Arnold Howard on mon 1 nov 99
Hi Laura,
It is important to fire only bone-dry greenware. The
firebricks can absorb moisture from the clay,
resulting in excessive rust.
I look forward to hearing suggestions on this topic
from others.
Arnold Howard
Mesquite, Texas
--- Laura Freedman wrote:
> ----------------------------Original
> message----------------------------
> I have an old Sno Kiln that I purchased used several
> years ago. It sits on
> a metal stand on cement flooring. I have noticed a
> dark residue under the
> kiln which looks like flaking rust from the
> underside. As usual things
> always happen when you are the busiest, but
> yesterday I noticed that there
> was an exact imprint of the kiln on the cement
> floor. This time I really
> stuck my hand down under and found what appears to
> be ground rust plus a
> 3"x3" mutilated piece of metal which looks as if it
> too is busy
> disintegrating. This kiln is no where near water
> but in a basement with
> some moisture. I have never looked at the bottom
> (underside) but am
> assuming there is some kind of sheet metal on the
> bottom of kilns to hold
> things together? I have been busily firing for a
> show but am concerned the
> damn bottom is going to fall out on to the cement
> floor. Is that a
> possibility? The firebrick inside looks fine. Any
> suggestions at this
> moment would be very welcome. Laura
>
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Ray Aldridge on tue 2 nov 99
At 04:26 PM 11/1/99 EST, you wrote:
>----------------------------Original message----------------------------
>Hi Laura,
>
>It is important to fire only bone-dry greenware. The
>firebricks can absorb moisture from the clay,
>resulting in excessive rust.
>
In my experience, this is not so. Anecdotally, I fire damp ware all the
time, and see no excessive rust (and I have a Paragon that I've been using
for close to 25 years.) Logically, I can't see how moisture in the the
typically thin firebrick lining of an electric kiln could remain throughout
a firing. Or even how it could get there in the first place, since the
firebrick is much hotter than the damp ware at the beginning of the firing,
and would, it seems to me, be unlikely to absorb much moisture.
Though maybe I don't have any trouble because I candle kilns on low for
several hours before closing them up.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Vince Pitelka on tue 2 nov 99
A rusted base on an electric kiln is most likely due to moisture coming up
from beneath - from the floor or the ground, rather than from the kiln
itself. The highly corrosive effects resulting from the outgassing of
sulfur dioxide and water vapor (producing sufluric acid), is responsible for
the corrosion of mild steel screws, hinges, and other components in the
upper portion of an electric kiln, but normally does not affect the lower
portion as much, and usually not at all the base of the kiln.
Kilns installed in dry locations usually do not experience any breakdown of
the mild steel base over time. If yours is pretty far gone, and if you
anticipate the same corrosion occuring with a manufacturer's replacement,
then consider having a welder make you a similar one using heavier
angle-iron. It would be a simple fabrication job.
There was a comment about using stainless steel and something about
differential expansion rates. I was a bit perplexed by this, because
differential expansion between base and kiln body is irrelevant, since they
are separate units. If you can come up with a stainless steel base, then go
for it. Unfortunately, stainless steel fabrication is very expensive.
Good luck -
- Vince
Vince Pitelka
Home - vpitelka@DeKalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Arnold Howard on wed 3 nov 99
Ray Aldridge mentioned candling the kiln with moist
greenware (see below). After 25 years, his kiln has
not rusted.
The problem arises when the lid is closed too soon and
the moisture in the greenware absorbs into the
firebrick. We know of kilns that dripped water from
behind the steel case. One woman complained that her
kiln fired very slowly, then added that it also
dripped water. That explained why it fired slowly. It
takes a lot of power to burn off the water in the
firebricks.
I would be interested in reading the opinions of
others on this subject.
Arnold Howard
Paragon Industries, Inc.
--- Ray Aldridge wrote:
> >Hi Laura,
> >
> >It is important to fire only bone-dry greenware.
> The
> >firebricks can absorb moisture from the clay,
> >resulting in excessive rust.
> >
>
> In my experience, this is not so. Anecdotally, I
> fire damp ware all the
> time, and see no excessive rust (and I have a
> Paragon that I've been using
> for close to 25 years.) Logically, I can't see how
> moisture in the the
> typically thin firebrick lining of an electric kiln
> could remain throughout
> a firing. Or even how it could get there in the
> first place, since the
> firebrick is much hotter than the damp ware at the
> beginning of the firing,
> and would, it seems to me, be unlikely to absorb
> much moisture.
>
> Though maybe I don't have any trouble because I
> candle kilns on low for
> several hours before closing them up.
>
> Ray
>
> Aldridge Porcelain and Stoneware
> http://www.goodpots.com
>
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Janet Kaiser on wed 3 nov 99
------------------
I agree with Ray, Vince =26 Co. Rusting could not be from inside the kiln =
because
it will have been burned off, so H2O in the ware could not be responsible.
However, what could be the cause is condensation. Either from the cold wet =
air
in the workshop, a cold floor beneath the kiln creating wet fallout in the
atmosphere under the kiln, or keeping buckets with glaze etc. under the =
kiln. Do
you do that?
One of my jobs this winter, is to sand down and repaint a badly rusted
radiator... It has rusted simply because it is next to a toilet bowl and the
evaporating water from that has rusted the whole radiator in just four =
years...
