JPS63242449A - Method for continuously casting metal strip - Google Patents

Abstract

PURPOSE:To operate the process from casting start to steady state under stable condition and to improve the yield of a metal strip by adopting a program control method at the time of producing the metal strip directly from molten metal by twin roll type continuous casting apparatus. CONSTITUTION:Two cooling rolls 1a, 1b are rotated mutually toward reverse direction and solidified shells 3 in the molten metal are formed on the surfaces of both rolls from molten metal pool 2 formed in gap between both rolls and pressure-welded and integrated by the roll gap 4, to continuously draw as the metal strip 5. In this case, by program-controlling pouring rate of the molten metal into the molten metal pool 2 and drawing speed of the metal strip 5 under consideration of capacity of the casting apparatus, the pouring rate and the drawing speed corresponding to the aimed strip thickness are held and the casting start can be executed under stable condition. The time from the casting start to the steady state is shortened and the operation is stabilized at early time and waste part to be cut at tip part of the metal strip is reduced and the yield of product is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for continuously manufacturing a metal ribbon by rapidly solidifying a molten metal on the surface of a cooling roll, such as the twin drum method.

[Conventional technology]

BACKGROUND ART Recently, a method of directly manufacturing a thin ribbon having a thickness of several squares, which is close to the final shape, from molten metal such as molten steel has been attracting attention. When using this continuous casting method, there is no need for a hot rolling process, and only a light rolling process is required to form the final shape, so that the process and equipment can be simplified.

One such continuous casting method is the twin drum method (see Japanese Patent Laid-Open No. 137562/1983). In this method, a pair of cooling drums that rotate in opposite directions are arranged horizontally, and a pool is formed in a recess defined by the pair of cooling drums and, in some cases, a side weir. The portion of the molten metal accommodated in this pool that contacts the cooling drum is cooled and solidified to form a solidified shell. As the cooling drums rotate, this solidified shell moves to a so-called roll gap area where a pair of cooling drums face each other at the closest position. In this roll gap, the solidified shells formed on the surfaces of the respective cooling drums are pressed together and integrated to form the desired metal ribbon.

In addition to this twin drum method, one cooling drum is used and a pool is formed on the circumference of the cooling drum.
Similarly, a single roll method for producing a metal ribbon by rapid solidification is also known (see JP-A-61-9948).

[Problem that the invention seeks to solve]

In this manner, when the molten metal is rapidly cooled and solidified on the surface of the cooling drum to form a solidified shell, a small amount of the molten metal comes into contact with the surface of the cooling drum near the end of the sump. The end of this pool, ie, the meniscus, is in an extremely unstable shape depending on fluctuations in the hot water level. Therefore, an extremely large quenching effect is applied to the molten metal at the beginning of the solidified shell formation, and cracks, non-uniform stress, etc. are likely to occur in the generated solidified shell.

This tendency is particularly noticeable at the beginning of casting. In other words, a sufficient pool is not yet formed on the surface of the cooling drum at the start of casting, and the level of the molten metal in the pool varies greatly. Therefore, the conditions for the formation of the solidified shell are unstable and very different from those in the steady state. For example, when the amount of molten metal is small, the growth of the solidified shell is insufficient and this appears as a small thickness in the resulting metal ribbon, which in extreme cases can lead to breakage. Furthermore, if the casting speed is too high, the wall thickness will similarly decrease. Conversely, if the amount of molten metal poured is too large, excess molten metal may overflow from the molten metal reservoir, causing molten metal leakage, breakout, etc., and may lead to inoperability.

In order to avoid this variation in wall thickness at the start of casting, a method can be considered in which the thickness of the cast metal ribbon is used as a control factor to control the amount of molten metal poured and the casting speed in a feedback manner. However, since the speed at which metal ribbon is produced from molten metal is extremely high, with this method it is not possible to adjust the casting conditions to correspond to the speed, and control delays are inevitable. do not have. Therefore, the proportion of the tip of the obtained metal ribbon being cut off due to uneven thickness increases. Further, even when controlling the pouring amount and casting speed using the feedforward method, the occurrence of control delays cannot be avoided.

