Trong quá trình luyện kim loại, Deslagging (Loại bỏ xỉ) is a critically important yet highly challenging operation. Effective deslagging techniques not only significantly enhance the purity of the metal by removing harmful impurities but also extend the service life of the furnace refractory lining, thereby reducing production costs and achieving a more efficient and sustainable smelting process. This article provides an in-depth exploration of different slagging agents and deslagging methods, and elaborates on how to strike a balance between effective impurity removal and the protection of the refractory lining.
Ⅰ. Precision Slag Formation: The First Step to Efficient Impurity Removal
The primary goal of slag formation is to introduce fluxing agents (slagging agents) that react with oxides, sulfur, phosphorus, and other impurities within the molten metal. This reaction forms a slag with a low melting point and low density that is immiscible with the metal melt, allowing it to float to the surface for subsequent removal. Selecting the appropriate slagging agents is the prerequisite for successful deslagging.
Common Slagging Agents and Their Functions
| Slagging Agent Type | Main Component | Primary Function |
| Lime/Limestone | Calcium Oxide (CaO) | Increases slag basicity for the effective removal of acidic impurities like phosphorus (P) and sulfur (S). It is the most widely used slagging agent. |
| Dolomite | Calcium-Magnesium Oxide (CaO·MgO) | Besides its desulfurizing and dephosphorizing capabilities, it provides magnesium oxide (MGO) to protect magnesia-based refractory linings and slow erosion. |
| Fluorspar | Calcium Fluoride (CaF₂) | A powerful flux that significantly lowers the slag’s melting point and increases its fluidity, promoting desulfurization and dephosphorization reactions. |
| Silica | Silicon Dioxide (SiO₂) | Increases slag acidity, primarily used when needing to remove basic oxides (like iron oxide). |
| Synthetic Slag | A mixture of various oxides and fluxes | Pre-formulated for specific steel grades or conditions, enabling multiple functions like rapid slag formation, foaming, and impurity absorption. |
The key to effective slag formation lies in controlling the slag’s “basicity.” Slag basicity (often expressed as the ratio CaO/SiO2) is a critical indicator of the slag’s chemical properties.
- High-basicity slag (>1): Favorable for removing phosphorus and sulfur, but can have poor fluidity and is aggressive towards acidic refractory linings.
- Low-basicity slag (<1): Has good fluidity but is less efficient at removing phosphorus and sulfur, and is aggressive towards basic refractory linings.
Vì thế, during the smelting process, the composition of slagging agents must be dynamically adjusted based on the composition of the metal being processed, the target impurities, and the refractory material to achieve the ideal slag basicity and fluidity.
Ⅱ. Intelligent Deslagging: The Art of Balancing Purity and Protection
Once the slag has formed and has fully absorbed the impurities, the core challenge of the deslagging operation is how to remove it efficiently and thoroughly while minimizing disturbance to the molten metal and damage to the refractory lining.
Common Deslagging Methods
- Manual Raking:
- Method: An operator uses a long-handled rake to manually pull the floating slag from the furnace door into a slag pot.
- Pros: Flexible, requires simple equipment, and is suitable for small furnaces or localized slag removal.
- Cons: High labor intensity, low safety, results depend heavily on operator experience, often leads to metal loss, and can be incomplete.
- Mechanical Skimming:
- Method: Utilizes a specialized deslagging machine with a rake or blade at the end of an arm that extends into the furnace. These can be pneumatically or hydraulically driven.
- Pros: High degree of automation, fast deslagging speed, safer operation, and significantly reduces labor intensity.
- Cons: Higher initial investment, specific requirements for furnace design, and higher maintenance costs for the mechanical arm.
- Tilting and Pouring:
- Method: The furnace is tilted to pour the molten metal from the taphole, while the less dense slag is held back by a slag dam, slag ball, or is raked off from a separate slag door.
- Pros: Suitable for large converters and EAFs, allowing for the rapid separation of large volumes of slag and steel.
- Cons: Requires highly effective slag-stopping technology; improper operation can lead to “slag carry-over,” compromising the purity of the molten steel.
- Siphoning/Chân không Deslagging:
- Method: A refractory-made siphon tube is inserted into the slag layer, and a vacuum is used to suck the slag out.
