JP2011016139A - Casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cast a casting wherein the temperature of a die is rapidly raised/dropped, the casting preparation and the casting cycle can be shortened, any so-called shrinkage cavity or shrinkage looseness easy to be formed during the solidification of the molten metal is not formed, and the surface of the castings is excellent.SOLUTION: A casting apparatus is constituted so that a molten metal is filled in a die 4 from a molten metal tank via a stoke 8, and then the molten metal is solidified in the die 4 to form the casting, wherein the die 4 is formed of isotropic graphite. Hard plating or the like such as Cr plating and chemical Ni plating is applied to at least an inner surface of a cavity 10 of the die 4. Further a cooling block 17 to be water-cooled is pressed against an upper die 6, and a heater 18 for independently heating the upper die 6 and the lower die 5, is provided individually on an upper die and a lower die respectively. The temperature gradient is formed thereby, in which the temperature is higher in the order of a sprue 9, the lower die 5 and the upper die 6, and the molten metal in the cavity is subjected to the directional solidification.

Description

  The present invention relates to a casting apparatus that fills a mold with molten metal from a molten metal tank in which the metal is stored in a molten state, and then solidifies the molten metal in the mold to form a casting, and in particular, the mold is filled. The present invention relates to a casting apparatus in which so-called shrinkage cavities and loosening caused by partial condensation of molten metal during cooling and hardening of the molten metal are difficult to occur.

  There are a low pressure casting method, a differential pressure casting method, a reduced pressure casting method, and the like as a method of casting by filling a molten metal into a cavity using a pressure difference between a molten metal and a casting-shaped cavity. Among these, the low-pressure casting method applies a relatively low pressure by a gas such as an inert gas or carbon dioxide to a closed furnace containing molten metal, and this pressure pushes the molten metal in the closed furnace upward through stalk. This is a method of manufacturing a casting by filling molten metal into a mold placed above a closed furnace. This low-pressure casting method is widely used for producing cast products such as aluminum alloys used for vehicle members and the like.

  FIG. 5 is a cross-sectional view showing a conventional low-pressure casting apparatus. A supply source (not shown) of a gas such as an inert gas or carbon dioxide is connected to a gas inlet 20 provided at the top of the hermetically sealed hermetic furnace 1, and the gas is pumped into the hermetic furnace 1. A crucible 2, which is a heat-resistant graphite container having an upper surface opened, is accommodated in the closed furnace 1, and a heater 3 is disposed along the outer wall of the crucible 2. The lower end of the stalk 8 attached to the lid of the closed furnace 1 is immersed in the center of the crucible 2. A mold 4 including a lower mold 5 and an upper mold 6 is disposed on the closed furnace 1. Concave portions are respectively formed on the mating surfaces of the lower die 5 and the upper die 6, and when the lower die 5 and the upper die 6 are overlapped, a casting-shaped cavity 10 is formed by the concave portions. Is done. A core 7 is accommodated in the cavity 10 as necessary. The upper end of the stalk 8 is connected to a gate 9 that leads to a cavity 10 provided at the bottom of the mold 4.

  In such a casting apparatus, an inert gas is injected into the closed furnace 1 from the gas injection port 20. With this gas pressure, the molten metal surface in the crucible 2 is pressurized and the molten metal is pushed up and filled into the mold cavity 10 via the stalk 8. After the molten metal filled in the cavity 10 is cooled and solidified, the upper mold 6 is raised by a hydraulic mechanism (not shown) to open the cavity 10 and take out the casting from the lower mold 5.

  FIG. 6 shows an example in which the molten metal stored in the closed furnace 1 ′ is sent to the sump 12 through the stalk 8 ′ and filled into the cavity 10 of the mold 4 from the sump 12. The molten metal in the closed furnace 1 ′ is heated by the immersion heater 13 to maintain the molten state. Molten metal is supplied from the molten metal supply port 11 into the closed furnace 1 ′. The portion from the stalk 8 'to the hot water reservoir is heated by the heater 3 to prevent the molten metal from solidifying due to a decrease in temperature. Other configurations are basically the same as those of the conventional example of FIG. 5, and the same portions are denoted by the same reference numerals.

