JPH0433537B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a twin drum system, a single drum system,
The present invention relates to a cooling drum used in continuous casting equipment such as a drum-belt system.

[Conventional technology]

In recent years, in the field of continuous metal casting, there has been a strong desire to develop casting technology for thin-walled slabs that closely resemble the final shape, with the aim of reducing manufacturing costs and creating new materials. 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, the twin-drum method uses a pair of drums with an internal water cooling mechanism as the main components of the mold, and the twin-drum method uses a single cooling drum. There is a single-drum method, which uses a cooling drum, and a drum-belt method, which forms a pool between the cooling drum and the belt. In these casting methods, it is an important issue to stably maintain the surface quality of the slab at a high level. In other words, unlike the case of slabs manufactured by conventional continuous casting equipment, these continuous casting methods aim to obtain thin slabs that can reduce the degree of rolling in subsequent steps. It was developed. Therefore, if there is a defect such as a variation in wall thickness on the surface of a thin slab, this becomes a defect on the surface of the product, and there is a great risk that its commercial value will be significantly impaired.

Therefore, various methods have been studied as a means of stably obtaining slabs with good surface quality. One of the methods is to provide unevenness on the circumferential surface of the cooling drum so as to form an air gap between the cooling drum and the solidified shell, which serves as a heat insulating layer.
It is proposed in the publication. This air gap reduces the heat removal capacity of the cooling drum, and slow cooling of the molten metal is performed. 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 that the invention seeks to solve]

However, according to the experiments conducted by the present inventors, sufficient effects can be stably obtained simply by uniformly forming irregularities of a certain depth on the circumferential surface of the cooling drum and maintaining the irregularities in the initial state. It turned out that I couldn't do it. For example, when large irregularities are continuously provided on the circumferential surface of a cooling drum, not only the irregularities are generated on the surface of the obtained thin slab, but also the concentration of thermal stress is promoted in that area, which can actually cause cracks. is encouraged. Additionally, if linear or angular irregularities are formed on the circumferential surface of the cooling drum, the corners of these irregularities will become the starting point for cracks.
Many cracks occur in thin slabs.

For this reason, in addition to ensuring the uniformity of the unevenness provided on the circumferential surface of the cooling drum and specifying the depth of the unevenness, it is necessary to ensure that the shape of the unevenness and the size of the recessed parts are large due to the poor surface texture of thin slabs. It was found that it had an impact.

Therefore, the present inventors created thin-walled cast slabs with excellent surface properties and shape characteristics without cracks or wall thickness fluctuations by providing mutually independent circular or oval depressions on the circumferential surface of the cooling drum. We have developed a method for manufacturing the product and have filed a separate application for this. However, even when such circular or oval depressions are formed, depending on the distribution of the depressions, there may be localized areas where thermal stress tends to concentrate in the solidified shell formed on the peripheral surface of the cooling drum. may occur. If such a location exists, defects such as cracks will occur in the thin slab at that location.

Therefore, the purpose of the present invention is to improve the distribution of these circular or elliptical depressions, thereby making use of the effects of the depressions, and manufacturing thin slabs with healthier surface properties. do.

[Means and actions for solving problems]

The cooling drum for continuous casting equipment for thin-walled slabs of the present invention has a depth of 5 to 100 μm on the circumferential surface of the drum, and a diameter of 5 to 100 μm.
A large number of circular or oval shaped depressions of various sizes in the range of 0.1 to 1.2 mm are arranged with the closest distance between the open ends of the depressions in the range of 0.1 to 2.0 mm. , in a range where the closest distance between the opening ends of adjacent depressions is 0.1 to 0.5 mm, four or more depressions with the same area are consecutively arranged in any direction such as a straight line, an arc shape, a hook shape, etc. It is characterized by the fact that it does not.

The diameter of the opening in the present invention is used to include both the short axis and the long axis.

In addition, the area referred to in the present invention refers to the opening area of a depression, and depressions having the same area have an area difference within 10%.

The cooling drum of the present invention has a large number of circular or oval depressions formed on its circumferential surface. When the molten metal contacts the circumferential surface of the cooling drum and a solidified shell is formed, the depressions form independent air gaps that are not continuous with each other. Therefore, due to this air gap, the high temperature part (thin wall part of the solidified shell) which has been slowly cooled and still has low rigidity.
are not continuous on the surface of the solidified shell, but are separated from each other. That is, this high temperature area due to the air gap effect is surrounded by a highly rigid area that is sufficiently cooled by direct contact with the cooling drum.

