JPH0768351A - Method for manufacturing cooling roll for thin strip continuous casting and cooling roll thereof - Google Patents

Abstract

PURPOSE:To stably cast a strip having good surface characteristic by arranging recessed part on the surface of a roll, packing coarse grain materials in the condition that spacing part is held and filling close material above the coarse grain materials to constitute the closed part in the recessed part. CONSTITUTION:Many recessed parts 3 are arranged on the surface 2 of the cooling roll. The coarse grain materials 5 are charged into the bottom part of the recessed part 3 in the condition that the spacing part 6 is held. The close material 4 is filled above the coarse grain materials 4 to the surface 2 of the cooling roll to close the recessed part 3. As the air having extremely low heat conductivity can be held in the recessed part 3, the slow cooling effect of the cooling roll can sufficiently be obtd. and also, the state of no recessed part on the cooling roll surface 2 is obtd. Therefore, the crack and the roughness of the cast strip surface are not developed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling roll used in a twin-roll system, a single-roll system, a drum-belt system and the like, which is a synchronous ribbon continuous casting apparatus.

[0002]

2. Description of the Related Art A number of techniques for continuously casting thin-walled slabs close to the final shape by a synchronous casting apparatus have already been disclosed. However, many proposals have been made for the surface shape of a cooling roll for the purpose of cooling relaxation. Has been done. Usually, in twin roll casting, Cu or a Cu alloy is used as a casting roll, and the surface layer may be plated with Ni or the like. In addition, a roll with a structure that can cool the inside of the roll with water is also used. When a thin plate is cast with such a roll, generally, the greater the cooling capacity of the roll, that is, the higher the cooling rate of the slab during casting, the more uneven the cooling of the slab surface (solidified shell) during solidification. And the heat shrinkage of the solidified shell becomes non-uniform, so cracks are likely to occur in the slab (the cause of non-uniform cooling of the solidified shell is due to other gas between the roll and the cast metal. And non-metallic materials (mainly oxides, also called scum) are locally entrained, and the meniscus vibration of the molten metal pool (molten pool) is considered).

In order to completely prevent the cracking of the slab, it is necessary to reduce the cooling rate of the slab during casting, in addition to trying to reduce the vibration of the meniscus and the inclusion of gas and non-metal substances. It is effective, and therefore, it is conceivable to reduce the thermal conductivity of the roll by (1) providing a large number of small depressions on the roll surface or (2) changing the material of the roll (particularly the material of the surface layer of the roll). . As an example of the case (1), for example, in JP-A-60-184449, the unevenness of a specific size is uniformly distributed on the surface of the cooling drum to make the thickness of the solidified shell uniform in the plate width direction. Also, JP-A-1-83340 and JP-A-1-218874.
In Japanese Patent Publication No. 3), a large number of small concave portions having a specific size and shape are provided in a uniform or predetermined distribution state on the surface of the cooling drum to prevent cracking.

Further, in the case of (2), a method of coating the surface of the cooling roll with a metal having a relatively low thermal conductivity to lower the cooling capacity of the roll is disclosed in JP-A-1-166862 and JP-A-1-162544. Etc. Further, as an example in which the methods (1) and (2) are combined, in JP-A-60-72649, the solidification rate of the molten metal is made inhomogeneous to form a ribbon of equiaxed crystals or fine crystal grains. In order to obtain the above, a technique has been disclosed in which a material having a thermal conductivity different from that of the roll material is partially embedded in the peripheral surface of the roll. In addition, the present applicants disclosed in JP-A-2-284.
Japanese Unexamined Patent Publication No. 748 discloses that a recess formed on the peripheral surface of a drum is filled with a refractory material having a low thermal conductivity to finish a flat surface.

[0005]

However, although the technique of providing irregularities on the surface of the cooling roll has the effect of relaxing the cooling rate and reducing fine cracks in the slab, the surface of the slab corresponding to the position of the depression is There are irregularities on the surface, and when the slab is cast and then rolled to form a thin plate product, the locations corresponding to the irregularities may remain as surface defects.

Also, in the method of coating the peripheral surface of the cooling roll, the roll material generally has a higher thermal conductivity than the coating material, so that the effect as the coating material cannot be sufficiently obtained, and a thin film as the coating material, For example, when the ceramics are attached, the ceramics peel off during casting and the effect of slow cooling for a long time cannot be obtained. In addition, the technique of embedding a material with different thermal conductivity from the roll material on the roll peripheral surface and the technique of filling with a refractory material with low thermal conductivity of the recess engraved on the drum peripheral surface to finish on a flat surface are Since it is completely filled, the difference in thermal conductivity from the roll material cannot be fully utilized, and it is difficult to achieve the original purpose.

The present invention solves the problems of the prior art, and provides a cooling roll having no depression on the surface of the cooling roll and having a structure having a thermal conductivity sufficiently different from that of the roll material. The purpose is to

[0008]

The present invention has the following features in order to achieve the above object. That is, the cooling roll of the present invention is provided with a large number of depressions on the surface of the cooling roll, the bottom of the depression is filled with a coarse grain material in a state where voids are held, and the upper portion of the coarse grain is filled with a dense material. It is filled to form a closed portion of the recess.

