JPH0451257B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to the twin-drum method, for example,
This invention relates to a method for continuously manufacturing metal ribbons by rapidly cooling and solidifying molten metal on the surface of a cooling roll.

[Conventional technology]

Recently, numbers close to the final shape have been obtained from molten metal such as molten steel.
A method for directly producing thin strips with a thickness of about mm is 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 Application 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 molten metal accommodated in this pool cools and solidifies at the portion that comes into contact with the cooling drum, becoming a solidified shell. As the cooling drums rotate, this solidified shell moves to a so-called roll gap section where a pair of cooling drums face each other at their closest positions. 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, there is also a single-roll method in which a single cooling drum is used, a pool is formed on the circumference of the cooling drum, and metal ribbons are similarly produced by rapid solidification. Known (Japanese Unexamined Patent Publication No. 1983)
-Refer to Publication No. 9948).

[Problem that the invention seeks to solve]

In this way, 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,
In other words, the meniscus portion is in an extremely unstable state in response to fluctuations in the molten metal level. Therefore, an extremely large quenching effect is applied to the molten metal at the beginning of the solidification shell formation, and cracks, non-uniform stress, etc. are likely to occur in the formed solidification shell.

This tendency is particularly noticeable at the start 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 a solidified shell are very different from those in the steady state and are unstable. For example, when the amount of molten metal is small, the solidification shell does not grow sufficiently, and this appears as a small thickness in the obtained metal ribbon, and in extreme cases, it breaks. Furthermore, if the casting speed is too high, the wall thickness will similarly decrease. Or, on the contrary,
If the amount of molten metal poured is too large, excess molten metal may overflow from the molten metal reservoir, causing molten metal leakage, breakouts, etc., and may even 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. Furthermore, even when controlling the pouring amount and casting speed using the feed-forward 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, when manufacturing a metal ribbon by rapidly solidifying the molten metal supplied to the surface of a cooling drum, the molten metal at the stage from the start of casting to a steady state is Regarding the metal pouring amount and casting speed, the pouring amount at the start of casting is larger than the pouring amount in a steady state, and after the start of casting, the pouring amount is gradually reduced to a steady pouring amount, and the above-mentioned casting speed is Immediately after, the casting speed is 0
This method is characterized in that a pattern is set in advance, after which the speed is gradually increased to a steady speed, and when casting is started, casting is started under the pouring amount and casting speed based on the set pattern.

[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 1a and 1b to form a molten metal pool 2. The molten metal in the molten metal pool 2 is cooled by the cooling drums 1a, 1b to form a solidified shell 3 along the surfaces of the cooling drums 1a, 1b. Then, the solidified shells 3 formed on the surfaces of the respective cooling drums 1a and 1b are pressed and integrated at the roll gap portion 4, and are carried out as a metal ribbon 5.

At this time, in the conventional method, the meniscus portions 2a and 2b of the molten metal pool 2 are detected by appropriate means, and the flow rate of the molten metal injected into the molten metal pool 2 and the roll gap portion 4 as the metal ribbon 5 are determined based on the measured values. It controlled the amount withdrawn from the 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 of 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. By this,
By sufficiently forming the pool at an early stage, it becomes possible to start casting under stable conditions. Furthermore, by adopting such a control method, the amount and number of wall thickness fluctuations caused by control delays 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 strip 5 can be made smaller, and the end portion that is cut off becomes smaller.
Product yield is 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 the pattern is controlled accordingly. This is what we do.

In FIG. 1, T _N is the time required for the casting speed and pouring amount to reach steady values V _N and Q _N. Also, T _L
is the time to start ramping up the casting speed. The casting speed V _N is set according to the target plate thickness, and is high speed when the plate thickness is thin, and low speed when the plate thickness is thick. Further, the pouring amount Q _N is set so as to be balanced with the slab production amount in a steady state.

The amount of molten metal poured at the start of casting Q _S is larger than the amount of molten metal poured during steady state Q _N . Amount of molten metal poured after starting casting Q _A
is gradually narrowed down and then brought to a steady value Q _N.

The casting speed immediately after the start of casting is 0. That is, the cooling drum is not rotated. The casting speed V _S at the start of casting is gradually increased, and then brought to a steady value V _N .

In this way, by increasing the amount of molten metal poured at the start of casting compared to the steady state, setting the casting speed to 0 immediately after the start of casting, and increasing the speed thereafter, it is possible to complete the sump portion quickly and sufficiently. can.

This prevents rapid cooling of the solidified shell and non-uniform stress due to fluctuations in the molten metal level, thereby eliminating the occurrence of cracks in the slab.

Insufficient growth of the solidified shell due to insufficient formation of the pool can be prevented, and the problem of insufficient wall thickness of the slab can be solved.

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, in this embodiment, the metal ribbon 5 does not break and reaches the target plate thickness in a short time from the start of casting.
stabilized at mm. Therefore, the length of the tip end of the thin metal strip 5 to be cut off due to thickness variation could be shortened from 12 m to 2 m.

〔Effect of the invention〕

As explained above, in the present invention, the amount of molten metal injected and the casting speed of the metal ribbon at the start of casting are set in advance in a pattern such that a puddle is formed early, and these settings are Start casting below. 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 the drawing]

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.
The figure is a graph specifically expressing the effects of the present invention.

Claims (1)

[Claims] 1. When producing 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 at the stage from the start of casting to the steady state are determined, and the amount of molten metal poured at the start of casting is determined from the steady state. After the start of casting, the amount of poured metal is gradually reduced to reach a steady pouring amount, and the casting speed is 0 immediately after the start of casting, and then gradually increases to a steady state. 1. A continuous casting method for metal ribbon, characterized in that a speed pattern is set in advance as a time function, and at the same time as casting is started, casting is started under the pouring amount and casting speed based on the set pattern.