JPH11745A - Apparatus and method for continuous melting and casting of metal - Google Patents

Abstract

(57) Abstract: An apparatus and a method for continuously casting and melting metal, which can produce a slab having no surface defects and increase the melting efficiency of metal. (1) A water-cooling type having a slit (4) formed in a side wall portion in a crucible axial direction and comprising a melting zone for melting continuously supplied metal (2) and a cooling zone for solidifying the melted metal. In a continuous melting and casting apparatus for a metal having a copper crucible 1 and an energizing coil 5 for melting the metal at the outer peripheral portion of the melting zone by electromagnetic induction, a slit exists near the molten metal in the crucible in contact with the crucible. A continuous melting casting apparatus having a magnetic flux density measuring coil 8 disposed in the crucible axial direction close to the position. (2) Using this continuous melting and casting apparatus, when melting a metal as a raw material in a crucible, the magnetic flux density of the magnetic flux density measuring coil is controlled to a predetermined value to adjust the position of the molten metal level in the crucible. how to.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous melting and casting apparatus for producing a slab free of surface defects by inductively heating the metal using a cooling crucible, and a continuous melting and casting apparatus using the apparatus. It relates to a casting method.

[0002]

2. Description of the Related Art There is a method called "cold crucible" as a method of melting metal by induction heating using a cooling crucible and continuously casting. This method is used, for example, when a high melting point and highly reactive metal such as titanium, zirconium, hafnium or an alloy of these metals is melted to produce a slab (ingot).

[0003] The apparatus used in this method is a coil for passing high-frequency current through the outer periphery of a water-cooled copper crucible provided with a slit in a vertical direction (hereinafter, referred to as an "energizing coil").
Or simply “coils”).

[0004] In order to manufacture a cast slab using this apparatus, first, a metal as a raw material is poured from a top of a crucible in a solid state or a molten state in a molten state. Next, when a high-frequency current is passed through the coil, the charged raw material is melted or further heated in the crucible by induction heating to form a molten metal portion. When the molten metal part is gradually moved downward to be pulled out from the bottom of the crucible, the molten metal part is cooled by the water-cooled crucible and solidifies. The solidified slab is continuously drawn down from the bottom of the crucible.

According to this method, metal can be continuously melted and cast, and the manufacturing cost of the electrode is not required as compared with the melting method using a consumable electrode. Suitable for mass production. Furthermore, since the molten metal portion that is melted by the induction heating is held in a non-contact state with the crucible by the electromagnetic force acting in the center direction of the crucible, there is no contamination from the crucible, and the melting of the metal having high reactivity is performed. Are suitable.

In the melting of metal by induction heating using a cold crucible, the shape of the interface between the molten metal and the solidified portion (solidified interface shape or molten metal shape) depends on the surface properties of the slab, particularly the slab surface cracks caused by tensile stress. It is known that it has a great influence on the occurrence. That is, there is an optimum solidification interface shape or melt shape. On the other hand, the molten metal holding position (the position of the molten metal in the crucible with respect to the position of the energizing coil) greatly affects the solidification interface shape. Therefore, it can be said that there is an optimum molten metal holding position in producing a cast piece having good surface properties.

In addition, the heating and melting efficiency of the metal by induction heating also changes depending on the molten metal holding position, and there is an optimum molten metal holding position. As described above, in the high-frequency induction heating using the cold crucible, it is important to control the position of the molten metal with respect to the position of the molten metal, that is, the position of the energizing coil (that is, the position of the molten metal surface).

In order to control the position of the molten metal level, a level detection sensor is essential. As a method for detecting the molten metal level, an eddy current sensor method, which is conventionally used in continuous casting of steel, applies a high-frequency magnetic field to the molten metal surface in a mold and detects an induced magnetic field generated on the molten metal surface with a coil for detection. Mainstream. However, in the case of a casting apparatus used in a cold crucible, a large high-frequency electromagnetic field for induction heating is applied in the mold, so that a large noise is generated in the eddy current sensor. Therefore, the use of the eddy current sensor method is impossible.

