JPH01224141A - Method and apparatus for continuous casting - Google Patents

Abstract

PURPOSE:To obtain long metal product having single crystal structure by continuously casting molten metal by passing through a mold projecting in the molten metal in a first vessel at one end thereof and cooling at the other end after refining by sucking the molten metal stored in the first vessel into a second vessel. CONSTITUTION:Pure copper rod is inserted into the graphite-mold 3 fitted to the bottom part of the graphite-made first vessel 1 under partially projecting state so that the one end of copper rod exists to a little inside from molten metal supplying side. In a cooling construction body 12 setting to opposite side to the molten metal supplying side, cooling water is flowed, and the solidified position of the pure copper is set to the molten metal supplying side in the mold. The high pure electrolytic copper M is melted in the vessel 1, and the molten copper is introduced by reducing the pressure in the alumina-made second vessel 2 to introduce the molten copper, and after that, by changing a valve 10, insert gas is blown and operation, which the molten copper is returned back into the first vessel 1, is repeated at the prescribed times. N2 gas is introduced into a mold 3 from a passage 15 and injected into the molten metal. The solidified rod R is pulsatively drawn with pinch rolls 17.

Description

Detailed Description of the Invention Star 1 - J January Feature ■ The present invention relates to a method and apparatus for continuous casting of high purity copper, silver, aluminum and other metals. , foil materials, tubing materials, etc., audio and imaging wires, foil materials, etc., and also in the production of semiconductor device materials.The present invention enables -directional solidification or continuous production of single-crystal materials.

In recent years, with the rapid development of advanced cutting-edge technology, the requirements for the metal materials used have become increasingly strict. For example, with the spread of audio and visual equipment such as compact discs and laser discs that use light to perform digital recording and playback, materials for transmission cables that connect equipment components and signal transmission circuits inside the components are used. There is a strong demand for materials that have extremely few inclusions, eliminate internal defects as much as possible, and have large crystal grains. This is because it has been found that impurities, internal defects, and grain boundaries impede the transmission of sound and image signals, impart noise and distortion, and deteriorate sound and image quality. In response to these demands, copper wire materials with a purity of 6N (99,9999%) or higher have been put into practical use. It has also been found that for copper foils for printed circuit boards or TABs, having fewer inclusions and grain boundaries in the direction of current flow is good for improving electrical signal transmission efficiency. Superconducting wire is
It is manufactured by filling a copper tube with superconducting material, elongating it, bundling about 100 elongated steel tubes, and surrounding them with a copper-colored coating. is needed.

Continuous casting is one method for efficiently producing metal materials, but it is difficult to obtain such high-quality metal materials using conventional methods. .

Throat. In continuous casting of metals, according to the conventional method, the dendritic structure grows in the same direction, resulting in columnar crystals growing from the side walls of the mold toward the center of the casting, and equiaxed crystals often grow in the center. Internal defects such as cavities and segregation of impurities are likely to occur in the center of the casting, and therefore grain boundary cracks are likely to occur when compressed in the direction of columnar crystal growth during plastic working.

One of the ways to solve these shortcomings is to
No. 46265 proposed a method in which the mold is heated and solidification is performed at the exit of the mold. Although this method was effective in improving the casting structure, it had the serious drawback that breakout was likely to occur because the formation of a solidified shell occurred near the mold outlet, creating operational hazards. Furthermore, a heater is built into the mold to heat the mold itself, which is not structurally preferable.

On the other hand, the vacuum melting method, which can achieve high purity, is attracting attention. However, since the vacuum melting method has been a batch method, it has been necessary to cast the material into an ingot after melting, which has caused contamination during the main steps such as casting and rolling, making it unsuitable for achieving high purity. Under these circumstances, a continuous casting furnace capable of continuously melting and casting copper alloy materials in a non-oxidizing atmosphere and producing long casting materials was developed in Japanese Patent Laid-Open No. 62-15125.
It was disclosed in No. 3. This continuous casting furnace includes a first tube in a vacuum chamber whose interior is connected to respective exhaust means and ventilation means.
A partition is installed to divide the chamber into a chamber and a second chamber, a melting furnace is installed in the first chamber, and a casting furnace is installed in the second chamber, one end of which is connected to the casting furnace and the other end of which is connected to the casting furnace. A nozzle open to the outside of the second chamber is provided, and a moving mechanism is installed to send the molten metal in the melting furnace to the casting furnace through the partition.

