JPH091304A - Method for controlling molten metal surface level in mold at the initial stage of casting in continuous casting apparatus - Google Patents

Abstract

PURPOSE: To provide a control method of molten steel surface level in a mold at the initial stage of casting in a continuous casting apparatus which secures holding temp. of the molten metal in the mold and can be smoothly shifted to a fixed value level control. CONSTITUTION: Pouring of the molten steel into the mold set with a dummy bar head is started by using a molten metal flow rate control device and also, pull-out of the dummy bar is started at the point of time when the molten steel surface reaches a preset pull-out starting level. Further, in the control method of the molten steel surface level in the mold at the initial stage of casting of shifting the device to the fixed value level control when reaching a preset molten steel surface level, as for a range from the preset molten steel surface level to the dummy bar pull-out starting molten steel surface level, the deviation between the preset surface rising speed and the actual molten steel surface rising speed is obtd. and a closed loop control is executed to the molten steel surface rising speed so as to eliminate the deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a molten metal level in a mold at the initial stage of casting molten steel poured into the mold of a continuous casting machine.

[0002]

2. Description of the Related Art Generally, in a continuous casting apparatus, as shown in FIG. 1, molten steel 2 temporarily stored in a tundish 1 is supplied into a mold 4 through a dipping nozzle 11 by adjusting an opening of a slide valve 3. . During continuous casting, the slide valve 3 is arranged so that the molten metal 2 in the mold 4 has a constant molten metal level.
Is controlled. Further, the cast piece (not shown) cast by the mold 4 is a dummy bar 5 (the cast piece during continuous casting).
The casting speed is controlled by the pinch roll 13 in contact with.

By the way, in the continuous casting as described above, the casting work in the steady state has been conventionally automated, and the work for starting and ending the casting is conventionally performed manually depending on the experience of the operator. However, automation has begun as proposed by the present applicant in Japanese Patent Application Laid-Open No. 1-254361.

The outline of the conventional molten metal level control in the mold at the early stage of casting proposed in the above publication is shown in FIG.
This will be described with reference to FIG.

As means for detecting the molten metal level in the mold 4, the eddy current sensor 8 provided in the upper part of the mold 4 is embedded in the mold wall at an appropriate interval capable of detecting the temperature distribution in the vertical direction of the mold 4. A plurality of thermocouples 14 are used, and the eddy current sensor 8 is for casting work in a steady state, and continuously detects a molten metal surface level near the steady operation level (hereinafter also referred to as a constant value level). On the other hand, the thermocouple 14 detects the temperature distribution in the vertical direction from the lower portion of the mold 4 to the position of the eddy current sensor 8.

Using the mold 4 having the means for detecting the molten metal surface level as described above, in the initial stage of casting, the slide valve 3 is opened at a fixed opening in the mold 4 in which the dummy bar head 12 is set, and the tundish 1 is removed. Molten steel 2 is injected.
After that, the thermocouple 14 detects the temperature distribution in the vertical direction up to the molten metal surface 2a of the molten steel 2 that rises with pouring, calculates the molten metal level from this temperature distribution, and presets the molten metal level obtained by this calculation. The opening signal of the slide valve 3 is determined according to the difference between the level of the molten metal and the level of the molten metal, and closed loop control (see FIG. 3) of the rising metal level is performed. Here, a function L (t) with time is used as the preset molten metal level.

When the molten metal surface 2a controlled as described above reaches a certain molten metal surface as shown in FIG. 3, the mold 4 starts to vibrate,
Next, when the molten metal reaches a certain level (L3), the pinch roll 13 starts pulling out the dummy bar 5, the level of the molten metal level is measured by the eddy current sensor 8, and the fixed value level control is performed.

[0008]

By the way, in controlling the molten metal level at the initial stage of casting, it is necessary to satisfy the following two points. That is, the first point is that after the injection of the molten steel into the mold is started, the dummy bar starts drawing when the molten metal surface reaches a predetermined level. In this case, it is necessary that the molten metal surface has reached a predetermined level at the start of the dummy bar withdrawal, and that the elapsed time after the start of injection is within a predetermined range and the solidified state is appropriate. If the elapsed (holding) time is too short, the solidified shell is not sufficiently generated, so that a breakout occurs in which the solidified shell is broken by the pulling force, making it impossible to continue casting. On the other hand, if the holding time becomes too long, the solidified shell will stick to the damibar head, making it difficult to separate the two.

Another point is that before the molten metal level enters the constant value level control, the hunting phenomenon of the molten metal level after the shift to the fixed value level control is small if the molten metal level is the optimum rising speed. Therefore, it is necessary to adjust the molten metal surface rising speed to a predetermined speed before the constant value level control. Here, the predetermined speed is the molten metal rising speed determined by the initial drawing speed at the start of drawing the dummy bar.

