JPH0566091A - Cold wall melting device using ceramic-made crucible - Google Patents

Abstract

PURPOSE:To equalize the components of iron pig by forming a side wall section of a crucible with a ceramic material and laying out an induction heating coil to the side wall section of the crucible so that the induction heating coil may serve as a supply and discharge pipeling of a cooling medium. CONSTITUTION:A side wall 12 is formed in the shape of a hollow cylinder where aluminum nitride, for example, is adopted as a ceramic material. Copper blocks are inserted into the hollow cylinder as a bottom wall 14. A copper pipeline 13 is laid out to the outer periphery of the side wall 12 of a crucible 10 where the copper pipeling serves as an induction heating coil and a cooling water pipeline. This construction prevents the side wall 12 from serving as a secondary heating coil to the induction heating coil so that it may not be heated. Therefore, no pig iron vibrated so that stabilized melting is available. Furthermore, the components of pig iron can be equalized by proper agitation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to 1) a high-purity metal or alloy known as a material for semiconductors, etc., 2) oxygen such as titanium or zirconium (Zr), oxygen (O), nitrogen (N) or carbon (C). Metals or alloys that are difficult to form as a high-purity product because they easily react with 3) Melting of metals that are handled as special metals such as W, Mo, Ta, and Nb, which have extremely high melting temperatures, and their alloys The present invention relates to a melting crucible furnace called a cold wall induction melting crucible furnace having a structure suitable for, and more specifically, the entire or at least the side wall of the crucible furnace including the side wall and the bottom wall is electrically conductive such as AlN. The present invention relates to a cold wall induction melting furnace composed of a ceramic material having a low thermal conductivity and a low thermal conductivity.

[0002]

2. Description of the Related Art As described above, high-purity metals known as materials for semiconductors, metals or alloys such as titanium or zirconium that easily react with oxygen, nitrogen or carbon, W, Mo, Ta, Nb with extremely high melting temperature, etc. An electron beam melting furnace, a non-consumable arc furnace, etc. have been used for melting special metals and their alloys. However, as will be described later, in these furnaces, in order to perform melting in a furnace or crucible made of a metal oxide refractory material such as alumina, magnesia, zirconia, beryllia, at high temperature, the refractory material and molten metal ( There is a problem that a chemical reaction occurs with the molten metal), and the reaction product is taken into the molten metal as an impurity and the quality deteriorates.As a furnace body or crucible that does not use metal oxide refractory material, water cooling A cold wall induction melting method (also called a cold crucible melting method or an induction skull melting method) using a copper crucible has been adopted.

As shown in FIGS. 4A and 4B, an induction crucible furnace called a cold wall type crucible furnace which has been generally used up to now has a good conductivity and a high thermal conductivity as shown in FIGS. A crucible body made of a metal such as a hollow cylinder with a bottom as a whole, and an induction heating coil 8 arranged on the outer periphery of the crucible body. The side wall portion of the crucible or a portion from the side wall to a part of the bottom portion is plural. Is a metal crucible melting furnace for induction melting in which a plurality of strip-shaped segments 3 are divided by narrow slits 2 and the inside 11 of each segment 3 is cooled by a coolant such as cooling water. When the melting of the molten metal progresses by the induction heating coil 8,
The molten metal 9 in contact with the inner wall of the water-cooled strip-shaped segment 3 is solidified into a thin-skinned skull 5, and the molten metal in contact with the side wall of the metal crucible melting furnace adheres to the side wall or enters into the slit portion and is removed. Play a role in preventing difficulty. On the other hand, due to the electromagnetic induction action, the molten metal is floated from the side wall in the upper part of the crucible and also has a function of preventing a short circuit between the copper water-cooled strip-shaped segments 3.

