Besides catastrophic damage due to mechanical abuse, eutectic melting or braze alloy spillage, vacuum furnace hot zones will deteriorate over time as a result of the repeated thermal cycling to which they are exposed.
The life of a hot zone may vary widely depending on operating conditions. Furnaces that are operated constantly in aggressive environments (eg. sintering) or consistently at temperatures over 1370ºC (2500ºF) may require fairly major hot zone maintenance as often as once per year. Hot zones in furnaces used for standard heat treating operations can be expected to last from 5 to 7 years. BY JEFF PRITCHARD