Precautions for using customized muffle furnace

As a high-temperature heat treatment equipment, the use of customized muffle furnaces should balance safety, efficiency, and equipment lifespan. The following are key precautions, covering aspects such as operating standards, maintenance, safety protection, and process optimization:

1. Preparation before operation: Ensure that the equipment matches the process
Equipment inspection
Appearance and sealing: Check whether the sealing rings of the furnace door, observation window, thermocouple interface and other parts are intact, without aging or damage; The furnace shell has no deformation or cracks.
Electrical system: Confirm that the power cord is not damaged and the grounding wire is reliably connected; Use a multimeter to check the resistance of the heating element (such as the cold resistance of a silicon molybdenum rod, which is about 10-20 Ω), to ensure that there is no open circuit or short circuit.
Vacuum/atmosphere system (if applicable): Check the oil level of the vacuum pump (at least 1/2 of the oil window), test the accuracy of the vacuum gauge (if compared with the standard pressure gauge, the deviation should be ≤ 5%); If using protective gases (such as nitrogen or argon), confirm that there are no leaks in the gas circuit (apply soapy water to the interface).
Confirmation of process parameters
Set the heating curve according to the material characteristics (for example, titanium alloy sintering requires segmented heating: room temperature → 500 ℃ (10 ℃/min) → 1000 ℃ (5 ℃/min) → 1600 ℃ (3 ℃/min)).
Confirm that the target temperature does not exceed the rated value of the heating element (e.g. the maximum operating temperature of the silicon molybdenum rod is 1800 ℃, and long-term use is recommended to be ≤ 1700 ℃).
If a vacuum environment is required, the maximum vacuum degree should be selected according to the process requirements (such as metal powder metallurgy requiring ≤ 10 ⁻³ Pa, semiconductor annealing requiring ≤ 10 ⁻⁴ Pa).
Workpiece preparation
Clean the surface of the workpiece of oil stains and oxides (such as wiping metal parts with alcohol) to avoid volatilization and pollution of the furnace at high temperatures.
Control the total mass of the workpiece to not exceed the furnace design load (for example, for a 50L furnace, it is recommended to process ≤ 20kg of metal per time), to prevent local overheating caused by heat concentration.
Reasonable placement of workpieces: Use alumina ceramic trays to distribute weight, leaving a gap of ≥ 20mm between workpieces to promote airflow circulation.

2.Standard operation: strictly follow the heating and insulation procedures
Heating stage
Segmented heating: When starting the cold furnace, first raise it to 300-500 ℃ at a low rate (such as 5 ℃/min) and keep it warm for 1-2 hours to remove the adsorbed moisture and gas in the furnace and reduce thermal stress impact.
Observation instrument: Pay close attention to the deviation between the displayed value of the temperature control instrument and the actual temperature (such as calibrating the furnace center temperature with an infrared thermometer). If the deviation is greater than 10 ℃, stop the machine and check the position of the thermocouple or instrument parameters.
Avoid rapid cooling and heating: The heating or cooling rate should not exceed the rated value of the equipment (such as ≤ 20 ℃/min for 10kW equipment) to prevent heating element embrittlement or furnace cracking.
Insulation stage
Temperature uniformity: Regularly use multi-point thermometers to detect the temperature at different positions of the furnace (such as the center, corners, and workpiece surface), ensuring that the temperature difference is ≤ 50 ℃ (high-end equipment requires ≤ 20 ℃).
Atmosphere control (if applicable): If protective gas is used, maintain a positive pressure inside the furnace (such as 0.01~0.05MPa) to prevent air infiltration; If vacuuming, regularly check the operating status of the vacuum pump (such as whether the molecular pump speed is stable).
Workpiece status monitoring: Check the color change of the workpiece (such as metal oxidation color, ceramic sintering shrinkage) by observing the window or intermittently opening the furnace door (wearing a protective mask), but the opening time of the furnace door should be ≤ 30 seconds to reduce heat loss.
Cooling stage
Natural cooling: It is recommended to cool high-temperature workpieces (such as>800 ℃) in the furnace to below 300 ℃ before removing them to avoid cracking caused by thermal stress (such as ceramic materials).
Forced air cooling (if supported by the device): In the low-temperature range (such as<500 ℃), the air cooling system can be turned on to shorten the cooling time, but it is necessary to prevent cold air from directly blowing on the heating element.
Power off sequence: first turn off the heating power supply, then turn off the temperature control instrument, and finally cut off the main power supply; If using a vacuum pump, wait for the furnace pressure to rise to atmospheric pressure before stopping the pump.

