JPH10156493A - Method for supplying molten steel into mold in continuous caster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten steel supplying method into a mold in a continuous caster which can precisely control the molten steel surface level over the whole operation of casting process and prevents the suction of the outer air into the molten steel and can cast a cast slab excellent in the quality. SOLUTION: (1) In the molten steel supplying method into the mold in the continuous caster by using two kinds of molten steel supply adjusting means showing flowing rate characteristic of a high flow rate gain or a low flow rate gain for controlling the molten steel level in the mold, in two kinds of the molten steel supply adjusting means, separated molten steel flow passages are arranged, respectively so as to separately use the molten steel supply adjusting means according to the casting condition of molten steel. (2) In the molten steel supplying method into the mold in the continuous caster as the same as the above, in two kinds of the molten steel supply adjusting means, the separated molten steel flow passages are arranged, respectively and the molten steel supply adjusting means are used with the combination according to the casting condition of the molten steel. In the molten steel supplying methods of (1) and (2), two kinds of the molten steel supply adjusting means are desirable to arrange in the molten steel in a tundish.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art In continuous casting, to stabilize the molten steel level in a mold, a powder film having a constant thickness is uniformly formed on the surface of a slab, and a uniform solidified shell is formed to prevent the occurrence of surface flaws. This is an important technology for reducing slag entrainment in molten steel and producing slabs with excellent internal quality.

FIG. 8 is a view for explaining a method of supplying molten steel for controlling the level of molten steel in a mold in conventional continuous casting. After the molten steel 2 in the ladle 1 is injected into the tundish 4 through the nozzle 3, the molten steel is injected into the mold 7 while adjusting the flow rate of the molten steel. At this time, in order to keep the molten steel level in the mold 7 constant, the level of the molten steel level in the mold is detected by the level meter 8, and the deviation between the detected value and the target level value becomes 0 (zero). Control. As shown in the figure,
The control method at this time includes a stopper method (hereinafter, simply referred to as “ST method”) that raises and lowers a stopper 5 (hereinafter, simply referred to as “ST”) to control the flow rate of the molten steel, and a sliding gate 6. There is a sliding nozzle system (hereinafter simply referred to as an "SN system") that opens and closes to control the flow rate of molten steel.

FIG. 1 is a diagram showing characteristics of hot water supply flow rates in the ST system and the SN system in controlling the level of molten steel in a mold. As is apparent from FIG.
Since the change of the flow rate of hot water for molten steel with respect to the opening degree of T becomes large, that is, the flow rate gain becomes high, excellent controllability is exerted at the time of steady casting in which a relatively high flow rate of hot water has to be secured. In particular, the feature becomes remarkable at the time of high-speed casting. On the other hand, at the start of casting, controllability becomes unstable due to the influence of errors in ST adjustment and the like. Here, the opening degree of ST indicates the amount of elevation of ST.

[0004] On the other hand, in the SN system, the change in the flow rate of molten steel with respect to the opening of the sliding gate is small, that is, since the flow rate gain is low, the flow characteristics are stable over a wide range from low flow rate to high flow rate. Stable controllability can be secured. However, at the time of high-speed casting in which high-precision controllability at a high flow rate is required, high-frequency disturbance that cannot be suppressed by a low flow-rate gain occurs, and thus controllability deteriorates.

[0005]

As described above, in the ST method and the SN method, the controllability of the molten steel surface level in the mold fluctuates according to the casting conditions such as at the beginning of casting, at the time of steady casting, and at the end of casting. . Therefore, conventionally, such ST
A molten steel hot water supply method has been proposed in which the control method is properly used in accordance with casting conditions in consideration of the control characteristics of the molten steel method and the SN method, and the molten steel level in the mold is controlled (for example, JP-A-6-15426). And JP-A-7-88607.

