বড় অ্যালুমিনিয়াম ব্রোঞ্জ ঢালাই উত্পাদন, induction furnaces are the preferred choice due to their strong electromagnetic stirring, rapid heating, and ability to ensure chemical homogeneity. যাহোক, the tendency of aluminum bronze (যেমন ZCuAl10Fe3) to oxidize and absorb gas easily presents significant challenges.
Technical analysis of porosity control and process optimization in aluminum bronze smelting
আমি. Porosity Mechanisms and Refining/Degassing Processes
Porosity in aluminum bronze is primarily caused by hydrogen (H₂) and entrapped alumina (আল₂O₃) films. At temperatures near the melting point, aluminum reacts readily with water vapor:
2আল + 3H₂O → Al₂O₃ + 6[এইচ]
1. Dynamic Refining and Degassing
While electromagnetic stirring ensures a uniform melt, it can also pull surface oxide films deep into the melt.
- Inert Gas Purging: Toward the end of the melting process, use a graphite tube to inject high-purity argon (Ar) or nitrogen (N₂) into the bottom of the furnace. Rising bubbles carry away dissolved hydrogen via partial pressure differences.
- Flux Refining: Use a covering flux composed of chlorides and fluorides (যেমন,NaCl, KCl, Na₃AlF₆). This isolates the melt from the air and uses physicochemical action to wet and adsorb floating alumina dross.
2. Static Holding
Before pouring, the power should be cut or held at low power for a short duration. This allows tiny bubbles and inclusions to float to the surface due to density differences.
Ii. Furnace Lining Selection and Slag Buildup (Hanging Slag) প্রতিরোধ
অ্যালুমিনা (আল₂O₃) buildup is a notorious issue in aluminum bronze melting. Slag “crusting” adheres to the furnace walls, reducing furnace volume, lowering electrical efficiency, and potentially causing severe inclusion-related porosity if the buildup peels off into the melt.
1. Recommended Materials
- Neutral or Basic Linings: Avoid acidic (silica-based) linings because aluminum will reduce SiO₂. Recommended materials include high-alumina (আল₂O₃) বা magnesium-aluminum spinel (MgO · Al₂o₃) dry-ramming mixes.
- Density Requirements: The particle size distribution of the lining material must be precisely graded to minimize physical penetration by the melt.
2. Anti-Buildup Techniques
- Surface Smoothness: Ensure the inner wall of the furnace is as smooth as possible during the lining process.
- Anti-Sticking Flux: Use specialized fluxes that alter the surface tension of the oxide slag, keeping it in a liquid or loose state for easier removal.
- Thermal Stability: Minimize drastic temperature fluctuations, which can cause micro-cracks in the lining where oxide slag can “take root.”
Iii. Temperature Control Strategy
Temperature is the most direct lever for controlling porosity.
| পর্যায় | Control Point | Logic |
| গলে যাওয়া | Rapid melting; strictly avoid overheating | Reduces exposure time at high temperatures and lowers gas absorption rates. |
| পরিশোধন | 1150°C – 1200°C | Ensures flux activity and facilitates slag-metal separation. |
| .ালা | 1100°C – 1150°C | Adjusted based on casting wall thickness; avoid high temperatures to prevent secondary gas absorption. |
মূল নীতি: “Melt fast, Control temp, Pour quickly.” Leverage the high power density of আনয়ন চুল্লি to minimize the time the metal spends above 1200° সে.
IV. Comprehensive Guidelines for Porosity Prevention
- Charge Pre-treatment: চুল্লি চার্জ (including returns) must be clean, dry, and free of oil. Preheating the charge to above 200° সে effectively removes surface moisture.
- Aluminum Addition Timing: Since aluminum oxidizes easily, it is typically added late in the melting process and immediately covered with flux.
- Gating System: For large aluminum bronze parts, একটি ব্যবহার করুন bottom-pour gating system to maintain a smooth filling process and prevent turbulence that traps air.
- Mold Preparation: Sand molds must be thoroughly dried. If using metal molds, apply an even coating and preheat them.
Expert Note: Oxidation and gas absorption in aluminum bronze are inextricably linked. If the flux cover is insufficient, broken oxide films will carry moisture into the melt, generating localized hydrogen. অতএব, maintaining a complete flux cover on the melt surface is the top priority.