Therefore, the present invention has been devised to solve the problem that the thickness of the tip of the metal ribbon becomes uneven due to this control delay. The purpose is to operate the process under stable conditions and increase product yield.

[Means for solving problems]

In order to achieve the purpose of the continuous casting method for metal ribbon of the present invention, the molten metal supplied to the surface of the cooling drum is rapidly solidified to produce a metal ribbon. The method is characterized in that the amount of molten metal poured and the casting speed corresponding to the plate thickness are set in advance, and casting is started under the set amount of molten metal and casting speed.

[Effect]

FIG. 2 is a diagram conceptually showing the process of forming a metal ribbon when the present invention is applied to the twin drum method.

Molten metal poured from a container (not shown) such as a tundish is collected between a pair of cooling drums la and lb to form a molten metal boule 2. The molten metal in the molten metal boule 2 is cooled by the cooling drums la, lb to form a solidified shell 3 along the back surfaces of the cooling drums la, lb.

and each cooling drum la.

The solidification well 3 formed on the surface of 1b is pressed and integrated at the roll gap portion 4 and is carried out as a metal ribbon 5.

At this time, in the conventional method, the meniscus portions 2a and 2b of the molten metal boule 2 are detected by appropriate means, and the flow rate of the molten metal to be injected into the molten metal boule 2 is determined based on the measured value, and the opening and closing gap portions as the metal ribbon 5 are determined. It controlled the amount withdrawn from 4. However, in such a control method, a control delay as described above occurs. In particular, the control delay becomes noticeable at the start of casting, when the fluctuations in the meniscus portions 2a, 2b are large.

Therefore, in the present invention, the injection amount of molten metal and the drawing speed of the metal ribbon 5 are controlled by a program in consideration of the capability of the casting apparatus. As a result, the injection amount and drawing speed corresponding to the target plate thickness are maintained, and it becomes possible to start casting under stable conditions. Furthermore, by adopting such a control method, the amount of wall thickness variation due to control delay.

The number of times can be significantly reduced.

Further, by adopting such a control method, it is also possible to shorten the time from the start of casting to a steady state. Therefore, the thickness variation region that occurs at the tip of the thin metal ribbon 5 can be made smaller, and the end portion that is cut off becomes smaller, so that the product yield can be improved.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained with reference to Examples.

FIG. 1 is a diagram showing a control pattern of the present invention. Based on the growth rate of the metal ribbon, the pattern for the start-up of the molten metal injection amount and casting speed is calculated in advance so that the plate thickness variation is the smallest and the time is the shortest, and control is performed accordingly. This is what we do.

FIG. 3 shows the thickness variation at the tip of the metal ribbon 5 obtained by controlling the initial casting conditions in this manner. As is clear from this figure, according to this embodiment, the metal ribbon 5 stabilizes in the order of target plate thickness 4 without breaking in a short period of time from the start of casting. Therefore, the length of the tip end of the thin metal strip 5, which is cut off due to thickness variation, could be reduced from 12 m to 2 m.

〔Effect of the invention〕

As explained above, in the present invention, the injection amount of molten metal and the casting speed of the metal ribbon at the start of casting are
It is preset based on the growth rate of the solidified shell. This makes it possible to start casting under favorable conditions without causing control delays. Therefore, it is possible to reduce the area where the wall thickness fluctuates, which occurs particularly at the tip of the metal ribbon, and improve product yield. Furthermore, since the period from the start of casting to a steady state is shortened, operations can be carried out under stable conditions at an early stage. As described above, the present invention is highly effective in carrying out a continuous casting method for metal ribbon using a cooling drum.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a control pattern in an embodiment of the present invention, FIG. 2 is a diagram schematically showing the process of manufacturing a metal ribbon from molten metal, and FIG. 3 is a diagram showing the effects of the present invention. This is a graph specifically expressing the following.

Claims (1)

[Claims] 1. When manufacturing a metal ribbon by rapidly solidifying the molten metal supplied to the surface of the cooling drum, the amount of molten metal poured and the casting speed corresponding to the target plate thickness are set in advance from the start of casting to the steady state. , a continuous casting method for metal ribbon, which adopts a so-called program control method and starts casting at a set pouring amount and casting speed.