Trong quá trình nấu chảy đồng nguyên chất (thường được gọi là “đồng đỏ”) trong lò cảm ứng, managing hấp thụ và oxy hóa khí is the ultimate challenge for ensuring high electrical conductivity and a dense, defect-free microstructure. Since liquid copper acts like a “magnet” for hydrogen (H₂) và oxy (O₂), improper technique leads to porosity or the notorious “Bệnh hydro.”
Here is the technical breakdown of charcoal covering and phosphor-copper deoxidation techniques optimized for induction melting.
1. The Mechanism of Gas Absorption
Trong lò cảm ứng, the high temperatures and liquid state of copper create a “sponge effect”:
- Hydro (H): Primarily sourced from moisture on the charge, oil/grease, or water vapor in the air.
- Oxygen (ồ): Sourced from direct contact with the atmosphere.
- The Problem: As the copper solidifies, hydrogen and oxygen react to form steam:
- 2H + [ồ] ⇋ H₂O↑
- This trapped steam results in microscopic or macroscopic blowholes, which drastically reduce the material’s conductivity and mechanical integrity.
2. Charcoal Covering: The Physical & Chemical Shield
Induction furnaces generate strong khuấy điện từ, which causes the liquid surface to become convex, increasing the surface area exposed to air. Charcoal serves as a vital barrier.
Key Techniques:
- Must be Pre-baked: Never add “cold” than. It must be baked at over 200°C to remove moisture. Adding damp charcoal is essentially “injecting” hydrogen directly into your melt.
- Thời gian & độ dày: Apply the covering as soon as the charge begins to melt. Maintain a layer thickness of 30–50mm so that no liquid copper is visible.
- Reducing Atmosphere: Ở nhiệt độ cao, charcoal reacts with oxygen to form carbon monoxide (CO), creating a protective reducing “blanket”:
- 2C + O₂ → 2CO
3. Phosphor-Copper Deoxidation: Deep Purification
Even with charcoal, some Cu₂O will inevitably form. Phosphor-copper (typically containing ~14% Phosphorus) is the industry standard for deep deoxidation in pure copper.
Operational Essentials:
- The Reaction: Phosphorus has a much higher affinity for oxygen than copper does. It forms phosphorus pentoxide (P₂O₅), which either escapes as gas or rises into the slag.
- 5Cu₂O + 2P → P₂O₅↑ + 10Củ
- Dosage Control:
- The Rule: You want enough to remove oxygen, nhưng một “residual phosphorus” level that is too high will sharply decrease electrical conductivity.
- Standard Amount: Thường xuyên 0.1% – 0.2% of the total melt weight.
- Các “Plunging” Phương pháp:
- Fractional Addition: Thêm vào 1/3 during the melting process for pre-deoxidation and the remaining 2/3 just before pouring.
- Use a Bell Jar: Do not simply toss phosphor-copper onto the surface; it will vaporize and be wasted. Use a graphite bell jar (plunger) to push the phosphor-copper to the bottom of the crucible and stir it gently.
4. Advanced Tips for Induction Melting
Temperature Management
Induction furnaces heat up rapidly. Keep your melting temperature between 1150°C and 1200°C. For every 100°C increase beyond the melting point, the hydrogen absorption capacity of copper increases exponentially.
Charge Cleanliness
Lò nung cảm ứng aren’t designed for heavy refining. Ensure your materials are:
- Scrap/Returns: Completely free of oil, nhũ tương, or heavy oxide scales.
- Vật liệu chịu lửa: Ensure the graphite crucible or furnace lining is bone-dry before starting the heat.
Gemini Pro-Tip:
If your application requires extreme conductivity (ví dụ., >100% IACS), consider using Rare Earth deoxidants (like Lanthanum or Cerium) in conjunction with phosphor-copper, or move to Cảm ứng chân không tan chảy (Vim) to eliminate the gas problem at the source.
