JPS63171249A - Continuous casting method for cast metal strip - Google Patents

Abstract

PURPOSE:To prevent the development of defect, such as breakage, traversing crack, etc., in a continuously cast strip just below a mold by controlling peripheral velocity of rolls, charging position of the advancing direction or cooling velocity for the continuously cast strip at the time of casting molten steel by twin roll type continuous casting method. CONSTITUTION:At the time of producing the continuously cast strip S by pouring the molten steel in a tundish T into the twin roll mold R, temp. of cast strip S is measured by thermometers (t), (t) at two points of upper and lower parts of cooling device (r) just below the twin roll type mold, and the cast strip cooling device (r) is controlled, so that cast strip temp. at position P1 of roll starting bending of continuously cast strip S is become to lower than temp. of brittle zone. Or, in case the casting velocity can be changed the peripheral velocity (v) of mold roll is changed and the time, when the continuously cast strip S is reached to P1 position, is changed to control the cast strip temp. Or, by changing the starting point of bending into the position of P1', the distance from out of mold roll till starting bending is changed, to control the cast strip S temp., and the continuously cast strip S is smoothly produced without any accident.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a casting method that prevents defects such as breakage and transverse cracking of slabs directly under the mold in vertical or inclined twin roll continuous casting methods. be.

(Prior Art) In recent years, in the field of continuous metal casting, there has been a strong desire to develop casting techniques for thin-walled slabs, and various methods have been proposed. For thin M slabs, it is particularly important to suppress oxide scale and prevent surface defects such as cracks. A method of casting and rolling is shown. In addition, in the belt and drum method, when a curved slab is rolled out into a straight line, the drum radius or slab thickness is specified so that the bending curvature applied to the slab falls within an allowable range to prevent slab cracking. The method for preventing this
It is shown in the publication No.

(Problems to be Solved by the Invention) When the advancing direction of the slab is changed from the casting direction, elongation strain occurs on the outer bending surface, and if the limit elongation rate is exceeded, breakage or cracking occurs. Therefore, it may be better not to change the direction of travel, or it may be necessary to change it due to equipment space or the relationship with subsequent equipment. Although a method of limiting the bending curvature to be applied as described above can be considered, it still imposes large restrictions on layout design. The present invention attempts to rationally solve this problem.

(Means for Solving the Problem) A feature of the present invention is that when continuous casting of molten metal is performed by a twin-roll continuous casting machine having a pair of rolls as the main components of the mold, the circumferential speed of the rolls, Control is performed to change at least one of the position where the traveling direction of the slab is changed from the casting direction and the cooling intensity of the slab, and the temperature of the slab at the position where the traveling direction of the slab is changed from the casting direction is adjusted based on the material of the slab. The reason is that the temperature is outside the embrittlement temperature range determined in accordance with the above.

The present invention will be explained in detail below.

After casting, in the process of decreasing the temperature of the slab, the slab has no cross-sectional shrinkage at all until it cools to a certain temperature. As the temperature decreases further, the cross-sectional shrinkage rate increases and saturates to a substantially constant value. Furthermore, even after that, there are one or two temperature ranges in which the cross-sectional shrinkage rate rapidly decreases. Therefore,
When changing the advancing direction of the slab from the casting direction, it is necessary to avoid a temperature range where the area shrinkage is low.

The following method will be adopted as a means for this purpose. ■Control the rotation speed of the mold roll. ■Install a slab cooling system. ■Mechanically change the bending start position. These methods are used alone or in combination to prevent breakage and transverse cracking of the slab by removing it from the brittle region at which the temperature is when the Pj slab passes through the bending start position.

(Operation) FIG. 1 shows a casting method using the above means. The molten metal supplied from Tanditshu T is cooled by a roll mold R consisting of twin rolls, and the temperature of the slab S cast by this roll mold R is measured with a thermometer t, and bending of the FJ piece is started. The slab cooling device r is controlled so that the slab temperature in the rolling roll p becomes below the brittle range temperature. Alternatively, if it is possible to change the casting speed, the temperature of the slab is controlled by changing the mold roll speed V and changing the time it takes for the slab to reach P+. Furthermore, by changing the bending start point to the position pl' in the figure, the distance from exiting the mold roll to the start of bending is changed to control the temperature of the slab. If there are rolls (for example, 92 in the figure) during the bending process of the slab, it is necessary to change their position in conjunction with each other as shown in P2'. In actual operation, it is preferable to prevent breakage and cracking of the slab by combining the above-mentioned controls on the cooling device, casting speed, and bending start roll position, taking into account the slab material, equipment constraints, productivity, etc. .

(Example) A method of casting a slab having the temperature characteristics of cross-sectional shrinkage ratio as shown in FIG. 2 using the apparatus shown in FIG. 1 will be described. Second
The characteristics of the diagram are known in advance. That is, in the case of this slab, it has been empirically known that the necessary cross-sectional shrinkage rate to prevent breakage and cracking is 8H. Therefore, in the example shown in FIG. 2, the bending start temperature must be 1300°C or lower and 1100°C or higher. Therefore, according to a preliminary simulation, under the conditions of roll speed V that satisfies the required productivity, the temperature of the slab at the bending start position is 1300, leaving a margin in the cooling capacity.
(coolant flow rate, pressure, number of nozzles used, etc.) and the position of the bending roll p1. When casting begins and slabs begin to come out, a thermometer measures the temperature of the slab, and a cooling device controls the temperature to a predetermined temperature.

(Effects of the Invention) According to the present invention described above, a thin metal slab could be smoothly manufactured without breaking or transverse cracking.

[Brief explanation of the drawing]

Figure f51 shows a method for manufacturing thin slabs using a twin roll continuous caster. Figure 2 shows the temperature characteristics of the cross-sectional shrinkage rate of the slabs used in the examples. In Figure 6, T...Tendish, R...Roll mold, V...
- Roll speed, r-... Slab cooling device, t... Thermometer. P+, P2... bending roll, S... slab.

Claims (1)

[Claims] When continuously casting molten metal using a twin-roll continuous casting machine that has a pair of rolls as the main components of the mold, it is important to The control is performed to change at least one of the components so that the slab temperature at a position where the traveling direction of the slab is changed from the casting direction is outside the embrittlement temperature range determined depending on the material of the slab. Continuous casting method for thin-walled metal slabs.