Being in a corner, it is not possible to ventilate properly, because air =
does
not circulated well.
I therefore suggest looking into better ventilation around and under the =
kiln if
at all possible. Maybe a wipe with an oiled cloth after each firing would =
help
to prevent the problem?
Janet Kaiser
The Chapel of Art: Home of The International Potters' Path
Criccieth LL52 0EA, GB-Wales, UK
WEBSITE: http://www.the-coa.org.uk
EMAIL: postbox=40the-coa.org.uk
If you experience difficulties accessing our web site, please e-mail me=21 =
Thank
you=21
Ray Aldridge on wed 3 nov 99
At 04:22 PM 11/3/99 EST, you wrote:
>----------------------------Original message----------------------------
>Ray Aldridge mentioned candling the kiln with moist
>greenware (see below). After 25 years, his kiln has
>not rusted.
>
>The problem arises when the lid is closed too soon and
>the moisture in the greenware absorbs into the
>firebrick. We know of kilns that dripped water from
>behind the steel case. One woman complained that her
>kiln fired very slowly, then added that it also
>dripped water. That explained why it fired slowly. It
>takes a lot of power to burn off the water in the
>firebricks.
>
This is what I'm having trouble understanding. After the firing, the
bricks would be dry, wouldn't they? I would guess that even in a low
bisque, 2.5" of insulation brick would reach 100 degrees C throughout most
of their depth. So then where does the moisture for the next firing come
from? Not from the greenware, since even densely packed damp greenware
would not contain enough water to saturate the lining of a kiln, even if
directly applied to the brickwork. And of course, it isn't. It comes from
the ware as vapor, which would not easily condense on the brickwork, since
that is hotter than the pots during the early stages of firing, when vapor
would be present.
I could surely be wrong, because I often am, but this strikes me as one of
those clay myths that got started in some odd circumstance (roof leaking
onto a kiln, wet basement, etc.) and just got handed down as gospel.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Louis H.. Katz on thu 4 nov 99
Hi,
It should take no more power to "burn water off" from the fire bricks than
from the pieces. Kilns should be vented, but if you only vent in the early
part of the firing then when the chemical water is given off you will also
get condensation.
More likely corrosion of the connections between the elements and the wires
took place and the resistance went way up and the power way down. One
reason for this corrosion is water and acid vapors and other compounds
escaping through the holes the elements come through.
At the same time it is important to remember that only the inside of the
firebricks will be warmer than the ware in the kiln and the steel case will
be near room temperature; a good place for condensation.
My kiln vent tubing is highly corroded and often drips with moisture, I see
no reason why kiln cases couldn't also.
Louis
Arnold Howard on thu 4 nov 99
Dear All:
We have been discussing the rust on a kiln, with began
with a thought-provoking comment from Ray Aldridge.
During firing, moisture from the greenware turns to
steam. As the air expands, it escapes the kiln by
pushing its way into the pores of the firebricks.
Though the firebricks are very hot, the moist air is
driven into the firebricks. When the moisture reaches
the cooler kiln case, it condenses, causing dripping
around the kiln.
When the kiln heats up to the point where the case is
hotter than 212 deg F., the moisture no longer
condenses on the case. The moisture condenses mostly
as the kiln heats up.
The galvanized steel base rusts for the same reason as
the steel case. As the moisture is driven through the
firebrick bottom, it condenses on the base plate.
I hope that the physics experts on this list offer
their opinions.
Thanks,
Arnold Howard
Mesquite, Texas
--- Ray Aldridge wrote:
> ----------------------------Original
> message----------------------------
> At 04:26 PM 11/1/99 EST, you wrote:
> >----------------------------Original
> message----------------------------
> >Hi Laura,
> >
> >It is important to fire only bone-dry greenware.
> The
> >firebricks can absorb moisture from the clay,
> >resulting in excessive rust.
> >
>
> In my experience, this is not so. Anecdotally, I
> fire damp ware all the
> time, and see no excessive rust (and I have a
> Paragon that I've been using
> for close to 25 years.) Logically, I can't see how
> moisture in the the
> typically thin firebrick lining of an electric kiln
> could remain throughout
> a firing. Or even how it could get there in the
> first place, since the
> firebrick is much hotter than the damp ware at the
> beginning of the firing,
> and would, it seems to me, be unlikely to absorb
> much moisture.
>
> Though maybe I don't have any trouble because I
> candle kilns on low for
> several hours before closing them up.
>
> Ray
>
> Aldridge Porcelain and Stoneware
> http://www.goodpots.com
>
__________________________________________________
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Ray Aldridge on fri 5 nov 99
At 12:35 PM 11/4/99 EST, you wrote:
>----------------------------Original message----------------------------
>Dear All:
>
>We have been discussing the rust on a kiln, with began
>with a thought-provoking comment from Ray Aldridge.
>
>During firing, moisture from the greenware turns to
>steam. As the air expands, it escapes the kiln by
>pushing its way into the pores of the firebricks.
>Though the firebricks are very hot, the moist air is
>driven into the firebricks. When the moisture reaches
>the cooler kiln case, it condenses, causing dripping
>around the kiln.
I'm still having a little trouble imagining this. How much steam pressure
is required to force any substantial amount of moisture through 2.5" of
firebrick?
Wouldn't the kiln be whistling like a teakettle?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
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