JPH07276004A - Method for controlling crown and thickness of cast slab in twin roll type continuous casting process - Google Patents

Abstract

PURPOSE:To simply and surely control the crown and the thickness of a cast slab without affecting the productivity and to reduce the production cost. CONSTITUTION:A molten metal basin part 4 formed in a gap between one pair of water cooling casting rolls 2a, 2b is sealed with inert gas of one kind or mixing two or more kinds and supplying temp. of this seal gas and/or the mixing ratio of the gases are adjusted to vary the heat flux from the molten metal L to the casting rolls 2a, 2b and thus, the crown and the thickness of the cast slab is controlled during casting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slab crown and a plate thickness control method in a twin roll type continuous casting method for continuously casting a thin plate slab, and particularly to a kind of an inert gas for sealing a basin. The present invention relates to a slab crown and a plate thickness control method in a twin roll continuous casting method, which focuses on the difference in thermal conductivity depending on the supply temperature.

[0002]

2. Description of the Related Art Generally, a twin-roll type continuous casting apparatus is known as an apparatus to which the Bessemer type continuous casting method is applied, and a molten metal is injected between a pair of water-cooled casting rolls to solidify the metal. Manufactures thin plates.

A thin plate is manufactured by this type of twin roll type continuous casting apparatus 11 as shown in FIG. As shown in the drawing, the molten metal L is injected from above between a pair of casting rolls 12a, 12b arranged at a predetermined interval, and the casting rolls 12a, 12a, 12b having an internal water cooling structure are provided.
Rotate 12b inward and downward. Then, the molten metal L contacts the casting rolls 12a and 12b and is cooled, and solidifies in an arc shape on the surfaces of the casting rolls 12a and 12b as the solidification shell S. Each solidified shell S is a casting roll 12a, 12b
The rotation speed of the rolls causes the rolls to approach each other, and the minimum part of the roll gap (hereinafter,
It is called "roll kiss point". ) K is pressed to form a cast slab C having a predetermined thickness, and the cast slab C is extracted downward between the casting rolls 12a and 12b.

In this case, the solidification of the solidified shell S starts at the point F at which the molten metal L comes into contact with the casting rolls 12a and 12b (hereinafter referred to as "solidification start point"). Each solidified shell S that has started to solidify from the solidification starting point F of each casting roll 12a, 12b continues to grow to the roll kiss point K, and each solidified shell S is pressure-bonded at the roll kiss point K to form a slab C having a predetermined thickness. Becomes

Although the thin plate slab C is manufactured in this manner, it is important to control the slab crown and the plate thickness to desired values in order to obtain a high quality thin plate product. As a related technique for controlling such a slab crown, JP-A-61-37
No. 354 (hereinafter referred to as "Prior Art 1") discloses "a water-cooled drum in a drum type thin plate continuous casting machine" and JP-A-2-307652 (hereinafter referred to as "Prior Art 2"). There is a "crown control method in thin-material continuous casting" disclosed in ".

The invention disclosed in the prior art 1 is "a drum-type thin plate continuous casting in which molten steel is continuously supplied between a pair of parallel water cooling drums and solidified into a plate shape to continuously cast thin plates. In the machine, the water-cooling drum is given a drum-like shape corresponding to thermal deformation in advance, and the water-cooling drum becomes a right cylinder during casting. "

The invention disclosed in the prior art 2 is
"The molten metal supplied to the surface of the pair of cooling drums is rapidly cooled.
When solidifying and continuously casting a thin cast piece, the profile of the thin cast piece sent out from the drum gap of the cooling drum is measured, and the flow rate of the cooling water supplied to the cooling drum is adjusted based on the measurement result. "What to do" is the gist.

On the other hand, as a related technique for controlling the thickness of the cast slab, there is a "twin roll type casting and rolling mill" disclosed in Japanese Patent Laid-Open No. 58-148056 (hereinafter referred to as "Prior Art 3"). JP-A-63-224846 (hereinafter,
It is called "Prior Art 4". ), "Continuous casting method and apparatus for metal ribbon".

