US20070215308A1 - Vertical Casting Apparatus and Vertical Casting Method - Google Patents

Vertical Casting Apparatus and Vertical Casting Method Download PDF

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Publication number
US20070215308A1
US20070215308A1 US11/569,149 US56914905A US2007215308A1 US 20070215308 A1 US20070215308 A1 US 20070215308A1 US 56914905 A US56914905 A US 56914905A US 2007215308 A1 US2007215308 A1 US 2007215308A1
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Prior art keywords
molten metal
casting
gas
pouring ladle
pressurizing
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US11/569,149
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Nagayoshi Matsubara
Takashi Koide
Kiyoshi Fujino
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Kosei Aluminum Co Ltd
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Kosei Aluminum Co Ltd
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Priority to JP2004147873 priority Critical
Priority to JP2004-147873 priority
Application filed by Kosei Aluminum Co Ltd filed Critical Kosei Aluminum Co Ltd
Priority to PCT/JP2005/008874 priority patent/WO2005110645A1/en
Assigned to KOSEI ALUMINUM CO., LTD. reassignment KOSEI ALUMINUM CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FUJINO, KIYOSHI, KOIDE, TAKASHI, MATSUBARA, NAGAYOSHI
Publication of US20070215308A1 publication Critical patent/US20070215308A1/en
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D18/00Pressure casting; Vacuum casting
    • B22D18/04Low pressure casting, i.e. making use of pressures up to a few bars to fill the mould
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D15/00Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor
    • B22D15/005Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor of rolls, wheels or the like
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/09Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using pressure
    • B22D27/11Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using pressure making use of mechanical pressing devices

Abstract

The present invention is to provide a vertical casting apparatus capable of easily manufacturing castings without causing shrinkage cavities and entrainment of gas, by filling a molten metal into a mold cavity at a high speed and by effectively pressurizing the molten metal in the closed cavity, which has high work efficiency, ease of maintenance, and a low cost of equipment, and a vertical casting method using the vertical casting apparatus. The vertical casting apparatus is provided with an apparatus body comprising a fixed mold 1 on the lower side and a movable mold 2 on the upper side, a closing means 13 for closing a molten metal in-flow gate 10 formed in the fixed mold 1, and a pressurizing means 20 for pressurizing the molten metal in the closed mold cavity, and a casting means for supplying and filling the molten metal into the mold cavity from the underside. The casting means has a gas-pressurized molten metal pouring ladle 6 attachable to and detachable from the apparatus body.

Description

    TECHNICAL FIELD
  • The present invention relates to a vertical casting apparatus capable of manufacturing castings such as aluminum alloys, in which a molten metal is filled into a mold cavity from underside, and, more particularly, to a vertical casting apparatus in which a molten metal is supplied and filled into a mold cavity from the underside by using a gas-pressurized molten metal pouring ladle, and a vertical casting method using the vertical casting apparatus.
  • BACKGROUND ART
  • In the case where castings such as light alloy products, especially parts requiring strength, are manufactured, a vertical casting apparatus are used to prevent entrainment of gas at the time when molten metal is poured.
  • In such a vertical casting apparatus, as a means for supplying molten metal into a mold cavity from a molten metal holding furnace while preventing the mixing of oxides and the entrainment of gas, use of a low-pressure gas is already known (see Japanese Laid-Open Patent Application No. 58-55166). However, although the low-pressure gas is effective in supplying molten metal quantitatively into a mold, only the use of low-pressure gas is not sufficient to avoid shrinkage cavities occurring at the time of solidification of molten metal and defective thin-wall products because the casting speed is slow and the pressure is low. Also, in a conventional apparatus, a large amount of molten metal was accommodated in a molten metal holding furnace fixed to an apparatus body, which increased the size of apparatus. Further, it is not easy to replenish molten metal into the molten metal holding furnace fixed to the apparatus body, and also it is very difficult to perform spraying work for cleaning and lubricating an in-flow gate of the apparatus body.
  • Moreover, one of the present inventors has invented a method of using an immersed electromagnetic pump as a means for supplying molten metal into the mold cavity (see Japanese Laid-Open Patent Application No. 2003-266168). However, the apparatus for carrying out this method also increases in size because high-speed casting requires a large electromagnetic pump. Therefore, the practical use of this apparatus is difficult, and additionally, they had the same problems as described above, such as the difficulty in replenishing molten metal.
  • Patent Document 1: Japanese Laid-Open Patent Application No. 58-55166
  • Patent Document 2: Japanese Laid-Open Patent Application No. 2003-266168
  • DISCLOSURE OF THE INVENTION OBJECT TO BE SOLVED BY THE INVENTION
  • In casting using a vertical casting apparatus, in order to manufacture high-quality castings, especially thin-wall and large-size castings, it is necessary to fill molten metal into the mold cavity at a high speed. Also, in order to prevent the mixing of oxides and the entrainment of gas, which cause defects of castings, and to prevent shrinkage cavities produced by solidification shrinkage, it is necessary to fill molten metal from underside and to replenish a sufficient amount of molten metal by pressurizing effectively. Also, at this time, to reduce troubles during operation, it is necessary to simplify the construction of cavity and of the whole casting apparatus, for practical use. High work efficiency and ease of maintenance are also very important factors.
  • An object of the present invention is to provide a vertical casting apparatus capable of easily manufacturing castings without causing shrinkage cavities and entrainment of gas by filling molten metal into a mold cavity at a high speed and effectively pressurizing the molten metal in the closed cavity, which has high work efficiency, ease of maintenance, and a low cost of equipment, and a vertical casting method using the vertical casting apparatus.
  • MEANS TO SOLVE THE OBJECT
  • The present inventors earnestly conducted studies to solve the above objects, and found out that by using an apparatus body and a gas-pressurized molten metal pouring ladle attachable to and detachable from the apparatus body, a vertical casting apparatus having high work efficiency, ease of maintenance, and a low cost of equipment can be provided, and by increasing the gas pressure in the gas-pressurized molten metal pouring ladle, molten metal can be supplied at a high speed, by which a casting without the mixing of oxide film and the entrainment of gas can be manufactured, leading to the completion of the present invention. Further, the present inventors found out that after the cavity has been filled with the poured molten metal, if the molten metal in the closed state is effectively pressurized at a plurality of places with the pressure transmission distance being short, a casting can be manufactured without causing shrinkage cavities, mixing of oxide film, and entrainment of gas, leading to the completion of the present invention.
