JPH07214267A - Method for controlling change of width for continuous casting - Google Patents

Abstract

PURPOSE:To efficiently and continuously cast slabs having different widths without interrupting the casting work by predicting the completing position of this charge just after starting the casting, obtaining the joint position, deciding a width change forbidding range and a changeable sparing length and obtaining the start of width change and the completing point. CONSTITUTION:At the time of changing the width of cast slab during the continuous casting, the completing position of this charge is predicted just after starting the casting based on the producing specification of molten steel quantity, width, thickness, sp. gr. of the molten steel, length of the cast slab, etc., to obtain the joint position based on the casting result and the remained molten steel quantity. The prescribed width change forbidding range and the changeable sparing length are decided from this joint position and the start of width change and the completing point are obtd. from the width changeable quantity of this kind of steel, changeable speed and casting speed to execute the width change in the permissible value of the cast slab. By this method, the necessary sparing length to the width change is minimized and the automatic width change at the joint part oft his charge can be executed and the yield is improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for changing the width of a slab during continuous casting.

[0002]

2. Description of the Related Art In order to efficiently produce slabs having different widths in continuous casting, a technique of continuously producing without interrupting the casting operation has been proposed and implemented.

In Japanese Patent Laid-Open No. 53-12722, when changing the width of a slab during casting, the moving speed of the short-side mold plate is adjusted according to the changing state of the slab width, and the casting speed is adjusted in conjunction with this. A method for safely changing the width in a short required time by changing the one-sided drawing speed is disclosed.

However, in the method described in Japanese Patent Laid-Open No. 53-12722, changing the mold width at the seam during continuous casting causes an accident such as so-called BO (breakout) in which molten steel cannot solidify in the mold and the shell breaks. It is not possible to change the width due to the occurrence of cracks and damage to the mold. Therefore, it becomes necessary to detect seams.

Japanese Patent Laid-Open No. 2-192861 discloses a method for detecting the seam of a slab in continuous casting, takes an average of the surface temperature of the slab before reaching the seam of the slab, and determines a predetermined value from the average surface temperature. A method is disclosed in which a value obtained by subtracting the temperature is set as a set surface temperature, and a portion having a temperature equal to or lower than the set surface temperature is detected as a seam of a slab to accurately detect the seam.

However, according to the method disclosed in Japanese Laid-Open Patent Publication No. 2-192861, the joint position can be determined only based on the actual results, and it is impossible to estimate it in advance.

[0007]

An object to be solved by the present invention is to accurately detect a seam necessary for width change control of continuous casting.

[0008]

In order to solve the above-mentioned problems, the continuous casting width change control method of the present invention is applied to production specifications such as molten steel amount and width, thickness, molten steel specific gravity and slab length immediately after the start of casting. The charge end position is predicted based on this, the seam position is obtained based on the casting results and the amount of remaining hot water, and the predetermined width change prohibited area and variable margin length are determined from this seam position, and the variable width amount and variable speed of the steel type The width change start and end points are determined from the casting speed, and the width is changed within the allowable value of the cast piece.

[0009]

In the present invention, in order to automatically change the width even at the seam of charge, the seam position is predicted in advance from the casting result and the amount of remaining hot water, and the width change prohibited area is determined in advance from the seam position. Furthermore, in order to prevent the deviation of the width of the slab unit caused by the deviation of the width change start position due to the disturbance such as the casting speed as the fluctuation error of the operating conditions when actually entering the width change operation and the time of prediction in advance, Determine the optimum margin according to the length required to change the width. The width change prohibited area and optimum margin length conditions determined in this way are combined with the width change amount for each slab and the width change speed of the steel grade, the tapering amount, and the casting speed, and within the specified slab allowable value. The width change starts at the width of and determines the end point.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples. FIG. 1 is a flow chart showing steps of a continuous casting width change control method according to the present invention. The steps will be described below in order.