The invention disclosed in the prior art 3 is that "a molten metal pool formed by two rolls,
A limiting plate is provided to adjust the contact area between the roll and the molten metal. "

The invention disclosed in the prior art 4 is
"When manufacturing a metal ribbon by rapidly solidifying the molten metal supplied to the surface of the cooling drum, the current molten metal surface on the surface of the cooling drum was detected, and the molten metal surface contacted the surface of the cooling drum. The wall thickness of the solidified shell that grows at the time T when the solidified shell generated at the point reaches the roll gap is calculated, and based on the calculated value, the flow rate of the molten metal supplied to the surface of the cooling drum and after the time T has elapsed. "Controlling the rotation speed of the cooling drum in".

[0011]

By the way, Prior Art 1
In the invention disclosed in, since the amount of thermal expansion of the water cooling drum is different for each cast plate thickness, in order to satisfy the appropriate crown amount in various plate thicknesses, a large number of water cooling drums corresponding to the plate thickness are prepared. There was a problem that I had to do.

Further, in the invention disclosed in Prior Art 2, there is a problem that the internal structure of the water cooling drum becomes complicated because it is necessary to control the amount of cooling water independently in the width direction of the water cooling drum. It was

Further, in the invention disclosed in the prior art 3, since the limiting plate is used, there is a problem that the equipment operation becomes complicated and the manufacturing cost increases.

In the invention disclosed in Prior Art 4, since the rotation speed of the roll and the flow rate of the molten metal are changed, there is a problem in that the productivity is changed.

In view of the above-mentioned problems, an object of the present invention is to simply and surely fix a slab crown without changing productivity.
It is an object of the present invention to provide a slab crown and a plate thickness control method in a twin roll type continuous casting method capable of controlling the plate thickness and reducing the manufacturing cost.

[0016]

In order to achieve the above-mentioned object, a slab crown and a plate thickness control method in a twin roll type continuous casting method according to the present invention are provided in a molten metal pool formed between a pair of water cooling casting rolls. In a twin roll type continuous casting method of continuously producing a thin plate cast by injecting molten metal, the molten metal pool part is sealed with an inert gas in which one kind or two or more kinds are mixed,
By adjusting the supply temperature of the seal gas and / or the mixing ratio of the gases, the heat flux from the molten metal to the casting roll is changed,
It controls the slab crown and plate thickness during casting.

In the above structure, preferably, the slab crown and plate thickness after the control are measured during casting to adjust the supply temperature of the seal gas and / or the gas mixing ratio.

[0018]

As shown in FIG. 1, in the molten metal meniscus portion M located between the solidified shell S and the casting rolls 2a, 2b during casting, the static pressure of the molten metal is small, so that the molten metal pool 4 is inactive. Entrapment of gas occurs. The entrapment thickness of the seal gas is substantially uniquely determined by the contact time between the molten metal and the roll (the ratio of the contact arc length of the molten metal and the roll to the casting speed). Therefore, in order to control the amount of heat transferred from the molten metal L to the casting rolls 2a and 2b during the contact time between a certain molten metal and the rolls, the thermal conductivity of the seal gas may be changed.

That is, according to the structure of the slab crown and the plate thickness control method described above, as a means for changing the thermal conductivity of the seal gas, an inert gas containing one kind or a mixture of two or more kinds is used as the seal gas, The supply temperature and / or the gas mixing ratio are adjusted. When the thermal conductivity of the seal gas is changed in this manner, the heat flux from the molten metal to the casting roll changes, so that the slab crown and plate thickness are controlled during casting.

If the crown and plate thickness of the slab after control as described above are measured during casting, and the measured values are fed back for adjusting the supply temperature of the sealing gas and / or the gas mixing ratio, the casting One-sided crown / thickness can be controlled more accurately.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a cast crown and plate thickness control method in a twin roll type continuous casting method according to the present invention will be described in detail below with reference to the accompanying drawings. The slab crown and plate thickness control method in the twin roll type continuous casting method of the present embodiment is performed using a general twin roll type continuous casting device.
That is, as shown in FIG. 1, twin roll type continuous casting apparatus 1
A pair of casting rolls 2a and 2b having a water cooling function are arranged at a predetermined interval. These casting rolls 2a,
Side weirs 3 are provided at both ends of 2b, and a pool 4 for pooling the molten steel L in the section partitioned by them.
Are formed.

Molten steel L is poured into the basin 4 from above, and when the internal water-cooled casting rolls 2a and 2b are rotated inwardly downward, the molten steel L is cast into the casting rolls 2a and 2b.
It is cooled by contacting b, and solidifies in an arc shape on the surface of each casting roll 2a, 2b as a solidification shell S. Each solidified shell S
Are moved closer to each other as the casting rolls 2a and 2b rotate, and are pressed at a roll kiss point K to form a slab C having a predetermined thickness, which is extracted downward from between the casting rolls 2a and 2b.