However, in the proposed molten steel hot water supply method,
Since the flow channel used when pouring molten steel into the mold by the ST method or the SN method is common, the flow path may be blocked when switching from the ST method to the SN method or vice versa. is there. For example, using the downstream sliding gate 6 shown in FIG.
When the control is performed by the N method, the molten steel may stay and solidify in the channel of the ST. When such a situation occurs, the flow path for injecting the molten steel is blocked, and it becomes difficult to continue the subsequent casting operation.

Further, when the SN method is adopted in the proposed molten steel hot water supply method, there is also a problem that outside air is sucked from a slideway surface of a sliding gate exposed to the air, and as a result, cast slab quality is deteriorated. .

The present invention has been made to solve the above-mentioned problems of the prior art, and can control the molten steel level accurately throughout the entire casting process from the start to the end of the casting. An object of the present invention is to provide a method for supplying molten steel in a mold of a continuous casting machine capable of preventing suction and producing a high quality cast slab.

[0009]

The present invention provides the following (1):
The gist is (2) hot water supply method.

(1) A method for supplying molten steel in a mold of a continuous casting machine using two types of hot water supply adjusting means exhibiting a flow rate characteristic of a high flow rate gain or a low flow rate gain to control the level of molten steel in the mold. A method for supplying molten steel in a mold of a continuous casting machine, characterized in that separate molten steel flow paths are provided for each type of hot water supply adjusting means, and the hot water supply adjusting means is selectively used according to the casting state of molten steel.

(2) A method for supplying molten steel in a mold of a continuous casting machine using two types of hot water supply adjusting means exhibiting a flow rate characteristic of a high flow rate gain or a low flow rate gain in order to control the level of molten steel in the mold. A method for supplying molten steel in a mold of a continuous casting machine, characterized in that each type of hot water supply adjusting means is provided with a separate molten steel flow path, and is used in combination with the hot water supply adjusting means according to the casting state of molten steel.

In the method (1) or (2) above, the molten steel hot water
It is desirable to provide various types of hot water supply adjusting means in the molten steel of the tundish. This is because it is possible to prevent deterioration of cast slab quality due to the suction of molten steel from the outside air.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of hot water supply adjusting means used in the method of the present invention will be described with reference to the drawings.

FIG. 2 is a view for explaining a specific configuration example of the hot water supply adjusting means of the present invention. FIG. 2 (a) is a component diagram of the hot water supply adjusting means, and FIG. (C) is a sectional view of the assembled hot water supply adjusting means.

As shown in FIG. 2 (a), the hot water supply adjusting means 10 of the present invention is constituted by combining components 11 and 12. The lower end of the component 11 has a pencil-like shape, like the shape of the normal ST tip. Further, a flow path hole 13 is formed in the side surface at a position of height L from the lower end of the component 11 so as to communicate with a lateral hole 14 opened at the lower side, and the lower portion of the component 11 has a hollow structure. On the other hand, the part 12
Is a cylindrical hollow body so that it can be fitted from the top,
Side hole 1 provided in part 12 while fitted to part 11
A lateral hole 15 having the same shape is provided at a height position corresponding to 4.

The hot water supply adjusting means 10 of the present invention can exhibit two types of flow characteristics, a high flow gain and a low flow gain. The characteristic of high flow rate gain is exhibited by adjusting the amount of hot water by changing the lower end of the pencil shape up and down and changing the opening cross-sectional area with the upper nozzle provided in the tundish, as in the normal ST method. Is done.

The part 11 fitted to the part 12 is rotatable. Therefore, the characteristics of low flow gain are:
The part 11 fitted with the part 12 is rotated and slid, and the part 1
This is achieved by adjusting the amount of hot water supply by changing the cross-sectional area of the opening where the side hole 14 opened to the side surface of the first part and the side hole 15 provided in the component 12 coincide.

