JPH06102252B2 - Control method of molten metal flow rate in thin plate casting - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a method for controlling a molten metal flow rate in thin plate casting, and in particular, a relatively small amount of molten metal is continuously supplied, such as a quenching ribbon process in which molten metal is poured into a cooling roll to solidify the molten metal and directly produced. The present invention relates to a method for controlling a flow rate when a molten metal is continuously supplied to a cooling body, which method is suitable for use in equipment that needs to operate.

[Prior art]

In the continuous casting of thin plates, for example, in the rapid cooling thin strip process in which molten metal is poured into a continuously moving cooling body such as a cooling roll to solidify and directly manufacture the plate, the flow rate of the molten metal supplied from the pouring nozzle is accurate. It is an indispensable technique to keep the product thickness at the target value. Therefore, for example, the molten metal is supplied from a molten metal holding facility such as a melting furnace to a tundish equipped with a pouring nozzle, and the amount of pouring from the tundish is controlled so that the plate thickness is kept constant. A way to keep is being developed. This method, for example, has the advantage of being superior in flexibility on the equipment, compared to the method of directly supplying the molten metal to the cooling body from the molten metal holding equipment, but particularly 10 kg.
There is a problem in that it is difficult to perform accurate control when the flow rate is relatively low, such as below / s. As another method of controlling the supply of the molten metal, a method of tilting the molten metal holding device such as a furnace to pour the molten metal, a method of pouring the molten metal from a sliding nozzle, and the like are also used. However, the former has a problem that precise control is difficult due to pulsation of the pouring amount and partial solidification at the pouring port, and the latter is not only large-scale equipment and expensive,
In order to prevent nozzle clogging, it is necessary to insert sand into the nozzle hole, and the inclusion of such inclusions in the tan dish can not be ignored in the small pouring system, such as clogging of the pouring nozzle and interference with plate making. However, its use has been limited. Further, in JP-A-61-296942 and JP-A-61-296943, a box body through which a nozzle from the tundish or the tundish passes is made airtight, and a tundish spray stopper bar is attached to a pouring nozzle of the tundish. A combination of pressure adjustment in the tundish or box and adjustment of the opening of the tundish stop stopper bar, that is, relatively fast fluctuation of the molten steel level is reduced by pressure adjustment, and relatively slow fluctuation is A method of reducing the opening by adjusting the opening of the push-up stopper bar is disclosed.

[Problems to be Solved by the Invention]

However, it is difficult to install a stopper rod on a tundish installed in a relatively narrow area.
In addition, in order to pressurize and depressurize the inside of the tundish and the inside of the box, the tundish including the high temperature melt and the box must have a completely airtight structure, which requires large-scale equipment and complicates the structure. I had a problem. In particular, when pouring the molten metal from the nozzle provided in the tundish while continuously feeding the molten metal into the tundish, this problem was particularly difficult. Therefore, in order to perform highly accurate molten metal control in the pouring method by the stopper bar method, which has relatively few restrictions on equipment,
It is important to supply molten metal from a melt holding device such as a melting furnace to a tundish equipped with a pouring nozzle so that the pouring speed from the tundish can be kept constant. Although the flow rate is adjusted intermittently by control, the controllability is low due to changes in the molten metal level and shaking of the stopper rod, etc.
It could not be used for precise control of minute flow rates. In addition, when the weight of the tundish is controlled to be constant,
Even if the weight of the tundish is kept constant, the tapping speed may change due to the change of the nozzle temperature, the melt temperature, the clogging of a part of the nozzle hole, etc. It should be noted that Japanese Patent Laid-Open No. 58-58964 discloses a configuration similar to the present invention, but it is not related to thin plate casting as in the present invention, and the specific configuration is different.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and measures the flow rate of molten metal in thin plate casting capable of accurately controlling a minute flow rate by a stopper rod method with few restrictions on equipment. The purpose is to provide a method.

[Means for solving problems]

The present invention provides a molten metal holding device having a stopper rod for controlling the amount of molten metal supplied to the tundish, and a tundish having a pouring nozzle for feeding the molten metal supplied from the molten metal holding device onto the surface of the cooling body. When casting a thin plate using the pouring equipment provided, as shown in FIG.
The object is achieved by measuring the pouring temperature from the tundish online and controlling the speed of the stopper rod based on the deviation between the measured value and the target value. Further, according to an embodiment of the present invention, at least one of a lower limit value and an upper limit value is set at the movement position of the stopper rod.

