JPH04162944A - Method for controlling molten metal surface level in strip continuous casting device - Google Patents

Abstract

PURPOSE:To maintain a fixed molten metal surface level and to continuously cast a strip having excellent surface characteristic by obtaining a molten metal surface angle showing the molten metal surface level from a boundary line position where the molten metal surface is in contact with a roll surface and controlling molten metal pouring rate based on the molten metal surface angle. CONSTITUTION:The molten metal surface angle theta is found based on the equation from the boundary line position W where mutually the molten metal surface in pouring basin part formed at between facing upper part of a pair of water- cooled casting rolls 1, 2 and side weirs, are in contact with peripheral part of roll barrel (radius: R), and based on the molten metal surface angle theta, the molten metal pouring rate is controlled so as to become the suitable molten metal surface level. Consequently, casting trouble is eliminated and the strip 3 having excellent surface characteristic can be continuously cast.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for controlling the level of hot water in a continuous thin plate casting machine, and in particular, the present invention relates to a method for controlling the level of hot water in a continuous thin plate casting machine. This is a proposal for a technique for controlling the amount of poured molten metal to maintain an appropriate level of molten metal, which is useful for improving the properties of one surface.

[Prior Art] Twin rolls are used as a device for continuously directly casting thin metal plates (the following will be explained using the example of "steel plates").

A belt-type casting machine has been put into practical use, and Figure 1 shows an example of a continuous twin-roll thin plate casting machine. The apparatus shown in FIG. 1 consists of a pair of water-cooled casting rolls 1 and 1' for casting a thin slab 3.
, side fixed weirs 2 and 2' for preventing leakage of molten metal between water-cooled casting rolls 1 and 1', a tundish 5 for storing molten metal 4 such as molten steel, and an immersion nozzle 6.

In such a casting apparatus, for example, the thickness of the plate to be cast is 2 to 5.
In the case of m, the time for the molten metal, that is, the molten steel, to solidify in contact with each casting roll, the so-called solidification time, is usually 0.5
~2 seconds. It is extremely difficult to strictly control the solidification phenomenon in such a short period of time, and proper control is important in order to maintain good properties of the obtained slab. For such proper control, it is necessary to strictly control the molten metal (metal surface) level between each roll.

However, the conventional method mainly relies on the constant supply of molten steel from the tandem steel, which is insufficiently controlled, resulting in rolling cracks due to oversolidification or bulging (bulging phenomenon on the surface of the slab) due to non-solidification. ,
The properties of the slab were not necessarily satisfactory.

In response to this, techniques have been developed and proposed to appropriately control the level of hot water in the pool between the rolls. For example, JP-A No. 61-140362 states, ``In a continuous casting apparatus having two rolls disposed horizontally and parallel to each other and a submerged nozzle for casting a strip-shaped thin metal plate, the meniscus width between the rolls is The company proposes a method to properly control the level of molten metal between the rolls by moving the immersion nozzle up and down based on this detected value.

[Problems to be Solved by the Invention] However, the above conventional technology is a method of controlling the molten metal level by detecting the width (area ratio) of the meniscus (molten metal surface) between the rolls using a photodetector. As is clear from the schematic diagram shown in Figure 2 (b), if there is a foreign object in the surface area, it will result in an error in the measurement of the area ratio of the hot water surface, and therefore the area ratio of the hot water surface (bright area surface) As a result, the calculated amount was less than the actual amount of molten metal, which had a negative effect on the surface quality of the slab.

In other words, because the molten steel in the pool cools faster in the vicinity of both side weirs than in the center, semi-solid material may grow abnormally on the inner surfaces of both side weirs, and sometimes this semi-solid material It leaves the side weir and moves to the hot water surface, which is within the field of view of the photodetector and acts to reduce the hot water surface area ratio.

Therefore, an oversupply of molten steel occurred due to such an insufficient count of the amount of molten steel, resulting in deterioration of the surface quality of the slab and non-uniform thickness distribution.

The steel of the present invention has a hot water surface level, that is, a hot water surface angle θ of the roll.
By accurately detecting and controlling the amount of molten steel, it is possible to ensure a constant supply of molten steel and continuously cast thin plates with good surface quality.

[Means for Solving the Problems] According to the research conducted by the present inventors, in order to achieve the above purpose, it is necessary to detect the meniscus width (metal surface width) that appears as a bright area when detecting brightness using a photodetector. Instead, the position of the boundary line between the bright part of the hot water surface and the dark part of the roll body circumferential surface in a specific field of view is detected, and the hot water surface angle θ is determined based on the reference determination of where this position is. Detect and calculate the surface angle (θ
) was found to be effective in controlling the amount of poured metal. That is, the present invention supplies molten metal to a pool formed between the abutting tops and side weirs of a pair of water-cooled casting rolls arranged in parallel, while solidifying slabs from the butting bottoms. In an apparatus that directly casts a thin plate from molten metal by drawing out the molten metal, the molten metal surface level is controlled by adjusting the amount to be poured by observing the molten metal surface condition in the molten metal sump. The hot water level angle θ indicating the hot water level is determined based on the boundary line position (W) where the hot water level of the part and the circumferential surface of the roll (radius: R) are in contact with each other. This is a method for controlling the amount of molten metal poured into a thin plate continuous casting apparatus, characterized in that the amount of molten metal poured is controlled so as to indicate a surface level.

