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How to Leak Detection of Vacuum Furnace
Blow-through method is a traditional leak detection method, which involves evacuating the furnace chamber, applying helium gas outside the furnace (such as connecting a helium mass spectrometer), and then observing the results. Another method is the nozzle detection method, which is suitable for situations where your test object cannot be evacuated. When using this method, a leak-indicating gas (such as helium) needs to be filled into the detected object. Examples of inspected objects include heat exchangers, water-cooled flanges, water-cooled fans and shafts, electrical feedthroughs, water jackets, and more. When the detected object is filled with the leaking gas, the sensor is used to check whether there is any gas leaking from the outside. Helium mass spectrometers can also be used for this detection method.
Leak detection of inert gases is also important. This is because the leakage rate of the entire recharge system – from the liquid gas storage system to the vacuum furnace – must be zero. If the inert gas leaks from the gas supply system or the gas valve on the furnace body, the vacuum furnace will show signs of errors such as poor pumping effect, poor sealing, poor ultimate vacuum, difficulty in discharging normal outgassing, and reflux.
There are also two commonly used detection methods for inert gas leaks, namely membrane (soap bubble) leak detection and vacuum leak detection. In general, the thin-film leak detection method is the easiest and fastest method for high pressure inert gas leak detection. It sprays some kind of leak-indicating liquid on a known suspicious area, and if air bubbles form at any of the inspection sites, you know a leak has been found.
Vacuum leak detection is a more accurate method. It separates the liquid nitrogen or liquid argon storage system from the vacuum furnace, ensures that the entire system is in a vacuum state, and then uses a helium mass spectrometer to check the system for leaks. When performing a vacuum leak test, you should:
1.Close the external gas valve to disconnect the external liquid gas system from the evaporator, backfill tank, vacuum furnace, and all associated depressurization and backfill lines.
2.Use the normal pumping system of the vacuum furnace to evacuate the furnace chamber.
3.Depressurize the backfill tank.
4.Manually apply power to the recharge valve on the furnace body to open it. This step should be performed by an experienced specialist in accordance with safety regulations.
Once the backfill valve is opened and the backfill tank is depressurized to atmospheric pressure, the vacuum furnace begins to degas the lines. The gas is pumped from the gas storage tank and the evaporator up to the closed external gas valve. Then, the entire refill system can be pumped using the pumping system of the vacuum furnace to bring the entire system to a vacuum state. Next, the system should be leak tested using a helium mass spectrometer.
When complete leak detection of the vacuum furnace and inert gas is completed, each leak must be eliminated individually.
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