JPH08290243A - Twin roll continuous casting method - Google Patents

Abstract

PURPOSE: To make continuous casting feasible by casting while changing roll pushing force and casting speed based on the relationship between tundish molten steel temp. and roll pushing force/casting speed so as to maintain set casting thickness constant. CONSTITUTION: By detecting a rotating speed of cooling drums 1a, 1b with a speedometer 11 and controlling a rotating speed of the cooling drums 1a, 1b through a drive controller 10 so as to satisfy set condition, the pulling speed is controlled. Further, a molten metal surface S1, that is, arc angle is detected by a level meter 15, a sheet thickness by a gap meter 16, a drum cooling water inlet/outlet temp. difference is detected by a thermometer 12 and is converted to a heat transfer rate of roll by a computing element 13, also, a tundish temp. is detected by a molten metal thermometer 14. The roll pushing force control is executed so as to satisfy the set condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin plate cast product using a twin-drum type continuous casting machine.

[0002]

2. Description of the Related Art The twin-drum type continuous casting method is an operating technique in which the casting speed is controlled so that the thickness of the slab becomes a predetermined thickness, and hot rolling or in-line heat treatment is carried out as necessary. What is important in carrying out stable casting for a long time in this process is to flexibly respond to changes in refining time and changes in operating conditions such as variations in molten steel temperature, that is, how to set the casting speed arbitrarily. In order to achieve such an object, various measures have been taken in the conventional casting technique, but in reality, none of them has been effective.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in manufacturing a thin plate cast product, the casting operation method is mainly intended to change the drum pressing force to control the casting speed. In addition, it provides an operating method that can flexibly respond to changes in operating conditions. Incidentally, conventionally, no proposal has been made regarding the casting speed control by the drum pressing force control.

[0004]

In the twin-drum type continuous casting method of the present invention, the drum pushing force is changed on the basis of the relationship between the predetermined tundish molten steel temperature, the drum pushing force and the casting speed during the continuous casting operation. However, it is possible to slow down the casting speed so that the casting speed is the one required for matching the charge and the next charge, and according to the change in the tundish molten steel temperature, the tundish molten steel temperature and the drum pressing are set in advance. By setting the drum pushing force commensurate with the tundish molten steel temperature based on the relationship between force and casting speed,
It is possible to suppress the change in casting speed to a small level, and the following four points are the gist.

(1) Based on the casting width w, the casting thickness d, and the casting speed W (t / min), the drawing speed V (m / min) is set to (1).
The point at which the cooling drum is closest to each other based on the arc angle θ formed by the pool of water formed between the pair of cooling drums, the heat transfer coefficient Q of the drum determined by the surface properties of the cooling drum, and the tundish molten steel temperature Ts. The central solid fraction fs at (drum kiss point) is determined by the equation (2),
Finally, the drum pushing force P is determined by the equation (3), and the drawing speed V, the central solid fraction fs, and the drum pushing force P are determined.
The number of rotations of the cooling drum and the molten steel supply amount to the molten metal pool are set so as to satisfy the value of, and continuous casting operation is performed while maintaining the set casting thickness d.

(2) When the twin drum type continuous casting described in the above (1) is performed, only the casting thickness d is changed without changing the casting speed W in the same charge and in the same cast. Based on the changed casting thickness d, the drawing speed V is determined by the equation (1), and then the central solid fraction fs and the drum pushing force P are determined by the equations (2) and (3). These casting speed W, drawing speed V, central solid fraction f
The rotation speed of the cooling drum and the molten steel supply amount to the molten metal pool are set so as to satisfy the values of s and the drum pressing force P, and continuous casting operation is performed while maintaining the changed casting thickness d.

(3) When the casting speed W is changed within the same charge and within the same cast during the twin drum type continuous casting described in the above (1) or (2), the changed casting Based on the speed W, the drawing speed V is determined by the equation (1), and then the central solid fraction fs and the drum pressing force P are determined by the equations (2) and (3) to determine the casting speed W, The rotation speed of the cooling drum and the amount of molten steel supplied to the molten metal pool are set so as to satisfy the values of the drawing speed V, the central solid fraction fs, and the drum pressing force P, and the changed casting speed W is maintained. While performing continuous casting operations.

