JPS62179859A - Auto-start controlling method for continuous casting machine - Google Patents

Abstract

PURPOSE:To execute continuous casting operation at low cost and to automate by combining a process of controlling for pouring speed of molten metal, with a process of drawing start for casting slab at ascending time of molten metal surface at a level of a fixed lower position from a stationary level and with a process of controlling the molten metal surface at the stationary level. CONSTITUTION:The molten steel in a ladle 11 is poured into a tundish 13 through an air-seal nozzle 12 and then poured into a mold 17 through a sliding nozzle 14 and a submerged nozzle 16. The casting slab 20 is drawn from the mold 17 by pinch-rolls 21. Pouring weight is controlled by calculating the pouring speed in accordance with opening degree of the sliding nozzle 14. The drawing start of the slab is executed at ascending time of the molten steel surface at a position with about 20mm lower than the stationary level. The molten steel surface is controlled to keep to the stationary level since passing 1sec after drawing start. As this auto-start controlling method is highly practical, automatic continuous casting operation is executed at low cost under automation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an auto-start control method suitable for a continuous casting machine, particularly a continuous casting machine for small cross-section slabs such as a continuous billet casting machine.

[Prior Art] In continuous casting, as shown in FIG. is injected into the mold G through the immersion nozzle 5 while being adjusted. The molten steel is cooled in the mold 6 and cast into the slab 7 with unsolidified molten steel remaining inside.
is pulled out from the mold 6.

In such continuous casting, automatic casting start (hereinafter referred to as autostart) technology has been put into practical use in continuous casting machines that produce large cross-section slabs, such as continuous slab casting. Figure 10(a).

(・b) and (C) are timing charts explaining this auto-start technology, with time on the horizontal axis and the opening of the sliding nozzle, the level of molten steel in the mold, and the drawing speed on the vertical axes, respectively. It is. Molten steel is injected into the mold with the sliding nozzle fully open, and when the molten steel level rises to a predetermined position, control of the nozzle opening is started, and the nozzle opening is adjusted so that the scene rises along a predetermined rising curve. is controlled. This is to ensure sufficient time for the molten steel injected into the mold to solidify. Then, when the surface level reaches a predetermined base surface level, pulling out of the slab is started. Thereafter, after the scene level reaches the steady level, the opening degree of the sliding nozzle is adjusted so that the scene reaches the steady level, and the hot water level is controlled.

[Problems to be Solved by the Invention] However, if the auto-start method for continuous slab casting is applied directly to continuous casting for producing small cross-section slabs, such as continuous billet casting, the following problems arise. There is a point.

First, in continuous billet casting, the rate of rise of the surface within the mold is about 10 times faster than in continuous casting of large cross-section slabs such as slabs. For this reason, the time it takes from injecting molten steel from the tundish into the mold to moving to steady pouring is 90 to 120 seconds in the case of a slab.
In the case of billets, it is as short as about 10 seconds. Therefore, it is difficult to increase the scene level along a predetermined curve in such a short period of time. In addition, since the rising speed of the scene is fast, the response of the control system is not in time, making it difficult to shift from rising hot water level to controlling the hot water level at a steady level.

Furthermore, in molds for small cross-section slabs such as continuous billet casting, the space within the mold is narrow and the size of the mold is small, which limits the usable level gauges. Generally known level meters for small cross-section molds include eddy current level meters and level meters using radioisotopes. The former has high accuracy and high responsiveness, but has the disadvantage of a short measurable distance of 10011 m, and the latter
Although the measurable distance can be increased, the disadvantage is that the equipment cost is high. For this reason, it requires a large amount of expense to control the rising speed of the hot water level while detecting the scene level over a long distance, as in the conventional auto-start technology.

This invention was made in view of such circumstances, and
The purpose of the present invention is to provide an auto-start method for a continuous casting machine that can automate the casting start operation at a relatively low cost and save labor even in a continuous casting machine for producing small cross-section slabs. .

[Means for Solving the Problems] The automatic start method for a continuous casting machine according to the present invention involves injecting molten metal into a mold of a continuous casting machine and adjusting the injection speed of the molten metal so that the rising speed of the scene becomes a predetermined speed. a process of controlling
A step in which the drawing of slabs is started when the surface rises to a level that is a predetermined distance below the steady level of the molten metal level in the mold, and an S-surface control that controls the surface to a steady level when a predetermined time has elapsed after the start of drawing. It is characterized by having the step of.

[Function] In this invention, first, when molten metal is poured into a mold from a tundish or the like, the wetted surface rises within the mold. Then, the injection speed is controlled so that the rising speed of the hot water level matches a predetermined speed.

In this case, in the process of the scene rising, the arrival of the scene is detected at at least two positions, and based on the detection results, the rate of rise of the hot water level at that time is determined, and based on this rate of rise of the hot water level,
i! By correcting the injection speed and performing predictive control so that the scene rising speed after i matches the predetermined speed, the scene rising speed can be made to match the predetermined speed.

