Joanne Van Bezooyen on sat 23 oct 99
disappointed again.
yesterday, I shortened the kiln (removed a ring) and sealed up some
leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
By midnight, feeling as exhausted as if I'd been heating it
myself....well, maybe it was a couple margaritas....I shut it all off.
I think it reached cone 3??? as my cone 5 glaze had melted but was
pitted.
the interesting part is that by 8 am the kiln was cool. Perhaps I need
insulation???? Can any of you recommend something? I suppose i should
coat the inside with itc100....do I wrap the outside with wool and
chicken wire?
this may be a lesson in
"I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper".
Joanne in Tucson Arizona
Nikom Chimnok on sun 24 oct 99
Oh for goodness sakes, Joanne,
Join the 20th century and get a pyrometer. Somebody recommended this
before, but you didn't listen, so I can only try to say it more forcefully.
If you have a pyrometer you can tell whether the temperature is
going up or down, and how fast it's going up or down. You can use the
scientific method: try experiments. Push in the damper and see if the temp
goes up. Pull out the damper and see if the temp goes up. Turn up the gas
and see. Turn down the gas and. Open the primary air shutters. Close them.
Find out what's going on.
I've been through this myself, a mere 10 years ago, and remember it
well. Before I got my first pyrometer I was mystified. After I got it I
started learning how to fire. If you can't tell which direction, if any, the
temperature is going, the learning curve is depressingly slow. If you can
tell, you learn quickly.
It's possible you will find out you don't have enough firepower, and
have to drill out the orifices or change regulators or something. Do you
have a gas pressure gauge?
But more likely you have too much air or not enough air, and either
problem is easy to fix. In an itty bitty gas kiln like you're using,
insulation doesn't determine much. If you pour the coals to it, you can hit
1400 C in 2 hours with 2 inches of fiber. Maybe it'd take 3 hours with soft
bricks. You can have so little insulation that it gets red hot on the
outside, but it'll still cook the load.
Don't worry, you'll get better. But unless you get a pyrometer or
the help of a friend who has some firing experience, it might take 2 years.
Or longer. Makes a hundred dollars sound cheap, no?
Good luck,
Nikom
****************************************************************************
At 22:58 23/10/99 EDT, you wrote:
>----------------------------Original message----------------------------
>disappointed again.
>the interesting part is that by 8 am the kiln was cool. Perhaps I need
>insulation???? Can any of you recommend something?
>this may be a lesson in
>"I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper".
>
>Joanne in Tucson Arizona
Pottery by Dai on sun 24 oct 99
Hi, Joanne - I am following your thread of firing problems with this
conversion kiln with great interest, as I may possibly convert one of my
older unused kilns to gas, if it seems workable. If you get any ideas or
suggestions off-list, I'd appreciate you posting them for the rest of us. I
hope you are keeping your sense of humour about this---I'm sure it's just a
matter of learning the tricks of gas firing! I'm keeping my fingers crossed
for you......
Dai in Kelowna, B.C.
potterybydai@home.com
I started out with nothing, and I still have most of it left.
Cindy Strnad, Earthen Vessels Pottery on sun 24 oct 99
Joanne,
I haven't been following this thread, as I'm not sure what a "cold
conversion" kiln is, but I sure wouldn't recommend wrapping the outside with
anything remotely inflammable.
First, if the elements came with the kiln, you may want to look into
replacing them. Check to see that all are intact (just look for breaks). You
can also turn the kiln to high and see if they turn red. (Some of the newer
elements won't, though, until much later in the firing. The really best way
is to check them with a meter.) For replacement elements, I recommend
Euclids--1-800-296-5456.
Second, check that your circuit is adequate. A 40 amp circuit if a 60 is
needed won't supply the power necessary to get your kiln up to temp. Also,
the wire from the circuit to the kiln must be both heavy enough and short
enough to deliver maximum power. Power available from the electric company
plays a vital part. You should have a qualified person check your kiln
during maximum firing to make sure it's getting the umph it needs.
>From what I hear, spraying the kiln with itc may help, but I have no
personal experience with this.
Finally, if you *do* decide to buy a new kiln, do *not* buy a Paragon.
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Lorraine Pierce on sun 24 oct 99
Dear Joan, are you using your danper and other controls to keep your heat IN the
kiln? Peter, at Summit Kilns, the owner of the company and builder of these kiln
should help you with this. +Also there is a small book by Ralph W. Ritchie, Gas
Kiln Firing, that should be a big help. Do you have a friend who has a gas kiln
and would help with the next firing? when you post your firing it sounds as tho
all you are doing is opening up the gas and letting it flow thru the kiln...can
you adjust the burner pressure and damper as needed? I don't know about these
little updraft kilns, but in a larger one you pre-heat (candle) for severl hours
or overnight at a stable temp below 200...then if all the steam has escaped, ope
the burners, and set the damper, to the adjustment that gives you the desired
temperature increase...to have a temperature rise , you have to have the right
combinations of damper and gas pressure settings, which you adjust as needed. I
wont happen by setting a switch as in an electric kiln...more like baking in a
wood stove , you control the imput as well as the exit of the heat.
Good luck to you...remember the time it took you to center? Well to learn to gas
fire takes time as well. Lori in New Port Richey Fl.
Joanne Van Bezooyen wrote:
> ----------------------------Original message----------------------------
> disappointed again.
>
> yesterday, I shortened the kiln (removed a ring) and sealed up some
> leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
> By midnight, feeling as exhausted as if I'd been heating it
> myself....well, maybe it was a couple margaritas....I shut it all off.
