JP2810511B2 - Method and apparatus for measuring meniscus flow velocity of molten metal - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for continuously measuring the flow velocity immediately below a free surface in a non-contact manner when handling a molten metal having a free surface.

[Conventional technology]

When refining or casting molten metal, the flow of molten metal is an important control factor from the viewpoint of product quality and reaction efficiency. In particular, the flow velocity of the free surface, which is the contact interface with the refining flux or the heat insulating material, is important, and good processing can be performed by appropriately controlling the flow velocity.

Generally, molten metal has a high temperature, and flow rate measurement using a normal flow rate sensor such as a pit-tube cannot cause problems such as clogging of the pipe due to solidification.

For this reason, for example, "iron and steel '82 -S920" and
As disclosed in Japanese Patent No. 04512, a flow velocity measuring method has been proposed in which a rod is immersed in a weld metal through a free surface, and a dynamic pressure received by the rod is detected by a strain gauge installed on a support arm of the rod. Was.

[Problems to be solved by the invention]

However, in this method, since the rod needs to be immersed directly in the molten metal, deformation of the rod due to solidification and adhesion of the metal or erosion is inevitable. For this reason, an error occurs in the dynamic pressure received by the rod, and stable continuous measurement for a long time cannot be performed. In addition, there is a disadvantage that the measuring device becomes large because the sensor rod is relatively large, and it is difficult to handle such as installation and removal of the sensor.

On the other hand, it is common to detect the meniscus level of the molten metal in a non-contact manner by an eddy current sensor, but since the conventional eddy current level sensor has only one secondary coil,
The meniscus flow rate could not be measured.

An object of the present invention is to provide a method and an apparatus capable of stably measuring the flow velocity of a meniscus portion for a long time in a molten metal having a flow just below a free surface.

[Means for solving the problem]

The gist of the present invention for achieving the above object is as follows.

(1) Immediately above the meniscus having a flow just below the free surface,
A primary coil is arranged in parallel with the flow direction, and a secondary coil is arranged on both sides of the primary coil in the horizontal direction. In the measurement of the meniscus flow velocity of the molten metal, which detects the meniscus flow velocity from the electromotive force difference generated in each secondary coil, it is possible to simultaneously detect the meniscus position based on the electromotive force of one of the secondary coils. Characteristic meniscus flow velocity measurement method.

(2) In addition to the above (1), based on the meniscus position detected from the electromotive force of the secondary coil on either side, the electromotive force difference generated in the secondary coils on both sides is corrected to detect the meniscus flow velocity. A method for measuring meniscus flow velocity, characterized in that:

(3) a primary coil; first and second secondary coils provided on both sides of the primary coil; an AC power supply connected to the primary coil; an electromotive force connected to the first secondary coil. A second voltage detecting means connected to the second secondary coil and detecting an electromotive force of the first voltage detecting means; a voltage generated in one of the first and second secondary coils; Calculating means for detecting a distance between the secondary coil and the molten metal meniscus position based on the generated electromotive force; and an electromotive force of the first secondary coil detected by the first voltage detecting means; Calculating means for detecting the flow rate of the molten metal from the difference between the electromotive force of the second secondary coil detected by the voltage detecting means and the distance between the secondary coil and the molten metal meniscus position. Meniscus flow velocity measuring device.

[Action]

The principle of measuring the meniscus flow velocity of the molten metal according to the present invention will be described with reference to the drawings.

Please refer to FIG. 1, FIG. 2 and FIG. In these figures, 1 is a primary coil, 2a and 2b are secondary coils, 3 is a molten metal free surface, and, 4 are lines of magnetic force. The secondary coils 2a and 2b have the same number of turns and are arranged on both sides of the primary coil 1 in the horizontal direction.

In such a configuration, when there is no flow directly below the free surface 3 of the molten metal, when an alternating current is applied to the primary coil 1, the symmetrical magnetic lines of force 4 are induced as shown in FIG. The electromotive force induced in the secondary coil 2b is equal to the electromotive force induced in the secondary coil 2b. However, if there is a flow directly below the free surface 3 of the molten metal, the molten metal moves in a magnetic field induced by the alternating current flowing through the primary coil 1 to generate an induced current, and as shown in FIG. 4 is distorted downstream. Therefore, there is a difference between the electromotive force induced in the secondary coil 2a arranged on the upstream side and the electromotive force induced in the secondary coil 2b arranged on the downstream side.

Therefore, for a molten metal whose flow velocity v is known and the distance between the secondary coils 2a and 2b and the free surface is constant,
When the difference ΔEo between the electromotive force induced in 2a and the electromotive force induced in the secondary coil 2b was measured, a graph as shown in FIG. 4 was obtained. As shown in the figure, the meniscus flow velocity v of the molten metal and the electromotive force difference ΔEo of each secondary coil have a unique correspondence, and the flow velocity v can be known by measuring the electromotive force difference ΔEo.

