JPH0454542B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control method for reducing variations in slab width of continuous slabs that are continuously cast and supplied to a rolling process.

(Prior art) Conventionally, slabs cast by continuous casting are sized to the slab width and thickness required for the rolling process using a sizing mill or a breakdown mill, and then supplied to the rolling process. Ru.

Recently, this sizing mill, etc. has been omitted, and in order to directly feed the slab from continuous casting to the rolling process, continuous equipment is equipped with a mold width variable device that changes the width of the mold during casting to obtain the width required in the rolling process. Width variable is implemented. Techniques for varying mold width during casting include those shown in Japanese Patent Publication No. 3452/1982 and Japanese Patent Application Laid-open No. 14825/1983.

However, although the width of a cast slab is basically determined by the width of the mold, in reality the actual width of the slab is determined by the width of the slab set based on various operating conditions. is changing.

Particularly in a continuous casting machine that performs high-speed casting, this fluctuation in slab width becomes large, and a high-capacity width reduction equipment is required in the rolling process. Therefore, even if the width during casting is varied using a continuous caster and the sizing mill step is omitted, it is often necessary to increase the capacity of the width reduction equipment on the rolling side.

Factors that influence this slab width variation include conditions such as casting speed, molten steel static pressure slab pulling resistance, and slab temperature. A specific outline of the width fluctuation is shown in FIG.

That is, when casting is performed with a constant mold width, the slab width gradually becomes wider at the beginning of casting, and gradually narrows at the end of casting. this is,
This is thought to be due to the difference in the deformation resistance of the slab due to bulging force and compressive force, which is caused by changes in slab pull-out resistance and molten steel static pressure that occur at the beginning and end of casting.

Furthermore, when the casting speed changes, the slab width also changes.
This is thought to be due to the difference in the degree of slab deformation caused by the bulging force due to the change in shell thickness as the casting speed changes.

Specifically, Fig. 6 shows an example of a cast slab cast at a casting speed of 1.6 m/min, measured at 1 m intervals. The difference between the maximum width part and the minimum width part is about 50 mm.

If you have a sizing mill, this width variation will not be much of a problem, but if you supply slabs directly to the rolling process without a sizing mill, the rolling process must have width reduction equipment that can absorb this width variation. This will lead to an increase in equipment costs. In order to solve this problem, the applicant has already proposed the following improvement measures in Japanese Patent Application No. 73499/1984 (Japanese Patent Application Laid-open No. 232049/1982).

In other words, the mold width at the start of casting is set in advance to be wider than the planned slab width, and at the beginning of casting, the mold width is gradually narrowed to compensate for width fluctuations that occur during the early casting period. I do. On the other hand, at the final stage of casting, wide mold width control is performed in response to width fluctuations.

Furthermore, when a change in casting speed occurs, the mold width is controlled according to the amount of speed change, and if there is a mold width change due to a change in the slab width required for the rolling process, this method is given priority. It is.

(Problems to be Solved by the Invention) However, the method described above also does not take slab pulling resistance as a factor in width control, and cannot achieve more accurate slab width control.

The present invention provides a control method that performs high-speed casting and reduces fluctuations in slab width in a continuous casting machine that has large fluctuations in slab width.

(Means for Solving the Problems) The present invention was made in view of the above situation, and is intended to obtain a target slab width by changing the width of the mold based on the drawing resistance of the slab.

Originally, the slab pull-out resistance is uniquely determined by the casting area, cast slab width, and casting speed (the value is hereinafter referred to as the standard slab pull-out resistance).
In reality, as shown in Figure 1, even under the same casting conditions, the pull-out resistance (actual value - reference value) changes by about 30 tons, and as a result, the width of the cast slab changes in proportion to the resistance, and the
It was found that it fluctuated by about 20 mm.

Factors that may cause this slab withdrawal resistance (actual value - standard value) to change include changes in the characteristics of the continuous casting machine due to aging, segment conversion, roll oiling, etc., but changes in this resistance can be predicted. It is currently impossible to do so.

Therefore, the present invention continuously measures and calculates this unpredictable slab pull-out resistance (actual value - reference value), calculates the required change in mold width from the resistance value,
The mold width is corrected online based on the obtained change amount, and a continuously cast slab width constant control method is devised to cast slabs with a constant width with higher precision. That is, the present invention provides a method for controlling a constant slab width in a continuous caster having mold equipment whose width can be varied during casting, by measuring the actual slab pull-out resistance of the continuous caster by measuring the current of the pinch rolls of the continuous caster. The standard slab pull-out resistance is calculated from the required slab width and casting speed as shown below.
Calculate the amount of slab width change using equation (1), calculate the slab width change from the difference between the actual slab pull-out resistance and the standard slab pull-out resistance using equation (3) below, and change the mold width according to the slab width change amount. The present invention also provides a method for controlling the width of continuously cast slabs to maintain a constant width, which is characterized by suppressing width fluctuations of the finally cast slabs within a certain range.

R ₁ = (a ₁ · V + b ₁ ) · W + (a ₂ · V + b ₂ ) ... (1) formula R ₁ : Standard slab withdrawal resistance, W: Required slab width, V : Casting speed, a ₁ ~ b ₂ : Constant R ₂ = Σ (1/9.8・K・Φi・Iai・1/γ)
...(2) Formula R ₂ : Actual slab withdrawal resistance, Φi : #i pinch roll motor magnetic flux, K : Constant, I _ai : #i pinch roll motor current measurement value, γ : pinch roll radius Yw=a・Xt+b...Equation (3) Yw: Amount of change in slab width, Xt: Difference between actual slab pull-out resistance and standard slab pull-out resistance, a, b: Constants The specific method of the present invention will be described below. .

