JPH03151149A - Method for controlling mold level in open casting - Google Patents

Abstract

PURPOSE:To accurately and stably start the drawing operation of a cast slab by correcting the detected molten metal surface information exceeding a setting level with splash at the period from pouring start of the molten metal in a mold to the drawing start of the cast slab to the setting level or below. CONSTITUTION:The molten metal is poured into the mold with an open casting. The molten metal surface level in the mold is detected through a level meter with a vortex range finder, etc. When this detected molten metal surface level reaches the preset prescribed level, the drawing for cast slab is automatically started through a dummy bar. In the mold level control method in the above open casting, at the period from the starting time of pouring the molten metal to the starting time of drawing the cast slab, the data of the detected molten metal surface level exceeding the above setting level caused by the influence of the splash is corrected to the above setting level or below. By this method, the development of molten steel leakage caused by starting the drawing of the cast slab before storing the fixed quantity of molten steel, is prevented, and the drawing operation of the cast slab can be accurately and stably started.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a mold level control method in open casting in which continuously cast molten steel is directly drop-injected into a mold without using an immersion nozzle.

[Prior art and its problems] In continuous casting, if the mold level (molten metal surface position) in the mold changes rapidly, surface defects occur in the slab. Therefore, it is necessary to monitor and stabilize the mold level during casting.

To stabilize the mold level, the mold level during casting is detected by a monitoring device, and the slab withdrawal speed is controlled based on the detected data. A differential feedback eddy current distance meter is used as a monitoring device to measure the mold level.

In this eddy current distance meter, an eddy current is generated on the surface of the mold inside the mold, thereby forming a magnetic field, and the mold level is detected by measuring the strength of this magnetic field.

This eddy current distance meter is placed directly above the molten metal level in the mold. A mold with a small cross section such as a bloom or a beam blank has a narrow casting area, and the installation location is limited. Further, since the measurement distance of this eddy current distance meter is short, the detection unit must be brought close to the scene, and it is easily affected by splash.

In open injection with a small-section mold, molten steel is injected into the mold without using a submerged nozzle, so splashes are generated within the mold when starting molten steel injection and when replacing the semi-nozzle.

In the conventional mold level control method, regarding the mold level, the distance from the upper end of the mold to the mold surface is set to a set value (SP
value). When the detection value (Pv value) detected by the mold level meter becomes the same as the SP value, the slab drawing operation is automatically started. After the start of operation, if the mold level change rate calculated from the PV value detected by the mold level meter is within the predetermined range, P
The operation output of the slab drawing speed is controlled based on the v value.

Further, if the mold level change rate falls outside the predetermined range during operation, the movement '1 is equalized until the mold level change rate falls within the predetermined range, and the average value is output. Here, moving average processing means 16 P points per second.
This is the process of sampling v values and outputting the average value as data.

However, with the conventional mold level control method, it is not possible to eliminate the influence on the mold level detection value of the splash that occurs during the period from when molten steel starts being poured into the mold until the molten steel accumulates to the mold level setting value. That is, if the splash generated at the start of molten steel injection reaches a level equal to or higher than the SP value, the mold level meter will falsely detect this and automatically start the slab drawing operation. If the drawing of slabs is started before a certain amount of molten steel has accumulated, the solidification of the molten steel and dummy bar will be incomplete, resulting in molten steel leakage and serious equipment trouble.

The present invention has been made in view of the above points, and provides a mold level control method in open casting that can eliminate the influence of splash at the start of injection of molten steel and stably start a slab drawing operation. The purpose is to

[Means for Solving the Problems] The present invention provides a mold level in open casting that detects the surface level in the mold and automatically starts drawing slab when the detected level reaches a predetermined level. The control method is characterized in that information on a detected metal surface level that exceeds the set level due to the influence of splash between the start of molten metal injection and the start of slab withdrawal is corrected to below the set level.

[Function] In the mold level control method in open casting of the present invention, data on splashes greater than or equal to the SP value between the start of molten steel injection and the start of the slab drawing operation are corrected to be less than the SP value.

Thereby, it is possible to prevent the slab drawing operation from starting before a certain amount of molten steel has accumulated in the mold, and to start the slab pulling operation properly and stably.

[Example] Hereinafter, an example of the mold level control method in open casting of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 3 is a schematic diagram showing a part of a continuous casting apparatus according to an embodiment of the present invention.

A molten steel ladle (not shown) is supported by a ladle car above the equipment for continuously casting blooms, billets, and beam blanks.

