JP2802373B2 - Ingot for casting - Google Patents

Description

The present invention relates to a casting ingot, and more particularly to a casting ingot used for producing a precision casting made of a material having a high temperature activity, such as a dental or plastic surgery. It relates to a suitable casting ingot.

b. Conventional technology Recently, titanium and titanium alloys having excellent affinity with a living body and corrosion resistance, and having high strength and low specific gravity have been widely used as materials for precision casting for dental and plastic surgery.

However, the melting point of titanium is as high as 1672 ° C., and under high temperature conditions, it reacts strongly with oxygen and almost everything else to deteriorate. As described above, the greatest drawback of titanium is that its high-temperature activity is extremely high, and its properties make it extremely difficult to cast. In particular, oxygen is dissolved in titanium in a large amount (solid solubility: 10% by weight or more), and thereby, the stretchability of titanium is inhibited. Incidentally, if the solid solubility of oxygen exceeds only 0.7% by weight, it becomes brittle, which is not preferable as a cast product for dental use or the like.

By the way, the material of the casting crucible widely used at present is generally made of aluminum oxide (Al ₂ O ₃ ) or magnerua (MgO). It cannot be used because it reacts with high-temperature titanium (reducing action). Under such circumstances, a material of calcium oxide (CaO) or yttrium oxide (Y ₂ O ₃ ), which does not easily react with titanium, is used, and titanium is melted in a short time as much as possible. The reality is that we try to minimize the reaction during the period.

c. Problems to be Solved by the Invention However, when a casting ingot made of a material having high activity at a high temperature such as titanium is melted in a short time, the temperature of the molten metal is too low, which causes a defect in the molten metal run. This causes inconvenience such as easiness. On the other hand, if the melting time is increased by increasing the heating time to eliminate such inconveniences, the titanium material and the crucible tend to react with each other, and the progress of oxidation of the titanium material increases. Become.

The present invention has been made in view of such circumstances, and its purpose is to melt a titanium material or a titanium alloy material at an appropriate temperature and react with a crucible (oxidation / reduction reaction).
It is an object of the present invention to provide a casting ingot which does not cause the above-mentioned problems and can obtain a cast product containing no oxygen.

d. Means for Solving the Problems In order to achieve the above object, in the present invention, the outer surface except for the upper surface of the high-temperature active high casting material,
A thin nitride layer is formed on the outer surface of the portion facing the inner surface of the crucible during casting heating.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a precision casting apparatus 1 for producing a dental casting product. This apparatus 1 includes a closed container 4 composed of an upper container 2 and a lower container 3 which are detachable from each other. I have it. 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.
And a flange portion 3b formed integrally with the upper end of 3a. Then, the flange portions 2b, 3b of the upper container 2 and the lower container 3 are tightly joined in an overlapped state so that one closed container 4 is formed, and the internal space is defined by the upper wall of the lower container 3. The partition 5 is vertically divided by the partition wall 5. Thus, the upper part of the partition wall 5 is constituted as the pressure melting chamber 6, and the lower part thereof is formed as the reduced pressure casting chamber 7.

A crucible 8 made of aluminum oxide (Al ₂ O ₃ ) made of aluminum oxide or the like is provided in the above-described pressure melting chamber 6. This crucible 8 is, as clearly shown in FIG.
It has a recess 10 for housing an ingot 9 for casting,
In the figure, it is configured to be rotated in the direction of arrow A about an axis X extending in a direction perpendicular to the paper surface. further,
An earth electrode 14 made of a tungsten material or the like is fitted on the bottom wall of the crucible 8 as clearly shown in FIG.

The arc electrode 15 is provided on the ceiling of the upper container 2.
The arc electrode 15 is supplied with power from an arc power supply circuit (not shown).