First, the standard slab withdrawal resistance R ₁ is calculated from the width of the slab to be cast and the casting speed using the standard slab withdrawal resistance calculating device 12 shown in FIG. The standard slab pulling resistance consists of line resistance, straightening resistance, and slab squeezing resistance, and each of these resistances changes depending on the cast slab width and casting speed, and can be expressed by the following equation (1). This equation (1) is determined in advance by actual measurements under the best equipment conditions when a continuous casting machine is newly installed or when a complete change is made thereafter.

R ₁ = f(W・V) (a ₁・V+b ₁ )・W+(a ₂・V+b ₂ )...Equation (1) W: Cast slab width [mm] V: Casting speed [m/min] a ₁ ~ b ₁ : Constant Figure 3 shows the relationship between the standard slab pull-out resistance, the required slab width, and the casting speed.

On the other hand, the current in the pinch rolls of the continuous casting machine is actually measured using the slab pulling resistance measuring device 10 shown in FIG. 2, and the actual slab pulling resistance R ₂ of the continuous casting machine is calculated from the following formula (2).

R ₂ = Σ (Ti/γ) = Σ (1/9.8・K・Φi・Iai・1/γ)……(2) Formula i: Pinch roll No. T _i : #i Pinch roll torque [Kg・m] γ: Pinch roll radius [m] K: Constant Φi: #i Motor magnetic flux [wb/ ^m2 ] I _ai : #i Motor armature current [A] Next, the mold is created using the slab withdrawal resistance shown in Figure 2. The width variation setting device 11 determines the difference between the standard slab pull-out resistance calculation value R ₁ obtained by equation (1) and the measured slab pull-out resistance R ₂ obtained by equation (2). Considering this as a change in resistance, the slab pull-out resistance (actual value -
Based on the proportional relationship between the standard value) and the measured width variation, the following formula (3) (in the form of the inverse correlation formula in Figure 1) is used to determine the amount by which the mold width should be changed due to slab pull-out resistance. Then, the amount of change Yw in the mold width of the continuous casting machine is determined using the equation (3), and is set in the mold width variation calculation device 6.

Yw=a・Xt+b...Equation (3) Yw: Amount of change in slab width [mm] Xt: Difference between actual slab pull-out resistance and standard slab pull-out resistance [ton] a, b: Constants In Figure 2 , 1 is a ladle, 2 is a tundish, 3 is a variable width mold, 4 is a slab, 5 is a mold width variable control device, 7 is a planned slab width setting device, 9 is a casting speed setting device, 11 is a slab drawing device Represents a width variation setting device using resistance.

(Effects of the Invention) By implementing the control of the present invention, if there is a change in the slab withdrawal resistance during casting, the width can be immediately changed in accordance with the change, and the effect shown in FIG. The amount of width variation of the actually cast slab can be suppressed to a small range. This enables high-speed casting and reduces fluctuations in slab width even in continuous casters with large fluctuations in slab width, without increasing the capacity of the width reduction equipment in the rolling process, and without a sizing mill from the continuous caster. This means that it becomes possible to directly supply slabs, which has a great industrial effect.

[Brief explanation of drawings]

Fig. 1 is a chart showing the relationship between the slab pull-out resistance and the measured width variation, Fig. 2 is an explanatory diagram showing the overall configuration of an embodiment of the present invention, and Fig. 3 is the standard slab pull-out resistance and the required slab. A diagram showing the relationship between width and casting speed,
Fig. 4 is a chart showing the effect of implementing the present invention in terms of the relationship between slab pull-out resistance and width fluctuation amount; Fig. 5 is a chart showing an overview of fluctuations in slab width when the conventional mold width is constant; FIG. 6 is a chart specifically showing fluctuations in slab width when the slab width is constant. 1: ladle, 2: tie date, 3: variable width mold, 4: slab, 5: mold width variable control device, 6: mold width variation calculation device, 7: planned slab width setting device,
9: Casting speed setting device, 10: Slab drawing resistance measuring device, 11: Width variation setting device based on slab pulling resistance, 12: Standard slab pulling resistance calculating device.

Claims (1)

[Claims] 1. In a method for controlling a constant slab width in a continuous casting machine having mold equipment whose width can be varied during casting, the actual slab pulling resistance of the continuous casting machine is measured by measuring the current of the pinch rolls of the continuous casting machine. The standard slab pull-out resistance is calculated from the required slab width and casting speed using the following formula (1), and the amount of change in slab width is determined by the actual slab pull-out resistance and the standard slab pull-out resistance. The series is characterized in that the mold width is determined by the difference value from the difference value from the following equation (3), and the width of the mold is changed according to the amount of change in slab width, and the width fluctuation of the finally cast slab is suppressed within a certain range. Control method for constant slab width. R ₁ = (a ₁ · V + b ₁ ) · W + (a ₂ · V + b ₂ ) ... (1) formula R ₁ : Standard slab withdrawal resistance, W: Required slab width, V : Casting speed, a ₁ ~ b ₂ : Constant R ₂ = Σ (1/9.8・K・Φi・Iai・1/γ)
...(2) Equation R ₂ : Actual slab withdrawal resistance, Φi: #i pinch roll motor magnetic flux, K: Constant, I _ai : #i pinch roll motor armature current measurement value, γ: pinch roll radius Yw= a.