JPH04135048A - Low pressure casting method - Google Patents

Abstract

PURPOSE:To prevent the generation of a casting defect of shrinkage hole, etc., at the thick part, etc., in a casting product by cutting off the product part and a stoke after pouring and filling up molten metal into a metallic mold and solidifying the molten metal while pressurizing the molten metal in the thick part, etc., in the product. CONSTITUTION:At first, by pressurizing the inside of a molten metal pressurizing chamber 1, the molten metal 20 is poured into the metallic mold through a stoke 12 as the same way as the ordinary method to fill up the this cavity 21 with a molten metal. Successively, e.g. after making semi-solidified-state of the molten metal 20 at the thick part 23, etc., in the casting product part in the cavity 21, the casting product part is cut off from the stoke part 12 at a gate part 22, and the molten metal at the thick part 23, etc., is solidified while being pressurized. By using local pressurization together with the low pressure casting method, while providing the merit of the low pressure casting method, takeout of the product from the metallic mold can be quickened and the productivity can be improved. Further, as the solidifying velocity in the casting product part is quickened, the structure is made fine and the mechanical strength is improved. Further, as this casting product is pressurized, the development of casting defect of shrinkage hole, etc., at this position, can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-pressure casting method suitable for casting aluminum and its alloys, magnesium and its alloys, etc.

[Prior Art] In a conventional low-pressure casting method, first, an upper mold and a lower mold are assembled together with a stalk, a container storing molten metal is placed in a pressurized chamber, and the stalk is immersed in the molten metal. do. Next, the inside of the molten metal chamber is pressurized, and the molten metal is gently injected into the mold through the stalk and solidified within the mold.

In this case, the temperature of the mold is controlled by cooling the mold with air or water, and the mold is solidified in order from the part farthest from the sprue. This achieves directional solidification while maintaining the effect of replenishing the molten metal from the sprue.

For example, when casting a cast product with a thick wall, the temperature of the sprue is raised and the thick wall is air-cooled or water-cooled to slow down the solidification of the sprue compared to the thick wall. It aims at solidification and suppresses casting defects such as cavities.

[Problems to be Solved by the Invention] However, the conventional low-pressure casting method has a drawback in that it takes a long time for the sprue to finally solidify to complete solidification, resulting in a long casting cycle time. For example, this low-pressure casting method has a casting cycle time that is approximately two to three times longer than that of a high-pressure casting method that promotes solidification through a pressurizing effect, resulting in low productivity.

In addition, the low-pressure casting method has a slow solidification rate, resulting in a coarse structure and inferior mechanical properties compared to the high-pressure casting method. Furthermore, since the low-pressure casting method has a slow solidification rate, there is a problem in that if the cast shape has thick parts, the bow is likely to have casting defects such as cavities.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a low-pressure casting method capable of producing sound castings free of casting defects such as cavities, and producing castings with excellent mechanical properties at high productivity.

[Means for Solving the Problems] The low-pressure casting method according to the present invention includes the steps of pressurizing the inside of a molten metal pressurizing chamber and injecting the molten metal in the chamber into a mold via a stalk, and After being filled with molten metal,
The method is characterized by comprising the step of isolating the cast product part of the mold cavity from the stalk part at the weir part, and then solidifying the molten metal in the cast product part while pressurizing it.

