JPH02179343A - Method for continuously casting strip - Google Patents

Abstract

PURPOSE:To prevent generation of surface crack and surface pattern in a cold- rolled product by specifying surface roughness on circular surfaces of one pair of rolls in contact with molten metal and flattening the rough surface transferred on surface of a strip with hot rolling roll. CONSTITUTION:The circular surfaces of one pair of the cooling rolls 1a, 1b mutually rotating to reverse direction in contact with the molten metal are made to the rough surfaces having 4-50mum in the range of surface roughness Ra. The strip 4 passed through gap between a pair of the rolls 1a, 1b is continuously passed through the light rolling reduction hot-rolling rolls 5a, 5b during keeping this to the hot temp. and the rough surface transferred on the strip surface is flattened with these rolls 5a, 5b. By this method, the generation of surface crack and surface pattern in the cold-rolled product caused by uneven cooling at the time of developing the solidified shell are prevented and the good quality strip can be produced at high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a twin-roll continuous thin plate casting apparatus for continuously casting thin plates directly from molten metal, and a method of operating the same.

[Background of the invention and prior art]

A pair of internal cooling rolls with horizontal axes that rotate in opposite directions are arranged facing each other in parallel with an appropriate gap. A so-called twin-roll continuous casting machine is known in which a puddle is formed on the surface of the melt, and the molten metal in the puddle is cooled by the circumferential surface of a roll that rotates nine times before being continuously cast into a thin plate through the gap. . There has also been a proposal to apply such a twin roll continuous casting machine to continuous casting of steel to directly produce thin steel plates from molten steel.

In such a twin roll continuous casting machine, a solidified shell is generated on the circumferential surface of the roll in contact with the molten metal, and this is rolled in the roll gap, but the solidified shell generated on the circumferential surface of the roll is Since the growth occurs at a location where there is a large temperature difference between the low temperature side of the roll surface and the high temperature side of the molten metal, distortion is generally generated due to thermal stress due to this temperature difference, and this causes a portion to separate from the roll surface. That is, a partial gap occurs between the solidified shell and the roll surface.

In the part where the close contact between the solidified shell and the roll surface is broken, the heat conduction is reduced due to the existence of the gap, and the cooling of that part becomes insufficient compared to the part where the solidified shell and the roll surface are in close contact. Therefore, the solidification rate from T8 hot water becomes slow, and the shell thickness becomes partially thin. Poor cooling occurs due to such reasons.

When subjected to stress due to thermal contraction during cooling after casting, this often causes cracks to occur on the surface of the thin plate.

[Problem that the invention seeks to solve]

In order to prevent surface cracking of the thin plate due to uneven cooling as described above, the cooling by the rolls should be slow.

One effective means is to reduce the thermal stress of the solidified shell by this slow cooling. As a means for slow cooling of the roll, it is also useful to coat the circumferential surface of the roll with a ceramic coating having low thermal conductivity, or to use the ceramic roll itself. However, in this case, there is a problem in terms of service life because it is easily destroyed during casting.

Furthermore, if the roll surface is uniformly roughened by sandblasting or the like, the roughened surface forms a heat insulating layer and allows for slow cooling, which also makes it possible to minimize cooling unevenness and prevent surface cracks.

However, there is a problem in that the rough surface of the roll is transferred to the cast thin sheet, and when this thin sheet is cold rolled, an irregular pattern remains on the sheet surface.

The present invention aims to solve such problems in twin-roll continuous sheet casting, and aims to prevent surface cracks and patterns in cold-rolled products caused by uneven cooling during formation of a solid shell, The purpose of this invention is to provide a method for manufacturing thin plates of high quality and high yield.

[Means for Solving the Problems] The present invention provides a pair of cooling rolls that rotate in opposite directions and are arranged in parallel to face each other, and the molten metal in a pool formed on the circumferential surface of the roll pair is extracted from the molten metal in a pool formed on the circumferential surface of the roll pair. In a thin plate continuous casting method in which a solidified shell is formed on the circumferential surface of the roll pair and the solidified shell is rolled down into a thin plate in the gap between the roll pairs, the circumferential surface of the roll pair that will be in contact with the molten metal has a surface roughness Ra. is 4-5
The rough surface is in the range of 0μ, and the thin plate that has passed through the gap between the pair of rolls is passed continuously between hot rolling rolls under light rolling while still maintaining high temperature, and the hot rolling rolls transfer the roughness to the surface of the thin plate. It is characterized by smoothing rough surfaces. In other words, the surface of the cooling roll is made to have an appropriate surface roughness, thereby uniformly reducing the heat conduction between the generated solidified shell and the roll surface over the entire surface, allowing gradual cooling, and eliminating the cause of thin plate surface cracks. This eliminates uneven cooling of the solidified shell, and smooths the rough surface transferred to the thin plate as it passes through the roll gap under light pressure with hot rolling rolls installed in-line on the downstream side of this twin-roll system.