(4) When the twin drum type continuous casting described in any of (2), (3) and (4) above is performed and the determined drum pressing force P exceeds the facility capacity, The casting speed W is reset, and the drawing speed V, the central solid fraction fs, and the drum pushing force P are determined again by the equations (1), (2), and (3), and the drum pushing force P is within the equipment capacity range. Casting speed W, drawing speed V, central solid fraction fs
And the continuous casting operation is performed while setting the rotation speed of the cooling drum and the molten steel supply amount to the molten metal pool so as to satisfy the value of the drum pushing force P and maintaining the set casting thickness d or casting speed W. To do.

Here, V = (1000 × W) / (d × w × γ) (1) fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, It is represented by Ts, θ, d) × V. P = J (fs) (3) V: Drawing speed (m / min) W: Casting speed (t /
Min) d: Casting thickness (mm) w: Casting width (mm) γ: Specific gravity of slab (t / m ³ ) θ: Arc angle (degree) fs: Central solid fraction (-) Ts: Tundish molten steel temperature (Degree) Q: heat transfer coefficient of drum (kcal / m ² / hr / ° C) g, h, J, M: function P: drum pressing force (t)

[0010]

According to the present invention, in the twin-drum type continuous casting method, the relationship between the casting thickness, the drawing speed, and the drum pushing force is set, and the setting conditions are changed so as to satisfy the relationship. Even if the supply amount and supply timing are deviated or the casting thickness is changed, the casting operation can be smoothly performed continuously while maintaining the set casting thickness constant.
Operability and yield of continuous casting can be improved.

[0011]

EXAMPLES In the present invention, when the casting size and casting speed are determined, the drawing speed is determined by the following equation. V = (1000 × W) / (d × w × γ) (1) V: drawing speed (m / min) W: casting speed (t /
Min) d: casting thickness (mm) w: casting width (mm) γ: specific gravity of slab (t / m ³ )

When the arc angle θ is set, the central solid fraction fs
Is set by the following equation. fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, Ts, θ, d) × V. fs: central solid fraction (-) V: drawing speed (m /
Min) θ: Arc angle (degree) Ts: Tundish molten steel temperature (degree) Q: Heat transfer coefficient of drum (kcal / m ² / hr / ° C) g, h: Function of θ, Q, Ts where g and h is a function determined by the drum cooling conditions, cast plate thickness, etc. g = a ₁ (θ, d) + a ₂ (θ, d) × Q + a ₃ (θ, d) × Ts h = b ₁ (θ , D) + b ₂ (θ, d) × Q + b ₃ (θ, d) × Ts. The coefficient changes depending on the arc angle θ and the plate thickness d,
a ₁ is −10 ^{5 to} 0, a ₂ is 0 to 10, and a ₃ is 0.1.
A value of 100, b ₁ is -100 to 100, and b ₂ is -10.
10, b ₃ takes a value of -100 to 100.

The drum pushing force P can be expressed by the following equation. P = J (fs) = A × 10 ^N (4) However, N = B × fs. Where A is 0.0
1-100 and B take the value of 0.01-10. The drum pushing force corresponding to the casting thickness and the drawing speed is obtained from the equation (4), and the set value of the drum pushing force can be changed in association with the change of the casting thickness or the drawing speed.

Although the setting of the drum pressing force is changed from the above, the central solid fraction fs affects the reheat of the slab under the drum, and thus has a proper control range. This range is determined by the slab strength, but generally fs =
It is set in the range of about 0.2 to 0.8.

Therefore, when the central solid fraction set by the above relational expression shows a value outside the control range, the casting speed is reset within an allowable range, and the drawing speed and the drawing speed are again set based on the above relational expression. The central solid fraction should be set and the central solid fraction should be within the control range before starting or continuing the operation.

