As a core piece of equipment in the precision heat treatment field, vacuum high-pressure gas quenching furnaces have become the first choice for processing high-hardness, high-toughness materials (such as high-speed steel, titanium alloys, and stainless steel) in industries like aerospace, high-end equipment, and precision molds. This is due to their advantages of oxidation-free heating, rapid and uniform cooling, and precise temperature control. Their "usage and maintenance" differs from that of traditional heating furnaces and must focus on three core aspects: "vacuum environment control, high-pressure gas flow management, and low-temperature uniform heating." Through standardized full-process operations and refined maintenance, stable equipment performance and qualified workpiece processing quality are ensured.
Before formulating a "usage and maintenance" plan, it is necessary to clarify the unique attributes of vacuum high-pressure gas quenching furnaces. They are not simply a combination of "vacuum heating + high-pressure cooling" but complex equipment integrating vacuum systems, heating systems, gas quenching systems, and temperature control systems. Their core characteristics and application scenarios determine the key directions of "usage and maintenance":
- Vacuum Environment: The vacuum degree inside the furnace can reach 1×10⁻²~1×10⁻⁵Pa, which effectively prevents oxidation and decarburization of workpieces during heating. It is particularly suitable for precision parts requiring high surface finish and stable chemical composition.
- High-Pressure Gas Quenching: Inert gases such as nitrogen and argon are used as cooling media, with gas quenching pressure up to 10MPa. Forced cooling via high-speed gas flow enables rapid quenching of workpieces (cooling rate up to 50~100℃/s), reducing the risk of workpiece deformation and cracking.
- Convective Heating: In the low-temperature range (≤600℃), convective circulation heating with inert gas is adopted, solving the problems of "slow low-temperature heating and poor temperature uniformity" in traditional vacuum furnaces. The furnace temperature uniformity can be controlled within ±3℃.
- Tool and Die Steel Processing: For example, the quenching of high-speed steel cutting tools and cold work dies requires vacuum heating to prevent oxidation of the cutting edge, and high-pressure gas quenching to ensure uniform hardness (HRC≥62).
- Aerospace Materials: For the solution treatment of titanium alloy components and superalloy parts, the vacuum environment prevents the volatilization of alloying elements, and precise temperature control ensures stable microstructure.
- Precision Components: For the heat treatment of automotive transmission gears and precision shafts in electronic equipment, high-pressure gas quenching enables integrated "quenching + low-temperature tempering," reducing subsequent machining allowances.
The first step in the "usage and maintenance" of vacuum high-pressure gas quenching furnaces is to strictly follow the five-step operation process: "pre-startup preparation → vacuum pumping → heating and temperature rise → high-pressure gas quenching → post-shutdown treatment." This avoids issues such as damage to the vacuum system and poor gas quenching effect caused by improper operation:
Before startup, focus on inspecting the vacuum, gas quenching, and electrical systems, while preparing auxiliary materials. Specific steps include:
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Vacuum System Inspection:
Check if the oil level of vacuum pumps (mechanical pumps, diffusion pumps) is at the standard scale (the oil level should cover 2/3 of the pump gears) and if the oil quality is clear (if the oil turns black or emulsified, replace it immediately).
Inspect the sealing surfaces of vacuum valves (angle valves, butterfly valves) for integrity, and wipe the valve interfaces with a lint-free cloth to prevent impurities from affecting sealing performance.
Test the normal operation of vacuum gauges (ion gauges, resistance gauges) to ensure the vacuum degree display error does not exceed 5%.
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Gas Quenching System Inspection:
Check the pressure of inert gas cylinders (nitrogen purity ≥99.999%, cylinder pressure ≥10MPa) and whether the connecting pipelines leak (detect with a helium mass spectrometer leak detector, requiring a leak rate ≤1×10⁻⁸Pa・m³/s).
Inspect the gas quenching fan and deflector for integrity; ensure the fan blades are not deformed and the deflector is not blocked to guarantee uniform gas flow circulation.
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Electrical System Inspection:
Check if heating elements (graphite tubes, molybdenum wires) are broken or deformed; the insulation resistance should be ≥5MΩ (test with an insulation resistance meter).
Test the temperature control system (thermocouples, PLC controllers) to ensure the error between the set temperature and the actual furnace temperature is ≤3℃, and that the over-temperature alarm device (the upper temperature limit is set 50℃ higher than the process temperature) is sensitive and reliable.
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Workpiece and Auxiliary Material Preparation:
Clean oil stains and rust from the workpiece surface (wipe with alcohol to prevent volatile substances from contaminating the vacuum system during heating). The workpiece loading capacity should not exceed 70% of the effective furnace chamber volume, and workpieces should be evenly distributed on the material rack to avoid local overheating.
Prepare vacuum sealant (for lubricating valve sealing surfaces) and high-purity nitrogen (for backup to prevent gas shortage during gas quenching).
