JPH02295669A - Suction casting method - Google Patents

Abstract

PURPOSE:To prevent the degradation in quality by oxidation by injecting a molten metal formed by vacuum melting into a shell mold from the sprue thereof, communicating a suction box and a hollow vessel and sucking the inside of a suction case to a reduced pressure. CONSTITUTION:A solenoid valve 5a of a suction pipe 5 is actuated to close the communication between the suction box 3 and a hollow case 4. Gaseous Ar is then fed from a gas supply tank 10 into a hermetic chamber 7. The molten metal in a high-frequency melting furnace 8 is in succession poured through the sprue 2 into the casting space of the shell mold 1, simultaneously with which the solenoid valve 5a is opened to suck the gaseous Ar in the suction box 3 into the hollow case 4 of a low pressure. The molten metal poured therein is pressurized from the sprue 2 part side into the casting mold by the internal pressure difference between the hollow case 4 and the hermetic chamber 7 and is simultaneously sucked into the casting space in the shell mold 1 subjected to the suction to the reduced pressure; therefore, the good run is obtd. and the sure and uniform packing is executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a suction casting method for precision casting a vacuum-melted molten metal in an inert gas atmosphere.
Ceramic thin-walled parts with complex shapes made from active metal materials such as base superalloys are produced using the Lost Works molding method.
This article relates to a suction casting method suitable for casting using a Kuschel mold. [Prior art] Precision casting methods, typified by lost wax (investment) casting methods, have recently been widely applied because they can produce products with thin walls and complex shapes that are difficult to produce with other casting methods. ．． Normally, the lost wax casting method involves heating a ceramic shell mold to a high temperature and injecting molten metal into it. However, depending on the shape, size, wall thickness, etc. of the target product, This may affect the flow of the hot water in the mold, making it impossible to obtain a product with the desired shape and dimensions. Therefore, in order to obtain a perfect flow, a suction casting method is used that reduces the pressure inside the mold when pouring molten metal. On the other hand, active metal materials such as Ni-based alloy materials are oxidized when melted in the atmosphere, making it difficult to obtain materials with the desired properties. This is done under vacuum. However, when applying the suction casting method to precision casting thin-walled, complex-shaped parts using ceramic shell molds, etc., which are made from these active metal raw materials, it is practical to perform the casting under vacuum. It becomes impossible to move. This is because in the suction casting method, the pressure is reduced around the breathable shell mold, and the pressure inside the mold is lowered by a relatively large pressure difference than the pressure on the sprue side where molten metal is injected. Although it is essential, under vacuum,
This is because it becomes difficult to generate the required pressure difference. Therefore, for example, as shown in FIG. 5, a breathable shell mold (52) is set in a suction box (51), and the molten metal melted under vacuum is poured into this shell mold (52). The injected molten metal is injected from the sprue, and the inside of the suction box (51) is vacuumed at the same time as the injection, and the inside of the shell mold (52) is degassed at the same time. A suction casting method has been proposed in which thin-walled and complex-shaped parts made of Ni-based superalloy materials are precisely cast by placing the parts in an atmosphere and improving the flow of hot water within the shell mold (52). (Unexamined Japanese Patent Publication No. 55-15365
(Publication No. 8) [Problem to be Solved by the Invention] However, in the above-mentioned conventional suction casting method, the vacuum suction is performed too early between the injection of the molten metal and the start of the vacuum suction of the suction box (51). Then, air is sucked into the shell mold (52) and oxidation occurs in the molten metal.
Additionally, if the vacuum suction is too slow, the molten metal will solidify in advance and the suction effect will be lost, both of which will impair the quality of the resulting cast product, so the timing of both needs to be carefully adjusted. In addition, during the process of pouring the molten metal into the sprue of the shell mold (52), oxidation inevitably occurs in the molten metal due to contact with air, reducing its quality. There is a problem of letting In addition, it is necessary to provide a dedicated vacuum pump to vacuum the inside of the suction box (51), which raises the problem of increased equipment costs. In view of the above problems, the present invention is capable of suction casting a molten metal into a shell mold in an inert gas atmosphere, prevents deterioration in quality due to oxidation of the molten metal, and has a sprue of the shell mold. The pressure difference between the side pressure and the pressure inside the suction box can be easily adjusted, and the suction effect can be ensured to ensure stable and good circulation of molten metal in the shell mold. The purpose of this invention is to provide a suction casting method that makes it unnecessary to install a dedicated vacuum pump in the suction box. [Means for Solving the Problems] In order to achieve the above object, the suction casting method according to the present invention includes an air-permeable shell mold that is airtightly placed in a suction box except for the sprue opening. A hollow container is built in and connected to the suction box so that it can be opened and closed, while the opening of the sprue of the shell mold is installed. , the melting furnace is arranged to open toward the inside of the airtight chamber having the melting furnace therein;
