Wear-Resistant Silicon Nitride Degassing Rotor for Aluminium Melt Treatment

Silicon Nitride Degassing Rotor Applications

Silicon nitride degassing rotors are widely used in aluminium melting, die casting, and continuous casting lines to control hydrogen content and melt cleanliness. Below are the main application scenarios where Si₃N₄ rotors show clear advantages over graphite in real production conditions.

• Automotive die-casting aluminium (HPDC)

  ✅Key Advantages

  1. Hydrogen reduction: typical targets ≤0.10 mL/100 g Al after treatment (reference operating range from AFS melt practice)
  2. Bubble dispersion: fine bubble field supports lower porosity rates in structural castings
  3. Rotor life: Si₃N₄ head maintains geometry across multiple cycles vs graphite

  ✅ Problem Solved

  A Tier-1 HPDC foundry processing Al-Si alloys reduced X-ray porosity rework by ~15–25% after switching to a Si₃N₄ degassing rotor with optimized vane angle; hydrogen measurements dropped from ~0.18 to ~0.09 mL/100 g Al over comparable runs. Data practices align with AFS (American Foundry Society) guidelines and NADCA porosity acceptance metrics.

• Primary and secondary aluminium melting

  ✅Key Advantages

  1. Consistent hydrogen removal on large bath volumes with N₂ or Ar
  2. Lower dross adhesion on the rotor head reduces cleaning downtime
  3. Stable dimensions help keep the shaft-to-seal gap predictable

  ✅ Problem Solved

  A remelt operation handling mixed returns reported longer cleaning intervals and steadier hydrogen values when replacing a 2-week graphite cycle with a Si₃N₄ rotor that held its edge features beyond the previous change-out point. Operating records align with plant SPC data and melt shop logbooks.

• Continuous casting/holding furnaces

  ✅Key Advantages

  1. Rotor balance tolerances support continuous degassing modules
  2. Surface integrity in air preheat up to ~1200 °C reduces oxidation flaking
  3. Low wettability limits inclusion carry-over downstream

  ✅ Problem Solved

  A slab caster logged fewer inclusion alarms and lower filter loading after standardizing a Si₃N₄ degassing shaft and rotor design across two lines; internal QC correlated fewer downstream filter changes per ton pr

Silicon Nitride Ceramic Degassing Rotor Usage Instructions

• Installation

  1. Inspect the silicon nitride degassing rotor and shaft for cracks, edge chipping, or thread damage. Check that the rotor fits securely with the coupling, seal block, and degassing unit.
  2. Preheat the rotor as required by equipment manuals (typically 200–400 °C) to prevent thermal shock when entering molten aluminium. Ensure the rotor is completely dry before immersion.

•  Operation

  1. Start N₂ or Ar gas flow before lowering the rotor into the melt. Gradually increase rotation speed until it reaches the required working range (around 1,200–3,000 rpm depending on alloy and furnace size).
  2. Monitor hydrogen content using RPT or an online hydrogen analyzer. Adjust dwell time, gas flow, or rotor speed until melt hydrogen reaches the target range (commonly ≤0.10 mL/100 g Al).

•  Storage

  Store the rotor in a dry, cushioned container away from graphite dust, moisture, and corrosive gases. If stored after use, clean and dry it before packing to prevent surface oxidation or metal adherence.

• Cleaning and Maintenance

  1. After the operation, allow the rotor to cool naturally in air or under controlled furnace cooling to avoid cracking.
  2. Remove aluminium oxide build-up using non-metallic scrapers or ceramic tools. Avoid hammering or hitting the vane area, as Si₃N₄ is strong but brittle to impact.

