JPS6220283A - Induction heating control for continuous casting - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for controlling induction heating, and more particularly to a method for protecting an induction furnace in controlling the temperature of molten steel in a tundish for continuous casting.

B1 Overview of the Invention The present invention provides a system for controlling the temperature of molten steel by controlling the power input to an induction furnace attached to a tundish, in which the power supplied to the induction furnace has a different limit value depending on when the induction furnace is formed, when the ladle is replaced, etc. This restriction was designed to protect the induction furnace and stabilize its operation.

C1 Prior Art The surface quality of slabs in continuous casting is affected by the temperature of the molten steel in the tundish. Therefore, it has been conventional practice to continuously measure the temperature inside the tundish and the steel, monitor the casting temperature, and adjust the heating amount of the induction heating furnace.

To control the temperature of molten steel in the tunnel, as shown in Fig. 3, an induction furnace IA is attached to the Kunditsha 1, and the inductor 2 of the induction furnace IA is connected to an electric power source consisting of an inverter INV, a converter CON, and a power factor adjustment capacitor C. AC power is supplied by the converter 3, and the control device 4 feedback-controls the output power or voltage of the power converter 3 according to the input power command Es for input power to the induction furnace IA. The input power command Es is set by a temperature feedback system in which the input power calculation section 7 calculates the input power from the detected temperature Or of the molten steel 6 by the continuous thermometer 5 and the target temperature O8.

It should be noted that feedback control of the molten steel temperature is difficult during unsteady conditions such as starting pouring or replacing a pot, and in unsteady conditions the input power command Es may be set by program control.

D Problems to be Solved by the Invention The induction furnace IA installed in the tundish 1 uses a cast steel template as the core and coil of the inductor 2.

The template is cased with a refractory together with a water-cooled jarret, etc., and the template is heated by supplying power to the inductor 2 to sinter the refractory around it. Thereafter, metal is poured into the tundish 1 from the ladle, and the electric power input to the induction furnace IA is increased to melt the template and heat the molten steel.

In such conventional induction furnace formation and molten steel heating methods, a sudden rise in the heating temperature immediately after sintering the refractory may cause cracks or increased wear in the refractory. There were problems that led to breakdowns and shortened service life. Induction furnace failures not only have a serious impact on the quality of slabs, but can also cause operational accidents such as breakouts and nozzle clogging.

Means for Solving Problem E1 In view of the problem described in -1-, the present invention provides that the power input to the inductor is determined by the limit value during refractory sintering and the casting stop period, and the first time from the ladle to the tundish. pouring hot water.

The limit value is set for each pouring period from the second time onwards.

By setting various limit values for the F1 action, sudden changes in the temperature of the refractory are avoided, the occurrence of cracks, etc. are prevented, and the temperature of the molten steel is quickly established.

G. Embodiment FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention. The difference between this figure and FIG. 3 is that a limiter circuit 8 is provided. The limiter circuit 8 is the calculation result E of the input power calculation section 7.
The input power command Es, which becomes O, is configured to set the input power limit at the time of forming the induction furnace and the minimum input power before pouring from the ladle.

This limiter circuit 8 has a minimum input power value set by a setter 8A, and limits the input power command Es with the characteristics shown in FIG. In FIG. 2, the horizontal axis shows the calculation result Eo of the input power calculation unit 7, and the vertical axis shows the input power command Es that becomes the output of the limiter circuit 8. When the input Eo is less than zero, the input power minimum value Eso is output, and if input Eo is positive, ESI,
ES2. The output Es is obtained with three limit values of ES3.

The first limit value Es, limits the power input during the first pouring of molten steel from the ladle when heating the molten steel immediately after forming the refractory in the induction furnace 1Δ, and the second limit value Es2 limits the power input from the second time onwards. The input power is limited during pouring, and the third limit value P, s3 is used to limit the input power during normal operation.

For example, when attaching a 100 OKW induction furnace to an 8-ton melting unit and installing a 100 OKW current inverter (maximum rating 15QQKW) in the power converter 3, the minimum input power Eso is 100KW, and Es, = 350KW.
, Es2=750KW.

Set Es3=100OKW.

By providing such a limiter circuit 8, the minimum input power Es is set for sintering to form a refractory.

Power is turned on for about an hour at In order to protect the refractory from the second time onwards, since the refractory is at a relatively high temperature, we set a high limit value Es2 to protect the refractory. P.S.

Improve controllability of molten steel temperature within the induction furnace's power rating range. In addition, during the refractory sintering before the first pouring and during the stoppage time of continuous casting (EO = 0), the lowest value Eso is set to compensate for the heat radiation from the surface of the induction furnace to prevent the refractory from cooling. This will speed up compensation and resumption of casting.

In addition, although the example shows the case of molten steel temperature control by temperature feedback control, this can be applied to a control method in which program control is performed at unsteady times such as starting pouring or replacing the pot, and switching to feedback control at other steady times.

=7- Moreover, it goes without saying that the limiter circuit 8 is realized by computer processing or analog calculation means together with other control means such as the calculation section 7.

Effects of H9 Invention As described above, according to the present invention, input power is limited according to operating conditions including refractory sintering for forming an induction furnace, thereby reducing failures of the induction furnace and extending its life. However, it is effective in stabilizing operations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention, FIG. 2 is a characteristic diagram of the limiter circuit shown in FIG. 1, and FIG. 3 is a block diagram of a conventional device. I... Tanditsh, IA... Induction furnace, 2... Inductor, 3 Power converter, 4... Control device, 5... Continuous type thermometer, 6... Molten steel, 7... Input power calculation unit, 8・
...Limiter circuit.

Claims (1)

[Claims] In induction heating control in which an induction furnace is attached to a tundish and refractory sintering, template melting, and heating of molten steel in the tundish are performed by controlling AC power to an inductor attached to the induction furnace, input to the inductor is performed. Electric power is the limit value for refractory sintering and casting stop period,
An induction heating control method in continuous casting, characterized in that the induction heating control method in continuous casting is characterized in that the induction heating control method is performed by setting limit values respectively in the first pouring period from the ladle to the tundish pouring period and the second pouring period and thereafter.