JPH03216241A - Method for measuring thickness of deposit on mold surface for thin cast strip continuous casting and method of continuous casting by adjusting casting condition based on this method - Google Patents

Abstract

PURPOSE:To always clean peripheral surface of a cooling drum and to obtain a cast strip having excellent quality by measuring IR intensity on the mold surface after contacting with molten metal, calculating emissivity from the measured value and holding temp. of the mold surface and obtaining thickness of stuck material on the mold surface. CONSTITUTION:By using the IR intensity measuring terminal 7 scanning the surface of cooling drum 1b to the axial direction, apparent temp. is measured with the IR emitted from the surface of cooling drum. In an arithmetic part 8, reduced energy intensity E is obtd. from this measured value and the thickness of stuck material is obtd. from the preset relational graph between E and the thickness of stuck material based on composition of the stuck foreign matter. After obtaining the stuck material quality in such way, when this quality reaches to the limited value or more, in order to lower oxygen partial pressure in the atmosphere in pouring basin part 3, indication, which inert gas is sealed into a sealing chamber 6, is transmitted from an indicating part 9 to execute atmosphere adjustment. Further, increase of the scum quantity in the pouring basin part 3 according to the stuck material quality, is recognized and the indication of scum removal is given from the indicating part 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for directly cooling and solidifying molten metal using a single drum or double drum method, or a drum-belt method.
The present invention relates to a continuous casting method that measures the thickness of deposits adhering to the drum or belt and controls casting conditions based on the obtained thickness of deposits when manufacturing thin slabs.

[Conventional technology]

BACKGROUND ART Recently, a method of directly manufacturing a thin slab having a wall thickness of several millimeters to several tens of millimeters close to the final shape from molten metal such as molten steel has been attracting attention. When using this type of continuous casting method,
Unlike the conventional method, a multi-step hot rolling process is not required, and rolling to the final shape can be done only lightly, thereby simplifying the process and equipment.

This type of continuous casting method includes the twin-drum method, in which a pool is formed between a pair of cooling drums that rotate in opposite directions, the drum-belt method, in which a pool is formed between the cooling drum and the belt, and the single-drum method, in which a pool is formed between a cooling drum and a belt. There is a single drum system in which a water reservoir is formed on a part of the circumferential surface of the cooling drum. In all of these methods, cooling and solidification of the molten metal progresses at the portion in contact with the surface of the cooling drum or belt, producing a solidified shell. Therefore, the surface condition of the cooling drum and the like has a great influence on the surface quality of the solidified shell. For example, if an oxide film is formed on the surface of the cooling drum, or if impurities from the pool are attached or deposited, the surface condition becomes non-uniform and the cooling conditions become locally irregular. As a result, the growth of the solidified shell becomes uneven, and thin slabs with uneven wall thickness are manufactured. In addition, the uneven surface condition
Localized stress concentration is applied to the solidified shell, causing defects such as cracks in the thin slab.

Therefore, in order to make the surface condition of the cooling drum uniform, Japanese Patent Laid-Open No. 60-184449, Japanese Patent Laid-Open No. 62-1766
No. 50, etc., discloses that a brush roll is provided to remove foreign matter or deposits adhering to the surface of the cooling drum.

[Problem to be solved by the invention]

However, the amount of deposits such as oxide films and impurities deposited on the circumferential surface of the cooling drum is not necessarily constant in the axial direction of the cooling drum. Furthermore, the adhesion force to the cooling drum circumferential surface is also not uniform. Therefore, deposits may remain on a part of the circumferential surface of the cooling drum after passing through the brush roll. When this deposit enters the pool, new oxide films, impurities, etc. are likely to adhere to the deposit, and will grow on a portion of the circumferential surface of the cooling drum.

In order to eliminate such residual deposits, the present inventors used an optical detector to detect the adhesion status of foreign matter in the axial direction of the cooling drum on the circumferential surface of the cooling drum. We have already proposed a continuous casting method characterized by selectively rubbing a brush roll against the peripheral surface of the drum (
(Patent Application No. 1983-250685).

