As the core equipment for material preparation, vacuum hot pressing furnace is widely used in advanced ceramics, hard alloys, functional crystals and other fields. It integrates three major functions: vacuum environment, high-temperature sintering, and directional pressure, and requires high operational accuracy. The following outlines the usage details from key aspects to help improve the success rate of experiments and equipment lifespan.
1、 Systematic preparation before startup
1. Material loading specifications: Select suitable graphite molds based on sample size, and lay high-purity graphite paper at the bottom to prevent adhesion; Powder materials need to be pre pressed into shape, while block materials should be chamfered to avoid stress concentration.
2. Sealing inspection: Focus on checking the integrity of the O-ring of the furnace door flange. If there are aging cracks, they should be replaced immediately; The electrode lead interface needs to be tightened to prevent loosening and avoid the risk of high voltage discharge.
3. Process card comparison: Set the temperature curve (such as segmented heating rate), target vacuum degree, and pressure value according to the experimental plan, input them into the PLC control system in advance, and verify the parameters twice.
2、 Coordinated control of vacuum and temperature rise
1. Step by step vacuum pumping: Start the mechanical pump to roughly pump to the level of 1 × 10 ³ Pa, switch the molecular pump to fine pump to the level of 1 × 10 ⁻ ³ Pa, and monitor the fluctuation of the vacuum gauge throughout the process. If there is an abnormal rebound, it is necessary to investigate the leakage point (commonly found at the sealing of the observation window).
2. Dynamic temperature control strategy: PID incremental heating is adopted in the low temperature range (<800 ℃) to suppress sudden boiling caused by organic matter escape; Real time calibration of thermocouple errors using infrared thermometers in the high-temperature section, with temperature differences controlled within ± 5 ℃.
3. Delayed pressure holding mechanism: After reaching the target temperature, stabilize the pressure for 10-15 minutes to eliminate pressure fluctuations caused by thermal expansion, and then apply axial pressure (recommended to increase at a rate of 5MPa/min).
3、 Pressure loading and insulation management
1. Gradient pressure principle: The initial pressure should not exceed 30% of the material's yield strength, and gradually increase to the set value (typical value 30-50MPa) as the temperature rises to prevent instantaneous high pressure from causing delamination.
2. Atmosphere protection technique: When introducing high-purity argon gas as a protective gas, it is necessary to first break the vacuum and then inflate it, repeatedly replacing it more than 3 times to ensure that the oxygen content is below 1ppm.
3. Insulation period monitoring: Monitor the downward displacement of the piston through displacement sensors to determine the material shrinkage rate; Record the actual temperature, pressure, and vacuum degree every 30 minutes, and draw the process curve for archiving.
4、 Key nodes for cooling and unloading
1. Graded cooling scheme: The high-temperature section (>1200 ℃) adopts slow cooling with the furnace, and the fan can be turned on to accelerate cooling when it drops below 600 ℃, avoiding lattice distortion caused by rapid cooling.
2. Safety start-up standard: The furnace door can only be slowly opened when the furnace temperature drops below 100 ℃ and the vacuum degree returns to normal pressure; Wear insulated gloves to remove the sample and prevent residual heat from burning.
3. On site cleaning requirements: Promptly remove volatile substances from the surface of graphite components, wipe the inner wall of the furnace with alcohol to avoid impurities contaminating the next experiment.
5、 Key points of daily maintenance
1. Replacement of vulnerable parts cycle: Measure the wear amount of graphite crucible/support every 50 cycles, and replace it if it exceeds 2mm; Check the deformation of the molybdenum wire heating element monthly.
2. Special maintenance of vacuum pump: The mechanical pump discharges waste oil and replenishes new oil every week, and the molecular pump returns to the factory for annual maintenance of the bearing lubrication system.
3. Electrical safety testing: Quarterly testing of insulation resistance (≥ 2M Ω), verification of thermocouple accuracy, ensuring grounding resistance<4 Ω.
The precision operation of vacuum hot pressing furnace directly determines the uniformity of material microstructure. Users need to establish standardized operating procedures (SOP) and dynamically adjust parameters based on specific material characteristics in order to fully utilize equipment efficiency.