Further, an in-line rolling machine (not shown) is provided downstream of the casting rolls 2a and 2b to reduce the solidified slab C to a desired plate thickness, if necessary. The thin plate slab C that has passed through this is sequentially wound by a coiler (not shown) installed on the downstream side of the inline rolling mill.

The pool 4 into which the molten steel L is poured is
It is sealed with an inert gas to prevent its oxidation. In the slab crown and plate thickness control method of the present embodiment, the molten metal pool portion 4 is an inert gas obtained by mixing one or more of helium (He), neon (Ne), argon (Ar) and the like. Seal with. The inert gas in which one kind or a mixture of two or more kinds is used is because the thermal conductivity differs depending on the kind of gas.

The thermal conductivity (W / mK) of gas is
Not only the type of gas but also the temperature (° C.) of the gas, as shown in FIG. It can be seen that the thermal conductivity (W / m · K) of the gas increases as the temperature (° C) of the gas increases.

As described above, the encapsulation thickness of the seal gas is substantially uniquely determined by the casting speed. Therefore, at a certain casting speed, the molten metal L is cast into the casting rolls 2a, 2b.
In order to control the amount of heat transferred to the seal gas, the thermal conductivity of the seal gas may be changed. Therefore, in this embodiment,
As a means for changing the thermal conductivity of the seal gas, its supply temperature and / or gas mixture ratio is adjusted.

In this way, the supply temperature of the seal gas and / or
Alternatively, if the gas mixing ratio is adjusted, the heat flux from the molten metal L to the casting rolls 2a, 2b changes as a result, but the heat flux q can be obtained by the following formula.

That is, dg: thickness of entrained gas, k
The thermal conductivity h = 1 / (dg / kg + 1 / hr) where g is the thermal conductivity of the gas and hr is the heat transfer resistance to the casting roll. Further, when Ts is the surface temperature of the molten metal and Tr is the surface temperature of the casting roll, the heat flux q = h (Ts-Tr). Therefore, when the thermal conductivity kg of the gas increases, the heat flux q increases, while when the thermal conductivity kg of the gas decreases, the heat flux q decreases.

As described above, the method for controlling the slab crown and the plate thickness of the present embodiment adjusts the supply temperature of the seal gas and / or the mixing ratio of the gas to change the thermal conductivity kg of the gas. The heat flux q from the molten metal L to the casting rolls 2a and 2b is changed to control the crown and plate thickness of the slab during casting.

Next, in order to confirm the operational effects of the cast crown and plate thickness control method of the present embodiment, an experiment was conducted to find the relationship between the gas temperature and the cast crown or plate thickness under the following conditions. . The casting rolls 2a and 2b have a roll width of 350 m.
m, roll diameter: formed to a size of 400 mmφ,
It is an internal water-cooled Cu roll. Also, the casting roll 2
As shown in FIG. 3, a and 2b are dead flat in the state before casting of (a) and are formed so as to expand like a drum in the state of (b) during casting.

The casting conditions are casting speed: 35 m / min,
Cast plate thickness: It is set to 2.2 to 3.1 mm. The contact arc length between the casting rolls 2a and 2b and the molten metal L is 17
It is set to 5 mm and the casting temperature is set to 1570 ° C. Furthermore, casting materials include low carbon steel (JIS
Standard SPHC, SS400 equivalent) was adopted.

Under the conditions as described above, Experiment 1 was conducted with He,
With respect to the gases of N ₂ , Ar, He-30% Ar, and He-60% Ar, the gas temperature was changed from 0 to 1200 ° C, and the cast crown amount with respect to the temperature of each gas was obtained.

FIG. 4 is a graph showing the result of Experiment 1 as a relationship between the gas temperature (° C.) and the slab crown amount (μm). As shown, as the temperature of each gas increases, the thermal conductivity of each increases,
It was found that the slab crown amount (Δd ₁ + Δd ₂ ) increased.

FIG. 5 shows the results of Experiment 1 as Ar in He gas.
6 is a graph showing the relationship between the concentration (%) and the cast crown amount (μm). Ar in He gas as shown
Since the thermal conductivity increases as the concentration decreases,
It was found that the slab crown amount increased.

