JPH0569620B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a calcia core or mold suitable for casting active metals such as titanium and zirconium, alloys thereof, or high melting point metals such as chromium and vanadium. The present invention relates to a method for preventing hydration.

[Prior Art] Calcia refractories are thermodynamically stable even at high temperatures and have a unique refining action, so the present inventors have proposed that they can be applied to the melting of various high-melting point metals and highly active metals. This is becoming clear.

According to the infusion method proposed by the present inventors, both high activity and/or
Alternatively, high melting point metals can be easily melted. Moreover, the obtained molten alloy is extremely clean.

Therefore, in order to obtain a highly clean cast body, it is necessary to melt a highly clean molten metal and use a mold that does not contaminate the molten metal.

Conventionally, molds for casting active metals such as titanium or zirconium (including alloys) have been used.
Known types include the rammed type, investment type, water-cooled copper type, and sand type (using zircon sand, olivine sand, etc.). The Lambed type uses graphite powder as an aggregate.
It is baked after molding and drying with a carbon-based or resin-based binder. Investment molds include tungsten powder coated molds, which use tungsten in a slurry and a metallic binder, oxide molds, which combine oxide slurry with an oxide binder, and There are three types of graphite molds made by hardening graphite-based slurry with a carbon-containing binder.

In addition, as mold materials for titanium or titanium alloys, hardening accelerators such as alkali metal hydrogen carbonates and aluminum powder are added to pure magnesia or magnesia mold materials whose main component is magnesia, or aggregates whose main component is magnesia. Mold materials are also known (Japanese Patent Publication No. 58-5749, Japanese Patent Publication No. 59-59-
218237).

[Problems to be Solved by the Invention] However, when active metals are cast into these molds, a reaction occurs with the mold material, and carbon is generated in the case of graphite mold materials, and carbon is generated in the case of graphite mold materials, and In the case of molds, oxygen contamination occurs, resulting in contamination of the casting surface. Furthermore, among the investment types, those based on oxide binders have intrusion of not only oxygen but also nitrogen. Such contamination of the casting surface requires a step to remove the contaminated layer on the surface of the casting, making the casting process extremely complicated. Further, the casting method using water-cooled copper has the problem that the mold is expensive and easily worn out.

Furthermore, molds made of oxides or graphite other than water-cooled copper have high thermal conductivity, resulting in a low shrinkage position and a problem of poor casting yield. Furthermore, since these oxide-based or graphite-based molds are dense, they have low thermal shock resistance, are prone to cracking, have poor durability, and are unsuitable for repeated use. There was a problem.

As a result of repeated studies to solve these conventional problems, the present inventors found that if a mold or core made of calcia, which has a high melting point and is thermodynamically stable at high temperatures, is used, and/or that highly active metals or alloys containing the same can be easily cast, and that it is possible to obtain castings without contamination on the surface of the casting surface.

Calcia molds or calcia cores have the advantage of being able to cast highly clean castings, as well as making use of the digestibility (water solubility) of CaO to hydrate them, allowing the mold to be easily removed and the ingot to be taken out. It also has the advantage of being able to

However, the disadvantage of calcia molds or cores is that they cannot be stored in a normal atmosphere because of their high hydration properties, and must be stored at high temperatures or in a vacuum or moisture-free atmosphere. have.

[Means for Solving the Problems] The present invention solves the problems caused by the high hydration of the calcia core or mold, prevents the hydration of the calcia core or mold, and allows The present invention provides a method for preventing hydration of cores or molds made of calcia refractory material, which can be stored in water and used directly for casting. A calcia core characterized in that the core or mold is coated with a polymer membrane impermeable to H ₂ O molecules, and a portion inside the polymer membrane is placed in a vacuum or dry gas atmosphere. or a method for preventing hydration of a mold.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a sectional view showing a mold employing the present invention, and FIG. 2 is a sectional view showing a state in which molten metal is poured into the mold.

As shown in FIG. 1, the present invention provides a core or mold 1
is covered with a polymer film 2. The calcia refractory material constituting the core or mold according to the present invention is a refractory material containing CaO.
It is effective for calcia refractory materials with hydration properties, such as those whose main component is

The present invention uses such a calcia refractory material together with other components and, if necessary, a binder, through die forming, slip casting, rubber pressing,
It can be applied to a core or mold made into a sintered body by molding by injection molding, warm pressing, etc. and then firing. Furthermore, a mold may be formed for hot pressing or as a stamp material. Furthermore, the mold may be constructed by using it like ordinary foundry sand. In addition, the present invention can also be applied to a core or mold using the so-called V process, in which calcia refractory material powder or the like is directly filled into a polymer film, vacuum-suctioned, and molded under reduced pressure.

