JPH02290651A - Method and apparatus for continuously casting cast strip - Google Patents

Abstract

PURPOSE:To continuously cast a cast strip having excellent shape characteristic and surface characteristic by causing the cast strip continuously cast with twin rolls to run while being brought into contact with the peripheral face of a roll of one side and making the outer face peripheral velocity of the cast strip to coincide with the peripheral velocity of the other roll. CONSTITUTION:Molten metal poured into pouring basin part 2 formed between one pair of cooling rolls 1a, 1b for twin rolls is rapidly cooled and solidified to cast the cast strip 4. Further, the above cast strip 4 just after fed out from kissing point 3 is caused to run while being brought into contact with the peripheral face of the cooling roll 1a of one side through a pressing roll 5 and cooled. In the above continuous casting method for cast strip 4, the peripheral velocities of one side or both sides of the cooling rolls 1a, 1b are adjusted through driving devices 6a, 6b, respectively according to the thickness of the cast strip 4 to make the outer face peripheral velocity of the cast strip 4 to coincide with the peripheral velocity of the other side cooling roll 1b in contact with the outer face thereof. By this method, internal structure in the cast strip 4 is made uniform and the development of the traverse crack on surface layer part is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing thin slabs with excellent shape characteristics and surface properties using a twin roll method, and to a necking.

[Conventional technology]

In recent years, in the field of continuous steel casting, the development of casting technology for thin-walled slabs has been progressing, and the twin-roll method is being developed. IL roll method.
Various methods have been proposed, such as the twin-belt method, single-belt method, and roll-belt method, and some of them have reached the level of industrial production. However, in terms of productivity, ensuring quality of slabs, etc., it is still far from being perfected.

BACKGROUND OF THE INVENTION For casting thin-walled slabs, for example, vertical or inclined twin roll type continuous casting equipment has been used frequently for many years. In this case as well, there are problems to be solved in terms of the quality of the thin-walled slabs, as well as the durability of the equipment and operational issues. One of these is to prevent heterogeneity in the internal structure of the slab. Incidentally, if a thin slab with a non-uniform internal structure is rolled without sufficient heat treatment, the surface of the cold-rolled product may lack smoothness, or defects such as cracks may occur.
Processability becomes insufficient. As a result, the commercial value of the product is significantly impaired.

When manufacturing thin-walled slabs using twin-roll continuous casting equipment, the time from the start to completion of solidification in the machine is relatively short, but the temperature of the slab immediately after solidification is extremely high at around 1400°C. Homogenization of the internal structure tends to become unstable, and it is difficult to prevent this phenomenon of heterogeneity of the structure by means such as spray cooling performed with a secondary cooling body in continuous casting of slabs, billets, etc.

As a means for preventing the occurrence of such a phenomenon, a method is known in which a cooling roll is used to bring thin slabs into contact with each other to rapidly cool them. In other words, the dynamic pressure of the gas and the traction force of the pinch roll. The thin slab coming out of the kissing point is wrapped for a certain length around the circumferential surface of one of the cooling rolls by the pressure of the pressing roll, and the heat retained in the thin slab is rapidly extracted by the cooling roll through contact heat transfer. It is intended to heat up.

For example, in Japanese Patent Publication No. 63-19258, cooling gas is injected onto a thin slab at a position close to the circumferential surface of a cooling roll on the downstream side of the kissing point, and a pinch gas is placed downstream of this injection position. Tension is applied to the thin slab by the roll, and the thin slab continues to be brought into close contact with the surface of the cooling roll in a predetermined range in the circumferential direction. As a result, the thin slab is rapidly cooled by contact heat transfer via the circumferential surface of the cooling roll, and it is said that a uniform, high-quality product without a black oxide film can be obtained.

Further, Japanese Patent Application Laid-Open No. 63-68248 discloses a roll type continuous casting equipment that combines a large diameter main roll and a small diameter auxiliary roll. Small-diameter water-cooled auxiliary rolls are densely arranged around the outer periphery of the main roll downstream of the kissing point with the same spacing as the roll gap in the casting section.

