I was doing some reading on Kanthal and came across the blurb below. After replacing elements I have always run the kiln empty up to around ^04 then shut it off but am wondering how significantly element life is improved if held for the 7 to 10 hours as recommended by Kanthal. Does anybody do this and have you found an increase in element life?
From the Kanthal Handbook, referring to their FeCrAl alloys (i.e. A-1 alloy):
"The durability of resistance alloys in air at high temperatures is greatly increased by an oxide surface layer formed by a reaction with the oxygen of the air. The protective nature of this oxide layer is proportional to its area and depth. Foreign matter usually interferes with the formation of the oxide layer, and this causes a reduced life. ... At high temperatures the protective layer of Kanthal materials consists almost entirely of aluminum oxide. This has a light grey colour and good chemical resistance. At temperatures below 1000oC (1832oF) the oxide layer has a dark colour since the aluminum oxide is impure."
In order to protect elements from the effects of harsh environments, it is very desirable to condition the elements, by pre-oxidizing them. This is accomplished by firing them to a temperature of 1050oC/1922oF and soaking for several hors, 7-10 if possible. The process is enhanced by allowing good air flow into the kiln - leave the peepholes open, or the KilnVent on. If you are doing reduction firings in an electric kiln it is desirable to periodically re-oxidize the elements, for best life expectancy. The results of element conditioning can be quite dramatic. It may not have much affect for normal, low temperature firings, but can be significant for harsh operating conditions."