KR100782689B1 - A method for manufacturing as-cast strip of high quality by twin roll strip casting process - Google Patents

Abstract

  Provided is a method for producing cast steel having excellent quality in a twin roll sheet metal manufacturing process.

The present invention is a twin-roll continuous casting process for producing a cast by rapidly solidifying the hot molten steel supplied between a pair of casting rolls in contact with the casting roll,

      Measuring a temperature distribution in the width direction of the cast piece exiting the casting roll ;; Obtaining an average temperature (To) of the slab by averaging the measured temperature distribution, and then comparing the measured slab width direction temperature distribution with the average temperature (To) of the slab; And determining a region where the measured temperature distribution is higher than the average temperature (To) as a cast non-uniform solidification region, and performing shot blasting on the surface of the casting roll corresponding to the region. It is about.

Twin roll type sheet casting process, cast temperature distribution, black skin, shot blast

Description

A method for manufacturing as-cast strip of high quality by twin roll strip casting process}

1 is a schematic view of a general twin roll sheet manufacturing apparatus

Figure 2 is a schematic diagram of a twin roll type sheet manufacturing apparatus according to the present invention

3 is a plan view schematically showing the shot blast nozzle vibration device of the present invention.

4 is an exemplary view showing a temperature distribution measurement according to the width of the cast steel of the present invention.

* Explanation of symbols for the main parts of the drawings *

       10: ladle 20: tundish

       30: nozzle 40: casting roll (twin roll)

       50: edge dam 60: cast

       70: brush roll 80: temperature measuring device

90: operation control device 100: short blast control device

110: air compressor 120: short ball

130: shot blast nozzle 140: shot ball collecting device

150: dust collector

The present invention relates to a thin plate manufacturing process using a twin roll plate manufacturing apparatus, and more particularly, to the casting roll surface corresponding to the section showing the temperature distribution of the slab during casting in the twin roll thin plate manufacturing process, showing the non-uniform coagulation The present invention relates to a method for manufacturing a slab which can obtain a cast of high quality by continuously removing contaminants formed on the surface of a casting roll, that is, oxide scale, molten steel reactant, and various other foreign substances, by shot blasting.

As shown in FIG. 1, in general, a thin sheet casting method receives molten molten steel in a ladle 10 and flows it into a tundish 20 along a nozzle, and the molten steel introduced into the tundish is installed between casting rolls. It is a process of manufacturing the thin plate 60 by supplying through the nozzle 30 between the edge dams 50, ie, between the casting rolls 40. FIG. Thus, an important point in the twin roll sheet metal casting process for directly manufacturing a thin plate 60 having a thickness of 10 mm or less from high temperature molten steel is an injection nozzle between the internal water-cooled casting rolls 40 rotating in the opposite direction at a high speed. Supplying molten steel through the (30) is how to produce a thin plate 60 excellent in quality of the desired thickness.

In the conventional twin-roll thin plate casting process, in order to improve the quality of the cast steel, the surface of the casting roll is provided with roughness or irregularities to suppress uneven solidification, and the surface surface of the roll is removed using a brush roll. . For example, in Japanese Patent Laid-Open No. 60-184449, uniform coagulation is achieved by applying a roughness of 4 μm or more to the casting roll surface.

In addition, Japanese Patent Application Laid-Open Nos. 64-83340, 64-83342 and 2-52152 disclose circular or oval shapes of 0.1 to 1.2 mm in diameter to form dimples having a depth of 5 to 100 microns on the casting roll surface to prevent cracks in cast steel. In addition, irregularities were formed by photoetching or laser etching such as setting the closest distance between irregularities to 0.1mm or more.

     In Japanese Patent Laid-Open No. 5-7997, in view of the problem that the uneven part is worn down to 30 microns due to the use of the cast roll surface having the unevenness formed by the above method, cracking occurs in the cast steel. By reprocessing the surface to extend the life of the casting roll. In Korean Patent Application Laid-Open No. 10-258339, a shot ball is sprayed onto the surface of a casting roll during casting to prevent cracking of the cast steel.

     In addition, Japanese Patent Application Laid-Open No. 5-177311 proposes a method of uniformly cleaning the surface of a casting roll by maintaining a constant pressing force according to casting time by controlling the pressing force by controlling the brush roll 70 by the starting current of the electric motor. In Japanese Unexamined Patent Application Publication No. 9-174203, the degree of removal of foreign matter on the surface of the roll 40 varies depending on the speed difference and direction of the rotation of the brush roll 70, and the rotation of the brush roll. Direction and speed were controlled.

