JPH0246950A - Method for continuously casting strip - Google Patents

Abstract

PURPOSE:To stabilize operation of continuous casting by starting pouring of molten metal while wearing by grinding a side dam with inner part cooling roll and successively, changing sending speed of the side dam in accordance with variety of casting direction. CONSTITUTION:To one pair of the rotating cooling rolls 1a, 1b, the side dams 3a, 3b as vertically shiftable are arranged. In the whole thickness of the side dam 3a, 3b, a part W1 at the inner part is made to the thickness set on the circumferential face of the roll and a part W2 at the outer part is slidingly brought into contact with the side faces of the rolls. In the case of starting casting, before pouring molten metal, the rotation of the rolls and sending of the side dams are executed, and the casting is started at the time, when the lower edges 13 of the dams come to the suitable position. Successively, the sending speeds of the side dams 3a, 3b are controlled based on edge shape of a casting strip 4. By this method, as leakage of the molten metal in the side dam can be surely prevented, the operation of continuous casting is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a casting method using a twin-roll continuous caster for continuously casting thin plates directly from molten metal (for example, molten steel).

[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 pool is formed in the pool, and the molten metal in the pool is continuously cast into a thin plate through the gap while being cooled by the circumferential surface of a roll rotating once. This kind of twin-roll continuous casting machine is applied to continuous casting of steel, and it fits from molten steel! Proposals have also been made to directly manufacture four plates.

To continuously cast thin sheet products from the gap between the roll pairs, a puddle of molten metal is formed on the circumferential surface above the gap between the roll pairs, and the surface level is maintained substantially constant. It is necessary to continuously inject molten metal into this pool. In order to form this pool, the flow of hot water in the direction along the roll axis on the circumferential surface of the roll is restricted. A pair of dams with surfaces perpendicular to the roll axis are always required.

This dam usually also serves to regulate the width of the sheet slab. In this specification, this dam is referred to as a ``side dam''. In addition to the side dams placed on the left and right, a pair of front and rear weirs (also called long side dams) with surfaces oriented along the roll axis are erected on the circumferential surface of the roll pair so as to be perpendicular to the side dams. A box-shaped pool may be formed by the side dam and the front and rear weirs, but if the radius of the roll pair is sufficiently large, the front and rear weirs in the direction along the roll axis are not necessarily necessary. The circumferential surface itself can serve as this front and rear weir.

The side dams that form this pair include a mobile side dam that presses an endless metal belt or track belt (caterpillar) against the side surface of the pair of rolls and moves it at a speed commensurate with the casting speed of the slab, and a refractory side dam. A fixed side dam is known in which a plate-like object is fixed to the left and right sides of a pair of rolls.

The latter type of side dam fixed to the shell has the advantage that the device configuration and operation control are not complicated like the former type.

For fixed side dams, there are two types of side dams, one in which the distance between the two side dams is smaller than the roll width (the length from one end of the roll to the other end), and the other in which it is equal to the roll width. . In the former case, both side dams are raised above the roll circumferential surface so that the bottom surface of one side dam comes into sliding contact with the roll circumferential surface. In the latter case, the inner surfaces of the two side dams should be in sliding contact with both side surfaces of the roll in the direction perpendicular to the roll axis (in this specification, both sides of the roll are referred to as roll side surfaces), that is, the inner surfaces of the two side dams should be in sliding contact with both side surfaces of the roll in the direction perpendicular to the roll axis (in this specification, both side surfaces of the roll are referred to as roll side surfaces). Side dams are fixedly installed so that both ends are sandwiched between the side dams.

Usually, the fixed side dam is made of refractory material with good heat insulation properties. This is because it is necessary to prevent the molten metal that comes into contact with the side dam from solidifying on the surface of the side dam. Such insulating refractories generally have poorer wear resistance than solidified metals and are more susceptible to scratching, resulting in damage to the refractories and, if severe, breakouts. In addition, in the above method of fixing the side dams so as to sandwich the roll side surfaces of the 9-car roll,
When the plate passes through the roll gap, the pressure of the end of the plate creates a gap in the sliding area between the roll side surface and the inner side surface of the side dam, and hot water is poured into the gap. If these troubles occur, casting cannot be continued stably.

Whichever side dam method you choose.

