JP2000158100A - Method for casting metallic strip and casting apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for giving resiliency with electromagnetic force and repulsion in the soft contacting state for preventing the stickiness of metal particularly to side weirs of a twin roll type continuous casting, etc., related to the casting method of a metallic strip. SOLUTION: In the method for casting the strip by pouring molten metal between one pair of water-cooled casting rolls 1a, 1b, forming a molten metal pool in the rolls with a pair of the refractory weirs 2a disposed at the end parts of the rolls, rotating the rolls and solidifying the molten metal, this casting apparatus has such characteristics that the molten metal containing semi- solidified state in the rolls is made to the soft contacting state with the refractory weir and further, induction-heated with an electromagnetic coil 13 in the inner part of the refractory weir or near the outer part of the refractory weir at the reverse side to the roll.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of casting a metal strip, and more particularly to a method of repelling electromagnetic force and preventing soft metal contact with a side dam in a twin-roll continuous casting. The present invention relates to a casting method and a casting apparatus for applying repulsion.

[0002]

2. Description of the Related Art Attention has been paid to a method for producing a slab having a thickness of several mm, which is directly close to a product, from a molten metal such as molten steel. In the case of the present continuous casting method, hot rolling is not required, and final rolling is small, so that the process and equipment can be simplified. However, in this method, an induction heating coil is installed outside the side dam, and the induced current causes
The first object is to suppress the solidification at the time of pouring the molten metal by heating the side weir before casting by causing the ferromagnetic material installed on the molten steel side surface of the side weir to induce heat generation,
As an incidental purpose, it aims to add induction heating when the heat of the molten metal near the side weir and the weir is insufficient, and to solve the problem of the metal formed at the triple point of roll, molten metal and refractory weir. The problem is not a sufficient countermeasure to respond.

FIG. 4 is a schematic explanatory view of a twin-roll type.
In this method, a pair of cooling rolls 1a and 1b rotating in opposite directions to each other are horizontally arranged,
The hot water pool portion 3 is formed by a, 1b and side dams (refractory dams) 2a, 2b. The molten metal is poured into the pool 3 through a container such as a tundish, and the molten metal 4 in the pool 3 is cooled by the cooling rolls 1a, 1
Cooled and solidified at the portion in contact with b to form a solidified shell.

The solidified shell moves with the rotation of the cooling roll, and the solidified shell is pressed into a thin steel sheet 5 at a close position where the cooling rolls approach each other, a so-called roll gap portion 6. Here, reference numeral 15 denotes a cooling roll end surface, and reference numeral 16 denotes a sliding surface. Also, Japanese Patent Application Laid-Open No. 10-4384
No. 0 discloses a method of preventing a bullion by exposing an end closure to a nearby electromagnetic field instead of preheating it to increase the temperature.

However, even in this method, a heating device is mainly provided outside the side weir, and the equipment is limited, so that a sufficient heating effect cannot be obtained. In addition, the effect of drawing in the jug cannot be expected from the positional relationship between the heating position and the metal, and this is not a sufficient measure for the metal that accumulates, leaving a problem. As described above, there is a demand for technology development that can further extend the life of the side weir by taking measures against overhang of the metal in twin-roll continuous casting.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to examine a method for preventing the formation of metal in the vicinity of a roll end face and a side weir in twin-roll continuous casting. Unlike conventional means such as vibration, A twin-roll system that increases the heat transfer resistance by bringing the molten metal into a soft contact state by applying an electromagnetic force, and suppresses the formation of metal by using Joule heat together with the induced current A continuous casting method and a casting apparatus are provided.

[0007]

The gist of the present invention to achieve the above object is as follows. (1) Injecting molten metal between a pair of water-cooled casting rolls, comprising a pair of refractory weirs installed at the ends of the rolls so as to form a pool of water in the rolls, and rotating the rolls. In the method of solidifying the molten metal by means of the method and casting a strip, the electromagnetic induction coil close to the inside of the refractory weir or the outside of the refractory weir on the side opposite to the roll makes soft contact with the electromagnetic field from the meniscus to the kiss point. A method of casting a metal strip, wherein a state or further induction heating is performed to control a triple point temperature Tt of a roll, a molten metal, and a refractory weir so as to satisfy the following expression.