At this time, in the cooling drum of the present invention, the size, shape and depth of the depressions and the closest distance between the depressions are arranged within appropriate ranges, and solidified shells that are formed at locations corresponding to the depressions and have low rigidity are formed. The part is
It does not form continuously over a long range on the surface of the solidified shell. As a result, stress concentration areas that cause cracks are dispersed, and a thin cast slab with a crack-free surface quality is obtained.

〔Example〕

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

FIG. 4 shows a twin-drum continuous casting machine to which the present invention is applied.

Molten metal is poured from an intermediate container such as a tundish 1 into a sump 3 partitioned by a pair of cooling drums 2 and a side weir (not shown). The injected molten metal is cooled and solidified on its peripheral surface by the heat removed by the cooling drum 2. In this way, the solidified shell formed on the circumferential surface of each cooling drum 2 moves downward as the cooling drum 2 rotates, is pressed at the kissing point 4, and is cooled as a single thin slab 5. It is sent out from between the drums 2. This thin slab 5 is conveyed toward the pinch rolls 6 while drawing a loop.

The cooling drum 2 of the present invention, which comes into contact with the molten metal in the sump 3, has a diameter as shown in an enlarged view in FIG.
A large number of depressions 11 of various sizes with circular openings in the range of 0.1 to 1.2 mm and depths of 5 to 100 μm are provided, with the closest distance d between the opening ends of adjacent depressions.
are spaced apart in the range of 0.1 to 2.0 mm, and in the range of the closest distance d of 0.1 to 0.5 mm, there are four or more depressions with the same area in any direction such as linear, arcuate, hook shape, etc. They are distributed without touching each other so that they are not continuous. Here, dents with the same area refer to dents in which the difference in opening area is within ±10%. Since the recess 11 has a circular opening, there is no corner that can be a starting point for cracking, unlike irregularities having linear or rectangular openings. Note that the opening of the depression 11 may have an oval shape in addition to a circular shape. When the opening has an oval shape, the ratio of the short axis to the long axis is preferably 0.6 or more. In this case, both the short axis and long axis are 0.1
Keep it within ~1.2mm.

According to the findings of the present inventors, when the diameter of the recess 11 is 0.1 mm or less, no air gap is formed and the slow cooling effect is small, cleaning is difficult, and the drum surface is easily affected by scratches and wear.
It is also difficult to process. On the other hand, if the diameter of the recess 11 exceeds 1.2 mm, the recess 11 itself tends to become a starting point for micro-cracks, and molten metal enters into the recess 11, forming a large number of fine protrusions on the surface of the resulting thin slab. be done. Moreover, if the depression 11 is shallow, less than 5 μm, no air gap will be formed, and the gradual cooling effect will be significantly reduced. In addition, the molten metal enters the recesses and many fine protrusions are generated on the surface of the slab, which is unfavorable in terms of product quality. On the other hand, for depressions 11 with a depth exceeding 100 μm, the opening diameter is 1.2
As far as dents smaller than mm were concerned, no significant increase in effectiveness was observed.

In addition, the closest distance between the opening ends of adjacent recesses 11 (hereinafter referred to as "the closest distance between recesses") is 0.1 mm.
When the following conditions occur, the air gap becomes continuous in the same way as when these depressions 11 are continuous, and a long stiffness-reduced portion occurs in the solidified shell. For this reason, it is necessary to set the closest distance d between the depressions 11 to 0.1 mm or more. Further, the upper limit of the closest distance d between the depressions 11 is preferably maintained at 2.0 mm or less in order to effectively generate an air gap by the depressions 11. And the distance of closest approach d is
In the range of 0.1 to 0.5 mm, linear, arcuate, hook-shaped, etc.
When the number of consecutively arranged depressions 11 having openings of the same size in either direction becomes four or more, the surface of the solidified shell in which the continuously arranged depressions 11 are arranged in a linear, arcuate, or
Since parts with decreased rigidity having a shape such as a hook shape or a similar shape are continuously generated, this often causes cracks to occur. In particular, in the case of circular depressions, this is noticeable when the sizes are the same (congruent), and this tendency is not noticeable when the sizes and shapes are different. Also, the closest distance d between the depressions is
It has been found that cracks are less likely to occur when the thickness is 0.5 to 2.0 mm, and that there is no significant difference in either case as long as the other conditions mentioned above are satisfied. FIG. 2 shows a comparative example in which recesses 11 of the same size (congruent) are uniformly distributed on the circumferential surface of the cooling drum with the closest distance d between the recesses being 0.3 mm. In this case, when looking at the entire circumferential surface of the cooling drum, air gaps are uniformly distributed between the cooling drum and the solidified shell due to the depression effect, and rapid cooling portions and slow cooling portions are uniformly distributed on the surface of the solidifying shell. However, if the closest distance d between the depressions is the same and they are arranged regularly, the stiffened shell may have a continuously long part of reduced rigidity (thin wall part), where thermal stress is concentrated. However, cracks occur.