  FIG. 7 shows the conventional casting apparatus described above with reference to FIG. 5, in which the molten metal is pumped into the mold 4 by a molten metal electromagnetic pump regardless of the gas pressure. That is, an inductor 14 of a molten metal electromagnetic pump is provided outside the intermediate portion of the stalk (duct) 8, and a core 15 for forming a magnetic path of a magnetic field generated by the inductor 14 in the stalk 8 correspondingly. Is arranged. A three-phase current is passed through the inductor 14, thereby generating a moving magnetic field between the inductor 14 and the core 15, and applying an upward thrust to the molten metal in the stalk 8, thereby The cavity 10 is filled. Other configurations are basically the same as those of the conventional example of FIG. 5, and the same portions are denoted by the same reference numerals.

  FIG. 8 shows the conventional casting apparatus described above with reference to FIG. 6, in which the molten metal is pumped into the mold 4 by a molten metal electromagnetic pump regardless of the gas pressure. That is, an inductor 14 of a molten metal electromagnetic pump is provided outside the middle portion of the stalk (duct) 8 ', and a magnetic path for a magnetic field generated by the inductor 14 is formed in the stalk 8' correspondingly. A core 15 is arranged. The inductor 14 is energized with a three-phase current, thereby generating a moving magnetic field between the inductor 14 and the core 15, and applying an upward thrust to the molten metal in the stalk 8 ′, whereby the mold 4 The cavity 10 is filled. Other configurations are basically the same as those of the conventional example of FIG. 6, and the same portions are indicated by the same reference numerals.

  In such a low-pressure casting apparatus, when the molten metal is solidified in the cavity 10 of the mold 4, the molten metal corresponding to the solidified and contracted volume must always be supplied through the gate 9 of the mold 4. For this purpose, as shown in FIGS. 5 and 7, the stalks 8 connected to the gate 9 are heated by heat radiation from the crucible 2 side or directly by the heater 3 '. As shown in FIG. 6 and FIG. 8, in the case where the mold 4 is arranged apart from the sealed furnace 1, a hot water reservoir 12 is provided under the mold 4, and the hot water reservoir 12 is heated by the heater 3. . By adopting such a structure, the mold 4 is formed with a temperature gradient in the order of the gate 9, the lower mold 5, and the upper mold 6 in descending order of temperature, and the molten metal in the cavity 10 flows from top to bottom. Directional solidification is performed in which the molten metal at the gate 9 is solidified. During this time, a volume of molten metal solidified and contracted is supplied into the cavity 10 from the gate 9 side. Thereby, it is possible to cast a casting having no so-called shrinkage nest or shrinkage.

  In the low-pressure casting method, bubbles and oxides are formed by gently filling the crucible 2 and the molten metal with a small amount of oxide in the closed furnace 1 ′ from the bottom into the cavity 10 of the mold 4 without entraining gas. There is an advantage that a casting containing no can be easily cast. Furthermore, due to the temperature gradient as described above, solidification of the molten metal occurs from the top to the bottom in the cavity 10, and finally the molten metal in the portion of the gate 9 solidifies, so that the molten metal solidifies in the cavity 10. The molten metal is additionally filled from the gate 9 by the contracted volume. Thus, no shrinkage or shrinkage occurs during the solidification of the molten metal in the cavity 10. For these reasons, the low-pressure casting method can cast a high quality casting as compared with other casting methods such as the gravity casting method and the die casting method.

  However, in the low pressure casting method, the heat capacity of the mold 4 is large, and heat is constantly supplied to the mold 4 by heat conduction from the molten metal in the stalk 8 and the sump 12. Further, the temperature of the mold 4 rises every casting cycle due to solidification latent heat released when the molten metal solidifies. For these reasons, the molten metal filled in the cavity 10 is difficult to solidify. Since the molten metal is solidified in the cavity 10 and becomes a certain strength, for example, in the case of aluminum, it must be 400 ° C. or lower, and the casting cannot be taken out from the mold without being deformed. The casting time will be longer.

  In the case of die casting with a short casting cycle and high mass productivity, molten metal is injected into the mold cavity, filled, solidified, then the mold is opened, the casting is taken out, and a mold release agent is applied to the inner surface of the cavity. One casting cycle between application and closing of the mold is about several tens of seconds for a small casting, and within several minutes for a large casting. On the other hand, generally, in low pressure casting, one casting cycle takes 7 to 10 minutes.