When melting raw materials in a vacuum using the melting furnace, the airtight chamber and the hollow container are communicated through the shell mold and the suction case to reduce the pressure inside the hollow container to a vacuum, and then the pressure between the suction box and the hollow container is reduced to a vacuum. After closing the communication and supplying an inert gas into the airtight chamber to increase the pressure inside the airtight chamber and the suction box, the molten metal vacuum-melted in the melting furnace is transferred to the sprue of the shell mold. At the same time, the suction box and hollow container are communicated with each other to vacuum the inside of the suction case. [Function] In the present invention, an air-permeable shell mold is airtightly assembled into a suction box except for the sprue opening,
In addition, a hollow container is provided which communicates with the suction box in an openable and closable manner, and the opening of the sprue of the shell mold is arranged to open toward an airtight chamber having a melting furnace therein, so that the hollow container is opened and closed. Since the shell mold and the airtight chamber are communicated through the suction case, the pressure inside the hollow container can be reduced to a vacuum by drawing a vacuum in the airtight chamber during vacuum melting of raw materials in the melting furnace. Next, the communication between the suction box and the hollow container is closed to cut off the communication between the hollow container and the airtight chamber, and an inert gas is supplied into the airtight chamber so that the airtight chamber and the suction box are closed. By increasing the pressure, the internal pressure of the hollow container can be made much lower than the internal pressure of the airtight chamber. Next, the molten metal vacuum-melted in the melting furnace is injected from the sprue of the shell mold, and the suction box and the hollow container are communicated with each other, so that the inert gas in the suction case is released into the hollow container at a low pressure. It is possible to vacuum the inside of this suction case and the casting space in the shell mold whose sprue is closed with molten metal. At this time, the molten metal injected into the shell mold is pressurized from the sprue side into the mold due to the internal pressure difference between the hollow container and the airtight chamber, and at the same time, the casting space inside the mold is depressurized. Since the hot water is sucked into the mold, good water circulation can be obtained even in thin casting spaces. In addition, this vacuum-melted molten metal is injected into a shell mold that is sucked under reduced pressure by a hollow container that is evacuated to vacuum in an airtight chamber that is supplied with inert gas, so that during the casting process. There is no concern that quality will deteriorate due to oxidation. The internal pressure difference between the hollow container and the airtight chamber for vacuum suction mentioned above is set based on the characteristics of the applied shell mold and molten metal, the thickness of the product to be cast, etc. The difference is mainly adjusted by the pressure of the inert gas fed into the airtight chamber. Furthermore, the internal volume of the hollow container shall correspond to the size and internal volume of the applied shell mold and suction case. [Examples] Examples of the present invention will be described below with reference to the drawings. First, a tree is created by joining a runner and sprue to a wax model that has approximately the same shape as the product. The tree is then soaked in a slurry consisting of zircon flour, colloidal silica as a binder, and a surfactant.
After forming a uniform coating layer on the surface, immediately sprinkle zircon sand powder as refractory powder evenly over the entire surface and dry. Repeat this several times to coat the entire surface of the tree with refractory powder. Form a thick layer. After sufficiently air-drying it, it is heated with pressurized steam to cause the wax inside to flow out, and as shown in Figure 2, it has a casting space inside that has approximately the same shape as the product and is breathable. Obtain a certain ceramic shell mold (1). Also, this shell mold (1)
There is a flat sealing surface (2a) on the top of the sprue (2).
Set it up. In this example, a shell mold (1
) was produced. Next, this shell mold (1) is preheated to 1050° C. or higher, and then placed in a suction box (3) as shown in FIG. At this time, the sprue (2) of the shell mold (1)
The sealing surface portion (2a) of the suction box (3) is brought into contact with the sealing material (3b) provided around the upper opening (3a) portion of the suction box (3). Here, this suction box (3) is vertically provided with a vertically movable mold support (3c) in its inner lower part, and a shell mold (3c) on the inner peripheral wall above the mold support (3c).
1) is equipped with a heater (3d) around it. Further, a hollow case (4) is integrally provided below the suction box (3), and the hollow case (4) and the suction box (3) are connected to a solenoid valve (5a). They are connected via a suction tube (5). Further, a branch pipe (5b) is provided in a portion of the suction pipe (5) closer to the suction box (3) than the solenoid valve (5a). Subsequently, the suction box (3) incorporating the preheated shell mold (1) is placed together with the hollow case (4) in the airtight chamber (7) of the vacuum melting setup @ (6) as shown in Figure 1. Charge and place. Here, this vacuum melting equipment (6) is equipped with a high frequency melting furnace (8) in its airtight chamber (7), a vacuum pump (9) that evacuates the airtight chamber (7), and a vacuum pump (9) that evacuates the airtight chamber (7). 7) and a gas supply tank 00 for supplying inert gas. Next, a back pressure pipe 00 communicating with the gas supply tank 0 [I] and equipped with a valve (Ila) in the middle thereof is connected to the branch pipe (5b) of the suction pipe (5), while the suction box (3
) is connected and communicated with an external energizing means (not shown here). After that, the pressure inside the airtight chamber (7) is reduced to a predetermined degree of vacuum. Then, vacuum melting of the raw materials loaded into the high frequency melting furnace (8) is started, but in parallel with this, the heater (3d) of the suction box (3) is energized to melt the shell mold (