> I think it reached cone 3??? as my cone 5 glaze had melted but was
> pitted.
>
> the interesting part is that by 8 am the kiln was cool. Perhaps I need
> insulation???? Can any of you recommend something? I suppose i should
> coat the inside with itc100....do I wrap the outside with wool and
> chicken wire?
>
> this may be a lesson in
> "I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper".
>
> Joanne in Tucson Arizona
Joanne Van Bezooyen on sun 24 oct 99
------------------
Thank you Francoise for writing back.
Okay....here are all the facts about my kiln....as I know them:
1. Old electric hexagon-shaped built of soft-bricks only. Soft brick, flat
base
with a number of =22rings=22 of bricks to set one on top of each other to =
make it
as
high as possible. Interior diameter of the kiln is 17.5=22. Each 'ring' is=
2.5=22
thick and 4.5=22 in height. I have 7 rings I can use.
2. I am using natural gas for fuel and my kiln is in a roofed area outside =
on a
cement slab. From the main natural gas connection to the house, my husband =
ran
a
3/4=22 pipe approximately 20 feet to the kiln site. He placed a shut-off =
valve at
this hook-up point.
3. We purchased, from Summit Kilns, a conversion kit =22 GV-18=22 . It =
does not
say
how many BTU's each burner is for this conversion kit, but the brochure =
says,
=22With these burner conversions shystems you can not only do raku but also =
reach
stoneware temperatures up to cone ten.=22 Discription of the conversion =
GV-18
says, =22It offers two burners, with an adjustable pilot system, ...=22. It=
is a
square, welded angle iron steel frame with a burner at each corner shooting
straight up, pilot at each burner and a valve to open the gas for lighting =
the
burners. There is also a gas valve to turn to adjust how much gas goes to =
both
burners. Included was a template for kiln cut-outs.
4. Kiln-cut-outs.....husband cut 3-3.5=22 diameter holes to fit over the =
2=22
diamter burners. The rectangular hole in the lid is cut 4.5=22 by 5.5=22.
5. Instructions with the conversion kit said to use 2=22-3=22 posts (I used=
2=22) on
each side of each burner hole and across the center to support a bottom =
shelf.
I
did not put any ware on this shelf but posted another ware shelf on top.
6. When husband ordered the burners kit, he asked the burners to be 'set' =
for
7=22
water column pressure of natural gas. Summit says 11=22 is normal. We may =
have
made a mistake there, and if it makes a difference, we'll call the gas =
company
again and then we'd need to learn how to correct the burners.
7. The kiln seems to heat quickly to orange heat but at yellow-orange it =
has
problems progressing.
8. I don't know of anyway to control air-intake at the base of the kiln as =
it
is
not forced-air, unless someone suggests covering part of the 3=22 holes with
something before loading the kiln.
9. I realize I need to purcase a pyrometer...digital, right? but hate to =
put
more money into this until I see the kiln can fire hot enough to use it.
The first time I fired it, I used 5 rings....times 4.5=22 equals an interior
height
of 22.5=22. I shut it down after 11 hours of orange heat.
The second time I fired it, I used 4 rings...equals interior height of =
18=22. I
shut it down after 15 hours of yellow-orange heat...approx. cone 3.
I've since removed the elements from 2 rings and stuffed them with strips of
kaowool I've had laying around.
I would really appreciate guidance. Hopefully the details provided above =
will
help someone see an obvious mistake on our part...or area to focus on. =
Thanks.
Joanne in Tucson
Fran=E7oise Melville wrote:
=3E Dear Joanne:
=3E Don't give up on your kiln yet=21
=3E I am no expert but so far I have had two gas kilns=3B one which had two
=3E burners and ran on propane, and my present one, a small Olympic updraft
=3E (23=22 wide x 27=22deep) which is fired with natural gas. Both had =
problems
=3E initially when I didn't understand them.
=3E You do not give us the measurements of your kiln, although you did =
mention
=3E 17=22 and I would think that it is fairly small.
=3E I certainly don't believe that removing one section would improve =
matters.
=3E Nor do I think that you need more insulation. Kaowool on the outside is
=3E unhealthy. ITC is expensive. My garbage can raku kiln with just one
=3E weed-burner and 1=22 of kaowool liner, heats up in no time. It would =
be
=3E helpful if you had a cheap pyrometer so that you could see more or less =
the
=3E rise in temperature before reaching red or yellow heat. Gas kilns cool =
down
=3E faster than electric ones. Your burners must have some kind of =
adjustable
=3E air intake. Light the kiln with nothing in it. Open the lid and adjust
=3E the gas pressure and air. Close the lid and compare. Study the flames =
which
=3E should not be smoky. Natural gas does give a lazier, more wavy flame =
than
=3E propane and is not so noisy. I single fire unusually fast to =5E6 now =
in
=3E just over 6 hours. To begin with I would prolong firings to 9 hours, =
but
=3E found this unnecessary for my type of clay and glazes. When I first
=3E installed my Olympic I just couldn't keep the temperature down at all: =
in
=3E the first hour the pyrometer would show a rise of 600C. The reason was
=3E that the orifices of the burners were not the right size for my gas line
=3E and meter and I had them re-bored. After that I found with practice I
=3E could control the flame from a tiny candle to full blast even though I =
have
=3E no manometer. After a few firings you learn to recognize the correct
=3E colour and sound of the flames and adjust them by ear and eye. Maybe =
the
=3E vent in the lid of the kiln is not the right size - 4=22 seems on the =
small
=3E side to me. Try posting the exact measurement of your kiln including =
the
=3E thickness of the bricks to the list, and with any luck Marc Ward, =
Cameron
=3E Harman or some other guru will give you good advice. How many BTUs are
=3E the burners supposed to supply? Once you do manage to get that thing up=
to
=3E =5E6, and you will, you may find you have another problem, namely that =
you
=3E have very uneven heat from top to bottom. This, too, can be remedied by
=3E placing an empty kiln shelf at the top of the kiln, about 1=BD=22 below =
the vent.