On the other hand, a cylindrical mold receiver 16 having a bottom and protruding into the vacuum casting chamber 7 is integrally formed with the partition wall 5 that partitions the pressure melting chamber 6 and the vacuum casting chamber 7. A communication hole 17 that connects these chambers 6 and 7 to each other is formed. Then, a gas-permeable mold 20 having a gate 18 and a molding cavity 19 is disposed in the mold receiver 16, and the communication hole 17 is formed in the mold 20.
Is closed. The gate 18 of the mold 20 is open upward, and is arranged corresponding to the opening 22 formed in the mounting table 21 of the support member 12.

Although not shown, an inert gas such as argon gas is supplied to the pressure melting chamber 6 to prevent oxidation of the casting ingot 9. A vacuum pump for evacuating the inside of the chamber 4 is provided.

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

As shown in FIGS. 2 (A), 2 (B) and 2 (C), the ingot 9 is provided on a predetermined outer surface of a titanium material 23 formed in a rectangular parallelepiped shape, a truncated cone shape or a flat plate shape as shown in FIG. ), (B) and (C), a thin nitride layer (Ti
(N layer) 24 is formed. More specifically,
The nitride layer 24 is formed on the entire outer surface of the titanium material 23 except the upper surface 23a. In manufacturing such an ingot 9, FIGS. 2 (A), (B),
As shown in (C), titanium material 23 (weight: 25 g to 55 g)
g) High frequency induction heating coil 25 on all outer surfaces except upper surface 23a
And the outermost surfaces are rapidly heated to a temperature of 800 ° C. or more in a short time in a nitrogen atmosphere. In this case, in order to reduce the thickness of the heating layer (and thus the thickness of the nitride layer 24) as much as possible, the frequency of the power supply to be supplied to the high-frequency induction heating coil 25 is increased, and the titanium material 23 due to heat conduction during heating is used. It is desirable to set the heating time to a short time within 1 second in order to minimize the heat transfer to the inside of the device. further,
In order to make the thickness of the nitride layer 24 after heating as small as possible, it is desirable to inject cooling water (tap water or the like) onto the heated titanium material 23 to rapidly cool it to room temperature.

Next, an operation and an operation when performing precision casting using the precision casting apparatus 1 and the casting ingot 9 configured as described above will be described.

First, the upper container 2 is opened, a predetermined mold 20 is stored in the mold receiver 16, and solid casting is performed in the concave portion 10 of the crucible 8 held horizontally as shown in FIGS. Put the ingot 9 for use. In this case, as shown in FIG. 4, the nitride layer 24 of the ingot 9 is arranged so as to correspond to the concave portion 10 of the crucible 8 and the nitride layer 24 on the bottom surface is in contact with the ground electrode 14. Thereafter, the upper container 2 is closed to bring the flange portions 2b and 3b into a tightly joined state, and the air in the closed container 4 is evacuated by a vacuum pump (not shown) to make a vacuum state. Then
An inert gas such as argon gas is injected into the pressure melting chamber 6 and pressurized to a predetermined pressure (for example, 10 to 760 Torr), and a predetermined pressure is applied between the pressure melting chamber 6 and the reduced pressure casting chamber 7. Let me make a difference.

After setting in such a state, power is supplied to the arc electrode 15 to generate an arc discharge, thereby heating the casting ingot 9. At this time, since 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., the heating temperature is set to 1672 ° C.
By setting the temperature to about 3000 ° C. (for example, about 1750 ° C.), only the titanium material 23 can be melted while the nitride layer 24 maintains a solid state. The molten titanium material 23 is as shown by a dashed line in FIG. Accordingly, in this case, since the nitride layer 24 remains solid without being melted as described above, the molten titanium material
23 does not come into contact with the surface of the concave portion 10 of the crucible 8, and the titanium material 23 does not react with the crucible 8 and is not oxidized.

