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Every day, the İpsen Aftermarket Support Helpline receives dozens of calls asking for troubleshooting assistance and technical insight on a wide range of manufacturers' furnaces.
When asked what some of the most common vacuum-related challenges were, we decided to poll our technical experts and review the data from their call logs. What we discovered is that customers regularly ask five specific questions. They are:
* How do I leak check my furnace?
* Why won't my vacuum furnace pump down?
* How do I determine the source of excessive outgassing?
* What should I do about poor ultimate vacuum?
* Why are my parts discolored?
Faced with these questions - and the frequency at which they are asked - we decided to compile a short guide that covers our experts' answers to these common challenges.
How do I leak check my furnace?
There are two primary techniques used to leak check a vacuum furnace: the spray probe and the sniffer probe methods. The spray probe technique seen in Figure 1 is the traditional form of leak checking. It involves pumping down the furnace, applying helium to the exterior of the furnace (e.g., with a helium mass spectrometer connected) and looking for a response.
Then there is the sniffer probe technique. This is for applications where it's not feasible to evacuate what you're testing for leaks. To use this technique, you should charge - or pressurize - a test piece with a trace gas, such as helium. Testpiece examples include the heat exchanger, water-cooled flange, water-cooled fans and shafts, power feed-through, water jacket, etc. Once you charge the test piece with the trace gas, the probe sniffs around the part for any gas that may be escaping through a leak. This leak is then reported by the helium mass spectrometer.
It is also important to check for inert-gas leaks. This is because the tolerance of leaks on the entire backfill system - from the liquid storage system out to the furnace - must be zero. If inert gas is leaking in from the inert-gas system or from valving on the furnace, it can cause the furnace to exhibit signs of poor pumping, poor leak rates, poor ultimate vacuum, poor ability to pump against normal outgassing loads,...