As described above, the crucible body of the cold wall type crucible furnace is made of copper and, like a normal melting furnace, a refractory material composed of a single or a mixture of metal oxides such as alumina, magnesia, beryllia, silica or zirconia. No material used. It is because the metals and alloys to be melted by the cold wall type crucible furnace have a high melting temperature, while the molten metals and the refractory materials that compose the crucible body as a container for containing the alloy have the thermal conductivity. Since the melting point is low, the temperature of the crucible body reaches a high temperature almost the same as the temperature of the molten metal inside as the melting progresses. As a result, a chemical reaction progresses between the elements that make up the metal and alloy and the elements that make up the refractory material of the crucible body, and the elements in the refractory material are taken into the molten metal as impurities and reduce the quality of the metal and alloy. Therefore, general ceramic refractory materials could not be adopted.

[0005]

The above-mentioned copper has been adopted as an alternative to general refractory materials. Since copper has a high thermal conductivity, the furnace wall of the crucible furnace can be cooled by a cooling medium such as water and kept at a temperature considerably lower than the melt inside, but as a common characteristic of metals,
Conductivity and thermal conductivity tend to be the same, typically copper, silver,
As seen in aluminum and the like, a material having high thermal conductivity has good conductivity. However, good conductivity is a problem in terms of induction heating, but by dividing the furnace wall vertically into strips, the continuous hollow tubular furnace wall itself forms a secondary coil for the induction heating coil. Since the strip-shaped copper segment itself is a conductor, it is still heated by the induction heating coil to some extent, like the material to be melted.
According to the measurement results, when the power consumption for the material to be melted is 1, the amount for the crucible is 1.3, and excluding the loss on the path and the coil primary side, it was used for the material to be melted. Only about 40% of the electric power is effectively used. Also, in order to compensate the power lost in the crucible, it is necessary to increase the coil voltage, but when vacuum melting is required, the higher the voltage in the vacuum, the more easily plasma discharge occurs, so the applied voltage is also several hundred volts. The input power is also limited to a certain degree. In induction melting, if the frequency is low, the molten metal inside the crucible is agitated greatly and the surface of the molten metal is not stable.In some cases, part of the molten metal jumps out of the crucible and adheres to the outer wall of the crucible, etc. Will decrease and the yield will decrease.
When the frequency is increased, the flow of the molten metal is reduced, and the electromagnetic force applied acts in the direction of stably preserving the surface shape of the molten metal, enabling stable melting. However, in a conventional cold wall type crucible furnace having a strip-shaped copper segment, it is necessary to increase the coil voltage in order to make up for the loss in the crucible furnace. Since the coil voltage also increases proportionally, there is a problem that the upper limit of the voltage required in the case of vacuum melting is exceeded. From this point as well, the heating that the crucible receives by the induction heating coil has a segment. It has been a challenge to provide a melting crucible that is negligible or significantly less than conventional copper cold wall crucibles.

[0006]

Means for Solving the Problems As a crucible capable of solving the above problems, 1) the crucible itself does not form a coil which is heated by an induction heating coil as a heating means or a conductor portion which is a body to be heated. 2) Even if the temperature of the material to be melted inside the crucible rises, the temperature of the crucible itself should be maintained by means such as water cooling. Lower than the temperature, high thermal conductivity so as to keep chemical reaction between the crucible and the molten metal, 3) The crucible withstands thermal stress due to repeated heating and cooling during melting work. The problem can be solved by using a heat resistant material having an obtained strength and having an appropriate structure, and if a material satisfying the above three conditions 1) to 3) can be selected, the problem can be solved. Sex is extreme There is no one that satisfies the condition of being extremely low and having high thermal conductivity. Therefore, as the material of the cold wall crucible, copper has been used as a fixed idea until now, but the inventors of the present invention have extremely low conductivity and high thermal conductivity in ceramics as the material of the crucible. We decided to select an appropriate material that satisfies the above condition.

