JPS58188550A - Continuous casting method of steel plate - Google Patents

Abstract

PURPOSE:To obtain a steel plate having a good surface characteristic stably by supplying molten steel at the specified flow rate corresponding to the rete of solidification that progresses on the surfaces of rolls under rotation from a supply means for molten steel onto the rolls. CONSTITUTION:Molten steel 7 is supplied from a pair of tundishes 6 onto the outside circumferential surfaces in the upper part of a pair of cooling rolls 1 which are horizontal and parallel in axial lines and are in proximity to each other. The molten steel 7 is cooled to a solidified shell by the rolls 1 and while the shell passes through the roll gap, the shell is rolled down and a cost plate 7' is removed. The steel 7 is supplied from the tundishes 6 to the rolls 1 by the specified flow rate corresponding to the rate at which the steel 7 solidifies on the surfaces of the roll 1 during the time when the molten steel is in contact with the rolls 1. The steel plate having a good surface characteristic is thus obtained stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method for steel plates, which enables stable and continuous casting of steel plates.

Conventionally, a method for directly casting steel plates from molten steel involves using a pair of cooling rolls that have the same length and diameter, their axes are horizontal and parallel to each other, and are close to each other to prevent molten steel from leaking. A substantially cylindrical weir that is close to or in contact with the upper end and both ends of the outer peripheral surface of each of the pair of cooling rolls is used to rotate the pair of cooling rolls in opposite directions. There is a method in which the molten steel injected into the layer is brought into contact with the outer circumferential surface of both rotating cooling rolls, solidified, and the cast plate is continuously taken out from the roll gap between the rotating cooling rolls downward. Are known.

However, in this method, since the molten steel pool is formed by the outer peripheral surfaces of the pair of cooling rolls and the weir, the molten steel in the molten steel pool is mixed with the solidified shell formed on the outer peripheral surface of the cooling rolls. If the temperature of the contact area is likely to drop, and as a result, the removal speed is slow, a large amount of solidified portion will be formed in the molten steel pool near the roll gap, and this will cause the cast plate to be removed from the roll gap downward. On the other hand, if the removal speed is too fast, unsolidified portions may be removed and bulging may occur. However, with this method, it is difficult to stably remove the cast plate. Furthermore, the solidification start point of the molten steel on the outer peripheral surface of the cooling roll is unstable, and as a result, the surface quality of the obtained cast plate tends to be unstable.

Therefore, this invention was made to solve the above problems, and includes a pair of cooling devices whose axes are substantially horizontal and parallel to each other, which are close to each other, and which rotate in opposite directions. Using rolls, the molten steel supplied from each of the pair of molten steel supply means is brought into contact with the upper outer peripheral surface of each of the pair of rotating cooling rolls to cool and solidify, thus cooling the pair of rotating cooling rolls. A method in which a pair of solidified shells obtained on the outer circumferential surface of each roll are rolled down each other by the pair of cooling rolls, and the shells are taken out from the roll gap of the pair of cooling rolls downward as a cast plate, , during the period when the molten steel supplied from each of the pair of molten steel supply means is in contact with the outer peripheral surface of each of the pair of cooling rolls, the molten steel progresses on the outer peripheral surface of each of the pair of cooling rolls. The continuous casting method of the steel plate is characterized in that molten steel is supplied from each of the pair of molten steel supply means to the outer peripheral surface of each of the pair of cooling rolls in an amount corresponding to the solidification thickness.

The present invention will be described below with reference to embodiments and drawings.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a continuous casting apparatus for steel sheets for carrying out the method according to the present invention. As shown in the figure, reference numeral 1 denotes a pair of cooling ports having the same length and diameter, whose axes are substantially horizontal and parallel to each other, and which are close to each other. The pair of cooling rolls 1 are rotated in opposite directions at the same circumferential speed by a driving means (not shown) (rotation directions are indicated by arrows in the figure).

As shown in FIG. 2, the peripheral wall 1a of each of the pair of cooling rolls 1 is made of a metal with high thermal conductivity (for example, copper or copper alloy), and therein is a strip of metal in the circumferential direction. A continuous cooling medium passage 2 is formed in a spiral shape.

The cooling medium such as water or high boiling point heat medium is
The cooling medium is supplied from one end of the hollow shaft (but the middle is closed) 3 through the supply A tube 4 to one end of the cooling medium passage 2 located at one end of the peripheral wall 1a; , reaches the other end of the cooling medium passage 2 located at the other end of the peripheral wall 1a, and from there passes through a discharge tube 5 and is discharged to the other end of the shaft 3. Therefore, the molten steel that has come into contact with the outer peripheral surface of the cooling roll 1 undergoes heat exchange [1] with the cooling medium supplied into the cooling medium passage 2 of the peripheral wall 1a, and is (cooled) and solidified.

