JPH11320059A - Continuous casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting apparatus which can coped with the small cross section of a mold for producing thinner cast slab than the thickness of the conventional cast slab and the increase of casting speed, in the continuous casting apparatus which can restrain generation of bulging and the variation of molten surface in the mold accompanying the push back caused by the bulging. SOLUTION: Pitches of plural pairs of guide rolls No.1-5 for supporting the cast slab 1 continuously drawn out from a mold after the outlet of the mold, contain two or more kinds (L1, L2), and the guide rolls are disposed so that two or more kinds of the pitches repeatedly appear. In this apparatus, it is desirable that the roll pitches contain two or more kinds in the range of 150-270 mm, and the difference of the roll pitches having two or more kinds is >=20 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus for metal, particularly steel, for producing a slab with less internal cracks by suppressing fluctuations in the molten metal level in a mold due to bulging of the slab. The present invention relates to a continuous casting apparatus capable of performing the following.

[0002]

2. Description of the Related Art In a continuous casting method, a molten metal, for example, molten steel is poured into a mold, cooled by a mold to form a solidified layer (shell), and then a plurality of pairs of rolls mainly arranged at a constant pitch. The shell is gradually thickened by cooling while being supported and moved by a guide device composed of (called a guide roll), and is gradually pulled out by a pinch roll.
It is a method to carry out outside the machine.

During the process of solidification from the surface of the slab, the solidified portion is formed between the rolls of the guide device (between a plurality of pairs of rolls, that is, a position where no supporting force or rolling force is applied by the pair of rolls). That is, a phenomenon occurs in which the shell expands due to the internal static pressure of the molten steel. This is called "roll bulging" and is a phenomenon that cannot be avoided by the continuous casting method. Generally, bulging between rolls increases as the molten steel static pressure increases and as the solidified shell strength decreases.

Normally, even if bulging between rolls occurs,
When the bulged slab moves to the position of the next roll, it is pressed down and pushed back. At the same time,
The slab portion at the position of the roll moves between the next rolls, where bulging occurs again. Therefore, almost no volume change occurs in the slab as a whole.

However, if the balance between the two bulging amounts (the bulging amount to be pushed back and the bulging amount newly generated) is lost for some reason, a volume change occurs and the molten metal level in the mold fluctuates up and down. . Since the bulging amount between one roll is usually several hundreds of μm, even if the bulging amount is pushed back, the fluctuation of the molten metal level is very small. However, when the roll pairs of the guide device are arranged at the same pitch, bulging occurs in the same cycle as the slab moves, and it is pushed back at once in the same cycle, so that the volume change increases. . Fluctuation of the bath surface at this time is ± 7 ~ 2
0mm, not only degrade the surface quality of the slab,
This may make the operation of the continuous casting machine unstable, and eventually cause troubles such as breakout. The present situation is to cope with such fluctuations in the molten metal level by lowering the casting speed.

As a countermeasure for reducing the fluctuation of the molten metal level caused by bulging, Japanese Patent Publication No. 4-65742 discloses that the distance between rolls adjacent to each other in the slab pull-out direction of guide rolls (ie, roll pitch) is made uneven. A continuous casting machine has been proposed. And, due to this uneven roll pitch,
It is stated that large fluctuations in the molten metal level that occur at a cycle corresponding to the roll pitch in a conventional continuous caster having a uniform roll pitch can be reduced.

[0007] In the continuous casting machine in which the pitch of the guide rolls is made non-uniform as proposed in Japanese Patent Publication No. 4-65742, there is a section where the roll pitch becomes excessively large unless the number of rolls is increased. If there is a section with a large roll pitch, the risk of internal cracking due to an increase in bulging in that section increases, and the molten steel static pressure load applied to the roll in that section increases, and the roll life due to roll bending and bearing wear etc. Is reduced.

As the above countermeasure, the number of rolls may be increased, but this causes a remarkable increase in equipment cost and maintenance cost. As a countermeasure, it is effective to increase the roll diameter. However, if there are rolls with different diameters in the same roll guide device, this is also necessary due to the complexity of the structure and increase in the number of spare parts. This leads to increased costs and maintenance costs.