Therefore, in the cold crucible, a method of monitoring the molten metal surface shape from above the crucible with a video camera has conventionally been used. However, in this method, since the detection of the molten metal surface shape depends on the video monitoring of the operator, the supply of the raw material has to be performed manually, and it is difficult to automate the supply. Further, it is impossible to accurately detect the position of the molten metal surface by a monitoring method using a video camera.

On the other hand, as a method of using a sensor, there is a method of measuring a distance to a molten metal surface using a laser distance meter that detects a laser reflected on the molten metal surface. However, this method also has a large error because the shape of the molten metal surface changes due to the flow in the molten metal induced by the electromagnetic force. The same is true for ultrasonic rangefinders.

In addition, Japanese Patent Application Laid-Open No. 7-146077 proposes a method for detecting the molten steel surface position by measuring the magnetic flux density in the radial direction of the mold by means of a magnetic flux density detecting means provided in a slit portion on the outer periphery of the mold. Have been. Although this method is possible in principle, it is detection from outside the mold, the rate of change of the magnetic flux density with respect to the metal surface position is small, and it is presumed that accurate detection of the metal surface position is difficult. You. In addition, it is necessary to manufacture a detection coil having a size that can be installed in a slit portion having a width of 1 mm or less, and a reduction in accuracy due to an error in the coil size may be considered.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in controlling the position of the molten metal surface when melting a metal by induction heating using a cooling crucible. The position of the molten metal in the crucible (the position of the molten metal surface) in the crucible with respect to the position of the metal is controlled to an optimum position to produce a slab without surface defects and to increase the efficiency of heating and melting the metal. It is an object of the present invention to provide a continuous melting and casting apparatus and a continuous melting and casting method using the apparatus.

[0013]

Means for Solving the Problems The inventors of the present invention have determined that the relative position between the surface of the molten metal in the crucible and the current-carrying coil is the shape of the solidification interface (the interface between the molten metal and the solidified portion), Investigations have been made on the occurrence of slab surface cracks, their effects on melting efficiency, etc. As a result, there is an optimum relationship between them, especially the position of the molten metal surface, especially the position of the upper end of the molten metal holding (the highest part where the molten metal surface is raised by the electromagnetic force acting on the molten metal surface by induction heating). Position) is close to the upper end of the current-carrying coil,
It was confirmed that the heating and dissolution efficiency was maximized.

The present invention has been made based on this finding, and the gist of the invention lies in the following (1) continuous melting and casting apparatus for metal and (2) a method for continuous melting and casting metal using the apparatus. .

(1) A water-cooled copper crucible having slits formed in the side wall portion in the axial direction of the crucible and comprising a melting zone for melting the metal supplied continuously and a cooling zone for solidifying the melted metal. In a continuous melting and casting apparatus for a metal having a current-carrying coil that melts the metal at the outer periphery of the melting zone by electromagnetic induction, the molten metal in the crucible is in the vicinity of being in contact with the crucible and close to the position where the slit exists. A continuous melting and casting apparatus for a metal, comprising a magnetic flux density measuring coil disposed in an axial direction of a crucible.

(2) Using the continuous melting and casting apparatus described in the above (1), the metal is continuously supplied into the crucible and the electromagnetic induction is generated in an electromagnetic field generated by passing a high-frequency current through a current-carrying coil. While melting the metal, a continuous melting and casting method of metal that is continuously pulled out while progressing solidification below the crucible, when the melting, the magnetic flux density of the magnetic flux density measurement coil to a predetermined value. A method for continuously melting and casting metal, comprising controlling the position of a molten metal in a crucible.

Here, the “metal that is continuously supplied” is not limited to a solid metal, but may be a metal (molten metal) that has been dissolved and melted.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention (the inventions of the above (1) and (2)) will be described below in detail with reference to the drawings.