[Function] FIG. 1 shows a continuous thin plate casting apparatus for carrying out the present invention. −
side fixed weirs 5, 6 for preventing leakage of molten steel 4 between 92;
Tundish 7 for storing molten steel etc. 4 and pouring nozzle 8
and a stopper 9, and furthermore, a photodetector (CCD camera) 11 is disposed above the water reservoir 10.

Next, a method of controlling the amount of molten steel supplied from the tundish 7 to the sump 10 using the above continuous thin plate casting apparatus will be described with reference to FIG.

First, from an image taken by a CCD camera installed above the hot water pool 10, the boundary W between the roll body circumferential surface and the hot water surface (meniscus)
By measuring the hot water surface width W, however, R...
Radius W of the roll...determined from the boundary between the hot water level and the roll body circumferential surface.

That is, the obtained image (divided into the hot water surface showing bright areas and the roll body circumferential surface showing dark areas) is processed by the image processing device 12, and then the hot water surface angle calculation device 13 calculates the current hot water surface. Find and output the face angle θ. Next, the output is used to drive the stopper drive motor 15 via the tundish stopper motor control device 14, and the tundish stopper 16 is actuated to perform the necessary pouring. be.

In this way, the accurate position of the hot water surface angle θ1, that is, the hot water surface level, can be detected, and in the case of the present invention, an appropriate amount of hot water is poured based on the accurately detected hot water surface level.

〔Example〕

A specific example of the method for controlling the pouring amount of the present invention as described above will be described below. The conditions of the device used are as follows.

The dimensions and conditions of the casting machine are as follows.

(1) Water-cooled casting roll; diameter 1200■φ1 width 1200
■The slab is 2mtXw and the casting speed at this time is about 65m/a.
It is kin.

(2) Injection part: Alumina graphite nozzle and inclined plate pouring type (3) Heating temperature Δt of molten steel in the tundish is 70±
The temperature was set at 30°C (4-inch photodetector; CCD camera was used. Casting was carried out under the conditions above, and the boundary W between the molten metal surface and the roll body circumferential surface as shown in Fig. 3 was measured, and θ was calculated from equation (1). is calculated, and the pouring amount is PID!1JiLJ: so that this θ is stabilized at a predetermined value.

As a result, when the conventional method of outputting the meniscus width in black and white binary format and measuring the hot water surface angle based on the area ratio of the hot water surface, even though the actual hot water surface exceeded the target value, the measurement of the hot water surface There were black pieces of solidified material within the area, as shown in Figure 2.
Even though the actual hot water level was as shown in Figure 4, the stopper did not tighten as shown in Figure 5. As a result, (1) the hot water level fluctuated greatly, and the plate thickness fluctuated ( 2)
The result was that the hot water level rose and the heat load on the rolls increased.

However, when the position of the boundary W is measured as in the control method of the present invention, the actual hot water level can be detected accurately, and as shown in FIG. It is now possible to pour hot water.

[Effects of the Invention] As explained above, according to the present invention, the hot water surface level and eventually the hot water surface angle are detected based on the boundary position between the hot water surface roll and the circumferential surface. The amount of poured metal can be controlled. As a result, casting problems such as excessive or insufficient cooling strength or nonuniform plate thickness are eliminated, and thin plates with excellent surface properties can be continuously cast.

[Brief explanation of the drawing]

Figure 1 is a route map of continuous thin plate casting equipment, Figure 2 (a),
(b) is a schematic diagram of an image of the photodetector pool; FIG. 3 is a route map of the pool including an explanatory diagram of the control system for carrying out the method of the present invention; FIGS. The figure is a graph showing an example of changes in the hot water level (both the actual hot water level and the detected hot water level). 1.2...Water-cooled casting roll, 3...Thin slab, 4
... Molten metal, No. 5, 6... Id fixed weir, 7.
... Tanditshu, 8... Pouring nozzle patent applicant Nippon Yakin Kogyo Co., Ltd. Agent Patent attorney Jun Ogawa Sando Patent attorney Morio Nakamura 1st Bureau Watto, □ (・) 4th factor time (mln) Figure 5 Time (min)

Claims (1)

[Claims] 1. Molten metal is supplied to the pool formed between the abutting upper part of a pair of water-cooled casting rolls arranged in parallel and the side weir, while solidification is carried out from the abutting lower part of the pair of water-cooled casting rolls arranged in parallel. In an apparatus that directly casts a thin plate from molten metal by drawing out a slab, the level of the molten metal is controlled by adjusting the amount of molten metal to be poured by observing the level of the molten metal in the sump. From the boundary line position (W) where the hot water surface of the hot water pool and the roll (radius: R) cylinder circumferential surface touch each other, the hot water level is calculated based on the following formula: θ=cos^-^1(R-W)/R A method for controlling the level of a hot metal surface in a continuous thin plate casting apparatus, characterized by determining a surface angle θ indicating the level, and controlling the amount of poured molten metal so as to indicate an appropriate level based on the surface angle θ.