Power-converting induction melting for aluminium alloys – Inductotherm

The first induction furnace to use an air-cooled coil achieves total energy efficiency of 92-94%, a rate never before achieved in either electric or gas-fired melting.

Standard aluminium melt furnaces, including electrical resistance (ER), induction, and fossil fuel-fired furnaces continue to be options for melting aluminium. Inductotherm Corp is offering a new method for melting aluminium and other non-ferrous metals that, in many applications, will melt metal quicker, cleaner and more efficiently.

The Acutrak® system with direct electric heat (DEH) technology is well suited for foundries, permanent mould casting and die-casting operations.

Prior to the introduction of this new furnace, foundries and die-casters had to rely on inefficient and costly ER and fuel-fired crucible furnaces, or refractory-lined reverb furnaces, to melt and hold aluminium for casting. In conventional induction furnaces, the magnetic field couples to the metal inside and the metal itself gets heated. In an Acutrak® DEH furnace system, the crucible conducts the electric current, becoming a resistive load for the system.

Acutrak® is a revolutionary induction melting furnace, the first in the industry to use an air-cooled coil. The total energy efficiency for the furnace is very high at 92 to 94%, which according to the company has never been achieved before by any other electric or gas-fired furnace. The system can transfer 94kW to the crucible to melt metal for every 100kW drawn from the utility line and is applied to the crucible for melting.

The DEH technology uses a silicon-carbide crucible, which provides faster, cleaner and more efficient melting and when combined with the Acutrak® furnace, it is able to apply electrical energy directly into the crucible. The metal is heated evenly and to a precise, preset selectable temperature with minimal overshoot by way of an immersion metal bath thermocouple, which is coupled to a digital temperature controller. This clean induction technology provides exceptional metal recovery and quality at the required casting temperature for their process.

Due to the fact that 95% of the power is concentrated in the crucible, the electromagnetic forces formed in the liquid metal are very low, therefore, the stirring effect is minimised. This reduces the disruption of the protective oxide layer on the surface of the molten bath and prevents contact of high temperature aluminium with oxygen. Thus, inclusion and dross formation, which is a result of oxidation, is greatly reduced along with metal loss.

The Acutrak® system uses a special, patented furnace coil coupled with the high resistance of the silicon-carbide crucible. By comparison, conventional ER furnaces that use fragile element panels cause a loss of production when they fail. Due to the reduction of the melt rate, the kilowatt rating of a traditional ER furnace drops with each panel failure. This decrease creates a domino effect making the functioning elements work harder to compensate for the failed panels. A complete shutdown of the furnace will need to be scheduled to replace the expensive element panels, compounding the production loss. Another by-product of this scenario is the reduction of crucible life from the ‘cold spots’ caused by element panel failure. The patented furnace coil on the Acutrak® system ensures excellent transfer of energy into the crucible, avoiding production loss.

The furnace provides precise temperature control via two thermocouples placed inside and outside the crucible. Since temperature control is achieved as only the crucible and the metal are heated, there is no stored excessive energy retained by heat-soaked furnace walls, tiles, refractory or insulations. Furthermore, when the molten metal temperature hits the desired set point, power is cut off by the automatic temperature controller, ensuring it remains within the required temperature range. This makes it possible to attain a melt temperature with a precision of 5 to 7°C.

One of the unique features of the Acutrak® system is that it is completely air-cooled. The power supply and the furnace body are cooled by forced airflow. Low furnace losses make water cooling for the induction coil unnecessary as is commonly required by induction furnaces. In addition, the air-cooled system does not require the excessive insulating materials needed by gas-fired and ER furnaces.

The furnace also provides the operator with a comfortable work environment. There is no excessive noise or heat generated by the exhaust from an Acutrak® system. Tasks such as hand ladling, adding ingots and scrap materials to the furnace are made easier with the smaller width of the exterior walls.

The Acutrak® DEH system is currently available in stationary and tiltable versions, with three capacities. A 300kg unit with 100kW power supply, a 500kg model with 125kW power supply and a 1 000kg unit with 150 kW power supply. With an integrated power supply, the furnace is compact and requires minimal time, effort and cost to install. Its rugged construction assures high reliability.

For more details contact Cerefco on TEL: 011 845 3253 or visit www.cerefco.co.za or www.inductotherm.com