  What is important in low-pressure casting is the above-described temperature gradient of the mold. That is, in order not to cause shrinkage or shrinkage in the casting, the molten metal filled in the cavity 10 starts to solidify first from a position farthest from the gate 9 and finally solidifies at the portion of the gate 9. Is required. For that purpose, it is particularly important to form a temperature gradient in the order of the gate 9, the lower mold 5, and the upper mold 6 in descending order of temperature. For example, after the stalk 8 is replaced, if the preheating is not sufficient, the temperature of the gate 9 is lowered, and the molten metal may solidify and block the cavity 10. In order to prevent this, it is necessary to measure the temperature at the upper end of the gate 9 and the stalk 8. However, since thermocouples generally used for temperature measurement are weak against molten metal such as molten aluminum and must be covered with a protective tube, the temperature at the upper end of the gate 9 and stalk 8 is measured directly and in real time. Cannot be performed, and the temperature measurement value has an error or a time lag.

  Still another problem in the low pressure casting is that after the solidification of the molten metal in the cavity 10 of the mold 4 is completed, the pressure in the closed furnace 1, 1 ′ shown in FIGS. When the output of the electromagnetic pump 14 shown in the figure is lowered and the liquid level of the molten metal in the stalk 8 and the sump 12 is lowered, air passes through the gap between the mold 4 and the stalk 8 and the sump 12 between the packings. Intrusion occurs, and an oxide film is formed on the molten metal in the stalk 8 and the water reservoir 12. Further, when the upper mold 5 is opened for mold removal and the casting is taken out, air may enter the stalk 8 or the hot water reservoir 12 from the gate 9 and an oxide film may be formed on the molten metal therein.

  The mold is generally made of steel, has a large heat capacity, and takes time to rise and fall. For example, in the temperature rise in preparation for casting, casting is started after preheating to a temperature of about 200 ° C. by gas burner heating for 1 to 2 hours. As the casting cycle is repeated, the temperature of the mold gradually rises. However, in order to prevent the mold temperature from becoming higher than a predetermined steady temperature (about 350 ° C in the case of aluminum casting), The peripheral member is designed to be naturally radiated and to have a saturation temperature. However, in this case, it takes time to lower the temperature to a temperature (350 ° C. in the case of aluminum casting) at which the casting can be removed without being deformed by heat supply from the molten metal at the gate of the mold.

JP 2006-334671 A JP 2006-272448 A JP-A-11-216555 Japanese Patent Laid-Open No. 10-193035

  In view of the problems in the conventional casting apparatus, the present invention has a high temperature rise and fall of the mold, can shorten the casting preparation and casting cycle, and is free from so-called shrinkage nests and loosening that tend to occur during solidification of molten metal. The object of the present invention is to provide a casting apparatus capable of casting a casting having a good surface texture.

  In the present invention, in order to increase the temperature of the mold and shorten the time for casting preparation and the casting cycle, the heat capacity is reduced, and even if the temperature distribution is formed, the thermal stress is small so that it is not easily deformed. A mold is made of a material having a small expansion coefficient and a thermal conductivity similar to or higher than that of a steel material generally used for the mold.

  It is isotropic graphite that can be selected as a mold material that meets such requirements. The heat capacity per unit volume of isotropic graphite is 427 kcal / m3 ° C., which is ½ or less of 858 kcal / m3 ° C. of steel. Therefore, when comparing the case where the same amount of heat is applied to a mold having the same volume, the temperature raising / lowering time of the mold made of isotropic graphite is ½ or less compared to the mold made of steel. Moreover, the thermal conductivity of isotropic graphite is 89 kcal / mh ° C., which is more than twice that of 39 kcal / mh ° C., and the linear expansion coefficient is 4.7 × 10 −6 / ° C. It is 1/2 or less of 10.5 × 10 −6 / ° C.

  On the other hand, the disadvantage of isotropic graphite is that the strength is weak. However, when low pressure of about 0.01 to 0.02 MPa (0.1 to 0.2 kg / cm 2) is applied as in low pressure casting, the mold is used. Will not be damaged. That is, sufficient strength can be ensured.

  Another problem with isotropic graphite is that the surface is soft and easily scratched. In order to solve this problem, Cr plating, Ni plating, chemical Ni plating containing phosphorus or boron, or the like is applied, and surface coating is performed. By applying such plating to the surface of the mold, not only can the surface be prevented from being scratched, but also the surface can be prevented from being depleted due to generation of carbon dioxide gas accompanying oxidation of the surface when heated. Therefore, it is necessary to form the plating on the inner surface of the cavity 10 of the mold 4 and the other parts of the mold are plated as necessary.

