Submerged Arc Furnace (SAF) Process

The Submerged Arc Furnace (SAF) Process

The submerged arc furnace process operates through the intermittent addition of raw materials into the furnace using a feeding system. A stoking machine ensures the material bed remains at the appropriate level. Molten alloy is periodically tapped from the furnace, flowing into ladles or other containers before being transported to molds for casting. The final product takes shape after cooling. Iron slag is discharged intermittently through a dedicated slag tap hole.

Main Equipment of the Submerged Arc Furnace

The SAF system comprises several key components:

Furnace Body & Lining
Furnace Cover
Short Network
Water-Cooling System
Exhaust Gas & Dedusting System
Waste Heat Treatment System
Electrode Shell
Electrode Holding, Slipping, and Lifting System
Charging & Discharging System
Control System
Burn-Through Device
Hydraulic System
SAF Transformer and Associated Electrical Equipment

Furnace Body

The furnace body consists of a steel shell and a refractory lining:

Furnace Shell‌: Constructed from a bottom plate, side plates, reinforcing hoops, and rib plates. It typically features a circular design with thick steel side plates supported by a channel steel framework anchored in concrete.
Lining‌: Made from high-alumina, magnesia, and carbon-based refractories. First-grade magnesia bricks and materials are used near the tap-hole, often combined with other refractories like carbonaceous silica bricks.
Shell Requirements‌: Must have sufficient strength to withstand severe thermal expansion of the lining, accommodate heating and cooling cycles, and be material-efficient and manufacturable. The shell includes an integrated tap-hole.
Furnace Cover

The cover on sealed furnaces is constructed with refractory bricks and materials, using water-cooled steel beams as its skeleton. It features three electrode ports for the electrode holders, which are insulated from the cover. Temperature measurement sockets with protective tubes are installed in the refractory brickwork to monitor furnace atmosphere temperature under the cover.

Fume Hood

The hood seals the furnace mouth, contains radiant heat, and captures flue gases generated during smelting, improving the working environment. It is a welded steel structure (often hexagonal) consisting of cover plates, side walls, doors, and a supporting skeleton that sits on the operating platform.

Flue Gas Outlet Pipe

This system creates negative pressure within the hood (via natural draft or a fan) to extract smoke. Each furnace typically has two flues, constructed from steel plates and profiles. A flue assembly includes a lower water-cooled section seated on the hood, a connecting pipe section leading outside, and a bell valve (operated by a hydraulic cylinder) to open/close the flue. When closed, gases are directed to the dedusting system.

Electrode Holder

This is a core SAF component, consisting of:

Conductive Device‌: Traditionally includes collector rings (for current distribution and equalization), conductive copper pipes, and copper tiles (water-cooled, red copper castings). Copper tiles transmit current to the electrode.
Holding Device‌: Applies pressure via copper tiles to the electrode shell.
Slipping & Lifting Devices‌: Used for electrode length adjustment and positioning.
Holding Cylinder‌: Also called the electrode outer cylinder, it suspends the holder and electrode, allowing for vertical movement.
Electrode Shell‌: Contains the electrode paste, which sinters to form the consumable electrode.

The copper tile-to-electrode contact pressure is typically 0.05–0.15 MPa. The electrode sintering zone is a critical area for strength.

Electrode Lifting Device

This device adjusts the electrode arc length to control circuit resistance and current. Lifting speed varies with furnace power and electrode diameter (e.g., 0.2–0.5 m/min for diameters >1m). The typical lifting stroke is 2.1–2.6 meters.

Short Network System

The short network transmits low-voltage, high-current power from the transformer to the electrodes. Its design is crucial for electrical efficiency and minimizing non-ferrous metal consumption. Key requirements are:

Adequate current-carrying capacity.
Minimized resistance.
Low inductive reactance.
Sufficient insulation and mechanical strength.
Short Network Compensation

The short network contributes approximately 70% of the system's reactance, resulting in a low natural power factor (often 0.7–0.8). This reduces transformer efficiency, wastes energy, and may incur utility penalties. Implementing compensation (power factor correction and phase balancing) is an effective means to lower energy consumption and improve smelting efficiency.

High-Voltage Power Supply System

This system includes high-voltage isolators, voltage/current transformers, and vacuum circuit breakers. It ensures reliable power delivery to the furnace while maintaining safety and operational control.

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