JPH02295668A - Ingot for casting - Google Patents

Abstract

PURPOSE:To obtain a casting product free from oxygen without coming into reaction with a crucible by forming thin nitride layer on outer surface except upper face of a material for casting having high activity at high temp. and on the outer surface of part set facing to inner face of the crucible at the time of heating in casting. CONSTITUTION:At the time of manufacturing an ingot 9, a high frequency induction heating coil is set facing to the whole outer surface except the upper face 23a of titanium material 23 and the outer surface is rapidly heated up to the prescribed temp. in a short time under nitrogen atmosphere. In this case, as the nitride layer 24 is allowed to remain as solid-state without melting, the molten titanium material 23 is not brought into contact with surface of recessed part 10 in the crucible 8 and the titanium material 23 is not oxidized by the reaction with the crucible 8.

Description

[Detailed Description of the Invention] a. INDUSTRIAL APPLICATION FIELD The present invention relates to ingots for casting, particularly materials with high high temperature activity. This invention relates to a casting ingot that is suitable for producing precision castings made of materials for dental purposes, plastic surgery, etc. b. Conventional technology Recently, as a material for precision casting for dentistry and plastic surgery,
Titanium, titanium alloys, etc., which have a low specific gravity, are widely used because they have excellent compatibility with living organisms and corrosion resistance, and are strong.

However, titanium has a high melting point of 1672°C, and at high temperatures it reacts strongly with oxygen and most other substances and deteriorates. As described above, titanium's biggest drawback is that it is highly active at high temperatures, and this property makes it extremely difficult to cast. In particular, oxygen forms a large amount of solid solution in titanium (solid solubility: 10% by weight or more),
This hinders the stretchability of titanium. Incidentally, if the solid solubility of oxygen exceeds only 0.7% by weight, the product becomes brittle and becomes undesirable as a cast product for dental purposes or the like.

By the way, the material of casting crucibles widely used at present is generally made of aluminum oxide (A j!t's> or magnelia (MgO), but in crucibles made of such materials, Oxygen cannot be used because it reacts with high-temperature titanium (reduction effect).For this reason, calcium oxide (Cab) or yttrium oxide (Yz), which does not easily react with titanium, cannot be used.
The current situation is that titanium is melted in as short a time as possible, and the reaction between the titanium and the crucible is suppressed as much as possible.

C. Problems to be Solved by the Invention However, when a casting ingot made of a material with high high temperature activity such as titanium is melted in a short time, the temperature of the molten metal is too low, which tends to cause defects in the hot water environment. This causes inconvenience. On the other hand, if you try to increase the melting temperature by increasing the heating time to solve this problem, the titanium material and the crucible will tend to react with each other, and the progress of oxidation of the titanium material will increase. That's what happens. The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to melt a titanium material or a titanium alloy material at an appropriate temperature, and to cause a reaction (oxidation and
It is an object of the present invention to provide a casting ingot that does not cause any reduction reaction (reduction reaction) and therefore allows obtaining a cast product that does not contain oxygen.

d. Means for Solving the Problems In order to achieve the above-mentioned object, in the present invention, the outer surface of the casting material with high high temperature activity excluding the upper surface, which is disposed opposite to the inner surface of the crucible during casting heating. A thin nitride layer is formed on the outer surface of the material. Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a precision casting apparatus 1 for producing dental cast products. Equipped with The upper container 2 includes a dome-shaped portion 2a and a flange portion 2b integrally formed at the lower end of the dome-shaped portion 2a.
The lower container 3 is composed of a cylindrical housing part 3a and a flange part 3b integrally formed on the upper end of the housing part 3a. Then, the upper container 2 and the lower container 3
The flanges 2b and 3b of the flange portions 2b and 3b are closely connected in an overlapping state to form one sealed container 4? The internal space is divided into upper and lower parts by partition walls 5 made of earthen walls of the lower container 3.

Thus, the upper part of the partition wall 5 is configured as a pressurized melting chamber 6, and the lower part thereof is configured as a reduced pressure casting chamber 7.

A crucible 8 made of aluminum oxide (An20,) made of aluminum oxide or the like is disposed in the pressurized melting chamber 6 . As clearly shown in FIG. 2, this crucible 8 has a recess 10 for accommodating a foundry ingot 9.
In FIG. 1, it is configured to be rotated in the direction of arrow A around an axis X extending perpendicular to the plane of the paper. Further, as shown in FIG. 4, a ground electrode l4 made of tungsten or the like is fitted onto the bottom wall of the crucible 8.