As an example, FIG. 2 shows the relationship between the drawing speed and the central solid fraction, and FIG. 3 shows the relationship between the central solid fraction and the drum pushing force. These are: casting amount: W = 1.5 t / min. Casting width: w = 1300 mm Drum heat transfer coefficient: Q = 12,000 kcal / m ² / hr /
℃ Tundish molten steel temperature: Ts = 1525 ℃, 1510
° C, 1495 ° C Arc angle: θ = 40 ° Plate thickness: d = 3 mm Function and coefficient: g = a ₁ + a ₂ × Q + a ₃ × Ts, h = b ₁ + b ₂ × Q + b ₃ × Ts a ₁ = −1307, a ₂ = 2.8 × 10 ⁻³ , a ₃ = 0.
886, b ₁ = 0.44, b ₂ = 1.0 × 10 ⁻⁷ , b ₃
= −3.0 × 10 ⁻⁴ P = J (fs) = A × 10 ^N However, N = B × fs, A = 1.477, B = 1.65
6 Drum diameter: 1200 mm. Coefficients _{a 1 ~a 3, b 1 ~b} 3, A and B are preliminarily experiment, steels through experience, has been determined for each operating condition, these relationships from the (1) (4)
FIG. 1 shows an example apparatus for practicing the present invention with formulas
Is set in the setting device 8 in FIG. Calculation is performed by the calculator 9 according to the setting and change of the operating conditions, and the conditions (casting thickness, drawing speed, drum pushing force) necessary for maintaining the set casting thickness constant are set.

The rotation speeds of the cooling drums 1a and 1b are detected by the speedometer 11, and the rotation speeds of the cooling drums 1a and 1b are set and controlled by the drive control device 10 so as to satisfy the above setting conditions. , The withdrawal speed is controlled.

The level S1 of the molten metal, that is, the arc angle θ is measured by the level meter 15, the plate thickness is measured by the gap meter 16, and the heat transfer coefficient of the drum is measured by the temperature difference ΔT between the drum cooling water and the thermometer 12.
And the tundish temperature is detected by the molten steel thermometer 14, respectively, and the drum pressing cylinder 17 presses the drum so as to satisfy the above set conditions. Force control is performed.

In the present invention, the molten steel supply amount,
Even if the supply timing is deviated or the casting thickness is changed in the same charge or the same cast, the casting thickness is kept constant,
The casting operation can be started or continued one after another.

The present invention is applied to the following, and the drum diameter 120
An example of continuously casting thin plates using a 0 mm twin-drum type continuous casting device will be described. Here, the heat transfer coefficient Q of the drum as the casting condition Q = 12,000 kcal / m ² /
Corresponding to hr / ° C and arc angle θ = 40 °, pulling speed V (t /
Min) and the central solid fraction fs and the drawing speed V (m / min), the functions g, h and A and B of the relational expressions (2) and (3) are expressed by g = a ₁ + a ₂ × Q + a ₃ × Ts , H = b ₁ + b ₂ × Q
+ B ₃ × Ts, when the plate thickness is 3 mm, a ₁ = 1307, a ₂ = 2.8 × 10 ⁻³ , a ₃ = 0.8
86, b ₁ = 0.44, b ₂ = 1.0 × 10 ⁻⁷ , b ₃ =
When −3.0 × 10 ⁻⁴ and plate thickness 4 mm, a ₁ = −2183, a ₂ = 9.7 × 10 ⁻³ , a ₃ = 1.
450, b ₁ = 0.61, b ₂ = 9.1 × 10 ⁻⁷ , b ₃
= −5.0 × 10 ⁻⁴ , when the plate thickness is 5 mm, a ₁ = −2193, a ₂ = 8.4 × 10 ⁻³ , a ₃ = 1.
475, b ₁ = 0.66, b ₂ = 1.6 × 10 ⁻⁷ , b ₃
= −5.0 × 10 ⁻⁴ , A = 1.477, B = 1.656. This value is obtained from the operation results. Further, the slab specific gravity γ is set to 7.5 t / m ³ , and the central solid fraction control range is set to 0.2 to 0.7.

(Example 1) The amount of molten steel at the first charge is 60
A continuous casting operation of a cast piece having a casting width of 0.86 m and a casting thickness of 3 mm was planned at an interval of 40 minutes from the refining furnace at t. At this time, since the casting speed is 1.5 t / min, the drawing speed is 77.5 m / min from the equation (1). The arc angle was set to 40 °. The temperature of the molten steel in the tundish was as low as 1495 ° C.

