JPS63140740A - Mold for casting active metal of high melting point - Google Patents

Abstract

PURPOSE:To restrain the reaction of a molten metal and mold and to prevent the generation of a surface hardening and the internal defect on a casting product by coating the powder of W, Mo, etc. on the cavity part coming into contact with the molten metal of a high melting point active metal of a mold consisting of a silica sand, zircon sand, etc. CONSTITUTION:One kind among a silica sand, zircon sand, mullite sand, chamotte sand and morrokite sand is used and stirred by mixing with a water glass, etc., and a mold is formed by an ordinary method. The powder of one kind selected among W, Mo, Nb, Ta and these oxides and Y2O3 is then coated by using a solvent on the cavity part bringing into contact with the molten metal (Ti or Ti alloy, etc.) of active metal of high m.p. of this mold. The necessary mold is then manufactured by sufficiently baking this mold at about 800-1,200 deg.C by its drying. In case of casting the high m.p. active metal by using this mold the reaction with the mold is restrained and a sound casting product is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a method for suppressing the reaction with the M-type and producing sound cast products in the casting of high melting point active metals, such as titanium or titanium alloys. It is related to molds.

[Conventional technology]

When casting active metals with high melting points such as titanium or titanium alloys, the metal in the molten state reacts with the #8 mold material, and the reaction layer hardens, making machining difficult and causing defects inside the cast product. This is because when the mold material is graphite, titanium carbide is created, and when the mold material is an oxide, this oxide is reduced and oxygen is dissolved into the titanium or titanium alloy. .

Casting methods for titanium or titanium alloys are broadly divided into the lambda graphite method and the investment precision casting method.

The former involves filling a model with graphite grains mixed with a binder, compacting them, and then removing the model to form a mold, and is used to manufacture medium to large castings that do not require high dimensional accuracy. It is used for.

For the latter, a wax pattern similar to that of the cast product is manufactured, which is immersed in a refractory slurry and then sprinkled with refractory granules to form a layer.This process is repeated several times, and when the thickness reaches 6 to 10 mm, wax is applied. This method eliminates the pattern and creates an R shape, and is used for casting and manufacturing 9 of complex shapes with high dimensional accuracy.

In addition, a method of making a mold using chromite sand in the same manner as a normal mold manufacturing method has been developed.

[Problem that the invention seeks to solve]

The above conventional method has the following problems.

In the lambda graphite method, the reaction layer of titanium carbide produced by the reaction between graphite and titanium or titanium alloy molten metal is thick and requires a great deal of effort to remove.

Investment precision casting requires special equipment and technology to produce molds.

The present invention aims to provide a mold that solves the above problems at the same time.

[Means for solving problems]

The present invention applies to a cavity portion of a mold made of silica sand, zircon sand, mullite acid, molochite sand, or chamotte sand, which is in contact with a molten metal having a high melting point.

A technical means for solving the problem is a mold for casting active metals with a high melting point, which is constructed by applying powder of any one selected from W, Mo, Nb, Ta, their oxides, and Y2O3. be.

[Effect]

Since the coating layer of the mold of the present invention comes into contact with the molten metal having a high melting point, the reaction between the molten metal and the mold is suppressed, preventing surface hardening and preventing internal defects in the cast product.

Furthermore, the mold of the present invention is easy to manufacture. In other words, in the same way as the general sand mold making method, the model is fixed on a surface plate, a casting flask is placed around it, and after filling the molding sand and compacting it, the flask is turned upside down. Then remove the model and use it as a mold. Next, a substance that does not react with the molten metal or reacts only to a small degree is applied to the mold cavity that comes into contact with the molten metal. As such a substance, one selected from W, Mo, Nb, Ta, oxides thereof, and Y2O3 is used.

This mold can prevent reactions from easily occurring at the contact surfaces between the mold material and the molten metal when titanium or titanium alloy molten metal is poured into the mold.

Figure 1 schematically shows the mold of the present invention.
A coating layer l is formed inside the cavity.