Thus, 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. . Along with this, the molten titanium material 23 flows out of the region surrounded by the solid-state nitride layer 24, falls toward the lower mold 20, and enters the molding cavity 19 through the gate 18 of the mold 20. Injected and cooled naturally. As a result, a dental cast product having a predetermined shape is obtained.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, 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, and a thin nitride layer is formed on the entire surface of the titanium material 23 in a combustion furnace, and then the upper surface of the titanium material 23 is formed. May be cut to remove the nitride layer on the upper surface. The shape of the casting ingot 9 is not limited to the shapes shown in FIGS. 2A, 2B, and 2C, but may be a spheroidal shape, an inverted triangular pyramid shape, or the like. The present invention can also be applied. Further, the present invention can be applied to ingots of various materials having high high-temperature activity other than the titanium alloy and the titanium material 23.

Further, the means for heating and melting the casting ingot 9 is not limited to the arc electrode 15, but may be a high-frequency induction heating coil 26 configured to be vertically movable as shown in FIG. Further, it goes without saying that the casting ingot 9 according to the present invention can be applied to a centrifugal casting apparatus in which the casting is performed by using the centrifugal force by rotating the mold 20.

e. Effects of the Invention As described above, the present invention is such that a thin nitride layer is formed on the outer surface except for the upper surface of a casting material having high high-temperature activity. By heating it to an appropriate temperature by arranging it so as to correspond to the inner surface of only the portion surrounded by the nitride layer, that is, only the material portion having a lower melting point than the nitride layer is melted, and the nitride layer having a higher melting point is It will remain as a solid. As a result, it is possible to reliably prevent a situation in which the molten casting material comes into contact with the inner surface of the crucible in a close contact state and is oxidized, and it is possible to obtain a cast product having a good oxygen-free property.

Further, according to the present invention, since the outer surface of the casting material is formed of a nitride layer (melting point 3000 ° C.) whose melting point is much higher than that of the casting material, the portion surrounded by the nitride layer The allowable range of the heating temperature when only the casting material is melted is large. For this reason, any of high-frequency induction heating by a high-frequency induction heating coil and arc discharge by an arc electrode can be adopted as a means for heating and melting the casting material, and the heating and melting according to the use of the casting material and the cast product can be performed. The means can be freely selected.

Furthermore, when the arc discharge method is adopted as the heating means, if the electric resistance of the outer surface layer of the ingot is large, it is necessary to make a hole in this outer surface layer and to contact the ground electrode with the casting material from that part. Since the electric resistance of the material layer is very small (40 μΩ · cm), there is an advantage that it is not necessary to adopt the above-mentioned complicated structure and a simple structure in which the earth electrode is brought into contact with the outer surface of the nitride layer is sufficient. .

[Brief description of the drawings]

The drawings are for explaining one embodiment of the present invention, and FIG. 1 is a cross-sectional view of a precision casting apparatus, and FIG.
(B) and (C) are cross-sectional views respectively showing a state where a high-frequency induction heating coil is arranged corresponding to the casting ingot in order to manufacture a casting ingot, and FIGS. 3 (A), (B) and (C) are FIG. 4 is a sectional view showing a casting ingot having a nitride layer, FIG. 4 is an enlarged sectional view showing a state in which the casting ingot is placed in a crucible, and FIG. 5 is heating the casting ingot with a high-frequency induction heating coil. It is sectional drawing of the precision casting apparatus made to perform. 1 …………………………………………………………………………………………………………………………………………………. 23 ... titanium material, 23a ... top surface, 24 ... nitride layer (TiN layer), 25, 26 ... high frequency induction heating coil.

Claims (3)

(57) [Claims] 1. A thin nitride layer is formed on an outer surface of a casting material having a high activity at a high temperature except for an upper surface thereof, the portion being opposed to an inner surface of a crucible when the casting is heated. Ingot for casting. 2. The casting ingot according to claim 1, wherein said nitride layer is the entire outer surface of said casting material except for the upper surface. 3. The casting material according to claim 1, wherein said casting material is titanium, and said nitride layer is titanium nitride. ingot.