  • In other words, the present invention relates to (1) a vertical casting apparatus comprising an apparatus body having a fixed mold on a lower side and a movable mold on an upper side, which can form a mold cavity, a closing means for closing a molten metal in-flow gate formed in the fixed mold, and a pressurizing means for pressurizing a molten metal in the closed mold cavity; and a casting means for supplying and filling the molten metal into the mold cavity from underside, wherein the casting means has a gas-pressurized molten metal pouring ladle attachable to and detachable from the apparatus body; (2) the vertical casting apparatus according to (1), wherein a hermetically sealed construction is formed by attaching the gas-pressurized molten metal pouring ladle to the apparatus body; (3) the vertical casting apparatus according to (1) or (2), wherein the gas-pressurized molten metal pouring ladle is provided with a casting stoke, and the hermetically sealed construction is formed by bringing an upper end portion of the casting stoke into close contact with the apparatus body; (4) the vertical casting apparatus according to (1) or (2), wherein the apparatus body is provided with a casting stoke, the hermetically sealed construction is formed by bringing an upper end portion of the gas-pressurized molten metal pouring ladle is brought into close contact with the apparatus body; (5) the vertical casting apparatus according to any one of (1) to (4), wherein a content of the gas-pressurized molten metal pouring ladle is a capacity capable of containing a molten metal necessary for one casting operation; (6) the vertical casting apparatus according to any one of (1) to (5), wherein the gas-pressurized molten metal pouring ladle has a heating means; (7) the vertical casting apparatus according to any one of (1) to (6), wherein the casting means has a vacuum attraction mechanism for vacuum attracting a gas in the mold cavity to fill a molten metal in the gas-pressurized molten metal pouring ladle by vacuum attraction; (8) the vertical casting apparatus according to any one of (1) to (7), wherein the mold cavity has a gas exhaust passage, and a molten metal solidification zone void linked with the gas exhaust passage is provided in the vicinity of the gas exhaust passage; and (9) the vertical casting apparatus according to any one of (1) to (8), wherein the gas-pressurized molten metal pouring ladle has a molten metal supply pipe linked with an opening provided in a lower part thereof, and a molten metal supply port lid which has a sealing force capable of withstanding gas pressurization and being openable/closable is provided at a molten metal supply port of the molten metal supply pipe.
  • Further, the present invention relates to (10) a vertical casting method using the vertical casting apparatus according to any one of (1) to (9), comprising the steps of casting a molten metal into the mold cavity from the gas-pressurized molten metal pouring ladle through the casting stoke; and closing the molten metal in-flow gate formed in the fixed mold by the closing means after the molten metal has been filled into the cavity; and subsequently pressurizing the molten metal in the mold cavity by a pressurizing means; (11) the vertical casting method according to (10), comprising the steps of releasing immediately the gas pressure in the gas-pressurized molten metal pouring ladle to the atmosphere, and detaching the gas-pressurized molten metal pouring ladle from the apparatus body, after closing the molten metal in-flow gate by the closing means; supplying a molten metal necessary for the next cycle into the gas-pressurized molten metal pouring ladle; and attaching again the gas-pressurized molten metal pouring ladle to the apparatus body to provide for the next casting operation; (12) the vertical casting method according to (10) or (11), wherein the gas pressure in the gas-pressurized molten metal pouring ladle is regulated to be 1 kg/cm2 or higher to perform casting at a high speed in a short period of time; and (13) the vertical casting method according to (10) to (12), wherein the casting is a thin-wall and large-size casting of a light metal alloy.
  • BRIEF DESCRIPTION OF DRAWINGS
  • [FIG. 1] It is a schematic longitudinal sectional view of a vertical casting apparatus of the present invention (at the initiation of the pouring of molten metal).
  • [FIG. 2] It is a schematic longitudinal sectional view of a vertical casting apparatus of the present invention (at the time of supply of molten metal).
  • [FIG. 3] It is a sectional view taken along the line A-A of FIG. 1.
  • [FIG. 4] It is an explanatory view showing a filling state of molten metal in a vertical casting apparatus of the present invention.
  • [FIG. 5] It is explanatory views showing states of operations in a vertical casting apparatus of the present invention, following the state shown in FIG. 4.
  • [FIG. 6] It is a schematic longitudinal sectional view of a mold at the time when a vertical casting apparatus in accordance with the present invention is applied to the production of an aluminum wheel.
  • [FIG. 7] It is a schematic longitudinal sectional view of a vertical casting apparatus in accordance with another example of the present invention.
  • EXPLANATION OF LETTERS OR NUMERALS
    • 1 fixed mold
    • 2 movable mold
    • 3 fixed platen
    • 4 movable platen
    • 5 molten metal pouring ladle (gas-pressurized molten metal pouring ladle)
    • 7, 16 molten metal
    • 8 molten metal surface
    • 8 a molten metal surface in molten metal supply pipe
    • 9 mold cavity
    • 10 circular gate
    • 11 cavity first well section
    • 12 side gate
    • 13 closing pin
    • 14 pressurizing stem
    • 15 jet flow
    • 17 pressuring stem molten metal solidification zone void
    • 18 pressuring stem gas exhaust void
    • 19 cavity second well section
    • 20 pressurizing pin
    • 21 pressurizing pin molten metal solidification zone void
    • 22 pressurizing pin outer periphery gas exhaust void
    • 23 pressurizing stem piston
    • 24 closing pin piston
    • 25 hydraulic cylinder
    • 26 a, 26 b, 26 c pressure oil inlet
    • 27 pressurizing stem seal packing
    • 28 closing pin seal packing
    • 29 pressurizing stem gas exhaust passage
    • 30 pressurizing pin piston
    • 31 pressurizing pin hydraulic cylinder
    • 32 pressure oil inlet
    • 33 pressurizing pin seal packing
    • 34 pressurizing pin gas exhaust passage
    • 35 mold seal groove
    • 36 pressurizing stem cooling water hole
    • 37 pressurizing pin cooling water hole
    • 38 molten metal pouring ladle seal packing
    • 39 stoke seal packing
    • 40 casting stoke
    • 41 pressurizing gas inlet
    • 42 molten metal supply ladle
    • 43 outer peripheral die
    • 44 molten metal supply pipe
    • 45 molten metal supply port sleeve
    • 46 molten metal supply port
    • 47 molten metal supply port lid
    • 48 molten metal supply port gas section
    • 49 gas introduction/discharge port
    • 9 a aluminum wheel hub section
    • 9 b aluminum wheel spoke section
    • 9 c aluminum wheel rim flange section
    BEST MODE OF CARRYING OUT THE INVENTION
  • The vertical casting apparatus of the present invention is not particularly limited as long as it is a vertical casting apparatus including an apparatus body having a fixed mold on the lower side and a movable mold on the upper side, which can form a mold cavity; a closing means for closing a molten metal in-flow gate formed in the fixed mold; and a pressurizing means for pressurizing molten metal in the closed mold cavity, and a casting means for supplying and filling molten metal into the mold cavity from the underside, wherein the casting means has a gas-pressurized molten metal pouring ladle that is attachable to and detachable from the apparatus body. The vertical casting apparatus in accordance with the present invention is a vertical casting apparatus that has high work efficiency, ease of maintenance, and a low cost of equipment. Further, by using the vertical casting apparatus in accordance with the present invention, castings, especially thin-wall and large-size castings, can be manufactured properly without causing shrinkage cavities and entrainment of gas at the time of solidification. Such casting is not particularly limited, while light metal alloys, especially aluminum alloys having high solidification shrinkage, are preferable. Since aluminum shrinks about 7 percent at the time of solidification, the casting apparatus and casting method in accordance with the present invention, which are capable of preventing the occurrence of shrinkage cavities, can be used advantageously especially in the case where thin-wall and large-size castings are manufactured from a molten metal comprising a light metal alloy having high solidification shrinkage, such as an aluminum alloy.
