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[Technology] Classification and selection of furnaces for smelting non-ferrous alloys (1)
Metal smelting is a critical step in the casting process, directly influencing the quality of the final cast product. This stage plays a vital role in liquid metal casting and molding, as it significantly impacts the quality, production cost, output, energy consumption, and environmental impact of the castings. Smelting furnaces are essential equipment in foundries, and selecting the right type can ensure better metallurgical quality, reduce energy use, lower costs, and improve productivity.
There are two main categories of non-ferrous alloy melting furnaces: fuel-fired and electric. Fuel-fired furnaces use coal, coke, gas, natural gas, or oil as fuel and include types like cupola and reverberatory furnaces. Electric furnaces, on the hand, convert electrical energy into heat and can be further divided into resistance, induction, and arc furnaces. Resistance furnaces may consist of muffle, reflector, or box types, while induction furnaces are categorized by frequency—industrial, medium, or high. Arc furnaces can be either non-consumable or self-consumable.
Each furnace is suitable for specific alloys. For example, the muffle resistance furnace uses electric heating elements made of materials like nickel-chromium or iron-chromium alloys, or silicon or silicon-platinum elements. These furnaces are typically used for small to medium-sized castings and have a capacity ranging from 30 to 400 kg. They come in fixed or rotating types, with fixed ones being more common due to their stability. However, they tend to take longer to melt metals, such as 5–5.5 hours for 150–200 kg of molten aluminum, which leads to higher power consumption and lower efficiency.
The reflector resistance furnace has heating elements at the top, heating the metal through radiant heat. It features a bath and one or more sloped front chambers where raw materials are placed. As melting progresses, the metal flows into the bath, and oxides remain in the front chamber. These furnaces are available in fixed or tiltable versions. Fixed models require pouring through an overflow port or a siphon, while tiltable ones allow for easier metal removal. Reflective furnaces offer advantages like stable gas conditions, reduced oxidation, and cleaner melts, making them ideal for large-scale production. However, they have limitations, such as inability to use fluxes or refine the melt in the furnace, leading to longer melting times and higher energy use.
Despite these drawbacks, reflector resistance furnaces are still widely used in some industries. However, with technological advancements, industrial frequency induction furnaces are increasingly replacing them due to their efficiency and performance. The future of smelting seems to favor induction technology, which offers faster melting, better control, and improved energy efficiency.