JPS63235044A - Mold for precision casting - Google Patents

Abstract

PURPOSE:To prevent invasion of gas into an inner tube at low cost and to obtain a casting without any defect by constituting molten metal siphon part of a mold for precision casting by an inner and outer tubes having gap at intermediate part composing of refractory. CONSTITUTION:In a lower chamber 2, a vacuum induction melting is executed by an induction furnace 4, to obtain molten metal 6. Next, Ar gas is sealed in the lower chamber 2 and by ascending the induction furnace 4, the molten metal siphon 5 is dipped. After that, the pressure in an upper chamber 1 providing the mold 3 connecting with the above molten metal siphon 5, is reduced to the prescribed vacuum degree. By this method, the molten metal 6 is sucked up to the mold 3 through the siphon 5 and poured, to execute casting. In the above lost wax type precision casting, the molten metal siphon 5 part consists of double tubes of refractory-made inner tube 51 and outer tube 52, and the lower end of the double tube is closed by refractory or is made to as opening- state. By this constitution, gas penetrating the outer tube 52 is released into the upper chamber 1 from the gap 53 between the inner and outer tubes 51, 52. By this method, the development of defect of pin hole, etc., in the casting is prevented.

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to an improvement of a lost wax precision casting mold. [Conventional technology] Products that require high precision, such as small turbine impellers, are generally manufactured by precision casting using lost wax molds using high alloy steel or nickel alloy. ! It is constructed. One of the representative technologies is a vacuum casting method called "rCLV method", which consists of the following steps. That is, as shown in FIGS. 1 and 2, a lost wax mold 3 having a molten metal suction pipe 5 is prepared in the upper chamber 1 of an apparatus having upper and lower chambers, and vacuum induction melting is performed in the lower chamber 2. Prepare molten metal by doing
The upper and lower chambers are filled with an inert gas such as A' to a predetermined pressure, the induction furnace 4 is raised, and the molten metal suction pipe is immersed in the molten metal 6, and the inside of the upper chamber 1 is maintained at a predetermined degree of vacuum. This is a series of steps in which the pressure is reduced to 100%, the molten metal 6 is sucked up and poured into the mold 3, the induction furnace 4 is lowered, the molten metal in the suction tube 5 is returned to the furnace, and the mold is taken out. As described above, lost wax molds are made by immersing a wax pattern, or in the case of small castings, a model called a "tree" in which multiple wax patterns are attached to a wax rod into slurry, pulling it up, and removing sand. It is manufactured by repeating the process of sprinkling and drying several times, and when the sand layer reaches the required thickness, it is heated to remove the wax and fired to create a strong mold. Using the lost wax mold manufactured in this way,
When a product having a thin wall part, such as a turbine impeller, is cast by the above CLV method, pinhole defects may occur in the thin wall part. This tendency is similar to T1, A, l! This is particularly noticeable when casting superalloys containing . This defect occurs because when the molten metal 6 is sucked up, gas such as Ar sealed in the lower chamber 2 passes through the molten metal suction pipe 5 and enters the molten metal, and is carried to the end of the mold 3. Conceivable. This is supported by the fact that when the molten metal suction tube 5 was made of an airtight fused silica tube in the production of lost wax molds, there were no defects. Needless to say, the mold is destroyed each time it is cast, while tubes of airtight refractory materials such as fused silica are expensive and therefore impractical. In industrial practice, it is desirable to use inexpensive refractory tubes such as sintered chamotte or mullite. However, since fired crystals are inevitably porous to varying degrees, defects in cast products cannot be eliminated.

[Problems to be solved by the invention]

The purpose of the present invention is to solve the above-mentioned problems and to provide a lost-wax precision casting method that does not cause defects in the cast product even if a refractory tube that is inexpensively available on the market is used as a molten metal suction pipe. The objective is to provide molds for In other words, it is necessary to achieve both mold performance and low cost requirements. 1 Kawa no Sato L

[Means to solve the problem]