Directly below the molten steel ladle, a tandem dish 30 is movably arranged. An inner nozzle 31 is installed at the bottom of the tundish dish 30. This inner nozzle 31
A semi-nozzle 32 is arranged below the casting area so that it can be moved in and out of the casting area by means of a semi-nozzle support member 33.

Further, a mold 34 is installed below the inner nozzle 31. The semi-nozzle 32 is supported by a member 33 of a turning device (not shown) so as to be inserted between the inner nozzle 31 and the mold 34.

A water cooling hose 36 is attached to the mold 34. A dummy bar (not shown) is inserted into the mold 34 from below at the start of casting, and is pulled out downward when the molten steel poured into the mold 34 solidifies. A mold level meter 35 is mounted along the upper stage of the mold 34, with its sensing portion pointing toward the scene.

Next, the control method of the present invention will be explained with reference to FIG.

First, when pouring molten steel into the mold is started, the PV value detected by the mold level meter 35 is manually input to the determination circuit 10. The determination circuit 10 compares a preset SP value and a detected PV value. In this case, usually SP
The value is set to the sum of the distance from the upper end of the mold to the detection part of the mold level meter inside the mold and the measurable distance of the mold level meter.

If the PV value does not exceed the SP value between the start of molten steel injection and the start of the slab drawing operation, the PV value is processed by the change rate limiting circuit 11 and corrected to be equal to or less than the SP value.

Thereafter, information on the corrected PV value is sent to the controller 14. Furthermore, in response to fluctuations in the mold level after the slab drawing starts, the slab drawing speed is controlled by a conventional method. That is, if the PV value is the rate of change detection circuit 12
, and the rate of change is calculated. If the obtained rate of change is larger than the set value, it is processed by the moving average processing circuit 13 to correct the PV value, and information on the PV value is sent to the controller 14. Furthermore, if the obtained rate of change is smaller than the set value, the PV value information is directly sent to the controller 14.

FIG. 2(a) is a graph showing the relationship between PV value and time from the start of molten steel injection to the start of slab drawing operation. In the figure, 20 is a characteristic line of PV value. Also, 21.
22 is a splash signal detected by the mold level meter. Note that the measurement range W of the mold level meter at this time was 100 m. FIG. 2(b) is a signal characteristic diagram when the PV value of the splash 21 that occurs between the start of molten steel injection and the time when the mold level reaches the SP value is corrected to the SP value. The splash signal 21 is corrected by the change rate limiting circuit 11 to a signal 23 that is less than or equal to the SP value.

Here, since the splash signal 21 is a narrow and sharp signal, when the splash signal is corrected, it is made into a wide signal. Specifically, the slope θ1 of the corrected signal 23 when rising is approximately 6 times the slope when the splash signal 21 rises.
%, and the slope θ2 of the corrected signal 23 when falling is set to 30% of the slope of the splash signal 21 when falling. In this way, the influence of splash is prevented from the time when molten steel injection starts until the mold level reaches the SP value.

FIG. 2(C) is a signal characteristic diagram when correcting the PV value of the splash 22 that occurs after the drawing of the slab starts. When the change rate exceeds a set value, the change rate detection circuit 12 corrects the splash signal 22 to a signal 24.

[Effects of the Invention] As explained above, the mold level control method in open casting of the present invention eliminates the influence of splash that occurs from the start of molten steel injection until the mold level reaches the SP value, and stabilizes the mold level. With this, the slab drawing operation can be started.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the control method of the present invention, and FIG. 2 (
a) is a graph showing the relationship between PV value and time, FIG. 2(b) and FIG. 2(c) are signal characteristic diagrams when correcting PV value, and FIG. 3 is an embodiment of the present invention. FIG. 2 is a schematic diagram showing a part of the continuous casting apparatus. 10... Judgment circuit, 11... Change rate limiting circuit, 12
... Rate of change detection circuit, 13... Moving average processing circuit,
14...Controller, 20...PV value characteristic line, 21°22...Splash signal, 23.24...Signal after correction, 30...Tandish, 31...Inner nozzle, 32... Semi-nozzle, 33... Semi-nozzle support member, 34... Mold, 35... Mold level meter, 36... Water cooling hose.

Claims (1)

[Claims] In a mold level control method in open casting, in which the metal level in the mold is detected and slab withdrawal is automatically started when the detected level reaches a preset level, slab withdrawal starts from the start of molten metal injection. A mold level control method in open casting, comprising: correcting information on a detected molten metal level that exceeds the set level due to the influence of splash to below the set level.