• Common Misuse & Solutions

  Issue	Cause	Solution
  Thermal shock cracks	Immersion without preheating or rotor absorbed moisture	Follow the preheating curve, ensure rotor dryness
  High vibration during rotation	Rotor imbalance, worn coupling, or incorrect shaft alignment	Re-balance rotor, check shaft run-out, tighten fixture
  Hydrogen level rising after replacement	Gas holes blocked or rotor depth incorrect	Clean vane slots, check the gas flow meter and immersion depth
  Rapid dross accumulation	Wetting or incorrect rotation speed	Verify the Si₃N₄ surface is clean, adjust the rpm and gas flow
  Surface oxidation during idle	Excessive air heating above 1000 °C	Maintain proper furnace atmosphere or use a protective preheat cycle

Silicon Nitride Ceramic Degassing Rotor FAQ

1. Q: What is the main function of a silicon nitride degassing rotor in aluminium casting?
   A: A silicon nitride degassing rotor disperses nitrogen or argon into fine bubbles inside molten aluminium. These bubbles extract dissolved hydrogen and lift oxides to the surface, improving melt cleanliness before casting.
2. Q: How does a Si₃N₄ rotor perform better than a graphite degassing rotor?
   A: Compared with graphite, a Si₃N₄ degassing rotor and shaft maintains its shape longer, absorbs less aluminium, and does not oxidize as quickly in air. This reduces rotor replacement frequency and helps maintain consistent hydrogen levels in the melt over time.
3. Q: What hydrogen level can be achieved using a silicon nitride rotor in aluminium melt treatment?
   A: Under standard conditions, well-controlled aluminium melt degassing with inert gas can reduce hydrogen to ≤0.10 mL/100 g Al. The Si₃N₄ ceramic rotor helps maintain this consistency because vane geometry remains unchanged throughout multiple cycles.
4. Q: Can a silicon nitride rotor be used with both nitrogen and argon gas?
   A: Yes. Both N₂ and Ar can be used through a ceramic degassing rotor. Nitrogen is more economical and widely used, while argon offers better inert behavior for critical castings such as automotive structural or aerospace components.
5. Q: What speeds are typically required for effective gas dispersion in molten aluminium?
   A: Most silicon nitride degassing rotors operate in the range of 1,200–3,000 rpm. The actual rpm depends on gas flow rate, bath depth, and alloy type. Higher speeds create finer bubbles but can increase surface turbulence.
6. Q: When should a silicon nitride rotor be replaced?
   A: Common indicators include reduced bubble dispersion, higher hydrogen readings, cracked vanes, imbalance during rotation, or gas exit holes becoming blocked with dross. Unlike graphite, wear is slower and more uniform, but monitoring shaft vibration and melt hydrogen is key.
7. Q: Can the silicon nitride rotor and shaft be customized to fit existing degassing machines?
   A: Yes. Manufacturers can produce a custom Si₃N₄ rotor and shaft assembly according to drawing—covering head diameter, shaft length, gas inlet size, taper connection, vane slot design or coupling interface.

Customer Reviews: Advanced Si3N4 Degassing Rotor

• ⭐️⭐️⭐️⭐️⭐️
  We replaced graphite with a silicon nitride degassing rotor on our 2,000-ton die casting line. Hydrogen levels in the melt dropped more consistently to 0.09–0.11 mL/100 g Al, and the rotor geometry stayed stable even after several production cycles. No sudden wear or imbalance like we used to see with graphite rotors.
  -- Process Engineer | Automotive Die-Casting Plant | Germany
• ⭐️⭐️⭐️⭐️⭐️
  We buy complete Si₃N₄ rotor and shaft assemblies for four continuous melting furnaces. The initial cost is higher than graphite, but rotor life is roughly three times longer, and we have fewer unplanned changeovers. Our maintenance team also reported less dross sticking on the ceramic surface.
  --Purchasing Manager | Tier-1 Aluminium Foundry | USA
• ⭐️⭐️⭐️⭐️⭐️
  Our main issue was rising hydrogen after long runs. Since switching to a ceramic degassing impeller, bubble dispersion has stayed uniform, and hydrogen doesn’t spike at the end of the shift anymore. The non-wetting surface means less cleaning, and shaft vibration has been minimal.
  -- Foundry Production Supervisor | Secondary Aluminium Recycling | Spain
• ⭐️⭐️⭐️⭐️⭐️
  We tested the silicon nitride degassing rotor in our inline treatment unit at 2,500 rpm with both nitrogen and argon. The rotor maintained balance, and gas flow through the slot design produced finer bubbles compared to graphite. For OEM integration, the dimensional stability and low thermal expansion of Si₃N₄ are strong advantages.
  -- Equipment OEM Engineer | Degassing System Manufacturer | Japan