By adopting the above configuration, the hot water supply adjusting means 10 of the present invention can select one of two types of flow characteristics depending on the casting state of molten steel and use it selectively.
It can be easily adopted and combined at the same time. Moreover, since different flow paths are used for injecting the molten steel into the mold, interruption of the casting operation can be avoided even if any of the flow paths is blocked. Further, even when two types of flow rate characteristics are combined, since each molten steel flow path is independent, each flow rate of hot water is affected by another flow rate of hot water within a speed range until the speed is controlled by the upper nozzle diameter. Never.

Further, the hot water supply adjusting means of the present invention is provided in molten steel of a tundish. For this reason, it is possible to prevent the outside air from being sucked from the slideway surface of the sliding gate exposed to the atmosphere, which is a problem in the conventional molten steel hot water supply method, and to prevent deterioration of cast slab quality.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the method of the present invention will be described below based on specific embodiments 1 and 2.

Example 1 Using the hot water supply adjusting means shown in FIG. 2, a test was conducted in which two types of flow characteristics were selectively used according to casting conditions. The target of the molten steel level in the mold was set at 50 mm from the top of the mold. At the start of casting, the amount of hot water is adjusted only by the low flow gain hot water supply adjusting means, and when the molten steel surface level is stabilized at the target level, switching to the high flow gain hot water supply adjusting means is performed. The flow rate of molten steel was controlled only by adjusting means, and the casting speed was increased to 5 m / min.

FIG. 3 is a diagram showing a control state of the molten steel surface level when the flow characteristic is selectively used from a low flow gain to a high flow gain according to casting conditions. As is clear from the figure, the molten steel level was suppressed to within ± 3 mm from the target level, indicating a good control situation. As a comparison with the method of the present invention, the hot water supply flow rate is controlled by the conventional ST method or SN method, and the results are shown in FIGS.

FIG. 4 is a diagram showing the control state of the molten steel level when the molten steel flow rate is controlled by the ST method.
Due to the influence of the ST adjustment error at the start of casting, a hot water supply flow rate larger than the design flow rate value was injected. For this reason, hunting occurred until the ST opening degree at which the hot water supply amount into the mold and the outflow amount from the mold (casting speed) were balanced, that is, the so-called balance opening degree, and controllability deteriorated. However, the casting speed was 1 m / min.

FIG. 5 is a diagram showing the control state of the molten steel level when the flow rate of molten steel is controlled by the SN method. At this time, the casting speed was 5 m / min. As shown in the figure, since the flow rate control by the SN method has a low flow rate gain, the casting operation during high-speed casting cannot cope with the fast-period disturbance generated in the drawing system, and the controllability of the level of the molten metal may deteriorate. I understand.

In the above SN system, the sliding gate is exposed to the atmosphere, whereas the hot water supply adjusting means of the present invention is provided in molten steel. Therefore, the method of the present invention and SN
The quality status of the slabs manufactured by this method was compared. FIG.
It is the figure which showed the pinhole generation | occurrence | production state of the slab manufactured by applying the method of this invention or the SN system by generation | occurence | production index. Here, the pinhole generation index indicates the number of pinholes generated per unit volume. From this result, in the method of the present invention, the invasion of outside air can be blocked, and the pinhole occurrence index of the slab is significantly reduced as compared with the SN system.

As described above, in the method for supplying molten steel of the present invention,
Either of two types of flow characteristics can be selected and used depending on the casting state of molten steel, so that the level of the molten steel surface in the mold can be accurately controlled in the entire casting operation from the start to the end of casting. . In addition, the quality of the manufactured slab also becomes excellent.

Example 2 When a casting operation was performed using the hot water supply adjusting means shown in FIG. 2, nozzle clogging occurred in one of the molten steel flow paths. Therefore, a test was conducted in which two types of flow rate characteristics were combined. . As in Example 1, the target of the molten steel level in the mold was set at 50 mm from the top of the mold,
Casting was performed at 5m / min. First, in the steady casting operation, the hot water supply flow rate was controlled by hot water supply adjusting means having a high flow rate gain.
At this time, the nozzle clogging occurs in the molten steel flow path of the high flow rate gain and further progresses. When the upper limit opening of the hot water supply adjusting means of the high flow rate gain is reached, the opening degree of the hot water supply adjusting means of the low flow rate gain is reached. Was opened to supplement the molten steel flow rate.

