JPH0252152A - Cooling drum for strip continuous casting device - Google Patents

Abstract

PURPOSE:To produce a thin cast strip having excellent surface property and shape characteristic without any defect of crack, etc., by specifying size of recesses and distance between the adjoining recesses arranged at circumferential face of the cooling drum constituting a part of a casting mold. CONSTITUTION:The above cooling drum 1 has opening parts having circle-shape or ellipse-shape of 0.1-1.2mm diameter D and forms the recesses 5 independently having 5-100mum depths on circumferential face constituting a part of the mold. The relation shown with the inequality I between the diameter D (mm) and the distance L (mm) of the dents is to be maintained. In this result, it is prevented that the excess stress to thin part 3b of solidified shell 3 having yet insufficient strength is concentrated, and the growth of the solidified shell is executed. Therefore, the cast strip having excellent surface property without any defect of crack, etc., can be produced. Then, in the figure, 4 shows 'air gas'.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses a twin drum system and a single drum system.

The present invention relates to a cooling drum used in a continuous ribbon casting apparatus such as a drum-belt method.

[Conventional technology]

BACKGROUND ART In recent years, in the field of continuous metal casting, there has been a strong desire to develop a technology for producing thin slabs close to the final shape, with the aim of reducing manufacturing costs, creating new materials, and the like. Various methods have been proposed to meet this requirement, some of which have reached the level of industrial production. However, the conventional methods are still not sufficient in terms of productivity, ensuring quality of slabs, etc.

Among these continuous casting methods for thin-walled slabs, one that uses relatively simple equipment is the twin-drum method, which uses a pair of drums equipped with an internal water cooling mechanism as the main components of the mold. There are a single-drum system that uses a cooling drum, a drum-belt system that forms a pool between the cooling drum and the belt, and the like. In these casting methods,
It is an important issue to keep the surface quality of slabs stable and at a high level.

In other words, unlike the case of slabs manufactured by conventional continuous casting equipment, these continuous casting methods were developed with the aim of obtaining thin slabs that can reduce the degree of rolling in subsequent processes. It is something that Therefore, if there is a thickness variation on the surface of a thin slab, this will cause a defect on the surface of the product, and there is a great risk that the product value will be significantly impaired.

Therefore, various methods have been studied with the aim of stably producing slabs with good surface quality. As one of the methods, Japanese Patent Application Laid-Open No. 184449/1983 proposes providing unevenness on the circumferential surface of the cooling drum so as to form an air gap serving as a heat insulating layer between the cooling drum and the solidified shell. There is. This air gap reduces the ability of the cooling drum to remove heat, resulting in slow cooling of the molten metal.

As a result, the solidified thickness is made uniform in the plate width direction, making it possible to manufacture thin slabs with excellent shape characteristics.

[Problem to be solved by the invention]

However, simply creating unevenness of a certain depth uniformly on the circumferential surface of the cooling drum and maintaining it in the desired state will not work.
It was found that sufficient effects could not be stably obtained. For example, if extremely large irregularities are continuously provided on the circumferential surface of a cooling drum, not only the irregularities of the cooling drum will be transferred to the surface of the thin slab obtained, but also the thermal stress in that part will occur. concentration is promoted, and conversely, the occurrence of cracks is promoted. Furthermore, when linear or angular irregularities are formed on the circumferential surface of the cooling drum, the corners of the irregularities serve as starting points for cracks, causing a large number of cracks to occur in the thin slab.

Therefore, in order to solve these problems, the present inventors
We investigated the unevenness formed on the circumferential surface of the cooling drum.
It was found that a depression having a diameter of 0.1 to 1.2 marks, a circular or oval opening, and a depth of 5 to 100 μm is effective, and the invention was filed as Japanese Patent Application No. 62-240479. The depressions thus formed on the circumferential surface of the cooling drum are
To improve the adhesion between the molten metal and the cooling drum, and to form small independent air gaps that are not continuous with each other during casting. As a result, the cooling conditions for the solidified shell are moderated,
This suppresses the effects of stress caused by concentration of stress in areas with locally low rigidity.

However, subsequent research has shown that defects such as cracks occur even when casting is performed using a cooling drum with the above-mentioned depressions provided on the circumferential surface. When we investigated the cause of this, we found that the size of the depressions on the circumferential surface of the cooling drum and the distance between adjacent depressions have a large effect on the occurrence of cracks.

Therefore, an object of the present invention is to manufacture a thin cast slab that is free from defects such as cracks and has excellent surface properties and shape characteristics by specifying the size of the depressions and the distance between adjacent depressions.