In recent years, for the purpose of greatly simplifying the hot rolling process, a technique of continuously producing a thin cast slab having a smaller thickness than in the past has attracted attention. For example, 250
A continuous casting machine for directly producing a thin slab having a thickness of 50 to 100 mm from a thickness of slab of 300 mm at a high casting speed has been put into practical use.

In such a thin slab continuous caster, since the mold has a small cross section, the amount of change in the molten metal level in the mold when the volume change occurs due to the bulging is large. Therefore, in a continuous casting machine for thin cast slabs, it is necessary to reduce the disturbance of such a volume change as compared with a conventional continuous casting machine. Furthermore, when high-speed casting is performed, the shell thickness between the rolls of the slab becomes thinner as a whole, so that the risk of internal cracking due to an increase in the amount of bulging increases.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous casting apparatus capable of suppressing the occurrence of bulging and the fluctuation of the molten metal level in the mold due to the pushing back thereof, without increasing the equipment cost. It is an object of the present invention to provide a continuous casting apparatus capable of producing a cast piece with few cracks.
In particular, it is an object of the present invention to provide a continuous casting apparatus that can cope with a reduction in the mold section and an increase in casting speed for producing a cast piece thinner than a conventional cast piece.

[0012]

SUMMARY OF THE INVENTION The gist of the present invention is that a plurality of pairs of guide rolls for supporting a slab that is continuously drawn from the inside of a mold at the mold discharge side and at least two pitches are provided. A continuous casting apparatus characterized in that guide rolls are arranged so that two or more pitches appear repeatedly in sequence. In this device, the roll pitch is 150
Two or more types in the range of 270 mm to 270 mm, and the difference between the roll pitches of the two or more types is preferably 20 mm or more.

[0013] In the apparatus of the present invention, the pitch of the plurality of pairs of guide rolls is not constant or non-uniform. That is, there are a plurality of types of roll pitches L1, L2, L3,..., Which are arranged so as to appear regularly in order. By doing so, the bulging and its pushing back do not occur significantly at a fixed period, and the fluctuation of the molten metal level in the mold is reduced. Further, by arranging the rolls so that the narrow pitch comes immediately after the wide pitch, the molten steel static pressure applied to the roll can be reduced.

In the section where the roll pitch is narrowed,
Since the time from contacting one roll to contacting the next roll is shortened, reheating of the slab is significantly suppressed,
Surface temperature decreases. Therefore, the strength of the shell increases,
The bulging amount after that section is reduced, and the occurrence of internal cracks is reduced.

It should be noted that the higher the casting speed, the shorter the time required to pass between the rolls, and the greater the effect of suppressing the recuperation in a narrow roll pitch. The effect becomes remarkable. Therefore, the apparatus of the present invention is particularly suitable for performing continuous casting at a high speed of 3.0 m / min or more.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating an example of a vertical bending type continuous casting apparatus. The molten metal (for example, molten steel)
, Where it is cooled from the surroundings to form a shell and is continuously withdrawn with an unsolidified layer inside. The slab is spray-cooled while being supported by the guide rolls R on and after the mold exit side, and the thickness of the shell gradually increases to reach complete solidification.

The guide rolls R are arranged in a range from immediately below the mold to a position in front of the pinch rolls 2 in the horizontal portion. As shown by A1, A2, and B1 in the drawing, a plurality of pairs of rolls are set as one set. Guide roll device (called a segment)
Usually, it is incorporated and arranged.

FIG. 2 is a diagram showing an example of a roll arrangement in the guide roll device (segment). In this case, the segment is composed of five rolls from No. 1 to No. 5, and the roll pitch is two of L1 and L2 (L1> L2).
Kind. A spray 3 is arranged between each roll, and the surface of the slab 1 is cooled by water or gaseous mixed water.

In the figure, the hatched portions 41 to 44 are bulging portions of the solidified shell. For example, Roll No.1 and No.2
And the bulging 41 moves downward as the slab is pulled out and is pushed back at the No. 2 roll position. At that time, the volume change of the slab occurs, but in the apparatus of the present invention, the bulging 4l and the bulging 42 have different timings to reach the next roll position due to the drawing of the slab, so the volume change occurs at the same time. It does not occur and the level fluctuation is minimized.

The bulging 43 is also pushed back at the same time as 4 l, but the roll pitch between the rolls No. 2 and No. 3 is short, and the reheat of the slab during this period is suppressed, and the slab surface temperature decreases. As a result, the bulging 43 becomes small, so that a large volume change does not occur and the fluctuation of the molten metal level does not become large.

