Abstract:
Provided is a die-casting die which is less likely to cause gas defects. A die-casting die in which a runner ( 1 ) is branched at a branch section ( 3 ), and cavities are connected to the respective downstream ends of the branched runner, wherein the runner ( 1 ) comprises a main runner ( 2 ) that is located upstream of the branch section ( 3 ) and a plurality of sub-runners ( 4 ) that are located downstream from the branch section ( 3 ), a volume section ( 5 ) having an opening ( 6 ) that opens toward the main runner ( 2 ) is formed at a portion of the branch section ( 3 ) that represents an extension of the direction of the main runner ( 2 ), and the width of the opening ( 6 ) is greater than the width of the main runner ( 2 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a die-casting die. 
       BACKGROUND ART 
       [0002]    Die-casting is a type of casting method in which, by forcing a melted nonferrous metal into a die under pressure, a high-precision casting having a superior casting surface can be mass-produced. The die comprises a cavity (product section) that corresponds with the shape of the product, and a passage (non-product section) through which the melted nonferrous metal flows to the cavity. 
         [0003]    Patent Literature 1 (PTL 1) discloses a casting method that uses a die-casting die. In typical die-casting, the inside of the die is first evacuated down to reduced pressure using a vacuum apparatus or the like, and the molten metal (the melted nonferrous metal) is then poured into a plunger sleeve. The molten metal passes through the plunger sleeve and a runner, and fills the cavity. The filled molten metal is cooled and solidified, and the metal is then released from the die as the product. 
         [0004]    For example, a compressor housing or the like, which represents one example of a pressure vessel, is produced by die-casting.  FIG. 7  illustrates one example of a compressor housing.  FIG. 7  illustrates a scroll-type compressor  100  for a car air-conditioning unit. The scroll-type compressor  100  has a housing  102  that constitutes the outer shell. The housing  102  is composed of a front housing  103  and a rear housing  104 , which are fastened into a single integrated unit using bolts  105 . 
         [0005]    A sealing material  106  such as an O-ring is interposed at the bonding interface between the front housing  103  and the rear housing  104 , thereby sealing the intake chamber formed inside the housing  102  in an airtight manner relative to the external atmosphere. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         {PTL 1} Japanese Unexamined Patent Application, Publication No. 2008-55487 (paragraphs [0002] and [0003]) 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In die-casting, even when the inside of the die is evacuated down to reduced pressure prior to the injection of the molten metal, gas still remains within the non-product section. As a result, a problem arises in that the molten metal incorporates this residual gas during the process of flowing through the non-product section into the product section. 
         [0008]    When the molten metal is cooled and solidified with this residual gas still incorporated therein, voids (gas defects) are generated within the product. If the product is a pressure vessel, then because the inside of the pressure vessel must be sealed in an airtight manner, if these voids occur at the sealing surface, they can cause pressure loss and coolant gas leakage and the like. 
         [0009]    The present invention has been developed in light of the above issues, and has an object of providing a die-casting die which is less likely to cause gas defects. 
       Solution to Problem 
       [0010]    In order to achieve the above object, the present invention provides a die-casting die in which a runner is branched at a branch section, and cavities are connected to the respective downstream ends of the branched runner, wherein the runner comprises a main runner that is located upstream of the branch section and a plurality of sub-runners that are located downstream from the branch section, a volume section having an opening that opens toward the main runner is formed at a portion of the branch section that represents an extension of the direction of the main runner, and the width of the opening is greater than the width of the main runner. 
         [0011]    Conventionally, when a molten metal is poured into a die, the molten metal incorporates any residual gas remaining inside the runner before reaching the cavity. This residual gas is incorporated mostly within the leading portion of the poured molten metal. In the present invention, by providing the volume section at the branch section of the runner, the leading portion of the poured molten metal is collected in the volume section. The opening of the volume section opens toward the main runner, and the opening is designed with a greater width than the main runner. Consequently, the leading portion of the molten metal is collected inside the volume section before it can branch into the sub-runners. As a result, the portion of the molten metal containing a large amount of incorporated gas can be prevented from flowing into the cavities. In other words, a product having minimal gas defects can be produced. 