A portion of the molten metal in the pool forms a thin solidified shell on each surface of each rotating roll, and as the roll rotates, this solidified shell grows and passes through the gap between the twin rolls. At that time, the solidified shell is rolled near the roll gap where the roll gap is closest to form a thin plate of a predetermined thickness. Therefore, by crushing and rolling the solidified shell, the solidified shell tends to expand in the width direction near the roll gap. As a result, the end of the cast plate applies a large pressure to the side dam. Therefore, especially in the case of a fixed side dam, it is inevitable that a large amount of friction will occur between the moving plate end and the fixed side dam, resulting in damage to the side dam refractories and excessive stress on the plate end. This can cause cracks at the ends, shape defects, and even the formation of hot water in the sliding contact areas, which is a major hindrance to stable operation. This problem is especially important for casting steel, which cannot be solved with soft non-ferrous metals with low melting points, due to the high melting point and high strength of the plate material.

In Japanese Patent Application No. 84555/1984, the present inventors have proposed a thin plate continuous casting machine that can be called a "grinding dam method or an earth moving grinding method between mobile and fixed types" which fundamentally solves this problem. We proposed an invention in which the side dam is made of a refractory material with good machinability, and by actively feeding the side dam in the casting direction during casting, the friction between the side dam and the roll surface and the end of the plate to be cast is reduced. The side dam is worn out by grinding in the process.After that, the inventors have repeated casting tests using this grinding dam method.As a result, several conditions must be met for stable casting using this method. It has been found to be advantageous to operate in this manner.

[Purpose of the invention]

Therefore, the present invention is aimed at solving the above-mentioned problems and is intended to provide a method for further improving the grinding dam method proposed in Japanese Patent Application No. 84555/1983.

[Structure of the invention]

In the present invention, a pair of internal cooling rolls that rotate in opposite directions are arranged facing each other with their axes horizontal, and a pair of side dams for forming a pool on the circumferential surface of the pair of rolls are installed approximately on the width of the casting plate. The side dams are arranged at corresponding intervals, and at that time, at least a part of the bottom of the side dams is in contact with the circumferential surface of the roll so that part or all of the thickness of the side dam is located on the circumferential surface of the roll. In addition to arranging side dams, the side dam portion that comes into contact with the circumferential surface of the roll during casting is made of refractory material with good machinability, and this side dam is sent out at a predetermined speed in the casting direction. This method continuously casts hot water from the pool into a thin plate through the gap between the pair of rolls while grinding and wearing out the side dam at the contact area, and while maintaining the state where the side dam is being ground and worn at the contact area. It is characterized by starting the injection of molten metal.Also, after starting casting.

Changes in the casting conditions after the start of casting (1) For example, change the feed speed of the side dam depending on changes in the edge shape of the casting plate, changes in the width of the casting plate, changes in the thickness of the casting plate, or changes in the casting speed, etc.
It is characterized by changing.

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

[Detailed description of the invention]

In FIG. 1, reference numerals 1a and lb refer to a pair of internal cooling rolls that are arranged opposite to each other with their axes horizontal so as to rotate in opposite directions (the direction of rotation of both is indicated by arrows), and 2 refers to these rolls la and lb. 3a and 3b are side dams, and 4 is a thin plate to be cast.

Roll pair 1a, lb is an internal cooling roll. In the illustrated examples, water-cooled rolls are used. More specifically, in both roll pairs 1a and lb, a groove-shaped cooling water passage is 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 tube.

The inner pipe is used as a cooling water supply pipe, and the annular pipe formed between the outer pipe and the inner pipe is used as a drain pipe. The annular pipe is connected to the cooling water outlet at the cooling water passage inlet. 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 side dams 3a, 3b are held by metal side dam cases 5a, 5b attached to their outer surfaces, and the side dam cases 5a, 5b are moved in the casting direction. The side dams 3a and 3b themselves are made of a refractory material with good machinability, and an example of their shape is shown in FIG. Second
As shown in the figure, of the total thickness W, the thickness of the inner part -2 is the thickness of the part installed on the roll circumferential surface R, and the thickness of the other outer part -2 is the thickness of the part installed on the roll circumferential surface R. The thickness of the installation part that is off the circumferential surface. That is, the inner thickness -
The first part has a bottom surface 6, 6' which is curved to correspond to the circumferential shape of the rolls la, 1b, and the outer thickness of the second part has a side surface (first part) of the rolls la, lb. It has a shape in which the portions 7, 7° that come into sliding contact with the bottom surface (indicated by S in FIG. 1) extend below the bottom surface 6.6°. As the material for the side dams 3a and 3b, a refractory is suitable since it must have good heat insulation properties, but in the case of the present invention, it must also have good machinability. This is because the bottom surface 6.6° needs to be ground by the rough surface 10 of the circumferential surface, and it is preferable that the material is such that the temporary end to be cast can also be ground. Suitable materials include insulating brick ceramic fiberboard, boron nitride (BN), etc., which have good machinability. In the illustrated example, all of the thicknesses 1 and h are made of refractory material with good machinability.

