redhat@digisys.net on sat 10 jul 04
wondering if anyone knows (can speculate) on the relationship between kiln=
size and element life=2E i fire a skutt 1227 (3 years now) it's 11-12 cu=2E=
feet and i get on average 100 firings per set of elements=2E that's half
bisque to 04 and half cone 6 with a bit of a cool down but no hold at peak=
temp=2E
i've used elements from skutt/euclids and currently a guy who makes 'em in=
oregon at kilnelements=2Ecom (super nice guy)(substantially less expensive=
)=2E=20
have not noticed much of a difference=2E=20
thoughts?
heidi haugen----west glacier, montana
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Cindi Anderson on sat 10 jul 04
Hi
It makes sense in your case because that kiln has a relatively low power to
size ratio (that is why it is rated at Cone 8 and not Cone 10). Because the
power is lower, the elements don't have to age very much before the kiln
doesn't have enough power. That is why there are kilns like the 1227PK,
or the similar sized Paragon Viking 28 which have a lot more power. If you
have the extra power you can run the kiln much longer on a set of elements.
Comparing for example,
Skutt 1227 9.9 cubic feet, 48 amps at 240v
Skutt 1227PK same size, 60 amps at 240v
Viking 28 10.57 cubic feet 60 amps at 240v
You can see 60 amps is much better than 48 amps for the same size kiln.
Also note that the Skutt 1027 is much smaller than these, 7 cubic feet, and
has the same 48 amps. So it will be able to fire longer on a set of
elements than the 1227.
The main reason many kilns stop at 48 amps is because people often prefer to
have a plug and that is the most amps you can put in a kiln and have a plug.
Otherwise it has to be direct wired. Or sometimes people are limited by how
much power they have in their house.
No favoritism is meant in my choice of kilns used in the above as
explanation. Most kiln manufacturers have similar low power vs high power
models.
Cindi
Fremont, CA
David Sturm on tue 13 jul 04
Cindi Anderson wrote:
The main reason many kilns stop at 48 amps is because people often prefer to
have a plug and that is the most amps you can put in a kiln and have a plug.
Otherwise it has to be direct wired. Or sometimes people are limited by how
much power they have in their house.
Actually, this is not quite accurate. The reason most kilns stop at 48
amps is because a kiln that draws more than 48 amps must be branch-fused
(this means the individual circuit branches in the kiln must be
individually fused. Anyone who has worked on an L&L J2927 would be
familiar with branch fusing as this kiln utilizes branch fusing in order
to accommodate the increased amperage draw of the kiln required for Cone
10 firing). Branch fusing increases the number of parts, wires, and
complexity of the control box, and can increase costs accordingly.
Further, to address the original question, chamber size is only one of
the many factors that effect element life. Larger kilns (with larger
firing chambers) require more energy in kilowatts to heat up the greater
space. However, larger kilns are designed with different elements,
different watt densities, and different surface loads to accommodate the
larger or higher required BTU input rate. This, however, is offset by
the BTU loss rate through the bricks which is demonstrated by a
logarithmic curve (changes as the bricks get hotter, but not linearly).
In Layman's terms, there are a few factors that are controllable by the
potter that affect element life, such as:
1- Longer firing times subject elements to longer periods of decay.
2- Hotter firings increase the rate at which elements decay
3- Greater mass inside the kiln increases firing time (see #1)
4- Burning out paper (as paper clay or paper used as a prop, form or
mask) causes excess carbon which burns out elements
5- Holding/soaking or firing down increases firing times (see #1)
6- Underpowered kilns (trying to fire a 240V kiln on 220 Volts or trying
to fire a 208V kiln on anything less than 204 Volts) increases firing
time (see #1) by reducing BTU output from element
7- Greater thickness of insulation decreases BTU loss rate and therefore
extends element life (since the elements do not have to fire as long to
get the kiln to a given temperature )
8- Using ceramic fiber as a gasket between sections/lid/floor reduces
BTU loss (see #7)
It really is a complicated issue. The best resources for this
information are "The Kiln Book" by Fred Olsen, and "The Electric Kiln"
by Harry Fraser.
David Sturm
Bracker's Good Earth Clays, Inc
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