FIG. 7 is a diagram showing a state of controlling the molten steel surface level when the molten steel flow rate is controlled by combining two types of flow rate characteristics with the occurrence of nozzle clogging. As is clear from the figure, even if the flow path of the molten steel is clogged, the subsequent casting can be continued without hindering the control of the flow rate of the molten steel. At this time, since the control of the hot water supply flow rate was also performed by the hot water supply adjusting means having a high flow rate gain, the controllability of the molten steel level in the mold was not impaired despite the high-speed casting operation. . In the case of the combination of the conventional SN method and the ST method, an excellent effect is exhibited as compared with the case where the closing of one of the molten steel passages causes the casting operation to be stopped or the casting speed to decrease.

[0029]

According to the method of supplying molten steel of the present invention, the level of the molten metal in the continuous casting machine can be accurately controlled over the entire casting operation from the start of casting to the steady casting and the end of casting. Further, even if the molten steel flow path is blocked due to nozzle clogging or the like, it is possible to avoid interruption of the casting operation or to reduce the casting speed, so that workability can be secured and productivity can be improved. Moreover, since the hot water supply adjusting means is provided in the molten steel, suction of outside air can be prevented, and a cast slab of excellent quality can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing characteristics of a hot water supply flow rate in an ST system and an SN system in controlling a molten steel surface level in a mold.

FIGS. 2A and 2B are diagrams illustrating a specific configuration example of the hot water supply adjusting means of the present invention, wherein FIG. 2A is a component diagram of the hot water supply adjusting device, FIG. Shows sectional views of the assembled hot water supply adjusting means.

FIG. 3 is a diagram showing a control state of a molten steel surface level when a flow characteristic is selectively used from a low flow gain to a high flow gain according to casting conditions.

FIG. 4 is a diagram showing a control state of a molten steel surface level when the molten steel flow rate is controlled by the ST method.

FIG. 5 is a diagram showing a control state of a molten steel surface level when the molten steel flow rate is controlled by the SN method.

FIG. 6 is a diagram showing a pinhole occurrence state of a cast slab manufactured by applying the method of the present invention or the SN method by an occurrence index.

FIG. 7 is a diagram showing a control state of a molten steel surface level when a molten steel flow rate is controlled by combining two types of flow rate characteristics with the occurrence of nozzle clogging.

FIG. 8 is a view for explaining a method of supplying molten steel for controlling the level of molten steel in a mold in conventional continuous casting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ladle, 2 ... Molten steel 3 ... Nozzle, 4 ... Tundish 5 ... Stopper 6 ... Sliding gate, 7 ... Mold 8 ... Level meter 10 ... Hot water supply adjusting means 11, 12 ... Parts, 13 ... Flow path holes 14, 15 ... Side hole, 16 ... Nozzle

Claims (3)

[Claims] 1. A method for feeding molten steel in a mold of a continuous casting machine using two types of hot water supply adjusting means exhibiting a flow rate characteristic of a high flow rate gain or a low flow rate gain to control the level of molten steel in the mold. The hot water supply adjusting means is provided with separate molten steel flow paths, and the hot water supply adjusting means is selectively used in accordance with the state of molten steel casting. 2. A method for supplying molten steel in a continuous casting machine using two types of hot water supply adjusting means exhibiting flow characteristics of a high flow rate gain or a low flow rate gain in order to control the level of molten steel in the mold. The method of supplying molten steel in a mold of a continuous casting machine, characterized in that separate molten steel flow paths are provided in the hot water supply adjusting means and the hot water supply adjusting means is used in combination in accordance with the casting state of molten steel. 3. The method for supplying molten steel in a mold of a continuous casting machine according to claim 1, wherein two types of hot water supply adjusting means are provided in the molten steel of the tundish.