The casting material is pulled upward from the outer end of the nozzle by pinch rollers.

However, this equipment does not necessarily provide the desired sufficient purification effect, and cannot sufficiently remove gas components such as S, 0, and H, which cannot be used for future high-quality metal materials as mentioned above. In some cases, pinholes and inclusions cannot be removed.

For the above-mentioned applications such as electric wires inside equipment, the material must have the following requirements: 1. It must be of high purity; 2. It must be extremely free from internal defects such as foreign objects and pinholes. 3. It is a long product with uniform quality and has little segregation. 4. It has a unidirectionally solidified structure and, if desired, a single crystal structure, making it safe without the risk of breakout. There is a need for a continuous casting method that can produce In particular, a continuous casting method that can completely eliminate gas components such as S, 0, and H is eagerly awaited.

As a result of study, the present inventors found that a degassing method using vacuum suction or a circulation method is particularly suitable for degassing high-purity materials. It has been found that continuous casting that satisfies the above requirements can be realized by combining a casting method using a mold with a structure that protrudes inward and has the other end in contact with the cooling structure. This makes it possible to thoroughly eliminate gas components such as S%0%H, thereby reducing pinholes and inclusions as much as possible. can be manufactured.

Based on this knowledge, the present invention provides: l) After suctioning and refining the molten metal stored in the first vessel into the second vessel, one end is protruded into the molten metal in the first vessel, and A continuous casting method characterized in that continuous casting is carried out through a mold whose other end is cooled; and 2) a first vessel for storing molten metal whose atmosphere can be controlled; and a conduit tube immersed in the molten metal in the first vessel. a second vessel comprising;
A continuous casting apparatus is provided, comprising means for depressurizing and pressurizing the second vessel, and a mold having one end protruding into a molten metal bath in the first vessel and the other end contacting a cooling structure.

In a preferred embodiment, 1) the first vessel contains an inert gas such as N2, Ar, etc.
The atmosphere is controlled by reducing gases such as O and H□.

2) Depressurization and pressurization are repeated in the second vessel depending on raw material purity and target quality.

3) It is a single pipe system in which the conduction pipe serves both as suction and descent.

4) It is a circulating double-pipe system in which the conducting pipe performs suction and descent separately.

5) A partition is provided between the suction pipe and the downcomer pipe in the first vessel.

6) N snow, inert gas such as Ar, and C01H2 in the conduction pipe.
A reducing gas such as the following is injected.

7) Inert gas such as N3 and Ar and reducing gas such as C01H2 are blown into the molten metal of the first vessel.

8) Fill the mold with an inert gas such as N3, Ar, or C0 or H.
A reducing gas such as No. 8 is injected.

9) Oxygen is blown into the second vessel.

10) The casting is pulled out horizontally or downwardly from the mold.

Although the present invention will be described in connection with the continuous casting of high purity steel, it will be appreciated that the invention may be applied to silver, aluminum and other non-ferrous metals.

In normal copper electrolytic refining, blister copper refined to around 98 to 99% purity is cast and used as a positive slurry, and a seed plate made from a rolled copper plate is used to reach a copper concentration of 40 to 50 g/l and free sulfuric acid. Electrical steel is produced by electrolyzing in an electrolytic solution having a concentration of 90 to 220 g/l under conditions of a liquid temperature of 50 to 70°C and a cathode current density of 1 to 3 a/dm2. The resulting electrical steel has a purity of about 4N (99.99%) and contains impurities such as O, S, Ag, and Fe up to 10ppm.

One method to produce even higher purity copper is re-electrolysis. Generally, re-electrolysis is carried out using a diaphragm method using the above electric steel as an anode. Free sulfuric acid concentration in re-electrolysis is 90-22
0 g/l and the copper concentration is 30 to 50 g/l, which is no different from normal electrolysis, and the free sulfuric acid concentration in the electrolyte is 9
If the free sulfuric acid concentration is lower than 0 g/l, the surface density and smoothness of the electrodeposited copper will be poor and impurities will be easily drawn in. On the other hand, if the free sulfuric acid concentration exceeds 220 g/l, the solubility of copper sulfate will decrease and production will be affected. decrease in sex. The preferred free sulfuric acid concentration is 90~
It is 150g/l.

The lower the copper concentration in the electrolytic solution, the better the density and smoothness of the surface of the electrodeposited copper, but on the other hand, the productivity will be reduced. 40g
It is said to be around /1.