The precision casting mold of the present invention, which achieves the above-mentioned object, consists of immersing a wax pattern in slurry, pulling it up, repeating the operations of sprinkling sand on it, and then melting and removing the wax.
In a lost-wax precision casting mold for producing a mold 3 as shown in FIGS. 1 and 2 by a method such as firing, the molten metal suction pipe 5 part of the mold is replaced with an inner pipe 51 and an outer pipe made of refractory material. It is characterized by having a double structure of 52. The refractory tube constituting the molten metal suction pipe may be made of chamots or mullite as described above. Of course, alumina and other materials are also suitable. The lower end of the double tube may be closed, as shown in FIG. 1, or open, as shown in FIG. If the seal is to be sealed, it is not necessary to mold it into the shape shown in FIG. You can create something similar by injecting refractory slurry and sealing it. The upper end of the double tube may be buried in the mold 31 as shown in FIG. 1, or a ventilation hole 55 may be provided in the outer tube 52 as shown in FIG. In this way, the outer tube 52 may be made shorter than the inner tube 51 so that the upper end thereof is not buried in the mold, and the gap 53 is opened into the upper chamber.

[For use]

When the lower end of the double pipe is sealed by making the suction pipe a refractory inner and outer double pipe structure, the lower chamber 2
Even if the gas permeates through the outer tube 52, it is sucked out into the upper chamber through the gap 53. As a result, gas is prevented from entering the inner tube. This effect was confirmed by applying a pressure of 500 mHg, which is almost the same as the pressure difference between the inside and outside during vacuum casting, to a double tube structure made by combining two mullite tubes with different diameters, and measuring the air permeability. , was confirmed to be zero. If the lower end of the double pipe is open, the molten metal will enter part or all of the gap 53, but in this case, the part where the molten metal has entered will be affected by this, and the part where it has not entered will be Now, with the same temple structure as above due to the gap, mold 3
Gas can be prevented from entering the interior. The penetration of the molten metal 6 into the gap 53 also provides a reinforcing effect against cracks in the double pipe.

【Example】

Wax-shaped tree for casting turbine impellers for automobile engine turbochargers (30 pieces)
We prepared several pieces, cut them into three sides, and made lost wax molds for each as described below. 1) The tree was dipped in a pre-coat slurry in which ethyl silicate and zircon flour were suspended, and the tree was pulled up and sprinkled with sand. 2) Mullite large-sized outer tube (inner diameter 60m, wall thickness 5I)
nIn) and an inner tube (outer diameter 60 m, wall thickness 5 tone), inject refractory into one end and seal it to create an inner and outer double tube, 1)
I did the same process. At that time, immersion was performed until the open ends of the suction tubes slightly overlapped, so that the lost wax mold and the suction tubes were integrally connected. 3) A mold was made in the same manner as in 2) except that the lower end of the double tube was not sealed. Using these three types of lost wax molds, N1 alloy (INCo 713C) was cast by the CLV method,
Manufactured turbine impellers. We looked at the pinhole incidence in each product group and obtained the following results. Mold 1) 10.5% Mold 2) 0% Mold 3) 0% The lost-wax precision casting mold of the present invention has a double structure in the molten metal suction pipe, so vacuum casting is possible. Even if external gas permeates through the outer tube due to the pressure difference between the inside and outside at the time, it can be handled into the upper chamber through the gap, or the external gas can permeate through the outer tube due to the molten metal that has entered the gap. This prevents gas from entering into the inner tube. As a result, castings obtained using the mold of the present invention have almost no defects such as pinholes or edge chips. Since the material of the molten metal suction pipe may be a sintered refractory tube that is inexpensively available on the market, the manufacturing cost of the mold does not increase.

[Brief explanation of drawings]

1 and 2 are conceptual cross-sectional views of the mold used for explaining the present invention in detail. The cases where the following molds were used are shown. FIG. 3, FIG. 4, and FIG. 5 are all sectional views corresponding to FIG. 1, showing other embodiments of the mold of the present invention. 1... Upper chamber 2... Lower chamber 3... Mold 4... Induction furnace 5... Molten metal suction pipe 51... Inner pipe 52... Outer pipe 53... Gap 6... Molten metal patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga Figure 1 Figure 3 Figure 4

Claims (3)

[Claims] (1) A lost wax precision casting mold, characterized in that the molten metal suction pipe portion of the mold has a double inner and outer refractory pipe structure. (2) The mold according to claim 1, wherein the lower end of the double pipe is sealed with a refractory. (3) The mold according to claim 1, in which the lower end of the double pipe is open.