The operation process is the core of "usage and maintenance," requiring precise phase-by-phase control of parameters such as vacuum degree, temperature, and gas quenching pressure:
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Vacuum Pumping Phase:
First, start the mechanical pump and pump until the vacuum degree inside the furnace is ≤1Pa (taking approximately 15~30 minutes), then start the diffusion pump (for oil diffusion pumps, first heat the diffusion pump oil to 200~250℃, keep it warm for 30 minutes, then pump to high vacuum).
High-vacuum pumping target: According to process requirements, general workpiece processing requires pumping to below 1×10⁻³Pa, while precision parts require pumping to below 1×10⁻⁵Pa. If the vacuum degree drops too quickly during pumping, stop the machine and check for leaks.
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Heating and Temperature Rise Phase:
In the low-temperature range (room temperature ~600℃), enable the convective heating mode, control the inert gas flow at 5~10m³/h, and set the heating rate ≤10℃/min to avoid workpiece deformation due to excessive temperature difference.
In the high-temperature range (above 600℃), switch to the radiant heating mode. Adjust the heating rate according to the workpiece material (≤8℃/min for high-speed steel, ≤5℃/min for titanium alloys). After reaching the target temperature, maintain the temperature (holding time is calculated based on workpiece thickness, generally 1~2min/mm).
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High-Pressure Gas Quenching Phase:
After the holding period, first fill the furnace with inert gas to atmospheric pressure (gas filling rate ≤0.5MPa/min to avoid impacting the workpiece), then start the high-pressure gas quenching system.
Gas quenching pressure setting: Adjust according to the workpiece hardness requirements. Generally, the quenching pressure for die steel is 5~8MPa, and the solution treatment pressure for titanium alloys is 3~5MPa. During gas quenching, monitor the cooling rate in real time to ensure it meets process requirements (e.g., high-speed steel needs to be cooled to below 200℃ in ≤30 minutes).
Shutdown is not the end of "usage and maintenance"; proper system cleaning and short-term protection are required:
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Vacuum System Treatment:
First, turn off the diffusion pump heating. After the diffusion pump oil cools to below 50℃, turn off the mechanical pump and fill the furnace with a small amount of inert gas to atmospheric pressure to prevent air from entering and contaminating the vacuum system.
Clean the filter at the inlet of the vacuum pump; if there is excessive debris on the filter, blow it with compressed air (pressure ≤0.5MPa).
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Furnace Chamber and Gas Quenching System Cleaning:
After the furnace temperature drops to below 100℃, open the furnace door and wipe residual impurities (such as graphite dust) from the inner wall of the furnace chamber and the deflector with a lint-free cloth. For stubborn stains, wipe with a cloth moistened with alcohol.
Inspect the filter in the gas quenching pipeline; if the filter element is blocked, replace it in a timely manner (generally replace the filter element after processing 50 batches of workpieces).
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Recording and Protection:
Fill out the Vacuum High-Pressure Gas Quenching Furnace Operation Record Form, recording parameters such as vacuum degree, heating temperature, gas quenching pressure, and processing time to provide a basis for subsequent process optimization.
If the machine is shut down for more than 7 days, start the mechanical pump once a week to pump vacuum (pump to below 1Pa and keep warm for 30 minutes) to prevent moisture damage to the vacuum system.
Core components of vacuum high-pressure gas quenching furnaces (such as vacuum pumps, heating elements, and seals) are prone to wear due to long-term operation. A "daily maintenance + regular inspection and repair" plan must be formulated to avoid equipment shutdown caused by hidden faults:
- Clean the furnace door sealing strip (wipe with a dry cloth to prevent poor sealing and reduced vacuum degree due to oil adhesion).
- Check for leaks at the inert gas pipeline interfaces (apply soapy water to the interfaces; no bubbles indicate normal operation).
- Clean dust from the surface of temperature controllers and vacuum gauges to ensure clear parameter display.
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Minor Repair (Monthly):
Inspect heating elements (graphite tubes, molybdenum wires) for local overheating or redness. If breaks are found, replace with elements of the same model (ensure power is cut off during replacement to avoid electric shock).
Calibrate the accuracy of vacuum gauges; if the error exceeds 5%, re-calibrate.
Replace mechanical pump oil (generally replace after 500 hours of operation; replace in advance if the oil quality deteriorates early).
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Major Repair (Quarterly):
Conduct a comprehensive inspection of the sealing surfaces of vacuum valves. If scratches are found, polish with fine sandpaper (grit ≥800 mesh) and apply vacuum sealant.
Inspect the gas quenching fan bearings; if abnormal noise or vibration occurs, replace the bearings and add high-temperature grease (the grease model must match the fan speed).
Inspect the furnace lining (graphite felt, refractory bricks) for damage; if the damaged area exceeds 10%, repair it in a timely manner (adhere graphite felt with high-temperature refractory adhesive).
Conduct insulation testing on the electrical system; the insulation resistance of the heating circuit should be ≥5MΩ, and that of the control circuit should be ≥2MΩ.
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