This improves the ability to support the thin slab after it leaves the kissing point and the ability to cool the thin slab.

Therefore, it is said that breakout of thin slabs that have not yet been completely solidified after leaving the kissing point is avoided, and continuous casting of thin slabs can be performed smoothly.

[Problem to be solved by the invention]

The proposal in Japanese Patent Publication No. 63-19258 aims at producing an extremely thin plate material of about 100 μm, as stated in the description of the embodiments. Therefore,
Even if a thin slab wraps around the circumferential surface of one cooling roll and the actual roll diameter increases, the increase in roll diameter is negligibly small, and both cooling rolls can be rotated at the same rotation speed. Even when driven at this speed, the difference in circumferential speed is very small, and there is no need to worry about horizontal cracking or the like.

However, when trying to manufacture relatively thin slabs with a thickness of one stroke or more using a pair of cooling rolls with the same diameter and constant speed, the following problems arise due to the thickness of the thin slabs. . In other words, the diameter of one of the cooling rolls around which the thin slab was wound substantially increased by the thickness of the thin slab. Therefore, if both cooling rolls are driven at the same rotational speed, the cooling roll on the side around which the thin slab is wound will have a higher circumferential speed than the other cooling roll. This circumferential speed difference causes shearing force to act on the surface of the thin slab, which has not yet developed sufficient strength, causing defects such as transverse cracks.

On the other hand, the method described in Japanese Patent Application Laid-Open No. 63-68248 is aimed at preventing breakout of thin slabs. However, in this method, there is no specific explanation about the circumferential speed of the main roll and the auxiliary roll, and there is no mention of prevention of horizontal cracking due to the difference in circumferential speed between the main roll and the auxiliary roll. It is difficult to say that these measures are being taken.

Therefore, the present invention eliminates the substantial peripheral speed difference between the pair of cooling rolls immediately after the completion of solidification, thereby preventing the occurrence of transverse cracks in the surface layer of the thin slab coming out from the kissing point immediately after the completion of solidification. Furthermore, the present invention provides a method and apparatus for casting thin slabs that can homogenize the internal structure.

[Means to solve the problem]

In order to achieve the purpose of the continuous casting method of the present invention,
When molten metal is injected into a pool formed between a pair of cooling rolls with adjustable circumferential speed ratios, and is rapidly cooled and solidified to cast thin-walled slabs, the thin-walled metal immediately after being sent out from the kissing point. In a method for casting thin slabs in which a slab is cooled by running in contact with the peripheral surface of one cooling roll, the circumferential speed of one or both of the cooling rolls is adjusted according to the wall thickness of the thin slab. The method is characterized in that the peripheral speed of the outer surface of the thin slab in contact with the one cooling roll is made to match the peripheral speed of the outer peripheral surface of the other cooling roll in contact with the outer surface of the thin slab.

The continuous casting apparatus of the present invention also includes a pair of cooling rolls that form a pool, and a pressing roll that runs while pressing the thin slab sent out from the kissing point of the cooling roll against the circumferential surface of one of the cooling rolls. and a drive device that rotationally drives each of the cooling rolls, and the drive devices are controlled independently from each other.

Here, it is possible to add a pressing means for pressing the thin slab against the peripheral surface of one of the cooling rolls from the kissing point to the pressing roll. As this pressing means, a plurality of auxiliary pressing rolls that increase the pressing force against the cooling roll on the kissing point side, a nozzle that injects liquid refrigerant onto the surface of the thin slab, etc. are used.

Moreover, as the pressing roll, one equipped with cooling means inside or outside is used. Furthermore, the cooling roll on the side that comes into contact with the thin slab sent out from the kissing point can have a larger diameter than the other cooling roll.

[Effect]

In the present invention, the thin slab immediately after leaving the kissing point is pressed against the circumferential surface of one of the cooling rolls by a pressing roll. The thin slab is rapidly cooled by contact heat transfer via the circumferential surface of the cooling roll. This suppresses heterogeneity of the structure of the slab after solidification is completed. At this time, the diameter of the cooling roll on the side against which the thin slab was pressed has substantially increased by the thickness of the thin slab.