The present invention provides a method for more efficiently detecting the foreign matter adhesion state, and reduces the amount of foreign matter adhesion by controlling the casting conditions in the pool based on the foreign matter adhesion state obtained by the above method. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention is directed to cooling and solidifying molten metal on the circumferential surface of a continuous casting mold to directly produce a thin slab. Measuring the strength, calculating the emissivity of the mold from the measured value and the holding temperature of the mold surface, and determining the thickness of the deposit on the mold surface based on the calculated value; The method is characterized in that the atmospheric oxygen concentration in the hot water pool or the amount of scum in the hot water pool is adjusted based on the amount of foreign matter attached.

[For production]

The present invention will be explained below based on the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a twin-drum type continuous casting apparatus.

In this device, the cooling drums la and 1b are arranged at a predetermined distance apart, and together with the side weir 2, form a sump 3. The molten metal reservoir 3 is sealed in a sealed chamber 6, and molten metal is injected from a tundish 54 through a pouring nozzle 5.

The heat of the molten metal is removed by the cooling drums la and lb to form a solidified shell, and a thin slab 10 is formed.

Foreign substances such as metal oxide films and impurities adhere to and accumulate on the cooling drum surface away from the solidified shell. The thickness of this deposit is determined by measuring the cooling drum surface temperature and infrared intensity.

That is, since the inside of the cooling drums la and lb are constantly controlled to be cooled to a predetermined surface temperature, the temperature at point A on the surface of the cooling drum 1b is already known. Measure intensity. This corresponds to measuring the apparent temperature at point A on the surface.

The energy emitted from the surface of an object is reduced by deposits on the surface of the object. Since this energy reduction has a one-to-one relationship with the thickness of the deposit, the thickness can be calculated by measuring the infrared intensity (that is, the apparent temperature due to infrared rays). The formula is as follows.

As shown in FIG. 2, the value of E has a linear relationship with the thickness of the deposit.

The present invention uses an infrared intensity measurement end 7 that scans the surface of the cooling drum 1b in the axial direction to measure the apparent temperature using infrared rays emitted from the surface of the cooling drum. The calculation unit 8 calculates the amount of energy decrease E using the above equation from this measured value, and calculates the thickness of the deposit from a graph of the relationship between E and the thickness of the deposit, which has been prepared in advance based on the composition of the deposited foreign matter.

After determining the amount of deposits in this manner, when the amount reaches a limit value or more, an inert gas is sealed in the sealed chamber 6 in order to lower the oxygen partial pressure in the atmosphere of the pool 3. An instruction is issued from the instruction section 9 to perform the cloud enclosure adjustment. Further, an increase in the amount of scum in the water reservoir 3 is recognized in accordance with the amount of deposits, and an instruction to remove the scum is given from the instruction section 9. Then, a scum removal device is inserted into the sump 3 and removes scum from the surface of the molten metal.

In addition, foreign matter attached to the surface of the cooling drum should be removed from the brush roll 1.
It is sufficient to remove the foreign matter by polishing it in step 1, and since the casting condition control according to the present invention is applied to the surface of the cooling drum after the foreign matter has been removed, re-adhesion of the foreign matter is extremely reduced. In addition, even if deposits increase due to changes in conditions, casting condition control and brush roll polishing are performed immediately, so the cooling drum circumferential surface can always have a uniform surface condition in the axial direction with less deposits. .

As a result, the cooling capacity for the molten metal is made uniform, and defects such as cracks and rough skin do not occur on the surface of the thin slab.

〔Example〕

SUS304 stainless steel (C:
0.06%, Si: 0.5%, Mn: 1. OO%, Ni
Cr: 8.80%, Cr: 18.20%, residual Fe) is injected into the pool 3 at 1490°C, and a thin slab 10 with a plate thickness of 3.0 mm and a plate width of 800 mm is cast at 80 m/min. Cast at speed. Five minutes after the start of casting, the infrared intensity measuring end 7 is scanned in the axial direction along the measurement point A on the circumferential surface of the cooling drum 1b after it has left the solidified shell at a pitch of 25+am at a rate of 200 times/second, and the average An apparent temperature of 90°C was obtained.