Further, since there is a narrow roll pitch L2 next to the wide roll pitch Ll, the static pressure of the molten steel applied to the roll No. 2 is equal to the length of the S portion, and the static pressure area received even when the roll pitch Ll is long. Becomes smaller. Therefore, it is possible to prevent the life of the roll and the bearing from being shortened.

Further, not only does the bulging amount 42 at a narrow roll pitch L2 decrease, but also the bulging amount 42 decreases due to the effect of lowering the surface temperature of the slab at the position of the roll pitch L2.
43 is also reduced, and the risk of occurrence of internal cracks in the slab is also reduced.

FIG. 3 shows three types of roll pitches (Ll>L2>
It is a figure showing the roll arrangement of the segment in case of L3).
In this case, the same effect as described above can be obtained by arranging Ll → L2 → L3 in order from Ll as shown.

The continuous casting apparatus of the present invention is not limited to the apparatus in which the guide roll is supported by the guide roll device (segment). However, it is desirable to have the guide roll device as described above, and it is preferable that all of the guide roll devices have rolls regularly arranged at two or more types of roll pitches. Further, in this case, it is preferable to select a combination of different roll pitches with the continuous upper and lower guide roll devices. For example,
In the example of FIG. 1, the combination of the roll pitches in the A1 segment and the A2 segment is preferably changed as in Test 7 of the embodiment.

As a method of selecting two or more types of roll pitches in one guide roll device, it is preferable that the difference is 20 mm or more. If the pitch difference is smaller than 20 mm, the effect of providing the difference is small.

As described above, the apparatus of the present invention exerts a greater effect when the casting speed is high. That is, when the casting speed is high, the passage time of the slab between the rolls is shortened, and the recuperation is suppressed. Therefore, the bulging amount is reduced, and the fluctuation of the molten metal level and the occurrence of internal cracks are prevented. However, if the roll pitch is widened, the bulging amount increases, and the risk of occurrence of internal cracks increases. Therefore, the roll pitch to be selected naturally has an upper limit. Its upper limit is approximately 270mm. Further, the lower limit of the roll pitch is inevitably determined by the roll bearing diameter that can be manufactured industrially at present. However, 15
If the pitch is smaller than 0 mm, the equipment cost increases due to an increase in the number of rolls, which is not preferable. For these reasons,
The roll pitch is selected in the range of 150 mm to 270 mm, and it is desirable to determine a plurality of pitches as described above so that the difference is 20 mm or more.

[0027]

EXAMPLES The effects of the present invention will be described below based on examples. Casting was performed by using a vertical bending continuous caster having the specifications shown in Table 1 while changing various conditions. The guide roll of the continuous casting machine is supported by a structure called a segment into which several rolls are incorporated. However, FIG. 1 shows only three sets of segments, A1, A2 and B1, and omits the others.

[0028]

[Table 1]

The roll pitches of the vertical segments A1 and A2 and the horizontal segment B1 shown in FIG. 1 were variously changed as shown in Table 2. The vertical segment is composed of five pairs of rolls, each of which has five rolls on both sides, Al and A2, each of which has a length of 1.Om. The horizontal segment Bl is also composed of five pairs of rolls in which five rolls are arranged vertically, and the length is 1.25 m. In each case, the roll pitch was defined as shown in FIG. Table 2 shows details of each roll pitch and casting conditions. In addition, between the segments A2 and B1, there is a repeating arrangement of the segments A1 and A2.

[0030]

[Table 2]

The cast steel types are a medium carbon high manganese steel and a high carbon steel whose compositions are shown in Table 2. Medium carbon high manganese steels are susceptible to uneven solidification, and bulging becomes uneven between rolls and in the width direction due to uneven shell thickness.
This type of steel is particularly susceptible to metal surface fluctuations caused by bulging. In addition, since the critical strain at the solid-liquid interface that determines the probability of occurrence of internal cracks is relatively small, this steel type has a high risk of internal cracks. High carbon steel is a steel type having a smaller critical strain and easily causing internal cracks.

The cooling was carried out under a strong cooling condition with a specific water volume of 1.5 liter / kg-steel. This aims at preventing the fluctuation of the casting speed due to the fluctuation of the friction coefficient between the drawn pinch roll and the slab by removing a large oxide scale on the slab surface, in addition to suppressing the bulging amount itself. .