In addition to this example, a side dam is used in which the thickness - 2 is made of an insulating material with good machinability, and the thickness -2 is made of a high-strength material that does not exhibit machinability, and the two are laminated together. A method of grinding and wearing out a part of thickness Hl by applying a sending stress in the casting direction to a part of high strength thickness 2, or a method of grinding and wearing out a part of thickness Hl of a machinable material and a part of thickness -2 of a high strength material. The present invention can also be applied to a method in which only a portion of thickness W is fed in the casting direction without joining the portions, and the thick portion is ground and consumed.

In Fig. 1, a refractory side dam 3 having the shape shown in Fig. 2 is shown.
A metal side dam case 5a is placed on the outer surface of a and 3b,
5b is attached so as to completely cover the outer surface and grip the side dams 3a, 3b, so that the curved bottom surfaces 6, 6' of the 11th part of the thickness are in contact with the circumferential surfaces R of the rolls la, lb. Moreover, a state is shown in which the inner surface portions 7 and 7' of the thickness gauge 2 are set so as to be in sliding contact with the side surfaces S of the rolls 1a and 1b. And side dam cases 5a, 5b
to the plurality of threaded columns 8.

The side dam cases 5a and 5b are moved in the casting direction by rotating each support column 8 around an axis while supporting it via a nut 9 fixed to the case side. This allows the side dam 3 to be
a, 3b descend as their bottom surfaces 6.6' are ground and worn out by the rotating roll circumferential surface R. In addition to mechanical engagement, the side dam cases 5a, 5b and the side dams 3a, 3h may be bonded together using a bonding agent at the bonding interface between the two, thereby increasing the tensile strength for boat fishing. Reinforces large objects with weak machinability. As the mechanism for moving the side dam downward, a method is adopted in which the downward speed can be arbitrarily controlled during operation of the device.

On the other hand, of the circumferential surface R of the roll, the bottom surface 6 of the side dam
．． The part that makes sliding contact with 6° is formed into a rough surface with grinding ability.

This rough surface portion is shown by 10 (four locations) in Fig. 1. If the roughness and hardness of this portion 10 are appropriate depending on the material of the side dam and the descending speed of the side dam, the bottom surface of the side dam 6,6° is well ground during casting, but it is desirable that this condition be maintained steadily and not change over time. For this purpose, the brush 11 is brought into contact with the rough surface portion 10 so that the grinding powder adhering to the rough surface portion 10 can be removed naturally as the roll rotates or by using a vacuum cleaner. This rough surface is preferably formed of a material having sufficient hardness so that the roughness of the surface 10 does not change over time. For example, it is preferable to form this rough surface by thermal spraying a hard metal, alloy, ceramic, or cermet, or to roughen a coating layer of a hard metal or alloy. It is also advantageous to blast this part 10 while the rolls are rotating to rejuvenate the rough surface.

FIG. 3 shows the inner surface state of the side dam according to the present invention at the initial stage of casting. On the inner surface of the side dam, the side ends of the solidified shells formed on the surfaces of both internal cooling rolls come into contact at the levels indicated by a and a' in the drawing, and merge at point A. In other words, a portion of the molten metal in the pool is cooled on the surface of each roll and solidified into a thin shell, and as the rolls rotate, the two solidified shells grow and merge, and are rolled to a predetermined thickness between the roll gaps. It turns out that.

The ends of the solidified shell formed on the roll surface come into contact with the inner surface of the side dam at the levels indicated by a and a'. The initial shape of the side dam (before being ground during operation of the device) is adjusted so that the position of the confluence A of this solidified shell is approximately at the same level as the lower edge 13 within the roll width of the side dam (inside L in Figure 2). However, during casting, one confluence point A may come to a position A° above the position of the lower edge 13 due to variations in casting conditions. In this case, the refractory material in this portion is scraped off due to the expansion in the width direction of the plate (the solidified metal plate after passing through the confluence point A) caused by rolling with the rolls. if,
If the side dam is not lowered in this state, the board width will continue to gradually expand, and if it exceeds the roll width, the cross section of the board will have a dog-bone shape with swollen ends. If it progresses further, the side dam will be damaged and a breakout will occur.

In the present invention, when starting casting, grinding is started by rotating the rolls and sending out the side dam before pouring the molten metal, so that the position of the lower edge 13 extends below the confluence point A in the steady casting state. One of the features is that the molten metal is injected after it has been brought out, thereby avoiding the need to pour hot water at the start of casting. It has been found that pouring water at the start of casting is a troublesome problem in the case of the fixed side dam method, but in the case of the grinding dam method according to the present invention, this problem can be effectively avoided by taking advantage of its grinding characteristics.

