JPS6027459A - Device for preventing corrosion of current-conducting roll and billet - Google Patents

Abstract

PURPOSE:To prevent corrosion at the contact point between current-conducting rolls and a billet in electrostatic stirring with a static magnetic field for continuous casting by detecting the fluctuation in the contact resistance between said rolls and the billet and limiting the current when the contact resistance exceeds a reference value. CONSTITUTION:Electric current is passed to a billet 1 by current-conducting rolls 2, 2' in a secondary cooling zone to stir electromagnetically the unsolidified metal of the billet. The analog signals for current I and voltages AE, BE are inputted to an arithmetic part 9 to which line resistance values 7, 7' are inputted by a setter of an arithmetic part 9. The arithmetic part compares the contact resistance of the rolls 2, 2' detected at all times during operation with the set value and emits a command C to a control part 8 to limit the current when said value exceeds the set value. When the contact resistance decreases, the output power is increased to control the contact resistance so that the corrosion is obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energizing roll that energizes a slab and a device for preventing erosion of the slab during static magnetic field electromagnetic stirring in continuous casting.

In order to improve the center segregation or center porosity of slabs in continuous casting, a technique of electromagnetically stirring the unsolidified portion during casting is widely used.

Furthermore, a static magnetic field electromagnetic stirring device has also been developed in which a current is applied to the slab during electromagnetic stirring in the drawing direction or cross-sectional direction.

In this static magnetic field electromagnetic stirrer, the slab is energized as part of an electric circuit via an energizing roll, so there is no risk of oscillation marks, scale, or powder adhesion on the slab surface.
Alternatively, due to fluctuations in the pressing force or the like, stable contact of the energizing roll cannot be obtained, and sometimes energization may become impossible. Furthermore, if the contact resistance becomes high, Joule heat may cause melting damage to the rolls and slabs, resulting in surface flaws or metal transfer. Furthermore, if a flaw is formed on the surface of the roll, the contact with the slab becomes even more unstable, resulting in an increase in melting loss by approximately 1 acceleration.

This invention was made in order to deal with these drawbacks, and its gist is to provide a cast iron that is constructed so that an electric current flows through the slab as part of an electric circuit from a predetermined roll in the secondary cooling zone of a continuous casting machine. In electromagnetic stirring of solidified molten metal, the contact resistance between the energized roll and the slab is detected, and if the contact resistance increases from a standard value, the current is increased to a current value that does not cause melting damage at the contact point between the energized roll and the slab. It is characterized by a restriction.

In static magnetic field electromagnetic stirring, a constant current is passed through the slab to keep the stirring force constant. For this reason, the power supply device is controlled with a constant current, and even if there is a variation in the contact resistance between the current-carrying roll and the slab, the current value does not vary and only the voltage varies up to the upper limit of the output voltage of the power supply device.

The power consumed by the contact resistance causes melting damage at the contact point between the current-carrying roll and the slab. If the contact resistance is low and the current is stably applied, it is thought that melting damage will not occur or will be negligible, so if the power consumed at the contact point is kept below the stable current value, melting damage of the roll and slab can be avoided. It doesn't happen.

The power consumed at the contact point is given by the following equation (1).

W=I”R・・・・・・・・・・・・・・・・・・
...... In order to keep it constant, the current may be limited as shown in equation (2) below.

■ Here, I'-Limiting current R': Contact resistance when increasing In contrast to the increase in contact resistance, if the time until current limitation is long, the amount of erosion increases as a time product. It is better for the response time to be as short as possible. Furthermore, since limiting the current reduces the stirring power, it is necessary to flow the current to a limit that does not cause melting damage.

From the above points, control using an arithmetic unit (analog or computer) is appropriate in terms of numerical setting and response speed.

FIG. 1 is a diagram showing an embodiment of the present invention.

(2) is a slab, (2), (2> is an energized roll, (3)
is AC power supply, (4) is rectifier, (5) is ammeter, (6)
is the voltage needle, (n, <i> is the line resistance, and (8) is the control unit. As shown in the figure, since the slab (1) is at ground potential, the contact resistance of the current-carrying roll is as follows (3). ), (
4) Detected by Eq.

■ Here, the voltage between AE: 00 and the voltage between BE: 00 ■: Current R,, R,: Line specific resistance AR': Contact resistance of the energizing roll (2) BR': Contact resistance of the energizing roll (2), that is, In the figure, the voltages ■ and ■ and the current ■ are calculated by the calculation section (9
), and detect the contact resistance of the energizing roll (2), (6+) using equations (3) and (4) above, and if the value is higher than the reference value, apply the current calculated using equation (2) above. This is to give an instruction ◎ to the control unit (8) to limit the amount.

The analog signals of current ■, voltage (@ and (D)) are processed by the calculation section (
9), and the line resistance value (7) is input by the setting device of the calculation section (9). The current limit starting point can be determined by inputting the rate of increase from the contact resistance (for example, 120%) or resistance value in the setting device when stable current is applied. The contact resistance is compared with the contact resistance constantly detected during operation, and if the resistance value is higher than the memory value or set value, a signal is sent to limit the current to a current that can be passed without melting. The output current of the power supply device is reduced, and if the contact resistance is reduced, the output power is increased.

This inventive device was applied to static magnetic field electromagnetic stirring of SW 480 (Cr-based stainless steel) continuous sweep casting.

The implementation results are compared with the conventional method and are shown in Table 1.

(Leaving space below) Table 1 Number of stubbatter defects (one slab surface only) However, line resistance = 0.18 mΩ Standard contact resistance = 0.28 mΩ As shown in Table 1, the contact resistance increase rate setting value is set to 120.
As a result of carrying out the test with settings of 180 and 140, the number of erosion flaws was greatly improved compared to the conventional method.

As described above, this invented device prevents melting damage that occurs on the energized roll and slab surface of static magnetic field electromagnetic stirring in continuous casting, and has a great effect on improving the quality and yield of slabs. There is.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention. In the figure, l... Slab, (2), (2)... Current roll, 3... AC power supply, 4... Rectifier, 5... Ammeter, 6... Voltmeter, (7) , (i)...Line resistance, 8...Control section, 9...Performance section.

Claims (1)

[Claims] During electromagnetic stirring of unsolidified molten metal in which an electric current flows through the slab as part of an electric circuit from a prescribed roll in the secondary cooling zone of a continuous casting machine, fluctuations in the contact resistance of the current-carrying roll E slab are detected. An apparatus for preventing erosion of a current-carrying roll and a slab, characterized in that, when the contact resistance increases from a reference value, the current is limited to a current value that does not cause melting damage at the contact point between the current-carrying roll and the slab.