If both cooling rolls are rotated at the same rotational speed in this state, stress due to the difference in circumferential speed will occur in the thin slab as described above. Therefore, the rotational speed of the cooling roll on the side around which the thin slab is wound is reduced in accordance with the thickness of the thin slab, and its circumferential speed is made to match the circumferential speed of the other cooling roll.

At this time, when the roll diameter of the cooling roll on the side around which the thin slab with wall thickness t is wound is d1 and the rotational speed is V, and the roll diameter of the other cooling roll is d2 and the rotational speed is v2, the rotational speed V ．． and v2, v+/vh=dz/(
a+±2t) . . . It is necessary to maintain the relationship (1). In addition, when using cooling rolls with the same roll diameter d, the rotation speed ratio is Vl/V2=1-2 t/(d+2 t)...
2).

By reducing the rotational speed of the cooling roll on the side around which the thin slab is wound in this way, the peripheral speed of the surface side of the thin slab is made to match the peripheral speed of the other cooling roll in contact with the surface. As a result, no stress is generated between the surface of the thin slab and the circumferential surface of the other cooling roll, and defects such as transverse cracks are prevented, especially for thin slabs with an intermediate thickness of 1 to 9 mm. It produces remarkable effects when applied to continuous casting. In addition, the structure of the thin slab obtained is homogenized by rapid cooling, and the surface quality is excellent.It is particularly suitable for manufacturing thin stainless steel slabs, and has surface texture defects such as uneven gloss during the subsequent rolling process. A product with no internal defects and excellent workability can be obtained.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 shows an outline of the continuous casting equipment used in this example. In this embodiment, a pair of cooling rolls la, lb
are arranged parallel to each other, and both ends of the circumferential surface in the roll axis direction are partitioned by side weirs (not shown) to define a pool 2. Molten steel was injected into this sump 2 from an intermediate container such as a dandinyu through a pouring nozzle. The injected molten steel is cooled and solidified by heat removal through the cooling rolls la and lb, and solidifies and grows on the circumferential surfaces of the respective cooling rolls la and lb.

The solidified slab is conveyed toward the kissing point 3 as the cooling rolls la and lb rotate, and is bonded together in the vicinity of the kissing point 3 to form a single thin slab 4. After passing the kissing point 3, the thin slab 4 is
It runs while being pressed against the circumferential surface of one of the cooling rolls 1a by a pressing roll 5 having an internal water cooling mechanism.

At this time, since the thin slab 4 is in close contact with the circumferential surface of the cooling roll la, its retained heat is removed via the cooling roll 1a. As a result, the thin slab 4 is rapidly cooled, and the non-uniformity of the structure is suppressed.

When the thin slab 4 is sent out from the kissing point 3 in close contact with the cooling roll 1a in this way, the substantial roll diameter of the cooling roll 1a increases by the thickness of the thin slab 4. Therefore, in order to offset the circumferential speed difference due to the substantial variation in the roll diameter, the cooling roll la,
The cooling rolls 1 are driven by separate drive devices 5a and 5b, respectively, and the circumferential speed of the surface of the thin slab 4 wound around the cooling roll la is opposite to each other at the kissing point 3.
Each drive unit it6a is adjusted so that the circumferential speed of
, 6b. Therefore, stress in the circumferential direction is not generated in the thin slab 4 at the king point 3, and even when manufacturing a thin slab 4 with a relatively thick thickness, transverse cracks in the thin slab 4 are prevented. It is possible to rapidly cool the thin slab 4 using the pressing roll 5 without causing this.

Note that the cooling rolls la,
The circumferential speed control of lb is performed by inputting the preset thickness of the thin slab 4, the detected values of the roll gaps of the cooling rolls la and lb, and the like. Further, the diameter of the pressing roll 5 is determined in consideration of the allowable strain when the thin slab 4 is sufficiently cooled and peeled off from the cooling roll 1a. The thin slab 4 peeled off from the cooling roll 1a is conveyed to a subsequent process such as rolling via a pinch roll 7.