Various casting speeds shown in Table 3 were selected in the range of 2 to 5 m / min. Table 3 shows the results of the molten metal level variation and the state of occurrence of internal cracks in the slab. Fluctuations in the molten metal level and the occurrence of internal cracks were evaluated according to the evaluation criteria shown in the margin of Table 3.

[0034]

[Table 3]

First, the effect of the method of the present invention will be described from the viewpoint of fluctuations in the molten metal level. Test 4 (conventional example) in which the guide roll pitch of A1 and A2 is constant at 200 mm and the guide roll pitch of B1 is constant at 250 mm Fluctuation of the molten metal level is large at all casting speeds.

Tests 1-3 and 5-7 are examples of the present invention. Among them, when the difference between the two types of roll pitches is as small as 10 mm even when the two types of roll pitches are alternately arranged as in Test 5, the level change of the molten metal level is smaller than that in Test 4 described above. However, large fluctuations were observed in high-speed casting at a casting speed of 3.0 m / min or more. On the other hand, by setting the difference between the two types of roll pitch to 20 mm as in Tests 1, 3, and 6,
Fluctuations in the bath level have become smaller. Furthermore, three types of roll pitches are alternately arranged in sequence as in Test 2, or two types of roll pitches arranged alternately are selected using a guide roll device that is continuous with A1 and A2 as in Test 7. By doing so, the fluctuation of the molten metal level was further reduced.

On the other hand, due to the high-speed casting, the susceptibility of the slab to internal cracking was increased, and internal cracking occurred at the solidification position corresponding to the segment of the B portion. By combining these roll pitches, the amount of bulging was reduced, and internal cracks could be prevented even in high carbon steel with extremely high crack susceptibility. However, when a roll with a large roll pitch of 280 mm was incorporated as in Test 6, small internal cracks occurred in high-speed casting, and cracks could not be completely prevented.

[0038]

According to the continuous casting apparatus of the present invention, a narrow roll pitch and a wide roll pitch are alternately arranged in a guide roll zone. Thereby, the fluctuation of the molten metal level in the mold due to the bulging can be suppressed. Also,
By suppressing the reheating of the slab in the narrow roll pitch region, the absolute amount of bulging is also reduced, and it is also effective in preventing the occurrence of internal cracks due to bulging. Furthermore, in the apparatus of the present invention, since a narrow roll pitch always exists after a wide roll pitch, load conditions such as roll bearings do not change significantly, and this does not lead to a change in the specifications of the apparatus, so that the equipment can be inexpensive. The present invention is applicable not only to the vertical bending type continuous casting machine shown in FIG. 1, but also to a vertical type or any other type of continuous casting apparatus.

[Brief description of the drawings]

FIG. 1 is a view schematically showing one example of a continuous casting apparatus of the present invention.

FIG. 2 is a schematic view showing an example of a roll arrangement of a guide roll device (segment) used in the device of the present invention.

FIG. 3 is a schematic view showing another example of a roll arrangement of a guide roll device (segment) used in the device of the present invention.

FIG. 4 is a diagram for explaining symbols of roll pitches in the embodiment.

[Explanation of symbols]

1 ... slab, 2 ... pinch roll, 3 ... spray, 41 ~
44… Bulging, M… Mold, R… Guide roll, A1,
A2, B1 ... segment, L1, L2, L3 ... roll pitch

Continued on the front page (72) Inventor Masahiro Ikeda 5-2 Sokai-cho, Niihama-shi, Ehime Pref. In the Niihama Works of Sumitomo Heavy Industries, Ltd. (72) Inventor Moriki Hashio 5-9-1-11 Kita Shinagawa, Shinagawa-ku, Tokyo Sumitomo Heavy Industries Machinery Co., Ltd.

Claims (2)

[Claims] A guide roll for supporting a slab which is continuously drawn from the inside of a mold on the mold discharge side and thereafter has two or more pitches, and the guide rolls are so arranged that the two or more pitches appear successively and repeatedly. A continuous casting apparatus, wherein: 2. The continuous casting apparatus according to claim 1, wherein the roll pitch is two or more in the range of 150 to 270 mm, and the difference between the two or more pitches is 20 mm or more.