Tips for Finding Leaks in a Vacuum Heat Furnace

11 August 2017

Vacuum heat furnaces perform expeditiously as atmosphere controlled heat treatment chambers. Drained of process-influencing oxygen and filled instead with an inert gas, the furnace stops scaling, stops parts discolouration, and generally improves the mechanical and physical characteristics of any processed workpiece. What happens if this sealed chamber develops a leak? The vacuum is tainted and the heat treatment process is compromised. We need to find that leak, and fast.

Fundamental Leak Management Tips 

Sudden leaks are often easier to diagnose, for they’re often preceded by some other equipment defect. However, a chamber breach that develops slowly is one that will likely go undetected for some time. An unpredictability factor, therefore, exists unless a proactive maintenance strategy is adopted. In short, a scheduled leak testing check and repair program should be monitoring vacuum integrity.

A Deeper Investigation 

A niggling thought occurs: if the leak is small enough, can it be ignored? The short answer is always a firm, “No.” The workpiece isn’t experiencing the full vacuum. That inert gas isn’t uniformly distributed, the reactive heating elements are showing signs of attack, and the pumping mechanism is running continuously. The leak, even if it’s a pinprick, must be found and sealed. At this point, a background history is handy. Is this a newer or older model? Has it been in service for years? Perhaps the seals have failed before? Consult past maintenance documentation, and look for a pattern.

Active Leak Detection Methods 

If you remember the old method of finding a hole in the walls of a bicycle inner tube, then you’ll know what’s coming next. In this case, however, the technology takes the principle to a whole other level. Advanced solvent test mediums are sprayed on suspect surfaces. Sealed once more, the vacuum is applied to the chamber. If the pressure gauge drops and the solvent indicates a leak, then a temporary putty seal is created. Tested again, the leak is said to be found if the gauge now holds steady. Alternatively, and this technique works best for those pinhole leaks mentioned earlier, a qualified operator sets up a helium mass spectrometer, a test instrument that traces small quantities of free-floating helium.

Solvent tests and inert gas spectrometer checks are effective vacuum heat furnace leak detection solutions. However, a predictive maintenance program can be just as effective, especially when the documentation held in that program contains the history of the chamber. Used as a tool to mark areas where wear and fatigue are occurring, the pattern detected by a scheduled maintenance plan isn’t quite as active as a spectrometer, but it can provide valuable clues, signs that point to certain seals and surfaces.

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