Further, an arc electrode 15 is provided on the ceiling of the upper container 2 mentioned above.
is attached, and power is supplied to this arc electrode l5 from an arc power supply circuit (not shown). On the other hand, a partition wall 5 that partitions the pressurized melting chamber 6 and the reduced pressure casting chamber 7
A cylindrical mold receiver 16 with a bottom that projects into the vacuum casting chamber 7 is integrally molded in the mold receiver 16, and a communication hole 17 is formed at the bottom of the mold receiver 16 to communicate the chambers 6 and 7 with each other. There is. A breathable mold 20 having a sprue l8 and a modeling cavity l9 is placed in the mold receiver 16, and the communication hole 17 is closed by the mold 20.

Note that the sprue l8 of the mold 20 opens upward, and the opening 2 formed in the mounting table 21 of the support member 12
2 is arranged correspondingly.

Although not shown, the pressurized melting chamber 6 is configured to be supplied with an inert gas such as argon gas to prevent oxidation of the casting ingot 9, and the reduced pressure casting chamber 7 is provided with an airtight container. A vacuum pump is provided to create a vacuum inside the chamber.

Next, the casting ingot 9 used in the above-mentioned precision casting apparatus 1 will be described.

This ingot 9 is shown in Fig. 2 (A), (B) and (
3(A) on a predetermined outer surface of the titanium material 23 formed into a rectangular parallelepiped shape, truncated cone shape, or flat plate shape as shown in FIG. 3(A). Thin nitride J as shown in (B) and (C)
i (TiN layer) 24 is formed. More specifically, the nitride layer 24 is formed on the entire outer surface of the titanium material 23 except for the upper surface 23a.

When manufacturing such an ingot 9, the steps shown in Fig. 2 (^). (B). As shown in (C), the upper surface 23a of the titanium material 23 (weight 1: 25 g to 55 g)
High-frequency induction heating coils 25 are arranged facing each other on all outer surfaces except for
Rapidly heat to a temperature of 00°C or higher. In this case, in order to make the thickness of the heating layer (and thus the thickness of the nitride layer 24) as thin as possible, the frequency of the power supply supplied to the high-frequency induction heating coil 25 is increased, and the titanium material 23 is reduced by heat conduction during heating. In order to suppress heat transfer to the inside of the container as much as possible, it is desirable that the heating time be short, within 1 second. Further, in order to reduce the thickness of the nitride layer 24 after heating as much as possible, it is desirable to inject cooling water (such as tap water) onto the heated titanium material 23 to rapidly cool it to room temperature.

Next, operations and effects when performing precision casting using the precision casting apparatus 1 and casting ingot 9 having the above-described configuration will be described.

First, the upper container 2 is opened, a predetermined mold 20 is stored in the mold receiver 16, and a solid mold is placed in the recess 10 of the crucible 8 held horizontally as shown in FIGS. 1 and 4. Place ingot 9. In this case, as shown in FIG.
The nitride layer 24 on the bottom surface corresponds to O and is arranged so as to be in contact with the ground electrode 14. After that, the upper container 2 is closed and the flange portion 2b. 3b is brought into a tightly coupled state, and the air inside the sealed container 4 is removed using a vacuum pump (not shown) to create a vacuum state. Next, an inert gas such as argon gas is injected into the pressurized melting chamber 6 to increase the pressure to a predetermined pressure (for example, lO to 760 torr), and a predetermined pressure is created between the pressurized melting chamber 6 and the vacuum casting chamber 7. A pressure difference of .

After setting such a state, Vt is increased by supplying power to the arc electrode 15 and causing arc discharge.
The manufacturing ingot 9 is heated. At this time, the melting point of the titanium material 23 portion of the ingot 9 is about 1672°C, while the melting point of the nitride layer 24 is about 3000"C, so the heating temperature is set between 1672°C and 3000°C. temperature(
For example, by setting the temperature to about 175°C), the titanium material 23 is
can only be melted. The molten titanium material 23 becomes as shown by the dashed line in FIG.

Therefore, in this case, as described above, the nitride layer 24 remains solid without being melted, so that the molten titanium material 23 does not come into contact with the surface of the recess 10 of the crucible 8, and the titanium material 23 remains in the crucible 8. It will not react with and be oxidized.

