STEEL

METAL LEVEL CONTROL IN A CONTINUOUS

MACHINE TUNDISH

Yu~ A . Sv i r idov , A . S. Oganesov , and V . N . Pyatkovsk i i

CAST ING

UDC 669.185.1:62L746,5.047

One of the conditions for obtaining high-quality semifinished products in the continuous casting of steel on a continuous casting machine (CCM) is stabilization of the level of the metal in the tundish. A constant static head of metal to be poured into the mold and the removal of cases and nonmetallic inclusions from the molten metal are achieved with a constant metal level in the tundish.

On a modern CCM, metal is poured into the tundish from steel ladles equipped with slide gates operated by a hydraulic servo. The operation of the slide gate is characterized by the following features. The gate can completely cover the working orifice of the steel ladle or leave it fully opened, correspondingly allowing a change in metal flow from zero to maximum. The gate can also occupy an intermediate position, at which the metal flow is insufficient to thoroughly heat the edges of the slide gate. The edges cool down and the through section of the slide gate begins to become closed with solidified metal, until metal flow ceases completely. This is an emergency situation. To avoid such occurrences, it is necessary to operate the gate in a two- position mode (open- closed), with the servo moving the gate through the range where closing up of the through section of the gate is possible at the maximum possible speed. In the working range of the gate, where closing up is eliminated, the gate may be stopped in any position, e.g. may operate in a mode of continuous control.

A system of automatic control of the metal level in a tundish which takes into account the features of slide gate operation was developed by the Central Planning and Design Office (CPDO) Soyuzpromavtomatika and its Lipetskii branch and put into operation on continuous slab casters at the Novolipetskii Metallurgical Plant.

The systems made use of control mechanism RP2. The position of the beginning of the range of gate movement over which closing up of the gate through section may occur is determined with a tappet switch. The automatic control system operates in the range from the fully open position to the tappet switch position according to the proport ional- integral (PI) law of control, and in the range from the tappet switch to the fully closed position of the gate according to the two-position law of control.

Production has now begun of unitized electrical control equipment system (UECES) devices possessing a number of qualities which distinguish them advantageously from earl ier-produced electronic control devices. The use of UECES devices in control systems has been determined to be expedient by virtue of their high reliability, greater number of possible functions, and small size, which is essential for CCS control stations. On the basis of UECES devices, CPDO has developed an automatic control system for the metal level in a tundish. Figure 1 shows a block diagram of the system.

The metal level in a tundish is proportional to the mass of the molten metal it contains and is measured with gravimetr ic gauges (load cells) placed underneath the tundish. The type of load cell used depends on the design and capacity of the tundish. A 0-5 mA dc signal proportional to the metal level is sent from the load cell (not shown in the diagram) to the input of an RBI2-Sh control pulse block with discrete automatic control. The control point is established by means of manual control-point-sett ing mechanism RZD. Adjustments of the controlblock define the effeciency of the P and I gate control components. Control pulses from the control block are sent through manual control unit BRU-3K (automatic remote-control mode selection) to contactless reversing starter PBR, which effects reverse control through block BU of the gate servo SP. The intermediate

Central Planning and Design Office (TsPKB), Lipetskii Branch. Translated from Metallurg, No. 6, pp. 27-28, June, 1977.

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Fig. 1. Block diagram of automatic control of metal level in an MNLZ tundish.

gate position tappet switch PV (which is closed within the range of gate movement over which closing up of the gate through section is possible) is connected to the inputs of coupling rate (transfer constant) and integration time discrete remote control block RBI2-Sh. With closing of the tappet switcht the coupling rate and integra- tion time settings are automatically diminished and the control block shifts to the two-position control mode. When the PV is opened, the control block reverts to the PI control mode with the earl ier-established settings.

The system may be realized in both the instrument and cabinet variants of a UECES device.

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