         [0012]    In one aspect of the invention described above, the opening may have a sloped surface that widens toward the main runner. 
         [0013]    By employing this configuration, the leading portion of the molten metal can be guided more readily into the volume section. 
         [0014]    In another aspect of the invention described above, the volume section may comprise a molten metal inlet portion that includes the opening, and a well portion that is connected to the molten metal inlet portion on the opposite side from the opening, and the well portion is preferably spherical. 
         [0015]    In die-casting, the molten metal is forced into the die under high pressure. By forming the well portion in a spherical shape, the stress concentration during introduction of the molten metal into the well portion can be reduced. This enables the lifespan of the die to be extended. In this description, the terms “sphere” and “spherical” include shapes that are substantially spherical and shapes that are at least partially spherical. 
         [0016]    In the aspect described above, a notch that narrows toward the well portion is may be provided in the side surface of the molten metal inlet portion at the end of the molten metal inlet portion that connects to the well portion. 
         [0017]    By employing this configuration, the molten metal and the residual gas collected in the well portion can be prevented from flowing back into the runner. 
         [0018]    In the aspect described above, a pillar that extends in a different direction from the extension direction of the main runner may be provided inside the well portion. 
         [0019]    Suspending a pillar inside the spherical well portion causes the molten metal introduced into the well portion to flow around the inner surface of the sphere. As a result, the molten metal can be more readily retained inside the well portion. 
         [0020]    Further, in die-casting dies, it is generally considered that reducing the volume of the non-product section of the die is preferable in terms of improving the material yield. By providing a pillar in the well portion, the effective volume of the well portion can be reduced. In other words, the volume of the non-product section can be reduced. 
         [0021]    In yet another aspect of the invention described above, the well portion is a circular channel, and the molten metal inlet portion is disposed along a tangential line of the well portion. 
         [0022]    By forming the well portion as a circular shape, the stress concentration can be reduced. Because the molten metal inlet portion is disposed along a tangential line of the well portion, the molten metal is introduced along the inner periphery of the well portion, and flows like a vortex. This improves the retention of the molten metal within the well portion. 
         [0023]    In the aspect described above, a spiral lap may be formed in the channel. This enables the molten metal to be retained even more reliably within the well portion. 
         [0024]    In yet another aspect of the invention described above, a notch that dents inward into the sub-runner, causing the opening to expand toward the main runner, may be provided at the connection portion between the sub-runner and the opening. 
         [0025]    By employing this configuration, the opening of the volume section is expanded, and the point of entry to the sub-runner is slightly narrowed, enabling the leading portion of the molten metal to be guided smoothly into the volume section. 
       Advantageous Effects of Invention 
       [0026]    In the present invention, by providing the volume section that can retain molten metal at the branch section of the runner, a die can be obtained which is capable of producing products having minimal gas defects. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]      FIG. 1  is a plan view of a branch section of a runner of a die-casting die according to a first embodiment. 
           [0028]      FIG. 2  is a plan view of a branch section of a runner of a die-casting die according to a second embodiment. 
           [0029]      FIG. 3  is a plan view of a branch section of a runner of a die-casting die according to a third embodiment. 
           [0030]      FIG. 4  is a plan view of a branch section of a runner of a die-casting die according to a fourth embodiment. 
           [0031]      FIG. 5  is a plan view of a branch section of a runner of a die-casting die according to a fifth embodiment. 
           [0032]      FIG. 6  is a plan view of a branch section of a runner of a conventional die-casting die. 
           [0033]      FIG. 7  is a diagram illustrating an example of a compressor housing. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    Embodiments of the die-casting die according to the present invention are described below with reference to the drawings. 
         [0035]    Generally, a die-casting die is composed of a fixed die and an ejector die. Appropriate grooves are formed in the fixed die and the ejector die, so that when the two dies are brought together, a cavity that corresponds with the shape of the product is formed. A runner is connected to the cavity to enable a molten metal to be poured into the cavity. 
         [0036]    Nonferrous metals such as aluminum or magnesium, or alloys of these metals, can be used as the molten metal material. 
