JPH0455768B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for controlling the flow rate of molten metal in thin plate casting, and in particular, the present invention relates to a method for controlling the flow rate of molten metal in thin plate casting.
This method is suitable for use in equipment that requires a continuous supply of a relatively small amount of molten metal, such as the quenched ribbon process that directly manufactures plates by pouring and solidifying molten metal. This invention relates to a stable and accurate flow rate control method when supplying water.

[Conventional technology]

Continuous casting of thin sheets, for example, by pouring molten metal onto a continuously moving cooling body such as a cooling roll and solidifying it.
Accurately controlling the flow rate of molten metal supplied from a pouring nozzle in the quenched ribbon process that directly manufactures plates is an essential technology for keeping the thickness of the product plate constant. Therefore, for example, by supplying molten metal from molten metal holding equipment such as a melting furnace to a tundish equipped with a pouring nozzle and controlling the supply amount so that the weight of the tundish remains constant, the pouring speed can be kept constant. Methods have been developed to maintain the plate thickness constant. However, there has been a problem in that it is difficult to perform accurate control, especially when the flow rate is relatively small, such as 10 kg/s or less. Other methods for controlling the supply of molten metal include a method of pouring the molten metal by tilting the molten metal holding device itself such as a furnace, and a method of pouring the molten metal from a sliding nozzle. However, the former method has the problem that it is difficult to accurately control the pulsation of the pouring amount due to partial solidification at the pouring port, and the latter method not only requires large-scale and expensive equipment, but also has the problem that the nozzle It is necessary to fill the nozzle hole with sand to prevent clogging, and if such inclusions enter the tundish, the negative effects such as clogging of the pouring nozzle and interference with plate making cannot be ignored in the micro-pouring system. It has problems and its use has been limited. In addition, in JP-A-61-296942 and JP-A-61-296943, the tundish or the box through which the nozzle from the tundish runs through is made airtight, and a tundish stopper rod is attached to the pouring nozzle of the tundish. This is a combination of pressure adjustment inside the tundish or box body and adjustment of the opening of the tundish stopper rod.In other words, relatively fast fluctuations in the molten steel level are reduced by pressure adjustment, and relatively slow fluctuations are reduced by the tundish stopper rod. A method of reducing this by adjusting the opening degree of a lever stopper is disclosed.

[Problems to be solved by the invention]

However, installing a stopper rod in a tundish installed in a relatively narrow area is difficult in terms of equipment, and in order to pressurize and depressurize the inside of the tundish or box, it is necessary to completely remove the tundish or box containing high-temperature melt. The problem was that the structure had to be airtight, requiring large-scale equipment, and making the structure complicated. Therefore, in the pouring method using the stopper rod method, which has relatively few restrictions on equipment, in order to perform high-precision pouring control, it is necessary to pour the molten metal directly into the cooling body from a molten metal holding device such as a melting furnace. When supplying molten metal to a tundish with a hot water nozzle attached, it is important to perform stable and accurate control when pouring from the tundish. Conventionally, the flow rate was controlled intermittently by on/off control of a stopper rod. Although adjustments have been made, the controllability is poor due to changes in the hot water level and swinging of the stopper rod, so it could not be used to accurately control minute flow rates. Incidentally, Japanese Patent Application Laid-Open No. 58-58964 discloses a structure similar to the present invention, but unlike the present invention, it does not relate to thin plate casting and the specific structure is different.

[Purpose of the invention]

The present invention was made to solve the above-mentioned conventional problems, and it prevents welding of the stopper rod and stably and accurately controls minute flow rates using a stopper rod method with fewer restrictions on equipment. The purpose of the present invention is to provide a method for controlling the flow rate of molten metal in thin plate casting.

