New Elements

[Min]

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."

 

 

 

 

[neilestrick]

All kiln manufacturers recommend an empty firing with new elements to oxidize them, but I have never heard of the hold time. Perhaps it's because typical use of an electric kiln doesn't qualify as 'harsh conditions', and therefore the hold time isn't all that beneficial.

 

L&L's first firing schedule in a new kiln is a slow bisque to cone 5, about 19 hours total, but it is for the benefit of the bricks, mortar and brick coating as much as the elements.

 

Interesting stuff.

[oldlady]

neil, is your figure of 19 hours a typo or is it really that long?

[High Bridge Pottery]

Interesting stuff, would be good to know what they exactly mean by harsh conditions. Seems to me they might include high fire in that but hard to work it out.

[David Woodin]

Euclids   recommends firing to 1922 F peep holes open hold for 8 hours.  That is what I have been doing and it is almost as good as coating with ITC 100, a lot cheaper too.

David

[neilestrick]

neil, is your figure of 19 hours a typo or is it really that long?

 

It's really that long. It's a slow bisque schedule, which is the slowest pre-programmed schedule, but going all the way up to cone 5 instead of just to low fire temps.