=3E Good luck,
=3E Fran=E7oise
=3E Indalo Pottery
=3E http://indalopottery.tripod.com
Burt Cohen on mon 25 oct 99
Hi Joanne: I think that the first solution to your problem of achieving
temperature is to find a potter who works with gas to take a look at your
set up. It is probably very simple/ Clayart is a lousy medium to
troubleshoot kiln problems.(My opinion) You have a few requirements to
advance temperature.-first- enough fuel-, ie enough gas (as well as
pressure) factors here are size of tank size of orifice on burner # of
burners in relation to the kiln size. Second-amount of air- at burner
(primary) coming into kiln (secondary) as well as the size of the chimney.
Lastly the kiln itself- But I tend to think that isn't your problem because
everything else being equal a good combustion system can usually overcome
even poorly insulated kilns-
ITC ain't gonna help you!
Sorry just had to say that
Yours-
Burt Cohen
-----Original Message-----
From: Joanne Van Bezooyen
To: CLAYART@LSV.UKY.EDU
Date: Saturday, October 23, 1999 8:06 PM
Subject: cold conversion kiln
>----------------------------Original message----------------------------
>disappointed again.
>
>yesterday, I shortened the kiln (removed a ring) and sealed up some
>leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
>By midnight, feeling as exhausted as if I'd been heating it
>myself....well, maybe it was a couple margaritas....I shut it all off.
>I think it reached cone 3??? as my cone 5 glaze had melted but was
>pitted.
>
>the interesting part is that by 8 am the kiln was cool. Perhaps I need
>insulation???? Can any of you recommend something? I suppose i should
>coat the inside with itc100....do I wrap the outside with wool and
>chicken wire?
>
>this may be a lesson in
>"I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper
".
>
>Joanne in Tucson Arizona
>
Gavin Stairs on mon 25 oct 99
At 19:47 1999.10.24 , Cindy Strnad wrote:
>...I haven't been following this thread, as I'm not sure what a "cold
>conversion" kiln is, ...
Me neither. What's a cold conversion kiln?
...
>Second, check that your circuit is adequate. A 40 amp circuit if a 60 is
>needed won't supply the power necessary to get your kiln up to temp. Also,
>the wire from the circuit to the kiln must be both heavy enough and short
>enough to deliver maximum power. ...
This is what got me up out of my rapid reading slump: A 60A appliance on a
40A circuit is not simply inadequate. It is DANGEROUS!!! Please do not
try to replace the 40A fuse or breaker with a 60A one. This could get you
seriously burnt up.
Moreover, there is more than one kind of 60A fuse, and the wiring to go
with it. The Canadian Electrical Code (1998) calls a continuous load any
load (under 225A) which operates for 1 out of every 2 hours. That is, a
kiln on full power. Such a load may be served over a circuit in which the
protection device (circuit breaker or fuse) AND the ampacity (capacity of a
wire or circuit element in Amperes) of the wiring BOTH meet or exceed the
capacity required. I won't attempt to explain the ampacity requirement: if
you don't already know, you need more instruction that I can give by
e-mail. Suffice to say that insufficient ampacity in wiring and
connections is what burns houses down. An installation may still meet code
if it can be demonstrated that the full, continuous capacity will not be
served in that circuit. Then the ampacity of the circuit may be derated by
a factor determined by consulting the tables in the code, which may be only
70% or 80% of the full, rated load. Such a circuit should be labelled for
80% load at the breaker box. (An example of a derated appliance circuit is
one in which a startup current exceeds the operating current, or the
appliance cycles on and off in less than two hours, and has a duty cycle
less than 50%. Small motor appliances, or some lighting circuits may
qualify. Heating appliances almost never do.)
Table 2 of the Canadian Code says that an enclosed residential cable
carrying 60A must be AWG 6 or greater for a cable rated at 60C. If you
read the fine print, it would probably be better to use AWG 4 cable for a
kiln service at 60A. Every cable conductor size has a stated ampacity limit.
I don't know what the equivalent codes are in the USA or elsewhere. And if
you live in a house with wiring which may not be up to recent codes, you
should assume that it is NOT up to rated ampacity. In any case, before
using a circuit to full rated capacity, check, or have a knowledgeable
person check for you, that the circuit ampacity is adequate. Make sure
that they understand that you intend to operate a CONTINUOUS, HEATING LOAD
on the circuit. Then, if they tell you that the circuit needs to be
upgraded, have the work done. An overheated wire or plug or switch can
ruin your whole day.
Gavin
Hank Murrow on mon 25 oct 99
Dear Joanne; I am very sorry you seem to be attracting flame
threads in the midst of your difficulties with the kiln. However, your post
gives much needed information with which to help you. I wonder since your
kiln is essentially a very small updraft if shortening the chamber is
somewhat counterproductive. You probably need more vertical just to achieve
some draft; the kiln itself being the flue in your case. I once built a
small lifting fiber test kiln, to which I had to add a fiber flue tube for
additional draft to get to C/10 because the kiln @ 24" was just too short.