3. Safety protection: prevent high temperature, electric shock, and gas risks
Personal Protection
Operators are required to wear insulated gloves (temperature resistance ≥ 500 ℃), protective face shields (anti radiation heat), and dust masks (to prevent inhalation of ceramic dust).
It is prohibited to wear synthetic fiber clothing (flammable) or metal jewelry (conductive), and long hair should be tucked into a safety helmet.
Equipment safety
Overtemperature protection: Set up a dual level overtemperature alarm (such as a first level alarm of 1650 ℃ and a second level alarm of 1700 ℃), and automatically cut off the heating power when the second level alarm is triggered.
Leakage protection: Equipped with a leakage circuit breaker (operating current ≤ 30mA), regularly test its sensitivity (press the test button once a month).
Emergency stop: Install red emergency stop buttons on both sides of the control panel and furnace body to ensure that all power can be immediately cut off in case of emergency.
environmental safety
Ventilation requirements: The equipment should be placed in a well ventilated laboratory or workshop (with a ventilation rate of ≥ 6 times/hour) to prevent the accumulation of high-temperature gases or harmful volatile substances.
Fire prevention measures: Flammable materials (such as alcohol and acetone) are prohibited from being stacked within 1 meter around the furnace body. Dry powder fire extinguishers (weighing over 2kg) should be equipped and pressure gauges should be checked regularly.
Anti scalding signs: Post “high temperature danger” warning signs on high-temperature areas such as furnace doors and observation windows, and mark the safe operating distance (≥ 0.5 meters) with red tape.

4. Maintenance and upkeep: the key to extending equipment lifespan
Daily cleaning
After each use, use a soft bristled brush to remove the oxide scale and workpiece residue inside the furnace (to avoid scratching the furnace lining); If using a vacuum environment, it is necessary to wipe the sealing surface with a dust-free cloth (to prevent particles from affecting the vacuum degree).
Regularly clean the oil mist filter of the vacuum pump (such as replacing the filter element every 200 hours) to prevent oil stains from blocking the air path.
Regular maintenance
Heating element: Check the surface of the silicon molybdenum rod/silicon carbon rod for oxidation and peeling every 500 hours (if the thickness of the oxidation layer is greater than 1mm, it needs to be replaced); Measure the resistance with a multimeter every 1000 hours, and replace it if the deviation is greater than 20%.
Thermocouple: Calibrate with a standard thermometer every 6 months, and replace when the deviation is greater than 5 ℃ (such as replacing K-type thermocouples with S-type thermocouples to improve accuracy).
Insulation material: Check the alumina fiber felt annually for shrinkage or cracking (if the thickness decreases by more than 20%, it needs to be replaced), and compact it to the original density (such as 0.3g/cm ³) when replacing.
Lubrication and fastening
Apply high-temperature lubricating grease (such as molybdenum disulfide grease, with a temperature resistance of ≥ 300 ℃) to the furnace door hinges and vacuum pump motor bearings every 3 months.
Check the heating element wiring terminals for looseness every 6 months (tighten with a wrench to the specified torque, such as 4N · m) to prevent overheating caused by increased contact resistance.

5. Process optimization: improving efficiency and quality
Pre oxidation treatment (for metal materials)
Pre oxidize in an air or oxygen atmosphere at 500-800 ℃ for 1-2 hours to form a dense oxide film (such as Al ₂ O3), reducing material volatilization at high temperatures (such as reducing titanium loss by 30% during titanium alloy sintering).
Segmented insulation
For complex shaped workpieces (such as turbine blades), multi-stage insulation technology (such as 1200 ℃ insulation for 2 hours → 1400 ℃ insulation for 1 hour → 1600 ℃ insulation for 0.5 hours) is adopted to promote internal stress release and reduce deformation rate (≤ 0.5%).
Atmosphere cycle optimization
If protective gas is used, gas guide plates (such as stainless steel plate openings) should be installed in the furnace to evenly cover the surface of the workpiece and avoid local oxidation (such as increasing the uniformity of surface oxidation color by 90% during bright annealing of stainless steel).