However, even if the distance l between the secondary coils 2a, 2b and the free surface 3 of the molten metal changes, each secondary coil 2a, 2b
The induced electromotive force changes. In FIG. 5, the electromotive force induced in each of the secondary coils 2a, 2b when the distance (meniscus position) 1 between the secondary coils 2a, 2b and the free surface 3 was changed with respect to the static molten metal was investigated. The results are shown. In this way, the distance l between the secondary coils 2a, 2b and the free surface 3 of the molten metal and the electromotive force induced in each of the secondary coils 2a, 2b have a unique correspondence, and the meniscus position can be measured. is there.

In the actual measurement of the molten metal meniscus flow velocity, a change in the meniscus position (l) results in an error in the measured meniscus flow velocity. Therefore, the electromotive force induced in the secondary coil is measured, and the distance l between one of the secondary coils 2a and 2b and the free surface of the molten metal is calculated from the relationship shown in FIG. The correct meniscus flow velocity can be calculated by correcting the electromotive force difference ΔE induced in each of the secondary coils 2a and 2b on the side based on the following equation (1).

v∝ΔEo = ΔE · l− ⁿ (1) v: meniscus flow velocity (m / sec) ΔE: electromotive force difference between secondary coils (mV) ΔE _O : distance l between the secondary coil and the meniscus position of the molten metal Is the reference value, the electromotive force difference between the first and second secondary coils (m
V) l: distance (mm) between the secondary coil and the meniscus position of the molten metal n: order (normally 0.2) Example FIG. 6 shows the configuration of the flow velocity measuring apparatus of the present invention. This device comprises a primary coil 1, a secondary coil 2a, 2b, an AC power supply 5, voltage sensors 6a, 6b, a distance calculator 15, and a flow rate calculator 7 (the same symbols are used for the same elements as described above). T). The primary coils 1, 2a and 2b are wound coaxially, and the secondary coils 2a and 2b have the same number of turns. Upstream,
The secondary coil 2b is arranged downstream of the primary coil 1 with respect to the flow of the molten metal.

The AC power supply 5 is connected to the primary coil 1 and supplies an AC current of about several amps there to generate a magnetic field.
Voltage sensor 6a detects an electromotive force induced in secondary coil 2a, and voltage sensor 6b detects an electromotive force induced in secondary coil 2b. The distance calculator 15 detects the secondary coil 2b detected by one of the voltage sensors 6a and 6b (6b in this example).
From the relationship between the distance l and the electromotive force shown in FIG.
Ask for.

The flow rate calculator 7 is a secondary coil detected by the voltage sensor 6a.
The difference ΔE = Ea−Eb between the electromotive force Ea induced in the secondary coil 2b and the electromotive force Eb induced in the secondary coil 2b detected by the voltage sensor 6b is calculated, and the secondary coil obtained by the distance calculator 15 is calculated. Electromotive force difference Δ at reference distance from distance 1 between 2a and 2b and molten metal free surface
E _O is given by the following equation: ΔE _O = ΔE (l / l _O ) ^-n (2) ΔE _O : Difference in electromotive force at reference distance l: Distance between secondary coil and free surface of molten metal l _O : Reference distance n: The meniscus flow velocity v of the molten metal is calculated from the relationship between the flow velocity v and the electromotive force difference ΔE _O shown in the graph shown in FIG.

Such a flow rate measuring device is used, for example, for measuring a meniscus flow rate in a continuous casting mold of molten steel.

An example will be described with reference to FIG. In FIG.
8 is a tundish, 9 is an immersion nozzle, 10 is a molten metal meniscus flow velocity measuring device having the configuration shown in FIG.
Denotes a meniscus flow (upward inversion flow), 12 denotes a mold, 13 denotes a shell, and 14 denotes a powder layer having a thickness of about 50 mm.

The flow velocity measuring device 10 is arranged such that the axis of the coil is parallel to the flowing direction of the upward reversal flow 11 of the molten steel supplied from the immersion nozzle 9 into the water-cooled mold 12, and the secondary coil 2 a moves upstream and the secondary coil
The tundish 8 is suspended at the bottom of the tundish 8 so that 2b is located downstream (the tundish 8 may be arranged directly above the meniscus by another method). Low carbon aluminum killed steel discharge port diameter 70mm,
Injected into a water-cooled copper mold 12 through an inverted Y-shaped immersion nozzle 9 with a discharge angle of 45 °, and with a drawing speed of 1.8 m / min, a thickness of 250 mm
A slab having a width of 1400 mm was continuously cast. During this time, an alternating current of 5 A, 2 KHz was applied to the primary coil 1 of the flow velocity measuring device 10 to form a magnetic field, and the meniscus flow velocity of the molten steel was measured. FIG. 8 shows an example of the measurement result.