A. Prediction of slab cutting position Prediction of slab cutting position is based on the slab cutting length (designated length) of the manufacturing specifications of the ordered product, satisfying various constraint conditions such as the length of equipment that can be cut. In order to minimize the influence of fluctuating operating disturbances such as quality anomalies due to surface fluctuations, and to obtain as many cast pieces as possible within the specified allowable range of minimum to maximum length. Create a cutting plan (see Figure 2). Since the slab width change is a slab unit width change, the reference positions for starting and ending the width change are determined based on the preliminary cutting plan obtained from the slab cutting position.

Determination of Presence / Absence of Width Change Parameters necessary for determining a width change margin length described later are determined. This determines whether or not the width is changed and the variable direction based on h / H of the front and rear slab width in the manufacturing specifications.

Width Enlarging Direction With h / H in FIG. 3, h = h ₁ and H = h ₂ , which are always greater than 1. Therefore, in this case, it is determined to be the width increasing direction.

Direction of width reduction With h / H in FIG. 3, h = h ₃ and H = h ₄ , which are always smaller than 1. Therefore, in this case, it is determined to be in the width reduction direction.

Target mold width determination Unless the thermal expansion coefficient in the width direction that differs depending on the steel type is taken into consideration, the slab width as a product specified in the manufacturing specifications cannot be sufficiently satisfied, so the width is actually changed. Determine the target mold width with the correction as width. Target width (W) = a × designated width + b (a and b are target width coefficients)

Determination of Target Width Coefficient The target width coefficients a and b differ depending on the steel composition for each steel type, the amount of cooling water in the secondary cooling zone, and the cooling method. So here
This aim range coefficient is learned and determined based on past operation results.

Estimated RB (Seam) Position Determination FIG. 4A is an explanatory diagram for determining the estimated RB position. The castable length 1 of the slab 12 is determined from the weight W of molten steel in the ladle 11. l = (molten steel weight W) / (width h × thickness t × molten steel specific gravity) Here, the width h is the width h _{1 to} h of the manufacturing instruction shown in FIG. 4B.
_{It is} a weighted average of ₄ . h = (l ₁ h ₁ + l ₂ h ₂ + l ₃ h ₃ + l ₄ h ₄ ) / (l ₁ + l ₂
+ L ₃ + l ₄₎

Determination of Width Change Prohibited Section FIG. 5 is an explanatory diagram for determining a width change prohibited section,
11 is a ladle, 12 is a slab, 13 is a tundish, and 14 is a mold. The procedure will be described below.

(1) Actual results 12a of cut slabs, cast slabs 12b to be cut, and cast slabs 1 to be cut before casting
From 2c, the casting amount ratio for each strand is determined, and the expected molten steel usage amount for each strand is determined from the ratio. Amount of molten steel used for 1 strand = {x / (x + y)} × (W-
A) = X 2 Strand Molten Steel Usage Amount = {y / (x + y)} × (W-
A) = Y where x is the weight scale of (a) to (c) on the one strand side y is the weight scale of (a) to (c) on the two strand side A is the ladle weight W is left in the ladle Molten steel weight

(2) The width change prohibited section is made into a table as the width change prohibited molten steel amount according to conditions such as steel type and tundish replacement, and a value corresponding to the condition is searched. 1 Strand side width change prohibited molten steel amount = w _k1 2 Strand side width change prohibited molten steel amount = w _k2

(3) When the molten steel weight whose width can be changed is obtained from (1) and (2), one strand width changeable molten steel amount = X−w _k1 = X ′ 2 strand width changeable molten steel amount = Y -W _k2 = Y '.

(4) Finally, the start and end positions of the width change inhibition are calculated (predicted value). First, as shown in FIG. 6 (a), the slab is applied to the molten steel weight whose width can be changed obtained in (3), and the excess weight w _x
Is the amount of residual molten steel whose width can be changed. _{w x = X '- (w} 1 + w 2 + w 3 + ··· + w i)

In order to reduce the calculation error, the weight of the slab to be cut is the average width (A + B) / 2 in consideration of the weight of the taper portion T in FIG. 6 (b). w ₂ = l ₂ × thickness × specific gravity × (A + B) / 2

Next, the surplus weight w _x (width-changeable residual molten steel amount) is converted into length. l _x = w _x / (thickness × specific gravity × average width of slab including l _x ) Therefore, width change prohibition start position = l ₁ + l ₂ + ... + l _i
It becomes + l _x .

