How to maintain the vacuum heat treatment electric furnace used in experiments?

The vacuum heat treatment electric furnace used in the experiment is a precision equipment, and its maintenance needs to be carried out around the core components (such as vacuum system, heating element, furnace, electrical system). Regular maintenance can extend the service life of the equipment and ensure experimental accuracy. The following are specific maintenance strategies and operational points:

1. Daily maintenance: basic maintenance to prevent hidden dangers
Furnace cleaning
Operation steps:
After each experiment, wait for the furnace temperature to drop below 100 ℃ and use a soft bristled brush or vacuum cleaner to remove any residue (such as alumina powder and carbides) inside the furnace.
Stubborn stains can be wiped with anhydrous ethanol, avoiding the use of strong acid or alkali solutions to corrode the inner wall of the furnace (such as zirconia coating).
matters needing attention:
Do not clean at high temperatures to prevent cracking of the furnace due to thermal stress.
After cleaning, dry nitrogen should be used to blow the furnace to prevent residual moisture from evaporating at high temperatures and causing oxidation.
Sealing ring inspection and replacement
Inspection cycle: Check the fluororubber sealing rings of the furnace door, observation window, and flange interface after each start-up.
Replacement standard:
When cracks, hardening, or compression deformation exceed 20%, immediate replacement is required.
It is recommended to use high temperature resistant (≥ 300 ℃) and vacuum resistant fluororubber or silicone rubber sealing rings.
Lubrication treatment: Before replacing the sealing ring, apply vacuum silicone grease (such as Apiezon L) on the contact surface to enhance sealing and reduce wear.
Heating element maintenance
Surface cleaning:
Gently sand the oxide on the surface of heating rods (such as molybdenum rods and graphite rods) with fine sandpaper (over 1000 grit) every quarter to maintain conductivity.
Avoid scratching with metal tools to prevent damage to the surface of the heating element.
Resistance detection:
Measure the resistance of the heating element with a multimeter every six months, and replace it if the deviation from the initial value exceeds 10%.
Example: The initial resistance of the molybdenum heating rod used in the 1700 ℃ furnace is 5 Ω. If the measured value is less than 4.5 Ω or greater than 5.5 Ω, it needs to be replaced.

2. Vacuum system maintenance: in-depth maintenance of core components
Vacuum pump maintenance
Mechanical pump:
Oil change cycle: Replace the vacuum pump oil every 200 hours of operation (it is recommended to use mineral oil type vacuum pump oil, such as HV-100).
Oil change method: Drain the old oil → Inject new oil to the oil level center line → Start the pump and run for 10 minutes to remove bubbles.
Molecular pump:
Bearing lubrication: Replace high-speed bearing grease (such as Mobil SHC 634) every 1000 hours.
Vibration detection: Use a vibration analyzer to monitor the vibration value of the molecular pump bearing during operation. If it exceeds 3mm/s, stop the machine for maintenance.
Cold trap cleaning:
Disassemble the cold trap every quarter to remove condensed oil and moisture (which can be cleaned with anhydrous ethanol).
After cleaning, it is necessary to blow with dry nitrogen to avoid residue affecting the pumping efficiency.
Vacuum valves and pipelines
Airtightness testing:
Every six months, use a helium mass spectrometer leak detector to detect valve and pipeline connections, with a leakage rate of ≤ 10 ⁻⁹ Pa · m ³/s.
Leakage point treatment: For minor leaks, vacuum sealing mud (such as Torr Seal) can be used to repair them. For severe leaks, valves or pipelines need to be replaced.
Valve lubrication:
Apply high-temperature resistant grease (such as Dow Corning Molykote 557) to the pneumatic valve piston every year to ensure flexible operation.

3. Electrical system maintenance: dual guarantee of safety and accuracy
Temperature controller calibration
Calibration cycle: Calibrate the temperature controller every six months using a standard thermocouple (such as an S-type platinum rhodium thermocouple).
Calibration method:
Insert the standard thermocouple into the furnace temperature measurement hole and measure synchronously with the built-in thermocouple of the equipment.
Compare the readings of the two, if the deviation is greater than ± 1 ℃, adjust the temperature controller parameters or replace the thermocouple.
Record management: Save calibration data, establish temperature deviation curves, and provide a basis for experimental parameter correction.
Electrical circuit inspection
Appearance inspection:
Check the outer skin of the power cord and temperature control cable for damage and loose joints every month.
If aging circuits are found, they need to be replaced immediately (it is recommended to use high-temperature resistant silicone cables with a temperature resistance rating of ≥ 200 ℃).
Insulation test:
Measure the insulation resistance of the equipment to ground with a megohmmeter every quarter, and the value should be ≥ 1M Ω (500V gear).
If the insulation resistance decreases, it is necessary to check whether the insulation layer of the heating element is damaged or the circuit is damp.

4. Quarterly and Annual Deep Maintenance: Systematic Maintenance
Quarterly maintenance items
Furnace structure inspection:
Check the welds on the furnace shell, observe whether there are cracks on the window glass, and whether the levelness of the furnace body meets the standard (measured with a level, deviation ≤ 0.1 °).
Water cooling system maintenance:
Clean the filter screen of the water cooler and check the water flow pressure (to be maintained at 0.2~0.5MPa) to avoid overheating and damage to the heating element caused by scale blockage.
Software upgrade:
Update the firmware of the temperature controller and vacuum gauge, fix known vulnerabilities, and optimize control algorithms.
Annual maintenance project
Furnace inner wall repair:
If there is peeling or cracking on the inner wall of the furnace, it is necessary to fill it with alumina fiber repair material (such as Fiberfrax 700) and re sinter and solidify it.
Overall leak detection of vacuum system:
Entrust a professional organization to conduct an overall leak detection of the vacuum system (including the furnace body, pump unit, and valves) to ensure that the maximum vacuum degree of the system meets the standard (such as 10 ⁻⁵ Pa).
Safety interlock test:
Simulate faults such as overheating, overpressure, and water leakage to verify the reliability of safety interlock devices (such as emergency stop buttons and overload protection).

5. Special scenario maintenance strategy
Maintenance after treatment with corrosive atmosphere
If corrosive gases such as hydrogen and chlorine are introduced into the experiment, it is necessary to:
Immediately after the experiment, purge the furnace with nitrogen for 30 minutes, and then turn off the furnace when the residual gas concentration is less than 1%.
Replace corrosion-resistant sealing rings (such as perfluororubber) and stainless steel valves to extend equipment life.
Long term disuse maintenance
Before discontinuation:
Clean the furnace and apply rust proof oil (such as WD-40).
Empty the old oil from the vacuum pump and inject anti rust oil (such as Vacuum Pump Conservative Oil).
Power on the equipment for 1 hour every month to prevent electrical components from getting damp.