The re-electrolysis conditions include an electrolysis temperature of 30 to 50°C and a temperature of 50°C.
Cathode current densities of ˜150 A/m are generally employed. A lower electrolysis temperature improves the density and smoothness of the electrodeposited copper surface, so the upper limit of the solution temperature is 50°C.
If the temperature exceeds 0°C, dendrite-like crystals are likely to form. If the temperature is lower than 30°C, the solubility of sulfate decreases and suitable electrolytic operation cannot be performed. The preferred liquid temperature is 35 to 45°C.
In particular, it is around 40°C. Temperature control is important to prevent Ag contamination. The cathode current density is 50 to 150 A/m, preferably 90 to 150 A/m, in consideration of the inclusion of impurities due to poor density and smoothness of the electrodeposited copper surface and productivity.
It is best to carry out the

The diaphragm is provided to prevent copper powder, cuprous oxide powder, and impurities generated when the electrical steel is melted from being mixed into the electrodeposited copper. The diaphragm is made of an ion exchange membrane, furnace cloth, ceramics, etc. In the case of furnace cloth, it may be in the form of a box stretched over a frame, or it may be in the form of a bag, or made of acid-resistant synthetic fibers such as Deviron, Teflon, Tetron, etc. Use is preferred.

5 to 20 g of glue is added to the electrolytic solution per ton of electrolytic copper. The addition of glue makes the surface of electrodeposited copper dense and effectively prevents the inclusion of impurities. Since glue does not contain sulfur, and the amount added is kept to a small amount, there is no need to worry about contamination with sulfur, etc. If the amount of glue is too large, it may cause wrinkles or deteriorate the surface quality. Addition of glue greatly contributes to stabilizing the reduction of impurity quality.

Electrolysis operation is carried out in an electrolytic cell by arranging an anode made of electrical steel and a cathode disposed within a box-shaped diaphragm in a facing state. A titanium plate, a stainless steel plate, or a high-purity copper plate is used as the cathode. The electrolytic solution is extracted from the electrolytic cell, sent to a circulation tank, and after its components are adjusted, it is returned to the diaphragm through a filter. Glue replenishment is also done within the diaphragm. Supplying electrolyte and replenishing glue directly into the diaphragm has the following advantages: 1. The electrodeposited surface is constantly exposed to clean electrolyte, which has a great effect on preventing impurities from being drawn in. 2. Glue does not touch the electrodeposited surface. It is extremely useful for achieving high purity because it works well, the amount of glue added can be reduced, and 3. the amount of electrolyte circulation can be reduced.

The produced electrolytic copper has a dense surface texture, with Ag and S content of 4.0 ppm or less, and Fe content of 0.05 ppm.
It is of 5N (99,999%) quality, which is the m level.

The above is an example of high purity copper that can be used as a raw material for the present invention.

Of course, high-purity copper (for example, 6N (99,9999%) grade) produced by methods other than those described above may also be used in the present invention.

The high-purity copper thus obtained is transported in a molten state to a continuous casting apparatus shown in FIGS. 1 to 5. Referring to Figure 1,
The apparatus basically consists of a first vessel 1, a second vessel 2 and a mold 3. Molten metal M is held within the first vessel 1. A heater 7 is installed around the first vessel l if necessary. The second vessel 2 installed directly above the first vessel l includes a conductive pipe 4 immersed in the molten metal held within the first vessel 1. A heater 8 is also installed around the second vessel 2, if necessary. The upper end of the second vessel 2 is switchably connected to a vacuum system for evacuating the upper part of the inside of the second vessel and an inert gas system for pressurizing it via a valve 1o. Here, the conduit pipe 4 is a single pipe type that serves both to suck up and lower the molten metal, and by repeatedly depressurizing and pressurizing the second vessel by operating the valve 10 according to the raw material purity and target quality, the molten metal is melted. The depressurization and pressurization are repeated, for example, 5 to 30 times, resulting in the purification of the metal.

After the predetermined operation, casting is carried out through the mold 3. Initially, a pure steel rod is inserted into the mold 3 so that its insertion end is slightly retracted from the molten metal supply side. One end of the mold 3 is fitted into a recess formed in the bottom of the first vessel, and is heated by the molten metal and heat from the first vessel wall. An auxiliary heater 9 is installed to provide additional heat.

