JPH07204826A - Casting method and casting apparatus - Google Patents

Abstract

PURPOSE:To avoid the contamination by a crucible and to obtain a cast product having unidirectional solidification by water-cooling a bottom wall of a vacuum chamber, cooling molten metal from the bottom part of a cavity in a mold and also, heating the mold to form the temp. gradient. CONSTITUTION:The pressure in the vacuum chamber 4 is reduced to introduce the molten metal into the cavity in the mold 5. The solidification of the molten metal contacting with the bottom wall of the vacuum chamber 4 is progressed gradually upward, but as the mold is heated, the solidification except the bottom surface is slowly progressed. On the other hand, the metal in a snout is solidified 9 in comparatively quick speed. The vacuum chamber 4 is ascended in a sleeve 3 and the snout is pulled in the inner part of the sleeve 3 and moved to the side direction from the upper part of a melting furnace. While continuing the cooling of the bottom wall of the vacuum chamber 4 at the separated position, a heated holding cylinder 7 is gradually ascended and the solidification is slowly progressed toward the upper part from the lower part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for precision casting of metal by suction casting using a ceramic shell mold, and an apparatus used for carrying out the method. Provide technology to facilitate. The present invention is particularly useful for manufacturing cast products such as turbine blades that require toughness.

[0002]

2. Description of the Related Art Turbine blades are often manufactured by precision casting using a ceramic shell mold manufactured by the lost wax method. Its crystal structure is unidirectional (D
The S) and the single crystal (SC) are preferable, but they can be produced only by casting.

The DS type and SC type blades that are currently being cast are prepared by melting the metal in a vacuum induction melting furnace, casting the molten metal into a preheated lost wax mold, and casting it at the bottom of the mold. This is done by cooling with a water-cooled chiller placed and proceeding to solidify upward. Another technique is to melt the metal in a crucible with an opening in the bottom,
At the same time as the meltdown, casting is performed in a mold placed below the crucible.

The precision casting method of such a turbine blade has a problem that the molten metal is first contaminated by the crucible mainly composed of oxide. Contamination impairs the mechanical properties of cast turbine blades. Further, performing the melting and casting under vacuum complicates the operation and maintenance of the vacuum device, and as a result, it is difficult to improve the efficiency. It takes a long time for the cast molten metal to solidify, which also reduces productivity. If the capacity of the melting furnace is increased as a countermeasure, it is possible to cast a large number of molds with one melting, but this is disadvantageous because the apparatus cost increases.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to produce precision castings, typified by turbine blades, which have directional solidification or single crystals, and which are clean and therefore have good mechanical properties. It is an object of the present invention to provide a method and an apparatus capable of efficiently producing a product that fully exhibits the characteristics of a material alloy without requiring an unreasonable equipment cost.

[0006]

The casting method of the present invention is a suction casting method using a ceramic shell mold, wherein a mold having an open bottom is placed on the bottom wall of a vacuum chamber, and the mold cavity is formed by the bottom wall and the mold. After cooling at least the bottom wall of the vacuum chamber and heating the mold from the surroundings, the molten metal prepared in the melting furnace is sucked up and cast, then the heating of the mold is gradually reduced from the lower part of the mold to the upper part. Or by stopping and gradually lowering the temperature of the cast metal while maintaining a temperature gradient that increases from the bottom of the mold to the top of the cast metal, the solidification of the cast metal is lowered. It is characterized in that it is designed to proceed in one direction from above to above.

In a preferred embodiment, the molten metal is sucked and cast using a snout of the same material as the molten metal, and when the molten metal solidifies in the snout, the vacuum chamber containing the mold is placed on the melting furnace. Then, the solidification of the metal is promoted in another place by moving from, and then suction casting is successively performed by another set of the mold and the vacuum chamber. This enables continuous operation.

The casting apparatus of the present invention has a table having an opening, a means for supplying molten metal to be cast provided below the opening, a sleeve placed on the table, and an airtight seal between the sleeve and the sleeve. A vacuum chamber that can be lifted and lowered while maintaining at least a bottom wall with cooling means, a ceramic shell mold that has a bottom opening and that is arranged on the bottom wall of the vacuum chamber and forms a casting cavity with the bottom wall, A heater with a control means that heats the mold from its surroundings and gradually reduces or stops heating from the lower part of the mold upward, and from the bottom wall of the vacuum chamber to suck molten metal into the mold for casting. And a vacuum suction means for reducing the pressure in the vacuum chamber.The cast molten metal is heated by the heater. A configuration the casting apparatus to a unidirectional solidification from the bottom to the top of the mold by the control of.