T _S ≦ Tt ≦ T _L + 50 ° C. where T _{S is} the solidus temperature of the metal, and T _{L is} the liquidus temperature of the metal. (2) The metal strip casting method according to (1), wherein a high-frequency current having a frequency f in the following range flows through the electromagnetic coil. 4 ≦ ln (f) ≦ 6 (3) When the distance from the meniscus to the kiss point is Lm, the triple point temperature Tt in the range of the kiss point height + 0.3 × Lm from the kiss point height is expressed by the following equation. A method for casting a metal strip, wherein the method is controlled to satisfy the following.

T _{fS = 0.7} ≦ Tt ≦ T _L + 20 ° C. where T _{fs = 0.7} : temperature at which the solid phase ratio of metal reaches 70%,
T _L : liquidus temperature of metal. (4) The metal strip casting method according to any one of (1) and (3), wherein the electromagnetic induction coil is a cooling metal coil.

(5) The method for casting a metal strip according to any one of (1) to (3), wherein the electromagnetic induction coil is an uncooled coil. (6) The metal according to any one of (1) to (5), wherein the weir is constituted by a metal segment that transmits an induced current, and a refractory that covers a contact surface of the molten metal. Strip casting method.

(7) The metal strip casting according to any one of (1) to (6), wherein a temperature measured by a thermocouple embedded in the refractory is monitored to control a coil current condition. Method. (8) The metal strip according to any one of (1) to (7), wherein the contour of the projection of the electromagnetic induction coil in the roll axis direction is inside the contour of the pool between the rolls. In the casting method.

(9) An apparatus for performing the method according to any one of (1) to (3), wherein an electromagnetic coil close to the outside of the refractory weir on the side opposite to the roll and induction heating are controlled. A metal strip casting apparatus comprising a thermometer and a high-frequency output control device.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first feature of the present invention is that a molten metal including a semi-solid state in a roll is provided by an electromagnetic induction coil located inside the refractory weir or outside the refractory weir on the side opposite to the roll. In soft contact with the refractory weir, or
Further, since the induction heating is performed, a repulsive force or a repulsive force acts on the adhered metal, so that the metal is cast with a reduced contact heat transfer resistance with the side weir. Further, the solidification of the base metal is prevented by the heat generated by the induction heating, and the molten state can be maintained. For this reason, the metal is promoted to move downward by the pulling force of the cooling roll, and this movement is continuously performed, so that the metal does not stick or solidify.

In this case, the electromagnetic induction coil performs a soft contact state by an electromagnetic field over the area from the meniscus to the kiss point, or further performs induction heating, and sets the triple point temperature Tt of the roll, the molten metal, and the refractory weir to the following equation. It is important to control so as to satisfy, and if the temperature is kept below the solidus temperature, a strong metal is generated at the end, so it is necessary to keep the temperature above the solidus temperature. In the place where it was grasped by casting results, when the liquidus temperature exceeded 50 ° C, molten metal flowed in between the refractory weir and the roll, forming metal and damaging the refractory. Becomes T
_It has been found that it is important to control the temperature to _L + 50 ° C. or lower.

T _S ≦ T _t ≦ T _L + 50 ° C. where T _{S is} the solidus temperature of the metal, and T _{L is} the liquidus temperature of the metal. Here, _Tt can be estimated from the molten steel temperature and the casting conditions. However, if _Tt is controlled by a temperature monitored by a thermocouple buried near the triple point of the refractory weir, the controllability is further enhanced.

As a condition for applying the electromagnetic force in this case, since the metal is formed mainly at the triple point, it is necessary to control this part intensively, and furthermore, the control is performed in a wider range than this part. This causes problems such as re-melting of the solidified shell formed by cooling by the roll and damage to the surface. That is, ln (f) with respect to the frequency f
If the value is less than 4, the effect of the skin effect is small and the electromagnetic force acts on a wide range, causing a problem. If the value is more than 6, the effect tends to be saturated, so that the range is limited to this range.

The electromagnetic induction coil may be a cooled metal coil or a non-cooled coil, and the coil temperature determined by the self-heating of the coil becomes equal to or lower than the solidus temperature except for the commonly used internal water cooling type made of Cu. On the premise that the coil supply current is controlled as described above, there is no particular problem even in the case of a non-water-cooled type that shields heat made of, for example, a Ni-based superalloy or stainless steel.

