II. Brown corundum:
Brown corundum is a brownish fused block formed by mixing high alumina alumina clinker, carbon materials, and iron filings into a DC electric arc furnace and cooling them after high-temperature melting and impurity reduction. Its main component is aluminum oxide, with a content of 94.5-97%.
Brown corundum smelting is based on the basic principle that aluminum has a greater affinity for oxygen than iron, silicon, titanium, etc. It can reduce the main impurities in bauxite by controlling the amount of reducing agents and using the reduction smelting method. The reduced impurities generate silicon iron alloy and separate from the corundum melt to obtain crystalline brown corundum with a quality that meets the requirements and an alumina content greater than 95%.
II. Smelting process:
1. Smelting method: There are generally three methods for smelting brown corundum:
1) Exile production: continuous production, high degree of automation, but with high investment and complex structure, suitable for high-power smelting.
2) Dumping method: Continuous production, high degree of mechanization, low investment, good production efficiency, currently commonly used method (dumping furnace smelting method).
3) Fixed method (block method): Intermittent production, low degree of mechanization, but with small investment, simple equipment, and convenient process, is currently the main method for small abrasive plants to smelt corundum (fixed furnace smelting method).
2. Brown corundum smelting process method and characteristics:
1) Process characteristics: ① Furnace liquid temperature>2050 ℃. ② Level of furnace material: upper solid layer, middle semi molten layer, and lower molten layer Distribution of electric energy inside the furnace: arc heat, resistance heat. ④ The smelting process ensures the depth and melting area of the molten liquid at any time by controlling power, ingredient ratio, and material layer thickness.
2) Process method:
Stewing furnace method (submerged arc method)
Features: ① A DC electric arc furnace with a thick material layer and a capacity of 1800-2500KVA. The initial thickness is generally around 600-1000mm; For furnaces below 1000KVA, the initial thickness is generally around 400-600mm Large particle size. ③ The arc light is completely covered by the material layer.
Advantages: ① High heat utilization rate. ② The electrode and furnace lining have low losses, and the upper equipment of the furnace body is less susceptible to high-temperature radiation Reduced the harm of radiation heat to workers.
Disadvantages: ① The fixed furnace has a high amount of recycled materials, increases raw material consumption, and requires a large amount of labor (which has little impact on the dumping furnace operation). ② The hourly feeding amount is large, the operation is improper, the melting speed of the molten liquid is fast, the center of the heat source moves upward, and the area of the molten pool is small Easy to cause furnace spraying. ④ Fixed furnaces are prone to producing mixed corundum and ferrosilicon, or uneven quality in various parts of the melt.
Open furnace method (open arc method)
Features: The material layer is thin, the particle size is fine, the arc light exposure time is long, and the material layer thickness is generally 300mm.
Advantages: ① High utilization rate of furnace materials. ② The melting pool has a high temperature and a large melting area The viscosity of the melt is low, and the silicon iron alloy is easy to concentrate and separate, resulting in a uniform quality of the melt.
Disadvantages: ① Low heat utilization rate. ② Long smelting time and low production efficiency The furnace lining and electrodes oxidize quickly, and some equipment is often in a high-temperature radiation zone, which affects their lifespan The environment in front of the furnace is poor.