After confirming that the titanium material 23 portion of the ingot 9 has been melted, the crucible 8 is rotated in the direction of arrow A in FIG. 1 by activating a crucible rotation air cylinder (not shown). and tilt it.
The molten titanium material 23 flows out from the area surrounded by the solid nitride 1124 and flows into the mold 20 below.
The mold 20 is injected into the modeling cavity 19 through the sprue 18 of the mold 20 and cooled naturally. As a result, a dental cast product having a predetermined shape is obtained.

Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above, and various modifications and changes can be made based on the technical idea of the present invention.

For example, the means for forming the nitride layer 24 is not limited to the high-frequency induction heating coil 25, but a thin oxide layer may be formed on the entire surface of the titanium material 23 in a combustion furnace, and then a thin oxide layer may be formed on the entire surface of the titanium material 23. The nitride layer on the top surface may be removed by cutting the top surface. The shape of the casting ingot 9 is shown in FIG. 2(A). (B). The present invention is not limited to the shape shown in (C), but can also be applied to shapes such as a spheroidal shape or an inverted triangular pyramid shape.

Further, the present invention can also be applied to ingots made of various materials with high high temperature activity other than titanium alloys and titanium material 23. Furthermore, as a means for heating and melting the casting ingot 9,
In addition to the arc electrode 15, as shown in FIG. 5, a high-frequency induction heating coil 26 configured to be vertically movable may be used. It goes without saying that the casting ingot 9 according to the present invention can also be applied to a centrifugal casting apparatus that rotates the mold 2o and performs casting using its centrifugal force.

e. Effects of the Invention As described above, in the present invention, a thin nitride layer is formed on the outer surface of the casting material, excluding the upper surface, which is highly active at high temperatures. By arranging it so that it corresponds to the inner surface and heating it to an appropriate temperature, only the part surrounded by the oxide layer, that is, the part of the material with a lower melting point than the oxide layer, is melted, and the oxide layer with a higher melting point becomes solid. It will remain as is. As a result, it is possible to reliably prevent the occurrence of a situation in which the molten casting material comes into close contact with the inner surface of the crucible and is oxidized, and it is possible to obtain a cast product with good properties that does not contain oxygen. Furthermore, according to the present invention, the outer surface of the casting material is formed with a nitride layer (
Since it has a melting point of 3000°C), there is a large permissible heating temperature range when melting only the part of the casting material surrounded by the nitride layer. Therefore, both high-frequency induction heating using a high-frequency induction heating coil and arc discharge using an arc electrode can be used as heating and melting means for casting materials, and heating and melting methods can be used to suit the purpose of the casting materials and cast products. You can freely choose the means.

Furthermore, when an arc discharge method is adopted as a heating method, if the electrical resistance of the outer surface layer of the ingot is large, it is necessary to make a hole in this outer surface layer and bring the earth electrode into contact with the casting material from that part. Since the electrical resistance of the nitride layer is very low (40 μΩ・cm), there is no need to adopt a complicated structure as described above, and there is an advantage that a simple structure of simply contacting the earth electrode with the outer surface of this nitride layer is sufficient. .

[Brief explanation of drawings]

The drawings are for explaining one embodiment of the present invention, and FIG. 1 is a cross-sectional view of a precision casting device, and FIG. 2 (A) and (B) are
) and (C) are cross-sectional views showing the state in which high-frequency induction heating coils are arranged correspondingly to the casting ingot for manufacturing the casting ingot, and Figures 3 (A), (B), and (C) are the nitride 4 is an enlarged sectional view showing the casting ingot placed in a crucible, and FIG. 5 is a cross-sectional view showing the casting ingot having layers, and FIG. 5 is an enlarged sectional view showing the casting ingot placed in a crucible. FIG. l... Precision casting device, 6... Pressure melting chamber, 7... Decompression casting chamber, 9... Casting ingot, l5... Arc electrode, 23... Titanium material, 24...・Nitride N (TiN layer), 25.26...High frequency induction heating coil. 8... Crucible, 10... Concavity, 20... Mold, 23a... Top surface,

Claims (3)

[Claims] (1) Casting characterized in that a thin nitride layer is formed on the outer surface of the casting material, which is highly active at high temperatures, except for the upper surface, and is located opposite the inner surface of the crucible during casting heating. ingot. (2) Claim No. 1, characterized in that the nitride layer covers the entire outer surface of the casting material except for the upper surface.
) Casting ingots as described in item ). (3) The casting ingot according to claim 1 or 2, wherein the casting material is titanium and the nitride layer is titanium nitride.