JP3238781B2 - Stable casting method for metal strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting a thin metal strip by a quenching process using a cooling roll, and more particularly, to stabilizing the casting at an early stage of casting when rapid solidification of molten metal on the cooling roll starts. That is what we are trying to achieve.

In recent years, there has been progress in development of a manufacturing technique for directly processing a molten metal (including an alloy) into a metal ribbon (hereinafter referred to as a ribbon) by a quenching process using a cooling roll such as a single roll or a twin roll. Have been. In particular, to cast a wide ribbon, from a pouring nozzle having a slit-like opening, inject onto a high-speed rotating single roll, rapidly solidify the molten metal and continuously cast the ribbon, The so-called single roll method is frequently used.

[0003]

2. Description of the Related Art To cast a ribbon by the single roll method,
It is known that management of operating conditions such as the tip shape of the pouring nozzle, the distance between the surface of the cooling roll and the pouring nozzle, and the speed and surface properties of the cooling roll is extremely important.
For example, Japanese Patent Publication No. 59-42586 discloses that the width of the slit-shaped opening of the nozzle is 0.2 to 1 with respect to the shape of the tip of the pouring nozzle.
mm, and the thickness of the lip (front lip) on the side where the molten metal flows out and the ribbon is manufactured is 1.5 to 3 times the opening width, and the thickness of the rear lip opposite to the front lip is the opening width. Of 1
It is disclosed that the distance between the surface of the cooling roll and the pouring nozzle is controlled to be 0.1 to 1 times the opening width. Similarly, regarding the tip shape of the pouring nozzle,
No. 77751 discloses that the opening width is 0.5 to 1.5 mm, the bottom thickness of the front lip is 0.2 to 1.5 mm, and the bottom thickness of the rear lip is
0.2 to 5 mm, and the thickness of the front lip at a height of 2 mm or more from the bottom of the front lip should be 1.5 mm or more,
Proposed. These devices and operating conditions have made it possible to cast wide ribbons.

[0004] However, the above-mentioned method can stabilize the casting when the casting is in a steady state. It is not enough to prevent troubles such as breakage of the hot water pool (paddle break). Since the occurrence of these troubles makes it impossible to continue casting in many cases, it is desired to develop a method capable of avoiding these troubles.

[0005] In order to prevent troubles due to nozzle clogging, a tundish or a nozzle is set at 700 to 1000 ° C.
In general, molten metal is injected into the nozzle after preheating to a high temperature, but it has not been possible to completely prevent nozzle clogging due to insufficient preheating.

Further, in order to prevent nozzle clogging,
In Japanese Patent Application Laid-Open No. 58-122157, after pouring a high-temperature molten metal into a tundish and keeping it warm, pouring the molten metal at an optimum temperature eliminates insufficient preheating of the tundish and the nozzle. There has been proposed a method utilizing dynamic pressure accompanying the fall of molten metal. However, according to this method, a paddle break is rather caused by the sudden flow of the molten metal when the stopper is opened.

On the other hand, JP-A-61-289953 and 61-29
No. 6941 discloses a perforated plate inside the nozzle, and Japanese Unexamined Patent Publication No. 3-155439 discloses a baffle plate having a branch channel inside the nozzle, thereby achieving a uniform molten metal flow.
Methods for preventing paddle breaks have been proposed. However, even with these methods, it is difficult to avoid the paddle break.In other words, if the temperature of the molten metal is increased to prevent nozzle clogging, the stability of the paddle is lost due to a decrease in the surface tension and viscosity of the molten metal, and the paddle break is caused. appear.

[0008]

The cause of nozzle clogging in the early stage of casting of a ribbon is essentially a decrease in the temperature of the molten metal in the nozzle or at its slit-shaped opening. This temperature drop is mainly due to heat flowing out to the tundish or the nozzle. Therefore, in order to prevent nozzle clogging, it is necessary to strengthen the preheating of the nozzle and the like and increase the temperature of the molten metal to be poured into the tundish. However, on the other hand, an increase in the molten metal injection temperature is a direct cause of a paddle break, and is not a sufficient solution.