  As described above, isotropic graphite has a thermal conductivity twice or more that of steel, so it is easy to equalize temperature and hardly form a temperature gradient. For this reason, it is necessary to cool the upper mold as necessary in order to form a temperature gradient in which the temperature increases in the order of the gate, the lower mold, and the upper mold and to solidify the molten metal in the cavity in a directional manner. For example, a cooling block that is water-cooled when the molten metal is solidified is pressed against the upper mold to form a temperature gradient. Furthermore, a heater for heating each of the upper mold and the lower mold individually is provided. For example, a rod-shaped cartridge heater is embedded in the upper mold and the lower mold.

  As described above, in the casting apparatus according to the present invention, by using an isotropic graphite mold having a small heat capacity, it is possible to quickly raise and lower the temperature of the mold during preheating and the casting cycle, efficiently and in a short time. Casting of castings can be performed. Further, the surface softness, which is a defect of isotropic graphite, can be improved by applying hard plating. Furthermore, the defects of isotropic graphite molds, which have high thermal conductivity and are difficult to form a temperature gradient, can be easily eliminated by using cooling means and heating means, and molten metal in the cavity. Directed coagulation is possible.

It is sectional drawing which shows one Example of the casting apparatus by this invention. It is sectional drawing which shows the other Example of the casting apparatus by this invention. It is sectional drawing which shows the other Example of the casting apparatus by this invention. It is sectional drawing which shows the other Example of the casting apparatus by this invention. It is sectional drawing which shows the prior art example of a casting apparatus. It is sectional drawing which shows the other conventional example of a casting apparatus. It is sectional drawing which shows the other conventional example of a casting apparatus. It is sectional drawing which shows the other conventional example of a casting apparatus.

In the present invention, in order to achieve the object, the mold is made of isotropic graphite, the surface is hard-plated, and the cooling means and the heating means are used individually or in combination to form a temperature gradient. did.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

FIG. 1 is a sectional view showing an embodiment of a low-pressure casting apparatus according to the present invention. The configuration of this low-pressure casting apparatus is basically the same as that of the conventional example described above with reference to FIG.
A gas supply source 20 such as an inert gas or carbon dioxide is connected to a gas inlet 20 provided in an upper portion of the hermetically sealed hermetic furnace 1, and the gas is pumped into the hermetic furnace 1. A crucible 2, which is a heat-resistant graphite container having an open top surface, is accommodated inside the closed furnace 1, and a heater 3 is disposed along the outer wall of the crucible. The lower end of the stalk 8 attached to the lid of the closed furnace 1 is immersed in the center of the crucible 2. A mold 4 including a lower mold 5 and an upper mold 6 is disposed on the closed furnace 1. Concave portions are respectively formed on the mating surfaces of the lower die 5 and the upper die 6, and when the lower die 5 and the upper die 6 are overlapped, a casting-shaped cavity 10 is formed by the concave portions. Is done. A core 7 is accommodated in the cavity 10 as necessary. The upper end of the stalk 8 is connected to a gate 9 leading to a cavity 10 provided at the bottom of the mold 4.

  In such a casting apparatus, in the present invention, a mold 4, that is, a lower mold 5 and an upper mold 6, and a core 7 as necessary, are made of isotropic graphite. Table 1 shows the physical properties of the isotropic graphite together with the physical properties of the steel.

  The heat capacity per unit volume of isotropic graphite is ½ or less that of steel. Therefore, when comparing the case where the same amount of heat is applied to a mold having the same volume, the temperature raising / lowering time of the mold made of isotropic graphite is ½ or less compared to the mold made of steel. On the other hand, the thermal conductivity of isotropic graphite is twice or more that of steel, and the linear expansion coefficient is ½ or less that of steel.

  However, isotropic graphite has a soft surface and is easily scratched. Therefore, Cr plating, Ni plating, chemical Ni plating containing phosphorus and boron, etc. are applied, and the surface is hard-coated. By applying these platings to the surface of the mold, it is possible not only to prevent scratches on the surface, but also to prevent the surface from being worn out due to the generation of carbon dioxide gas accompanying the oxidation of the surface when heated.

  As described above, isotropic graphite has a thermal conductivity twice or more that of steel, so it is easy to equalize temperature and hardly form a temperature gradient. Therefore, a cooling means for cooling the upper mold as shown in FIG. 1 is provided in order to form a temperature gradient in which the temperature is higher in the order of the gate, the lower mold, and the upper mold and to solidify the molten metal in the cavity in a directional manner. Provide. As shown in FIG. 1, the cooling block 17 provided with the cooling water channel 19 is pressed against the upper surface of the upper mold 6 to form a temperature gradient. Cooling water circulates in the cooling water channel 19 as indicated by arrows in FIG. A pressing spring 21 is provided to elastically press the cooling block 17 against the upper surface of the upper mold 6.