All the conventional methods described above are very helpful in suppressing cracking of cast steel and improving surface quality of cast steel, and have been applied in various ways. However, the above techniques can solve the large cracks of the cast iron to some extent, but when impurities are accumulated on the roll surface while casting, there is a problem that micro cracks or local coagulation unevenness, which are difficult to observe with the naked eye, cannot be avoided. In other words, imparting roughness to the surface of the casting roll suppresses large cracks, but does not solve such microcracks, and it is impossible to remove dense black skin even when brush rolls are used to remove impurities.

The microcracks of the cast steel may cause plate breakage during rolling, and even if the plate breakage does not occur, the gloss and corrosion resistance of the cold rolled material are poor, which is a critical factor in the quality of the cast steel. In addition, defects due to solidification non-uniformity in the width direction of the slab develop into abnormal cast during cold rolling due to the difference in the internal microstructure of the cast, and causes unstable casting, such as locally unsolidified molten steel flows during casting.

Accordingly, the present invention is to solve the above problems of the prior art, by measuring the lateral temperature distribution of the slab during the twin-roll thin plate casting process by performing a short blast treatment on the surface of the casting roll corresponding to the portion showing the uneven solidification Its purpose is to provide a thin plate manufacturing method that can improve the quality of casts by controlling the impurities produced on the surface of the casting roll to the appropriate thickness to ensure uniform solidification of the casts and to prevent the microcracks of the casts.

     Hereinafter, the present invention will be described.

    As described above, it is reported that the solidification shell partially floats with the surface of the roll due to solidification shrinkage or transformation shrinkage during solidification of the cast steel, whereby uneven solidification is encouraged and cracks of the cast steel are generated. Therefore, conventionally, molten steel improves contact with the surface of the roll and uniformly solidifies the cast by imparting a certain roughness to the surface of the roll in order to prevent the cast from lifting.

    In addition, not only the roll surface roughness but also contaminants unevenly present on the roll surface during the solidification of the cast steel affect the cooling ability of the cast steel, thereby causing the cast solidification to be non-uniform, causing cracking or surface defects. Therefore, in the past, the brush roll was used to remove the contaminants of the roll surface, but the brush roll was not able to remove the black skin formed by tightly adhering to the roll surface, thus causing nonuniform coagulation and causing fine cracks in the cast steel. There was a problem.

    This film called black skin is generally formed as a contaminant on the surface of the casting roll when molten steel is in contact with the casting roll during casting, and the black skin is reached to a certain thickness (when the roll is rotated two or three times after the start of casting). However, a thickness of about 5 to 10 microns is appropriate, which improves contact with molten steel and causes uniform coagulation. However, as the casting is repeated, the impurity layer becomes thicker, resulting in uneven solidification. The uneven solidification does not cause large cracks, but causes very fine surface cracks.

    In addition, such black skin is not uniformly formed in the roll width during casting, and a locally thick portion is formed, which causes the widthwise uneven solidification of the cast steel. In particular, uncoagulation can occur at both ends of the cast steel.

    Therefore, in order to effectively remove contaminants, that is, black skin, which are formed unevenly on the surface of the casting roll in a twin roll thin sheet casting process, causing surface defects of the cast steel, the widthwise temperature distribution of the cast steel during casting is measured. It is characterized by controlling the impurity (black skin) generated on the surface of the casting roll during casting by performing a short blast treatment on the surface of the casting roll corresponding to the portion exhibiting non-uniform coagulation due to the nonuniform presence of.

   Therefore, in the twin roll type continuous casting process of rapidly solidifying a hot molten steel supplied between a pair of casting rolls through contact with a casting roll to produce a cast, the width direction of the cast piece exiting the casting roll 닢 Continuously measuring the temperature distribution in the furnace; Obtaining an average temperature (To) of the slab by averaging the measured temperature distribution, and then comparing the measured slab width direction temperature distribution with the average temperature (To) of the slab; Determining a region higher than the average temperature (To) in the measured slab width direction temperature distribution as the cast non-uniform solidification region, and performing a short blast treatment on the surface of the casting roll corresponding to this region; It is about a method.

    Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

    Figure 2 is an example showing a twin-roll thin plate manufacturing apparatus according to the present invention. As shown in FIG. 2, the apparatus of the present invention includes a temperature measuring device 80 capable of measuring a temperature distribution in the width direction of the slab 60 exiting the casting roll 40. Infrared cameras are used.

    In addition, the temperature measurement result is received from the temperature measuring device 80 to calculate the average value of the slab width direction temperature distribution, that is, the average temperature (To), and compare the average temperature with the individual width direction temperature distribution to determine the non-uniformity of the slab. The operation control device 90 for determining a is provided.

    The thin sheet manufacturing apparatus of the present invention also includes a shot blasting apparatus for short blasting the surface of the casting roll 40 corresponding to the non-uniform solidification region according to the temperature comparison result in the operation control apparatus 90. In addition, the shot blister facility uses a shot blast control device 100 and an air compressor 110 to control the shot blasting process of the casting roll surface according to the temperature comparison result of the operation control device 90. The shot blast nozzle 130 for projecting the 120 to the casting roll surface, the shot ball collecting device 140 for collecting the shot balls dropped after being projected onto the casting roll surface, and removing only impurities in the ball collecting device 140 It is configured to include a dust collector (150).