[Means to solve the problem]

The present invention provides a method for forming a thin plate using pouring equipment that includes at least a pouring nozzle that supplies molten metal onto the surface of a cooling body, and a molten metal holding device that has a stopper rod that controls the amount of molten metal supplied to the pouring nozzle. When casting,
As shown in FIG. 1, the pouring amount or the rate of change thereof is measured online, the position or moving speed of the stopper rod is controlled based on the deviation between the measured value and the target value, and the The position of the stopper rod is determined by the following formula: dmin≧50/√... (1) Where, ρ: Density of the molten metal (g/cm ³ ) C: Specific heat of the molten metal (cal/g) ΔT: Temperature of the molten metal Difference from its melting point (℃) (10≦ΔT
≦500) h: Height from the top of the pouring hole to the surface of the molten metal (mm)
(30≦h≦2000) The above objective is achieved by regulating the opening degree so that it does not become less than the minimum opening degree dmin shown by the following formula.

[Effect]

Since it is difficult to precisely adjust the distance between the bottom opening of the furnace and the tip of the stopper rod, which is generally made of refractory material, the present invention aims to develop a high-flow pouring system that can tolerate relatively large pulsations. This was achieved through a more detailed study of the stopper rod method, which was previously thought to be unsuitable for micro-pouring systems that require stable and accurate control of minute flow rates, even if it could be adopted. be. When supplying molten metal by moving a stopper rod up and down from a molten metal holding device such as a melting furnace, the position of the stopper rod is controlled so that the amount of poured metal is constant. Stability and high controllability can be achieved by setting a lower limit on the opening degree of the stopper rod and, if necessary, setting an upper limit on the opening degree of the stopper rod in order to improve controllability. Hereinafter, the specific structure of the present invention will be explained by taking as an example the case where the present invention is applied to a single roll method used for manufacturing an amorphous alloy. FIG. 2 schematically shows an example of the single roll method, in which a stopper rod 14 for controlling the amount of molten metal 10 supplied to the tundish 12 is provided in the melting furnace 16, which is a molten metal holding device, and the melting furnace is 16, for example
A stopper rod drive device 18 using a drive unit that is easy to control, such as a DC servo motor, is installed. or,
For example, a load cell 20 is attached to the lower tundish 12 so that the weight of the molten metal inside can be measured together with the tundish 12. In the figure, 22 is a pouring nozzle, 24 is a control device, 26 is a cooling roll, and 28 is a ribbon. During casting, the position of the stopper rod 14 is controlled by the control device 24, for example, so that the weight corresponds to the target level of the molten metal in the tundish.
PID control. That is, for example, the opening degree of the stopper rod 14 is instructed by P (proportional) control based on the deviation between the measured weight and the target weight. P control alone will cause a steady-state deviation, so if the value is large, add I (integral) control to reduce the deviation, and if necessary, add D (differential) control to quickly correct the deviation. It becomes possible to make the deviation extremely small. The problem here is that when the opening degree of the stopper rod 14 becomes very small, the stopper rod 14 and the stopper seat 16A (the part around the furnace bottom opening that comes into contact with the stopper rod 14 when the supply of molten metal is stopped) ), there is a possibility that the molten metal will temporarily stay there and solidify due to the temperature drop, resulting in the stopper rod 14 being welded to the stopper seat 16A. For example, depending on the setting of the PID constant, such as the gain in the case of P control, such a situation is possible, especially at the beginning of control, so in the present invention, a lower limit value dmin is set for the stopper opening degree. This avoids welding of the stopper rod and improves operational stability. Note that since the flow rate when welding occurs in a short time is almost zero, even if a lower limit value dmin is provided, controllability will not be significantly impaired. Regarding the method of determining this lower limit value dmin, as a result of examining the area of the pouring hole, the tip shape of the stopper rod 14, the composition of the pouring metal, etc., the lower limit value dmin was determined as follows.
Depends on the density ρ of the pouring metal, the specific heat C, the difference ΔT between the molten metal temperature and the solidification temperature (melting point), and the height h from the top surface of the pouring hole (the contact position of the tip when the stopper rod 14 is closed) to the molten metal surface. I found out what to do. Figure 3 shows that the density ρ is 6.5 g/cm ² and the specific heat C is
