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What is the working principle of tungsten and tungsten alloy sintering furnace
source：www.szmtly.cn | publish time：2026年05月08日1、 Core working principle (three elements)
1. Vacuum/protective atmosphere environment (anti oxidation+densification aid)
High vacuum (10 ⁻¹～ 10 ⁻⁴ Pa): mechanical pump+molecular pump/diffusion pump staged pumping, deoxygenation, water vapor and impurities, to prevent tungsten from evaporating and contaminating at high temperatures.
Hydrogen/Inert Atmosphere: Vacuum filled with H ₂ (reducing residual oxides) or Ar (non-volatile), suitable for different alloys (such as W-Ni-Fe liquid-phase sintering).
Function: Reduce sintering temperature, promote surface purification, and accelerate atomic diffusion.
2. Ultra high temperature heating (resistance/induction two mainstream)
Resistance heating (most commonly used):
Heating element: tungsten wire, molybdenum wire, graphite rod/plate (resistant to 2000 ℃+).
Principle: Low voltage and high current pass through the heating element, and Joule heating heats the workpiece through radiation and convection; Equipped with multi-layer graphite felt/molybdenum sheet insulation screen, with a temperature field uniformity of ± 5 ℃.
Temperature: 1500-2300 ℃ (tungsten melting point 3422 ℃, sintering below melting point).
Induction heating (medium frequency, suitable for high density):
Principle: Intermediate frequency power supply → coil → alternating magnetic field → tungsten crucible/workpiece generates eddy current heating, and thermal radiation is conducted to the billet.
Advantages: Fast heating (up to 2500 ℃), uniform temperature field, suitable for large-sized/high-density tungsten alloys.
3. Powder densification system (solid phase+liquid phase)
Solid phase sintering (pure tungsten/low-alloy):
1000-1500 ℃: Atomic diffusion on the surface of particles forms "necking" connections and reduces pores.
1500-2200 ℃: Grain boundary migration, grain growth, closed cell shrinkage, density reaching theoretical 92-98%.
Liquid phase sintering (W-Ni-Fe/Cu high-density alloy):
1400-1500 ℃: Ni Fe first melts into liquid phase, infiltrates tungsten particles, and capillary force promotes rearrangement and densification.
Insulation: Tungsten is slightly soluble in the liquid phase and forms a W skeleton+bonding phase after cooling, with a density of ≥ 17 g/cm ³.
2、 Typical structure (horizontal/vertical vacuum furnace)
Furnace body: double-layer water-cooled furnace shell (inner stainless steel, outer carbon steel), anti deformation and cooling.
Heating/Insulation: Graphite/tungsten heating element+multi-layer graphite felt insulation screen.
Vacuum system: mechanical pump (low vacuum)+molecular pump (high vacuum)+valves/pipelines.
Atmosphere system: H ₂/Ar gas path+flow control, vacuum atmosphere automatic switching.
Temperature Control System: PLC+Infrared Temperature Measurement (2400 ℃)+PID Program Control, Temperature Control Accuracy ± 1-2 ℃.
Workpiece bearing: graphite/tungsten sintering boat/tray, anti pollution and deformation.
3、 Complete process flow (5 stages)
Material sealing: The tungsten powder compacts are loaded into a graphite boat, closed before entering the furnace, and sealed with water cooling.
Vacuum pumping: Mechanical pump pre pumping → Molecular pump high vacuum (10 ⁻²~10 ⁻³ Pa), degassing for 2-4 hours.
Heating and degreasing: Keep at 600-800 ℃ under vacuum to remove molding agents (such as paraffin and PEG).
High temperature sintering:
Pure tungsten: Keep at 1800-2200 ℃ for 1-3 hours (vacuum or H ₂).
High density alloy: Keep at 1450-1550 ℃ for 0.5-2 hours (H ₂ or Ar).
Cooling out of the furnace: After insulation, slowly cool down with the furnace to below 200 ℃, fill with nitrogen to break the vacuum, and remove the finished product.
4、 Key parameters (determining quality)
Vacuum degree: Pure tungsten ≥ 10 ⁻ ³ Pa; Alloy 10 ⁻¹~10 Pa.
Temperature: Pure tungsten 1900-2100 ℃; W-Ni-Fe at 1480-1520 ℃.
Insulation time: 1-3 hours (adjusted according to size/density).
Atmosphere: Pure tungsten with vacuum or H ₂; Alloy is made of H ₂ (reducing) or Ar (non-volatile).
5、 Difference from ordinary sintering furnace
Higher temperature: 1500-2300 ℃ (ordinary furnace ≤ 1200 ℃).
Vacuum requirements are stricter: 10 ⁻⁴ Pa level (ordinary furnace 10 ²~10 ³ Pa).
Special heating/insulation material: tungsten/graphite element+graphite felt insulation (ordinary furnace silicon carbon rod/ceramic fiber).
Higher temperature control accuracy: ± 1-2 ℃ (ordinary furnace ± 5-10 ℃).
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