Further, heaters 18 and 18 for individually heating the upper mold 6 and the lower mold 5 are provided. For example, as shown in FIG. 1, rod-shaped cartridge heaters 18 and 18 are embedded in the upper mold 6 and the lower mold 5.
By using these cooling means and heating means in combination, the mold 4 has a temperature gradient in which the temperature is high in the order of the gate 9, the lower mold 5, and the upper mold 6, and the molten metal in the cavity 10 flows from above. Directional solidification is performed in which the molten metal solidifies downward and finally the molten metal in the gate 9 solidifies. Thereby, when the molten metal in the cavity 10 is solidified, the molten metal corresponding to the solidified and contracted volume can be additionally supplied into the cavity 10 from the gate 9 side. Thereby, it is possible to cast a casting having no so-called shrinkage nest or shrinkage.

  When casting a casting with this casting apparatus, an inert gas is injected into the closed furnace 1 from the gas inlet 20. With this gas pressure, the molten metal surface in the crucible 2 is pressurized and the molten metal is pushed up and filled into the mold cavity 10 via the stalk 8. After the molten metal filled in the cavity 10 is cooled and solidified, the upper mold 6 is raised by a hydraulic mechanism (not shown) to open the cavity 10 and take out the casting from the lower mold 5.

  FIG. 2 shows an example in which the molten metal stored in the closed furnace 1 ′ is sent to the sump 12 through the stalk 8 ′ and filled into the cavity 10 of the mold 4 from the sump 12. The molten metal in the closed furnace 1 ′ is heated by the immersion heater 13 to maintain the molten state. Molten metal is supplied from the molten metal supply port 11 into the closed furnace 1 ′. The portion from the stalk 8 'to the hot water reservoir is heated by the heater 3 to prevent the molten metal from solidifying due to a decrease in temperature. Other configurations are basically the same as those of the embodiment of FIG. 1, and the same portions are denoted by the same reference numerals.

  FIG. 3 shows a conventional casting apparatus described above with reference to FIG. 1, in which the molten metal is pumped into the mold 4 by a molten metal electromagnetic pump regardless of the gas pressure. That is, a molten metal inductor 14 is provided outside the middle portion of the stalk (duct) 8 and a core 15 for forming a magnetic path of the magnetic field generated in the inductor 14 is disposed in the stalk 8 correspondingly. is doing. A three-phase current is applied to the inductor 14, thereby generating a moving magnetic field between the inductor 14 and the core 15, and applying an upward thrust to the molten metal in the stalk 8. The cavity 10 is filled. Other configurations are basically the same as those of the embodiment of FIG. 1, and the same portions are denoted by the same reference numerals.

  FIG. 4 shows the conventional casting apparatus described above with reference to FIG. 2, in which the molten metal is pumped into the mold 4 by a molten metal electromagnetic pump provided in the middle of the stalk 8 regardless of the gas pressure. That is, a molten metal inductor 14 is provided outside the middle portion of the stalk (duct) 8 and a core 15 for forming a magnetic path of the magnetic field generated in the inductor 14 is disposed in the stalk 8 correspondingly. is doing. A three-phase current is applied to the inductor 14, thereby generating a moving magnetic field between the inductor 14 and the core 15, and applying an upward thrust to the molten metal in the stalk 8. The cavity 10 is filled. Other configurations are basically the same as those in the embodiment of FIG. 2, and the same portions are denoted by the same reference numerals.

  Since the present invention can perform casting by shortening the time of casting preparation and casting cycle, it can be used for efficiently producing casting products such as aluminum alloys used for vehicle members and the like. Is possible.

4 Mold 5 Mold lower mold 6 Mold upper mold 9 Mold gate 10 Mold cavity 17 Cooling block

Claims (4)

In a casting apparatus in which molten metal is filled in a mold 4 through a stalk 8 from a molten metal tank in which a metal is stored in a molten state, and then the molten metal is solidified in the mold 4 to mold a casting. A casting apparatus characterized in that 4 is made of isotropic graphite. The casting apparatus according to claim 1, wherein at least the inner surface of the cavity 10 of the mold 4 is plated. The casting apparatus according to claim 1, wherein a heating means for heating the mold 4 is provided in order to form a temperature gradient from the gate 9 to the opposite side in the mold 4. The cooling means for cooling a part of the mold 4 is provided in order to form a temperature gradient from the gate 9 to the opposite side in the mold 4. Casting equipment.

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