Further, the cooling drum surface temperature at measurement point A at this time was 160°C.

Next, the calculation unit 8 calculates the emissivity E from the temperature value,
Its value is 0. It became 543. Figure 2 shows S[IS30
The relationship between deposit thickness (-) and emissivity in the case of 4-series stainless steel is shown, and from this figure, a deposit thickness of 0.337- is obtained for the above emissivity value. Since the thickness of the deposit exceeded the limit value of 0.30 which makes it unnecessary to remove it, the brush roll l1 was operated to remove the deposit, and the indicator 9 was shown inside the sealed chamber 6 of the water reservoir 3. An instruction was given to lower the oxygen partial pressure, and N2 gas was introduced at a flow rate of 5 m''/min to lower the oxygen partial pressure in the sealed chamber 6 from 1% to 0.2%. The deposit thickness did not exceed the limit value until the casting was completed, so there was no need for further atmosphere adjustment or scum removal.

Thus, according to the present invention, the molten metal in the sump 3 is cooled and solidified under uniform conditions in the axial direction of the cooling drum, and the thin slab 1 has stable surface texture and shape characteristics.
0 is obtained.

On the other hand, cooling drum 1a. In a comparative example in which the circumferential surface was polished over the entire axial direction without detecting the amount of deposits on the lb circumferential surface, when the remaining deposits reentered the pool 3, oxidation was added to the deposits. If a film of substances or impurities adheres to the
observed to grow. As a result, unevenness was formed on the surface of the cooling drum, the gap between the cooling drums la and lb became uneven, and the thickness of the slab became uneven. On the other hand, the surface crack index (vertical crack length (m) per lm″) of the thin slab 10
0.01 m/m' in the case of the present invention, but 1 m/m', and the cracks generated on the surface of the slab seriously deteriorate the surface properties.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to accurately measure the amount of deposits on the circumferential surface of the cooling drum using a dynamic measurement method.
Furthermore, since the casting conditions can be controlled in a timely manner based on this, the peripheral surface of the cooling drum is always kept clean, making it possible to produce thin slabs of excellent quality.

[Brief explanation of drawings]

Fig. 1 is a partially sectional side view illustrating an embodiment in which the present invention is applied to a twin-drum continuous casting machine, and Fig. 2 is a diagram showing the relationship between the thickness of deposits on the cooling drum surface and emissivity. . 1a, 1b... cooling drum, 2... side weir, 3... hot water pool, 4...
- Tundish, 5... Pouring nozzle, 6... Sealed chamber, 7... Infrared intensity measurement end, butt... Calculating section, 9... Indicating section, 10... Thin slab, 1
1... Brush roll. Base 2 Drawing procedure amendment (voluntary) July 1991!

Claims (1)

[Claims] 1. When directly manufacturing a thin slab by cooling and solidifying molten metal on the peripheral surface of a continuous casting mold, the infrared intensity of the mold surface after contact with the molten metal is measured; Deposits on the mold surface for continuous casting of thin-walled slabs, characterized in that the emissivity of the mold is calculated from the measured value and the holding temperature of the mold surface, and the thickness of the deposits on the mold surface is determined based on the calculated value. How to measure thickness. 2. When cooling and solidifying molten metal on the peripheral surface of a continuous casting mold to directly produce a thin slab, measure the infrared intensity of the mold surface after contact with the molten metal, and compare the measured value with the mold surface. Calculate the emissivity of the mold based on the holding temperature, determine the thickness of deposits on the mold surface based on the calculated value, and adjust the casting conditions in the molten metal pool based on this value. Continuous casting method for thin-walled slabs. 3. The method according to claim 2, wherein the oxygen partial pressure in the atmosphere of the sump is adjusted depending on the thickness of the material deposited on the peripheral surface of the continuous casting mold. 4. The method according to claim 2, wherein the scum in the sump is removed by suction depending on the thickness of the material deposited on the peripheral surface of the continuous casting mold.