One of the foremost quality characteristics of SCHOTT glass-to-metal seals is our hermeticity. Because of its importance to the functionality of components, the vacuum tightness of our glass-to-metal seals is constantly monitored through random sample inspections. Tightness tests are performed with helium leakage detectors that work according to the mass-spectrometer principle.
Using helium as a test medium, modern leakage detectors are capable of tracing minute leaks of 10-12 mbar l/s. However, this is only possible under laboratory conditions and requires long pumping and measurement cycles.
In tough everyday usage, leakage rates of up to 10-8 mbar l/s can realistically be measured. That is why SCHOTT glass-to-metal seals are generally guaranteed to a leakage rate of 10-8 mbar l/s; in this case, the pressure differential between the interior and the exterior is 1 bar. In special cases and upon agreement, leakage rates down to 10-11 mbar l/s can be confirmed and guaranteed, because, as a rule, SCHOTT glass-to-metal seals also meet these lower leakage requirements.
The leakage rate of SCHOTT glass-to-metal seals can also be tested under non-static conditions. For example, it is possible to conduct cap welding tests with increased welding stresses and then to determine the remaining leakage rate.