    On the other hand, the nozzle 130 is preferably located at a distance of about 100 ~ 150mm to the casting roll 40 surface.

      In addition, since the area in which one shot blast nozzle can project the shot ball 100 is about 30 mm, there is a problem that a large number of nozzles must be used to short blast the roll width. Therefore, in the present invention, the nozzle is vibrated in the left and right width directions by using the nozzle vibrator 160 as shown in FIG. 3 to enlarge the projection area to 100 to 200 mm.

      Figure 3 is an exemplary view showing the shot blast nozzle array and the vibration device in the present invention, by connecting the two nozzles in a bundle, each bundle is connected by a cross-nozzle joint 161, the final connection portion Connected to the nozzle vibration motor 163 to allow each nozzle to vibrate from side to side at a time. However, in the present invention, such a vibration method is merely an example, and various methods may be employed.

    EMBODIMENT OF THE INVENTION Hereinafter, the manufacturing method of the cast steel of this invention is demonstrated in detail.

    First, the present invention is a twin-roll continuous casting process for producing a cast by rapidly solidifying the hot molten steel supplied between a pair of casting rolls through contact with the casting roll, in the width direction of the cast piece exiting the casting roll 닢 The temperature distribution of is measured continuously. This temperature distribution is continuously measured using the temperature measuring device 80, and the measured temperature distribution is provided to the operational control device 90 in real time. 4 shows an example of such a measured temperature distribution, in particular, the temperature of the edge portion of the cast steel is shown to be substantially high, which is due to the non-coagulation of the edge portion of the cast steel and the unevenness of the thickness of the skin surface or other contaminants This phenomenon is caused by uneven adhesion.

     Next, after calculating the average temperature (To) of the slab by averaging the measured temperature distribution, and compares the measured slab width direction temperature distribution with the average temperature (To) of the cast. The measurement of this temperature distribution and the calculation of the average temperature To of the cast are made in the arithmetic controller 90.

Subsequently, the arithmetic and control device 90 compares the measured temperature distribution with the average temperature (To) of the slab, and if there is a region higher than the average temperature in the measured slab width direction temperature distribution, it is a non-uniform solidification region Decide on In this case, the average temperature To may be embedded in the operation control device as a preset program.

     As described above, when the cast nonuniform solidification region is determined by the arithmetic and control unit 90, the roll surface by controlling the shot blast control apparatus 100 so that the roll surface corresponding to the widthwise cast nonuniform solidification region of the cast steel is shot blasted. Black skin attached to the can be removed.

At this time, the shot blasting throughput is determined by the shot blast control apparatus 100 in consideration of the size of the temperature deviation in the cast non-uniform coagulation.

     In addition, other conditions of the shot blast for removing contaminants formed on the surface of the casting roll are determined in consideration of the type, size, air pressure, and projection amount of the medium, and the shot blast method is performed by using air pressure or by rotating the impeller. You can also project.

   As described above, the present invention measures the widthwise temperature distribution of the cast steel in order to control the nonuniform solidification of the cast steel, and based on this, the shot surface is shot blasted using a shot blast nozzle at regular intervals in the roll width direction. As a result, it is possible to effectively remove black skin and to achieve uniformity in slag width direction solidification.

As described above, the present invention measures the widthwise temperature distribution of the slab at the time of casting, predicts the widthwise uneven solidification of the slab, and short-blasts the cast roll surface corresponding to the unevenly solidified area so that the black skin of the roll surface is appropriate. Can be controlled by thickness. Therefore, it is possible to promote uniform solidification of the cast during casting and to prevent micro cracks, so that not only the cast having excellent quality can be obtained, but also the surface quality can be improved, and the gloss and corrosion resistance of the cast can be improved during the post-treatment and the shot blast Roll surface hardening according to the treatment has a useful effect in terms of roll durability.

Claims (1)

In the twin-roll continuous casting process for producing a cast by rapidly solidifying the hot molten steel supplied between a pair of casting rolls in contact with the casting roll,      Continuously measuring the temperature distribution in the width direction of the cast piece exiting the casting roll ;;     Obtaining an average temperature (To) of the slab by averaging the measured temperature distribution, and then comparing the measured slab width direction temperature distribution with the average temperature (To) of the slab; And     A region higher than the average temperature (To) in the measured slab width direction temperature distribution is determined as a cast nonuniform solidification region, and the shot roll surface corresponding to this region is short blasted to obtain a black thickness of 5 to 10 on the casting roll surface. Quality casting method comprising a step of controlling to a good quality.

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