  • The gas-pressurized molten metal pouring ladle in the casting means is not particularly limited as long as it is a molten metal pouring ladle to which gas pressure can be applied, and is attachable to and detachable from the apparatus body. For the gas pressurization, it is necessary that the gas-pressurized molten metal pouring ladle has a hermetically sealed construction. For example, a hermetically sealed construction can be made by providing a lid on the gas-pressurized molten metal pouring ladle, which top is open. However, it is preferable that the hermetically sealed construction is formed by attaching the gas-pressurized molten metal pouring ladle to the apparatus body. As a configuration for forming the hermetically sealed construction by attaching the gas -pressurized molten metal pouring ladle to the apparatus body, in the case where the gas-pressurized molten metal pouring ladle has a casting stoke, the hermetically sealed construction can be formed by bringing the upper end portion of casting stoke into close contact with the apparatus body. Specifically, the hermetically sealed construction can be formed, for example, by pushing the upper surface of the stoke against the lower surface of a gate inlet of the mold. Also, in the case where the apparatus body has the casting stoke, the hermetically sealed construction can be formed by bringing the upper end portion of the gas-pressurized molten metal pouring ladle into close contact with the apparatus body. Specifically, the hermetically sealed construction can be formed, for example, by pushing the upper surface of the gas-pressurized molten metal pouring ladle against the lower surface of a fixed plate, or by pushing the upper surface of the gas-pressurized molten metal pouring ladle into a seal packing provided in a lower part of the fixed plate of fixed mold. At this time, it is preferable that the upper part of the gas-pressurized molten metal pouring ladle is smaller than the lower part thereof in order to have a shape that can be sealed easily in the apparatus body.
  • By using the gas-pressurized molten metal pouring ladle attachable to and detachable from the apparatus body in this manner, molten metal can be introduced from the upper part (open portion) of the detached (removed) gas-pressurized molten metal pouring ladle, so that molten metal can be replenished very easily. Also, since spraying work for cleaning or lubricating the in-flow gate of the apparatus body can be performed by detaching the gas-pressurized molten metal pouring ladle, maintenance can be performed very easily.
  • Also, the gas-pressurized molten metal pouring ladle may have a molten metal supply pipe (molten metal supply passage) communicating with an opening provided in a lower part of the gas-pressurized molten metal pouring ladle. In this case, a molten metal supply port of the molten metal supply pipe is provided with a molten metal supply port lid which is openable and closable, having a sealing force withstanding the gas pressurization. Herein, the lower part of the gas-pressurized molten metal pouring ladle in which an opening is provided means a portion lower than the surface of molten metal in the (filled) molten metal pouring ladle. The opening is preferably located in a portion lower than the lower end of the casting stoke so that molten metal can be poured more efficiently and/or molten metal can be dropped from the stoke more efficiently. In this case, it is not always necessary that the gas-pressurized molten metal pouring ladle is moved by being detached at the time of molten metal supply. However, in the case where molten metal is supplied while the molten metal pouring ladle is detached, the movement distance can be shortened, and thus work can be performed more efficiently.
  • The above-described gas-pressurized molten metal pouring ladle preferably has a heating means. Thereby, the generation of solidification layer is restrained, and misrun is prevented, so that the production of defective casting products can be restrained as much as possible.
  • The capacity of the gas-pressurized molten metal pouring ladle is preferably a capacity capable of containing molten metal necessary for, for example, one to three casting operations from the viewpoints of the prevention of increased apparatus size and the ease of conveyance of gas-pressurized molten metal pouring ladle. Moreover, it is more preferable that it is a capacity capable of containing molten metal necessary for one casting operation. By making the capacity capable of containing molten metal necessary for one casting operation, the quantity of molten metal in the molten metal pouring ladle at the time of casting is always constant, and it is not necessary to regulate the pressure. Therefore, the filling operation can be performed continuously more easily, and as table operation can be performed while restraining the mixing of oxides and the entrainment of gas. That is to say, in the case of the capacity for several casting operations, the liquid level is different at the time of each casting operation, so that the pressure must be adjusted delicately. However, by making the capacity to containing molten metal necessary for one casting operation, it is not necessary to make such delicate adjustment.
  • Moreover, such down sizing of the gas-pressurized molten metal pouring ladle can raise the molten metal surface and decrease the volume of gas portion, so that higher gas pressure can be achieved. Further, molten metal can be supplied into the mold cavity quantitatively, the supply rate can be increased, and the shot time lag can be shortened, so that high-quality castings and thin-wall and large-size castings can be manufactured. Further, the use of such molten metal pouring ladle can shorten the production cycle time, and the productivity can be improved.
  • Furthermore, the casting means preferably has a vacuum attraction mechanism for filling the molten metal in the gas-pressurized molten metal pouring ladle by vacuum attracting the gas in the mold cavity, in addition to the gas-pressurized molten metal pouring ladle. Thereby, molten metal can be filled into the mold cavity at a high speed, and the gas in the mold cavity can be exhausted to prevent the entrainment of gas. The vacuum attraction can be accomplished through a gas exhaust passage, described in the following.
  • The above-described mold cavity is preferably a mold cavity that can manufacture thin-wall and large-size castings. It is preferable that the mold cavity has a cavity product section and a cavity well section, and the cavity well section preferably comprises a cavity first well section located above the molten metal in-flow gate, and one or more cavity second well sections located above a portion near the end opposite to the cavity first well section of the cavity product section. Further, it is preferable that the cavity product section and the cavity first well section are linked each other via a side gate, and that the cavity first well section has a larger volume than that of the cavity second well sections.
  • The fixed mold on the lower side is formed with a linking portion between a casting stoke for supplying molten metal from the molten metal pouring ladle under the fixed mold and the cavity first molten metal well section, and the linking portion is provided with a molten metal in-flow gate. The shape of this molten metal in-flow gate is not particularly limited, but it is preferable that the molten metal in-flow gate usually has a circular shape in cross section from the viewpoint of ease of manufacturing. In this case, the inner diameter of a circular molten metal in-flow gate is preferably smaller than that of the stoke. By this configuration, the molten metal supplied from the underside can be spouted into the cavity first well section. Therefore, as described later, the oxide layer on the surface of molten metal poured into the stoke and the chill layer (solidification layer) produced by being cooled by the inner surface of stoke, which cause defective casting products, can be prevented from being mixed in the product.
  • As a closing means for closing the molten metal in-flow gate formed in the fixed mold, any means that has a mechanism capable of closing the molten metal in-flow gate can be used. For example, a closing pin disposed on the upper side of the gate capable of opening and closing the circular molten metal in-flow gate can be cited specifically. In this case, it is preferable that the diameter of the insertion portion of the closing pin inserted in the circular molten metal in-flow gate is slightly smaller than the inner diameter of the circular molten metal in-flow gate from the viewpoint of closing sealability. This closing pin is preferably held so that it is capable advancing and retreating slidably in a fluid-tight manner with respect to the movable mold. Further, as described later, in a case where a pressurizing stem is held slidably in a fluid-tight manner with respect to the movable mold, the closing pin can also be provided in the center of the pressurizing stem coaxially and so that it is slidable in a fluid-tight manner.
  • In the case where the pressurizing stem and the closing pin are disposed in the movable mold above the circular molten metal in-flow gate as described above, it is preferable that the cavity first well section is configured so that the diameter of the inlet of the circular cavity first well section formed in a state in which the pressurizing stem and the closing pin are retreated (raised) is larger than 1.4 times the diameter of the circular molten metal in-flow gate, and that the height of the ceiling of well section at the time when the pressurizing stem and the closing pin are located at the retreat upper limit is 10 mm or more higher than the height of molten metal jet flow spouting from the circular molten metal in-flow gate. In the case where the diameter of the inlet of the well section is larger than 1.4 times the diameter of the circular gate in this manner, the height “h” of molten metal jet flow can be calculated approximately from the formula h=v2/2 g, wherein “v” is passage rate of molten metal at the circular gate, and “g” is gravitational acceleration. Therefore, when the casting rate is v=2.0 m/sec, which is a high rate in the general range, the jet flow height becomes h=2.02/2 g=0.204 mm.