Burners are best understood as mixers of gas & air. There probably
is an air shutter(disc) at the base of each mixer, which could be opened to
allow primary air to the mixer. Primary air is that which enters the burner
WITH the gas and burns as it exits the mixer. Secondary air enters the kiln
around the burner WITHOUT mixing with the fuel. If there is an air shutter,
three to four turns is full primary air. After air control you need to know
the relative gas pressure; so try to build the manometer I mentioned in my
post of the 18th for relative pressure control. Even if it is not
"accurate" in terms of inches of water; it will tell you "more and less",
and be repeatable with precision. You did not mention whether any other
devices share this gas line; but you can easily adjust the gas pressure at
the regulator by removing the cap on the front of the regulator and
screwing the washer there clockwise a turn at a time while checking the
pressure on your manometer. I asked about other devices sharing the line
because they too would have an increase in pressure, which may or not be
beneficial. In any case, you may also drill out the orifices a little to
increase the flow of gas at whatever pressure you currently have (like
having a bigger hose in your garden). I reccommend that you do the other
things before drilling the orifices. I have even drilled them during a fire
when it was apparent that I needed more. Perhaps this would be possible
with your mixers. Feel free to call me @ 541-342-8429 Pacific Coast Time if
you get in a bind or want clarification on some point. And Good Luck! Hank
in Eugene
>----------------------------Original message----------------------------
he asked the burners to be 'set' for 7"
>water column pressure of natural gas. Summit says 11" is normal. We may have
>made a mistake there, and if it makes a difference, we'll call the gas company
>again and then we'd need to learn how to correct the burners.
>
>7. The kiln seems to heat quickly to orange heat but at yellow-orange it has
>problems progressing.
>
>8. I don't know of anyway to control air-intake at the base of the kiln as it
>is
>not forced-air, unless someone suggests covering part of the 3" holes with
>something before loading the kiln.
>The first time I fired it, I used 5 rings....times 4.5" equals an interior
>height
>of 22.5". I shut it down after 11 hours of orange heat.
>
>The second time I fired it, I used 4 rings...equals interior height of 18". I
>shut it down after 15 hours of yellow-orange heat...approx. cone 3.
>
>I've since removed the elements from 2 rings and stuffed them with strips of
>kaowool I've had laying around.
>
>I would really appreciate guidance. Hopefully the details provided above will
>help someone see an obvious mistake on our part...or area to focus on.
>Thanks.
>
>Joanne in Tucson
Lorraine Pierce on mon 25 oct 99
Joanne, I believe your kiln damper is a piece of kiln shelf that you slide over
the hole in the top lid, varying the opening to vent or keep the heat in...just
one would in a raku kiln. also, Like a raku kiln, I think you must have a needle
valve or other controll on the gas line to regulate the flow of gas into the kil
What book or source did you use for your gas line dimentions...if it was a kiln
book there should be quite complete instructions; Don't think of cracks and
insulation right now...think of learning how to fire...Nikom's advice is
excellent. Lori in New Port Richey Fl. Joanne, it will be OK...put your
energy into making lots of pots to put in your new kiln so you can fire often an
LEARN how to fire.
Nikom Chimnok wrote:
> ----------------------------Original message----------------------------
> Oh for goodness sakes, Joanne,
>
> Join the 20th century and get a pyrometer. Somebody recommended this
> before, but you didn't listen, so I can only try to say it more forcefully.
>
> If you have a pyrometer you can tell whether the temperature is
> going up or down, and how fast it's going up or down. You can use the
> scientific method: try experiments. Push in the damper and see if the temp
> goes up. Pull out the damper and see if the temp goes up. Turn up the gas
> and see. Turn down the gas and. Open the primary air shutters. Close them.
> Find out what's going on.
>
> I've been through this myself, a mere 10 years ago, and remember it
> well. Before I got my first pyrometer I was mystified. After I got it I
> started learning how to fire. If you can't tell which direction, if any, the
> temperature is going, the learning curve is depressingly slow. If you can
> tell, you learn quickly.
>
> It's possible you will find out you don't have enough firepower, and
> have to drill out the orifices or change regulators or something. Do you
> have a gas pressure gauge?
>
> But more likely you have too much air or not enough air, and either
> problem is easy to fix. In an itty bitty gas kiln like you're using,
> insulation doesn't determine much. If you pour the coals to it, you can hit
> 1400 C in 2 hours with 2 inches of fiber. Maybe it'd take 3 hours with soft
> bricks. You can have so little insulation that it gets red hot on the
> outside, but it'll still cook the load.
>
> Don't worry, you'll get better. But unless you get a pyrometer or
> the help of a friend who has some firing experience, it might take 2 years.
> Or longer. Makes a hundred dollars sound cheap, no?
>
> Good luck,
> Nikom
> ****************************************************************************
> At 22:58 23/10/99 EDT, you wrote:
> >----------------------------Original message----------------------------
> >disappointed again.
>
> >the interesting part is that by 8 am the kiln was cool. Perhaps I need
> >insulation???? Can any of you recommend something?
> >this may be a lesson in
> >"I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper".