FIG. 1 is a view showing an example of the configuration of a continuous melting and casting apparatus for a metal according to the invention (1) (hereinafter, also referred to as “the apparatus of the invention”). FIG. 2B is a cross-sectional view taken along the line II of FIG.

As shown in FIG. 1, a supply device 3 for a metal 2 as a raw material is provided above a water-cooled copper crucible (hereinafter simply referred to as a “crucible”) 1. Through the metal 2 is continuously supplied into the crucible 1. The crucible 1 has a slit 4 formed in the side wall portion in the axial direction of the crucible, a melting zone for melting the metal 2 continuously supplied into the crucible 1, and a melting zone below the melting zone for melting the metal. It consists of a cooling zone for solidification. Both the melting zone and the cooling zone are water-cooled. Note that a plurality of slits 4 (eight in this example (see FIG. 1B)) are provided over the entire circumference of the crucible.

A coil 5 for supplying a high-frequency current is wound around the melting zone provided with the slit 4 on the outer peripheral portion of the crucible 1, and is connected to a high-frequency power supply (not shown).
By passing a high-frequency current through the current-carrying coil 5, the metal 2 in the crucible passes through the portion where the slit 4 exists.
Is applied with a high-frequency electromagnetic field. Generally, the frequency of the applied high-frequency current is 1 kHz, at which the effect of induction heating is obtained.
from z to 500 kHz. If the frequency is higher than this, the voltage of the terminal of the coil 5 becomes high, and the voltage between the slits 4 of the crucible 1 also becomes high, which may cause a spark.

In the apparatus of the present invention, a magnetic flux density measuring coil 8 for adjusting the position of the molten metal surface is arranged at a predetermined position in the crucible 1.

This continuous melting and casting apparatus is installed in a chamber 7 provided with a gas supply and exhaust system capable of adjusting the atmosphere.

FIG. 2 is a perspective view of a part of the crucible 1. As shown in the figure, a magnetic flux density measuring coil 8 for adjusting the position of the molten metal surface is arranged near the position where the slit 4 of the inner wall of the crucible exists. The magnetic flux density measuring coil 8 has a spirally wound shape, and is held so that its axial direction is parallel to the axial direction of the crucible 1.

The height at which the magnetic flux density measuring coil 8 is installed is in the vicinity of a portion where the molten metal in the crucible raised by the electromagnetic force contacts the crucible. It is preferable to bring the coils close to each other as much as possible.
In order to avoid contact with the molten metal or exposure to high temperature due to the radiant heat of the molten metal, it is recommended that the tip of the magnetic flux density measuring coil 8 be located at a position at least 20 mm away from the molten metal part (the molten metal surface). preferable. Usually, the upper end position of the molten metal is adjusted so as to be the same as the upper end of the energizing coil. Therefore, as shown in FIG. 1 or FIG. To the top of

The reason why the magnetic flux density measuring coil 8 is brought close to the position where the slit 4 exists (hereinafter, simply referred to as "slit position") is that the magnetic flux density at the slit position is the largest in the crucible, as described later. This is because the closer the position is, the higher the detection accuracy is. The reason why the magnetic flux density measuring coil 8 is arranged so as to be parallel to the axial direction of the crucible 1 is that the magnetic flux in the crucible mainly includes the axial component of the crucible.

Since the coil 8 for measuring the magnetic flux density is arranged very close to the molten metal part which is maintained at a high temperature, in practice, as shown in FIG. Used in the state stored in the box.

The device of the present invention has the above-described configuration,
By using this apparatus and adjusting the position of the molten metal surface in the crucible to an optimum position by the method described below, it is possible to manufacture a slab without surface defects.

The invention (2) is a method for continuously melting and casting metal (hereinafter, also referred to as "the method of the present invention") using the apparatus of the present invention.

First, the principle that the position of the molten metal surface can be detected by disposing the magnetic flux density measuring coil close to the position of the slit 4 near the portion where the molten metal in the crucible 1 contacts the crucible 1 as described above. explain.