Recent advances in ceramics-related technologies have led to the development of ceramic materials that can meet the above three conditions. Among them, industrial products include aluminum nitride (AlN), cubic boron nitride abbreviated as cBN, beryllium oxide (BeO), and the like, but all of them except aluminum nitride are expensive, It is not suitable for a large member such as a crucible.
Aluminum nitride has a wurtzite type crystal structure, and has extremely high hardness of Hv1200 as mechanical properties, high compressive strength and bending strength, and does not decrease in strength even at high temperature. As for thermal properties, its thermal conductivity is about half that of copper,
The coefficient of thermal expansion is slightly larger than that of copper, and electrically corresponds to an insulator and has a low dielectric constant. In addition to this, it is stable even at high temperatures, has excellent corrosion resistance to molten metal, and has low wettability to molten metal, so the molten metal does not easily adhere to the inner walls of crucibles, etc. ,
In particular, aluminum nitride was selected as the optimum crucible material because it is extremely suitable as a material for cold wall crucibles. Using aluminum nitride as the material, basically
As shown in Fig. 1, it is assumed that the side wall has a hollow cylindrical shape, a copper block is inserted as a bottom wall, and a copper pipe that also functions as an induction heating coil and a cooling water pipe is arranged on the outer periphery of the side wall of the crucible. , Or one in which the side wall and the bottom wall are integrated into a hollow cylindrical shape with a bottom, and a hollow block dedicated to cooling is provided directly below the bottom wall, or inside the side wall of a rubo with a hollow cylindrical shape and a copper block inserted as the bottom wall. The problem was solved by embedding a copper pipe that also served as the cooling water pipe.

[0008]

[Function] As the refractory material forming the cold wall crucible, aluminum nitride, which has extremely low conductivity and also serves as an insulating material, is adopted, so that the side wall of the crucible is heated as a secondary coil for the induction heating coil. In addition, its thermal conductivity is about half that of copper, which is almost the same as aluminum, and is superior to structural metal materials such as zinc, iron and other alloys, so cooling media such as water passes through pipes. The crucible furnace body is maintained at the same temperature as the water-cooled copper crucible by a normal cooling method that performs heat exchange by forming a thin solidified layer of molten metal called a skull between the melt and the crucible like the water-cooled copper crucible. Apparently, the thin solidified layer of this molten metal constitutes the inner wall of the crucible and is melted, and the melting is performed by avoiding the inclusion of impurities due to the chemical reaction with the ordinary crucible of refractory material. It is possible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view showing a first embodiment,
Reference numeral 10 denotes the whole cold wall crucible of the present invention, 12 is a side wall made of aluminum nitride, 13 is a copper pipe arranged on the outer periphery of the side wall and serving as an induction heating coil and a pipe for cooling water, and 14 is It is a copper block wall inserted as a bottom wall, as shown by the dotted line on this copper block wall,
In order to prevent a short circuit, a plurality of slits 15 are circumferentially spaced and cut in the axial direction. The induction heating coils arranged on the outer circumference of the side wall are arranged with an appropriate interval in order to improve the insulating property, and an insulating material is inserted between the coils. It is preferable that the outer periphery of the side wall 12 made of aluminum nitride is metallized for joining a copper pipe, but it is preferable that the joining is continuous without a gap, and if the crucible wall is sufficiently cooled, it is formed in the circumferential direction. They may be joined at a predetermined angle, or a substance that improves heat transfer may be inserted between the outer periphery of the side wall 12 and the copper pipe. Reference numeral 16 is a coil retainer. If the coil and the outer periphery of the crucible are tightly joined, it is not always necessary to hold down the coil, but if a substance that improves heat transfer is used, it is necessary to hold the coil down.

FIG. 2 is a schematic view showing a second embodiment. Similar to the embodiment shown in FIG. 1, a copper block 2 is used as a bottom wall on the bottom of a hollow cylindrical side wall 22 made of aluminum nitride.
4 is inserted, and a copper pipe 23 which also functions as a pipe for cooling water is embedded in the side wall 22. Although illustration is omitted, a coil retainer is provided if necessary.