The other end of the mold 3 is cooled by a cooling structure 12 . An inert gas such as N3 is injected into the mold through the passage 15. A gas seal 16 is provided so that inert gas is released only to the molten metal side. The casting rod R is pulled out by the pinch rolls 17.

The first vessel contains an inert gas such as Na, Ar, etc. and Co,
The atmosphere is controlled by a reducing gas such as Hl. An inert gas such as N2 or Ar and a reducing gas such as C01H2 are blown into the conduit. N in the molten metal of the first vessel
Inert gas such as a, Ar, etc. and reducing gas such as Co, Hz, etc. are injected.

By using a mold with one end protruding into the molten metal bath and the other end in contact with a cooling structure, there is no need for a separate mold-specific heating means; This makes it possible to maintain the solidified surface near the entrance side of the mold without fear of overheating.

This eliminates the risk of breakouts. This also easily allows unidirectional solidification or single crystallization.

The mold is preferably made of a refractory material that is a good thermal conductor, such as silicon nitride, silicon carbide, or graphite.

Pulse drawing is useful for stably casting cast bodies with large crystal grains. Pulse withdrawal is a process in which withdrawal is repeated after stopping the withdrawal for a certain period of time. For example, while stopping the withdrawal for 2 to 10 seconds, the pulse withdrawal is repeated.
This is an intermittent withdrawal method in which withdrawal is repeated for 1-1 seconds.

Suitable casting speeds are 5 to 150 mm/min, particularly preferred are lO to 70 mm/min, which allows stable casting of cast bodies with very few grain boundaries.

The casting speed is the value obtained by dividing the drawing length by the drawing time, and when pulse drawing is employed, the casting speed is the value obtained by dividing the drawing length by the total time of the stop time and the drawing time.

By blowing an inert gas near the solidification interface, the temperature gradient near the interface can be further increased, making unidirectional solidification or single crystallization easier. In addition, by introducing an inert gas into the mold through the passage 15 and blowing the inert gas into the molten metal bath while covering the surface of the casting with the inert gas, the inert gas flows into the molten metal bath. Stirring acts to eliminate variations in temperature and impurity components.

The resulting cast rod can be further processed into tubes, sheets, etc., if desired.

Alternatively, horizontal drawing can be performed by placing a mold horizontally at the bottom of the first vessel, as shown in FIG. The configuration itself is the same as that shown in FIG.

FIG. 3 shows another example of continuous casting equipment.

Elements that are the same as in FIG. 1 are given the same reference numerals.

Here, unlike in FIG. 1, a circulating dual-pipe system is shown in which the conduit pipes perform suction and descent separately. Conduit pipe 4 is a suction pipe, and conduit pipe 5 is a downcomer pipe. The molten metal is sucked up through the conduction pipe 4, exposed to vacuum in the second vessel, and then descended by its own weight through the conduction pipe 5.

An oxygen inlet 20 is shown in the second vessel, and an inert gas tuyere 21 is provided in the conduit 4.
3 indicates an additive inlet.

Furthermore, in this example, the mold 3 is completely embedded in the first vessel wall, with one end protruding into the molten metal. Therefore, the mold is sufficiently heated, so no auxiliary heater is required.

FIG. 4 shows the case of horizontal drawing shown in FIG. 3, and the explanation thereof will be omitted.

Figures 5 and 6 show a continuous type vacuum refining continuous casting equipment. Like Figures 3 and 4, it is a circulating double pipe system in which the conduction pipe performs suction and descent separately, and there is a partition between the two. 24 are provided. The conduction pipe 4 as a suction pipe is composed of three pipes. Molten metal is continuously supplied from the supply port 26, sucked up through the conduction pipe 4 before the partition wall, exposed to vacuum in the second vessel, and then lowered behind the partition wall by its own weight through the conduction pipe 5. The second vessel is provided with an oxygen blowing port 20, and the conduit pipe 4 is provided with an inert gas tuyere 20.
1 is provided. Furthermore, a tuyere 30 for blowing reducing gas into the molten metal bath of the first vessel is also provided.

By combining the degassing method using vacuum suction or circulation method with the casting method using a mold with one end protruding into the molten metal and the other end in contact with the cooling structure, high-purity castings with no internal defects can be produced. Obtained safely and stably.