In the present invention, a state in which the overhang of the rheological sherbet-shaped metal is pressed by the gap between the rolls and pulled and rolled so as to continuously melt and mix in the longitudinal direction of the rolls so as to be relatively soft and flowing. By doing so, sticking is prevented. FIGS. 1 (a) and 1 (b) show the mechanism of metal adhesion observed by the present inventors through observation between the roll and the side weir. In these figures, FIG. 1 (a) shows a situation in which the massy molten steel 8 adheres to the side weir surface, and the massy molten steel in the massy zone 8 comes to adhere to the side weir. FIG. 1B shows a situation in which the adhered metal is entangled near the kissing point. In this figure, as the casting proceeds, the central part of the metal is drawn in 11
Occurs, so that the top bullion starts to move 10 downward. Further, the solidified material at the lower part of the drawn-in member 11 has considerable solid strength.
Opens the gap in the drum, causing a partial increase in plate thickness. At this time, a gap is also formed between the side weir and the drum, and the molten metal is inserted. As a result, it becomes a jug and destroys the sealing performance of the side weir.

In order to prevent the adhesion of the bullion as described above, it is necessary to prevent the solidification of the bullion that has been initially adhered while continuously applying the action of rapidly sending the bullion downward. is there. The vibration in the casting direction, that is, the moving direction component of the molten metal, is small only by the conventional vibration caused by the rotation of the side dam in the roll side direction. For this reason, it becomes a base metal having the strength at which solidification has begun, which is disadvantageous against the occurrence of a jug in which the contact between the roll end surface and the side weir is alienated.

Further, in the present invention, a control has been studied with particular emphasis on a region near a kiss point where a pair of rotating rolls is near and cooled by heat transfer. That is, assuming that the distance from the meniscus to the kiss point is Lm, the triple point temperature Tt is controlled so as to satisfy the following expression in the range of the kiss point height + 0.3 × Lm from the kiss point height. T _{fS = 0.7} ≦ Tt ≦ T _L + 20 ° C. where T _{fS = 0.7} is the temperature at which the solid phase ratio of the metal reaches 70%,
T _L : liquidus temperature of metal. Here, the lower limit of the temperature is that when the cooled sherbet-like molten metal has a solid fraction of 70% or more (below the temperature of the solid fraction of 70%), the strength is remarkably increased, and the hot band is caused. This is a satisfactory condition, as it may cause damage to the refractory weir, and the upper limit is the risk that the sherbet-shaped molten metal will roll out from the roll and weir especially when the molten metal is rolled by the roll. This is a constraint condition that is required to keep the temperature control range narrower than the above-mentioned temperature control range and 20 ° C. below the liquidus temperature due to the increase in the temperature.

Further, regarding the outer shape of the coil, it is useful to efficiently generate an electromagnetic force or an induced current at the triple point. Therefore, it is necessary to install a coil near the triple point. By making the outline of the projection of the coil in the roll axis direction inside the outline of the pool shape between the rolls, the guiding efficiency can be further improved.

Hereinafter, the present invention will be further described with reference to examples.

[0023]

Embodiment 1 In this embodiment, an induction coil formed as a metal segment as shown in FIG. 2 is embedded in a side weir. As the conditions of the induction coil tested, the coil position was a triangular shape so as to surround the position up to the outside of the outline of the pool shape of the cooling roll as shown in FIG. The coil used was of two turns, the energizing condition was 300 KHz, and the effective current value was 100 A. Casting conditions are: SUS
304, casting amount: 100 t, casting dimensions and speed: casting width 1 m, casting thickness 6 mm, casting speed 35 m / min, roll radius: 0.6 m, molten steel pool depth: 0.4 m. The test results were evaluated by hot band evaluation. In the hot band, the base metal is caught in the slab, an unsolidified portion is generated at the center of the slab, and the slab thickness becomes uneven in the longitudinal direction of the casting. At this time, since the temperature of the unsolidified portion is high, the slab portion becomes a band shape glowing red in the casting width direction, and is called a hot band.

The frequency of occurrence of the hot band and the observation of the metal after casting were evaluated. When no electromagnetic force was applied, the hot band generation index was 5 to 10, the metal had a maximum thickness of 5 mm, and a maximum length. It was about 5 cm. On the other hand, when the electromagnetic force of the present invention is present, the hot band index is 1-2.
And almost no bullion was observed. Embodiment 2 In this embodiment, an induction coil formed as a metal segment as shown in FIG. 3 is embedded in a side dam.

As a condition of the induction coil tested, the coil position is a triangular shape so as to surround a position inside the outline of the pool shape of the cooling roll as shown in FIG. The coil used had two turns, and the energizing condition was 300 KHz, and the effective current values were 50 A and 100 A. The casting conditions were as follows: Class: SUS304, Casting amount: 10
At 0t, casting dimensions and speed are: casting width 1m, casting thickness 6m
m, casting speed 35 m / min, roll radius: 0.6 m, molten steel pool depth: 0.4 m. The test results were evaluated by hot band evaluation.