In order to improve the contact state between the thin slab 4 and the cooling roll 1a while the thin slab 4 travels from the kissing point 3 to the pressing roll 5, various means are adopted as shown in Fig. 2. be able to.

In FIG. 2(a), a plurality of auxiliary pressing rolls 3a and 3b are arranged between the kissing point 3 and the pressing roll 5 along the circumferential surface of the cooling roll 1a. These auxiliary pressing rolls 8a, 8b improve the contact state of the thin slab 4 with the circumferential surface of the cooling roll 1a. At this time, it is preferable to make the pushing force of the uppermost auxiliary pressing roll 8a larger than the pushing force of the auxiliary pressing roll 8b located on the downstream side. As a result, the thin slab 4
The tensile force caused by the thermal contraction of the thin cast slab 4 in the kissing point 3 area is significantly reduced.

FIG. 2(b) shows a thin slab on the circumferential surface of the cooling roll 1a in order to compensate for the lack of cooling capacity when contact cooling the thin slab 4 with the cooling roll 1a and to prevent uneven cooling. 4 shows a state in which liquid refrigerant is being sprayed onto the refrigerant. By spraying this liquid refrigerant, more uniform cooling can be achieved especially when casting a thick and thin slab 4. However, the nozzle tip 9 must be selected so that the liquid refrigerant does not directly hit the kissing point 3. Therefore, a plurality of louvers 10 are attached to the side of the nozzle chip 9 on which the nozzle holes are opened, and the liquid refrigerant injected from the nozzle holes is guided to the surface of the thin slab 4 by the louvers 10.

In FIG. 2(C), the pressing roll 5 is of an external cooling type. That is, the cooling water nozzle l1 is opposed to the circumferential surface of the pressing roll 5, and the cooling water injected from the cooling water nozzle 11 cools the circumferential surface of the pressing roll 5. According to this method, the pressing roll 5 can be made smaller, and adverse effects such as vibrations can be suppressed from being exerted on the cooling roll 1a.

In FIG. 2(d), of both cooling rolls la and lb, the cooling roll 1a used for contact cooling of the thin slab 4 has a larger roll diameter than the other cooling roll 1b. In this case, it is easy to increase the length over which the thin slab 4 is contact-cooled, and it is easy to install and maintain the roll for pressing the slab and the liquid refrigerant nozzle.

Note that in any of the above-described figures 2(a) to 2(d), the cooling rolls la and lb are connected to separate drive devices 5a and 6b, respectively, as shown in FIG. , the peripheral speed at the surface of the thin slab 4 is made to match the peripheral speed of the other cooling roll 1b by controlling the driving devices 5a and 5b.

This method of casting the thin slab 4 while rotating the cooling rolls la and lb at different circumferential speeds is particularly effective when the thickness t of the thin slab 4 exceeds 1/500 of the roll diameter d. It has a remarkable effect when That is, t
When /d is 1/500 or less, 2t
/(d+2t)=0 does not cause any problem in actual operation. However, when t/d exceeds 1/500, it is necessary to incorporate this correction factor to match the substantial circumferential speeds of the cooling rolls la and lb.

Furthermore, the present invention is capable of rapid cooling, and can be applied to the casting of thin stainless steel slabs of 1 to 9 cylinders, which have a high risk of cracking due to the difference in circumferential speed between cooling rolls, and has a remarkable effect. It is.

Next, specific operational data will be shown.

Molten stainless steel having a composition of SOS 304 and a temperature of 1500° C. was poured into the sump 2, and a thin slab 4 having a wall thickness of 2 mm and a plate width of 800 mm was cast at a casting speed of 90 m/min.

The cooling rolls la and lb used both had a roll diameter of 1200 m. Then, the thin slab 4 coming out of the kissing point 3 is rolled along the circumferential surface of the cooling roll 1a.
After traveling 50 mm, it was separated from the circumferential surface and transported to a subsequent process.

