What is the working principle of the box type atmosphere annealing furnace?

The box type atmosphere annealing furnace achieves heat treatment of workpieces (such as annealing, sintering, quenching, etc.) through the synergistic effect of heating system, atmosphere control system, and temperature control system. The core principle can be decomposed into the following key steps:

1. Heating System: Energy Supply and Temperature Control
heating element
Types: Silicon carbon rod (suitable for temperatures below 1200 ℃), silicon molybdenum rod (suitable for temperatures between 1200~1800 ℃), resistance wire (for low-temperature scenarios).
Working mode: The current passes through the heating element to generate resistance heat, which radiates to the interior of the furnace.
Case: Silicon molybdenum rod works stably at high temperature of 1600 ℃ and is suitable for ceramic sintering.
Temperature transfer and uniformity
Heat conduction method: radiation (primary)+convection (auxiliary, through circulating fans).
Uniformity guarantee:
Multi zone independent temperature control (such as three zone or five zone heating).
The circulating fan inside the furnace forces convection to eliminate temperature gradients.
Data: The typical furnace temperature difference is ≤ ± 5 ℃, ensuring consistent heating of the workpiece.

2. Atmosphere Control System: Protection and Reaction Environment
Atmosphere type and function
Inert gases (nitrogen, argon): prevent oxidation (such as metal annealing).
Reductive gas (hydrogen): Reduces metal oxides (such as powder metallurgy deoxidation).
Mixed gas: regulating the oxidation/reduction atmosphere (such as controlling the oxygen partial pressure in ceramic sintering).
Vacuum environment: eliminate gas interference (such as high-purity material processing).
Atmosphere supply and control
Gas pathway:
Inlet → Mass Flow Meter (MFC) → Furnace.
Exhaust port → exhaust gas treatment device (such as burner, adsorption tank).
Key parameters:
Gas purity ≥ 99.999%, flow accuracy ± 0.1L/min.
The vacuum degree can reach 10 ⁻³ Pa to 10 ⁻⁶ Pa (mechanical pump+molecular pump combination).
Case: In the annealing of semiconductor silicon wafers, the hydrogen flow rate is precisely controlled to 0.5L/min to avoid the risk of hydrogen embrittlement.

3. Temperature control system: precise regulation and stability
Temperature measuring element
Thermocouples (K-type, S-type): measure furnace temperature with an accuracy of ± 1 ℃.
Infrared thermometer (non-contact): monitors the surface temperature of the workpiece, suitable for high temperature scenarios.
Closed-loop control logic
PID algorithm: dynamically adjust the heating power based on the deviation between the set temperature and the actual temperature.
Heating curve programming: supports multi-stage heating, insulation, and cooling processes (such as step annealing).
Case: Tool steel is quenched and tempered, with a heating rate of 5 ℃/min, held for 2 hours, and a cooling rate of ≤ 3 ℃/min.

4. Furnace structure and insulation design
Furnace material
Refractory materials: mullite bricks (high temperature resistance), alumina fibers (lightweight insulation).
Metal casing: made of carbon steel or stainless steel, coated with anti rust paint on the surface.
Thermal insulation performance
Multi layer composite structure: inner refractory layer+middle insulation layer+outer protective layer.
Reduced heat loss: Compared to traditional furnace types, it reduces 30% and energy consumption by 20%.
Case: At a working temperature of 1200 ℃, the surface temperature of the furnace body is ≤ 60 ℃ to ensure safe operation.

5. Safety and auxiliary systems
Safety protection
Overtemperature alarm: Dual circuit temperature control, automatic power-off when temperature exceeds the limit.
Gas leakage detection: Real time monitoring of hydrogen sensors, alarm for concentration exceeding standards, and cutting off the gas source.
Pressure interlock: When the pressure inside the furnace is abnormal, the pressure relief valve will automatically open.
Auxiliary functions
Vacuum system: Mechanical pump pre evacuates, molecular pump achieves high vacuum.
Cooling system: water-cooled or air-cooled to protect heating elements and seals.
Data recording: PLC or touch screen records parameters such as temperature, atmosphere, time, etc., supporting process traceability.

6. Typical Process Flow Example
Taking metal annealing as an example, explain the workflow of a box type atmosphere annealing furnace:
Loading: Place the workpiece in the furnace, close the furnace door and seal it.
Vacuum pumping/inflation:
If a vacuum environment is required, start the mechanical pump to evacuate to 10 ⁻ ² Pa.
Fill nitrogen to atmospheric pressure and repeat 2-3 times to eliminate air.
Heating up:
Heat up according to the set curve (e.g. 5 ℃/min) to the target temperature (e.g. 800 ℃).
Insulation: Maintain the temperature for 2 hours to eliminate internal stress.
Cooling:
Cooling along with the furnace or controlling the cooling rate (such as ≤ 3 ℃/min).
Discharge: After cooling to room temperature, fill with nitrogen to break the vacuum and remove the workpiece.

7. Summary
The working principle of the box type atmosphere annealing furnace is based on the collaboration of three core systems: heating, atmosphere control, and temperature regulation
The heating system provides energy and achieves uniform heating through radiation and convection.
The atmosphere system protects the workpiece from oxidation or participation in chemical reactions.
The temperature control system ensures process accuracy and repeatability.
Its advantages lie in precise temperature control (± 1 ℃), atmosphere purity (99.999%), high efficiency and energy saving, suitable for heat treatment needs in fields such as metals, ceramics, semiconductors, etc. In the future, with the development of intelligence and ultra-high temperature technology, box type atmosphere annealing furnaces will further improve process accuracy and production efficiency.