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to advantageously solving the above-mentioned problems, and it is possible to advantageously avoid troubles such as nozzle clogging and paddle breaks which occur in an unsteady state at the early stage of casting. The purpose is to propose a casting method that has been used.

[0010]

SUMMARY OF THE INVENTION According to the present invention, when a molten metal is injected from a pouring nozzle onto the surface of a cooling roll rotating at a high speed, and the molten metal is rapidly cooled and solidified to cast a metal ribbon, the casting is started from the start of casting. In the initial stage of casting until the casting reaches a steady state, the interval between the surface of the cooling roll and the pouring nozzle, when the nozzle is not clogged, has a relationship satisfying the following formulas (1) and (2), Interval L at the start of casting
₁ , the thermal unsteady state interval L ₂ and the steady state interval L
_This is a stable casting method for a metal strip, which is changed in the order of ₃ . Note L ₁ ≦ L ₂ ---- (1) L ₃ ≦ L ₂ ---- (2)

[0011]

Here, the thermal unsteady state is a process in which the temperature of the tundish and the pouring nozzle rises due to the supply of heat from the molten steel. In this state, the temperature of the molten steel is lowered due to heat removal. The determination of the steady state should be accurately made based on the fact that the molten steel temperature in the pouring nozzle is constant. However, simply, time management or pouring nozzle based on the actual temperature measurement data should be used. By observing the red hot state of

FIG. 1 shows an apparatus for manufacturing a ribbon which is adapted to the method of the present invention. In the figure, reference numeral 1 denotes a tundish into which molten metal from a supply nozzle 2 is charged,
A pouring nozzle 4 is provided at the bottom of the tundish 1 via a stopper 3. The pouring nozzle 4 has a heater 5 on the outer periphery thereof to keep the temperature of the molten metal in the molten metal reservoir 6, and injects the molten metal onto a cooling roll 8 from a slit-shaped opening 7.

As shown in FIG. 2 in which the vicinity of the opening 7 of the pouring nozzle 4 is enlarged, the molten metal 11 injected from the opening 7 surrounded by the front lip 9 and the rear lip 10 in interval L _i between the cooling roll 8, to form a paddle portion 12, the molten metal 11 is a thin strip 13 is rapidly solidified here.

In the present invention, the above-mentioned interval
L_i, For example, during the start of casting
Interval L₁The thermal unsteady state interval L_TwoAnd during steady state
Interval L _ThreeIn a relationship that satisfies the above equations (1) and (2).
As described in detail below,
Avoid nozzle clogging and paddle breaks.

[0016]

The cause of nozzle clogging in the early stage of casting of a ribbon is essentially a decrease in the temperature of the molten metal in the nozzle or in the slit-shaped opening thereof. Prevention of nozzle clogging is achieved by injecting molten metal into a tundish. As described above, it is necessary to increase the temperature of the molten metal, but increasing the temperature of the molten metal injection increases the incidence of paddle breaks.

The inventors of the present invention have studied various ways of stabilizing the paddle portion. The rear portion of the paddle portion is formed in a substantially arc shape between the pouring nozzle and the cooling roll. The condition of generation is as follows: P is the internal pressure of the paddle, σ is the surface tension of molten steel, and Li is the interval.
Since it is expressed as 4σ / Li, it has been found that if the interval Li is reduced, the paddle portion is stabilized under the same pressure, and the occurrence of paddle break can be avoided even when the molten metal injection temperature is increased. At the same time, it was also confirmed that if the distance between the pouring nozzle and the cooling roll was too narrow, the nozzle tip was cooled by the atmospheric gas entrained in the cooling roll, and nozzle clogging was rather promoted.

From the above findings, by changing the distance between the pouring nozzle and the cooling roll according to the casting state,
It has been found that nozzle clogging can be avoided without causing a paddle break.

