Application

DESCRIPTION

The Electromagnetic Mold Level Detector consists of an electromagnetic sensor fastened to a mold top, a preamplifier, an evaluation unit and (if necessary) a mold oscillations reader.

The detector can be utilised for:

• slab casters and twin-casters, if the slab size is bigger than about 600 × 100 mm. Mold copper plates can be plated by chrome or nickel.
• billet and bloom casters with assembled – type molds and tube-type molds of 160 × 160 mm size or bigger, if submerged entry nozzle and casting powder are used, if mold upper flange is designed in such a way as to enable the sensor to be in a contact (through insulation gasket) with a top of copper and if an upper part of the mold tube is cooled well.

For other molds it is necessary to discuss the feasibility with the producer.

Modifications of the mold and the mold cover with respect to sensor installation are mostly negligible.

PRINCIPLE OF THE LEVEL MEASUREMENT

• electromagnetic field generated by exciting coil induces eddy currents in molten steel and surrounding conductive parts. Distribution of electromagnetic field of eddy currents depends on change of steel level in the mold. This field induces a voltage in sensing coils. The changes are read by sensing coils, the induced voltage is amplified and then processed in the evaluation unit.
• the frequency of the electromagnetic field ensures sensitivity of the Electromagnetic Mold Level Sensor only to changes in molten steel level regardless of a molten slag and casting powder layer thickness on the surface of molten steel.

SENSOR DESIGN

• for slab caster a beam-shaped sensor is used. It is fixed to the mold top by sensor cover as a clamp.
• for bloom casters frame-shaped or universal electromagnetic sensors are used. The frame-shaped sensor has inner dimensions identical with those of a mold top. The universal sensors consist of two universal beam-shaped sensors and two passive inserts that match the frame to a mold shape. One pair of universal sensors may be used for wide scope of mold sizes and shapes.
• each sensor is equipped with a heavy-duty flexible cable with a connector. Depending on local conditions it is possible to split the cable by intermediate connector placed on the mold or next to the mold. The short movable sensor cable can make sensor handling easier.
• protection of the sensor against damage caused by a short-term overflow of steel is ensured by an efficient water-cooling of the sensor body and by special design of the sensor cover. In spite of that, after a long-term overflow the coils, sealings etc. inside the sensor can be damaged. The sensor is designed in such a way that it is repairable nearly regardless of the damage extent.

ELECTRONICS

• the preamplifier is placed in a sheet-metal junction box (protection IP 55) at the distance of maximum 10 m from the sensor
• the evaluation unit is built-in into one 19" rack. It is equipped with an auto-diagnostic system, an alpha-numerical display and a keypad for setting-up of parameters and other functions.

CALIBRATION

The manufacturer provides for basic calibration of each mold level detector before shipment.

This calibration is checked during commissioning on site and the parameters can be slightly modified so that the magnitude of sensor signal for nominal meniscus level corresponds to the value required by the customer. This value can be checked with an aluminium simulating plate, e.g. after mold change or after a sensor change. This check is not necessary before start of casting.

Before start of casting no calibration is required. Only the remote zero setting AUTOSET procedure must be executed, preferentially by PLC.