The present invention will be described in detail below with reference to the drawings. In FIG. 1, a large number of depressions 3 are provided on a surface 2 of a cooling roll 1, a coarse grain material 5 is inserted in a state where a void 6 is held at the bottom of the depression 3, and a dense material 4 is placed on the upper portion of the coarse material 5. Fill up to 2 and close the recess 3. With such a structure, air having extremely low thermal conductivity (for example, the thermal conductivity K of air is about 2.5 × 10 ^-2 W / mK, that of alumina is about 21 W / mK; Conductivity is about 4
(Which is 00 W / mK) can be held in the depression, so that the effect of gentle cooling of the cooling roll can be sufficiently obtained and the depression is not formed on the surface of the cooling roll. When a dent is formed on the surface of the cooling roll, molten metal enters the dent depending on the type of gas in the dent and the surface of the slab becomes convex, or the molten metal becomes dented and the surface of the casting surface becomes concave. To do.
Therefore, the cooling roll structure of the present invention is extremely suitable for practical use.

Although the above description is based on the twin roll casting machine, it is naturally applicable to other synchronous casting machines, and the structure of the cooling roll is not limited to the above-mentioned embodiment. A filling material having a low height may be embedded in the depression. In short, in the cooling roll of the synchronous casting machine, it is within the scope of the present invention if the recess is closed with a gap provided at the bottom of the recess.

[0011]

【Example】

(1) Implementation conditions (a) Casting machine Cooling roll: Diameter: 400 mm, Width: 350 mm Material: Copper Surface: Ni plating coating with a thickness of 1 mm Machining recesses by photo etching or engraving (b) Cast metal Austenitic stainless steel (SUS304) (C) Operating conditions Casting speed: 10 to 100 m / min Contact arc length between cooling roll and molten metal: 170 mm (depth of basin part 150 mm) Under the above conditions, the diameter of the depression of the cooling roll surface 0.1 to 5 mm, depth 10 μm to 1.5 mm, area ratio 5
The average particle size of 50
Alumina powder having a thickness of ˜300 μm was applied according to the depth of the recess such that a void remained at the bottom of the recess, and the dense material was filled on the upper part thereof up to the roll surface by the following means.

[0012] Over the entire surface of the recessed roll,
Ni plating having a thickness of 1.5 mm was applied again, and then the roll surface was polished. Zirconia was sprayed over the entire surface of the roll having the depressions to form a film having a thickness of 1.5 mm, and then the roll surface was polished. On the other hand, as a comparative example, all casting was performed under the same conditions as above except that the filling material was not filled in the depressions on the roll surface.

(2) Implementation results (a) Under the above implementation conditions, the recess diameter is 1 mm and the depth is 100.
The relationship between the casting speed and the height of the unevenness on the surface of the slab was determined with μm and the area ratio of 15%. The result is shown by line A in FIG.
Irregularities were not formed on the surface of the slab and there was no cracking of the slab regardless of the casting speed.

Under the conditions of (b) and (a), the depression area ratio is 5 to 1
If it is less than 0%, the relaxation cooling effect of the cooling roll is reduced, and relatively large cracks or fine cracks are generated in the cast slab. (C) When cast as a comparative example, the result is shown by a curve B in FIG. That is, when the casting speed (cooling roll surface speed) is less than 40 m / min, the portion of the slab surface corresponding to the depression of the cooling roll surface forms a concave portion as shown by 12 in FIG. 4, and when it exceeds 40 m / min. The part is 11 in FIG.
4 was formed (as can be seen from FIG. 4, when the casting speed is 80 m / min, the height of the protrusion is h≈70 μm).

[0015]

EFFECTS OF THE INVENTION According to the present invention, in continuous casting of thin strips, it is possible to stably cast thin strips having no surface cracks and unevenness and good surface properties.

[Brief description of drawings]

FIG. 1 shows a cooling roll of the present invention, in which (a) is a front view and (b) is an enlarged view of a portion A of FIG.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a diagram showing the relationship between the casting speed and the height of irregularities on the surface of a slab in Examples of the present invention and Comparative Examples.

FIG. 4 is a diagram showing a surface of a slab of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling roll 2 ... Cooling roll surface 3 ... Cavity 4 ... Dense material 5 ... Coarse grain material 6 ... Void part 7 ... Cooling roll inside 8 ... Cooling roll shaft 9 ... Cast surface 10 ... Cast inside 11 ... Cast convex Part 12 ... Recessed slab

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumi Yasuda 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. A dent is provided on the surface of a cooling roll, and the bottom of the dent is filled with a coarse-grained material in a state where voids are held,
A method for producing a cooling roll for continuous casting of thin strips, characterized in that a dense material is filled in an upper portion of the coarse grain material to form a closed portion of the recess. 2. The bottom of the depression provided on the surface of the cooling roll is filled with a coarse grain material while maintaining a void, and the upper portion of the coarse grain material is filled with a dense material up to the surface of the cooling roll. A cooling roll for thin strip continuous casting, which is characterized in that