  • That is to say, if the ceiling height is set at 204+10=214 mm, the jet flow does not collide with the ceiling, forming a free surface, and the oxide film on the surface of molten metal is confined without flowing backward, and also the entrainment of gas caused by the collision can be prevented.
  • For example, for the pouring/filling rate of molten metal, depending on the shape of product, generally, the initial passage time in the circular gate is preferably 1.0 to 2.4 m/sec. In this case, the jet flow height from the circular gate is usually about 50 to 300 mm. In a case where the ceiling height of the cavity first well section is 10 mm or more higher than the height of molten metal jet flow, a free surface is formed, the oxide film remaining on the molten metal surface also remains, and the gas remaining in the upper part of the well section does not form a downward flow as being still enclosed. Further, the gas is exhausted by vacuum through a void on the outer periphery of the pressurizing stem, so that the gas is not entrained in the molten metal. On the other hand, if the jet flow velocity is low, the molten metal jet flow does not collide with the ceiling, and the gas entrainment is eliminated. However, the casting time becomes long, and the rate at which the molten metal flows in the cavity product section becomes low, the cooling solidification will proceed during this time, and the resistance will increase. Therefore, the flow velocity will decrease further, and the filling of molten metal into the cavity product section will be insufficient, so that even the pressure is applied, the pressure transmission will be poor and the possibility of occurrence of shrinkage cavities will increase. Thereupon, when the molten metal fills the first well section and begins to enter into the product section, it is preferable to raise the gas pressure in the molten metal pouring ladle to regulate the casting rate so that the casting rate is as high as possible. At this point of time, the first well section is filled with molten metal, so that the flow at the in-flow gate does not entrain the oxide film and gas remaining on the ceiling because the filled molten metal provides resistance.
  • In the case where molten metal is supplied by a high-pressure gas, the casting rate is high, and the cooling solidification of molten metal in the cavity is little, and the molten metal can also be filled into a limited space of the cavity product section having high resistance, by the driving force. Even if the filling is insufficient, there is no problem because the volume thereof is small and therefore molten metal can be replenished and filled by sufficient pressurization using the pressuring stem etc.
  • By forming the cavity first well section in the cavity as described above, in the case where the closing pin and the pressurizing stem are advanced (lowered), the oxide film and gas entrainment layer existing in the uppermost part of well stay at the upper end of the cavity first well section without being pushed out, and do not enter into the cavity product section. Further, in the case where casting is performed by using the molten metal pouring ladle, the molten metal pouring port of stoke lies under the molten metal surface in the molten metal pouring ladle, and the oxide film produced on the molten metal surface floats on the molten metal surface, so that the oxide film does not enter into the stoke. A small amount of oxide film on the molten metal surface in the stoke lies at the tip end of jet flow, all plunging into the cavity first well section, and does not flow out toward the cavity product section through the side gate. Therefore, the oxide film is no more mixed in the casting product, and thereby defectives and varied strengths of casting product are eliminated.
  • Next, by pressurizing the molten metal filled in the closed mold cavity, a casting without shrinkage cavities caused at the time of solidification and moreover without gas entrainment caused by jet flow can be manufactured. As a pressurizing means for pressurizing the molten metal in the closed mold cavity, the pressurizing stem which is slidably provided on the movable mold in the upper side of the cavity first well section, with a closing pin slidably provided in the center thereof, and a pressurizing pin which is disposed slidably on the movable mold in the upper part the cavity second well section located distant from the cavity first well section via the cavity product section can be cited specifically. The pressurizing pin is preferably provided in plural numbers. Moreover, the diameter of the pressurizing pin is preferably ⅔ to 1 times the depth of the cavity second well section. Further, the pressurizing stem and the pressurizing pins are preferably used together. By pressurizing the molten metal by the pressurizing stem and the pressurizing pins located at distant positions to shorten the distance of pressure transmission to the molten metal in the cavity, and to make the pressure transmission uniform and sufficient, a casting in which shrinkage cavities do not occur at the time of solidification can be manufactured with a low pressure. Further, by arranging the pressuring stem and the pressurizing pins at suitable positions according to the shape of product, the distance of pressure transmission to the molten metal in the cavity product section is shortened further, and the pressure transmission is made more uniform and sufficient, by which the occurrence of shrinkage cavities can be prevented with a lower pressure.
  • In a conventional casting apparatus, generally, in order to manufacture a casting in which shrinkage cavities do not occur at the time of solidification, the pressurization rate of molten metal is increased by a pressurizing means, and pressurization is accomplished rapidly. In this case, pressure transmission is too fast and increases the mold opening force and produces burrs, so that the mold clamping force must also be increased. However, if the pressurization rate is decreased contrarily, the pressurization does not follow the solidification shrinkage of molten metal, and hence shrinkage cavities occur. On the other hand, according to the present invention, uniform and sufficient pressure transmission can be accomplished even with a small mold clamping force enough to prevent burrs. Therefore, a casting in which shrinkage cavities do not occur at the time of solidification can be manufactured with a low pressure. Thus, in the present invention, by regulating the pressurization rate, for example, by carrying out program control such that the advance rates of the pressurizing stem and the pressurizing pins at the time of pressurization are made to be a rate suitable for the solidification shrinkage rate of molten metal in the cavity product section, the occurrence of shrinkage cavities can be prevented by a press device with a small mold clamping force while burrs are prevented. For example, by controlling the pressurizing force and the pressurization rate for the molten metal during solidification shrinkage, in which Pascal's law does not act, according to the solidification rate in the range in which no burrs are produced, a casting having a fine structure can be manufactured without the mixing of oxide film and solidification layer and the entrainment of gas by using an apparatus with a small mold clamping force that is ⅓ to ⅕ that of the conventional high pressure process.
  • Further, in the case of vertical casting method such as squeeze casting, if the pressurization using an accurad pin (center pin) is accomplished rapidly, a casting plunger is pushed down. Therefore, after little time has elapsed, namely, after the solidification of gate portion has proceeded and the pressure transmission to the casting plunger has become small, the pressurization is accomplished. For this reason, the solidification of molten metal in the cavity also proceeds during this time, and a high pressure is required for replenishing molten metal. In some cases, the timing does not coincide, and shrinkage cavities sometimes occur. In contrast, in the present invention, since a closing means for the molten metal in-flow gate is provided, the pressurization is accomplished from a stage at which solidification proceeds yet less immediately after the closure of gate, by which molten metal can be replenished and filled. Furthermore, since the pressurization is accomplished by the pressurizing stem and the pressurizing pins disposed at predetermined positions, the pressure transmission distance is short, thus uniform and sufficient replenishment and filling can be performed with a low pressure. Since the applied pressure can be made low in this manner, only a small mold clamping force of mold is needed, so that the costs of mold clamping device and mold can be kept low. Further, the casting rate and the pressurization starting rate are higher than those of squeeze casting, so the thin-wall casting can be performed. Moreover, by the maintenance of contact between molten metal and mold surface, proper heat transmission is kept, the cooling time is made short, the crystals are made small, the quality is improved, the production cycle time is made short, and the productivity is improved.
