  26  with die runner  34  of  FIG. 1 . The specific size, depth and location of runners  30 A and  30 B depend on the specific needs as dictated by the requirements of the die and die cavity. Additional runners can also be used.  
         [0033]      FIG. 4A  shows an exploded sectional view of runner cooling block  18  taken along section  4 B- 4 B of  FIG. 2 . Runner cooling block  18  includes spreader block  40 , spreader  50 , bushing block  38 , sprue bushing  42  and water jacket  52 .  FIG. 4A  shows the location of mounting bores used in conjunction with threaded fasteners to secure runner cooling block  18  to die casting system  10 . Spreader block  40  includes spreader block mounting bores  78 A- 78 D, of which  78 A is shown and  78 B is shown in hidden lines. Spreader block  40  also includes spreader mounting holes  80 A- 80 D, of which holes  80 A and  80 B are shown in hidden lines. Spreader  50  includes spreader mounting bores  82 A- 82 D, of which bores  82 A and  82 B are shown in hidden lines. Bushing block  38  includes bushing block mounting bores  48 A- 48 D, of which bore  48 A is shown and bore  48 B is shown in hidden lines.  
         [0034]      FIG. 4B  shows an assembled sectional view of runner cooling block  18  taken along section  4 B- 4 B of  FIG. 2 . Runner cooling block  18  includes spreader block  40 , spreader  50 , bushing block  38 , sprue bushing  42  and water jacket  52 . Threaded fasteners are inserted through spreader mounting holes  80 A- 80 D and into spreader mounting bores  82 A- 82 D to fasten spreader  50  to spreader block  40 . Spreader block mounting bores  78 A- 78 D receive threaded fasteners that extend from moving die half  14  and are used to secure spreader block  40  to moving half  14 . Bushing block mounting bores  48 A- 48 D receive threaded fasteners that extend from stationary die half  12  and are used to secure bushing block  22  to stationary die half  12 .  
         [0035]      FIG. 5A  shows spreader  50  with baffle type cooling. Baffle  84  is placed in baffle channel  62  which seals base water channel  60  with plug  86 . Cooling water flows in spreader water channel  46 B and exits spreader water channel  46 A (not shown). Incoming cooling water from spreader water channel  46 B is directed into baffle channel  62  by the use of baffle  84 . Water flow through baffle channel  62  cools down spreader post  28 , which in turn assists in regulating the temperature of molten metal flowing through runner cooling block  18 . The cooling water continues around baffle  84  and out the other side of spreader  50  through spreader channel  46 A (not shown).  
         [0036]      FIG. 5B  shows a runner spreader with cascade type cooling. A cascade water junction  88  is placed into base water channel  60 . Spreader water channel  46 B is not used and is sealed up with plug  90 . Spreader water channel  46 A (not shown) is sealed up in a similar manner. Cooling water flows in base water channel  60  through water junction  88 . Cooling water enters through water junction entrance  92  and empties inside baffle channel  62  at water junction tip  94 , whereby the cooling water can cool down spreader post  28  in order to assists in regulating the temperature of molten metal flowing through runner cooling block  18 . Cooling water returns through water junction return  96  and exits at water junction exit  98 .  
         [0037]     The relative size of runner cooling block  18  shown in  FIGS. 1-5B  are exemplary only. Spreader block  40 , spreader  50 , bushing block  38 , sprue bushing  42  and water jacket  52  can be made having various dimensions for use in smaller or larger die casting operations. Smaller dimensioned runner cooling blocks  18  are suitable for a double mold systems, where two runner cooling blocks  18  are disposed next to each other in the die. This allows the cooling of two streams of metal to be injected into a mold, either simultaneously or sequentially. Larger runner cooling blocks can be used for dies requiring a higher throughput of molten metal.  
         [0038]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.