Precautions for operating a tube muffle furnace

As a high-temperature experimental equipment, the tubular muffle furnace must strictly follow safety regulations during operation to avoid equipment damage, experimental failure, and even personal injury. The following are the key precautions for operating a tubular muffle furnace, covering the entire process before, during, and after the experiment:

1. Preparation before the experiment
Equipment inspection
Sealing: Check whether the flanges at both ends of the furnace tube, inlet/outlet ports, temperature sensor interfaces, and other parts are well sealed to avoid air leakage or vacuum failure.
Electrical system: Confirm that the power cord is not damaged and the grounding wire is reliably connected; Check that the temperature control instruments, pressure gauges, flow meters, etc. display normally.
Vacuum system (if vacuum pumping is required):
Test the pumping capacity of the mechanical pump/diffusion pump to ensure that the vacuum degree meets the experimental requirements (such as ≤ 10 ⁻ ³ Pa).
Check whether vacuum gauges, valves, corrugated pipes and other components are aging or leaking.
Gas system (if ventilation is required):
Confirm that the gas cylinder pressure is sufficient and the gas purity meets the requirements (such as high-purity argon gas ≥ 99.999%).
Check that the gas pipeline is unobstructed and that the Mass Flow Meter (MFC) is calibrated accurately.
Sample preparation
Size matching: The length of the sample should be less than the effective heating zone length of the furnace tube to avoid local overheating or obstruction of the temperature sensor.
Cleaning treatment: Remove impurities such as oil stains and oxides from the surface of the sample to prevent contamination of the furnace or affecting experimental results.
Placement method:
Use specialized containers such as corundum boats and graphite boats to carry samples, avoiding direct contact with the inner wall of the furnace tube.
The samples should be evenly distributed to avoid temperature unevenness caused by accumulation.
Environmental Requirements
The laboratory is well ventilated and kept away from flammable and explosive materials.
The operating table should be flat and leave sufficient heat dissipation space around the equipment (recommended ≥ 30cm).

2. Operation during the experiment
temperature control
Heating rate:
Strictly follow the process curve to set the heating program, avoiding rapid heating that may cause furnace tube cracking or sample splashing.
Typical heating rate: Metal materials ≤ 10 ℃/min, ceramic materials ≤ 5 ℃/min.
Target temperature:
Do not exceed the maximum operating temperature of the furnace tube (such as alumina tube ≤ 1600 ℃, silicon carbide tube ≤ 1550 ℃).
Long term use temperature is recommended to be 100-200 ℃ lower than the rated temperature to extend the service life of the equipment.
Temperature uniformity:
Regularly calibrate the position of thermocouples to ensure accurate temperature measurement.
Avoid creating dead corners of airflow inside the furnace tube, which can affect temperature distribution.
atmosphere control
Vacuum extraction operation:
First, start the mechanical pump to pre pump to low vacuum (such as ≤ 10 Pa), and then start the diffusion pump to pump high vacuum (such as ≤ 10 ⁻ ³ Pa).
Close the furnace door when vacuuming to avoid air backflow.
Ventilation operation:
Blowing stage: First, pass inert gas (such as N ₂) at a flow rate of 50-100 mL/min for 10-30 minutes to remove air.
Reaction stage: Introduce target gases (such as H ₂, CH ₄) according to process requirements, and adjust the flow rate to the set value (such as 10-50 mL/min).
Maintain a slight positive pressure inside the furnace (such as+0.01~0.05 MPa) to prevent air infiltration.
Gas switching:
When switching gases, it is necessary to first close the original gas circuit valve and then open the new gas circuit valve to avoid explosion of the mixed gas.
Flammable gases such as hydrogen require separate pipelines and explosion-proof devices.
pressure control
Under vacuum environment: Monitor the vacuum degree to avoid sudden pressure changes that may cause furnace tube rupture.
In a ventilated environment: control the gas flow rate to prevent excessive pressure inside the furnace (generally ≤ 0.1 MPa).
security monitoring
Real time observation: Monitor the status of the sample through the observation window or camera, and immediately stop the machine if any abnormalities are detected.
Alarm handling:
When there is an alarm for temperature exceeding the limit, vacuum leakage, gas leakage, etc., immediately press the emergency stop button.
Record the alarm code, investigate the cause of the malfunction, and then resume the experiment.
Personnel protection:
Wear protective equipment such as heat-resistant gloves and goggles.
Avoid direct contact with high-temperature furnace bodies or samples.

3. Post experimental processing
Cooling operation
Natural cooling: Turn off the heating power, keep the furnace door closed, and use the residual heat of the furnace body to slowly cool down (suitable for experiments with no requirements for cooling rate).
Forced cooling:
Air cooling: Turn on the furnace fan to accelerate heat dissipation (cooling rate ≤ 50 ℃/h).
Water cooling: Cooling furnace tubes through circulating water (with equipment support, cooling rate ≤ 100 ℃/h).
Cooling limit:
The furnace door can only be opened when the temperature drops below 200 ℃ to prevent cracking of the furnace tube due to thermal stress.
Avoid sudden temperature changes (such as direct water cooling from 1000 ℃).
Sampling and cleaning
Sampling:
Use long handled tweezers or specialized tools to remove the sample and avoid burns.
The sample needs to be placed on a heat-insulating pad and cooled to room temperature before processing.
Furnace cleaning:
After the furnace body has completely cooled down, use a soft bristled brush or vacuum cleaner to remove any residue inside the furnace.
Avoid using hard objects to scratch the inner wall of the furnace tube to prevent scratching.
Gas processing:
Close the valve of the gas cylinder and empty the residual gas in the pipeline.
Flammable gases such as hydrogen need to be treated through combustion or catalytic oxidation before being discharged.
Equipment maintenance
Daily maintenance:
After each experiment, check whether the furnace tube, flange, sealing ring and other components are damaged.
Clean temperature control instruments, pressure gauges, and other display panels to avoid dust accumulation.
Regular maintenance:
Replace the vacuum pump oil every 3 months and check the sealing of the pump body.
Calibrate key components such as thermocouples and pressure sensors every 6 months.
Perform annual non-destructive testing on furnace tubes to identify cracks or deformations.
Long term discontinuation:
Evacuate the gas inside the furnace and keep it dry.
Cover with a dust cover and store in a dry and ventilated place.

4. Common faults and emergency response
Temperature out of control:
Phenomenon: Abnormal or continuous temperature display.
Solution: Immediately cut off the heating power and check if the temperature control instrument and thermocouple are damaged.
Vacuum leakage:
Phenomenon: The vacuum degree cannot reach the set value or continues to decrease.
Solution: Turn off the vacuum pump, check for leaks in flanges, valves, bellows, and other parts, and replace the sealing ring.
Gas leakage:
Phenomenon: Smelling a pungent odor or hearing a leak sound.
Solution: Immediately close the gas cylinder valve, open the ventilation system, and check if the pipeline connections are loose.
Furnace tube rupture:
Phenomenon: Hearing a cracking sound or seeing furnace tubes shattered.
Solution: Immediately press the emergency stop button, cut off the power and gas sources, evacuate personnel, and report for repairs.