       First Embodiment 
       [0037]    In a die-casting die according to this embodiment, the runner has a branch section, and the main runner branches into two sub-runners at the branch section. A separate cavity is connected to the downstream end of each of the sub-runners. 
         [0038]      FIG. 1  illustrates a plan view of the branch section of a runner  1  of the die-casting die according to this embodiment. As illustrated in  FIG. 1 , the runner  1  is composed of a main runner  2  which branches into two sub-runners  4  at a branch section  3 . The sub-runners  4  are positioned perpendicularly to the longitudinal axial direction of the main runner  2  and extend left and right in opposite directions, so that the molten metal flowing through the main runner  2  can be distributed stably into the two sub-runners  4  at the branch section  3 . 
         [0039]    A volume section  5  is provided at a portion of the branch section  3  that represents an extension of the direction of the main runner  2 . The volume section  5  is formed with a volume that is capable of collecting the gas remaining in the main runner  2 . The volume section  5  has an opening  6  that opens toward the main runner  2 , and is connected to the runner  1 . The width (d 1 ) of the opening  6  is preferably as narrow as possible, but is greater than the width (d 2 ) of the main runner  2 . Here, the term “width” refers to the distance across the widest portion of the main runner  2  or the opening  6 . 
         [0040]    The opening  6  preferably has a sloped surface  7  that widens toward the main runner at the connection portion with the runner  1 . 
         [0041]    Further, a notch that dents inward into the sub-runner  4 , causing the opening  6  to expand toward the main runner, may be provided in the sub-runner  4  at the connection portion with the opening  6 . This notch is formed with a size that does not impede the flow of the molten metal from the main runner  2  to the sub-runner  4 . 
         [0042]    In this embodiment, the end of the volume section  5  opposite the opening  6  is formed with a substantially hemispherical shape. 
         [0043]    Next is a description of the actions and effects obtained upon using a die-casting die of the structure described above. The molten metal poured into the die-casting die of the above structure flows through the main runner  2  while incorporating any residual gas remaining in the main runner  2 , and the leading portion of the molten metal, which incorporates much of the residual gas, flows into the volume section  5  provided at the branch section  3 . The opening  6  of the volume section  5  opens toward the main runner  2 , and is formed with a greater width than the width of the main runner  2 , and therefore the molten metal flows preferentially into the volume section  5 , rather than branching into the sub-runners  4 . The molten metal introduced into the volume section  5  is retained inside the volume section  5 . When the volume section  5  becomes filled with the molten metal, the following molten metal branches and flows into the sub-runners  4  that extend left and right from the branch section  3 , and then eventually enters the cavities connected to the downstream ends of the sub-runners. 
         [0044]    If the opening  6  is sloped so as to widen toward the main runner  2 , then the molten metal can be guided more readily into the volume section  5 . 
         [0045]    If a notch is provided in the sub-runners  4 , then the molten metal that has entered the volume section  5  can be prevented from flowing into the sub-runners. 
       Example 1 
       [0046]    Using a die-casting die of the above structure, a rear housing for a scroll-type compressor for use in a car air-conditioning unit was produced. The main runner  2  had a width of 25 mm. The sub-runners  4  had a width of 20 mm. The volume section  5  had a volume of approximately 2,000 mm 3  (and a radius of 25 mm), and the width of the opening  6  was 50 mm. An aluminum alloy that had been melted at a temperature of 660° C. was used as the molten metal. 
       Comparative Example 1 
       [0047]    Using a conventional die-casting die in which no volume section had been formed at the branch section, a rear housing was produced in the same manner as above. With the exception of not providing the volume section, the die-casting die was formed with the same structure as that described in the above embodiment.  FIG. 6  illustrates a plan view of the branch section of a runner  50  of a conventional die-casting die. The runner  50  has a configuration in which a main runner  52  branches into two sub-runners  54  at a branch section  53  partway along the runner. 
         [0048]    The amount of gas incorporated in the molten metal during the production processes of the example 1 and the comparative example 1 was measured to evaluate the level of gas defects. For the example 1, the value of an index that indicates the degree of oxidation of the molten metal was approximately half that observed for the comparative example 1. This result confirmed that by providing the volume section at the runner branch section, a product having fewer gas defects could be produced. 