[Operations] In the present invention, first, the inside of the molten metal pressurizing chamber is pressurized and the molten metal is injected into the mold through the stalk as in the conventional method,
The molten metal is filled into the mold cavity. Next, for example, after the molten metal becomes semi-solidified in the thick inside of the casting product part of the cavity, the casting product part is isolated from the stalk part at the weir part, and the molten metal in the thick part etc. is pressurized. Let it solidify. By using local pressure in combination with the low-pressure casting method in this way, while having the advantages of the low-pressure casting method,
Product removal from the mold can be accelerated, improving productivity. Furthermore, since the solidification rate of the cast product part becomes faster, the structure becomes finer and the mechanical strength improves. Furthermore, since this cast product part is pressurized, it is possible to prevent casting defects such as shrinkage cavities from occurring in this part.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing an apparatus used in an embodiment method of the present invention. A pressurized chamber 1 is installed on the floor. A molten metal container 6 storing molten metal 20 is placed in the pressurizing chamber 1, and a heater 5 is disposed in the pressurizing chamber 1 so as to surround this container 6. Furthermore, a pressurizing valve 2 for introducing pressurized gas into the pressurizing chamber 1 and an exhaust valve 3 for sucking the gas in the pressurizing chamber 1 to reduce the pressure are arranged in the upper part of the pressurizing chamber 1. It is set up. A lid member 4 is placed on the upper edge of the pressure chamber 1, and the molten metal container 6 can be inserted into the pressure chamber 1 with the lid member 4 removed. With the lid member 4 placed on the pressurizing chamber 1, the inside of the pressurizing chamber 1 can be shut off from the outside air.

On the other hand, above the pressurizing chamber 1, a mold support member 8 is provided.
is installed so that it can at least be raised and lowered by a suitable drive device (not shown). This support member 8 has a lower mold 10
is installed. A runner 24 extending downward is provided approximately at the center of the lower mold 10, and the runner 24 is connected to a stalk 12 installed at the center of the support member 8 so as to extend vertically downward. .

An upper mold 11 is superimposed on the lower mold 10. The upper mold 11 is fixed to the movable platen 7 via a plurality of supports 9 suspended from the movable platen 7. The movable platen 7 can be raised and lowered to approach or move away from the support member 8 by means of a suitable drive device (not shown).

Therefore, when the lower mold 10 and the upper mold 11 are overlapped,
A cavity 21 having a shape corresponding to the shape of the casting to be manufactured is formed on the overlapping surfaces. Four portions are provided on the overlapping surface of the lower die 10 at positions that align with the thick portion 23 of the cavity 21, and a pressure pin 14 is disposed within the recess. The pressure pin 14 is driven by the hydraulic cylinder 13 to advance into the recess and press the molten metal in the recess toward the thick wall portion 23 .

Further, a shirting pin 16 is disposed within the upper die 11 at the weir portion 22 between the thick wall portion 23 of the cavity 21 and the stalk 24. This shirting pin 16 is driven by a hydraulic cylinder 5 installed on the upper mold 11 to move downward and close the weir part 22.

Next, an embodiment of the present invention using a device configured as described above will be described. First, with the supporting member 8 retracted upward, the lid member 4 is removed, and the container 6 storing the molten metal 20 is inserted into the pressurizing chamber 1 . In addition, the movable platen 7 is lowered relative to the support member 8, and the upper mold 1 and the lower mold 1 are assembled.
0 and then clamp them together to assemble the mold. In this case, the pin 16 attached to the hydraulic cylinder 15 is retracted and the weir portion 22 is left open. Next, the lid member 4 is placed on the pressurizing chamber 1, and the support member 8 is lowered while the stalk 12 is inserted into the hole at the center of the lid member 4. As a result, the stalk 12 is immersed in the molten metal 20. Note that the molten metal 20 in the container 6 is heated by the heater 5 and maintained at a predetermined temperature.

In this way, after the assembly of each member is completed, the pressurizing valve 2
High pressure air is introduced into the pressurizing chamber 1 through the pressurizing chamber 1 to pressurize the inside of the pressurizing chamber 1. Then, the pressure of the molten metal in the container 6 increases, so that the molten metal rises in the stalk 12 and is injected into the cavity 21 of the mold.

Next, the molten metal 20 is filled into the cavity 21, and after the solidification of the molten metal 20 in the mold progresses and the thick part becomes a semi-solidified state, the hydraulic cylinder 15 is driven to advance the pin 16. The weir portion 22 is closed by the pin 16. Thereby, the thick portion 23 and the runner 24 are cut off. Then, the air inside the pressurizing chamber 1 is removed via the exhaust valve 3, and the inside of the pressurizing chamber 1 is brought into a reduced pressure state. As a result, the molten metal filled from the dam 22 to the stalk 12 is returned to the container 6 in the pressurizing chamber 1.