When the second charge of continuous casting was cast for 30 tons, the arrival time of molten steel for the third charge was delayed by 5 minutes due to the circumstances of the refining furnace, and the time adjustment was immediately started. It is necessary to cast the remaining 30 t of molten steel at 1.5 t / min for 20 minutes, which is to be cast for 20 minutes. For this reason, the drawing speed was changed to 62.0 m / min in order to set the casting speed to 1.2 t / min, and at the same time, the central solid fraction was determined to be 0.67 so as not to change the casting thickness by the formula (2). , Drum pushing force was calculated from the equation (4) and the setting was changed to 19t. After the start of the third charge casting, the withdrawal speed was returned to 77.5 m / min and the drum pushing force was returned to 4.5 t to prepare for the arrival of the fourth charge pot 40 minutes later.

In this way, even though the arrival of molten steel was delayed by 5 minutes at the third charge, by changing the setting of the drawing speed and the pushing force of the drum, the initial set casting thickness of 3 mm was not changed, It was possible to cast a thin plate in a continuous casting operation of 4 charges within the scheduled casting time.

(Example 2) The amount of molten steel at the first charge is 60
At the same time, the casting width is 0.
Successive casting operations for casting 8 m slabs were planned. At this time, since the casting speed was 1.2 t / min and the initial casting thickness was 4 mm, the drawing speed was set to 50.2 m / min from the formula (1) and the drum pushing force was set to 4.6 t from the formula (4). And then started casting.

Since the casting thickness had to be changed from 4 mm to 3 mm when 30 t of the second charge of the continuous casting had been completed, the thickness was changed. It is necessary to maintain the same 1.2 t / min in order to match the casting end timing of the next charge with the molten steel supply time from the refining furnace in continuous casting. Therefore, the drawing speed was calculated to be 66.7 m / min, and the drum pushing force was changed to 10.7 t from the expression (4) at the same time, which was calculated from the expression (1), and the casting was continued.

Next, since the casting thickness was to be changed from 3 mm to 5 mm from the charge start at the third charge of casting, the second thickness change was started. The molten steel temperature at the 3rd charge is as high as 1525 ° C. In order to maintain the casting speed of 1.2 t / min, the drawing speed is 40.0 m / min from the formula (1), and the drum pushing force is 1.93 t from the formula (4). At this time, the central solid fraction is calculated from the formula (2). Was 0.07.

This central solid fraction cannot be adopted because it is outside the range of 0.2 to 0.8. Therefore, the molten steel supply interval from the refining furnace was extended from 50 minutes to 60 minutes, the casting speed was 1.0 t / min, and the drawing speed was calculated from equation (1) to 33.3 m / min. The central solid fraction was again determined from the above to be 0.29.

Since the central solid fraction falls within the control range, the calculation operating conditions of this time are adopted, and the drawing speed is 33.3 m /
Min, drum pressing force 4.46 t, central solid fraction at this time 0.
At 29, the casting operation was continued, the refining furnace was also contacted, and the molten steel supply interval was extended to 60 minutes.

In this way, even when the casting thickness was changed in the middle, the continuous casting operation could be realized while adjusting the molten steel supply timing from the refining furnace and the casting end timing for each charge.

[0030]

EFFECTS OF THE INVENTION According to the present invention, in the twin drum type thin plate continuous casting method, when the conditions are changed during the operation, for example, the supply amount of molten steel, the supply timing, the charge, the casting thickness in the cast, etc. are changed. In addition, the set casting thickness (size) can be maintained constant and continuous casting operations can be realized.
Operability and yield can be greatly improved.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing an example of an apparatus for carrying out a twin drum type thin plate continuous casting method adopting the present invention.

FIG. 2 is an explanatory view showing a relationship between a casting rate and a central solid fraction in a twin-drum type thin plate continuous casting method.

FIG. 3 is an explanatory diagram showing a relationship between a central solid fraction and a drum pushing force in a twin drum type thin plate continuous casting method.