       Second Embodiment 
       [0049]      FIG. 2  illustrates a plan view of the branch section of a runner  10  of a die-casting die according to this embodiment. In this embodiment, with the exception of the volume section, the structure is the same as that of the first embodiment. 
         [0050]    A volume section  15  is composed of a molten metal inlet portion  18  and a well portion  19 . 
         [0051]    The molten metal inlet portion  18  has an opening  16  that opens toward a main runner  12 , and is connected to a runner  10 . In the same manner as that described in the first embodiment, the width of the opening  16  is greater than the width of the main runner  12 . A well portion  19  is connected to the molten metal inlet portion  18  on the opposite side from the opening  16 . The molten metal inlet portion  18  is formed with the same width from the opening  16  toward the opposite end of the inlet portion. The length of the molten metal inlet portion  18  from the opening  16  to the opposite end of the inlet portion is set appropriately in accordance with factors such as the width of the main runner  12 . The inner surface of the molten metal inlet portion  18  is a smooth shape with no unevenness. 
         [0052]    A notch  17  that dents inward into the sub-runner  14 , causing the opening  16  to expand toward the main runner  12 , may be provided in the sub-runner  14  at the connection portion with the opening  16 . This notch  17  is formed with a size that does not impede the flow of the molten metal from the main runner  12  to the sub-runner  14 . 
         [0053]    Further, the opening  16  may be sloped so that the connection portion with the runner widens toward the main runner. 
         [0054]    The well portion  19  is formed with a spherical shape, and is formed with a volume that is capable of collecting the residual gas remaining in the main runner  12 . 
         [0055]    In die-casting, the molten metal is forced into the die at a pressure of approximately 1,000 atmospheres. In the die-casting die of the structure described above, because the well portion  19  is spherical, the stress concentration that occurs when the molten metal enters the volume section  15  can be reduced. As a result, the lifespan of the die-casting die can be extended. Further, by making the well portion  19  spherical, the molten metal that flows into the well portion collides with the end face of the volume section  15 , changes flow direction, and flows around the inner surface of the well portion  19 . As a result, the introduced molten metal can be more readily retained inside the well portion  19 . The molten metal inlet portion  18  is formed with the same width from the opening  16  toward the opposite end of the inlet portion. The inner surface of the molten metal inlet portion  18  has a smooth shape. Accordingly, the molten metal can be guided more smoothly into the well portion  19 . Further, if a notch is provided in each of the sub-runners  14 , then the molten metal that has entered the volume section  15  can be prevented from flowing into the sub-runners  14 . Furthermore, if the opening  16  is sloped so as to widen toward the main runner  12 , then the molten metal can be guided more readily into the molten metal inlet portion  18 . By using a die-casting die having this type of structure, a product having minimal gas defects can be produced. 
       Third Embodiment 
       [0056]      FIG. 3  illustrates a plan view of the branch section of a runner  20  of a die-casting die according to this embodiment. In this embodiment, with the exception of the molten metal inlet portion, the structure is the same as that of the second embodiment. 
         [0057]    A volume section  25  is composed of a molten metal inlet portion  28 , and a well portion  29  that is connected to the molten metal inlet portion  28 . 
         [0058]    A notch  21  is formed in the side surface of the molten metal inlet portion  28 , at the end where the inlet portion connects to the well portion  29 , so that the width of the molten metal inlet portion  28  narrows toward the well portion  29 . 
         [0059]    In the die-casting die of the above structure, by providing the notch  21  in the molten metal inlet portion  28  at the end that connects to the well portion  29 , the molten metal introduced into the well portion  19  can be prevented from flowing back into the molten metal inlet portion  28 . Consequently, the molten metal containing a large amount of incorporated gas can be more easily retained in the well portion  29 . By using a die-casting die having this type of structure, a product having minimal gas defects can be produced. 
       Fourth Embodiment 
       [0060]      FIG. 4  illustrates a plan view of the branch section of a runner  30  of a die-casting die according to this embodiment. In this embodiment, with the exception of the provision of a pillar inside the well portion, the structure may be the same as that of the second embodiment or the third embodiment. 
