Introduction of neutral ramming mass for induction furnace
An induction furnace consists of a nonconductive refractory crucible, surrounded by a coil of copper tubes. Running a powerful alternating current through the coil creates a magnetic field that induces electric currents inside the metal and quickly melts the charge inside the furnace by Ohm effect. The coil is made of hollow copper tubing in which cooling water flows. The water picks up the heat conducted from the bath through the refractory lining, and is then recirculated through a heat exchanger. Proper and well – maintained refractory linings are important for a safe operation of the induction furnace. The physics of electrical induction demand that the refractory lining be as thin as possible. At the same time it must be thick enough to fully protect the coils and prevent metal run out due to corrosion and mechanical shocks. Assuring that the furnace lining remains within the manufacturer specified limits requires careful usage of the lining during operation as well as inspection and monitoring procedures.
Refractory linings used in induction furnace are commonly made of acidic (Silica) or basic (Magnesia) compounds. Choosing the right refractory material
for a given melting or holding application is important. The selection of a refractory lining depends on many factors such as melting temperature, holding time, volume, inductive stirring, additive & alloying agents, etc. Considering that magnesia has a poor thermal shock resistance and silica-based linings are quickly corroded. So the new eneration concept is the Neutral Ramming Mass
(NRM). It is mainly composed of Al203, with MgO addition in the matrix, which results in in situ spinel formation (MgO.Al203.) at steel melting temperature. The in situ spinel formation is associated with a significant volume expansion and provides a rigid structure. It also provides a hard sintered refractory surface layer to the metal bath, leading to a good resistance to erosion. The inner refractory layer will remain in powdery form. If the hot face erodes, the next inner layer is exposed to higher temperature and sinters in turn by in situ spinel formation.