In the present invention, the H ₂ O molecule-impermeable polymer membrane 2 used may be any material as long as it does not allow H ₂ O molecules to pass through, and is not particularly limited. Preferably, it is inexpensive and thin enough. It is desirable to have elongation and strength, and to generate as little gas as possible when pouring the molten metal.

Examples of such polymer membranes include low-density polyethylene, high-density polyethylene, nylon,
Examples include thin films of ionomers, ethylene monovinyl acetate copolymers (vinyl acetate content 17% or 14%), polyvinyl chloride, polyvinyl alcohol, epoxy, and the like.

If such a polymer membrane is too thin, its strength etc. will be insufficient, and if it is too thick, a large amount of gas will be generated when molten metal is injected, which is undesirable. For this reason, the thickness of the polymer film is preferably about 0.03 to 0.3 mm, although it varies depending on the type.

In the present invention, the core or mold 1 is coated with such a polymer film 2, and at that time, as shown in FIG. 1, the polymer film 2 is brought into close contact with the core or mold 1 by vacuum suction. Alternatively, a dry gas, preferably an inert gas such as argon, is enclosed by coating the polymer film 2 in a dry gas atmosphere. Among these methods, the method of bringing the polymer membrane into close contact with the core or mold by vacuum suction prevents the mold from deforming, has a high protective effect, and is highly effective in cleaning the surface of the resulting casting. Therefore, it is more advantageous.

In addition, when the present invention is adopted for the core or mold by the above-mentioned V process, calcia refractory material powder is used as a raw material and a polymer membrane impermeable to H ₂ O molecules is used for casting the core or mold. The method of the present invention can be easily carried out by vacuum suction and molding.

In the present invention, when vacuum suction is performed,
It is preferable to set it to about 400 Torr or less. Also,
As a dry gas, the H ₂ O content is converted to 1 atm.
It is preferable that the amount is about 0.1 g/m ³ or less.

A core or mold that has been subjected to hydration prevention treatment according to the method of the present invention can be used for casting in exactly the same way as a normal core or mold. In use, as shown in FIG. 2, the polymer film evaporates due to the high temperature caused by the injection of the molten metal 3 and disappears without causing any trouble to casting.

[Function] A core or mold made of calcia refractory material is covered with a polymer membrane impermeable to H ₂ O molecules,
To create a vacuum or dry gas atmosphere inside,
Even if the core or mold is made of highly hydrated calcia, it can be stored well for a long period of time at normal temperature, normal pressure, and normal humidity without any deterioration in quality.

Furthermore, during its use, since the polymer film evaporates, the molten metal can be poured as is without any pre- or post-processing.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 Film thickness 0.04 on calcia template (CaO content 98%)
A polyethylene film of mm was coated and the polyethylene film was adhered by vacuum suction.

The mold that has been treated to prevent hydration is heated to 25°C.
After being left in air at 100% humidity for 30 days, the polyethylene membrane was removed and the wall surface was observed, but no changes had occurred, indicating that it had been stored well.

Comparative Example 1 A mold similar to that used in Example 1 was left under the same conditions without anti-hydration treatment. One day later, the wall surface was observed, and some areas were found to be damaged due to hydration of CaO.

From the above results, it is clear that the method of the present invention effectively prevents hydration of a core or mold made of calcia refractory material.

[Effects of the Invention] As detailed above, the method for preventing hydration of a calcia core or mold of the present invention provides a method for preventing hydration of a calcia core or mold by hydrating the core or mold with H ₂ O.
It is coated with a molecularly impermeable polymer membrane and has a vacuum or dry gas atmosphere inside, and can effectively prevent hydration of CaO with an extremely simple method.

Therefore, according to the present invention, under a normal atmosphere without requiring strict atmosphere control,
Cores or molds made of calcia refractory material can be stored well for a long period of time, which is extremely advantageous in terms of storage work, storage equipment, etc. In addition, when using the core or mold, the polymer membrane is vaporized and can be used as is without any pre- or post-processing, which is extremely advantageous industrially.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a mold employing the method of the present invention, and FIG. 2 is a sectional view showing a state in which molten metal is poured into the mold of FIG. 1. 1...mold, 2...polymer membrane, 3...molten metal.

Claims (1)

[Claims] 1 A method for preventing hydration of a core or mold made of calcia refractory material, which comprises covering the core or mold with a polymer membrane impermeable to H ₂ O molecules, and 1. A method for preventing hydration of a calcia core or mold, the method comprising applying a vacuum or dry gas atmosphere to the inner part of the calcia core or mold.