JP2012106277A - Low-pressure casting apparatus and low-pressure casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a casting which has high filling density, and does not contain a discontinuous portion, a pore and a bubble during the solidification.SOLUTION: The casting is molded by filling molten metal into a cavity 10 of a casting mold 4 at low pressure, then cooling and solidifying the molten metal in the cavity 10 of the casting mold 4. A low-pressure casting apparatus includes: an inductor 14 for filling the molten metal into the cavity 10 of the casting mold 4; a level gage 17 for detecting the level of the molten metal filled in the cavity 10 by the inductor; and a control means performing control in such a manner that the raising speed of the molten metal is made low in a portion of a relatively large flow passage sectional area in the cavity 10, and the raising speed of the molten metal is made high in a relatively small flow passage sectional area, according to the level of the molten metal to be measured by the level gage 17.

Description

  The present invention relates to a casting apparatus that fills a molten metal into a mold and then solidifies the molten metal in the mold to form a cast product. In particular, the molten metal is compared from a spout at the bottom of a heated mold to a cavity therein. The present invention relates to a low-pressure casting apparatus that fills at a low pressure and cools and cures the molten metal together with a mold.

  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 the molten metal and the cavity. Among these, the low pressure casting method applies, for example, a relatively low pressure of a gas such as an inert gas or carbon dioxide to a closed furnace containing molten metal, and the molten metal in the closed furnace is moved upward via stalk at this pressure. This is a method for producing a cast product by pushing up and filling a mold placed above the closed furnace with molten metal. Since this low-pressure casting method can obtain a dense and high-strength metal cast product, it is widely used to produce a metal cast product used for a vehicle member or the like. The following Patent Document 1 and Patent Document 2 show such a low-pressure casting method.

  Such a low pressure casting method does not contain bubbles or oxides by gently filling the molten metal with low oxide in the crucible or the closed furnace into the mold cavity without entraining gas from the bottom to the top. There is an advantage that a cast product can be easily cast. Furthermore, when the molten metal is filled into the mold cavity, a temperature gradient is formed so that the temperature decreases from the back of the cavity toward the pouring gate, so that the molten metal solidifies from the back of the cavity toward the pouring gate. The molten metal in the gate is solidified. For this reason, the molten metal is additionally filled from the gate by the volume of the molten metal solidified and contracted in the cavity. Thereby, when the molten metal is solidified in the cavity, the shrinkage and the loosening caused by the shrinkage do not occur. For these reasons, the low-pressure casting method has an advantage that a high-quality casting can be cast as compared with other casting methods such as the gravity casting method and the die casting method.

  In this low-pressure casting device, when molten metal is filled into the mold cavity, hot water does not dance in the mold, and it is filled without entraining bubbles, so it is a very slow speed of about 5 cm / s. Therefore, the mold is preheated to a temperature of about 350 ° C. in advance so that the filled molten metal is not immediately cooled, solidified and cured. Depending on the shape of the product (cavity) and the heat capacity, the molten metal is filled into the cavity of the preheated mold, including the case where the temperature difference is previously set as described above, and then as described above. While forming a temperature gradient in the mold, the molten metal in the cavity together with the mold is cooled, solidified and cured.

  The mold cavity has various shapes depending on the part in order to mold the outer shape of the casting, and there is a core for molding the inner shape of the casting in the cavity. Therefore, when the molten metal is filled into the cavity from the gate at the bottom of the cavity, the cross-sectional area of the flow path at the liquid level of the molten metal rising in the cavity, that is, the plane area of the space in the cavity varies depending on the vertical position of the cavity. In general, the cross-sectional area of the flow path from the bottom of the cavity to the bottom surface of the core is relatively wide, and the cross-sectional area of the flow path is narrowed at the intermediate part in the cavity where the core exists. The channel cross-sectional area is relatively wide at the upper part in the cavity above.

