Choosing the Right Melting Furnace

Foundries selecting a new furnace will consider production goals, equipment maintenance, safety standards, and product lifespan, among other factors, but finally the choice will come down to identifying a furnace that can match a high-throughput target while withstanding the foundry’s harsh environmental conditions. The Heavy Steel Shell Furnace and Steel Frame Furnace (Figure 1) from Inductotherm are designed according to those guiding principles, to achieve high output and to last for years of reliable service. There are some similarities and key differences between these two furnaces.

Both furnace designs offer superior performance and outstanding durability that will meet the demanding requirements of foundry applications and environments. Each combines strength and accessibility to provide maximum furnace rigidity and strength for long lining life and serviceability. But there are distinctions.

Each furnace provides effective shunt coverage of more than 50% of the coil’s circumference which redirects the electromagnetic field into the melt (Figure 2). The shunts are carefully designed to provide positive support of the coil, held in place by multiple shunt bolts. Vertical tie rods are used to create a clamping force and hold the coil in place.

Both are designed with a high freeboard to provide extra space for solid charge materials, allowing the furnace’s optional cover to close easily as the charge melts, greatly reducing heat loss, and providing better protection and safety for the operators (Figure 3). Using a high freeboard also ensures molten metal is contained within the active section of the coil. Consistently containing the molten bath within the active section of the coil allows maximum stirring, inclusion of scrap material when nearing the end of the melt.

Every Inductotherm furnace is designed for structural strength with the aid of custom computer-aided software. Using application specific information, Inductotherm engineers will use this information to predict how the furnace will perform before it is released for production (Figure 4).

Both designs use heavy-wall, water-cooled extruded copper tubing designed especially for induction melting (Figure 5). Inductotherm engineers design coils with optimal space between turns to minimize resistance and maximize electrical efficiency, ensuring more energy goes into the melt, which results in more metal, faster. The coils are designed with space between turns to enhance their current-carrying efficiency and allow moisture to dissipate easily from the refractory, resulting in lower ground leakage. This space also eliminates the possibility of resistance losses caused by interference from the magnetic fields – a common problem in furnaces that uses closely spaced tubing.

Taking advantage of Inductotherm’s patented extended coil design, which extends the induction coils well below the bottom of the refractory, the resulting magnetic field improves furnace efficiency by coupling with the load much more evenly from top to bottom. Traditional coil designs produce magnetic fields that are especially curved in the bottom of the furnace, and the resulting stirring action is responsible for premature lining erosion in the bottom corners of the refractory, commonly known as “Elephant’s Foot Erosion” (Figure 6).

Both furnace designs have stainless steel cooling sections at the top and bottom of the power coil to provide uniform temperature gradients that extend furnace lining life.

The Steel Frame furnace has an open-frame design providing easy visibility and access to the coil, shunts, and other furnace components for scheduled maintenance or unexpected production interruptions, decreasing downtime. In contrast, the Heavy Steel Shell furnace is fabricated with a rolled steel shell, which creates what is called “Hoop” strength. The shunt bolts pass through the shell to create a clamping force, and the additional hoop strength from the rolled steel shell maximizes support for the shunts and creates a rigid structure to support the coil and refractory lining.

The inductive magnetic field exerts an outward force on the coil, causing an insufficiently supported coil to expand over time. In addition to the shunts, vertical tie rods secure the coil in place and provide high strength with flexibility, resisting refractory expansion while keeping the coil in compression. Using advanced composite materials, our coil stabilizer system locks each turn of the coil firmly in place, eliminating turn-to-turn arcing as well as minimizing distortion during tilt, pour, and lining push-out operations. All these factors result in longer lining life with each melting campaign and increased yield per melt.

The Heavy Steel Shell furnace shields the coil and shunts to protect them from stray scrap, sparks, and metal splash. Heavy steel splash shields (Figure 7) and covers bolted on to the exterior of the shell can be removed for scheduled maintenance or to reveal a service opening large enough to examine the interior components. This ensures that interior components of the shell are always protected. The Heavy Steel Shell is not only stronger than competing frame-based designs, but significantly quieter as the shell’s design characteristics will contain ambient noise within the shell.

Careful consideration of the advantages of the Heavy Steel Shell and Steel Frame furnaces will allow you to choose what is right for your foundry. The Inductotherm designs offer high efficiency, high productivity, and increased durability, adapted to specific application and production requirements, and combined with low life-cycle cost, to give you a competitive advantage for years to come.

Patrick O’Connor is a District Manager with Inductotherm Corp.