Next, when the surface level rises to a level lower than the steady level by a predetermined distance 1, for example, 20 cm, handling of the slab is started at a predetermined drawing speed. As a result, the molten metal level overshoots by about 20 mm and rises above the level at the start of drawing, but since the pouring speed is almost the same as the drawing speed, once the spreading speed settles to a steady state, the situation becomes a substantially constant level near a predetermined steady level.

In this way, when the transient state of the scene level has passed and it is close to the steady level, that is, after a predetermined time after the start of extraction (
For example, after 1 second has elapsed, hot water level control is started to control the scene to a steady level. In this way, the scene rises and
By linking with scene control at a steady level, it is possible to smoothly auto-start even small-section continuous casting where the rate of rise of the molten metal level is fast.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. FIG. 1 is a schematic diagram showing the state of implementation of the present invention. The molten steel in the ladle 11 is injected into the tundish 13 through an air seal nozzle 12 installed at the bottom of the ladle, and is injected into the mold 1 through a sliding nozzle 14 and an immersion nozzle 16 installed in the tundish 13.
Injected into 7. The sliding nozzle 14 is driven to open and close by a cylinder 15, and by adjusting its opening degree, the speed at which molten steel is poured from the tundish 13 into the mold 17 is adjusted. Molten steel is poured into a mold 17 and cooled by the mold to form a solidified shell. Then, the slab 20 is pulled out from the mold 17 by the pinch rolls 21 with unsolidified molten steel remaining inside.

For example, an eddy current level meter 18 is installed in the mold 17 at a position 201IIIllT from the upper end of the mold, and when the scene is controlled at a predetermined steady level, the scene level is detected and the detection result is controlled. The data is sent to the system. Further, an electrode type level sensor 19 having three electrodes is installed inside the mold 17. Detection signals from the eddy current level meter 18 and the electrode level sensor 19 are input to the level control device 22 . The level control device 22 calculates the required opening degree of the sliding nozzle 14 based on this detection result, and calculates the required opening degree of the sliding nozzle opening degree control hydraulic system W1.
An opening signal is output to 24. This hydraulic device 24 adjusts the hydraulic pressure supplied to the cylinder 15 to control the nozzle opening to a predetermined opening. On the other hand, level system T! The D device 22 outputs a drawing start signal to the drawing speed control device 23 at a predetermined time of starting the drawing, and when the control device 23 receives this drawing start signal, it drives the pinch rolls 21 to pull out the slab 20.

Next, an autostart control method according to an embodiment of the invention will be described.

(I) Molten Steel Injection Amount Prediction Control At the start of molten steel injection, the molten steel injection amount is controlled so that the molten steel level in the mold rises at the same speed as the predetermined drawing speed. This hot water level rising speed Vll is equalized by the following equation (1).

VQ - μ0 (1/A) f (L)
゛ (1) However, μa; discharge coefficient L; sliding nozzle opening degree f (L) varnish sliding nozzle opening area 0:
Gravitational constant W; Tundish weight H (W): Molten steel head height A in tundish; Slab cross-sectional area In this equation (1), head difference H (W) and outflow coefficient μ
is an unknown quantity. According to the experimental results of the inventors,
It has been found that this head difference H(W) differs between when the sliding nozzle 14 is fully open and when it is narrowed down. That is, as shown in FIGS. 4 and 5, the cap portion 32 of the sliding nozzle 14 is six-fitted to the bottom wall 30 of the tundish 13.
The molten steel in the tundish 13 flows out into the mold 17 via the sliding nozzle 14. Those who have lost their original application, etc.
When the sliding nozzle 14 is fully open (FIG. 4), the head difference H (W> is the distance between the melt surface in the tundish 13 and the minimum diameter part of the cap portion 32, and the sliding nozzle 14 is narrowed. In this state (Fig. 5), if the head difference H (W') is the distance between the molten steel scene in the tundish 13 and the sliding nozzle 14, then
It has been found that the equation (1) and the actual outflow rate agree well. Therefore, the level control device 22 appropriately selects the head difference H(W) in the equation (1) according to the open/closed state of the sliding nozzle 14 to calculate the outflow velocity VQ of the molten steel.

Further, the outflow coefficient μ changes depending on the state of nozzle clogging. Therefore, in the present invention, such factors of μ mouth fluctuation are removed by actually measuring the rate of rise of the lake surface at the beginning of injection.