[Means to solve the problem]

In order to achieve the purpose, the cooling drum for a continuous ribbon casting apparatus of the present invention has a circular or oval opening with a diameter of (1.1 to 1.2 I++ω) and a depth of 5 to 100 μm. Recesses are formed on the circumferential surface of a cooling drum that constitutes a part of the mold without touching each other, and the diameter of the recess is set to D(a).
s) and the distance between adjacent depressions is L (IIll), then 0.05 D between the diameter and the distance between adjacent depressions.
+O, l≦L≦1.4D+0.5. It is characterized by maintaining a relationship of L≦1.2.

[Effect]

FIG. 4 is a diagram schematically showing the state of growth of a solidified shell on the circumferential surface of an ordinary cooling drum.

The molten metal 2 in contact with the circumferential surface of the cooling drum 1 is cooled by heat removal through the cooling drum 1, and becomes a solidified shell 3. In areas where the cooling effect is large, the solidified shell 3 grows quickly and becomes a relatively thick shell 3a. On the other hand, at locations where the cooling effect is small, the growth of the solidified shell 3 is delayed, resulting in thin walled portions 3b. This thin wall portion 3b has a lower strength than the thick wall portion 3a, and is a location where stress concentration is likely to occur. Further, as the thick wall portion 3 a solidifies and contracts, the thin wall portion 3 b is stretched, and an air gap 4 is generated between the thin wall portion 3 b and the circumferential surface of the cooling drum 1 .

Since this air gap 4 acts as a heat insulating layer, the thin wall portion 3
The growth of b is further delayed, and defects such as cracks occur there.

In contrast, the previous application in which a depression was provided on the circumferential surface of the cooling drum 1
In the cooling drum of Japanese Patent Application No. 62-240481, since the molten metal and the cooling drum are in close contact with each other and a small air gap is created, a large number of thick-walled portions 3a and thin-walled portions are formed in the axial direction of the cooling drum 1. 3b are formed at such intervals that large air gaps that could lead to cracks are not formed. Further, since there are a large number of three-walled portions 3b, stress concentration is dispersed, and force that may cause cracking is suppressed from being applied to the thin-walled portions 3b.

However, even with such depressions, it may not be possible to completely prevent the occurrence of cracks.

This is because even if the circumferential surface of the cooling drum is uniformly uneven to improve the adhesion between the molten metal and the cooling drum, if the diameter and spacing of the recesses are not appropriate, the air gap that will be formed will be This is because if the thickness is not reduced, stress will be concentrated in the thin wall portion, which will easily lead to cracking.

Optimal conditions to obtain the uneven effect.

In this case, it is necessary to: 1) restrain the solidified shell by the depressions so that it does not separate from the cooling drum, so that cooling proceeds uniformly, and 2) create a small air gap in both the depressions and the protrusions as shown in Figure 1. The idea is to form air gaps a and b to achieve a slow cooling state. Therefore, the method of arranging the depressions, that is, the diameter of the depressions and the adjacent pressure ML, are important parameters in determining the effect of the unevenness. Note that the distance between adjacent
As shown in the figure, it refers to the closest distance between adjacent depressions 5.

Therefore, in the present invention, the diameter of the depressions provided on the circumferential surface of the cooling drum 1 and the distance between adjacent depressions are specified. Third
The figure shows the relationship between this diameter and the distance between adjacent units.

In the case of a depression with an extremely small diameter (D < O, l ar
m.

In region (3) of FIG. 3, the molten metal cannot enter the depression, so good adhesion between the molten metal and the cooling drum cannot be obtained. Therefore, the solidified shell cannot be restrained by the depression, and the solidified shell separates from the cooling drum, making it impossible to maintain a uniform cooling state. Therefore, the effect of unevenness cannot be obtained.

Also, if the diameter is extremely large (D>1.2mm).

Area ■) in Figure 3, the diameter is larger than the air gap that occurs in a cooling drum with no unevenness, so a large air gap is created inside the depression, and a small air gap cannot be formed. The air gear tubes are not evenly distributed. As a result, the cooling of the solidified shell becomes non-uniform, and the effect of unevenness cannot be obtained.

Similarly, in the case of a depression where the distance between adjacent regions is extremely large (L>
1.2 mm (region III in Figure 3), the distance between adjacent areas is larger than the air gap that occurs in a cooling drum with no unevenness, so a large air gap is created at the convex part, forming a small air gap. This prevents small air gaps from being evenly distributed. Therefore, the cooling of the solidification tube becomes uneven, and the effect of unevenness cannot be obtained.

