Combined furnaces are open-top type and divided with a longitudinal wall into two chambers; one for melting and the other for holding the melt. The wall is open at the bottom allowing melt to flow freely from the melting side to the holding side. Casting takes place from the holding side by submerging die-equipped coolers into the melt covered with a layer of flake graphite to burn oxygen (contained in cathodes) and to protect it from ambient air.
Melting furnaces are closed-type and typically cylindrical in shape. Melt is covered with a layer of charcoal to burn oxygen (contained in cathodes) and to protect it from ambient air. Cathodes are fed through a hatch-covered opening and melt is transferred through an airtight launder into a separate holding furnace.
Holding furnaces used in double-furnace lines are open-top type divided with a transverse wall into two chambers; a smaller one for charging melt from the melting furnace and a bigger one for holding the melt. Casting takes place from the holding side by submerging die-equipped coolers into the melt covered with a layer of flake graphite to burn any excess oxygen left and to protect it from ambient air.
UPCAST® technology for low oxygen contents
Oxygen content in UPCAST® rod is typically 1-2 ppm. The removal of oxygen from the melt is a slow process. To reach the above oxygen levels it is necessary for the melt to be in contact with the deoxidizing medium (flake graphite in combined furnaces and charcoal in melting furnaces) for a long enough time. To ensure a sufficient “dwell-time” the total furnace volume (in tons) needs to exceed the hourly production by a certain multifold.
In UPCAST® lines total furnace volumes are close to ten times the respective hourly production which exceeds the requirement with a clear margin. Flake graphite and charcoal are in the form of thick layers on top of the melt thus also acting as protective barriers against ambient air.
Clean melt and long service life
UPCAST® furnaces are lined with high alumina refractory bricks. During furnace start-up these bricks become sintered forming a hard surface preventing any mass flow through it thus ensuring a clean melt. Another important characteristic is the lining’s service life. In a well-operated furnace the time between re-linings can easily reach and even exceed 10 years.
Efficient heating with inductors and stepless power supply
Channel type inductors offer the most efficient means of heating. A single inductor in combined and holding furnaces and normally two in melting furnaces provide the heating power. Both single- and double-loop types are used. A stepless power supply and control system is used as standard. The resulting smooth power adjustment reduces energy consumption, extends inductor service life and eliminates harmonic resonances from the inductor circuit.