When the position of the melt in the crucible changes, the inductance of the system including the crucible and the melt changes, so that the state of the electromagnetic field in the crucible changes and the distribution of the magnetic flux density in the crucible changes. . In general, an electromagnetic field generated by a high-frequency current is hard to penetrate into a metal having high electric conductivity, so that near the surface of the molten metal raised by electromagnetic force, the magnetic flux density is concentrated in a narrow area, and the magnetic flux density is high. The density is highest in the crucible. Further, when the position of the molten metal surface relative to the current-carrying coil changes, the applied state of the electromagnetic force also changes, so that the shape of the held molten metal, particularly the contact angle with the crucible, changes. As a result, the gap between the crucible and the molten metal changes, so that the degree of concentration of the magnetic flux density changes, and the magnetic flux density on the inner wall portion of the crucible greatly changes.

Since this phenomenon is remarkable in a portion where the slit exists, a change in the position of the molten metal can be detected by measuring the magnetic flux density at the slit position. Since the magnetic flux density at the slit position is the largest in the crucible,
The detection accuracy is considerably improved. In addition, since it is inside the crucible, it is possible to install a considerably large detection coil. A larger coil diameter is advantageous because a larger magnetic flux density and a change in magnetic flux density can be detected.

By controlling the magnetic flux density detected as described above to a predetermined value, which will be described later, the molten metal surface can be adjusted to a predetermined position. As a result, a slab having no surface defects can be manufactured, and the heating efficiency and melting efficiency of the metal can be increased.

FIG. 3 is a diagram showing an example of a control system used when carrying out the method of the present invention.

As shown in FIG. 3, the spirally wound coil 8 for measuring the magnetic flux density is placed in the crucible 1 several tens of millimeters above the target molten metal surface position and at the slit position. The coils 8 are arranged so that the centers of the coils 8 coincide with each other and in the axial direction of the crucible, and as close to the slit position as possible. Note that the diameter of the magnetic flux density measuring coil 8 must be smaller than the radius of the crucible 1 because it needs to be a size that does not hinder the supply of the metal as a raw material from above the crucible 1 and that allows insertion. I do.

The AC voltage induced in the magnetic flux density measuring coil 8 is converted into a DC voltage by the rectifier 9, and further, a signal such as a frequency of a high-frequency current flowing through the coil 5, a coil voltage, a coil current, and an output voltage of a power supply. And is converted into a magnetic flux density by the arithmetic circuit 10. If the feed rate of the raw material is set by the control circuit 11 so that the value of the magnetic flux density becomes a predetermined value, it is possible to adjust the position of the molten metal surface to an optimum position. In addition, the predetermined value determined in advance, the raw material is actually dissolved in a crucible,
The coil for measuring the magnetic flux density may be arranged so as to be at a molten metal surface position suitable for melting and casting, and the value of the magnetic flux density at that time may be grasped.

Depending on the melting and casting conditions, the coil 5
In some cases, the operation of dividing the value of the magnetic flux density obtained by the magnetic flux density measuring coil 8 by the coil current value in the arithmetic circuit 10 may be performed. . This is because the magnitude of the magnetic flux density in the crucible 1 is proportional to the coil 5 current.

As described above, by controlling the value of the magnetic flux density obtained by the magnetic flux density measuring coil 8 to a predetermined value of the magnetic flux density, the level of the molten metal 6 can be adjusted to the optimum level.

Since the coil 8 for measuring the magnetic flux density is arranged very close to the molten metal 6 held at a high temperature, it is necessary to suppress a rise in temperature. Therefore, when the method of the present invention is actually applied, for example, as shown in FIG. 4 as an example, the coil 8 for measuring the magnetic flux density is housed in a protective box 12 made of a non-electrically conductive and refractory material. It is preferable to arrange them. Further, for cooling, for example, A
Protective box 1 for cooling gas such as r gas or N ₂ gas
It is desirable to have a structure that can be supplied to the inside of the container.