  • Additionally, in the vertical casting apparatus in accordance with the present invention, the gas exhaust passage capable of exhausting the gas existing in the cavity when molten metal is filled into the mold cavity and a molten metal solidification zone void communicating with the gas exhaust passage are preferably provided. The gas exhaust passage is preferably constituted of a gas exhaust hole penetrating the movable mold and a gas exhaust void. The molten metal solidification zone void is preferably provided near the gas exhaust passage, and in particular, is preferably close to the pressuring means. The molten metal solidification zone void may be any void as long it can solidify molten metal in the void serving as a molten metal solidification zone, for example, after the gas in the cavity has been exhausted through the gas exhaust passage, and can hermetically close the cavity easily. By merely providing such a molten metal solidification zone void, the cavity can be hermetically closed easily without disposing an air vent valve, a filter, etc. and without using complicated selector valves and valves. Further, when the casting apparatus is operated, a complicated operation such as pressure regulation is not needed, and further failure etc. do not occur, so that it can be said that the casting apparatus in accordance with the present invention is very practical. Furthermore, the area of the docking contact surface between the upper surface of stoke and the lower surface of mold and between the upper surface of molten metal pouring ladle and the lower surface of fixed plate is small, so that pressure sealing for preventing pressurizing gas from leaking at the time of pouring can be performed easily.
  • Specifically, as the molten metal solidification zone void, a molten metal solidification zone void linked with the gas exhaust passage via the gas exhaust void formed between the outer peripheral surface of the pressurizing stem and/or pressurizing pin and the inner peripheral surface of the movable mold can be cited as an example. As a molten metal solidification zone void, avoid serving as a molten metal solidification zone, which is provided coaxially with the pressurizing stem and/or pressurizing pin and has an inner diameter being 1 to 5 mm larger than the diameter of the pressurizing stem and/or pressurizing pin and a depth (length) of about 10 to 40 mm can be cited specifically. By making the outside diameter of each well section slightly larger than the external shapes of the pressurizing stem and pressurizing pin in this manner, the solidification layer generated on the outer peripheral wall of each well section is prevented from being pushed in the product by the pressurizing stem/pressurizing pin, and the pressurization resistance of the pressurizing stem and pressurizing pin can be decreased. If the molten metal solidification zone void is designed so as to have a size suitable for the temperature and the casting rate of molten metal, when molten metal is filled, the molten metal is cooled and solidified in this void portion, and therefore does not intrude into the gas exhaust void.
  • Further, the gas exhaust void preferably has a construction and size such that the molten metal does not flow in. For example, as the gas exhaust void, a gas exhaust void which is provided coaxially with the pressurizing stem and/or pressurizing pin and has an inner diameter which is about 0.4 to 1 mm larger than the diameter of the pressurizing stem and/or pressurizing pin can be cited specifically. When the mold cavity is made in vacuum, in order to prevent the intrusion of air, the gas exhaust passage consisting of the gas exhaust hole and the gas exhaust void is not provided on the parting surface, and if possible, the seal packing is installed, or a gas exhaust groove connected to a gas exhaust port is provided, by which the intrusion of air from the outside of mold into the mold cavity is prevented.
  • If the casting start rate of molten metal in the case where the gas-pressurized molten metal pouring ladle and the vacuum attraction mechanism are used together has an optimum value of 1.0 to 2.4 m/sec, the air resistance in a two-stage void portion such as the molten metal solidification zone void and the gas exhaust void provided close to the outer peripheries of the pressurizing stem and the pressurizing stem increases. However, by appropriately selecting the number and arrangement of the pressurizing pins, the provision of the molten metal solidification zone void and the gas exhaust void can also achieve the object. Specifically, a person skilled in the art can easily design a construction in which molten metal is cooled and solidified in the molten metal solidification zone void of two-stage void, and does not intrude into the gas exhaust void narrower than the molten metal solidification zone void. Further, in order to surely cool and solidify molten metal in the molten metal solidification zone void, the configuration can be made such that a highly heat conductive material such as beryllium copper is used as the pressurizing stem and the pressurizing pin, and the interior thereof can be water cooled.
  • For the above-described vertical casting apparatus in accordance with the present invention, the constructions of the gas exhaust systems around the pressurizing stem and the pressurizing pin are simple, so that the trouble occurring during operation decreases. Further, by filling molten metal into the mold cavity at a high speed by the combined use of the gas pressurization in the closed molten metal pouring ladle with a small volume and the vacuum attraction mechanism, a large-size and thin-wall product can be cast, and also since the molten metal flows into the narrow molten metal solidification zone void, it solidifies and stops there, and does not intrude into a gas exhaust void passage. Furthermore, since the depth of the cavity first well section is increased, the stroke of the pressurizing stem can be prolonged, so that molten metal of a volume enough for filling and solidification shrinkage in the cavity product section is supplied under pressure by the pressurizing stem. Thereby, a casting having a fine structure and high strength can be obtained additionally by high cooling rate and decreased crystal size. Additionally, when the circular gate is closed by the closing pin having a diameter slightly smaller than the inside diameter of the circular gate, and the gas pressure in the molten metal pouring ladle is released to the atmosphere and lowered rapidly, the molten metal in the stoke is returned rapidly to the molten metal pouring ladle to prevent a trouble caused by solidification sticking in the stoke.
  • Further, when the mold is opened, by taking the molten metal pouring ladle out of the apparatus, spraying work for cleaning the in-flow gate and for cooling and lubricating the mold surface can be performed easily and safely.
  • Further, in the casting apparatus in accordance with the present invention, which is provided with the gas-pressurized molten metal pouring ladle and the vacuum attraction mechanism, when molten metal is filled into the mold cavity, the gas in the cavity is exhausted almost completely, and at the same time, after the filling, the circular gate is closed, and necessary and sufficient pressurization can be accomplished with a low pressure. Therefore, the mold clamping force can be ⅓ to ⅕ of the mold clamping force in the conventional high-pressure process. Thereby, the cost of casting apparatus is reduced significantly. Moreover, since the productivity is high, the cost of casting can be reduced significantly. Since molten metal is directly supplied from under the molten metal surface in the molten metal pouring ladle, no oxide film is mixed in. Since the passage is short, the occurrence of solidification layer is less. By providing the cavity first well section having a suitable height at the outlet of the circular gate, the jet flow does not collide with the ceiling, the entrainment of gas is eliminated, and the oxide film and solidification layer remaining in small amounts can be allowed to stay in the cavity first well section. As a result, a casting having a fine structure and without impurities can be obtained. Further, since the molten metal pouring ladle is small and the gas pressure can be increased, a high casting rate can be secured, and thin-wall casting can be performed. By the movement of molten metal pouring ladle, the replenishment of molten metal is made easy. Therefore, not only the cost of equipment is reduced, but also the arrangement and operation of apparatus are easy.
  • Further, the vertical casting method in accordance with the present invention is not particularly limited as long as it is a casting method using the above-described vertical casting apparatus, comprising the steps of casting a molten metal into the mold cavity from the gas-pressurized molten metal pouring ladle through the casting stoke; and after the molten metal has been filled into the cavity, closing the molten metal in-flow gate formed in the fixed mold by the closing means; and subsequently pressurizing the molten metal in the mold cavity by a pressurizing means. The upper end of the gas-pressurized molten metal pouring ladle having received a molten metal, for example, for one casting operation or more is pushed into the seal packing provided in the lower part of the fixed plate to provide a seal, a gas pressure of preferably 1 kg/cm2or higher is applied to the molten metal pouring ladle, and the molten metal is poured into the mold cavity through the casting stoke by pressurizing the molten metal surface in the ladle. At this time, in the case where the gas-pressurized molten metal pouring ladle is provided with the molten metal supply pipe, the same gas pressure may be applied from above the molten metal surface of the supply pipe at the same time. Subsequently, after the cavity has been filled with the molten metal, the molten metal in-flow gate provided in the fixed mold is closed by the closing means, and then the molten metal in the mold cavity is pressurized by the pressurizing means (pressurizing pin), by which a casting without shrinkage cavities at the time of solidification and without the entrainment of gas, preferably a thin-wall and large-size casting of light metal alloy, is manufactured.