> >
> >Joanne in Tucson Arizona
Joanne Van Bezooyen on tue 26 oct 99
Thanks, Hank,
We'll order a gas pressure gauge, and a digital pyrometer when they come back on
the market (they're getting out a kink or two)
I understand secondary air....I have no shutter or control for primary air, so I
probably need to call Summit Kilns, where I bought the burneres, to ask them abo
that. Increasing the vertical height is something new to ponder as well.
Interesting, isn't it, how one person says shorten the height and leave the damp
wide open....others say close up the damper a bit and add height. Regardless, I
beginning to understand what makes this all work and at least know avenues to
experiment with. Now I only (?) need to know how to check my orifice openings t
see if they are the right size for 7" water column pressure....and figure a way
attach a shutter disc to regulate primary air. (Summit should help me with this
one)_
Hank Murrow wrote:
> ----------------------------Original message----------------------------
> Dear Joanne; I am very sorry you seem to be attracting flame
> threads in the midst of your difficulties with the kiln. However, your post
> gives much needed information with which to help you. I wonder since your
> kiln is essentially a very small updraft if shortening the chamber is
> somewhat counterproductive. You probably need more vertical just to achieve
> some draft; the kiln itself being the flue in your case. I once built a
> small lifting fiber test kiln, to which I had to add a fiber flue tube for
> additional draft to get to C/10 because the kiln @ 24" was just too short.
> Burners are best understood as mixers of gas & air. There probably
> is an air shutter(disc) at the base of each mixer, which could be opened to
> allow primary air to the mixer. Primary air is that which enters the burner
> WITH the gas and burns as it exits the mixer. Secondary air enters the kiln
> around the burner WITHOUT mixing with the fuel. If there is an air shutter,
> three to four turns is full primary air. After air control you need to know
> the relative gas pressure; so try to build the manometer I mentioned in my
> post of the 18th for relative pressure control. Even if it is not
> "accurate" in terms of inches of water; it will tell you "more and less",
> and be repeatable with precision. You did not mention whether any other
> devices share this gas line; but you can easily adjust the gas pressure at
> the regulator by removing the cap on the front of the regulator and
> screwing the washer there clockwise a turn at a time while checking the
> pressure on your manometer. I asked about other devices sharing the line
> because they too would have an increase in pressure, which may or not be
> beneficial. In any case, you may also drill out the orifices a little to
> increase the flow of gas at whatever pressure you currently have (like
> having a bigger hose in your garden). I reccommend that you do the other
> things before drilling the orifices. I have even drilled them during a fire
> when it was apparent that I needed more. Perhaps this would be possible
> with your mixers. Feel free to call me @ 541-342-8429 Pacific Coast Time if
> you get in a bind or want clarification on some point. And Good Luck! Hank
> in Eugene
>
> >----------------------------Original message----------------------------
> he asked the burners to be 'set' for 7"
> >water column pressure of natural gas. Summit says 11" is normal. We may hav
> >made a mistake there, and if it makes a difference, we'll call the gas compan
> >again and then we'd need to learn how to correct the burners.
> >
> >7. The kiln seems to heat quickly to orange heat but at yellow-orange it has
> >problems progressing.
> >
> >8. I don't know of anyway to control air-intake at the base of the kiln as i
> >is
> >not forced-air, unless someone suggests covering part of the 3" holes with
> >something before loading the kiln.
>
> >The first time I fired it, I used 5 rings....times 4.5" equals an interior
> >height
> >of 22.5". I shut it down after 11 hours of orange heat.
> >
> >The second time I fired it, I used 4 rings...equals interior height of 18".
> >shut it down after 15 hours of yellow-orange heat...approx. cone 3.
> >
> >I've since removed the elements from 2 rings and stuffed them with strips of
> >kaowool I've had laying around.
> >
> >I would really appreciate guidance. Hopefully the details provided above wil
> >help someone see an obvious mistake on our part...or area to focus on.
> >Thanks.
> >
> >Joanne in Tucson
John Baymore on wed 27 oct 99
------------------
(snip)
Me neither. What's a cold conversion kiln?
(clip)
What.....you've never heard of cold fusion =3Cbg=3E?????
Best,
....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
Micheal E Rector on thu 28 oct 99
Joanne,
I have a few comments that may help. As the temperature in a kiln
increases the pressure inside the kiln also increases. This causes less
secondary air to be drawn into the kiln, which means that less gas will
burn and the unburned gas will carry away heat as it leaves the kiln.
If you are firing in oxidation the decrease in secondary air will
eventually cause the fire to go into reduction on its own. If you are
firing in reduction eventually an equilibrium will be reached where the
kiln stalls, which means that it stays at the same temperature
indefinitely. When this happens opening the damper a small amount will
allow more gas to escape and hence more secondary air to get in. The
kiln will should then go out of reduction or start climbing in
temperature whichever applies. In my experience when the kiln is
stalled adjusting the primary air does not help, because any air you
force in will be compensated for by a corresponding decrease in
secondary air.
Elsewhere in this thread others have suggested that you may be using to
much gas. Consider what would happen if your kiln was stalled and you
added more gas. Not only would none of that gas burn, but it would also
cause less secondary air to enter the kiln, which would mean even less
gas would burn. More unburned fuel would carry away more heat, and the
temperature of the kiln would drop until it reached a new equilibrium.
Similarly if you increase the gas without also opening the damper you
may stall the kiln for the same reasons.