         [0061]    A well portion  39  is spherical, and a pillar  31  that extends in a different direction from the extension direction of a main runner  32  is provided inside the well portion  39 . The pillar  31  is preferably disposed at a location across an internal diameter of the well portion. Further, the pillar  31  is preferably positioned perpendicularly to the longitudinal axial direction of a main runner  32 . The pillar  31  preferably has a circular cylindrical shape, wherein the thickness of the pillar is set appropriately in accordance with the volume of the well portion  39 . 
         [0062]    In a die-casting die of the structure described above, by providing the pillar  31  inside the well portion  39 , the flow direction of the molten metal that has entered the well portion  39  can be adjusted to a desired direction. This enables the molten metal containing a large amount of incorporated gas to be more easily retained in the well portion  39 . By using a die-casting die having this type of structure, a product having minimal gas defects can be produced. Furthermore, by using a circular cylindrical pillar, the stress concentration can be reduced, enabling the lifespan of the die-casting die to be extended. 
       Fifth Embodiment 
       [0063]      FIG. 5  illustrates a plan view of the branch section of a runner  40  of a die-casting die according to this embodiment. In this embodiment, with the exception of a difference in the shape of the volume section, the structure may be the same as that of the first embodiment or the third embodiment. 
         [0064]    A volume section  45  is composed of a well portion  49  and a molten metal inlet portion  48 . 
         [0065]    The well portion  49  is a circular channel, and is formed with a volume that is capable of collecting the residual gas remaining in a main runner  42 . The well portion  49  and the molten metal inlet portion  48  are arranged so that one side surface of the molten metal inlet portion  48  is disposed along a tangential line of the well portion  49 . In other words, the volume section  45  has a structure in which the molten metal inlet portion  48  and the well portion  49  are connected together to form a P-shape. 
         [0066]    A spiral lap  41  may be formed in the channel of the well portion  49 . The lap  41  is disposed in a location that does not impede the entry of the molten metal into the well portion  49 . 
         [0067]    The molten metal inlet portion  48  has an opening  46  that opens toward the main runner  42  at the opposite end from where the well portion  49  is connected, and is connected to the runner  40  at this opening  46 . In the same manner as that described for the first embodiment, the width (d 41 ) of the opening  46  is greater than the width (d 42 ) of the main runner  42 . The molten metal inlet portion  48  is formed with the same width from the opening  46  toward the opposite end of the inlet portion. The length of the molten metal inlet portion  48  from the opening  46  to the opposite end of the inlet portion is set appropriately in accordance with factors such as the width of the main runner  42 . The inner surface of the molten metal inlet portion  48  is a smooth shape with no unevenness. The opening  46  may be sloped so that the connection portion with the runner  40  widens toward the main runner  42 . 
         [0068]    In a die-casting die of the structure described above, the molten metal inlet portion  48  is disposed along a tangential line of the well portion  49 . Consequently, the molten metal that enters the well portion  49  flows around the inner periphery of the well portion  49 , and is more readily retained within the well portion. By using a die-casting die having this type of structure, a product having minimal gas defects can be produced. 
         [0069]    In the first embodiment through to the fifth embodiment, the sub-runners were provided perpendicularly to the longitudinal axial direction of the main runner, but the positioning of the sub-runners is not limited to this particular configuration. For example, the sub-runners may branch so as to form a Y-shape. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 ,  10 ,  20 ,  30 ,  40 ,  50  Runner 
           2 ,  12 ,  22 ,  32 ,  42 ,  52  Main runner 
           3 ,  13 ,  23 ,  33 ,  43 ,  53  Branch section 
           4 ,  14 ,  24 ,  34 ,  44 ,  54  Sub-runner 
           5 ,  15 ,  25 ,  35 ,  45  Volume section 
           6 ,  16 ,  26 ,  36 ,  46  Opening 
           7  Sloped surface 
           17  Notch (sub-runner) 
           18 ,  28 ,  38 ,  48  Molten metal inlet portion 
           19 ,  29 ,  39 ,  49  Well portion 
           21  Notch (molten metal inlet portion) 
           31  Pillar 
           41  Lap