When the frequency of occurrence of the hot band and the observation of the ingot after casting were evaluated, the comparative electromagnetic coil shown in FIG.
7, the metal had a maximum thickness of 3 mm and a maximum length of about 4 cm. At 100 A, the hot band occurrence index is 1-2.
And almost no bullion was observed. On the other hand, in the case of the shape of this example, the hot band occurrence index was 1 to 2 at 50 A, and bare metal was hardly observed. This is because, in the case of the present embodiment, the rate at which the induced current from the coil is extinguished to the rolls is reduced, so that the same effect can be obtained even at a low current.

[0027]

According to the present invention, an electromagnetic force under specific conditions can be applied to the side weir, so that the base metal can be continuously moved in a molten state below the rolls, and the By avoiding the initial solidification of the metal, the contact between the roll and the side weir is made to be in soft contact, and the adhesion of the metal can be suppressed, thereby preventing the metal ingot. For this reason, the life of the side weir is improved, which is advantageous in terms of quality and cost.

[Brief description of the drawings]

FIG. 1 is a view showing a mechanism of metal adhesion according to the present invention, in which (a) is an adhesion on a surface and (b) is a figure showing winding.

FIG. 2 is a diagram illustrating an outline of an overall structure of a side weir according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating an outline of an overall structure of a side weir according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an outline of a conventional twin-roll type continuous casting machine.

[Explanation of symbols]

 1a, 1b: Cooling rolls 2a, 2b: Side dams 3: Hot water pool 4: Molten metal 5: Cast slab 6: Roll gap 7: Shell 8: Massy zone 10: Downward movement 11: Retraction of the center 12: Entangled 14: Meniscus 15: End face of cooling roll 16: Sliding surface

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Eiichi Takeuchi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Kenichi Miyazawa 20-1 Shintomi, Futtsu-shi, Chiba New Japan F-term in Technical Development Division of Steel Corporation (reference) 4E004 DA13 DA18 RA02 SB10

Claims (9)

[Claims] 1. A pair of refractory weirs is provided at a roll end so that molten metal is poured between a pair of water-cooled casting rolls and a pool of water is formed in the rolls. In the method of solidifying the molten metal by casting and casting a strip, the electromagnetic induction coil near the inside of the refractory weir or the outside of the refractory weir on the side opposite to the roll, by the electromagnetic field from the meniscus to the kiss point. A method of casting a metal strip, wherein the triple contact temperature Tt of a roll, a molten metal, and a refractory weir is controlled so as to satisfy the following expression in a soft contact state or further by induction heating. T _S ≦ Tt ≦ T _L + 50 ° C. where T _{S is} the solidus temperature of the metal, and T _{L is} the liquidus temperature of the metal. 2. The metal strip casting method according to claim 1, wherein a high frequency current having a frequency f in the following range flows through the electromagnetic coil. 4 ≦ ln (f) ≦ 6 3. The distance from the meniscus to the kiss point is Lm.
From the kiss point height, the kiss point height + 0.3 × L
A method for casting a metal strip, wherein the triple point temperature Tt is controlled in the range of m so as to satisfy the following expression. T _{fS = 0.7} ≦ Tt ≦ T _L + 20 ° C. where T _{fS = 0.7} is the temperature at which the solid phase ratio of the metal reaches 70%,
T _L : liquidus temperature of metal. 4. The metal strip casting method according to claim 1, wherein the electromagnetic induction coil is a cooling metal coil. 5. The method according to claim 1, wherein the electromagnetic induction coil is an uncooled coil. 6. The metal according to claim 1, wherein the weir is composed of a metal segment transmitting an induced current and a refractory covering a contact surface of the molten metal. Strip casting method. 7. The metal strip casting method according to claim 1, wherein a temperature measured by a thermocouple embedded in the refractory is monitored to control a coil current condition. 8. The metal strip according to claim 1, wherein the contour of the projection of the electromagnetic induction coil in the roll axis direction is inside the pool in the shape of a pool between the rolls. Casting method. 9. An apparatus for performing the method according to claim 1, wherein an electromagnetic coil is provided near the outside of the refractory weir on the side opposite to the roll, a thermometer for controlling induction heating, and a thermometer. An apparatus for casting a metal strip, comprising a high-frequency output control device.