Figure 4 shows the inner surface of the side dam when casting has progressed and the side dam has descended considerably. Bottom surface 6,6° and lower edge 1
3 are scraped off by the rough surface 10 of the roll and the side edges of the casting plate, respectively, and their positions 1 have moved relatively upward compared to the initial position in FIG. 3, and the state of the lower edge 13 has been The edge of the board has been cut slightly diagonally. Further, in the lower part of this lower edge 13, the inner surface 16 of the part protruding from the roll width becomes more exposed as the casting progresses, and this part also plays the role of preventing leakage in the unlikely event of leakage. However, even if the bottom surfaces 6, 6° and the lower edge 13 are scraped off in this way, the side edges of one solidified shell will still meet at point A while touching at the levels a and a' in the drawing. There isn't.

However, in order to maintain this steady state at all times, it is necessary to appropriately control the delivery speed of the side dam. One feature of the present invention is that the device is configured so that the feed speed of the side dam can be arbitrarily controlled, and the feed speed is controlled in accordance with changes in the casting conditions. A number of tests were carried out with the value fixed at the set value, but due to various factors, such as changes in the grinding ability of the rough surface of the roll, or the encroachment of foreign objects or solidified matter, the edges of the cast plate may change during casting. I encountered a situation where the edge shape changed or the shape of the lower edge 13 of the side dam changed. It was also found that it is necessary to set the feed speed appropriately when changing the thickness of the cast plate. Based on these findings, the present invention has two methods: one is to continuously observe or detect the edge shape of the cast plate during casting, and if the edge shape deviates from the normal shape, the side dam is sent out. In other words, the feed speed is controlled so that the edge shape of the casting plate is detected as a value and falls within the appropriate range.If the edge shape is out of the appropriate range and becomes disordered, it is likely that the edge shape is below the side dam. This means that the shape of the edge 13 has been chipped or excessively removed for some reason, and in this case, the feeding speed is increased to restore the original normal shape. Instead of using this edge shape as the detected value, the width of the cast plate can also be used as the detected value.

Also, the casting speed during casting (i.e. the rotational speed of the rolls)
In a device that maintains a steady state by controlling the rotation speed of the rolls, the grinding ability of the rough surface portion 10 changes depending on the rotation speed of the rolls, so it is necessary to control the feeding speed according to the rotation speed of the rolls. . For example, if the rotational speed of the rolls is reduced but the feed rate remains the same, there is a risk that excessive compressive stress will be applied to the side dam, which is a material that can withstand large machinability, resulting in damage. Therefore, it is necessary to adjust the feed speed to match the grinding ability of the rough surface portion 10. Instead of adjusting the feeding speed of the side dam using this casting speed as a detected value, it is also possible to detect the feeding load of the side dam and adjust the feeding speed.

For example, the current value of the motor that provides the power for sending out the side dam increases or decreases depending on the sending load, so feedback control is performed such that when the current value becomes large, the sending speed is slowed down, and when the current value becomes small, the sending speed is increased.

Furthermore, when adjusting the roll gap (or distance between roll axes) for some reason.

In other words, in the case of a device in which the thickness of the cast plate is changed due to changes in load, etc., the sliding between the bottom surface 6.6 of the side dam and the rough surface portion 10 of the roll occurs as the roll gap changes. The contact status changes.

Therefore, when opening the roll gap, the bottom surface 6.
In order to prevent a gap from forming between the bottom surface 6 and the rough surface portion 10, it is necessary to send out the side dam rapidly and quickly to grind and repair the bottom surfaces 6 and 6′ into a shape corresponding to the rough surface portion 10. On the other hand, when narrowing the roll gap, stress is applied such that the bottom surface 6.6° is compressed by the rough surface portion 10, so while the bottom surface 6.6° is properly ground due to this compression, the side dam It is necessary to stop feeding or reduce the feeding speed. Therefore, it is necessary to control the feeding speed based on the distance between the roll axes or the thickness of the cast plate as a detected value.

In this way, during casting, by controlling the delivery speed of the side dam according to fluctuations in various casting conditions, stable casting can be performed while avoiding causes of breakage of the hot water pourer or the side dam.