An example of the results of investigating the relationship between the molten metal temperature at which welding occurs and the height h from the pouring hole to the molten metal surface for several stopper openings for 0.15 cal/g molten metal is shown below. For example, if the stopper opening is 0.5 mm and the difference ΔT between the temperature of the molten metal and its melting point is 60°C,
As welding occurs when the molten metal height h is 160mm,
Although there is a possibility that welding will occur in the region below the dashed-dotted line in FIG. 3, welding will not occur in the region above the dashed-dotted line that satisfies the above-mentioned formula (1). In other words, welding will not occur if the opening is set to the opening expressed by equation (1). In addition, Fig. 4 shows the relationship between the stopper opening degree and the pouring speed when the radius of the pouring hole is changed using a stopper rod 14 with a diameter of 50 mm and a hemispherical tip. In the case of control, the relationship between the stopper opening and the molten metal supply rate is not a simple proportional relationship; as the stopper opening increases, the molten metal flow rate is controlled by the cross-sectional area of the pouring hole, so the supply rate becomes saturated. For example, when the gain is relatively large in P control, depending on the setting of the PID constant, especially at the beginning of control, the increase in supply speed with respect to the increase in the stopper opening may become saturated or extremely small. Even if the stopper opening is
This may cause unnecessary operations such as further increasing dmax, but since there are restrictions on the moving speed of the stopper rod, controllability may deteriorate.
In such a case, the upper limit value for the opening degree of the stopper rod should be set.
By providing dmax, it is possible to avoid the aforementioned deterioration in controllability. According to fluid mechanics theory, this upper limit value dmax may depend on the kinematic viscosity coefficient of the molten metal, but as a result of experiments, we found that the position of the stopper rod
When performing PID control or controlling the speed of the stopper rod by P, the cross-sectional area of the pouring hole S (mm ² )
It was found that it depends on In other words, although it varies somewhat depending on the control theory, it is appropriate to set the value as shown in the following equation. 0.3√≦dmax≦0.8√ ...(2) In actual control, for example, the deviation between the target weight and the measured weight of the tundish 12 is input into the microprocessor of the control device 24 and set in advance. By calculating the opening degree of the stopper rod 14 according to the PID constant and issuing, for example, a position command, stable and accurate flow control can be performed with relatively simple control logic. If the tip of the stopper rod is severely damaged during pouring, even if the stopper opening degree is reduced, the amount of poured metal will be large and the weight of the tundish 12 will exceed the target value. In such a case, there is a method of temporarily lowering the stopper rod 14 to the lowest movable limit, temporarily interrupting the supply of molten metal, and restarting control after the tundish weight, etc. has decreased to near the target value. Casting can then be continued. In the above description, the amount of molten metal in the tundish was measured using the load cell 20, but the method for measuring the amount of molten metal is not limited to this.
Using a load cell other than a load cell, or
A laser level gauge or the like that optically measures the hot water level can also be used. Furthermore, in the above description, in the pouring equipment equipped with the melting furnace 16 and the tundish 12, the tundish 1
Hold the stopper rod 1 so that the amount of molten metal in 2 reaches the target value.
Although the present invention has been described taking as an example the case where the position of the stopper rod is controlled, the application of the present invention is not limited to this. When controlling the moving speed of the stopper rod 14 (Japanese Patent Application No. 62-192336), the position of the stopper rod 14 is adjusted so that the pouring speed (change rate of the amount of molten metal) from the tundish 12 becomes the target value (Japanese Patent Application No. 62-205720). ) or movement speed (patent application 1982-
275108), when controlling the position of the stopper rod 14 (Japanese Patent Application No. 1983-1996), in a device that pours melt directly from the melting furnace 16 to the cooling roll 26, so that the rate of change of the melting furnace weight (molten metal amount) reaches the target value. It is clear that the present invention can be similarly applied to the case of controlling the moving speed (Japanese Patent Application No. 62-275109).