- Pros: Extremely thorough slag removal with almost no metal loss, yielding very high metal purity.
- Cons: Complex equipment and high maintenance costs; primarily used in the refining of specialty alloys or steel grades with stringent quality requirements.
- Gas Purging Assisted Deslagging:
- Method: While deslagging, an inert gas (like argon) is blown into the molten bath through permeable bricks in the furnace bottom or wall. The stirring action of the gas pushes the floating slag towards the slag door, facilitating its removal.
- Pros: Effectively clears slag from “dead zones,” improving the efficiency and completeness of deslagging.
- Cons: Requires an additional gas supply system and may cause a slight temperature drop in the molten metal.
Ⅲ. Refractory Lining Protection: The Core Strategy for Extending Service Life
The erosion of the refractory lining is a complex physicochemical process driven by three main factors: chemical corrosion, physical abrasion, and thermal spalling.
Primary Mechanisms of Refractory Erosion
- Chemical Corrosion: This is the most significant cause of erosion. Certain components in the slag (ví dụ., FeO, SiO2) react chemically with the basic oxides of the refractory lining (ví dụ., MGO, CaO), forming low-melting-point compounds that cause the lining material to melt and degrade. Ví dụ, acidic slag containing SiO2 will corrode a basic magnesia-carbon brick lining.
- Physical Abrasion: The flow of molten metal and slag creates continuous scouring and wear on the lining, particularly at the charging door, taphole, and slag line.
- Thermal Spalling: Drastic temperature fluctuations during the smelting cycle induce thermal stress in the refractory material. When this stress exceeds the material’s strength, it leads to cracking and spalling.
Effective Measures for Protecting the Refractory Lining
- Slag Conditioning:
- Increase MgO Saturation: Ensuring the slag contains a sufficient and saturated level of MgO is the most effective way to protect magnesia-based linings (common in EAFs and converters). When the slag is saturated with MgO, its tendency to “leach” MgO from the lining is greatly reduced. This can be achieved by adding dolomite or light-burned magnesia during slag formation.
- Maintain a Reasonable Basicity: Maintaining a relatively stable and moderate slag basicity and avoiding sharp fluctuations can slow down the rate of chemical corrosion on the lining.
- Reduce FeO Content: An excessively high FeO content in the slag accelerates the oxidation of carbon-containing refractories and the corrosion of magnesia-based linings. This can be managed by properly controlling oxygen blowing and the carbon-oxygen balance.
- Slag Splashing:
- This is a proactive lining maintenance technique. After tapping the steel, a small amount of compositionally-adjusted slag is intentionally left in the furnace.
- High-pressure nitrogen is then blown through the oxygen lance to splash this viscous slag evenly onto the furnace walls, forming a protective coating.
- Cái này “slag glaze” effectively insulates the refractory from direct contact with and corrosion by the high-temperature molten steel and slag of the next heat, significantly extending the lining’s life. Slag splashing is a key technology for achieving long campaign lives in modern large converters.
- Improving Deslagging Operations:
- Gentle Operation: Avoid violent impacts on the refractory lining from mechanical deslagging arms.
- Control Deslagging Time: Minimize the time the furnace door is open to reduce thermal radiation loss and thermal shock to the lining.
- Avoid Excessive Skimming: Trong một số trường hợp, leaving a thin layer of well-conditioned slag at the slag line can actually serve as a protective barrier.
Phần kết luận
Effective deslagging is not a single operation but an integrated system encompassing độ chính xác slag formation, intelligent deslagging, Và proactive refractory protection. It is a core element in the modern metallurgical industry’s pursuit of high quality, low cost, and long furnace life. By scientifically selecting and proportioning slagging agents, the properties of the slag can be controlled from the outset, laying the foundation for efficient impurity removal. By adopting advanced deslagging methods and equipment, metal purity can be guaranteed while reducing metal loss and operational risks. Most critically, by optimizing slag chemistry and implementing cutting-edge techniques like slag splashing, what was once waste can be transformed into a tool for protecting the furnace lining.
Mastering and applying these comprehensive techniques is the key to achieving the dual victory of enhanced metal purity and robust refractory protection, ultimately leading to efficient, stable, and low-consumption smelting operations in a competitive market.