[Action]

The present invention is generally difficult to precisely control the gap between the furnace bottom opening made of refractory and the stopper rod tip. This was done by studying in more detail the stopper bar system, which was conventionally thought to be unsuitable for a trace amount pouring system that requires accurate control of a minute flow rate even if it can be adopted. That is, the melt level can be kept constant by controlling the rate of supplying the melt to the lower tundish from the melt holding device such as a melting furnace so as to keep the melt speed from the tundish constant. . In order to keep this molten metal level constant by the stopper rod provided in the molten metal holding device, the method of controlling the position of the stopper rod is important, but in the present invention, the speed of the stopper rod is measured as the pouring speed. By controlling in accordance with the deviation between the target value and the target value, the molten metal can be continuously supplied from the molten metal holding device to the tundish, thereby enabling accurate control of the pouring amount from the nozzle. Hereinafter, the specific constitution of the present invention will be described by taking as an example the case where the present invention is applied to the single roll method used for producing an amorphous alloy. FIG. 2 schematically shows an example of the single roll method, in which a stopper bar 14 for controlling the supply amount of the molten metal 10 to the tundish 12 is provided in a molten metal holding device (melting furnace) 16 and the molten metal holding The device 16 is equipped with a stopper rod drive device using a drive part 18 such as a DC servo motor which can be easily controlled.
In addition, the molten metal holding device 16 and the tan ditch below it.
For example, load cells 20 and 21 are attached to 12, respectively, so that the weight of the molten metal inside can be measured together with the molten metal holding device 16 and the tundish 12. In the figure, 22 is a pouring nozzle, 24 is a controller, 26 is a cooling roll, and 28 is a ribbon. During casting, the pouring speed is measured from the time change of the total weight of the molten metal holding device 16 detected by the load cell 20 and the total weight of the tundish 12 detected by the load cell 21, and the target pouring speed is obtained. So that the stop stick 14
The ascending / descending speed of is controlled by the controller 24. That is, as shown in FIG. 1, when the measured pouring speed is lower than the target value, for example, the stopper rod 14 is raised at a speed corresponding to the deviation, and conversely when the pouring speed is higher than the target value. For example, a speed instruction for lowering the stopper rod 14 at a speed corresponding to the deviation is given. For example, by determining and instructing the speed of the stopper rod 14 by proportional control, there is no steady-state deviation as seen in the case of proportional control of the position of the stopper rod, and
High followability is also obtained. Further, since this method does not use a particularly complicated theory, it can be realized by a relatively inexpensive control circuit, and moreover, it responds quickly to changes in the molten metal level during pouring, and There is an advantage that troubles such as slag welding or breakage of the stopper rod tip can be relatively easily dealt with. The problem here is that when the opening of the stopper rod 14 becomes very small, the stopper rod 14 and the stopper seat 16A (around the furnace bottom opening, the portion that comes into contact with the stopper rod 14 when the molten metal supply is stopped) It is possible that the molten metal temporarily stagnates between the above and) and solidifies due to the temperature decrease, and the stopper rod 14 is welded to the stopper seat 16A. For example, such a situation may occur depending on the setting of the parameter used for the control such as the gain in the case of the proportional control of the speed, and thus the lower limit value can be set for the stopper opening. In this case, welding can be avoided and the operation stability can be improved. Since the flow rate when welding occurs in a short time is almost zero, controllability is not significantly impaired even if the lower limit value is set. Further, in the case of the stopper rod control, the relationship between the stopper opening and the molten metal supply rate is not a simple proportional relationship, and when the stopper opening becomes large, the molten metal flow rate is limited by the opening area of the stopper seat 16A. Is saturated. For example, in the case of increasing the gain in the case of proportional control of speed, depending on the setting of the parameter used for control, such a saturated state or a state in which the increase of the supply speed with respect to the increase of the stopper opening is extremely small is set. Even so, there is a case where an unnecessary operation is performed to further increase the opening degree of the stopper, and there is a restriction on the moving speed of the stopper rod, so that controllability may be deteriorated. In such a case, by setting an upper limit value for the opening degree of the stopper rod, it becomes possible to avoid the above-mentioned deterioration of controllability. In the actual control, the speed control of the stop bar, for example, a method of determining the speed of the stop bar by proportional control based on the deviation between the target pouring speed and the measured pouring speed, is relatively simple. Accurate flow control can be performed by the control logic. When the stopper rod tip is greatly damaged during pouring, there is a situation in which the pouring speed from the tundish 12 exceeds the target value due to the large pouring amount even if the stopper opening is reduced. In such a case, the stop bar 14 is temporarily lowered to the lower limit that can be moved, the supply of the molten metal is temporarily interrupted, and the control is restarted after the pouring speed is reduced to near the target value. Therefore, the casting can be continued. In the above description, the amount of molten metal in the molten metal holding device or the tandem was measured by the load cells 20 and 21, but the method of measuring the amount of molten metal is not limited to this, and a load cell other than the load cell is used. Alternatively, as in the other example shown in FIG. 3, laser liquid level gauges 30, 31 for optically measuring the molten metal level may be used.