+) to a temperature of 1050°C or higher, evacuating the inside of the shell mold (1) and the suction box (3), and turning off the magnetic valve (5a) of the suction pipe (5). At the same time, the hollow case (4) is opened and the pressure inside the hollow case (4) is reduced to a vacuum. At this time, the back pressure pipe (l1)
The valve (lla) is kept closed. In the vacuum melting of this example performed as described above, Ni-based sardine alloy (
While loading the raw materials for Inconel 713C into the high-frequency melting furnace (8), the inside of the airtight chamber (7) was
The raw material was rapidly melted by reducing the pressure to less than 1 torr. Next, when this vacuum melting is completed, the solenoid valve (5a) of the suction pipe (5) is operated to close to block the communication between the suction box (3) and the hollow case (4), and the gas supply Ar gas is fed into the airtight chamber (7) from the tank 00), and the internal pressure in the airtight chamber (7) is set to 400 torr.
Let the atmosphere be r. At this time, the inside of the shell mold (1) and the suction box (3) are also in an Ar atmosphere with the same pressure as the inside of the airtight chamber (7), but the hollow case (4) whose communication with the suction box (3) is blocked is Inside is almost 0. 1
The vacuum level remains at torr. Next, the molten Ni-based superalloy in the high-frequency melting furnace (8) is injected into the casting space of the shell mold (1) through the sprue (2), but at the same time as the injection of this molten metal starts, the suction pipe (
5) Open the solenoid valve (5a) to suck the Ar gas in the suction box (3) into the low-pressure hollow case (4). At this time, even if the start timing of this suction is shifted a little earlier, the sprue (2) of the shell mold (1) is quickly blocked by the injected molten metal, so the casting space inside the shell mold (1) is is also suctioned under reduced pressure. Then, the injected molten metal is pressurized from the sprue (2) side into the mold due to the internal pressure difference between the hollow case (4) and the airtight chamber (7), and at the same time, the shell is depressurized and suctioned. Since the liquid is sucked into the casting space in the mold (1), good circulation is obtained in the casting space, and it is possible to reliably and uniformly fill the tip of the impeller blade, which is thin with a thickness of 1++n. Note that even after the molten metal has spread into the shell mold (1) and completely filled the casting space, an internal pressure difference is maintained between the hollow case (4) and the airtight chamber (7).
There is a risk that the shell mold (1), whose strength has decreased due to the heat of the molten metal, may be damaged and cause leakage or deformation of the cast product, so in this example, the casting space in the shell mold (1) is When enough molten metal is injected to completely fill the tank, the valve (
lla) was opened and Ar gas was supplied into the suction box (3) to eliminate the internal pressure difference between the hollow case (4) and the airtight chamber (7). The impeller obtained by the suction casting method of this example performed as described above has the desired precise dimensions and shape. Upon close inspection of the surface of the boss, no quality deterioration due to oxidation was observed as there was no contact with the atmosphere during the entire process of melting and casting. In this example, a hollow case (4) with a relatively large internal volume is provided, and when the injection of molten metal is completed, Ar gas is fed into this hollow case (4) to apply back pressure. However, this was done in accordance with the target product shape and the characteristics of the shell mold (1), and the first one in the suction box (3). The inner volume may be sufficient for lIN pressure reduction, and when the injection of molten metal is completed, instead of supplying Ar gas into the suction box (3) to apply back pressure, an airtight chamber (7) may be used. You can reduce the pressure inside. Furthermore, backup particles may be filled in advance around the shell mold (1) in the suction box (3) as long as air permeability is not hindered. Furthermore, the shell mold manufacturing method applied in this example is just one example, and other molding methods may be applied as long as a shell mold with air permeability can be obtained. In addition, we used vacuum melting equipment equipped with a single airtight chamber, but if this is equipped with both a melting airtight chamber and a casting airtight chamber, a suction box incorporating a shell mold inside the casting airtight chamber. Then, the molten metal vacuum-melted in the melting airtight chamber is injected into the shell mold in the casting airtight chamber in the same manner as described above. On the other hand, if the vacuum melting equipment is equipped with a single, relatively small airtight chamber, and it is not possible to insert a suction box or hollow case incorporating a shell mold into the airtight chamber, For example, as shown in FIG. 4, which is an explanatory diagram of another embodiment of the present invention, a slide gate (a sliding gate that penetrates the inside and outside of the airtight chamber (41) of the vacuum melting equipment (40) and that can be opened and closed) ( 41a) is provided, and a suction box (3) having the same structure as that of the above-mentioned embodiment and in which the shell mold (1) is incorporated is provided, and the upper opening (3a) is connected to the opening of the slide gate (41a). and the upper surface of the upper opening (3a) is placed in airtight contact with the lower surface of the periphery of the opening of the slide gate (41a) via the enclosing sealing material (42). ,
Even in a relatively small-scale vacuum melting facility, suction casting with the same effect as the above embodiment can be performed. here,
This vacuum melting equipment (40) is equipped with a high frequency melting furnace (43), a vacuum bomb (44), and a gas supply tank (45), as in the previous embodiment. Additionally, in this example, a suction pipe (46) equipped with a solenoid valve (46a)
The hollow case (4), which is communicated with the suction box (3) through the suction box (3), is not provided integrally below the suction box (3) as in the previous embodiment, but is provided independently. be.