FIG. 3 is a graph showing the crack occurrence index in the example of the present invention shown in FIG. 1 and the comparative example shown in FIG. In both the present invention and comparative example, the results are shown when thin slabs with a wall thickness of 2.4 mm and a width of 800 mm were manufactured from molten steel having a stainless steel composition at a temperature of 1500° C. at a casting speed of 65 m/min. In the same figure, the vertical axis is the casting length of 1 m.
The total crack length (cm) is expressed as a crack occurrence index. When the cooling drum of the present invention having unevenly distributed depressions 11 arranged as shown in FIG. 1 is used, the occurrence of cracks is extremely small. In contrast,
When a cooling drum of a comparative example having a uniformly distributed array of depressions as shown in FIG. 2 was used, the occurrence of cracks became noticeable.

The shape and distribution of the depressions 11 in the present invention have a great influence on forming a suitable air gap.
Therefore, since a high degree of precision is required for forming the depressions 11, it is preferable to form the depressions 11 by etching, electric discharge machining, plasma machining, electron beam machining, laser machining, etc. rather than by using ordinary machine tools. .

When producing thin slabs using the cooling drum 2 having the depressions 11 formed on its circumferential surface in this manner, oxides, impurities, etc. are likely to accumulate and adhere to the depressions 11. Such deposition/adhesion reduces the effect of providing the depressions 11. Therefore, as shown in FIG. 4, it is preferable to arrange the cleaning brush 7 so as to face the circumferential surface of the cooling drum 2. The cleaning brush 7 removes deposits accumulated on the circumferential surface of the cooling drum 2, particularly in the recesses 11.

With respect to the cleaned circumferential surface of the cooling drum 2,
Further, the drum coater 8 can also apply a drum coating agent containing zircon, alumina, or the like as a main component. This will further improve the quality of the slab and extend the life of the drum.

[Effects of the Invention] As explained above, in the present invention, depressions having circular or oval openings formed on the circumferential surface of the cooling drum are irregularly distributed under predetermined conditions. Therefore, an air gap is formed between the circumferential surface of the cooling drum and the solidified shell, without making the stress concentration part that causes cracks long, and the cooling conditions are relaxed. It is possible to produce slabs. At this time, since the depression has a circular or oval opening with no corners, it will not become a starting point for cracking. The thus obtained thin slab has excellent surface properties without cracks, and even when it is rolled in a subsequent process, problems such as cracking and breakage will not occur.

[Brief explanation of drawings]

Fig. 1 is a plan view showing depressions provided irregularly on the circumferential surface of the cooling drum of the present invention, Fig. 2 shows a comparative example in which the depressions are regularly distributed, and Fig. 3 shows the distribution of the depressions. FIG. 4 is a graph showing the influence of conditions on cracking of slabs, and FIG. 4 is an overall view showing a twin-drum continuous casting machine incorporating the cooling drum of the present invention.

Claims (1)

[Claims] 1. On the drum circumferential surface, a depth of 5 to 100 μm and a diameter of
A large number of circular or oval shaped depressions of various sizes in the range of 0.1 to 1.2 mm are arranged with the closest distance between the open ends of the depressions in the range of 0.1 to 2.0 mm. In the range where the closest distance between the opening ends of adjacent depressions is 0.1 to 0.5 mm, four or more depressions with the same area are consecutively arranged in any direction such as a straight line, an arc shape, a hook shape, etc. A cooling drum for continuous casting equipment for thin-walled slabs, characterized in that