Thereafter, the hydraulic cylinder 13 is driven to raise the pin 14, and the pin 14 is advanced into the recess provided in the lower part of the thick wall part 23 of the lower die 10, thereby moving the molten metal 20 in the recess into the thick wall. Press fit into the section 23. As a result, the thick part 2
The molten metal 20 that existed in a semi-solidified state inside 3 is pressurized,
The molten metal 20 is completely solidified in this pressurized state.

Note that the timing of pressurizing the molten metal in the thick part by the pin 14 driven by the hydraulic cylinder 13 and the timing of the depressurization process in the pressurizing chamber 1 are as follows. The setting is not limited to the case where it is set before the pressure treatment of the meat part, and the reverse setting is also possible. In any case, the molten metal may be pressurized by the pin 14 after shirting by the pin 16. The timing of each of these processes can be defined by setting the time from the end of mold clamping to a timer or the like.

In the method of this embodiment, after the cavity 21 of the mold is filled with molten metal, the weir part 22 is blocked by the pin 16,
Since the pin 14 pressurizes the molten metal in the thick wall portion 23 of the casting product, it is possible to prevent casting defects such as cavities that tend to occur in the thick wall portions of the casting product. In addition, this local pressurization speeds up the solidification of the thick portion 23 and the like. Therefore, due to the fast solidification rate, the secondary dendrite arm spacing (DA) of the casting is
Sn) becomes smaller, and the strength of the casting, such as tensile strength, improves. Furthermore, due to the increased solidification rate, the time required for the molten metal to solidify after injection is shortened, so that the casting cycle time can be shortened.

Furthermore, in this embodiment, after shirting with the pin 16, the pressure inside the pressurized chamber 1 is reduced and the molten metal existing from the weir part 22 to the stalk 12 is expelled into the container 6. In addition, even after the product part has solidified, unlike the case where the cast product cannot be taken out until the solidification of the weir part 22 and the runner 24 is completed, the product can be taken out immediately after the product part has solidified. As a result, the casting cycle time can be further reduced. Therefore, the method of this embodiment has extremely high productivity.

Next, the results of casting a compressor casting from an AC8C aluminum alloy using the method of this embodiment will be explained in comparison with the case using a conventional method. In this example and the conventional example, two cast products were manufactured from one mold, and casting was performed using two molds. Table 1 below shows the casting conditions and product characteristics. For comparison, Table 1 also shows product characteristics when similar cast products were manufactured using conventional low-pressure casting methods and high-pressure casting methods.

Table 1 As is clear from Table 1, in the method of this example, the secondary dendrite arm spacing is the same as in the high-pressure casting method, and therefore the tensile strength is equal to or higher than that in the high-pressure casting method. It has a high value. In addition, solidification is promoted by pressurizing the thick-walled part, and shirting at the weir part makes it possible to take out the product after only the product part has solidified, which reduces the casting cycle time compared to conventional low-pressure casting methods. It was possible to reduce the time by about 40% compared to .

[Effect of the invention] According to the invention, after pouring and filling the molten metal into the mold,
Since the product part and the stalk are isolated and the molten metal in the thick parts of the product is solidified while being pressurized, casting defects such as G-force bubbles are prevented, and the interval between secondary dendrite arms is shortened, improving tensile strength. A cast product with excellent strength can be obtained. Furthermore, as solidification in the product part is promoted, the casting cycle time can be shortened, and the molten metal remaining in the runner can be removed after the product part and the stalk are separated and shut off. Casting cycle times can be reduced even further. Therefore, the present invention has extremely high productivity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. 1: Pressure chamber, 7: Movable platen, 8: Support member,
10: Lower mold, 11: Upper mold, 12 Nistoke, 21: Cavity, 22: Weir, 23: Thick wall part, 24: Runner

Claims (1)

[Claims] (1) The process of pressurizing the inside of the molten metal pressure chamber and injecting the molten metal in the chamber into the mold via the stalk, and after the molten metal is filled into the mold, the mold cavity is A low-pressure casting method comprising the steps of isolating the cast product part from the stalk part, and then solidifying the molten metal in the cast product part while pressurizing it.