〔Effect of the invention〕

As described above, according to the suction casting method of the present invention, vacuum-melted molten metal can be suction-casted into a shell mold in an inert gas atmosphere, thereby preventing quality deterioration due to oxidation of the molten metal. It is possible to easily adjust the pressure difference between the pressure on the sprue side of the shell mold and the pressure in the suction box during suction casting, and to ensure the suction effect in the shell mold of molten metal. As a result, thin-walled, complex-shaped parts made of active metal materials such as Ni-based superalloys can be stably cast with precision and high quality. In addition, since the pressure in the suction box is reduced by the vacuum evacuation means attached to the vacuum melting equipment, a dedicated vacuum pump is not required and equipment costs can be kept low.

[Brief explanation of the drawing]

FIG. 1 is a conceptual explanatory diagram of a suction casting method according to an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams according to the present invention, and FIG. 4 is a conceptual diagram of a suction casting method according to another embodiment of the present invention. Figure 5 is a conceptual diagram of the conventional suction casting method. (l) One shell mold, (2) One outlet, (3) One suction box, (4) One hollow case, (5) One suction pipe, (5a
) - Solenoid valve, (6) one vacuum melting equipment, (7) one airtight chamber, (8) one high frequency melting furnace, (9) one vacuum pump, 0
0) - Gas supply tank. Patent applicant Kobe Steel, Ltd. Agent Patent attorney Shoichi Kanemaru

Claims (1)

[Claims] A shell mold having air permeability is airtightly assembled in a suction box except for the sprue opening thereof, and a hollow container is provided which communicates with the suction box in an openable and closable manner, while the sprue opening of the shell mold is arranged to open toward the inside of an airtight chamber having a melting furnace therein, and when the melting furnace vacuum melts raw materials, the airtight chamber and the hollow container are communicated through the shell mold and the suction case. , the inside of this hollow container is reduced to a vacuum, and then the communication between the suction box and the hollow container is closed, and an inert gas is supplied into the airtight chamber to increase the inside of this airtight chamber and the suction box. After the molten metal is vacuum-melted in the melting furnace, it is injected through the sprue of the shell mold, and the suction box and the hollow container are communicated with each other to vacuum the inside of the suction case. Suction casting method.