[Clayart] kiln elements - how many firings to expect?

[Marcia Kindlmann via Clayart]

Greetings all,

speaking of crickets -- I posted a question last
week about how many firings should one expect to
get from electric kiln elements. (before the
voltage drops so much that firings are too slow
and you change the elements.)

Got no answer.

My question was rather long, since there are so
many variables. Maybe specifying the variables
created confusion? Or was unnecessary? Or was I
missing something obvious that the question
should've included?

so, here's the question again. BTW I'm not
trying to pitch a beef at any element
manufacturer. I'm just trying to learn what's
the consensus out there.

the question:

How many firings should I expect to get from
Kanthal A-1, 13-guage elements in an 8-cu-ft kiln
used for both bisque and glaze firings;
glaze-firing to cone 10-half-down? That is,
_approximately_ what number of firings -- to
nearest 20 or so -- I know there's variables
here. Kiln is vented only w/ lid slightly ajar
to about 800°F in bisque & glaze (latter for wax
resist burning off). Firings are slow, using
cones not kiln-sitter, 20 hrs for bisque & 23
hrs glaze, going 130°F/hour in bisque from
steam-out to 1750°F & slower after that, and in
glaze, after quartz-inversion, 140°F/hr to 1750°F
& slower after that.

thanks,
marcia in CT
MAILMAN_MIMEDEFANG WRAP
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[via Clayart]

Hi Marcia,

I have not answered because I have no experience firing to cone 10 in
electric kilns - lots of firing to cone 8 - we fired where I was
teaching maybe 100 times a year and replaced elements about every year
- whenever one element stopped working.

We would have gotten much better results if we has a vent running - no
such thing then. You are closing up your kilns just when the organics
in your clay start to burn up - thats hard on elements.

My best advice is to get a vent system - good for your to.

RR

Ron Roy
ron...@ca.inter.net

[David Woof via Clayart]

Hi Marcia,

I remember the essence of your posted question and I thought it got answered during the on going "Elements" thread.
Though because of the variables, (the ones you mention are just the tip of the iceberg of possibilities,) it is as you say, really hard to give a definitive answer. In retrospect, I think you may have been answering your own question.

***Perhaps there is someone who can get you in the ball park of expectation for that particular element and the experience you are putting it through. ***

I note that you keep record of your firings and observations. It would also be a good thing to do regular multi-meter readings of the resistance changes over time and changing firing conditions.
You will receive your own most definitive answer from your own extensive records. It will be a heads up as you progress toward replacement time.

Note my recent example: last bisque and glaze firing cycle I had run out of my usual ^010 for the bisque, and with a "what the hell, see what happens" fired sitter ^013 which in reality with that particular sitter would have been ^015.5 for a ^6 tight red clay body. Glazing that very open bisqued body was a chore, had to adjust glazes and application, and when unloading the glaze firing I noted that the upper two shelves of pots appeared reduced in body as well as that my familiar oxidation glazes also had a changed appearance including five pots who sit waiting for a "Salvation Glaze" re-fire.

First thought, then, was that my low bisque left too much organic crud in the clay body which burned out after I had closed the lid on the glaze firing and so reduced the upper portion of the stacking enough to be noted. There is a small vent hole in the lid.
Second thought, was re burning off the protective aluminum oxide coating from the elements. As I'm sure you know, each time we burn off the oxide coating in a reduction atmosphere; in a subsequent oxidation firing new oxide forms, taken from the material of the elements which over time and occurrence decreases the diameter of the element and thus in itself changes the resistance. So how much did I shorten my element life by this one cavalier bisque firing attitude?

Wishing best of all of clay and fire has to offer to all,

David Woof
*********************************
<Marcia said: <"speaking of crickets -- I posted a question last

week about how many firings should one expect to
get from electric kiln elements. (before the
voltage drops so much that firings are too slow

and you change the elements. Got no answer.>"
********************************************
********************************************

> Date: Sun, 7 Sep 2014 07:42:19 -0400
> To: cla...@lists.clayartworld.com
> Subject: [Clayart] kiln elements - how many firings to expect?
> From: cla...@lists.clayartworld.com

[William & Susan Schran User via Clayart]

Marcia,

Is the length of time for your firings because you are firing sculpture
that is thicker and may have some unevenness?
18 gauge elements are on the smaller side, so will not last as long as
larger gauge for slow firings to cone 10.
With your firing schedule I would think perhaps 50 firings before you have
enough element wear to need to change elements.
Probably in the 30 - 40 firings after which you notice a longer firing.

Bill
--
William "Bill" Schran
wsc...@cox.net
wsc...@nvcc.edu
http://www.creativecreekartisans.com

On 9/7/14, 7:42 AM, "Marcia Kindlmann via Clayart"

[Arnold Howard via Clayart]

On 9/7/2014 6:42 AM, Marcia Kindlmann via Clayart wrote:
> speaking of crickets -- I posted a question last week about how many
> firings should one expect to get from electric kiln elements. (before
> the voltage drops so much that firings are too slow and you change the
> elements.)
>
> Got no answer.

Many factors affect element life besides the cone temperature--type of
clay, element wire gauge, hold time, controlled cooling, kiln wall
thickness, and even low voltage. So it is difficult to say.

Nevertheless, here is a general estimate that the late Tom Buck sent me
years ago. It comes from Kanthal, a manufacturer of element wire. (Tom
Buck was a Clayart member from Canada.)

Kanthal A-1 wire elements:

Firing to Cone06/05 (1000+ oC, 1832+ oF) repeatedly ONLY, ie, a bisque
firing, the lifetime is over 1000 firings under normal conditions
(claybody is low on sulfur and nitrogen materials, and silico-fluorides).

Firing to Cone 6 (1240 oC, 2264 oF), the lifetime is 200 firings.

Firing to Cone 10 (1305 oC 2380 oF), the lifetime drops to 120 firings.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
aho...@paragonweb.com / www.paragonweb.com

[Vince Pitelka via Clayart]

My colleague Jeanne Brady (fibers studio) and I are in a two-person exhibition entitled "Surface and Volume" at Vanderbilt University's Sarratt Gallery in the Sarratt Center in Nashville. Almost all of my work in the show is from 2014. The exhibition will be up until October 10th, but the gallery talks and reception are this Thursday, September 11, from 4:30 to 6:30. Sorry for the short notice. If you are in or near the Nashville area it would be great to see some Clayart members there.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpit...@dtccom.net
http://iweb.tntech.edu/wpitelka/