Can the bell type lifting high-temperature muffle furnace be evacuated?

The bell type lifting high-temperature muffle furnace can be evacuated, and its vacuum performance is one of the core advantages of this type of furnace, which can meet the strict requirements of oxygen free or low oxygen environments for metal annealing, ceramic sintering, material synthesis and other processes. The following provides a detailed explanation from five dimensions: technical principles, vacuum system configuration, vacuum degree range, typical application scenarios, and industry cases:

1. Technical principle: The sealing structure and vacuum system work together to achieve a high vacuum environment
The bell jar furnace achieves vacuum function through the following design:
Fully sealed furnace structure
The furnace body adopts a double-layer water-cooled or air-cooled jacket design, combined with high-precision sealing rings (such as silicone rubber, fluororubber or metal sealing rings), to ensure that the furnace always maintains airtightness during the lifting process. For example, the leakage rate of a certain model of bell jar furnace is lower, providing the basic conditions for vacuum pumping.
Vacuum interface and pipeline design
A standard vacuum interface (such as KF or CF flange) is installed at the bottom or side of the furnace body, which can be directly connected to the vacuum pump unit. The pipeline is polished on the inner wall to reduce the risk of gas adsorption and leakage, ensuring the efficiency of the vacuum system.
Anti vacuum heating element
Heating elements (such as silicon molybdenum rods and graphite rods) need to work stably in a vacuum environment to avoid volatilization and pollution of the furnace at high temperatures. For example, the use temperature of silicon molybdenum rods in vacuum can reach 1600 ℃, and the volatility is extremely low, making them suitable for long-term vacuum processing.

2. Vacuum system configuration: graded pumping to meet different process requirements
Bell type furnaces are usually equipped with graded vacuum systems, covering a wide range from coarse vacuum to high vacuum:
Mechanical pump (rotary vane pump): 10 ⁻¹ Pa (coarse vacuum), quickly removes air from the furnace, providing pre pumping conditions for subsequent high vacuum pumps; Suitable for processes such as metal annealing and ceramic pre firing that do not require high vacuum requirements.
Roots pump (booster pump) 10 ⁻ ² Pa (medium vacuum), used in series with mechanical pump to increase pumping rate and shorten pumping time; Suitable for material synthesis or surface treatment that requires moderate vacuum degree.
Molecular pump (turbo molecular pump): 10 ⁻⁴ Pa (high vacuum), capable of extracting light gases (such as H ₂ He）， Realize ultra-high vacuum environment; Suitable for processes such as semiconductor material processing and optical thin film deposition that are extremely sensitive to oxygen.
Typical configuration example:
A high-end bell jar furnace adopts a three-stage pumping system of “mechanical pump+Roots pump+molecular pump”, which can pump the vacuum degree inside the furnace from atmospheric pressure to 10 ⁻⁴ Pa within 30 minutes, meeting the needs of most high-temperature vacuum processes.

3. Vacuum degree range: covering the complete spectrum from coarse vacuum to ultra-high vacuum
The vacuum degree range of bell jar furnaces is usually from 10 ⁵ Pa (atmospheric pressure) to 10 ⁻⁴ Pa (ultra-high vacuum), depending on the configuration of the vacuum pump and the sealing performance of the furnace body. The requirements for vacuum degree in different processes are as follows:
10 ⁵ -10 ² Pa (coarse vacuum): metal annealing, ceramic sintering, heat treatment, removing oxygen from the air to prevent material oxidation; For example, when annealing titanium alloys, rough vacuum can avoid hydrogen absorption and reduce oxygen content.
10 ² -10 ⁻¹ Pa (medium vacuum): Chemical vapor deposition (CVD), physical vapor deposition (PVD), reduce gas molecule collision frequency, control reaction rate; For example, in CVD deposition of diamond films, medium vacuum can suppress the formation of graphite phase and improve the purity of the film.
10 ⁻¹ -10 ⁻⁴ Pa (high vacuum): semiconductor material annealing, optical thin film deposition, thorough removal of gas molecules, avoiding material contamination; For example, during annealing of silicon wafers, high vacuum can control surface metal impurity contamination.

4. Typical application scenario: solving key industry problems
Metal Annealing: Preventing Oxidation and Hydrogen Absorption
Case: When annealing TA15 titanium alloy, first evacuate to 10 ⁻ ³ Pa, then heat to 750 ℃ and hold for 2 hours. After annealing, the material surface has high smoothness, no oxide layer or hydride generation, and high tensile strength at room temperature.
Advantages: Compared to air annealing, vacuum annealing can improve the fatigue life and fracture toughness of titanium alloys.
Ceramic sintering: inhibition of decomposition and pore formation
Case: When sintering silicon nitride (Si ∝ N ₄) ceramics, nitrogen gas is introduced after vacuuming, resulting in high material density and good bending strength after sintering.
Advantages: The vacuum environment can suppress the decomposition of Si ∝ N ₄ into Si and N ₂, avoiding material performance degradation; At the same time, under high vacuum, the pores are easily expelled, which increases the density.
Semiconductor Manufacturing: Protecting Sensitive Materials
Case: When annealing a silicon wafer, vacuum it to 10 ⁻⁴ Pa and then heat it to 1000 ℃. After annealing, the surface roughness of the wafer is reduced, and the degree of metal impurity contamination is low, meeting the requirements of integrated circuits.
Advantages: The ultra-high vacuum environment can completely remove surface oxides and adsorbed gases, avoiding an increase in device leakage current or threshold voltage drift.

5. Industry case: Validating the effectiveness of the vacuum performance of bell jar furnaces
A certain aviation materials research institute
TC4 titanium alloy was vacuum annealed using a bell jar furnace. By optimizing the vacuum degree (10 ⁻ ³ Pa) and annealing process (750 ℃× 2h → furnace cooling), the fatigue life of the material was improved, meeting the performance requirements of key components of the J-20 fighter landing gear.
A semiconductor packaging enterprise
Using a bell jar furnace to sinter silver paste under vacuum, by controlling the vacuum degree (10 ⁻ Pa) and sintering temperature (250 ℃), the bonding strength between the silver paste and the chip interface is higher, the thermal resistance is reduced, and the heat dissipation performance of the device is significantly improved.
A certain new energy battery manufacturer
Vacuum carbonizing the negative electrode material (graphite/silicon composite material) of lithium-ion batteries in a bell jar furnace, by vacuuming to 10 ⁻⁴ Pa and controlling the carbonization temperature (1000 ℃), the first coulombic efficiency of the material is improved and the cycle life is longer.