Brown fused alumina is an artificial corundum abrasive made by melting bauxite clinker, anthracite coke (reducing agent), and iron filings (clarifying agent) in a dumping electric arc furnace at 2000~2200°C. The main component is Al₂O₃ ≥ 95%.

1. Raw material preparation and batching

1). Select and crush the bauxite raw ore, then calcine in a vertical kiln or rotary kiln to remove crystallizing water to obtain bauxite clinker;

2). According to formula ratio: bauxite clinker, carbon reducing agent, iron filings;

3). Mix the material evenly, feed it into the silo for preparation for furnace entry.

Iron filings function: At high temperatures, silicon and iron oxides are reduced to form ferrosilicon alloys, relying on density differences and corundum melt layering to separate impurities.

2. High-temperature electric arc furnace smelting (core process)

Equipment: Three-phase tilting electric arc furnace

- Arc starting: Arc starting coke is laid at the furnace bottom, electrodes are energized to start the arc and heat up;

Smelting: Batch feeding, the arc generates high temperatures above 2000°C, bauxite melts; carbon reduces impurities such as SiO₂ and Fe₂O₃;

- Refining: holding reaction, impurity reduction, and settling, melt layering; the upper layer is brown fused alumina melt, the lower layer is ferrosilicon alloy (by-product);

- Iron Tapping and Dumping: After smelting is complete, pour the molten brown alumina into the cooling mold and cooling pit.

3. Cooling and solidification

The molten material is naturally and slowly cooled in the cooling pit for several dozen hours, forming large pieces of brown alumina melt. Cooling speed is controlled to ensure the crystals are dense and have good toughness. After cooling, manual sorting removes non-conforming material blocks, such as furnace skin and slag inclusions.

4. Breakup and shaping

1). Coarse crushing: The jaw crusher breaks large blocks of corundum into smaller pieces;

2). Medium crushing and shaping: cone crusher and Barmac impact crusher shape the particles to reduce needle-like shape.

5. Magnetic separation removes iron

Multi-stage magnetic separator removes residual iron and ferrosilicon alloy particles from smelting, reduces magnetic content (sandblasting and abrasive material generally ≤0.3%), preventing rust in finished products.

6. Screening and grading

Vibrating screens and airflow classifiers are classified according to national standard particle size numbers: coarse sand, medium-sized sand, fine powder, and fine powder;

Optional washing process: removes dust and reduces free silicon, mostly used for high-end sandblasting abrasives.

7. Drying, quality inspection, packaging

1). Drying washed materials;

2). Testing: Al2O3 content, magnetic substances, particle size distribution, bulk density, hardness;

3). Packaging and warehousing qualified products.

Brief Process in One Sentence

Bauxite calcination→ batching mixing→ high-temperature melting in electric arc furnace→ tilting cooling→ crushing and shaping→ magnetic separation of iron removal→ screening and grading (washing optional), → drying, quality inspection→ finished brown fused alumina.