  • The filling of molten metal into the mold cavity is started at the retreat position of the pressurizing pin, the flow velocity of molten metal is reduced in the cavity second well section, and the molten metal in the molten metal solidification zone void is cooled and solidified, by exhausting gas in the mold cavity through a gas exhaust void. After the molten metal has been filled into the mold cavity, the molten metal in the well section is preferably pressurized by advancing one or a plurality of pressurizing pins. Further, it is preferable by venting vacuum gas from the gas exhaust void adjacent to the plurality of molten metal solidification zones, to reduce the entrainment of gas, and that by pressurizing the molten metal by the pressurizing stem and the plurality of pressurizing pins, to shorten the pressure transmission distance. By this replenishment and filling, the contact of molten metal with the mold surface is maintained, proper heat transmission is kept, the cooling rate is made high, the crystals are prevented from becoming coarse, and a structure with small crystals is formed. After the replenishment and filling of molten metal corresponding to solidification have been finished at the time of solidification, the movable mold is raised by the movable platen after short cooling time has elapsed, and the product material raised together with the movable mold is pushed out of the movable mold by the pressurizing stem and pressurizing pin and knockout pin. Further, the product material is drawn out of the pressurizing stem and the pressurizing pin by pushing it out by the knockout pin to remove the product material. Thereby, a casting product with a fine structure can be obtained without causing shrinkage cavities and entrainment of gas. Furthermore, since the above-described operations are repeated in each cycle, the molten metal solidified in the molten metal solidification zone void is removed each time, so that the gas exhaust passage is not clogged. Moreover, in the case where the stoke upper surface of movable gas-pressurized molten metal pouring ladle and the mold lower surface are pushed against each other to provide a seal, the seal can be provided easily because the contact area is small.
  • The work can be performed efficiently by performing casting using a plurality of gas-pressurized molten metal pouring ladles. However, it is preferable that after the molten metal in-flow gate has been closed by the closing means, the gas pressure in the gas-pressurized molten metal pouring ladle is immediately released to the atmosphere and is detached from the apparatus body, so that a molten metal necessary for the next cycle is supplied into the ladle, and the ladle is again attached to the apparatus body to be provided for the next casting operation. Thereby, casting can be performed very efficiently by using one gas-pressurized molten metal pouring ladle. Moreover, in the case where the gas-pressurized molten metal pouring ladle provided with the molten metal supply pipe is used, the gas in the molten metal pouring ladle is released to the atmosphere, and the molten metal for the next cycle is supplied by opening the lid of the molten metal supply pipe with the molten metal pouring ladle being detached or not detached from the apparatus body. By designing the apparatus so that after the molten metal in-flow gate has been closed by the closing means, the gas in the molten metal pouring ladle is released to the atmosphere and the gas at the molten metal supply port of the molten metal supply pipe is attracted to raise the molten metal surface in the molten metal supply pipe and to lower the molten metal surface in the molten metal pouring ladle to the lower end of the stoke, the molten metal in the stoke can be dropped more rapidly, and thereby the work can be performed more efficiently.
  • Hereunder, the present invention is explained in detail with reference to examples. The technical scope of the present invention is not limited to these illustrated examples.
  • FIG. 1 is a schematic longitudinal sectional view of a vertical casting apparatus of the present invention (at the initiation of the pouring of molten metal). FIG. 2 is a schematic longitudinal sectional view of the vertical casting apparatus of the present invention (at the time of supply of molten metal). FIG. 3 is a sectional view taken along the line A-A of FIG. 1. FIG. 4 is an explanatory view showing a bottom pouring state of molten metal. FIG. 5 is explanatory views showing states of operations following the state shown in FIG. 4. In FIGS. 1 to 5, symbol 1 denotes a fixed mold, 2 denotes a movable mold, 9 denotes a cavity product section, 10 denotes a circular gate, 11 denotes a cavity first well section, 13 denotes a closing pin, 14 denotes a pressurizing stem, 17 denotes a molten metal solidification zone void (pressuring stem outer periphery), 19 denotes a cavity second well section, 20 denotes a pressurizing pin, 21 denotes a molten metal solidification zone void (pressuring pin outer periphery), 29 denotes a pressurizing stem gas exhaust passage, 34 denotes a pressurizing pin gas exhaust passage, 40 denotes a casting stoke, and 41 denotes a pressurizing gas inlet.
  • The casting apparatus in accordance with the present invention shown in FIGS. 1 to 5 comprises: the fixed mold 1 attached to a horizontal fixed platen 3 in the lower part of the casting apparatus, the movable mold 2 attached to a horizontal movable platen 4 in the upper part of the casting apparatus, which can move vertically to open and close a mold, and a gas-pressurized molten metal pouring ladle 6 located under the fixed platen 3. By the opening/closing of the fixed mold 1 and the movable mold 2, a mold cavity provided with a side gate for connecting the cavity product section 9 to the cavity first well section 11, as well as the cavity product section 9, the cavity first well section 11, and the cavity second well section 19, is formed. The mold is mounted as follows: a mold set consisting of the fixed mold 1 fitted with the casting stoke 40 and the movable mold 2 is inserted in a state in which the movable platen 4 of a mold clamping press (not shown) is pulled up, being placed on the fixed platen 3, and the movable platen 4 is lowered until it comes into contact with the upper surface of the movable mold 2, by which the fixed mold 1 is attached to the fixed platen 3, and the movable mold 2 is attached to the movable platen 4. The gas-pressurized molten metal pouring ladle 6 is hermetically sealed by pushing the upper end thereof into a seal packing 38 provided in a lower part of the fixed platen 3.
  • The fixed mold 1 is provided with the casting stoke 40 extending downward in a lower part thereof, and is also provided with the circular gate 10 for spouting out molten metal from the casting stoke 40. When a pressurizing gas is fed through the pressurizing gas inlet 41, and the interior of the cavity is depressurized, a molten metal 7 in the molten metal pouring ladle 6 is pushed up into the casting stoke 40, and is filled in the cavity product section 9 through the circular gate 10 of the fixed mold 1. The pouring rate at this time is controlled by regulating the gas pressure in the molten metal pouring ladle 6 and the degree of vacuum in the cavity so that the passage rate of molten metal through the circular gate 10 is high and the molten metal spouts upward as a jet flow.
  • Further, as shown in FIG. 4, an inlet diameter d1 of the cavity first well section 11 is 1.4 times or more the diameter of the circular gate 10, and an external shape ds of the pressurizing stem 14 is slightly smaller than the inlet diameter d1 of the well section 11. Further, the ceiling height of the cavity first well section 11 is higher than a height h at which a molten metal jet flow 15 passing through the circular gate 10 arrives, the height h being calculated by the formula h=v2/2 g (wherein h denotes a jet flow arrival height, v denotes a circular gate passage rate, and g denotes the gravitational acceleration) Therefore, at the early stage of filling, the jet flow does not arrive at the ceiling of the cavity first well section 11, the free surface of the molten metal jet flow 15 being formed in the upper part thereof, and no downward flow exists in this portion. Therefore, the oxide film remaining slightly on the surface of molten metal keeps a fixed state, and the gas remaining in the upper part of the well section 11 is not entrained in a molten metal 16. As a result, small amounts of oxide film and gas entrainment layer existing at the tip end of the molten metal jet flow 15 passing through the circular gate 10 remain in the ceiling. After the well section 11 has been filled with molten metal, even if the pouring rate is increased, the flow does not arrive at the ceiling, so that only a clean molten metal without oxide film and gas entrainment passes through the side gate 12 and is filled into the cavity product section 9.
