Types of Aluminum Melting Furnaces and Their Refractory Materials

Aluminum melting furnaces mainly include reverberatory furnaces, rotary furnaces, and induction electric furnaces. The operating temperature is usually 700–1000°C. The main reason furnace linings get damaged is aluminum penetration and erosion, so the linings are usually made of fire clay bricks, high-alumina refractory bricks, or corundum-mullite bricks. They can also be made with high-alumina castable or refractory plastic materials. Because of good operating conditions, these furnaces have relatively long lifetimes.

1. Refractory Materials for Reverberatory Furnaces

Reverberatory furnaces can be fixed or tilting types, usually fired with gas or heavy oil.

• Non-working layer: made with refractory fiber blankets or fire clay insulating bricks.
• Above the molten pool (working layer): usually built with fire clay bricks, or precast high-alumina castable blocks. They can also be cast in place or shaped with high-alumina plastic refractories.
• Molten pool layer: normally made of high-alumina bricks with >75% Al2O3. For higher purity aluminum, use mullite bricks, zircon bricks, or corundum bricks.
• Pouring spouts and channels: for strong resistance to aluminum corrosion, usually made of large silicon carbide bricks.

Other parts like holding furnaces and alloy treatment rooms use similar refractory materials. When using aluminum ingots or scrap, material can be loaded directly. For electrolytic aluminum, it is first siphoned from the electrolysis cell and then melted. Siphon tubes are lined with fiber-reinforced light castable refractories or fire clay insulating bricks, with the working layer built from dense fire clay bricks or corundum bricks. Under normal conditions, reverberatory and holding furnaces last 2–5 years.

2. Refractory Materials for Rotary Furnaces

• Non-working layer: fire clay insulating bricks or perlite bricks; can also use lightweight castables with density ~1.0 g/cm³.
• Working layer: dense fire clay bricks or high-alumina bricks (>55% Al2O3).
• Furnace life: about 300–500 batches, shorter if salt fluxes are used due to chemical attack.

3. Refractory Materials for Induction Electric Furnaces

• Furnace lining: fire clay bricks or high-alumina bricks.
• Furnace bottom: sometimes first cast with high-alumina castable then brick-lined.
• Small furnaces (<10t) can use 75% Al2O3 castable, plastic refractories, corundum castable, or dry vibrated materials.
• Around the induction coil: use corundum castable or dry vibrated material.
• Furnace life: 0.5–4 years, with 1–5 minor repairs for high-wear areas.

4. Refractory Materials for Holding Furnaces

Holding furnaces include trough induction furnaces, resistance-heated pool furnaces, and gas-fired furnaces. Because the working temperature is lower, they usually use fire clay bricks, resulting in a long service life.

5. Refractory Materials for Trough Induction Furnaces

• Base lining: 10mm ceramic fiber board, then fire clay insulating bricks or perlite bricks as insulation.
• Working layer and coil lining: fire clay refractory castables, or high-alumina bricks (>55% Al2O3) for large furnaces.

6. Refractory Materials for Resistance-Heated Pool Furnaces

• Non-working layer: fire clay insulating bricks, perlite bricks, or insulating panels; can also use lightweight castables (density ~0.8 g/cm³).
• Molten pool layer: high-alumina bricks (~80% Al2O3) or high-alumina castable (density 2.4 g/cm³).
• Above the pool: fire clay bricks, prefabricated castable blocks, or high-alumina plastic refractories.

7. Refractory Materials for Gas-Fired Furnaces

• Composed of furnace bottom, walls, and roof, can work alone or with a reverberatory furnace.
• Lining materials: fire clay bricks and high-alumina bricks.

8. Refractory Materials for Aluminum Ladles

Used for holding, transporting, and pouring molten aluminum:

• Non-working layer: fire clay insulating bricks or light castables (density 1.5 g/cm³).
• Working layer: fire clay bricks, high-alumina bricks, or Bubble Alumina Brick castable.
• Bottom: high-alumina bricks or corundum castable, with a protective coating on the surface.
• Pouring spout: exposed to erosion, use silicon carbide bricks, corundum bricks, or fused silica bricks.

9. Refractory Materials for Aluminum Refining

• Equipment: electrolytic cells.
• Wall: magnesia bricks; other parts: fire clay bricks or high-alumina bricks.
• Operating temperature: 720–800°C, good conditions mean a long service life.

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