That is, as shown in FIG. 3, at the start of casting, the interval L ₁ between the pouring nozzle and the cooling roll is made as small as possible to suppress the occurrence of paddle break due to the initial dynamic pressure. Next, until the pouring nozzle reaches a thermal steady state, the ambient gas is entrained by the ambient gas entrained by the cooling roll so that the nozzle tip is cooled so that nozzle clogging is not promoted. to the extent that but does not generate, spread apart L ₂ between the pouring nozzle and the cooling roll.
Thereafter, if reached thermal steady state, in order to control the thickness of the ribbon, the distance L ₃ between the teeming nozzle and the cooling roll with a predetermined value.

[0020]

EXAMPLE C: 1 at%, as shown in FIG.
A molten alloy maintained at a temperature of 1320 ° C. and containing 9 at% of Si and 10 at% of B and substantially having a balance of iron,
It is supplied to a tundish 1 preheated to 1000 ° C. When the weight of the molten metal exceeds 25 kg, a stopper 3 is pulled up and a pouring nozzle 4 having a slit-shaped opening 7 having a width of 200 mm 4
(Preheated to about 1300 ° C.), and injected onto the peripheral surface of a copper alloy cooling roll 8 rotating at a high speed (25 m / s). At the start of casting, the gap between the pouring nozzle and the cooling roll is set to 0.15 mm.
After holding for 2 seconds, and then increasing the interval to 0.30 mm in 15 seconds and holding for 15 seconds, when adjusted to the predetermined interval of 0.25 mm in the steady state, 25 μm without clogging of the nozzle and paddle break Can be cast stably.

For comparison, when casting under the same conditions as above was performed with the distance between the pouring nozzle and the cooling roll kept constant at 0.15 mm, no paddle break occurred. In seconds, the nozzle was clogged from the opening of the pouring nozzle, and after 15 seconds, the entire opening was clogged, making it difficult to continue casting. Similarly, when the distance between the pouring nozzle and the cooling roll was kept constant at 0.25 mm, a paddle break occurred, and it became difficult to continue casting.

[0022]

According to the present invention, it is possible to stably and smoothly perform casting of a ribbon without causing nozzle clogging and paddle break.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus for manufacturing a ribbon which conforms to the present invention.

FIG. 2 is a schematic view showing an opening of a pouring nozzle.

FIG. 3 is a diagram showing a change in an interval between a pouring nozzle and a cooling roll.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tundish 2 Supply nozzle 3 Stopper 4 Pouring nozzle 5 Heater 6 Molten reservoir 7 Opening 8 Cooling roll 9 Front lip 10 Rear lip 11 Molten metal 12 Paddle part 13 Thin strip

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shun Suhara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Saburo Moriwaki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Inside Chiba Works, Ltd. (72) Nozomi Tamura 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Works, Ltd. Chiba Works, Ltd. 289355 (JP, A) JP-A-61-103652 (JP, A) JP-A-3-77751 (JP, A) JP-A-58-122157 (JP, A) JP-A-61-289953 (JP, A) JP-A-61-296941 (JP, A) JP-A-3-155439 (JP, A) JP-B-59-42586 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/06 360

Claims (1)

(57) [Claims] 1. Injecting molten metal from a pouring nozzle onto the surface of a cooling roll rotating at a high speed and rapidly solidifying the molten metal to cast a thin metal ribbon, from the start of casting to the time when casting reaches a steady state. in casting the initial, the distance between the surface and the pouring nozzle of the cooling roll, when the nozzle clogging does not occur, a relationship satisfying the following formula (1) and (2), distance L ₁ at the start of casting, Thermal unsteady state interval L ₂
And stable casting method for a metal strip, characterized in that changing the order of the distance L ₃ in the steady state. Note L ₁ ≦ L ₂ ---- (1) L ₃ ≦ L ₂ ---- (2)