The feature is that the causes of pattern formation during cold rolling are eliminated in advance. The rolling reduction ratio with the hot rolling rolls may be in the range of 1 to 20%.

The content of the present invention will be specifically explained below with reference to the drawings.

(Detailed Description of the Invention) Fig. 1 shows an example of a twin roll continuous casting machine to which the present invention is applied.In Fig. 1, reference numerals 1a, lb
are a pair of internal cooling rolls that are arranged facing each other with their axes horizontal so as to rotate in opposite directions (the directions of rotation of both are shown by arrows); 2 is formed on the circumferential surface R of these rolls la and lb; 3a and 3b are side dams, and 4 is a thin plate to be cast.

In the illustrated example, each of the internally cooled roll pairs 1a and 1b uses water-cooled rolls. More specifically, each roll pair 1a, lb has a groove-shaped cooling water passage formed inside the roll sleeve forming the circumferential surface R (not shown in the figure). ), the circumferential surface R is cooled to a predetermined temperature by passing water through this cooling water passage.

Supply of cooling water to the cooling water passage inside this circumferential surface R and drainage thereof are performed from the roll shaft. For this reason, the roll shaft is constructed in the shape of a double pipe, with the inner pipe serving as the cooling water supply pipe and the annular pipe line formed between the outer pipe and the inner pipe serving as the drain pipe. The cooling water supply pipe of the pipe is connected to the cooling water passage inlet inside the circumferential surface R, and the annular pipe is connected to the cooling water outlet. With this configuration, when cooling water is continuously supplied to the inner pipe from the pump P as shown in the figure, the cooling water circulates through the cooling water passage inside the circumferential surface R and is drained through the annular pipe. This cooling water flow operation can be continued even while the device is in operation. The circumferential surfaces R of the roll pairs 1a and 1b that come into contact with the molten metal are roughened within the range defined by the present invention by sandblasting or the like.

FIG. 2 shows a line from which the thin plate 4 continuously manufactured from the twin-roll continuous casting machine of FIG. 1 is wound up by the winding machine 8.
, 5b are arranged. The hot rolling rolls 5a and 5b are arranged close to the rolls la and lb to the extent that the temperature of the cast thin sheet does not fall below a predetermined value, and to the extent that it can respond to changes in the casting speed. A position away from roll pair 1a, 1b is desirable, therefore roll pair 1a+tb
The rotational speeds of the hot rolling rolls 5a and 5b must be approximately synchronized.

It is preferable that the thin plates between the roll pairs 1a, lb and the hot rolling rolls 5a, 5b flow with some play, rather than with tension applied, and in some cases it is more preferable to provide a louver or the like. It is.

In addition, roll pairs 1a, Lb and hot rolling rolls 5a*5
Between b, guide rolls 6 a + 6 are installed as necessary.
b or vinyl rolls may be installed, or heat insulation equipment or heating equipment may be installed to avoid a drop in the temperature of the thin plate.
The thin plate that has passed through the hot rolling rolls 5a and 5b is conveyed by a conveying means such as a roller table 7 or a belt conveyor.

It is wound up by a winding roll 8 to form a coil.

FIG. 3 schematically shows the rough surface condition on the circumferential surface R of the roll pair 1a, lb, and shows the rough surface condition of the roll pair 1a, lb.
The surface of O that comes into contact with the molten metal is formed into a rough surface 11 having unevenness, and a solidified shell 12 is formed from the molten metal 2 on this rough surface 11. When this rough surface 11 is formed evenly over the entire surface that comes into contact with the molten metal by sandblasting, for example, an extremely thin air gap layer consisting of a gas layer trapped in the unevenness of the rough surface is created evenly between the roll surface and the shell 12. This produces a heat insulating effect and causes slow cooling. This reduces the temperature difference between the surface and the inside of the shell 12, reduces the thermal stress acting on the shell 12, reduces the phenomenon of the shell 12 being partially separated from the roll, and reduces the variation in thickness caused by this.

As a result of various experiments, the present inventors found that at least the surface of the roll circumferential surface R that comes into contact with the molten metal in the pool is R.
It has been found that a rough surface in the range of 4 to 50 u- can reduce uneven cooling of the thin plate and prevent surface cracking.

