Tech Team · Kintek Solution

Testing for leaks in a vacuum furnace is a critical maintenance task to ensure optimal performance and safety. The process involves a combination of visual inspections, pressure tests, and specialized techniques to identify and address leaks. Common methods include using leak detectors, helium gas tests, and vacuum-level monitoring. Key areas to inspect include valves, seals, thermocouples, and the furnace door. Regular maintenance and timely replacement of worn-out components are essential to maintain the furnace's integrity and efficiency.

Key Points Explained:

1. Using a Leak Detector:

   • A leak detector is essential for identifying gas leaks, particularly at critical points like the vacuum gauge protection valve.
   • If leaks are detected, the affected valve or component should be replaced immediately to prevent further issues.

2. Inspecting Bearings and Seals:

   • Check for bearing wear, especially in moving parts, and replace severely worn bearings to avoid mechanical failures.
   • Inspect all seals, including those on the main valve stem, pre-extraction valve, bleeder valve, pneumatic ball valves, and furnace door.
   • Replace aging or cracked seal rings with high-temperature-resistant fluorine rubber material to ensure a tight seal.

3. Thermocouple Leak Testing:

   • Use a specialized method involving a plastic bag and helium gas to test for leaks at the thermocouple metal head.
   • If leaks are found, replace the thermocouple to maintain accurate temperature readings and prevent vacuum loss.

4. Leak Rate Test:

   • Perform a leak rate test by pumping the furnace down to a high vacuum (e.g., 1 x 10^-4 torr or better).
   • Isolate the pumping system and record the vacuum level after 30 and 60 minutes.
   • Calculate the leak rate and compare it to acceptance criteria. A leak rate of 20 microns/hour is generally acceptable, but tighter furnaces may achieve less than 1 micron/hour.

5. Positive Pressure Leak Detection:

   • Use an analyzer to measure residual oxygen levels. A sudden increase may indicate a leak in the furnace shell or circulation pipe.
   • Ensure hydrogen levels are above 3% and use a mobile hydrogen detector to verify gas tightness in suspected areas.

6. Addressing Abnormal Vacuum Phenomena:

   • Check the vacuum source and compressed air pressure to ensure they are functioning correctly.
   • Inspect the vacuum gauge and furnace door for proper operation, damage, or contamination.
   • Examine pipelines, pneumatic valves, and thermocouple inlets for issues. Reseal compromised areas with AB adhesive.

7. Temporary and Permanent Leak Repairs:

   • Use high-temperature sealant for temporary repairs while the furnace is operational.
   • Once the furnace is stopped, perform a full treatment by welding cracked parts, replacing aged gaskets and snap rings, and tightening loose screws.

8. Shutdown Procedures:

   • After completing the vacuum process, sequentially close the molecular pump switch, circulating water switch, external circulating water valve, and the main power supply gate to ensure safe shutdown.

By following these steps, you can effectively identify and address leaks in a vacuum furnace, ensuring its longevity and optimal performance. Regular maintenance and timely repairs are key to preventing costly downtime and maintaining a safe working environment.

Summary Table:

Method	Key Steps
Leak Detector	Identify gas leaks at critical points; replace affected valves or components immediately.
Inspecting Bearings/Seals	Check for wear; replace worn bearings and aging seals with high-temperature-resistant materials.
Thermocouple Leak Testing	Use helium gas and a plastic bag to test for leaks; replace thermocouples if leaks are detected.
Leak Rate Test	Pump furnace to high vacuum; record and calculate leak rate; compare to acceptance criteria.
Positive Pressure Detection	Measure residual oxygen levels; verify gas tightness with a hydrogen detector.
Abnormal Vacuum Phenomena	Inspect vacuum source, gauge, and door; reseal compromised areas with AB adhesive.
Temporary/Permanent Repairs	Use high-temperature sealant for temporary fixes; perform full repairs during shutdown.
Shutdown Procedures	Close molecular pump, circulating water, and power supply sequentially for safe shutdown.

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