Some things to watch out for: Look under your kiln; if the flame is not
being drawn up into the kiln and is spilling around the outside of the
ports you need to turn down the gas and/or open the damper. In the
early stages of the fire watch for as signs of reduction the smell of
unburned gas, carbon building up around the door, flue, or peeps, or
smoke. Sometimes smoke or a faint flame will appear as if out of
nowhere several feet above the flue. When this happens your kiln is
full of unburned gas and is probably loosing heat.
I hope this helps,
Michael
Joanne Van Bezooyen wrote:
>
> ----------------------------Original message----------------------------
> disappointed again.
>
> yesterday, I shortened the kiln (removed a ring) and sealed up some
> leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
> By midnight, feeling as exhausted as if I'd been heating it
> myself....well, maybe it was a couple margaritas....I shut it all off.
> I think it reached cone 3??? as my cone 5 glaze had melted but was
> pitted.
>
> the interesting part is that by 8 am the kiln was cool. Perhaps I need
> insulation???? Can any of you recommend something? I suppose i should
> coat the inside with itc100....do I wrap the outside with wool and
> chicken wire?
>
> this may be a lesson in
> "I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper".
>
> Joanne in Tucson Arizona
Joanne Van Bezooyen on fri 29 oct 99
Wow!
Michael.....I can tell you've studied Physics thoroughly. Yes....it makes good
sense and although I wrote, "try using less gas" on my "LIST" I now understand
what I will be doing by using less gas.
How many university ceramics programs require chemistry and physics courses? No
the University of Arizona. Others?
Joanne
Micheal E Rector wrote:
> ----------------------------Original message----------------------------
> Joanne,
>
> I have a few comments that may help. As the temperature in a kiln
> increases the pressure inside the kiln also increases. This causes less
> secondary air to be drawn into the kiln, which means that less gas will
> burn and the unburned gas will carry away heat as it leaves the kiln.
> If you are firing in oxidation the decrease in secondary air will
> eventually cause the fire to go into reduction on its own. If you are
> firing in reduction eventually an equilibrium will be reached where the
> kiln stalls, which means that it stays at the same temperature
> indefinitely. When this happens opening the damper a small amount will
> allow more gas to escape and hence more secondary air to get in. The
> kiln will should then go out of reduction or start climbing in
> temperature whichever applies. In my experience when the kiln is
> stalled adjusting the primary air does not help, because any air you
> force in will be compensated for by a corresponding decrease in
> secondary air.
>
> Elsewhere in this thread others have suggested that you may be using to
> much gas. Consider what would happen if your kiln was stalled and you
> added more gas. Not only would none of that gas burn, but it would also
> cause less secondary air to enter the kiln, which would mean even less
> gas would burn. More unburned fuel would carry away more heat, and the
> temperature of the kiln would drop until it reached a new equilibrium.
> Similarly if you increase the gas without also opening the damper you
> may stall the kiln for the same reasons.
>
> Some things to watch out for: Look under your kiln; if the flame is not
> being drawn up into the kiln and is spilling around the outside of the
> ports you need to turn down the gas and/or open the damper. In the
> early stages of the fire watch for as signs of reduction the smell of
> unburned gas, carbon building up around the door, flue, or peeps, or
> smoke. Sometimes smoke or a faint flame will appear as if out of
> nowhere several feet above the flue. When this happens your kiln is
> full of unburned gas and is probably loosing heat.
>
> I hope this helps,
>
> Michael
>
> Joanne Van Bezooyen wrote:
> >
> > ----------------------------Original message----------------------------
> > disappointed again.
> >
> > yesterday, I shortened the kiln (removed a ring) and sealed up some
> > leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
> > By midnight, feeling as exhausted as if I'd been heating it
> > myself....well, maybe it was a couple margaritas....I shut it all off.
> > I think it reached cone 3??? as my cone 5 glaze had melted but was
> > pitted.
> >
> > the interesting part is that by 8 am the kiln was cool. Perhaps I need
> > insulation???? Can any of you recommend something? I suppose i should
> > coat the inside with itc100....do I wrap the outside with wool and
> > chicken wire?
> >
> > this may be a lesson in
> > "I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper"
> >
> > Joanne in Tucson Arizona
Gavin Stairs on sat 30 oct 99
At 13:47 1999.10.28 , you wrote:
>----------------------------Original message----------------------------
>Joanne,
>
>I have a few comments that may help. As the temperature in a kiln
>increases the pressure inside the kiln also increases.
Not so. The pressure inside a firing kiln at temperature must be slightly
decreased, not increased. What drives the pressure differential in a kiln
is primarily the stack effect. The pressure above the mouth of the stack
is atmospheric. The pressure decreases as you move back down the stack,
against the flow. There are two reasons for this. One is the speed of the
gas flow: Bernouli famously said that the pressure in a fluid is inversely
proportional to the speed of the flow. This is the effect of inertia. So,
as you move from the static atmosphere to the moving stack flow, the
pressure drops. The other reason is buoyancy: the hot gas is less dense
than the cold atmosphere. This is owing to Boyle's or Charles' law
depending on how you phrase it: the density of a gas at standard pressure
depends inversely on the absolute temperature. The relationship of
temperature, pressure and density of a gas is summarized in the ideal gas
law: PV=mRT. The pressure times the volume equals the mass times a
constant times the absolute temperature. This relationship is one of the
earliest indicators of absolute zero on the temperature scale. For an
ideal gas, in which the atoms of gas occupy insignificant volume, the
volume of the gas goes to zero at T=0 Kelvin.