For the above-mentioned precise level control, it is best to continuously detect the level and perform closed loop control. According to the molten metal level control method for determining the set level L (t) described in the prior art, when the molten metal level reaches the drawing start level (L3), the molten steel holding time in the mold can be secured. However, even when the predetermined level rising speed is set for the time t from before the constant value level control (L2) to the above (L3), the discharge amount of the slide valve changes due to the adhesion of metal, Molten steel drift, and molten steel temperature,
When the molten metal level fluctuates due to disturbances such as molten steel composition, casting speed, molten steel head pressure in the tundish, the molten metal level controller enters a correction operation, and the correction operation targets the set level L (t) at that time. Therefore, the slide valve is adjusted so that the rising speed does not always reach the intended level, and as a result, the surface rise time gets on the planned curve, but when the dummy bar is drawn Surface ascent rate may be different than planned. In that case, overshoot and hunting phenomenon of the molten metal surface occur.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a continuous casting apparatus which can secure a molten steel holding time in a mold and can smoothly make a transition to a fixed value level control. It is intended to provide a method for controlling a molten metal level in an initial casting mold.

[0012]

In order to achieve the above-mentioned object, a method of controlling a molten metal level in a casting initial mold in a continuous casting device according to the present invention is a molten steel flow rate control device in a mold equipped with a dummy bar head. While starting the injection of molten steel, the molten steel level inside the mold is detected, and when the molten level is detected to reach a preset drawing start level, the dummy bar head withdrawal is started, and it is preset. In the casting initial mold level control method in the continuous casting apparatus, the range from the preset level to the dummy bar drawing start level in the continuous casting apparatus is set when the level reaches the preset level. Calculate the deviation between the level of rising surface and the actual speed of rising surface,
In order to eliminate this deviation, the rising speed of the molten metal is closed-loop controlled.

In the casting initial level of the molten metal level in the continuous casting apparatus, the molten metal level is closed-loop controlled up to the preset molten metal level with the molten metal level pattern of the preset time function as the target value. It may be one that does.

Further, in the method of controlling the level of the molten metal in the initial casting mold in the continuous casting apparatus, the closed loop control of the molten metal rising speed may be performed by adjusting the opening of the slide valve.

[0015]

In the method for controlling the level of molten metal in the initial casting mold of the present invention, the range from the preset molten metal level to the level of the dummy bar drawing start molten metal is set at the set value of the molten metal rise rate obtained from the cross-sectional area in the mold. Since the closed-loop control (referred to as the molten-metal-rise speed control) is performed based on the actual molten-metal rising speed at each time, a smooth transition can be made to the fixed value level control that is performed almost at the same time as the molten-metal level at which the dummy bar is pulled out.
It is possible to suppress the overshoot and hunting phenomenon of the molten metal surface that occurs at the time of transition, and it is possible to relatively easily secure the molten steel holding time in the mold.

In order to obtain the above effect more effectively, from the start of pouring the molten metal to the preset level of the molten metal surface, the molten metal level at each time determined by the time-molten metal level pattern With the set value as the target value, closed-loop control (hereinafter referred to as the molten metal level pattern control) can be performed with the actual molten metal level at each time, which ensures the appropriate molten steel holding time in the mold. , Breakout or seizure of solidified shell on the Damibar head is reduced.

Further, the range in which the level rising speed control is performed in order to enjoy the above-mentioned effects is not particularly limited, but the shortest range is the level level control up to the dummy bar drawing start level. It is also possible to perform the molten metal level pattern control with most of the first level as the first step, and then perform the molten metal level rising speed control with the last part immediately before the dummy bar drawing start molten metal level as the second level. By switching the stages, it is possible to secure a predetermined molten steel holding time and to suppress overshoot and hunting on the molten metal surface that occurs during the transition to the fixed value level control. In addition, the molten steel level rising speed control is started near the tip of the immersion nozzle, and the molten steel level is controlled by slowly increasing the molten metal level rising speed control while the molten metal level passes through the molten steel discharge hole of the immersion nozzle. It is expected that the splashes can be prevented, which will prevent problems caused by the splashes adhering to the eddy current sensor and improve the surface properties of the ingot.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a continuous casting apparatus applied to the casting initial mold level control method according to the present invention, which has the same configuration as that conventionally used. FIG. 2 is a molten metal level chart of the initial molten metal level control method in a casting mold, which is carried out using the apparatus shown in FIG.

In FIG. 1, when the molten steel 2 stored in the tundish 1 reaches a certain weight, the slide valve 3 is opened and the dummy bar head 12 is set according to the opening pattern preset in the molten steel level controller 10. It is poured into the mold 4. When the level of the molten metal surface 2a of the molten steel 2 injected into the mold 4 rises and the temperature rise is detected at the lower end of the thermocouple 14, the molten steel level controller 10 changes the molten metal level by the temperature gradient in the vertical direction of the mold. Is calculated.