As described above, the method of the present invention can be carried out by the control system illustrated in FIG. 3 incorporating the device of the present invention. That is, the raw material (metal 2) put into the crucible 1 is melted by induction heating in the melting zone, and the molten metal surface position is adjusted to an optimum position. When the molten metal is moved to the cooling zone, the molten metal is cooled and solidified, so that the metal can be continuously melted and cast by drawing the solidified slab downward from the bottom of the crucible.

As a result, a slab having no surface defects can be manufactured, and the efficiency of heating and melting the metal can be increased.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which titanium is melted and continuously cast using the apparatus of the present invention having the structure shown in FIG. 1 will be described.

Table 1 shows the experimental conditions. The magnetic flux density measuring coil was placed in a protective box made of heat-resistant silica refractory. The position for holding the molten metal was set so that the melting efficiency was highest and the upper end of the molten metal came to the upper end of the current-carrying coil, which is a condition where there is no defect on the surface of the slab. The value of the magnetic flux density in the crucible axis direction at that time is 300 g
auss.

The supply of the raw material and the drawing of the slab are continuously performed while controlling the supply speed of the raw material so that the magnitude of the magnetic flux density obtained by the magnetic flux density measuring coil becomes a predetermined value. did. Slab drawing speed is 2
0 mm / min. The interior of the chamber was replaced with Ar gas, and the high-frequency current flowing through the current-carrying coil was 25 kHz in frequency and 1500 A in magnitude.

The slab was pulled out for 40 minutes, and the diameter was 1 mm.
A slab (ingot) having a length of 00 mm and a length of 800 mm was manufactured. The surface of the obtained slab had no cracks such as lateral cracks, and had a smooth surface. The surface roughness of the slab was measured at two locations in the circumferential direction over the entire length.
The average was as good as 100 μm.

[0046]

[Table 1]

[0047]

According to the method of the present invention, the position of the molten metal in the crucible with respect to the current-carrying coil (that is, the position of the molten metal surface) is controlled to the optimum position, and the surface is free from surface defects such as lateral cracks. A slab having a surface property can be manufactured, and the heating efficiency and the melting efficiency of the metal can be increased. This method can be easily implemented using the apparatus of the present invention.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of an example of a continuous melting casting apparatus of the present invention, in which (a) is a longitudinal sectional view of a main part, and (b) is I-
FIG.

FIG. 2 is a perspective view of a part of a crucible which is a component of the continuous melting and casting apparatus of the present invention.

FIG. 3 is a diagram showing an example of a control system used when carrying out the method of the present invention.

FIG. 4 is a diagram showing an example of a magnetic flux density measuring coil of the present invention.

[Brief description of reference numerals]

 1: Crucible 2: Metal 3: Raw material supply device 4: Slit 5: Coil for energization 6: Molten metal 7: Chamber 8: Coil for measuring magnetic flux density 9: Rectifier 10: Operation circuit 11: Control circuit 12: Protection box

Claims (2)

[Claims] 1. A water-cooled copper crucible having a slit formed in a crucible axial direction in a side wall portion and comprising a melting zone for melting continuously supplied metal and a cooling zone for solidifying the melted metal, In a continuous melting and casting apparatus for a metal having an energizing coil for melting a metal by an electromagnetic induction action at an outer peripheral portion of a melting zone, a crucible is provided near a position where a molten metal in a crucible is in contact with the crucible and a slit exists. A continuous melting and casting apparatus for metal, comprising a magnetic flux density measuring coil disposed in an axial direction. 2. The continuous melting and casting apparatus according to claim 1, wherein the metal is continuously supplied into a crucible, and the metal is subjected to electromagnetic induction in an electromagnetic field generated by passing a high-frequency current through a current-carrying coil. A method of continuously melting and casting a metal that is continuously drawn while being solidified below a crucible while being melted.When melting, the magnetic flux density of a magnetic flux density measuring coil is controlled to a predetermined value. A method for continuously melting and casting metal, comprising adjusting the position of the molten metal in the melting pot.