  • Further, the movable mold 2 above the circular gate 10 is provided with a hydraulic cylinder 25 via a seal packing 27 in a fluid-tight manner. The hydraulic cylinder 25 houses a pressurizing stem piston 23 via the seal packing 27, the pressurizing stem piston 23 being capable of advancing and retreating the pressurizing stem 14 into and from the cavity first well section 11 by means of oil pressure. The pressurizing stem piston 23 houses a closing piston 24 coaxially with the pressurizing stem piston 23, the closing piston 24 being capable of advancing and retreating the closing pin 13 capable of closing the circular gate 10. After the filling of molten metal into the mold cavity has been finished, the closing pin 13 is advanced by the piston 24 to close the circular gate. Subsequently, the pressurizing stem 14 is immediately advanced by the piston 23, by which molten metal corresponding to the volume of unfilled void in the cavity product section 9 and the solidification shrinkage volume is pressurizedly replenished from the cavity first well section 11. At this time, since the stroke of the pressurizing stem 14 is large, a sufficient amount of molten metal can be replenished and pressurizedly filled.
  • When a pressure is applied by the pressurizing stem 14 as well, the oxide film slightly produced on the molten metal surface in the stoke, the solidification layer of molten metal surface formed by cooling at the inlet of the circular gate 10, and the gas entrainment layer generated by jet flow are collected in the uppermost portion of the well section 11 by the gate jet flow 15, and remain in an upper part of the cavity first well section 11 without being pushed out by the pressurizing stem 14, without flowing into the cavity product section 9. As a result, all of the casting defectives caused by these are eliminated. Further, on the outside of the pressurizing stem 14, a two-stage void consisting of a gas exhaust void 18 linked with the gas exhaust hole 29 and the molten metal solidification zone void 17 is provided. The molten metal solidification zone void 17 and the gas exhaust void 18 are secured each time casting is performed because as shown in FIG. 5(d), the solidification layer formed by the molten metal solidification zone void 17 and the gas exhaust void 18 is taken out together with the product material.
  • Further, as shown in FIGS. 1 and 2, one or more small cavity second well sections 19 are formed above the end portion of the cavity product section 9. On the movable mold above the well section 19, a hydraulic cylinder 31 is provided, and the hydraulic cylinder houses a pressurizing pin piston 30 capable of advancing and retreating the pressurizing pin 20 to and from the cavity second well section 19 by means of oil pressure The aforementioned one or two or more pressurizing pins 20 each have an axis of a direction parallel with the mold opening/closing direction and perpendicular to the mold parting surface, and are provided on the movable mold 2 via a seal packing 33 in a fluid-tight manner. After the interior of the cavity product section 9 has been replenished and filled with molten metal by the pressurizing stem 14, the pressurizing pins 20 are pushed out, and thereby the molten metal in the cavity product section 9 is pressurized via the cavity second well sections 19. Further, the outside diameter of the pressurizing pin 20 is slightly smaller than the diameter of the inlet of the cavity second well section 19. Since the pressurizing pins 20 slide each time, the solidification layer formed by the molten metal solidification zone void 21 is pushed out by a knockout pin, not shown, in a state of adhering to the product material, so that no gas passage hole remains, by which the gas exhaust passage is secured each time.
  • Next, the operation of the above-described vertical casting apparatus will be explained. After the mold clamping has been finished, the molten metal 16 in the molten metal pouring ladle 6 is pushed up into the cavity first well section 11 by the pressure of pressurizing gas fed into the gas-pressurized molten metal pouring ladle 6 and the vacuum attraction force into the cavity. The molten metal 16 rises in the casting stoke 40, passing through the circular gate 10 of the fixed mold 1 and spouting out (FIG. 4), and then is filled into the cavity product section 9. Generally, since flow resistance exists in the cavity product section 9, the cavity first well section 11 located above the circular gate 10 is filled with molten metal (FIG. 5 a) before the molten metal reaches the cavity second well section 19 under the pressurizing pin. When the molten metal enters into the molten metal solidification zone void 17 of two-stage void, the cooling rate is high because the passage is narrow, the heat capacity of molten metal is low, and contrarily the cooling area is large, so that the solidification proceeds, and the flowability decreases. Therefore, the tip end of molten metal stops at an intermediate position of the molten metal solidification zone void 17 and solidifies, not intruding into the gas exhaust void 18.
  • When the flow of molten metal in the cavity stops, this operation is detected as a signal of filling termination, and thus the closing pin 13 is immediately advanced and inserted into the circular gate 10 to close the circular gate 10 (FIG. 5b). After the circular gate 10 has been closed in this manner so that the molten metal in the cavity product section 9 and the cavity first well section 11 does not flow backward in the stoke, the pressurizing stem 14 is immediately advanced for pressurization, by which the semi-solidified molten metal in the cavity first well section 11 is replenished and filled into the cavity product section 9 (FIG. 5 c). When the filling is finished and the cooling is started, solidification shrinkage of the molten metal 16 occurs. Therefore, the pressurizing stem 14 is advanced by applying a high pressure to perform replenishment according to the solidification shrinkage volume. At this time, the contact between the molten metal and the mold surface is maintained, the cooling rate is high, and the crystals are small. Also, when the circular gate 10 is closed by the closing pin 13, even if the contact between the closing pin 13 and the circular gate 10 is incomplete, the molten metal existing in the small void is cooled and solidified rapidly, so that even if the cavity first well section is pressurized, the molten metal does not flow backward from the circular gate 10 into the molten metal pouring ladle 6 through the casting stoke 40. Therefore, as shown in FIG. 2, after the circular gate 10 has been closed by the closing pin 13, the gas pressure in the molten metal pouring ladle is immediately released to the atmosphere, and the molten metal pouring ladle 6 is lowered to a position lower than the lower end of the stoke by using a vertical moving device (not shown) in a state in which the gas pressure lowers to a non-dangerous pressure, by which the molten metal remaining in the casting stoke 40 is dropped into the molten metal pouring ladle 6. The lowered molten metal pouring ladle 6 is moved to a position outside the casting machine by a horizontal moving device (not shown). After molten metal necessary for the next casting operation has been supplied into molten metal pouring ladle 6 by a molten metal supply ladle 42, the molten metal pouring ladle 6 is attached again to the apparatus body in preparation for the next casting operation.
  • In the case where molten metal is replenished and filled by using the pressurizing stem 14, the pressurizing stem 14 can be advanced in a state in which the temperature of molten metal in the mold cavity is high, the pressurization distance is short, the pressure transmission resistance is significantly low, only a small force is needed for the pressurizing cylinder of the pressurizing stem 14, and the oil pressure in the hydraulic cylinder is low as compared with the conventional die casting process. After the molten metal has been replenished and filled into the cavity product section 9 and the cavity second well section 19 by the replenishment and filling performed by the advance of the pressurizing stem 14, the pressurizing pin 20 is advanced. The pressurization using the pressurizing pin 20 increases the flow resistance and thus raises the oil pressure at the same time that the filling using the pressurizing stem 14 is finished. Therefore, the advance of the pressurizing pin 20 is started by detecting the increased oil pressure. When the molten metal is replenished according to the solidification shrinkage volume by means of the advance of the pressurizing stem 14, since it is difficult for the pressure to be transmitted to the end portion on the opposite side of the cavity product section 9, the pressurizing pin 20 around the end portion is operated to apply pressure, by which a product having a fine structure without shrinkage cavities caused by solidification shrinkage as a whole can be obtained. After the cooling and solidification of molten metal in the cavity product section 9 have been finished, the mold is opened. The product material raised by the movable mold 2 is pushed out by the pressurizing pins and the knockout pin and then can be taken out (FIG. 5 d).