At this time, the rotation speed of the cooling roll la is set to 24. Orpm
The rotational speed of the cooling roll 1b is maintained at 24. lrp
It was maintained at m. As a result, at the interface between the surface of the thin slab 4 and the circumferential surface of the cooling roll 1b, the circumferential speeds of the surface of the thin slab 4 and the cooling roll 1b were both 24 m/min. The thin slab 4 obtained in this state had no surface defects such as transverse cracks, and its internal structure was homogeneous. When this thin slab 4 was rolled, it was possible to obtain an excellent product free of surface defects such as uneven gloss and internal defects.

On the other hand, when the cooling rolls la and lb were driven at the same rotational speed and the thin slab 4 was cast under the same conditions, considerable transverse cracking occurred on the surface of the thin slab 4 obtained. Since this transverse crack causes plate breakage or the like when the thin slab 4 is rolled, it was not rolled and was scrapped.

〔Effect of the invention〕

As explained above, in the present invention, the thin slab coming out of the kissing point is brought into contact with the circumferential surface of one of the cooling rolls, and the heat retained in the thin slab is removed through the cooling roll. At this time, by adjusting the rotational speed of the cooling roll, stress caused by the difference in circumferential speed is prevented from being applied to the thin slab. As a result, no shearing force is applied to the thin slab, and a product with excellent shape characteristics can be obtained. Furthermore, the manufactured thin slab is rapidly cooled to homogenize its structure, and when rolled in a subsequent process, surface defects such as uneven gloss and internal defects such as cracks can be prevented.

[Brief explanation of drawings]

FIG. 1 shows an outline of the equipment configuration used in the embodiment of the present invention, and FIG. 2 shows several examples of means for improving the pressing state of the thin slab against one of the cooling rolls. la, lb: cooling roll 2: sump 3: kissing point 4: thin slab 5; pressing roll 6a, 6b: driving device 7: pinch roll 8a, 8b: auxiliary pressing roll 9:
Nozzle tip lO: Louver l1: Cooling water nozzle

Claims (1)

[Claims] 1. When casting a thin slab by injecting molten metal into a pool formed between a pair of cooling rolls whose circumferential speed ratio can be freely adjusted and rapidly cooling and solidifying it, kissing In a casting method for thin-walled slabs, in which a thin-walled slab immediately after being sent out from a point is cooled by running in contact with the circumferential surface of one of the cooling rolls, one of the cooling rolls is cooled according to the wall thickness of the thin-walled slab. Alternatively, the peripheral speeds of both are adjusted to match the peripheral speed of the outer surface of the thin slab in contact with the one cooling roll and the peripheral speed of the outer peripheral surface of the other cooling roll in contact with the outer surface of the thin slab. Continuous casting method for thin-walled slabs. 2. A pair of cooling rolls that form a pool, a pressing roll that runs while pressing the thin slab sent out from the kissing point of the cooling roll against the circumferential surface of one of the cooling rolls, and each of the cooling rolls. 1. A continuous casting apparatus for thin-walled slabs, comprising: a drive device for rotationally driving; and the drive devices are controlled independently of each other. 3. A thin slab, characterized in that a pressing means for pressing the thin slab against the circumferential surface of one of the cooling rolls from the kissing point to the pressing roll according to claim 2 is added to face the circumferential surface of the cooling roll. Continuous casting equipment. 4. A continuous casting apparatus for thin-walled slabs, wherein the pressing means according to claim 3 is a plurality of auxiliary pressing rolls, and the pressing force of the auxiliary pressing rolls on the kissing point side against the cooling roll is increased. 5. A continuous casting apparatus for thin-walled slabs, wherein the pressing means according to claim 3 is a nozzle that injects a liquid refrigerant onto the surface of the thin-walled slabs. 6. An apparatus for continuous casting of thin slabs, characterized in that the pressing roll according to claim 2 is provided with a cooling means inside or outside. 7. Among the cooling rolls according to claim 2, the diameter of the cooling roll on the side that presses the thin slab fed from the kissing point with the pressing roll is larger than the diameter of the other cooling roll by the thickness of the thin slab. A continuous casting device for thin-walled cast slabs.