[Explanation of symbols]

 1a, 1b Cooling drum 2a, 2b Side weir 3 Hot water pool 4 Tundish 5 Stopper 6 Nozzle 7 Cast slab 8 Setting device 9 Calculator 10 Drive controller 11 Speedometer 12 Cooling water thermometer 13 Heat transfer coefficient calculator 14 Molten steel Thermometer 15 Level gauge 16 Drum gap meter 17 Drum pressing cylinder S Molten steel S1 Molten steel level

Claims (5)

[Claims] 1. When manufacturing a thin plate slab using a twin-drum type continuous casting machine, the drum pressing force and the casting speed are changed based on a predetermined relationship between the tundish molten steel temperature, the drum pressing force and the casting speed. A twin-drum type continuous casting method characterized in that the casting operation is carried out. 2. When performing twin-drum type continuous casting, the drawing speed V (m / min) is determined by the formula (1) based on the casting width w, the casting thickness d and the casting speed W (t / min) to be produced. Then, based on the arc angle θ formed by the pool of water formed between the pair of cooling drums, the heat transfer coefficient Q of the drum determined by the surface properties of the cooling drum, and the tundish molten steel temperature Ts, the point where the cooling drum comes closest (drum kiss point). ), The central solid fraction fs is determined by the equation (2), and finally the drum pressing force P is determined by the equation (3).
2. The continuous casting operation according to claim 1, wherein the number of revolutions of the cooling drum and the amount of molten steel supplied to the molten metal pool are set so as to satisfy the values of the central solid fraction fs and the drum pressing force P. Twin drum type continuous casting method. Here, V = (1000 × W) / (d × w × γ) (1) fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, Ts, θ , D) × V. P = J (fs) (3) V: Drawing speed (m / min) W: Casting speed (t /
Min) d: Casting thickness (mm) w: Casting width (mm) γ: Specific gravity of slab (t / m ³ ) θ: Arc angle (degree) fs: Central solid fraction (-) Ts: Tundish molten steel temperature (Degree) Q: heat transfer coefficient of drum (kcal / m ² / hr / ° C) g, h, J, M: function P: drum pressing force (t) 3. When performing twin-drum type continuous casting according to claim 2, when changing only the casting thickness d without changing the casting speed W within the same charge and within the same cast, Based on the changed casting thickness d, the drawing speed V is (1)
Then, the central solid fraction fs and the drum pressing force P are determined by the equations (2) and (3),
The rotation speed of the cooling drum and the amount of molten steel supplied to the molten metal pool are set so that the values of the casting speed W, the drawing speed V, the central solid fraction fs, and the drum pressing force P are satisfied.
A twin-drum type continuous casting method, characterized in that continuous casting operation is performed while maintaining the changed casting thickness d. V = (1000 × W) / (d × w × γ) (1) fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, Ts, θ, d) It is represented by × V. P = J (fs) (3) 4. When the twin drum type continuous casting according to claim 2 or 3 is being performed, when the casting speed W is changed within the same charge and within the same cast, based on the changed casting speed W Then, the drawing speed V is determined by the equation (1), and then the central solid fraction fs and the drum pressing force P are determined by the equations (2) and (3). The continuous casting is performed while setting the rotation speed of the cooling drum and the molten steel supply amount to the molten metal pool so as to satisfy the values of the central solid fraction fs and the drum pressing force P, while maintaining the changed casting speed W. A twin-drum type continuous casting method characterized by performing operations. V = (1000 × W) / (d × w × γ) (1) fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, Ts, θ, d) It is represented by × V. P = J (fs) (3) 5. When performing the twin-drum type continuous casting according to any one of claims 2, 3 and 4, when the determined drum pressing force P exceeds the facility capacity, the casting speed W
And the drawing speed V, the central solid fraction fs, and the drum pushing force P are determined again by the equations (1), (2), and (3), and the drum pushing force P is within the equipment capacity range. The rotation speed of the cooling drum and the molten steel supply amount to the molten metal pool are set so that the values of the casting speed W, the drawing speed V, the central solid fraction fs, and the drum pressing force P are satisfied, and the set casting thickness d is set. Alternatively, the twin-drum type continuous casting method is characterized in that the continuous casting operation is performed while maintaining the casting speed W. V = (1000 × W) / (d × w × γ) (1) fs = g (Q, Ts, θ, d) × 10 ^M (2) where M = h (Q, Ts, θ, d) It is represented by × V. P = J (fs) (3)