Precautions for operating large industrial vacuum electric furnaces
11-14-2025 Author: KJ technology
The operation of large-scale industrial vacuum electric furnaces requires strict adherence to safety regulations and process requirements. Its high vacuum, high temperature, high pressure, and complex atmosphere control characteristics place extremely high demands on the skills of operators and equipment maintenance. From the four dimensions of preparation before operation, monitoring during operation, post-treatment after shutdown, and safety protection, the system summarizes key precautions:
1. Preparation before operation: Ensure that the equipment and process conditions meet the standards
Equipment inspection and calibration
Vacuum system: Check the oil level, sealing, and cooling water circulation of vacuum equipment such as mechanical pumps, molecular pumps, and Roots pumps to ensure that the vacuum degree meets the process requirements (such as 10 ⁻ Pa level).
Heating system: Verify the integrity of heating elements (such as graphite and molybdenum wire) to avoid short circuits or open circuits; Check the calibration accuracy of the temperature controller and thermocouple, with an error of ≤± 1 ℃.
Gas system: Confirm the gas source pressure (such as nitrogen cylinder pressure ≥ 5MPa), gas flow meter accuracy (such as ± 1% FS), pipeline sealing to prevent leakage from causing explosion or poisoning.
Mechanical components: Check the integrity of the furnace door sealing ring, observation window, and furnace structure to ensure that there are no cracks or deformations; Verify the grounding resistance of the furnace body (≤ 4 Ω) to prevent static electricity accumulation.
Process parameter setting
Vacuum degree: Select the initial vacuum degree according to the process (such as 10-100Pa for carburizing and 10 ⁻ ³ Pa for annealing) to avoid oxidation caused by residual oxygen.
Temperature curve: set heating rate (such as ≤ 10 ℃/min), holding time (such as 2-8 hours for carburizing), and cooling method (such as gas quenching pressure reaching 6-10 bar).
Gas flow rate: Adjust the gas ratio according to the process (such as ammonia flow rate should account for 50% -70% during nitriding), and the timing of inflation (such as adding active gas after heating to 500 ℃).
Pressure control: Set the upper limit of furnace pressure (such as ≤ 1.1 times the working pressure) to prevent explosion caused by overpressure.
Specification for workpiece loading
Cleanliness: The surface of the workpiece should be free of oil stains, rust, and moisture to avoid the generation of volatile substances that can contaminate the furnace during heating.
Placement method: Leave a gap (≥ 50mm) between workpieces to ensure even gas circulation; Avoid obstructing heating elements or thermocouples.
Fixed device: Use high-temperature resistant fixtures (such as ceramics, graphite) to fix the workpiece to prevent high-temperature deformation or falling.
2. Monitoring during operation: Real time response to abnormal working conditions
Dynamic management of vacuum degree
Vacuum pumping stage: Monitor the rate of vacuum degree decrease. If the target value is not reached within 10 minutes, check for leaks in the vacuum pump, valves, or furnace body.
Insulation stage: Regularly record the fluctuation of vacuum degree (such as ≤± 10%). If it suddenly rises, it may be due to workpiece volatilization or gas leakage, and the furnace needs to be stopped immediately for inspection.
Vacuum breaking operation: Dry nitrogen gas should be introduced to atmospheric pressure first, and then the furnace door should be opened to prevent air from entering and causing oxidation or explosion.
Coordinated control of temperature and atmosphere
Temperature uniformity: Monitor the temperature difference inside the furnace through a thermocouple array (such as ≤± 5 ℃). If there is local overheating, adjust the heating power or gas flow rate.
Gas reaction monitoring: In processes such as carburizing and nitriding, the atmosphere composition is monitored in real-time using carbon and nitrogen potential meters. If it deviates from the set value, the gas ratio or flow rate needs to be adjusted.
Cooling rate control: During gas quenching, it is necessary to gradually increase the pressure (such as from 0.1MPa to 6MPa) to avoid cracking of the workpiece due to thermal stress.
Emergency response to abnormal working conditions
Vacuum pump failure: Immediately switch to the backup pump and close the intake valve to prevent the pressure inside the furnace from rising.
Heating element circuit breaker: Replace the element after stopping the furnace and cooling down. Live operation is strictly prohibited.
Gas leakage: Close the gas source valve, open the ventilation system, evacuate personnel to a safe area, and use a gas detector to confirm the leakage point.
Fire or explosion: cut off the power supply and gas source immediately, use dry powder extinguisher to put out the fire, and do not use water or foam to put out the fire.
3. Post shutdown treatment: ensuring long-term stability of equipment
Furnace cleaning and maintenance
Residual cleaning: After the furnace temperature drops to ≤ 80 ℃, use a vacuum cleaner or soft brush to remove impurities such as oxide scale and carbon black from the furnace to avoid contaminating subsequent workpieces.
Sealing ring replacement: If the sealing ring ages or deforms, it should be replaced in a timely manner to ensure the efficiency of the next vacuum pumping.
Heating element inspection: Observe whether graphite, molybdenum wire and other elements are oxidized or broken, and repair or replace them if necessary.
Gas system emptying and maintenance
Pipeline blowing: Use nitrogen to blow gas pipelines to remove residual active gases (such as ammonia) and prevent pipeline corrosion.
Gas cylinder replacement: Close the gas cylinder valve, release the pipeline pressure, and replace the gas cylinder to avoid high-pressure gas impact.
Flow meter calibration: Regularly send the flow meter for inspection to ensure that the measurement accuracy meets the process requirements.
Equipment lubrication and rust prevention
Lubrication of mechanical components: Apply high-temperature grease (such as molybdenum disulfide) to the furnace door guide rail, transmission chain, and other parts to reduce wear.
Rust prevention of furnace body: After cleaning the surface of the furnace body, apply rust proof oil to avoid corrosion caused by humid environment.
4. Security Protection: Building Multiple Protection Systems
Personal protective equipment
Protective clothing: Wear heat-resistant and anti-static work clothes to avoid direct skin contact with high-temperature components.
Protective gloves: Use insulated gloves (such as aramid material) to operate furnace doors or workpieces to prevent burns.
Protective glasses: Wear radiation resistant glasses to avoid eye damage from strong light or infrared radiation.
Respiratory protection: When operating in poorly ventilated environments, wear a gas mask (such as a specialized canister for ammonia and methane).
Safety signs and warnings
Dangerous Area Identification: Warning signs such as "High Pressure Danger" and "Flammable and Explosive" should be set up in locations such as vacuum pumps and gas cylinder storage areas.
Publicity of operating procedures: Post operation flowcharts and emergency response guidelines next to the control cabinet or furnace body for quick response.
Safety interlock device: Ensure that heating cannot be started when the furnace door is not closed, and active gas cannot be introduced when the vacuum degree does not meet the requirements.
Training and emergency drills
Operation training: Regularly organize operators to learn about equipment principles, process parameter settings, and abnormal handling procedures. Only those who pass the assessment can take up their posts.
Emergency drill: Simulate scenarios such as vacuum leaks and fires, and train personnel in the skills of using fire extinguishers and emergency equipment (such as eye washers).