Back to the kiln. So the pressure is falling as you descend the
stack. But another effect mitigates this fall: in a fluid flow through a
pipe (i.e., the stack), fluid viscosity (friction) causes a pressure drop
in the direction of the flow. So, the pressure rises as we go against the
flow. Also, the pressure in a fluid rises as we descend in the
fluid. This pressure rise due to gravity is called the head.
All of these effects sum up to give the pressure at any point in the
flow. The same effects act at the burners. As the air is moving at the
burner ports, the pressure is below atmospheric. Heat is injected (by
burning fuel) which increases the volume. The fuel also adds to the mass
of the flow, also increasing the volume. If the stack effect is not
working, this leads to a drastic increase in the internal pressure, and the
burners will blow back through their ports. This is burner stall, and the
only remedy is to get the stack operating by gently heating it before
turning up the burners. Pull the damper all the way out, and throw
something burning down the stack. When the stack is drawing, it sucks the
burner flames in through their ports. So the pressure at the burner ports
must be below atmospheric.
This is not true of forced air, closed burner ports, which can operate at
positive pressure. I am talking here about open port, natural draft, or
Venturi burners. Venturi was another Italian natural philosopher who
studied the pressure of fluids flowing in pipes. The pressure drop in a
flow at the centre of a smooth constriction is named after him. In a
Venturi burner, the flow constriction serves to suck the primary air into
the region of the burner nozzle by reason of the flow of gas from the
nozzle. So a Venturi burner tends to resist stalling for this reason. A
burner without the constriction will be somewhat more prone to stalling, or
back flashing. You get a ball of red and yellow flame around the burner
instead of a blowpipe flame coming out the end.
In the middle of the kiln volume, the flow almost comes to rest, so the
pressure rises again. In the static volume of the kiln, the high
temperature means that the density (m/V) of the gas will be lower than air,
so although the pressure will fall with increasing head (as you go up), it
will do so less than air pressure outside the kiln. So relative to
atmosphere, the pressure rises as you go higher in the kiln. When a
downdraft kiln is drawing properly at some elevated temperature, you may
see that below a certain height on the kiln the pressure is below
atmospheric (a peep or a crack will suck air) while above it, the kiln will
be above atmospheric (the peep will blow). The actual pressure gradients
in the kiln are quite subtle, and are more complex than I want to get into
here. They involve the flame path, the position of the flame fronts, and
the thermal gradients in the flows.
In a downdraft kiln, the stack port is low. It is possible for an
inversion to form, in which the flame front moves across to the stack port
without moving high. This is one of the functions of a bag wall, or a
vertically directed burner: to force a vertical flow.
Anyway, we now have the pressure profile more or less complete: The
pressure goes from atmospheric to below in the burners, then rises almost
to atmospheric inside the kiln, may rise above atmospheric in some parts of
the kiln, but exits the kiln to the stack in a region of low pressure. The
flow in the stack, and therefore in the kiln, is defined by the pressure
gradient in the stack. If it is high, the flow is large. If low,
small. Stacks are built to have a potentially large pressure gradient, and
therefore a large flow. This permits a high rate of burning and quick
temperature rise. How to regulate this? The damper does this by
introducing a lossy flow restriction. Lossy means that, unlike in a smooth
Venturi, the pressure on either side of the restriction is not the
same. The pressure behind the damper gate will be less than it is before
the gate, so it reduces the pressure gradient in the rest of the stack, and
therefore reduces the flow. Another way of looking at it is to say that
the damper controls the pressure in the kiln. The farther in the damper,
the higher the pressure in the kiln. Push the damper in too far, and you
may stall the kiln, and get a blowback at the burners. Pull it out too
far, and the burners will run lean, and not heat the air sufficiently. The
damper setting at the stack and at the secondary ports depends on the
burner setting.
To set up the kiln for firing, you need to set the burner gas rate to get
the proper heat for the temperature ramp you are trying to achieve. Then
you need to set the primary air to burn much of the gas in primary
air. Then, set the secondary dampers to give enough air to burn the rest
of the fuel. If you do this with the stack damper wide open, you will
undoubtedly have the kiln at negative pressure. That means it will be
sucking air through every crack, and will probably be in oxidation. The
ideal damper position is where the secondary air ports can be almost wide
open. Then the kiln will be balanced in pressure, just a bit below
atmospheric. It will be easy to control the atmosphere by small
adjustments of the stack damper.
When the kiln is drawing strongly, lots of secondary air will be drawn in
through the burner ports and also through any open peeps and cracks. So it
will be harder to develop a reduction atmosphere in this case, even with
strong fuel flow. When the damper is closed down, the kiln pressure will
rise slightly, and the secondary flow will be inhibited. The burners will
burn rich, and it will be easier to establish reduction. However, the
carbon monoxide will also find it easier to leak out of the kiln, so beware
of CO during reduction.
Having said all this, every fireman will have his or her own preferences
about just how to set up the burners and dampers. All that is really
happening is that the internal pressure of the kiln is being set sightly
higher or lower. You can successfully fire with the damper wide open, or
with it some way in. If the kiln was designed properly, the damper will
most often be perhaps a quarter to three quarters of the way in for most
firers.
That's the story on gas flow and pressure in a kiln. The design of the
proper rates of flow is another matter which will have to wait until
another evening.
Gavin
Gavin Stairs
Stairs Small Systems
921 College St., # 1-A
Toronto, Ontario, Canada M6H 1A1
phone: (416)530-0419 stairs@stairs.on.ca
Hank Murrow on sat 30 oct 99
>----------------------------Original message----------------------------
>How many university ceramics programs require chemistry and physics
>courses? No the University of Arizona. Others?