  • FIG. 6 shows a case where the vertical casting apparatus in accordance with the present invention is applied to the production of an aluminum wheel. The molten metal passing through the gate 10 enters into a hub section 9 a of product aluminum wheel, which corresponds to the cavity well section 11 in Example 1, passing through a spoke section 9 b of aluminum wheel, which corresponds to the side gate 12, and enters into a circumferential rim flange section 9 c. At several places on the circumference at the upper end of the rim flange 9 c, the cavity second well sections 19 are provided to perform venting and pressurization. Other operations are the same as those of Example 1, and a high-quality aluminum wheel can be cast. Further, according to this method, the cavity first well section 11 and the side gate 12 of Example 1 are included in a product 9 (aluminum wheel), and excess molten metal is little. Further, the hole formed by the closing pin serves as an axis hole of the aluminum wheel. The casting weight of the cavity first well section 11, namely, the hub section 9 a is reduced, the cooling solidification rate being increased, and thus the cycle time is shortened, by which the productivity of casting is enhanced, and also the axis hole working time in machining is shortened. The fast cooling rate reduces the sizes of crystals, so that the surface can be beautiful, which is important for the design of aluminum wheel.
  • Also, FIG. 7 shows another example of the vertical casting apparatus in accordance with the present invention. As shown in FIG. 7, in the vertical casting apparatus of this example, the gas-pressurized molten metal pouring ladle 7 is provided with a molten metal supply pipe 44 linked with an opening provided in a lower part of the gas-pressurized molten metal pouring ladle 7, and a molten metal supply port 46 of the molten metal supply pipe 44 is provided with a molten metal supply port lid 47 capable of being opened and closed, having a sealing force withstanding the gas pressurization. In a molten metal supply port sleeve 45 provided in the upper part of the molten metal supply pipe 44 in the vertical casting apparatus of this type, a gas introduction/discharge port 49 is provided. At the time of gas pressurization, pressurizing gas is supplied from the pressurizing gas inlet 41 above the gas-pressurized molten metal pouring ladle 7, and also the same pressurizing gas is supplied from the gas introduction/discharge port 49, by which molten metal can be supplied and filled more efficiently. After the molten metal in-flow gate 10 has been closed by a closing means, the gas pressure in the gas-pressurized molten metal pouring ladle 7 is immediately released to the atmosphere, and also the gas in a molten metal supply port gas section 48 of the molten metal supply pipe 44 is vacuum attracted through the gas introduction/discharge port 49. Thereby, a molten metal surface 8a in the molten metal supply pipe 44 is raised, and a molten metal surface 8 in the molten metal pouring ladle 7 is lowered to the lower end of the stoke 40, by which the molten metal in the stoke 40 is dropped more rapidly.
  • INDUSTRIAL APPLICABILITY
  • According to the present invention, it is possible to provide a vertical casting apparatus capable of easily manufacturing castings without causing shrinkage cavities and entrainment of gas by filling molten metal into a mold cavity at a high speed and effectively pressurizing the molten metal in the closed cavity, which has high work efficiency, ease of maintenance, and a low cost of equipment and a vertical casting method using the vertical casting apparatus.

Claims (13)

1. A vertical casting apparatus comprising an apparatus body having a fixed mold on a lower side and a movable mold on an upper side, which can form a mold cavity, a closing means for closing a molten metal in-flow gate formed in the fixed mold, and a pressurizing means for pressurizing a molten metal in the closed mold cavity, and a casting means for supplying and filling the molten metal into the mold cavity from underside, wherein the casting means has a gas-pressurized molten metal pouring ladle attachable to and detachable from the apparatus body.
2. The vertical casting apparatus according to claim 1, wherein a hermetically sealed construction is formed by attaching the gas-pressurized molten metal pouring ladle to the apparatus body.
3. The vertical casting apparatus according to claim 1 or 2, wherein the gas-pressurized molten metal pouring ladle is provided with a casting stoke, and the hermetically sealed construction is formed by bringing an upper end portion of the casting stoke into close contact with the apparatus body.
4. The vertical casting apparatus according to claim 1 or 2, wherein the apparatus body is provided with a casting stoke, and the hermetically sealed construction is formed by bringing an upper end portion of the gas-pressurized molten metal pouring ladle is brought into close contact with the apparatus body.
5. The vertical casting apparatus according to any one of claims 1 to 4, wherein a content of the gas-pressurized molten metal pouring ladle is a capacity capable of containing a molten metal necessary for one casting operation.
6. The vertical casting apparatus according to any one of claims 1 to 5, wherein the gas-pressurized molten metal pouring ladle has a heating means.
7. The vertical casting apparatus according to any one of claims 1 to 6, wherein the casting means has a vacuum attraction mechanism for vacuum attracting a gas in the mold cavity to fill a molten metal in the gas-pressurized molten metal pouring ladle by vacuum attraction.
8. The vertical casting apparatus according to any one of claims 1 to 7, wherein the mold cavity has a gas exhaust passage, and a molten metal solidification zone void linked with the gas exhaust passage is provided in a vicinity of the gas exhaust passage.
9. The die-cast casting apparatus according to any one of claims 1 to 8, wherein the gas-pressurized molten metal pouring ladle has a molten metal supply pipe linked with an opening provided in a lower part thereof, and an open- and closable molten metal supply port lid which has a sealing force capable of withstanding gas pressurization is provided at a molten metal supply port of the molten metal supply pipe.
10. A vertical casting method using the vertical casting apparatus according to any one of claims 1 to 9, comprising the steps of casting a molten metal into the mold cavity from the gas-pressurized molten metal pouring ladle through the casting stoke; and closing the molten metal in-flow gate formed in the fixed mold by the closing means after the molten metal has been filled into the cavity; and subsequently pressurizing the molten metal in the mold cavity by a pressurizing means.
11. The vertical casting method according to claim 10, comprising the steps of releasing immediately the gas pressure in the gas-pressurized molten metal pouring ladle to the atmosphere, and detaching the gas-pressurized molten metal pouring ladle from the apparatus body, after closing the molten metal in-flow gate by the closing means; supplying a molten metal necessary for the next cycle into the gas-pressurized molten metal pouring ladle; and attaching again the gas-pressurized molten metal pouring ladle to the apparatus body to provide for the next casting operation.
12. The vertical casting method according to claim 10 or 11, wherein the gas pressure in the gas-pressurized molten metal pouring ladle is regulated to 1 kg/cm2 or higher to perform casting at a high speed in a short period of time.
13. The vertical casting method according to claims 10 to 12, wherein the casting is a thin-wall and large-size casting of a light metal alloy.
US11/569,149 2004-05-18 2005-05-16 Vertical Casting Apparatus and Vertical Casting Method Abandoned US20070215308A1 (en)

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JP4054051B2 (en) 2008-02-27

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