FIG. 5 schematically shows the process during casting corresponding to FIG. 4. As seen in this figure, by forcibly moving (lowering) the side dam downward at an appropriate speed, the lower edge 13 can be moved to the narrowest pubic area of the twin rolls (roll axis 1
In addition, the lower edge 13 is shaved off to form a sloped shape, and this allows the width direction of the plate end 14 past the confluence point A of the solidification wells to be maintained. Control expansion. At the start of casting,
By starting pouring the molten metal when the position of the lower edge 13 has been lowered by grinding to the vicinity of the narrowest pubic region, pouring of the molten metal from this part can be prevented, and the sending speed (lowering speed) during casting can be adjusted appropriately. It will be appreciated that by controlling the steady state of FIG. 5 is maintained. By lowering the side dam at an appropriate speed according to the present invention, a steady state can be realized in which the lower edge 13 of the side dam maintains a constant shape. Therefore, by increasing the length of the side dams in advance and lowering them, or by adding side dams one after another and lowering them, stable long-term casting is possible. Contrary to the conventional idea of using wear-resistant refractories, the present invention uses a side dam made of abrasion-resistant refractories and forcibly moves the side dams downward to actively remove refractories. The shape of the bottom surface 6.6 degrees of the side dam in contact with the roll circumferential surface and the inner surface of the side dam (actually near the lower edge 13) in contact with the edge of the plate to be cast are substantially the same and similar. The stated purpose is achieved by controlling the feed speed to a speed that allows the grinder to maintain its shape.

In addition, 1 or more descriptions include a part of j7 within the roll width,
Although a side dam having a thickness outside the roll width has been described as an example, the present invention is also applicable to a method in which the side dam is installed so that the entire thickness is within the roll width. An example of this is shown in FIG. In this case as well, it goes without saying that the side dams 3a and 3b are installed so as to be moved downward as shown by the arrows, and the side dams 3a and 3b themselves are made of refractory material with good machinability.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing essential parts of an embodiment of the apparatus for carrying out the present invention, FIG. 2 is a perspective view showing an example of the shape of the refractory of the side dam in the apparatus shown in FIG. FIG. 4 is a perspective view of the side dam in the device shown in FIG. 1, showing a state in which the degree of grinding is small in the initial stage of casting; FIG. 4 is a perspective view of the side dam in the device shown in FIG. 1; FIG. 5 is a schematic cross-sectional view of the casting state of the device as seen in a plane parallel to the casting plate to be cast, and FIG. 6 is a diagram showing another example of the side dam according to the present invention. FIG. la, Ib... Pair of internal cooling rolls, 2... Hot water reservoir. 3a, 3b...side dam, 4...cast plate. 6.6''...Bottom surface of the side dam that is curved to correspond to the circumferential shape of the roll, 7.7'...The part of the side dam that comes into sliding contact with the side surface of the roll. 10...The bottom surface of the side dam The part of the roll circumferential surface that comes into sliding contact (roughened surface treated part), 11. Brush. 13. Lower edge within the roll width of the side dam.

Claims (3)

[Claims] (1) A pair of internal cooling rolls that rotate in opposite directions are arranged facing each other with their axes horizontal, and a pair of side dams are installed to form a pool on the circumferential surface of the pair of rolls, which corresponds approximately to the width of the casting plate. At that time, the side dams are arranged with at least a part of their bottoms in contact with the circumferential surface of the roll so that part or all of the thickness of the side dam is located on the circumferential surface of the roll. At the same time, the side dam portion that will come into contact with at least the circumferential surface of the roll during casting is made of a refractory material with good machinability, and by sending this side dam at a predetermined speed in the casting direction, the above-mentioned contact portion is This method continuously casts hot water from the pool into a thin plate through the gap between the pair of rolls while grinding and wearing out the side dam, and pouring the molten metal while maintaining the state where the side dam is being ground and worn at the contact area. A thin plate continuous casting method characterized by starting with. (2) A pair of internal cooling rolls that rotate in opposite directions are arranged facing each other with their axes horizontal, and a pair of side dams to form a pool on the circumferential surface of this pair of rolls is installed approximately equal to the width of the casting plate. At that time, the side dams are arranged with at least a part of their bottoms in contact with the circumferential surface of the roll so that part or all of the thickness of the side dam is located on the circumferential surface of the roll. At the same time, the side dam portion that will come into contact with at least the circumferential surface of the roll during casting is made of a refractory material with good machinability, and by sending this side dam at a predetermined speed in the casting direction, the above-mentioned contact portion is This method continuously casts hot water from the pool into a thin plate through the gap between the pair of rolls while grinding and wearing out the side dam, and the delivery speed of the side dam is changed according to changes in the casting conditions after the start of casting. A thin plate continuous casting method characterized by: (3) The change in casting conditions is any one of a change in the edge shape of the casting plate, a change in the width of the casting plate, a change in the thickness of the casting plate, a change in the distance between roll axes, or a change in the casting speed. The thin plate continuous casting method according to item 2.