JPS59215257A - Casting method in twin roll type continuous casting machine - Google Patents

Abstract

PURPOSE:To permit easy startup of continuous casting for a thick steel strip by starting casting at a small roll gap in the stage of starting charging of a molten metal with a twin roll type continuous casting machine then increasing gradually the roll gap. CONSTITUTION:A twin roll type continuous casting machine is so constituted as to draw a metallic strip from a roll gap by rotating plural horizontally and parallelly disposed rolls and supplying a molten metal thereon. The roll gap is decreased in the state of starting charging of the molten metal and casting is started from the metallic strip thinner than the prescribed thickness at a relatively high circumferential speed of the rolls to prevent generation of splashes and V-blocks. The roll gap is then increased and at the same time the circumferential speed of the rolls is made lower than the speed for casting the thinner strip, by which the thick metallic strip is cast. The generation of splashes right after the start of charging the molten metal is avoided by the above-mentioned method without using a dummy bar to permit easy startup and casting efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting method in a twin-roll continuous casting machine that allows easy start-up when continuously casting thick metal strips.

In recent years, various methods have been proposed for continuously casting metal strips using a twin-roll type continuous casting machine. The roll (1) (21 is configured so that the roll gap G can be adjusted according to the thickness of the plate using a screw shaft, and is configured so that it can be rotated in the direction of the arrow by a drive device. A barrel seal is provided at the top of (1) and (2), and side seals are provided on both sides of the rolls (1) and (2), and the rolls (1) and (2) are surrounded by the barrel seal and the side seals. ) The upper space is designed to store molten steel.

When continuously casting metal strips using the above-mentioned twin-roll continuous casting machine, adjust the roll gap G to a predetermined size, rotate the rolls (1) and (2) in the direction of the arrows, and press the ladle (3).
Molten steel (4) is supplied into the space above the rolls (1) (2) surrounded by barrel seals and side seals, and is cooled on the surface of the rolls (1) (21) to form a solidified layer. The metal strip is continuously cast by punching.

However, when the thickness of the metal strip to be cast is thick, the roll gap G is large, so that the molten steel immediately after the start of hot water supply from the ladle (3) flows through the roll (1) surrounded by the barrel seal and the side seal. (2) It cannot accumulate in the upper space and scatters downward from the roll gap as splash (5). Therefore, such a method has problems such as poor yield and production efficiency.

Therefore, when starting hot water supply, rolls (1) and (2) are stopped, and a dummy bar made of asbestos or heat insulating material is inserted between the roll gaps, and after the molten steel has accumulated, rolls (1) are stopped.
(Although it is possible to rotate the roll 21 and pull out the dummy hole to start casting, it is possible to rotate the roll after supplying the hot water instead of keeping the roll rotating during hot water supply.)
) (This is difficult because the molten steel between 2+ has cooled and solidified into ■ block shapes.

Also, if you rotate the roll (It(2+) and insert a dummy hole between the rolls, the dummy hole (-) cannot be made that long, so it will come out from between rolls (1) and (2) in a short time after insertion. In this case, too, the molten steel cannot be collected on the rolls immediately after the start of hot water supply.

In view of the difficulty of using a dummy bar when continuously casting thick metal strips using a twin-roll continuous casting machine, the present invention has been developed to enable the start of water supply without using a dummy bar. The purpose of this is to enable casting of a thick metal strip to be started immediately without splashing.

According to the present invention, the roll gap is made small at the start of hot water supply to prevent splashing, and when the metal strip begins to be pulled out, the roll gap is changed to a roll gap corresponding to the desired thickness. Therefore, even without using a dummy bar, it is possible to easily start constructing a thick metal strip without splashing immediately after starting casting.

Examples of the present invention will be described below.

First, the principle of the present invention will be explained with reference to the graph in FIG. If the roll circumferential speed V exceeds the value, the molten steel becomes a splash and leaks downward. There is a range Y where the molten steel solidifies between the rolls and becomes a V block shape, and a range Z where a metal strip can be cast between this range X and Y (range surrounded by curves (a) and (b))
There is. If you plot the intermediate position of curves (a) and (b), it will look like a curve (c), but this curve (c) is generally t
It is expressed as =K・■. Here, K is a constant, which varies depending on the steel type, temperature conditions, etc., but is approximately in the range of 8 to 10 for twin rolls of 500wnφ. Therefore, curve (a) (
The values at each point in (b) are approximately ±10% of the values in curve (c), and the range Z within approximately ±10% of the ideal state is the range Z in which metal strips can be cast. Furthermore, range Z where metal strips can be cast
There is an upper limit C of the roll gap G or the thickness at which a metal strip can be cast without using a dummy bar.

Therefore, for example, the operating point for starting pouring is set to point A, which is 0.1 nig below the upper limit within range Z, and the operating point for obtaining a predetermined plate thickness is set to point B, which is above upper limit C within range Z. point,
Even when changing the operating conditions from point A to point B, the plate thickness should be adjusted so as not to deviate from the range Z, or the roll gap 0 and roll circumferential speed V
By changing , it becomes possible to cast thick metal strips without splashing into molten steel without using a dummy bar.

Next, to explain a specific example, when the diameter of the roll (H2) shown in Fig. 1 is 500 mm and the continuous casting machine is used to continuously cast mild steel (material: 51 oc) with a plate thickness of 4 mm, the operation At the start, roll circumferential speed v1 is 20m1m
1n-binding, molten steel without using a dummy bar (1)
(2) First, a metal strip having a thickness t1 of about 2 is cast by supplying hot water to the top. The operating point in this case is point A in FIG. Therefore, at the start of operation, molten steel does not leak downward from between the rolls (1) and (2), and no splash occurs.

Roll circumferential speed V1” 207rL/mL R% plate thickness t1
The casting of the metal strip starts at =2tmn, and then the roll circumference and speed V are gradually decreased and the roll gap G is gradually increased. Or, ensure that the intersection of the roll gap G) on Figure 2 is within the range Z where the metal strip can be cast.
The roll peripheral speed and plate thickness (or roll gap) must be adjusted. Therefore, when the plate thickness t2 becomes a predetermined value of 4 mm, the roll circumferential speed v2 is approximately 10 m/mi? L, and the operating point is point B in Figure 2.

In this way, thick metal strips can be smoothly and continuously cast.

Note that the present invention is not limited to the above embodiments,
Of course, various changes can be made without departing from the gist of the invention.

According to the casting method in the twin roll continuous casting machine of the present invention,
Since it is possible to perform S construction of thick metal strips and plates without using a dummy bar and without splashing, it is possible to perform stand-up easily and casting work can be carried out efficiently. Since loss due to molten steel splash is eliminated, yield speed is improved, and other excellent effects can be achieved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the splash that occurs when directly starting the casting of a thick metal strip, and FIG. 2 is a graph showing the relationship between the castable sheet thickness or roll gap and the roll circumferential speed. In the figure, (1) f2) indicates a roll, (3) indicates a ladle, and (4) indicates molten steel.0 Patent applicant Ishikawajima-Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] 1) In a twin-roll continuous casting machine in which multiple rolls are arranged in parallel, molten steel is supplied onto the rolls, and the metal strip is continuously pulled out from the roll gap, the roll gap is closed at the start of hot water supply. Start casting from a metal strip with a smaller thickness than the specified thickness, then increase the roll gap and set the peripheral speed of the rolls at a slower speed than when casting a thinner sheet. A casting method using a twin roll continuous casting machine, which is characterized by casting a thick metal strip.