In a preferred embodiment of this apparatus, the sleeve is slid laterally on a table to move it from above the molten metal supply means, and a pair of a vacuum chamber and a sleeve having another mold is placed in the next injection chamber. For the mould, it is provided with means for carrying one after another on the means for supplying the molten metal. Thereby,
Continuous operation is possible.

[0010]

EXAMPLE A typical example of the casting apparatus of the present invention is shown in FIGS. This casting apparatus comprises a table (1) having an opening (11) and a molten metal to be cast below the opening.
On the table (1), the levitation melting furnace (2) using the supply means of (8), in the example shown, a split type water-cooled copper crucible (21) and an induction heating coil (22) surrounding the outer periphery thereof. A vacuum that has a cylindrical sleeve (3) to be placed and can move up and down while keeping airtight between the sleeve and the sleeve, and has a cooling water flow path (42) as a cooling means at least on the bottom wall (41). A chamber (4), a ceramic shell mold (5) which is open at the bottom and which is arranged on the bottom wall of the vacuum chamber and forms a casting cavity (51) with the bottom wall, the mold being heated from its surroundings , A heater (71) having control means capable of reducing or stopping heating from the lower part of the mold to the upper part in sequence
And a snout (6) extending downward from the bottom wall of the vacuum chamber for sucking and casting molten metal into the mold, and a suction means (not shown) such as a vacuum pump for reducing the pressure in the vacuum chamber. It consists of a vacuum suction pipe (73).

The sleeve (3) is for guiding the vacuum chamber (4) so that it can be moved up and down, and does not need to have a continuous shape over the entire circumference unless there is a problem in controlling the atmosphere. Bottom wall (4) of the vacuum chamber (4)
1) The cooling water flow path (42) provided inside the water supply port (44)
To the drainage port (45) through the communication path (43). Water inlet (44) and drain (4
5) can be located below the illustrated example by providing a vertical cut (not shown) in the sleeve (3). Bottom wall of vacuum chamber (4)
At the center of (41), there is provided a cylindrical hanging part (46) for receiving the runner (52) of the mold (5) and supporting the upper end of the snout (6).

[0012]

In order to control the heating of the mold, the heater surrounding the mold may be divided into several parts in the vertical direction, and the power supply may be stopped or reduced in order from the bottom. And a heater (71)
The heater holding cylinder (7) may be provided inside a heater holding cylinder (7) having a lid-like cylindrical shape that is vertically movable in the vacuum chamber, and the heater holding cylinder (7) may be gradually raised. The inside of the holding tube (7) is lined with a heat insulating material (72). The vacuum suction pipe (73) is preferably provided on the upper surface of the holding cylinder.

As is well known, the formation of a single crystal is carried out by selectively growing by a selector one of several crystals that are growing due to the progress of directional solidification. In the present invention, the narrowed portion between the upper portion of the snout of the molten metal passage and the mold cavity may be used as a selector for forming a single crystal.

As shown in FIG. 1, when the snout (6) is put into the molten metal (8) and the inside of the vacuum chamber is depressurized by sucking it from the vacuum suction device, the molten metal passes through the snout to form the mold ( It is guided into the cavity of 5). The molten metal that has entered the cavity immediately solidifies at the portion in contact with the bottom wall (41) of the vacuum chamber that is being cooled, as shown in FIG. 3, and solidification gradually progresses upward. Since the mold is heated, solidification of the molten metal in the cavity progresses slowly except for the bottom surface.

On the other hand, the metal in the snout solidifies relatively quickly. Then, the vacuum chamber (4) is raised in the sleeve (3), the snout is retracted into the sleeve, and is moved laterally from above the molten metal supply means, that is, the melting furnace (2), as shown in FIG. Can be moved to another location. While continuing to cool the bottom wall of the vacuum chamber at another place, the heater holding cylinder (7) is gradually raised so that the solidification proceeds from bottom to top as shown in FIG.