Melting and casting of high-purity electrical steel was carried out using the apparatus shown in Figure 1. A pure copper rod with an outer diameter of 10.6 mm was inserted into a graphite mold having a hole with a diameter of 11 mm that was partially inserted into the bottom of the first graphite vessel so that it was 1 cm inside from the molten metal supply side. The cooling structure installed on the side opposite to the molten metal supply side has an 81
The solidification position of the pure copper was set on the molten metal supply side in the mold by passing water for 2 minutes.

20kg of high-purity electrical steel is melted in the first vessel, the pressure inside the second alumina vessel installed directly above is reduced to 1mmHH, molten steel is introduced there, and the molten steel is melted by switching the valve and blowing inert gas. was returned to the first vessel. This operation was repeated 20 times.

N2 gas was introduced into the mold and jetted into the molten metal.

The solidified rod was continuously pulled out by 2 mm in 0.5 seconds,
Thereafter, pulse extraction was performed using a pinch roll that was stopped for 4.5 seconds.

The pure copper obtained as a result had a unidirectional solidification structure, and the crystal grains were extremely large.

The analytical values were as follows (unit: ppm).

Casting u Lot S O,050,05 H1,Q<0.5 0 4.6 <1.0
Electrolytic copper at a level of 5N was melted in a standing machine, and the molten steel was transferred to the apparatus shown in FIG. 3 to produce a high-purity copper plate. 12mm thick x 100mm attached to the bottom of the first vessel
A pure copper plate was inserted into a wide graphite mold, and the molten steel was simply allowed to solidify. Water was passed through the cooling structure at a rate of 20 β/min on the side opposite to the molten metal supply side, and the solidification position of the pure copper was set on the molten metal supply side in the mold.

100 kg of molten steel was charged into the first vessel, and while flowing 02 gas into the RH type second vessel installed directly above, the inside of the second vessel was maintained at lmmHg, and the molten steel was poured through the tuyere installed in the suction conduit. N□ gas was blown at a rate of 204/min and maintained for 30 minutes. After that, stop the inflow of 02, and
Hold at lmmHg for 0 minutes. N2 gas was introduced into the mold and jetted into the molten metal.

The solidified plate was pulse drawn using pinch rolls at 100 mm/min.

The analytical values were as follows (unit: ppm).

- Ruiichi Kenwa - One evening - 31,60,4 H1,0<0.5 0 8,2 2.5 Tachiyu Yu melted ordinary electric steel and used the equipment shown in Figures 5 and 6. , refined and cast. The implementation conditions were based on Example 2. However, the zero analysis values obtained when reducing gas was blown into the molten metal in the No. 1 vessel from the tuyere 30 were as follows.

1. Long metal islands with unidirectional solidification or single crystal structure can be obtained without the risk of breakout.

2. It is possible to obtain long metal islands without foreign matter or pinholes.

3. It is possible to obtain long metal islands of unidirectional solidification or single crystal fibers with little segregation.

4. The ingot surface is flexible and smooth.

5. Extremely good workability due to unidirectional solidification.

6. Long metal islands with large crystal grains or single crystals can be obtained.

7. The degree of purification can be easily adjusted according to raw material and product requirements, providing flexibility.

8. Plate materials can be directly cast.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical sectional view of a single-tube type vertical extraction refining and casting apparatus. FIG. 2 is a cross-sectional view of the mold portion of the apparatus of FIG. 1, which has been changed to a horizontal extraction mold. FIG. 3 is a schematic vertical cross-sectional view of a double-tube circulation type vertical extraction type refining and casting apparatus. FIG. 4 is a sectional view of the mold portion of the apparatus of FIG. 3, which has been changed to a horizontal extraction mold. FIG. 5 is a schematic vertical sectional view of a continuous type horizontal extraction type refining and casting apparatus. 6 is a horizontal sectional view through the first vessel of FIG. 5. FIG. 1: First vessel 2: Second vessel 3: Mold 4.5: Conduction pipe 12: Cooling structure M: Molten metal R: Casting rod, 1)

Claims (1)

[Claims] 1) After sucking the molten metal stored in the first vessel into the second vessel and refining it, one end is protruded into the molten metal bath in the first vessel and the other end is cooled. A continuous casting method characterized by continuous casting through a mold. 2) A first vessel for storing molten metal whose atmosphere can be controlled, a second vessel including a conductive pipe immersed in the molten metal in the first vessel, and means for depressurizing and pressurizing the second vessel. and a mold having one end protruding into a molten metal bath in the first vessel and the other end contacting a cooling structure.