Next, the end position where the width change is prohibited is determined. The idea of determining the width change prohibition end position is considered to be the distance until the seam existing in the mold exits the mold. Figure 7
(A) shows the state at the time of starting the primary channel injection at the time of charge change, and the position of the molten metal from the bottom surface of the mold 14 at this time is L. Next, (b) shows a state in which the seam 15 is lowered as the casting proceeds.
(C) shows a state in which the seam 15 is completely removed from the mold 14. Therefore, the width change prohibition end position = estimated seam position + L. The value obtained here is a predicted value, and when the seam is actually detected, the "width change prohibition end position"
Is calculated at the actual seam position.

Width change allowance length determination The width change allowance length is determined by the difference between the casting conditions when predicted (parameters necessary for determining the width change start position such as casting speed) and the conditions when actually changing the width. This is a safe length for optimally obtaining the error in the width change start and end positions that occurs and eliminating the deviation from the manufacturing instruction. FIG. 8A shows the difference between the manufacturing instruction and the actual casting image.

This will be described more specifically in the case of width expansion and the case of width reduction. <In the case of widening width> ・ Absorption of casting speed fluctuation As shown in FIG. 9 (a), if the casting speed is as planned, the taper length is L, but if the casting speed is fast, L is long. And L '. As a result, the width of the slab A cannot be satisfied. Therefore, if the width change start position is corrected to a ′ in advance in consideration of the variation amount, this disturbance can be absorbed. This aa 'is the "margin length".

Absorption of cutting position fluctuation Another possible factor is the cutting position. This means that no matter how much the taper of L as planned is obtained, the slab is not cut at the cutting point b, and the width of the slab A cannot be satisfied even at the cutting point b ′. This is due to a fixed error of the cutting device.

Therefore, in order to obtain the optimum value of this margin length, it is considered as "fixed error of cutting device + casting speed fluctuation amount". That is, the amount of fluctuation in the casting speed is calculated from the casting speed and H / h, which is determined by the steel type, and L in FIG.
And the difference of L ′ calculated when the casting speed is increased.

<In case of width reduction> In case of changing width reduction, FIG.
The width change start position a shown in (b) is corrected to a '. This is because the cutting position is corrected, and the cast slab A is not affected even if L changes to L'due to fluctuations in the casting speed. That is, the cutting point b− for the fixed error of the cutting device
Consider b ′ as “margin length”.

As described above, there is no problem if the width change ends at the taper length L as expected, but L actually changes due to fluctuations in the casting speed and the like. Under this condition, if L becomes longer than the prediction, it becomes as shown in FIG.
As shown in (b), the ears at the portion a are chipped, and the width of this slab comes off. Therefore, as shown in FIG. 8 (c), l is set so that the start position has a margin.

Here, l is defined by the manufacturing command width H / h,
It is necessary to determine the optimum length that does not allow too much room. As shown in FIG. 8D, the tapering length L changes depending on the relationship between the front and rear slab widths H / h. That is,
When H / h is large, the taper length L becomes long. H
When / h is small, the taper length L becomes short. Therefore, the margin length is controlled based on the length of L. Margin length l = L × β β: Margin length coefficient

By obtaining l by this method, even if the taper length L varies, the width of the post slab does not deviate, and a slab with a minimum margin and good yield can be manufactured. it can. β is set by the actual value.

Width change start / end position determination Information obtained above determines how much the casting length should be changed from a predetermined reference position for counting the casting length ( Slab cutting position obtained in
The estimated seam position obtained in, the width change prohibited section obtained in
It is determined using the width change allowance obtained in ().

10 to 13 are explanatory views of the width change start / end positions. In these figures, (a) shows the relationship between the slab cutting position obtained in the above step and the estimated RB (seam) position obtained in the step, and (b) further shows the slab 8 to The relationship between the taper length required for changing the width of the charge slab 1 and the width change allowance obtained in step is shown. (C) further considers the width change prohibition section obtained in step. The figure shows the final optimum width change start position.