As shown in FIG. 1, a pair of tundishes 6 are each provided on the upper part of the outer peripheral surface of each of the pair of cooling rolls 1. Each of the molten steel discharge openings of the pair of tundishes 6 is provided with a pair of vertically sliding gooses 6a that can adjust the amount of hot water supplied.
Molten steel 7 in an amount corresponding to the vertical sliding amount of a is supplied from the tundish 6 to the outer peripheral surface of the rotating cooling roll 1 through the molten steel discharge opening.

In this way, the molten steel 7 supplied onto the outer peripheral surface of each of the pair of cooling rolls l is cooled by the cooling roll 1 and becomes a solidified shell.
A pair of solidified shells obtained on the outer circumferential surface of each of are pressed against each other by cooling rolls 1 of −r and J as they pass through the roll gap as the cooling roll 1 rotates ( It is then taken out from the roll gap downward as a single cast plate 7'.

Molten steel 7 is injected into the tundish 6 from an injection nozzle 8a of a molten steel container 8 disposed above the tundish 6 while its flow rate is controlled. The injection nozzle 8a is provided with a rotary nozzle (not shown), and the flow rate of molten steel injected into the tundish 6 is controlled by this rotary nozzle. Inside the tundish 6 is a hot water level meter 10 for detecting the hot water level 9.
The rotary nozzle is controlled based on the detected value of the level meter 10, and the level of the molten steel 7 in the tundish 6 is kept constant.As a result, according to Pernoulli's theorem, The flow rate of the molten steel 7 supplied from the tundish 6 onto the outer peripheral surface of the cooling roll 1 becomes constant, and the molten steel 7 thus supplied onto the outer peripheral surface of the cooling roll 1 flows down along the surface. Assuming that there is no solidification, the thickness h of the flowing molten steel 7 is approximately:
Based on hydrodynamic calculation, it is given by equation (1).

1A2 When formula (1) is solved by numerical calculation, as shown in Figure 3,
It can be seen that the flow velocity increases and the thickness h of the molten steel 7 decreases as it flows downward.

On the other hand, according to the empirical formula for solidification of molten steel, the solidification thickness t is t-, I′T...(2)
(k: constant) Therefore, the thickness h obtained by the m formula and (2
It is considered that when the solidification thickness t determined by the equation (2) becomes equal to the solidification thickness t, the molten steel 7 supplied from the tundish 6 completes solidification while flowing down on the outer peripheral surface of the cooling roll 1. For these reasons, during the period when the molten steel 7 supplied onto the outer peripheral surface of the cooling roll 1 is in contact with the outer peripheral surface of the cooling roll 1, the solidification thickness progresses on the outer peripheral surface of the cooling roll 1. By supplying molten steel 7 from the tundish 6 onto the outer circumferential surface of the cooling roll 1 at a constant flow rate corresponding to When passing through, they can be optimally pressed against each other. Furthermore, even if no weirs are provided at both axial ends of the outer circumferential surface of the cooling roll 1, the molten steel 7 will not spill from both axial ends of the outer circumferential surface of the cooling roll 1. Furthermore, since the solidification start point is stable, the obtained cast plate 7' has good surface properties. In addition, since there is no molten steel pool like in the past, it is extremely easy to start casting.

As shown in FIG. 1, the part where the solidified shell is formed on the outer peripheral surface of the cooling roll 1 is filled with an inert gas such as N2 in order to prevent oxidation of the surface by active V. The shape detector I2 using the optical cutting method detects the shape of the coagulation tubes 11 that are about to pass through the caps of the pair of cooling rolls 1. The shape of the crimped portion may be monitored.

As explained above, in this invention, stably,
Steel plates with good surface quality can be continuously cast.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a continuous casting apparatus for steel sheets that implements the method according to the present invention, FIG. 2 is a cross-sectional view of a cooling roll, and FIG. 3 is a molten steel on the outer peripheral surface of the cooling roll. FIG. 3 is a diagram showing changes in solidified thickness of 1...Cooling roll 6...Tandish 6a
... r-) 10 ... Hot water level meter applicant Nippon Kokan Co., Ltd. agent Keitabe Tsutsumi - 1 other person

Claims (1)

[Claims] A pair of cooling rolls whose axes are substantially horizontal and parallel to each other, close to each other, and rotating in opposite directions, the pair of cooling rolls being rotated. The molten steel supplied from each of the pair of molten steel supply means is brought into contact with the outer circumferential surface of the upper part of each of the molten steel to cool and solidify, and thus the obtained pair of molten steel is placed on the outer circumferential surface of each of the pair of rotating cooling rolls. A method in which solidified shells are rolled down each other by the pair of cooling rolls and taken out from the roll gap of the pair of cooling rolls as a tone cast plate, the solidified shell being supplied from each of the pair of molten steel supply means. The molten steel of the pair is heated by an amount corresponding to the solidification thickness of the molten steel that progresses on the outer peripheral surface of each of the pair of cooling rolls during the period when the molten steel is in contact with the outer peripheral surface of each of the pair of cooling rolls. A continuous casting method for a steel plate, characterized in that molten steel is supplied from each of the supply means to the outer circumferential surface of each of the pair of cooling rolls.