It takes a long time to take out a cast product from the mold, because it is necessary to slow the cooling not only for forming a single crystal but also for unidirectionally solidifying a polycrystal. Therefore, a new set of vacuum chamber and sleeve containing the mold may be successively carried onto the melting furnace (2), and suction and casting may be continued. After the solidification is completed, the mold is taken out, a new note and mold are attached to the vacuum chamber, and the mold is recycled. The path for circulating the set of the vacuum chamber and the sleeve may be either on the circumference or on a straight line (reciprocating).

[0017]

According to the present invention, precision castings such as turbine blades can be manufactured with high efficiency while avoiding contamination of the melting crucible. The device is not very complicated,
As for the capacity of the melting furnace, it is sufficient to supply the molten metal required for one casting, so the equipment cost does not become excessive. Therefore, the casting cost can be kept low.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing an example of a casting apparatus of the present invention.

2 is a cross-sectional view of the device of FIG. 1 in the AA direction.

FIG. 3 is a slightly simplified vertical cross-sectional view for explaining an operating condition of the apparatus of FIG.

FIG. 4 is a vertical cross-sectional view subsequent to FIG. 3 for explaining the operating state of the apparatus of FIG.

[Explanation of symbols]

1 Table 2 Melting Furnace 3 Sleeve 4 Vacuum Chamber 41 Bottom Wall 42 Cooling Water Flow Path 43 Communication Channel 44 Water Supply Port 45 Drainage Port 5 Ceramic Shell Mold 51 Mold Cavity 52 Water Run 6 Snoto 7 Heater Holding Cylinder 71 Heater 72 Insulation 73 Vacuum Suction Pipe 8 Molten metal 9 Solidified metal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B22D 27/04 A

Claims (7)

[Claims] 1. A suction casting method using a ceramic shell mold, wherein a mold having an open bottom is placed on the bottom wall of a vacuum chamber to form a mold cavity with the bottom wall and at least the bottom wall of the vacuum chamber. After cooling and heating the mold from the surroundings, the molten metal prepared in the melting furnace is sucked up and cast, then the heating of the mold is gradually reduced or stopped from the bottom of the mold to the top, and the cast metal is cast. By gradually decreasing the temperature of the cast metal while maintaining a temperature gradient that rises from the bottom to the top of the mold, solidification of the cast metal proceeds in one direction from bottom to top. A casting method characterized by the above. 2. The suction casting of the molten metal is performed using a snot of the same material as the molten metal, and when the molten metal solidifies in the snort, the vacuum chamber containing the mold is moved from above the melting furnace. 2. The casting method according to claim 1, wherein the continuous operation is made possible by advancing solidification of the metal at another place and then successively performing suction casting with another set of the mold and the vacuum chamber. 3. The casting method according to claim 1, wherein the unidirectional solidification is the formation of a single crystal. 4. A table having an opening, a means for supplying molten metal to be cast provided below the opening, a sleeve placed on the table, and the inside of the sleeve can be moved up and down while maintaining airtightness between the sleeve and the sleeve. There is a vacuum chamber with a cooling means at least on the bottom wall, a ceramic shell mold that has an opening at the bottom and is placed on the bottom wall of the vacuum chamber to form a casting cavity with the bottom wall, and this mold from its surroundings. A heater having a control means capable of heating and sequentially reducing or stopping the heating from the bottom of the mold upward, a snout extending downward from the bottom wall of the vacuum chamber for sucking and casting molten metal into the mold, and It consists of vacuum suction means for decompressing the inside of the vacuum chamber, and the cast molten metal is controlled by the heater to control the heating of the mold. A casting device configured to perform unidirectional solidification from the bottom to the top. 5. The sleeve is slid laterally on the table to move it from above the molten metal supply means, and the set of vacuum chamber and sleeve provided with another mold is melted for the next casting. 6. The casting apparatus according to claim 5, further comprising means for carrying one after another on the means for supplying metal. 6. A heater for heating the mold is provided inside a heater-holding cylinder having a cylindrical shape with a lid, which is vertically movable in a vacuum chamber, and the mold is heated by gradually raising the heater-holding cylinder. The casting apparatus according to claim 5, wherein the casting apparatus is configured to be controlled. 7. The casting apparatus of claim 5 wherein the narrowed portion of the molten metal passage between the snout top and the mold cavity acts as a selector for single crystal formation.