That is, in order to increase the amount of slab crown, it is sufficient to increase the supply temperature of the seal gas and / or the mixing ratio of the gas having good thermal conductivity, while in order to decrease the amount of slab crown, the seal amount is reduced. It suffices to lower the gas supply temperature and / or the mixing ratio of the gas having good thermal conductivity.

Experiment 2 was conducted under the same conditions as Experiment 1.
Is He, N ₂ , Ar, He-30% Ar, He-60
With respect to the% Ar gas, the gas temperature was changed from 0 to 1200 ° C., and the slab thickness for each gas temperature was obtained.

FIG. 6 is a graph showing the results of Experiment 2 as a relationship between the gas temperature (° C.) and the slab thickness (mm). As shown in the figure, it was found that as the temperature of each gas rises, the thermal conductivity of each gas increases, so that the thickness of the cast slab increases.

FIG. 7 shows the results of Experiment 2 as A in He gas.
It is a graph represented by the relationship between r concentration (%) and the cast crown amount (μm). A in He gas as shown
It was found that as the r concentration decreases, the thermal conductivity increases, so that the slab plate thickness increases.

That is, as in Experiment 1, in order to increase the thickness of the slab, it is sufficient to increase the supply temperature of the seal gas and / or the mixing ratio of the gas having good thermal conductivity, while the thickness of the slab is increased. In order to reduce the temperature, the supply temperature of the seal gas and / or the mixing ratio of the gas having good thermal conductivity may be lowered.

As described above, the cast crown and plate thickness control method of this embodiment simply and reliably controls the cast crown and plate thickness only by adjusting the supply temperature of the seal gas and / or the gas mixing ratio. Therefore, the productivity is not changed. In addition, since existing equipment can be used, the versatility is high and the manufacturing cost can be reduced.

Further, the slab crown and plate thickness after the control as described above are measured during casting, and the measured values are fed back to the supply temperature of the seal gas and / or the gas mixing ratio adjustment. By doing so, the slab crown and plate thickness can be controlled more accurately.

[0042]

As described above, according to the slab crown and the plate thickness control method in the twin roll type continuous casting method according to the present invention, the slab crown and the strip crown can be easily and surely changed without changing the productivity. It has an excellent effect that the plate thickness can be controlled and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a side view of essential parts showing an example of a twin roll type continuous casting apparatus used in the present invention.

FIG. 2 is a graph showing the relationship between gas temperature and gas thermal conductivity.

FIG. 3 shows casting rolls used in Experiment 1 and Experiment 2, where (a) is a state before casting and (b) is a state during casting.

FIG. 4 is a graph showing the relationship between the gas temperature and the slab crown amount, which is the result of Experiment 1.

FIG. 5 is a graph showing the results of Experiment 1 regarding the relationship between the Ar concentration in He gas and the amount of slab crown.

FIG. 6 is a graph showing the relationship between the gas temperature and the thickness of the slab as a result of Experiment 2.

FIG. 7 is a graph showing the results of Experiment 2 regarding the relationship between the Ar concentration in He gas and the amount of slab crown.

FIG. 8 is a side view of an essential part showing an example of a conventional twin roll type continuous casting apparatus.

[Explanation of symbols]

 1 Twin roll type continuous casting device 2a, 2b Casting roll 3 Side weir 4 Hot water pool part 11 Twin roll type continuous casting device 12a, 12b Casting roll C Cast piece F Solidification start point K Roll kiss point L Molten metal (molten steel) M Melted meniscus part S solidification shell

Claims (2)

[Claims] 1. A twin roll type continuous casting method for continuously producing thin plate casts by injecting a molten metal into a molten metal pool formed between a pair of water-cooled casting rolls, wherein one or two types of the molten metal pool are provided. Sealing with the above-mentioned mixed inert gas, adjusting the supply temperature of the sealing gas and / or the mixing ratio of the gases to change the heat flux from the molten metal to the casting roll, and the cast slab crown / plate during casting A slab crown and a plate thickness control method in a twin roll type continuous casting method characterized by controlling the thickness. 2. The twin roll type continuous casting method according to claim 1, wherein the controlled slab crown and plate thickness are measured during casting to adjust the supply temperature of the sealing gas and / or the gas mixing ratio. Cast slab crown and plate thickness control method.