Note that Ra is JIS standard (e.g. JIS B 0601)
The average roughness at the reference plane (center line) of

On the other hand, when a roll with such a rough surface is used, when the solidified shell 12 is pressed against the roll at the narrowest gap between a and lb, the rough surface is transferred to the surface of the thin plate. If a thin plate with this rough surface is subjected to processing such as cold rolling as it is, the rough surface of the plate may be crushed well in some areas and not in others due to slight fluctuations in the plate thickness due to slight unevenness in cooling. Understood. This appears as an irregular pattern on the surface of the cold rolled sheet. This irregular pattern disappears when a polishing process is performed, but this increases the cost.

The inventors of the present invention investigated various measures to solve this problem, and found that ``if light hot rolling is applied to the thin plate that has come out of the IIL plate continuous caster while it is still hot, the plate surface roughness will become considerably finer, and the plate thickness will increase. It was found that this problem could be solved by a simple treatment, as the plate thickness could be made uniform without slight fluctuations in the thickness.The rolling reduction of this light hot rolling should preferably be in the range of 1 to 20%, and if it is less than 1%, the surface If the roughness improvement effect is insufficient and exceeds 20%,
The light hot rolling equipment of the present invention has a reduction ratio that is too high to crush the rough surface of the thin sheet or eliminate slight fluctuations in sheet thickness due to slight cooling unevenness, resulting in excessive equipment.

The purpose is not to reduce the pressure to a large extent, but to improve the surface quality of the board to the same degree as a skin bath. The temperature of the plate during light hot rolling varies depending on the type of molten metal, so it cannot be stated unconditionally, but 1. For example, in the case of molten stainless steel, it is 5uS304T! ;! 900° to 1230°C is appropriate for 5Us430.

As described above, according to the present invention, fluctuations in thermal stress due to temperature differences in the solidified shell are minimized, and the problems of surface cracking of cast plates and quality deterioration due to rough surfaces are effectively solved. However, the thin plate continuous casting apparatus to which the present invention is applied is not limited to the illustrated example of the earth-rolling type twin roll machine, but can also be applied to an oblique pouring type twin roll machine, a different diameter twin roll machine, etc.

〔Example〕

Using a twin-roll thin plate continuous caster consisting of internal water-cooled copper alloy sleeve rolls with a diameter of 400 mm and a diameter of 300 mm.

! 500kg of 1lJs304 steel was cast into a thin plate with a thickness of 2cm. The roll circumferential surface is sandblasted to Ra-5μ.
The roughness was set to m. The thin plate is subjected to light hot rolling in-line when the temperature of the thin plate reaches 1000° to 1100°C.

It was then rolled up to form a coil. The rolling reduction of light hot rolling is 3
%. As a result, the roughness and flatness of the coil surface before cold rolling were significantly improved, irregular patterns disappeared from the surface of the cold rolled sheet, and an extremely good surface texture was obtained. Moreover, no surface cracks were observed.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main parts of a twin-roll continuous sheet casting machine for carrying out the method of the present invention, and Fig. 2 is a schematic cross-section showing the line from the continuous casting machine to the winding machine for carrying out the method of the present invention. FIG. 1 is a conceptual diagram for explaining slow cooling by roughening the roll surface in a twin-roll continuous casting machine. la, lb... internally cooled roll, 2... molten metal in the pool, 3... side dam, 4... cast thin plate, 5a, 5b... light hot rolling roll, 8...
Winder, 11. Rough surface of twin rolls, 12. Solidified shell.

Claims (2)

[Claims] (1) A pair of cooling rolls that rotate in opposite directions are arranged in parallel to face each other, and a solidified shell is formed on the circumferential surface of the pair of rolls from the molten metal in a pool formed on the circumferential surface of the pair of rolls. In a thin plate continuous casting method in which the solidified shell is rolled down into a thin plate in the gap between the pair of rolls while forming the solidified shell, the circumferential surface of the pair of rolls that will be in contact with the molten metal has a surface roughness Ra of 4 to 50μ.
The thin plate having passed through the gap between the pair of rolls was made to have a rough surface in the range of m, and while the temperature was still maintained, it was passed continuously between hot rolling rolls under light rolling, and the hot rolling rolls transferred the sheet onto the surface of the thin plate. A twin-roll continuous thin plate casting method characterized by smoothing rough surfaces. (2) The method according to claim 1, wherein the rolling reduction with the light rolling hot rolling roll is in the range of 1 to 20%.