Next, a method of correcting μ mouth using this measured lake level rise rate will be explained. When pouring molten steel from the tundish into the mold, insert the dummy bar into the mold 17 so that its upper end is at a position 450++u++ from the upper end of the mold, fully open the sliding nozzle 14 of the tundish 13, and pour the molten steel from the tundish 13 into the mold 17. Inject into. Figures 2 (a), (b), and (C) are timing charts showing the relationship between time on the horizontal axis and wet surface level, sliding nozzle opening degree, and withdrawal speed on the vertical axis, respectively. It is. Thus, when the sliding nozzle is fully opened, the level of molten steel blood in the mold increases rapidly. Figure 3 shows the distance from the top of the mold on the vertical axis.
FIG. 2 is a schematic diagram showing the lake surface level detection position of the N-pole sensor 19. The lower ends of the three electrodes of the electrode type sensor 19 are respectively 300m+e, 1501all, and 90Ill from the upper end of the mold.
is set in the position. When the lake surface rises and contacts the lower end of the electrode, it is detected by the conduction that the wetted surface has reached the position of the lower end of the electrode. Therefore, in the hot water level control device 2, first, the lowest electrode (#!
0111) to start time counting, input a conductive signal from the electrode at position 150111 from the upper end of the mold to stop the timing, and find the time interval therebetween. Then, the control device 22 calculates the rate of rise V of the lake surface by dividing the distance between the lower end positions of both electrodes by the liI interval at that time.

Based on the melt level rising speed V actually measured in this way, the actual outflow coefficient μ when the nozzle is clogged is as follows (
2) Calculated using the formula.

μ-μo (V/vo)
(2) Therefore, if the above-mentioned head difference correction value is h, then the lake surface rising speed V in actual use is calculated using the following formula (3).
It appears in

■-μ(1/A)f(L)F]1105汀]]Hundredth level control device f22 is based on this equation (3), and when this lake level rising speed V matches the predetermined drawing speed of the slab, The opening degree of the sliding nozzle is calculated, and the sliding nozzle 14 is sent to the hydraulic device 24 for controlling the sliding nozzle opening degree.
Outputs the required opening degree. The hydraulic pressure 81124 is applied to the cylinder 15 so that the opening degree of the sliding nozzle 14 is L.
Activate. In this way, the degree of opening when the rate of rise of the lake level is V is determined, in other words, the rate of rise of the hot water level at the degree of opening is calculated predictively. In the second step, the lake level rises at this predicted lake level rise rate (slab withdrawal rate). In addition, the rate of lake level rise! 1II
The target IIl is not limited to the predetermined drawing speed of the slab as described above, but may be anything close to the predetermined drawing speed. The reason why this lake surface rising speed is made to correspond to the slab withdrawal speed is because if the lake surface rising speed and the drawing speed match, the lake surface will, in principle, remain at a constant level.

(II) Pulling start control ``Assuming that the steady level of the lake surface in the mold is at a position of 70 II from the upper end of the mold, the third electrode of the electrode sensor 19 is set so that its lower end is at a position of, for example, 901111 from the upper end of the mold. will be installed in This electrode becomes conductive when the lake surface rises to a position 901 m from the upper end of the mold, and outputs the detection signal to the level control device N22. When the control device 22 receives this detection signal, it outputs a drawing start signal to the drawing speed control device 23, and the control device 223 operates the vinyl roll 21 to start drawing the dummy bar and the slab 20. This drawing speed is 1ljJ as mentioned above.
tie (I>), which was used as a standard for predictive control of the lake surface.

Next, a description will be given of a series of mountains in which the drawing of slabs is started when the lake surface rises to a position 20 m below the steady I-side bell. FIG. 6 is a graph showing changes in the scene level, with the horizontal axis representing the time after the start of extraction, and the vertical axis representing the scene level, based on the scene level at the start of extraction.

In the figure, the dashed-dotted line is 1.2m/1.2m without injecting molten steel into the mold.
The dotted line shows the rate of descent of the scene when the slab is pulled out in minutes, and the dashed line shows the rate of rise of each scene when molten steel is injected into the mold without pulling out the slab. The solid line is a combination of the broken line and the dashed-dotted line, and indicates the change in the scene level from the point in time after the start of pouring molten steel into the mold and the start of drawing. As is clear from Fig. 6, there is a time lag before the slab (or dummy bar) reaches a predetermined drawing speed even after drawing starts, and due to the existence of this transient state of drawing, the molten metal surface level increases by about 2011 after the start of withdrawal. In this way, due to the overshoot of the scene level, the handling of slabs is not started when the scene reaches a predetermined steady scene level, but when the scene reaches a position 20+e− below this steady m1ni level. Point in time.

(III) Scene Level Control After a predetermined period of time, for example, 1 second, has elapsed after the start of extraction, scene control for controlling the scene level to a predetermined steady scene level is started.

As is clear from FIG. 6, even after the handling starts, the molten steel surface level overshoots by about 20IIllIl, and the scene level fluctuates during this period. In this case, such scene level fluctuations are significant during a period of approximately 1 second after the start of extraction. For this reason, it is preferable to enter the steady level control of the scene while avoiding this transition period of 1 second after the start of extraction. For this reason, in this invention,
After a predetermined period of time has elapsed after the start of extraction, scene control is entered.