Next, the molding method of the present invention will be explained according to the flowchart shown in FIG.

A wooden, synthetic resin, or hard rubber model made considering the solidification shrinkage rate and thermal expansion coefficient of titanium or titanium alloy and the thermal expansion coefficient of the mold is fixed to a surface plate, and a casting flask is erected around it. . One type of silica sand, zircon sand, mullite acid, molochite sand, or chamotte sand is used as the aggregate, and one type of water glass, silica sol, alumina sol, or zirconia sol is used as the binder, and furan and phenol are used as necessary. These organic binders are mixed, stirred, and filled into the flask.

At this time, use a hardening agent if necessary. After the mold material has hardened, the model is demolded. Also, remove the flask if necessary.

In the cavity of the mold obtained by the above method, W
, M o , N b , Ta and their oxides, and any one type of powder selected from Y2O3 powder is mixed with water, an organic solvent such as alcohol or acetone, and one type of silica sol, alumina sol, or zirconia sol as a solvent. After coating and drying of the solvent, the mold cavity is coated with the high melting point metal or fermentation powder.

An upper mold, a lower mold or, if necessary, a core are prepared by the above method, and these are combined to form a set of molds.

The above-mentioned mold is sufficiently fired in an atmospheric furnace or reducing atmosphere furnace at 800 to 1200°C to remove moisture or organic matter, or to increase the strength of the mold by sintering between sand particles. Used for pouring molten metal.

When pouring titanium or titanium alloy, the temperature of the mold may be at room temperature or higher.

Further, the casting method may be gravity casting, pressure casting, or centrifugal casting.

〔Example〕

Example 1 As aggregate for mold material, 5f02:53% by weight, AJlj
2Oa: 42% by weight sintered clay sand (chamotte sand)
(particle size: 0.3 to 1.0 mm), and as a binder, 8 parts by weight of water glass was added to 10 parts by weight of chamotte sand, and the outer diameter was 80 mm using the CO2 gas method.
A mold with a height of 60 mm, an inner diameter of 40 mm, and a depth of 40 mm was molded.

A slurry prepared at a ratio of 2 parts by weight of Y2O3 powder and 1 part by weight of alumina sol was applied to the mold cavity to a uniform thickness.

After drying, it was fired at 1200° C. in an air atmosphere using an electric furnace, and pure titanium was cast into a mold that was lowered to room temperature using an argon arc melting pressure casting machine.

The cast surface condition, tensile strength, elongation, and hardness of the titanium cast material after casting were measured, and the results shown in Table 1 were obtained. × according to the judgment in Table 1
indicates an unusable state, O indicates a usable state, and Δ indicates a usable state with some problems.

Example 2 A mold was formed in the same manner as in Example 1, and a slurry prepared by mixing W powder at a ratio of 4 parts by weight to 1 part by weight of zirconia sol was uniformly applied to the inner surface of the mold to various thicknesses. did.

After drying, 12O0 was added in a reducing atmosphere using a hydrogen atmosphere furnace.
Pure titanium was cast into a mold fired at .degree. C. and then cooled to room temperature using an argon arc melting pressure casting machine, and the results shown in Table 2 were obtained in the same manner as in Example 1.

〔Effect of the invention〕

Compared to conventional graphite molds or precision casting molds, the molding method is the same as the general sand molding method, so the molding technology is easier and the cost is lower.

When an oxide is used as the coating material, there is no need to use a vacuum furnace or a reducing atmosphere furnace as in conventional methods, and a normal atmospheric furnace can be used.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of the mold of the present invention, and FIG. 2 is a flowchart of its manufacturing process.

Claims (1)

[Scope of Claims] 1. W, Mo, Nb, Ta and their oxides, and Y are added to the cavity portion of a mold made of silica sand, zircon sand, mullite sand, molochite sand, or chamotte sand that comes into contact with the high melting point active metal molten metal.
A mold for casting high melting point active metals coated with one type of powder selected from _2O_3.