FIG. 10 shows a slab 18 that can be collected by the previous ladle.
It shows a case where there is a width change between the slab and the slab that is sampled in this ladle. In FIG.
In the state of (b), since the width changing portion enters the prohibited section, the start position a is shifted to a'of (c) so that the width change is completed before entering the prohibited section.

FIG. 11 shows the difference between whether the position of the estimated RB (seam) is in the pre-charge or the post-charge, and the case is the same as in FIG.

FIG. 12 shows a case in which the position for changing the width of the slab occurs within the charge, and the concept is the same as in the case of FIG.

FIG. 13 shows a case where the width is changed by reducing the width. In this case, since the width changing portion enters the prohibited section in the state of (b), the width change should be started after the prohibited section.
The starting position a is shifted to a ′ as shown in (c).

For the set width change, the information (width, width change start position, etc.) necessary for the width changing device to actually operate is set.

B. Actual results As a result of setting, the width change operation is actually started and the width of the slab is formed in the direction of expansion or contraction. However, the length and width of the slab actually formed are not always 1 due to various operating disturbances. It is not always a 1-to-1 match. In order to eliminate these errors to the utmost limit, it is necessary to apply real-time correction from the operating state (cooling water amount, casting speed), the production slab size, and the actually measured slab size at that time. Therefore, consider the following correction.

Actual cutting length It is necessary to reflect the cutting error at the cutting position of the slab and the intervention of the cutting length due to the occurrence of slab defects which cannot be judged by a computer by human eyes.

Actual seam position The estimated seam position is obtained by converting the molten steel weight of the ladle into a length, but since the heat insulating material and the like are actually formed as slag, an error due to these weights may occur. Become. Therefore,
It is necessary to make a correction when the seam is actually detected.

Achievement width Used for learning data of the target mold width coefficient for determining the target mold width.

[0045]

As described above, the present invention has the following effects. It is possible to realize automatic width change at the joint of charge. You can minimize the margin length required for width change,
As a result, the width can be changed with good yield. The out-of-width slab disappears. There is no cutting loss.

[Brief description of drawings]

FIG. 1 is a flowchart showing steps of a continuous casting width change control method according to the present invention.

FIG. 2 is an explanatory diagram of a slab cutting position prediction step according to the present invention.

FIG. 3 is an explanatory diagram of a process for determining whether or not there is a width change according to the present invention.

FIG. 4 is an explanatory diagram of a method for determining an estimated seam position according to the present invention.

FIG. 5 is an explanatory diagram for determining a width change prohibited section.

FIG. 6 is an explanatory diagram for determining a width change prohibited section.

FIG. 7 is an explanatory diagram showing a state of movement of a seam in a mold.

FIG. 8 is an explanatory diagram showing a method for determining a margin length according to the present invention.

FIG. 9 is an explanatory diagram showing a concept of a margin length.

FIG. 10 is an explanatory diagram of determining a width change start / end position.

FIG. 11 is an explanatory diagram of determining a width change start / end position.

FIG. 12 is an explanatory diagram of determining a width change start / end position.

FIG. 13 is an explanatory diagram of determining a width change start / end position.

[Explanation of symbols]

11 ladle, 12 cast, 13 tundish, 14
Mold, 15th seam

Continued Front Page (72) Inventor Isao Oshita 1-1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Toshio Murayama 1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka No. 1 inside the Nippon Steel Co., Ltd. Yawata Works

Claims (1)

[Claims] 1. Immediately after the start of casting, the charge end position is predicted based on manufacturing specifications such as molten steel amount and width, thickness, molten steel specific gravity, slab length, etc., and the seam position is determined based on the actual casting results and the amount of residual hot water. The predetermined width change prohibited area and variable margin length are determined from this seam position, the width change start and end points are calculated from the width change amount and variable speed of the steel type, and the casting speed, and the width is within the allowable value of the slab. A continuous casting width change control method characterized by making a change.