Craig Martell on tue 16 dec 97
At 11:38 AM 12/15/97 Karl Platt, wrote:
>----------------------------Original message----------------------------
>Most electric kilns are make of 2300 brick. This is owing to a number of
>things -- not the least of which is that Kanthal elements aren't very
>useful abive 2300 F or so. Cone 10, unless you want to wait a very long
>time to reach maturity, requires higher temperatures. Sure youy can take
>the kiln built of 2300 IFB to higher temperatures, but you run the clear
>risk of melting it
Karl:
K-23s aren't going to melt at cone 10. There are many gas kilns made with
2300 degree IFB's that are fired continually to cone 12 with no severe
problems developing for many years and many firings. You need to use
refractories in the fire boxes that are stouter than k-23s if you want the
kiln to last a LONG time but even there, it takes a lot of firing to cone 10
to start the bricks to spall from what I've seen.
Kanthal elements do a fine job of getting electrics to cone 10 IF they are a
heavy enough guage. Unfortunately, some kiln manufacturers use element wire
that is too light for cone 8 and above. Fournier recommends 13 gauge for
high fire but it's hard to wind and stretch these. I built a 16 cubic foot
electric with k-23s backed up with AP Green Insblock 19 (a 1900 degree
material) and used 14 gauge kanthal elements. This kiln fired to cone 10 in
about 12 hrs and lasted for years and hundreds of firings. It was in fine
shape when I finally sold it to another potter. The real problem with a lot
of electrics is that they are underinsulated and underpowered so they take a
long time to get to high temperature. Most of the decagon type kilns sold
are considered as "hobby kilns" and not really suited for "commercial" use.
They still do the job though. If you increase the thickness of the walls
from 2.5 or 3 inches to 5 inches and beyond they fire faster and cool
slower. The heavier guage elements lengthen the life of the elements and
make it less painless to fire continually to cone 9-10 because of less
frequent element replacements.
regards, Craig Martell-Oregon
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