Precautions for using vacuum heat treatment electric furnace for experiments

The vacuum heat treatment electric furnace used in the experiment is a precision equipment, and its use involves multiple risks such as high temperature, vacuum, and electrical control. Improper operation may lead to equipment damage, experimental failure, and even safety accidents. The following are key precautions for use, covering core aspects such as safety, operation, and maintenance:

1. Safety operation standards
Personnel protection and training
Protective equipment: High temperature resistant gloves, protective face shields, and lab coats must be worn during operation to avoid high-temperature burns or splash injuries.
Training requirements: Operators need to undergo professional training, familiarize themselves with equipment structure, emergency shutdown procedures, and accident handling plans.
Vacuum system safety
Extraction sequence: Start the mechanical pump first to pre pump to a low vacuum (such as below 10 ³ Pa), then start the molecular pump or diffusion pump to avoid damaging the pump body during heavy load startup.
Deflation operation: After cooling, slowly fill dry nitrogen gas to atmospheric pressure before opening the furnace to prevent negative pressure inside the furnace from causing the furnace cover to close and injuring people or glass pieces to break.
Vacuum gauge calibration: Regularly calibrate with a standard vacuum gauge to ensure accurate display of vacuum degree (error ≤ 10%) and avoid oxidation or contamination caused by misjudgment.
high temperature protection
Furnace temperature: During the heating process, the surface temperature of the furnace can reach over 200 ℃, and warning signs should be set up and a safe distance should be maintained.
Sample placement: Use high-temperature resistant ceramic crucibles or trays to avoid direct contact between metal tools and heating elements, to prevent short circuits or melting.
Quick cooling taboo: It is strictly prohibited to directly pass water or open the furnace door for rapid cooling at high temperatures, otherwise it may cause cracking of the furnace body or sample explosion.

2. Key points of operation process
Sample installation and fixation
Sample cleaning: Clean the surface of the sample with alcohol or acetone to prevent oil stains and dust from evaporating and contaminating the furnace at high temperatures.
Uniform distribution: The sample should be evenly placed in the center of the furnace to avoid uneven temperature field caused by local overheating.
Fixed device: Use ceramic brackets or graphite fixtures to fix the sample and prevent it from moving or tipping during the heating process.
Parameter setting and monitoring
Heating curve: Set up a multi-stage heating program (such as 30 stages) based on material characteristics, with a heating rate of ≤ 10 ℃/min for each stage to avoid thermal stress cracking.
Vacuum degree control: When sintering alumina ceramics, the vacuum degree should be maintained below 10 ⁻ ³ Pa; Silicon nitride ceramics require nitrogen gas to maintain a positive pressure of 0.1~0.5MPa.
Real time monitoring: Real time monitoring data is obtained through temperature sensors and vacuum gauges, and heating is immediately paused and checked in case of abnormalities.
Cooling and Sampling
Natural cooling: During the high temperature stage (>800 ℃), it must be cooled along with the furnace, and forced air or water cooling is prohibited.
Cooling time: Calculate the cooling time based on the material thickness (such as cooling for 4-6 hours for every 10mm thickness), and ensure that the temperature drops below 100 ℃ before starting the furnace.
Sampling tool: Use long handled tweezers or specialized tools to take samples, avoiding direct contact with high-temperature samples.

3. Equipment maintenance and upkeep
Daily cleaning
Furnace cleaning: After each experiment, use a vacuum cleaner or soft bristled brush to remove the residue inside the furnace to avoid the accumulation of carbides and short circuits.
Sealing ring inspection: Regularly inspect the fluororubber sealing rings of the furnace door and observation window. If there are cracks or aging, they should be replaced immediately.
Heating element maintenance: Wipe the surface oxide of the heating rod with alcohol to maintain stable conductivity.
Vacuum system maintenance
Pump oil replacement: Replace the vacuum pump oil every 200 hours of operation for mechanical pumps, and replace the bearing grease every 1000 hours for molecular pumps.
Gas path inspection: Regularly check for air leaks at vacuum valves and pipeline connections, which can be detected using a helium mass spectrometer leak detector (leakage rate ≤ 10 ⁻⁹ Pa · m ³/s).
Cold trap cleaning: Clean the condensate in the cold trap every quarter to prevent blockage from affecting the pumping efficiency.
Electrical system inspection
Grounding test: Use a grounding resistance tester to check the grounding resistance of the equipment every month (should be ≤ 4 Ω) to avoid the risk of leakage.
Circuit aging: Regularly check whether the outer skin of the power cord and temperature control wire is damaged, and replace the aging circuit in a timely manner.
Temperature control calibration: Calibrate the temperature controller with a standard thermocouple every six months to ensure temperature control accuracy within ± 1 ℃.

4. Common fault handling
Insufficient vacuum degree
Possible reasons: damaged sealing ring, pump oil contamination, and blocked air path.
Processing steps: Check the sealing ring → Replace the pump oil → Clean the air circuit → Re vacuum test.
Temperature out of control
Possible reasons: thermocouple breakage, temperature controller malfunction, heating element short circuit.
Processing steps: Check the thermocouple connection → Restart the temperature controller → Disconnect the power supply and check the resistance of the heating element.
Abnormal noise from the pump body
Possible reasons: lack of oil in the mechanical pump, worn bearings in the molecular pump, and foreign objects entering the pump chamber.
Processing steps: Add pump oil → Replace bearings → Disassemble and clean the pump chamber.

5. Special scenario precautions
Corrosive atmosphere treatment
If corrosive gases such as hydrogen and chlorine need to be introduced, a 316L stainless steel furnace body should be selected, and gas purification devices (such as drying towers and deaerators) should be added.
Immediately blow the furnace with nitrogen after the experiment to prevent residual gas from corroding the equipment.
Processing of large-sized samples
When the height of the sample exceeds half of the furnace, alumina fiberboard should be laid at the bottom of the furnace to improve the uniformity of the temperature field.
The heating power should be adjusted according to the sample volume (such as adding 1kW power for every 1000cm ³ sample) to avoid slow heating.
Long term continuous operation
If the continuous operation exceeds 72 hours, a dedicated person should be arranged to be on duty, and temperature and vacuum data should be recorded every 2 hours.
During operation, it is prohibited to touch the external heat dissipation fins of the furnace to prevent burns.