FIG. 3 is a schematic view showing a third embodiment, in which the crucible body is a cylindrical side wall 3 made of aluminum nitride.
2 and the bottom wall 32a are integrally formed, and are in close contact with the back surface of the bottom wall 32a, and are hollow copper blocks 36 dedicated as cooling devices.
Are arranged. Reference numeral 33 is a copper pipe which is arranged on the outer periphery of the side wall and serves as an induction heating coil and a pipe for cooling water. Although illustration is omitted, a coil retainer is provided if necessary.

[0012]

In the crucible made of aluminum nitride of the present invention, the electric power for induction heating is not used to heat the crucible unlike the copper crucible, but is supplied only for heating the melted inside the crucible. The power consumption can be reduced. Since the power consumption can be reduced, the coil voltage can be reduced as compared with the copper crucible, and the frequency can be correspondingly increased, and the advantage is that the molten metal does not fluctuate and stable melting is possible, and the molten metal has an appropriate stirring effect. The components of can be made uniform.

[Brief description of drawings]

FIG. 1 is a front view showing an aluminum nitride cold wall crucible according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing a cold wall crucible made of aluminum nitride according to a second embodiment of the present invention.

FIG. 3 is a schematic view showing a cold wall crucible made of aluminum nitride according to a third embodiment of the present invention.

FIG. 4 is a schematic side sectional view and a plan view showing a conventional cold wall crucible furnace.

[Explanation of symbols]

 10, 20, 30 Crucible main body 2 12, 22, 32 Side wall 13, 23, 33 Cooling pipe also serving as coil 14 Copper bottom wall 15 Slit 16 Coil holder 32a Integrated bottom wall 36 Water cooling hollow block

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Tadoko, Motoyashiki 150, Miyaya-cho, Toyohashi-shi, Aichi Shinko Electric Co., Ltd. Toyohashi Works

Claims (6)

[Claims] 1. A furnace chamber is formed by a side wall portion which is substantially vertically erected and a bottom wall which closes the bottom portion and forms a furnace bottom,
A crucible body whose top is released and a material to be melted is housed in the furnace chamber, an induction heating coil which is arranged in close contact with the side wall portion for heating and melting the material to be melted in the furnace chamber, and induction heating In a cold wall melting apparatus comprising a supply / discharge pipe for a cooling medium such as water for cooling the crucible body while being performed, at least a side wall portion of the crucible is formed of a ceramic material, and the induction heating coil is the cooling A cold wall melting apparatus using a ceramic crucible, which is arranged on the side wall of the crucible as a medium supply / discharge pipe. 2. The melting apparatus according to claim 1, wherein the crucible body has a hollow cylindrical crucible side wall made of a ceramic material, and a copper bottom wall inserted into the bottom of the side wall defines a furnace chamber. The induction heating coil is arranged on the outer circumference of the side wall also as a water supply / drainage pipe for water as a cooling medium, and a cold wall melting apparatus using a ceramic crucible. 3. The cold wall melting apparatus according to claim 2, wherein an induction heating coil that also serves as the cooling water pipe is embedded in the side wall. apparatus. 4. The cold wall melting apparatus according to claim 2 or 3, wherein the bottom wall is further provided with a predetermined width along the axial center of the crucible while keeping a predetermined interval in the inner circumference of the bottom wall. A cold wall melting apparatus using a ceramic crucible, characterized in that a slit having a depth and a depth is provided. 5. The cold wall melting apparatus according to claim 1, wherein the crucible body has a side wall and a bottom wall integrally formed of a ceramic material in a hollow cylindrical shape with a bottom, and also serves as a supply / discharge pipe for a cooling medium. The induction heating coil is arranged in close contact with the outer circumference of the side wall, and is further provided with a hollow block for cooling the bottom wall part in close contact with the back surface of the bottom wall part of the crucible. Cold wall melting equipment using ceramic crucible. 6. The cold wall melting apparatus according to claim 1, wherein the induction heating coil also serves as the side wall and the supply / discharge pipe for the cooling medium, and is provided on the back surface of the bottom wall portion. A cold wall melting apparatus using a ceramic crucible, characterized in that the hollow block is joined continuously or intermittently through a metallized layer formed on the wall surface of the crucible body.