  When the molten metal is filled into the mold cavity, if the flow rate of the molten metal is too high, that is, if the flow cross-sectional area from the bottom of the cavity to the lower surface of the core is relatively large, When the molten metal surface reaches a portion where the flow path cross-sectional area where the core exists is relatively narrow, the molten metal suddenly blows up due to inertia. The molten metal blown up then flows down in the cavity and falls to the molten metal surface. At this time, the molten metal blown up solidifies when it falls and rides on the molten metal surface in a semi-solid state, so that a discontinuous molten metal is formed between the solid phase and the liquid phase on the molten metal surface. It is formed. Therefore, there is a problem that a cast product in which the structure of the casting is partially discontinuous is formed.

  Further, in the mold cavity, the portion where the core is present has a smaller flow area of the molten metal, that is, the flat area, which is higher than the portion where the core is not present. Therefore, the molten metal tends to lose heat from the mold and the core, and the fluidity of the molten metal is easily lost. Therefore, the metal filling density is partially roughened, and it is easy to leave voids and bubbles in the metal. As a result, there is a problem that the obtained cast product has a variation in the filling density of the metal depending on the part, or easily includes an internal cavity called a so-called nest.

  Moreover, a normal casting apparatus performs by the pressurization pump which sends compressed air. Molten metal stored in a closed furnace is sent to a sump through stalk and filled into a mold cavity from the sump. Therefore, as the casting progresses, the molten metal surface decreases, the molten metal surface and the mold distance change, and a corresponding pressure must be applied. For this reason, it is difficult to control the pressure with high accuracy in proportion to the cross section of the flow path, causing variations, and there is a problem that the injection pressure control accuracy is inferior because the pressure response of the molten metal is low.

JP 2000-94120 A Japanese Patent Application Laid-Open No. 08-332563 JP 07-214238 A Japanese Patent Application Laid-Open No. 07-185739

  In view of the problems in the conventional low pressure casting apparatus, the present invention prevents the molten metal from blowing up in the cavity when filling the molten metal into the cavity, so that the molten metal can be filled in the cavity without being disturbed. In addition, a low-pressure casting apparatus that can maintain the fluidity of the molten metal even in the portion where the core is present, and thereby can mold a casting product having a high filling density and not including discontinuous portions or bubbles. An object is to provide a low pressure casting method.

In order to achieve the above object, the present invention appropriately controls the rising speed of the molten metal according to the flow path cross-sectional area of the molten metal in the cavity when filling the molten metal in the cavity of the mold.
That is, the low-pressure casting apparatus according to the present invention is a method in which molten metal is low-pressure filled into the cavity 10 of the mold 4 and then the molten metal is cooled and solidified in the cavity 10 of the mold 4 to form a cast product. An inductor 14 for quickly filling and filling the molten metal into the cavity 10 of the mold 4 with high precision, and a level meter 17 for detecting the level of the molten metal filled in the cavity 10 cavity. Depending on the level of the molten metal measured by the level meter 17, the rising speed of the molten metal is slowed at a portion where the flow passage cross-sectional area in the cavity 10 is relatively wide, and the molten metal is melted at a portion where the flow passage cross-sectional area is relatively narrow. Control means for controlling the metal ascending speed to be increased.

  In the low pressure casting method according to the present invention, after the molten metal is filled into the cavity 10 of the mold 4 at a low pressure, the molten metal is cooled and solidified in the cavity 10 of the mold 4 to form a cast product. While filling the cavity 10 with molten metal, the level of the molten metal filled in the cavity 10 is detected by the level meter 17, and the level of the molten metal measured by the level meter 17 determines the level of the molten metal in the cavity 10. Control is performed such that the rising speed of the molten metal is slowed at a portion where the flow path cross-sectional area is relatively wide, and the rising speed of the molten metal is increased at a portion where the flow path cross-sectional area is relatively narrow.

  In the present invention, since the rising speed of the molten metal is slowed at a portion where the flow path cross-sectional area in the cavity 10 is relatively wide, it is possible to prevent the molten metal from being rapidly blown up in the cavity 10. In addition, since the flow rate of the molten metal is increased at the part where the cross-sectional area of the flow path is relatively narrow and easily solidified, it is easy to maintain the fluidity of the molten metal at that part, and the gas melts while pushing up the gas in the narrow part of the flow path. Since the metal is filled, it is possible to prevent solidification of the molten metal and to expel bubbles left in the molten metal. Thereby, the filling density of the metal as a whole can be increased, bubbles left behind in the metal can be eliminated, and a cast product having a uniform filling density of the metal and not including discontinuous portions and cavities can be formed.

