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For Greater Aluminum Melt Flexibility, Consider Induction Melting

Jan. 1, 2018
Among the available options, induction melting promotes greater purity and uniformity in finished products

There is high demand for aluminum across many industries, and that is creating greater demand for efficient aluminum melting processes. While fuel-fired furnaces such as gas-fired (reverb) and gas and electric crucibles have been go-to solutions for decades, there are now benefit-rich melting options, such as induction furnaces that should be seriously considered.

Induction melting — Induction, for example, is a viable option for practically all aluminum melting applications that offers many advantages over conventional aluminum melting furnaces, including operational flexibility, high efficiency, better alloy recovery and a higher-quality result.

Induction melting of aluminum works by placing conductive material within the magnetic field of a coil energized by alternating current. The current flows through the material, generating heat. This current induces Ohmic heating and an electromagnetic stirring of the metal into a highly homogenous mix with precise control. In recycling applications with lightweight scrap such as chips or used beverage cans (UBCs), the natural stirring action reduces exposure to process oxides that cause oxidation to pre-melted aluminum. Special care should always be taken when melting UBCs to ensure that they are properly shredded and de-lacquered prior to melting. Reducing exposure and oxidation is critical to producing high-quality alloys and achieving maximum metal recovery. For casters, for example, an increase in alloy quality in castings results in greater product consistency and low rejection rates.

Induction melting is ideal for the highly thermal and electrically conductive properties of aluminum, allowing efficient heat generation and transfer. Since energy is delivered directly to the aluminum molten bath and heat is not stored, induction produces the best thermal regulation of all aluminum melting options. Compared with fossil fuel-fired furnaces that are 20-30% efficient, induction furnace efficiencies range from 60-92% depending on the type of furnace. This efficiency depends on the heat source being the aluminum itself or the crucible. Another efficiency factor is the ability to run small batches that can result in less holding power and less refractory losses. The smaller furnace footprint and smaller batch size capabilities make different alloy production and changeovers less complicated. Furnace shutdowns and startups are easily and cost-effectively accommodated.

Induction melting permits a high degree of purity and uniformity in the end product. A cleaner melt allows recycled aluminum scrap to be used in applications where primary or secondary ingot was previously specified.

Fossil fuel-fired furnaces — In comparison, a gas-fired furnace is a refractory-lined box with gas burners designed to heat the surface of the metal indirectly by focusing heat to the roof of the furnace. The downside is inefficiency as metal chips typically oxidize before they can be melted, causing the metal recovery percentage to be low. Other downsides to fuel-based furnaces include:
• Gas entrapment;
• Temperature control more difficult to maintain; and
• Added cost through the use of launder systems to deliver molten metal to casting stations or die-cast machines.

Often, electromagnetic pumps (EMPs) are attached to improve metal recovery so that the liquid metal is pumped through the side wall into a cylindrical well and flows back from the well into the furnace.

Induction-based options — A recent advance in induction melting is the Direct Electric Heat (DEH) furnace with an air-cooled induction coil that directly heats an electrically resistive crucible. The patented Acutrak® furnaces deliver electric energy via a coil into a silicon-carbide crucible. These furnaces do not provide inductive stirring options and therefore are not ideal for chip melting. They are, however, extremely efficient furnaces to melt ingots and foundry returns. The Acutrak® furnace is ideal for diecast, permanent mold, and aluminum foundry operations.

Given silicon carbide’s high resistivity, the coil current frequency ensures that 95% of the energy is released in the crucible wall for even greater efficiency. It uses a special conductor that replaces traditional copper tubing to deliver exceptionally high efficiency of approximately 97.5%. It also minimizes the loss of metal to dross.

In addition to DEH systems, there are many induction-based furnaces available that target a variety of applications including those that provide rugged use and high-power density melting in aluminum foundries, or that combine the exceptional strength of a rugged steel shell with easy accessibility, ideal for melting a wide range of metals. These induction furnaces are the workhorses of large secondary aluminum producers, recyclers, and aluminum foundries.

Induction produces a high-quality metal with low levels of inclusion and porosity. With the constant motion of the metal in the induction setting, the metal is cleaner and alloying materials mix in completely for more homogenous alloys. The process is quiet with no combustion noise and delivers high productivity. Electricity heats the charge and not the environment, so the melt shop is a more comfortable and more productive workplace.

The induction advantage — Precisely controllable, induction melting is increasingly turned to when processing today’s highly engineered materials. The unique capabilities of induction technology offer engineers and designers a fast, clean and efficient melting method to meet growing demands.

Inductotherm has nearly 1,200 aluminum installations and has had many success stories of how induction can truly offer benefits that other melting methods simply cannot. Snapshots of Inductotherm’s success include:
• A leading manufacturer of high-quality aluminum alloy uses induction melting to produce pistons that meet global stringent quality standards;
• An aluminum foundry in the Midwest melts chips in its three 14,000-lb. furnaces powered by a 1,500-kW, 60-Hz solid-state power supplies;
• Another industrial company uses seven 2,200-lb. Direct Electric Heat (DEH) furnaces to produce finished aluminum alloy parts;
• A highly automated melt shop employs clean and quiet induction melting in its melt-shop automation configuration.

While Inductotherm does not get into the process side of aluminum melting—understanding metallurgy is key to ensuring our products performance as promised. Hydrogen control is critical to aluminum melting as molten aluminum can absorb hydrogen from the atmosphere, which can cause porosity in the castings. Whether you use induction, gas-fired, oil-fired, electric resistance furnaces, or stack melters—aluminum will most likely have to be treated after melting. The level of post-treatment typically depends on the operation and the application, and can range from filtering, degassing, or grain refining. With induction, post-treatment often can be reduced. It is for this reason, that Inductotherm induction systems can be designed with very light stirring or very heavy stirring simply by changing the frequency, furnace size, and power.

Inductotherm’s experts acts as consultants to the industry and take the time to listen to what each potential customer wants to achieve before recommending an aluminum melt system that is properly sized and rated. With over 60 years of induction melting experience and more systems operating around the world than any other manufacturer, Inductotherm’s expertise in induction furnace technology, product support and comprehensive training services represent the lowest total-cost choice for melting aluminum and other non-ferrous metals.  

Michael Nutt, is Director of Sales for Inductotherm Corp. Contact him at [email protected], or visit