In the uppermost column in FIG. 8, the electromotive force difference between the secondary coils measured in the relationship between the flow velocity v and the electromotive force difference shown in FIG. 4 is introduced without correcting the meniscus position l. FIG. 8 shows the result of calculating the flow velocity v. The middle column in FIG. 8 shows the relationship between the distance 1 and the electromotive force shown in FIG. 5 by introducing one measured electromotive force of the secondary coil. The lowermost column of FIG. 8 shows the calculated meniscus position l, and the correction operation corresponding to the calculated meniscus position l [the above (2)
Equation] is shown.

When the meniscus flow velocity is directly calculated from the difference between the electromotive forces induced in the upstream and downstream secondary coils, the meniscus flow rate is affected and the meniscus flow velocity cannot be measured with high accuracy (the uppermost column in FIG. 8). ). On the other hand, from the value of the meniscus position obtained from the electromotive force induced in any one of the secondary coils (the middle column in FIG. 8), the meniscus flow velocity is stably calculated from the electromotive force difference corrected using the equation (2). Highly accurate meniscus flow velocity measurement was possible (bottom column in FIG. 8).

〔The invention's effect〕

As described above, in the present invention, non-contact flow velocity measurement using electromagnetic action is performed, so that a problem such as adhesion of metal to the measurement apparatus or burning of the apparatus is prevented, and stable continuous measurement for a long time is performed. For example, in continuous casting or the like, it is possible to manufacture a good cast piece with less nonmetallic inclusions.

In addition, the device according to the present invention is compact because it is non-contact, has low equipment costs, is easy to maintain, and has a long life.

[Brief description of the drawings]

FIG. 1, FIG. 2, and FIG. 3 are explanatory diagrams for explaining the principle of the present invention. FIG. 4 is a graph showing the relationship between the flow rate of the molten metal and the difference between the electromotive force induced in each of the secondary coils 2a and 2b shown in FIGS. FIG. 5 is a graph showing the relationship between the electromotive force induced in each secondary coil by the distance l between the secondary coils 2a and 2b and the free surface of the molten metal. FIG. 6 is a block diagram showing a configuration of a molten metal flow velocity measuring device in which the present invention is implemented as an example. FIG. 7 is an explanatory diagram showing an application example of the device shown in FIG. FIG. 8 is a graph showing the results of actual measurement and calculation of the meniscus flow velocity in the application example of FIG. 7, and the uppermost column shows the meniscus flow velocity v calculated without correcting the distance l fluctuation, and the middle column. Indicates the calculated distance l, and the lowermost column indicates the meniscus flow velocity v calculated by performing a correction related to the calculated distance l. 1: Primary coil (primary coil) 2a, 2b: Secondary coil (first and second secondary coils) 3: Free surface of molten metal, 4: Line of magnetic force 5: AC power supply (AC power supply) 6a, 6b: Voltage sensor (first and second voltage detection means) 7: Flow velocity calculator (calculation means) 8: Tundish, 11: immersion nozzle 10: Meniscus flow velocity measuring device for molten metal 11: Meniscus flow, 12: Mold 13: Shell, 14: Powder 15: Distance calculator

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01P 5/08 G01F 1/58

Claims (3)

(57) [Claims] 1. A primary coil is disposed immediately above a meniscus having a flow directly below a free surface in parallel with a flow direction thereof, and secondary coils are disposed on both sides in a horizontal direction of the primary coil, and an alternating current is applied to the primary coil. In the measurement of the meniscus flow velocity of the molten metal, the secondary coil on either side is used to detect the meniscus flow velocity from the difference in electromotive force generated in each secondary coil due to the distortion of the magnetic flux due to the flow just below the free surface. A meniscus position is simultaneously detected based on the electromotive force of the molten metal. 2. The method according to claim 1, wherein the meniscus position detected from the electromotive force of the secondary coil on either side corrects an electromotive force difference generated in the secondary coils on both sides to detect a meniscus flow velocity. The method according to claim (1). A primary coil; first and second secondary coils provided on both sides of the primary coil; an AC power supply connected to the primary coil; and an AC power supply connected to the first secondary coil. First voltage detecting means for detecting electromotive force; second voltage detecting means connected to the second secondary coil and detecting the electromotive force; one of the first and second secondary coils Calculating means for detecting the distance between the secondary coil and the molten metal meniscus position based on the electromotive force generated in the first voltage detecting means; and the electromotive force of the first secondary coil detected by the first voltage detecting means; The second voltage detected by the second voltage detecting means
Calculating means for detecting a flow velocity of the molten metal from a difference between an electromotive force of the secondary coil and a distance between the secondary coil and the molten metal meniscus position;