Therefore, the necessary conditions to obtain the effect of unevenness are 0.1 mark ≦ D ≦ 1.2 strokes and L ≦ 1.2 degrees, and this is the area indicated by the broken line in Fig. 3. represented.

Furthermore, in the region of D<0.5mi+ in this broken line region, the molten metal is difficult to enter into the depression, and therefore the solidified shell is weakly restrained by the depression. Furthermore, when the distance between adjacent shells is large, the restraint of the solidified shell by the depressions becomes even weaker, and when solidification is accelerated and the solidified shell contracts, the solidified shell separates from the depressions, and cooling does not proceed uniformly. This phenomenon was experimentally confirmed that L>1,4D
It has been confirmed that this occurs when +0.5, which corresponds to area (■) in FIG. Therefore, the effect of unevenness cannot be obtained in this region (3).

In addition, if the distance between adjacent parts is extremely small, the convex part will come into close contact with the molten metal, and the air gap b shown in Figure 1 will not be formed, and the small air gap will not be evenly distributed. . This phenomenon was experimentally confirmed that L < 0.0
It has been confirmed that this occurs when 5 D +0.1, which corresponds to area ■ in FIG. Therefore, even in this region V, the effect of unevenness cannot be obtained.

From the above, the effect of unevenness can be obtained when the diameter is 0. l = 1.2 mcd, distance between neighbors is 1
．． 2111II or less, and 0.05 D +0.
The range is l≦L≦1.4D+0.5.

When casting is carried out using the cooling drum l with the depressions 5 formed on the circumferential surface while maintaining the relationship between the diameter and the distance between adjacent parts specified in this way, the growth occurs on the circumferential surface of the cooling drum 1. The shape of the solidification tube 3 is regulated, resulting in a high-quality product free of defects such as cracks.

〔Example〕

As a continuous casting device, a pair of cooling drums 1 are arranged, molten metal is injected between them to form a pool, a solidified shell is grown on the circumference of each cooling drum, and it is integrated at a sinking point. Using a normal twin-drum system, 2.4 fins with a wall thickness of 2.4 fins are produced from molten steel with a stainless steel composition at a temperature of 1500°C at a production speed of 65 m/min.
Thin slabs with a plate width of 800 mm were manufactured.

Then, the surface cracks of the obtained thin slab were observed, and the relationship between the diameter of the recess 5 and the distance between adjacent recesses was investigated. The results are shown in FIG. Incidentally, the crack occurrence index is expressed by the longitudinal crack length (m) per rn' of thin slab. In the figure,
Items marked with a circle have a cracking index of 0.01m/rn
``Those marked with a △ below have a cracking index of 0.2m.
/m'', those marked with an X have a cracking index of 0.
2m/m' or more.

As is clear from FIG. 3, almost no cracks occur in the area of diameter and distance between adjacent areas specified by the present invention, and the present invention is significant in that the effect of unevenness can be obtained in this area. The gender can be confirmed.

〔Effect of the invention〕

As explained above, in the present invention, by specifying the relationship between the diameter of the recesses carved on the peripheral surface of the cooling drum and the distance between adjacent recesses, it is possible to Avoiding excessive stress concentration on
This causes the growth of a solidified shell. Moreover, the shape mode of the growing solidified shell is also controlled by the depression identified in this way. As a result, it becomes possible to produce a thin slab with excellent surface properties and no defects such as cracks.

[Brief explanation of the drawing]

Figure 1 shows the unevenness formed on the circumferential surface of the cooling drum, Figure 2
The figure is a diagram showing the diameter of the depression carved on the circumferential surface of the cooling drum and the adjacent open circuit jlL, FIG. 3 is a graph specifically expressing the effect of the present invention, and FIG. FIG. 3 is a diagram schematically showing the state. ]: Cooling drum 2: Molten metal 3: Solidified shell 3a: Thick wall portion 3b: Thin wall portion 4
: Air gap 5: Hollow

Claims (1)

[Claims] 1. Hollows having a circular or oval opening with a diameter of 0.1 to 1.2 mm and a depth of 5 to 100 μm constitute a part of the mold without touching each other. It is formed on the circumferential surface of the cooling drum, and when the diameter of the depression is D (mm) and the distance between adjacent depressions is L (mm), between the diameter D and the distance L between adjacent depressions, 0. 05D+0.1≦L≦1.4D+0.5, L≦1.
2. A cooling drum for a continuous ribbon casting apparatus, characterized in that the following relationship is maintained.