It is sectional drawing which shows one Example of a low pressure casting apparatus. It is a block diagram which shows an example of the molten-metal level rising control of a molten metal in a low pressure casting apparatus. It is a time chart which shows an example of the molten-metal level rising control of a molten metal in a low pressure casting apparatus. It is sectional drawing which shows the other Example of a low pressure casting apparatus.

In the present invention, in order to achieve the object, when the molten metal is filled into the cavity, the rising speed of the molten metal is appropriately controlled according to the cross-sectional area of the flow path of the molten metal in the cavity.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

FIG. 1 is a cross-sectional view showing an embodiment of the low-pressure casting apparatus according to the present invention, and shows an embodiment in which the molten metal is pumped into the mold 4 by a molten metal electromagnetic pump.
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 comprising a lower mold 5 and an upper mold 6 is disposed on the closed furnace 1. Space portions are respectively formed on the mating surfaces of the lower mold 5 and the upper mold 6, and when the lower mold 5 and the upper mold 6 are overlapped, the space portion becomes a cavity 10 in the shape of a cast product. . A core 7 is accommodated in the cavity 10. In the illustrated example, the core 7 has a cavity, but there may be no such cavity.

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. 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 corresponding to this. It is arranged. 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.
The mold 4 is provided with a level gauge 17 such as a molten metal level sensor. The level gauge 17 detects the level of molten metal filled in the cavity 10 in the mold 4 from the gate 9.

  The inductor 14 is covered with a protective case 16 made of a heat-resistant material such as ceramics, and the lower end of the stalk 8 is closely joined to the lower end of the protective case 16. Therefore, the inductor 14 does not contact the molten metal in the crucible 2. The molten metal in the crucible 2 flows in from the lower end of the stalk 8 joined to the lower end of the protective case 16 and thrusts upward on the molten metal in the stalk 8 by the moving magnetic field generated inside the stalk 8 by the inductor 14. Is fed from the gate 9 of the mold 4 to the cavity 10. A heater 3 ′ is provided around the stalk 8 in the protective case 16 so that the stalk 8 is heated and the molten metal therein is not solidified.

  The inductor 14 is controlled by the level of molten metal in the cavity 10 detected by the level meter 17, and the filling amount of molten metal into the cavity 10 per unit time is controlled. This control system is shown in FIG. 2 and represents that the drive power source 18 of the inductor 14 is controlled by the controller 21 based on the level of molten metal in the cavity 10 detected by the level meter 17. . The controller 21 has a built-in recording device in which a pattern controlled by the level meter 17 is recorded and can be repeatedly filled with the same pattern. The mold 4 has an observation hole for the level meter 17, and since this observation hole is easily clogged with molten metal, glass or the like is fitted therein to prevent the molten metal from blowing up. Glass is easy to adhere with molten metal, and the inside cannot be seen soon, so it is necessary to record a good injection pattern. The controller 21 has this recording device built in, and the output of the electromagnetic pump with good controllability is the same. Control is performed with a control pattern.

  Specifically, while the molten metal is filled into the cavity 10 from the gate 9 of the mold 4, the level of the molten metal filled in the cavity 10 is detected by the level meter 17 and measured by the level meter 17. Depending on the level of the molten metal, control is performed so that the rising speed of the molten metal is slowed at a portion where the flow passage cross-sectional area in the cavity 10 is relatively wide, and the rising speed of the molten metal is increased at a portion where the flow passage cross-sectional area is relatively narrow. .

  As shown in FIG. 1, when the cavity 10 is divided into upper and lower portions A and C where the core 7 is not present and an intermediate portion B where the core is present, the rise of the molten metal at the respective portions A to C. FIG. 3 shows a speed control chart. As shown in FIG. 3, in the middle part B where the core is present, the rising speed of the molten metal in the cavity 10 is increased, but in the parts A and C before and after that, the rising of the molten metal in the cavity 10 is performed. The speed is slow.