This scene control may be performed using normal PIDIIIm.

In other words, the vortex level meter 18 is placed, for example, at two points from the upper end of the mold.
The level meter 18 detects the hot water level and sends the detection result to the level control device 22.
Enter. The level control amount W122 is calculated by calculating P10 between the detection result of the scene level and a predetermined steady scene level (control target value) at a predetermined sampling period to obtain the required correction amount of the opening degree of the sliding nozzle 14. It is output to the hydraulic device 24. The hydraulic system [24 opens and closes the nozzle opening degree via the cylinder 15 based on this control amount.

In continuous casting of large cross-section slabs such as slabs, the surface rises slowly after the start of drawing, so there is no problem in starting the scene control at the same time as the start of drawing.

As described above, in this embodiment, first, the dummy bar is inserted into the mold from the upper end of the mold to the position 45011,
The sliding nozzle 14 is fully opened and injection of molten steel is started. The electrode sensor 19 is 30Qa* from the top of the mold.
Then, it is detected that the molten steel scene has risen at a position of 150 mm, and the rising speed of the molten steel is determined. As a result, the level control amount f[22 corrects errors in injection speed due to nozzle clogging, etc., and the hydraulic system for sliding nozzle relationship control fff2
4 and the cylinder 15, and then the injection speed is predictively controlled so that the molten metal level rises at a predetermined rate of rise (for example, a predetermined withdrawal rate of the slab).

When the electrode sensor 19 detects that the scene has risen to a position of 9Qm+++ from the upper end of the mold, the level control device 22
outputs a pull-out start signal to the pull-out speed control device 23, and the control amount! 23 drives the pinch rolls 21 to start drawing out the slab. Then, one second after the start of this drawing, the level control device 22 adjusts the scene level to a predetermined steady level based on the output of the eddy current level meter 18.

71st! I and FIG. 8 have cross-sectional diameters of 2101111, respectively.
FIG. 2 is a graph diagram showing control results when automatic start is performed according to the present invention when continuously casting billet slabs Nos. 1 and 1701111. In the figure, the sliding nozzle's rfa degree ratio changes, the drawing speed changes, and 1 in the mold.
111 shows changes at the level. As is clear from this figure, according to the present invention, the autostar 1- can be stably and reliably cast.

[Effects of the Invention] According to the present invention, casting can be reliably and stably automatically started even in continuous casting for small-section slabs in which the rising speed of the molten metal level is extremely fast. Therefore, since continuous casting of such small cross-section slabs can be automated from the start to the end of casting, the present invention is extremely practical. Moreover, because of such automation, there is no need to use expensive sensors, so automatic continuous FA casting can be performed at low cost.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the implementation state of this invention, Figure 2 (a
), (b), and (c) are graphs showing the relationship between the surface level, nozzle opening, and withdrawal speed, Figure 3 is a schematic diagram showing the detection position of the electrode sensor, and Figures 4 and 5 are the head The diagram showing the difference, Figure 6, is a graph diagram showing the variation of the part level, Figure 7, and Figure 85! U is a graph diagram showing the effects of the present invention, and FIGS. 9 and 10 are diagrams showing a conventional auto-start method. 11; ladle, 13; tundish, 14; sliding nozzle, 15; cylinder, 17; mold, 18: eddy current level meter, 19: electrode sensor, 20; slab, 21: pinch roll, 22; level control TM device , 23: Drawing speed control device, 24; Oil pressure v for sliding nozzle opening control
ltff. Applicant's agent Patent attorney Takehiko Suzue Figure 1 vJ2 Figure

Claims (4)

[Claims] (1) The process of injecting molten metal into the mold of a continuous casting machine and controlling the injection speed of the molten metal so that the rising rate of the molten metal level becomes a predetermined rate; Continuous casting characterized by having a step of starting drawing of the slab when the surface rises, and a step of starting level control of controlling the molten metal level to a steady level after a predetermined time has elapsed after the start of drawing. How to control automatic start of the machine. (2) The step of controlling the injection speed of the molten metal includes the step of detecting that the molten metal level has reached at least two positions lower than the molten metal level at which drawing starts, and the initial rise of the molten metal level by this molten metal level detection. Claim 1, characterized by comprising the steps of determining the velocity, and modifying the molten metal injection velocity based on this initial melt level rising velocity so that the melt level rising velocity matches the predetermined velocity. The auto-start control method for a continuous casting machine described in . (3) The automatic start control method for a continuous casting machine according to claim 1, wherein the predetermined distance is 20 mm. (4) The automatic start control method for a continuous casting machine according to claim 1, wherein the predetermined time is 1 second.