william schran on sun 10 apr 05
With all the recent messages regarding firing or not firing to cone
10 in an electric kiln, I think we're agreed that elements will wear
out faster at higher temperature. But now we have to ask: what are
the factors contributing to them wearing out faster if, as some
contend, cone 10 is not that much hotter then cone 6? And why would
somebody get 30 firings out of a set of elements, while somebody else
get 50 firings, both firing to the same temperature?
Some factors:
1.Length of firing, especially the length of time between ^6 & ^10
(longer time at higher temperature),
2. How the kiln is loaded - tight or loose & distance between
pots/shelves and the elements (closer pots/furniture is to element,
the more heat reflected back to element, heating it more, degrading
faster).
3. The ingredients of the glaze - at higher temperatures I would
expect more out gassing of certain materials that may degrade
elements.
4. Materials in clay/bisque firing- more organic materials in clays
will release more corrosive gasses that strip away protective layer
on elements.
5. Venting of kiln - Using a vent system during the entire firing
(not cooling phase - unless you want to crash cool) will help a great
deal to remove gasses created at various times during the firing.
Kilns without a venting system - well, the stuff just has to make
its way out any openings, but have time to linger around eating away
at the kiln.
6. Pickyness of the potter - how long will each individual allow
their firings go before changing the elements. With my crystalline
firings, the speed through the last few hundred degrees is critical
for me.
Perhaps the kiln manufactures may want to take their products on
extended test drives at different temperatures, different loads, with
& without venting and report back.
Bill
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