【Example】

As shown in FIG. 2, as the molten metal holding device 16, a melting furnace equipped with a stopper rod 14 driven by a DC motor was used, and by raising the stopper rod 14, the nozzle below the melting furnace was used. The control method of the present invention was applied to an apparatus for supplying molten metal to the tundish 12 equipped with the pouring nozzle 22. That is, a molten Fe-Si-B alloy is held at 1350 ° C. by the molten metal holding device 16 (melting furnace), and a stopper bar 14 having a hemispherical tip and a diameter of 50 mm is used to form a hole having a diameter of 15 mm. Then, the lower tundish 12 was poured at an average rate of 0.8 kg / s. The weight signals from the load cells 20 and 21 attached to the melting furnace 16 and the tandem 12 are sent to the microprocessor of the controller 24, and according to a program written in advance,
DC so that the pouring speed from the tank
The speed of the stopper rod 14 was controlled by controlling the motor current. In the case of the on-off control of repeating the conventionally performed state in which the nozzle hole of the molten metal holding device is closed by lowering the stopper rod and the state in which a large amount of molten metal is supplied by sufficiently widening the stopper opening is repeated, and in the present invention. When controlling the stopper opening by the proposed speed control, if there is no restriction on the opening,
If only the lower limit (2 mm) is set, the upper and lower limits (upper limit 6 m
m, lower limit value 2 mm), examples of changes in the stopper opening and the molten metal speed are shown in FIGS. 4, 5, and 6, respectively.
Shown in the figure. Compared with the case of the conventional on / off control (broken line), in the speed control of the stopper rod according to the present invention (solid line or one-dot chain line),
It is clear that the deviation of the pouring speed is getting smaller. As shown by the alternate long and short dash line in FIG. 4, according to the present invention, when the stopper rod opening is not limited, welding of the stopper rod occurs when the stopper rod opening becomes small. Sometimes. This also applies to the conventional on / off control. However, as shown by the solid line in FIG. 5, when the lower limit of the stopper opening is set, there is no welding of the stopper rod and the stopper seat, and fairly good control is performed. Further, as shown by the solid line in FIG. 6, it is apparent that the controllability is further improved when the upper limit value is also set. In addition, in the said Example, this invention was applied to the continuous thin plate manufacturing equipment provided with the single cooling roll, However, the application range of this invention is not limited to this.

【The invention's effect】

As described above, according to the present invention, in the thin plate continuous pouring equipment, it is possible to accurately control the pouring amount by a relatively simple method of moving the stopper rod. Therefore, the plate thickness can be maintained at the target value, and the plate thickness becomes uniform and the surface properties are improved, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a flow chart showing a basic procedure of a molten metal flow rate control method according to the present invention, FIG. 2 is a sectional view showing a constitution of an example of a continuous pouring device to which the present invention is applied, and FIG. Similarly, FIG. 4 is a sectional view showing the configuration of another example, and FIG. 4 shows target values of the stopper opening and the pouring speed of the conventional example by the on / off control and the embodiment in which the stopper opening is not limited in the present invention. FIG. 5 is a diagram showing the time variation of the deviation from the actual measured value, and FIG. 5 is a target of the stopper opening and the pouring speed of the conventional example and the embodiment in which the lower limit is set for the stopper opening in the present invention. FIG. 6 is a diagram showing the time variation of the deviation between the measured value and the measured value, and FIG. 6 shows the stopper opening and pouring of the same in the conventional example and the embodiment in which the upper and lower limit values are set for the stopper opening. It is a diagram which shows the time change of the deviation of the target value of speed, and a measured value. 10 …… Molten metal, 12 …… Tandem, 14 …… Stopper rod, 16 …… Melt holding device (melting furnace), 18 …… Drive part, 20, 21 …… Load cell, 22 …… Pouring nozzle, 24 …… Control device, 26 ... Cooling roll, 28 ... Thin strip, 30, 31 ... Laser level gauge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Morito 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Ryo Miyake 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. (72) Inventor Yasuo Hayashi 5520 Minamitamagaki-cho, Suzuka-shi, Mie Fuji Electric Co., Ltd. Suzuka Factory

Claims (2)

[Claims] 1. A molten metal holding device having a stopper rod for controlling the amount of molten metal supplied to the tundish, and a tundish having a pouring nozzle for feeding the molten metal supplied from the molten metal holding device onto the surface of the cooling body. When casting a thin plate using a pouring equipment provided with, the pouring temperature from the tundish is measured online, and the speed of the stopper bar is controlled based on the deviation between the measured value and the target value. A method for controlling a molten metal flow rate in thin plate casting, which is characterized by the above. 2. The method for controlling the flow rate of molten metal in thin plate casting according to claim 1, wherein at least one of a lower limit value and an upper limit value is set at the movement position of the stopper rod.