【Example】

As shown in Figure 2, as a molten metal holding device,
Melting furnace 16 equipped with a stopper rod 14 driven by a DC motor (molten metal surface height used: 30 to 500 mm)
The control method of the present invention was applied to a device that supplies molten metal from a nozzle in the lower part of a melting furnace to a tundish 12 equipped with a pouring nozzle 22 by raising the stopper rod 14 using a molten metal. That is, molten metal of Fe-Si-B alloy (solidification point 1180
℃) is maintained at 1300℃ in the melting furnace 16, and using a stopper rod 14 with a hemispherical tip and a diameter of 50mm, an average of 0.8Kg/s is applied to the lower tundish 12 from the pouring hole with a diameter of 15mm. The water was poured at a speed of . Load cell 20 attached to tandem tray 12
The tundish weight signal from the control device 24
The position of the stopper rod 14 was controlled by controlling the current of the DC motor so that the tundish weight reached a target value according to a program sent to a microprocessor and written in advance. In controlling the opening degree of the stopper rod by position control, if there is no limit on the opening degree, and if only the lower limit value dmin is provided according to the present invention, the upper and lower limits dmax,
When I experimented with the case where dmin was also set up, I found that
The presence or absence of welding on the stopper rod and the variation in pouring speed during control were as shown in Table 1 below. As is clear from Table 1, welding may occur when the lower limit value dmin is not set (experiment numbers 1 to 3), but when the lower limit value dmin is set (experiment numbers 4 to 7), welding does not occur. Furthermore, controllability has also been improved. Furthermore, if an upper limit value dmax is set (experiment number 6,
7), it can be seen that the controllability is further improved.

[Table] Note that in the above embodiments, the present invention was applied to continuous thin plate manufacturing equipment equipped with a single cooling roll, but the scope of application of the present invention is not limited thereto.

【Effect of the invention】

As explained above, according to the present invention, it is possible to prevent welding of the stopper rod in thin plate continuous pouring equipment, and it is possible to stably and accurately control the pouring amount by the relatively simple method of moving the stopper rod. becomes. Therefore, it has the excellent effect of making the plate thickness uniform and improving the surface quality.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the basic procedure of the molten metal flow rate control method according to the present invention, FIG. 2 is a sectional view showing the configuration of an example of a continuous pouring device to which the present invention is applied, and FIG. , for inventing the principles of the present invention,
Figure 4 is a diagram showing the relationship between the molten metal temperature and the height from the pouring hole to the molten metal surface when nozzle clogging occurs, and also shows the stopper opening degree and pouring speed when the radius of the pouring hole is changed. FIG. 10... Molten metal, 12... Tundishyu, 14
... Stopper rod, 16 ... Melting furnace, 18 ... Stopper rod drive device, 20 ... Load cell, 22 ...
Pouring nozzle, 24... control device, 26... cooling roll, 28... ribbon.

Claims (1)

[Scope of Claims] 1. Using pouring equipment that includes at least a pouring nozzle that supplies molten metal onto the surface of a cooling body, and a molten metal holding device that has a stopper rod that controls the amount of molten metal supplied to the pouring nozzle. When casting a thin plate, the amount of molten metal or its rate of change is measured online, the position or moving speed of the stopper rod is controlled based on the deviation between the measured value and the target value, and the stopper rod is The position of dmin≧50/√...where, ρ: Density of molten metal (g/cm ³ ) C: Specific heat of molten metal (cal/g) ΔT: Difference between molten metal temperature and its melting point (°C) ) (10≦ΔT
≦500) h: Height from the top of the pouring hole to the surface of the molten metal (mm)
(30≦h≦2000) A method for controlling the flow rate of molten metal in thin plate casting, characterized by regulating the flow rate so that it does not become less than the minimum opening dmin expressed by (30≦h≦2000).