mel jacobson on sun 15 sep 02
i totally agree with snail, and recommend to most
friends that they keep their electric kilns firing in the
cone 6 and under.
at hopkins high, i fluxed down a bit, use gb and volcanic
ash...and fired at cone 3.
when firing almost every day, cone 3 is really good.
the problem in those days, no good cone 3-5 clay.
we were always at the low end for the claybody.
now there are good clays for that range.
and, for sure, i do not like long range clay body.
`hey, this clay is good for cone 1 to 10.`
not. ever.
anything you do at cone 6, cannot be improved
usually going to cone 10 electric. just kicks the
devil out of your kiln.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
Wes Rolley on sun 15 sep 02
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At 11:38 AM 9/15/02 -0500, you wrote:
>i totally agree with snail, and recommend to most
>friends that they keep their electric kilns firing in the
>cone 6 and under.
This is good practical advice. I know that the elements in my Skutt did=20
not last as long as I believe that they should have. I am not sure if the=
=20
cause was firing to cone 10 or using unwashed wood ashes in many of my=20
glazes or the combination of the two. I have two questions:
Why do kiln manufacturers rate kilns for use at Cone 10 if they are not=20
capable of sustaining a production workload with firing temperatures in=20
that range?
If the major problem is with the elements, what would it do to the cost of=
=20
a kiln to provide efficient elements that were capable of sustaining=20
production firings in that range? Is it only a matter of cost?
Given that I would have to sell my house and move somewhere else to utilize=
=20
any combustible fuel, this is a real issue for me. There are things that I=
=20
like to do which are effective at Cone 6. Some are effective at Cone 8.=20
There are others that I like to do which are effective at Cone 10.
I know that there are electric kiln manufacturers who monitor this list and=
=20
I would like to hear their answers to these two questions.
"I find I have a great lot to learn =96 or unlearn. I seem to know far too=
=20
much and this knowledge obscures the really significant facts, but I am=20
getting on." -- Charles Rennie Mackintosh
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
wrolley@charter.net
(408)778-3024
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Stephen J Lewicki on mon 16 sep 02
Dear Wesley,
You ask some good questions and I appreciate the opportunity to respond. I
am sure some of my fellow kiln manufactures will also take you up.
First, we could and in fact do make kilns and furnaces in our industrial
division that easily can sustain Cone 10 temperatures and beyond. These use
silicon carbide elements with low voltage power transformers or other
exotic elements. An 8 cubic foot 2500 Deg F furnace starts at about
$35,000. Actually, however, the periodic cycling of pottery firing is not
good for the life of silicon carbide elements. We also make front loading
kilns with 6-1/2=94 of insulation using the same iron-aluminum-chrome alloy
elements used on the pottery kilns. These are also very expensive (8 cubic
feet is about $12,000). To some extent it is not a question of technical
capability but one of cost and the ability of potters and their customers
to afford the technology. Cone 10 temperatures push the limits of the low
cost technology of ceramic top loading kilns. However, even with the
reduced element life at Cone 10 temperatures and the energy losses it is
still very cost effective when compared to the alternatives. I do agree
that extra insulation would help. We do recommend 3=94 for high firing and w=
e
have a heavier gauge element that we also recommend. In addition there is
another alloy, Kanthal APM, which will improve element life at these high
temperatures and work at line voltages. However these elements cost three
times as much as the standard elements and they can break or get ruined
just as easily from glaze. We do offer APM elements but we don=92t feel they=
are cost effective in general.
Actually you asked why do we rate the kilns for Cone 10. The kilns do work
at Cone 10, some better and more reliably than others. Perhaps a good
analogy is your car. Your car will go 120 miles per hour. That does not
mean you want to use it at those speeds all the time and if you do you
certainly know you will be doing more maintenance than the person who
drives slower. One thing to keep in mind is that the element life is
logarithmic with respect to temperature. If you only fire to Cone 05 your
biggest problem will probably getting the elements out of the groove in 20
years (after the grain growth of the alloy). Cone 6 firing will give you
fairly reasonable life with most kilns. If you fire to Cone 10 be prepared
for 10 or 20 firings on a set of elements. If you are going to fire to Cone
10 you must be prepared for the extra cost and build it into the price of
your work.
A company who makes special machines for industry just bought one of our
automatic pottery kilns for an industrial process. One of their engineers
looked it over and remarked how amazing it was that he could get do much
for so little money. I mention this story to illustrate how the idea of
value can depend so much on your perspective.
I hope this helps. You can find more information on element life on our web
site at www.hotkilns.com.
Stephen Lewicki
President
L&L Kiln Mfg., Inc.
877.513.7869
steve@hotkilns.com
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