When the molten metal level is detected by calculation, the molten metal level feedback control is started with the molten metal level controller 10 having a preset molten metal level pattern as a target value, and the opening adjustment signal is sent to the valve opening controller 9 The opening degree of the slide valve 3 is adjusted by a command to the stepping cylinder 6 via. After that, when the molten metal surface 2a reaches a certain molten metal surface (L2 '), the mold 4 starts vibrating, and the molten metal level (L2') at that time and the pinch roll 13 are reached.
Starts pulling out the dummy bar 5 Start of pulling out dummy bar Level of molten metal [almost stationary level control level of molten metal] (L
During the period 3 ′), the desired level of molten metal rise rate obtained from the initial dummy bar drawing speed and the cross-sectional area in the mold is set as the target, and the molten metal level measurement by the eddy current sensor 8 is performed at each time. After controlling the rising speed of the level with
Move to fixed value level control. Reference numeral 7 is an opening meter, which measures the opening amount of the slide valve 3 and inputs the amount to the valve opening controller 9.

Next, a method of controlling the molten steel level, which is carried out by the apparatus constructed as described above, will be described with reference to FIG. In Fig. 2, when the level reaches the level (L0 ') at which the level pattern control switches to the level pattern, the actual level calculated by the thermocouple 14 rather than the planned level rise curve Is above, and it has greatly exceeded the planned level of the molten metal, but the correction operation is started.
By adjusting the opening of the slide valve 3 while reaching the level of starting level (L2 ') of rising level of molten metal, the level of molten metal is being converged to the expected level of molten metal level.

Next, at the molten metal level (L2 '= L3'-10 mm), the molten metal level detection is switched from the thermocouple 14 to the eddy current level meter 8, and the molten metal level control is performed at this molten metal level (L2'). Is shifted from the molten metal level pattern control to the molten metal rising speed control. At this time, although the actual rising speed was faster than the preset rising speed ΔLSV3, the opening correction operation of the slide valve 3 was started, and the target rising speed immediately converged. Then, after this, withdrawal of the dummy bar 5 is started at the molten metal level (L3 '), and the molten metal level control is switched to the constant value level control,
Good level control without hunting was started.

As described above, most of the molten metal level control uses the molten metal level pattern closed loop control by the time function to secure the molten steel holding time and to start the constant value level control molten metal level, that is, the dummy bar drawing starting molten metal level. Immediately before, by controlling the rising speed of the molten metal in a closed loop, the hunting phenomenon at the molten metal level was suppressed, quality deterioration was prevented, and good automation was possible.

[0024]

As described in detail above, according to the molten metal level control method of the present invention, it is possible to suppress the molten metal level fluctuation while securing the molten steel holding time at the initial stage of casting. In particular, automatic start control can be performed easily and stably, the product quality at the initial stage of casting can be improved, and the yield can be expected to be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a continuous casting device applied to a method for controlling a molten metal level in an initial casting mold according to the present invention.

FIG. 2 is a molten metal level chart of a molten metal level control method in a casting initial mold which is carried out using the apparatus shown in FIG.

FIG. 3 is a molten metal level chart of a conventional molten metal level control method in an initial casting mold.

[Explanation of symbols]

1: Tundish 2: Molten steel 2
a: molten metal surface 3: slide valve 4: mold
5: Dummy bar 6: Stepping cylinder
7: Valve opening meter 8: Eddy current sensor 9: Opening controller 10: Molten steel level controller 1
1: Immersion nozzle 12: Dummy bar head 13: Pinch roll 1
4: Thermocouple L0 ', L1', L2 ', L3': Level of molten metal surface: Planned rising curve of molten metal surface: Actual rising speed of molten metal surface

Claims (3)

[Claims] 1. A molten steel flow control device starts pouring molten steel into a mold equipped with a dummy bar head, detects the molten steel level in the mold, and the molten level reaches a preset drawing start level. In addition to starting the withdrawal of the dummy bar head at the time when it is detected, when the preset molten metal level reaches a preset molten metal level control, the casting initial mold molten metal level control method in the continuous casting apparatus shifts to the constant value level control. For the range from the molten metal level to the dummy bar drawing start molten metal level, the deviation between the preset molten metal rising speed and the actual molten metal rising speed is obtained, and the molten metal rising speed is closed-loop controlled to eliminate this deviation. A method for controlling a molten metal surface level in an initial casting mold in a continuous casting apparatus, comprising: 2. The molten metal level in the initial casting mold of the continuous casting apparatus according to claim 1, wherein the molten metal level is controlled in a closed loop by using a molten metal level pattern of a preset time function as a target value up to a preset molten metal level. Control method. 3. The method of controlling a molten metal level in an initial casting mold in a continuous casting apparatus according to claim 1, wherein the closed loop control of the molten metal rising speed is performed by adjusting the opening of a slide valve.