Induction Furnace And Charging Material
The induction furnace is a very important equipment for small metal producers, induction furnace is easy to install, operate and maintain. Induction furnace is smaller in heat size with a low cost investment and preferred by lower capacity steel plants. In these furnaces, steel is produced by melting the charge material using the heat produced by electromagnetic field.
The induction furnace consists basically of a crucible, power unit (IGBT), transformer, inductor coil, and shell, cooling system and tilting mechanism. The crucible is formed from refractory material, which the furnace coils is lined with. This crucible holds the charge material and subsequently the melt. The choice of refractory material depends on the type of the charge and basically consist of either acidic, basic or neutral refractories.
The shell is the outer part of the furnace. This houses the crucible and the inductor coils, and has higher thermal capacity. It is made of rectangular parallelepiped with low carbon steel plate and joined at the corners by edge carriers from angular pieces and strips of non-magnetic metal.
The cooling system is normally a through one way flow system with the tubular copper coils connected to water source through flexible rubber hoses. The cooling process is important because the circuit of the furnace appears resistive, and the real power is not only consumed in the charged material but also in the resistance of the coil. This coil loss as well as the loss of heat conducted from the charge through the refractory crucible requires the coil to be cooled with water as the cooling medium to prevent undue temperature rise of the copper coils.
The induction coil is a tubular copper coil with specific number of turns. An alternating current (AC) passes through it and magnetic flux is generated within the conductor. The magnetic flux generated induces eddy currents that enable the heating and subsequently the melting process in the crucible.
Raw materials and energy source
Steel melting scrap, direct reduced iron and pig iron/cast irons are the input raw materials for an induction furnace. The ratio of these items and the technology of melting these input materials varies according to the availability of raw materials and location of the plant. Further selected raw materials is required for the production of specific quality steel. For better and efficient operation of melting in induction furnace, raw material charge must fulfill the following criteria.
It must be clean. Rust, oil, grease, and sand etc. should preferably be nil.
There are no or less sharp pointed edges, particularly in case of heavy and bulky scrap.
It must be segregated from harmful ingredients like explosives, closed containers, evaporative substances and readily available in chargeable sizes on the shop floor.
It must be metallurgically clean, i.e. free from slag lumps, oxides etc., particularly for direct reduced iron, skull and ferro alloys.
It must be as dense as possible. Compaction of scrap is important for ensuring uniform and rapid heating as well as for energy saving.
Electricity is the only energy source for steel melting in the induction furnace. Induction furnace is to run at maximum power since beginning. There are some misconception of running furnace at low tap initially and then gradually increase to higher tap. Maximum power input increases rate of melting and hence reduces cycle time of a heat. Power factor to be maintained near to one.
Drop of voltage from the source also to be monitored for better energy efficiency. Further power consumption rate is dependent on the furnace size and it is lowered as the furnace capacity is increased approximately up to 15 to 17 tons and thereafter consumption rate remains almost constant at around 600 kWh/ton.