  Among the cavities 10, the portion B where the core 7 is present has a narrow channel area of the molten metal, that is, a flat area, which is higher than the portions A and C where the core 7 does not exist. For this reason, the molten metal tends to lose heat from the mold 4 and the core 7 and the fluidity of the molten metal is easily lost. Moreover, since it is easy to solidify, it is easy to leave voids and bubbles in the metal. Therefore, in this part B, the rising speed of the molten metal is increased to prevent solidification of the molten metal, and it is easy to discharge without leaving voids or bubbles.

In the portions A and C where the core 7 does not exist in the cavity 10, the flow path of the molten metal is relatively wide, so that the fluidity of the molten metal is not easily lost. However, when the rising speed of the molten metal is increased in this portion, in the portion A, when the molten metal reaches the portion B where the core 7 exists, the molten metal blows up when the portion C passes through the portion B. Cheap. Therefore, for the portions A and C where the core 7 does not exist, the rising speed of the molten metal is slowed.
FIG. 3 shows a molten metal filling time chart as described above. In FIG. 3, two time charts (A) and (B) are illustrated.

  FIG. 4 shows an embodiment in which the molten metal stored in the closed furnace 1 is sent to the water reservoir 12 through the stalk 8 ′ and filled into the cavity 10 of the mold 4 from the water reservoir 12. A core for forming a magnetic path of a magnetic field generated by the inductor 14 in the stalk 8 ′ corresponding to the inductor 14 of the molten metal electromagnetic pump provided outside the intermediate portion of the stalk (duct) 8 ′. 15 is arranged. A three-phase current is applied to the inductor 14, thereby generating a moving magnetic field between the inductor 14 and the core 15, giving an upward thrust to the molten metal in the stalk 8 ′, and applying the molten metal to the mold 4. The cavity 10 is filled.

  Other configurations are basically the same as those of the embodiment described above with reference to FIG. 1, and the same portions are denoted by the same reference numerals. Also in this embodiment, as described above, the rising speed of the molten metal in the cavity 10 is increased in the intermediate part B where the core exists, and the rising of the molten metal in the cavity 10 in the parts A and C before and after that. Reduce the speed.

  The present invention can be applied to the field of low-pressure casting in which molten metal is filled in a cavity of a heated mold at a low pressure, and the molten metal is cooled and cured together with the mold. In particular, the present invention can be applied as a low-pressure casting apparatus and method capable of producing a cast product having a uniform filling density at the time of molding and a small number of internal cavities and high accuracy.

4 Mold 7 Mold core 10 Mold cavity 14 Inductor 17 Level meter 21 Controller

Claims (2)

A thrust is applied to the molten metal in the stalk 8 to supply the molten metal, and the molten metal is filled into the cavity 10 of the mold 4 at a low pressure, and then the molten metal is cooled and solidified in the cavity 10 of the mold 4 to be cast. In a low-pressure casting apparatus for molding a product, an inductor 14 that pushes up the molten metal in the stalk 8 to fill the cavity 10 of the mold 4 with the molten metal, and a melt that is filled into the cavity 10 by the inductor 14. The level meter 17 that detects the level of the metal and the level of the molten metal measured by the level meter 17 slows the rising speed of the molten metal at a portion where the cross-sectional area of the channel in the cavity 10 is relatively wide. It has a control means for controlling the rising speed of the molten metal at a relatively small cross-sectional area and a control means for repeatedly storing the control pattern and repeating the control. Low-pressure casting apparatus according to claim. A thrust is applied to the molten metal in the stalk 8 to supply the molten metal, and the molten metal is filled into the cavity 10 of the mold 4 at a low pressure, and then the molten metal is cooled and solidified in the cavity 10 of the mold 4 to be cast. In the low-pressure casting method, the molten metal in the stalk 8 is pushed up by the inductor 14 to fill the molten metal in the cavity 10 of the mold 4, and the level of the molten metal filled in the cavity 10 is set to a level. According to the level of the molten metal detected by the total meter 17 and measured by the level meter 17, the rising speed of the molten metal is slowed at a portion where the flow channel cross-sectional area in the cavity 10 is relatively wide, and the flow channel cross-sectional area is relatively A low-pressure casting method characterized by controlling to increase the rising speed of molten metal in a narrow portion.

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