>
>Joanne
Dear Joanne; When I was a student at the U.of Oregon, we had a course
called Geology for Potters and one called Physics for Potters. They were
taught by Grad fellows in those departments and were very popular. The
great thing was seeing the teachers' changing views on craft/art stusents
as they tried to make pots. The questions got very lively indeed. Sorry you
missed it, as I think you would have had fun. Hank in Eugene
Dave Finkelnburg on sun 31 oct 99
Gavin,
Your technical knowledge always amazes me! Wow, you have a great grasp
of a lot of the fundamentals!
Your lengthy post below may confuse some folks who fire simple
atmospheric, fuel kilns. If I may, I think the original idea was explain
how too much fuel can stop a kiln from heating to the desired final
temperature.
To explain that, one needs to visualize a fixed flow of gas into a
kiln. As the kiln heats up during the
firing, the volume of the products of combustion from that gas will
naturally increase because the water and excess air and oxygen are being
heated. If carried too far, this increase in volume will eventually stall
the kiln by preventing adequate air getting in with the fuel to burn it.
Michael Rector did a good thing by describing this process, though as
you point out, the wording may not
have been exactly correct.
The important point, which you obviously understand well, and all of us
who fire fuel kilns need to remember, is this. A fuel kiln can "stall" just
as effectively from too much fuel as from too little.
Now if I could just do a better job of getting the same cones in my gas
kiln down all at the same time..... :-(
Good potting!
Dave Finkelnburg enjoying another sunny day in Idaho
dfinkeln@cyberhighway.net
-----Original Message-----
From: Gavin Stairs
To: CLAYART@LSV.UKY.EDU
Date: Saturday, October 30, 1999 11:03 AM
Subject: Re: cold conversion kiln
----------------------------Original message----------------------------
At 13:47 1999.10.28 , you wrote:
>----------------------------Original message----------------------------
>Joanne,
>
>I have a few comments that may help. As the temperature in a kiln
>increases the pressure inside the kiln also increases.
Not so. The pressure inside a firing kiln at temperature must be slightly
decreased, not increased. What drives the pressure differential in a kiln
is primarily the stack effect. The pressure above the mouth of the stack
is atmospheric. The pressure decreases as you move back down the stack,
against the flow. There are two reasons for this. One is the speed of the
gas flow: Bernouli famously said that the pressure in a fluid is inversely
proportional to the speed of the flow. This is the effect of inertia. So,
as you move from the static atmosphere to the moving stack flow, the
pressure drops. The other reason is buoyancy: the hot gas is less dense
than the cold atmosphere. This is owing to Boyle's or Charles' law
depending on how you phrase it: the density of a gas at standard pressure
depends inversely on the absolute temperature. The relationship of
temperature, pressure and density of a gas is summarized in the ideal gas
law: PV=mRT. The pressure times the volume equals the mass times a
constant times the absolute temperature. This relationship is one of the
earliest indicators of absolute zero on the temperature scale. For an
ideal gas, in which the atoms of gas occupy insignificant volume, the
volume of the gas goes to zero at T=0 Kelvin.
Back to the kiln. So the pressure is falling as you descend the
stack. But another effect mitigates this fall: in a fluid flow through a
pipe (i.e., the stack), fluid viscosity (friction) causes a pressure drop
in the direction of the flow. So, the pressure rises as we go against the
flow. Also, the pressure in a fluid rises as we descend in the
fluid. This pressure rise due to gravity is called the head.
All of these effects sum up to give the pressure at any point in the
flow. The same effects act at the burners. As the air is moving at the
burner ports, the pressure is below atmospheric. Heat is injected (by
burning fuel) which increases the volume. The fuel also adds to the mass
of the flow, also increasing the volume. If the stack effect is not
working, this leads to a drastic increase in the internal pressure, and the
burners will blow back through their ports. This is burner stall, and the
only remedy is to get the stack operating by gently heating it before
turning up the burners. Pull the damper all the way out, and throw
something burning down the stack. When the stack is drawing, it sucks the
burner flames in through their ports. So the pressure at the burner ports
must be below atmospheric.
This is not true of forced air, closed burner ports, which can operate at
positive pressure. I am talking here about open port, natural draft, or
Venturi burners. Venturi was another Italian natural philosopher who
studied the pressure of fluids flowing in pipes. The pressure drop in a
flow at the centre of a smooth constriction is named after him. In a
Venturi burner, the flow constriction serves to suck the primary air into
the region of the burner nozzle by reason of the flow of gas from the
nozzle. So a Venturi burner tends to resist stalling for this reason. A
burner without the constriction will be somewhat more prone to stalling, or
back flashing. You get a ball of red and yellow flame around the burner
instead of a blowpipe flame coming out the end.
In the middle of the kiln volume, the flow almost comes to rest, so the
pressure rises again. In the static volume of the kiln, the high
temperature means that the density (m/V) of the gas will be lower than air,
so although the pressure will fall with increasing head (as you go up), it
will do so less than air pressure outside the kiln. So relative to
atmosphere, the pressure rises as you go higher in the kiln. When a
downdraft kiln is drawing properly at some elevated temperature, you may
see that below a certain height on the kiln the pressure is below
atmospheric (a peep or a crack will suck air) while above it, the kiln will
be above atmospheric (the peep will blow). The actual pressure gradients
in the kiln are quite subtle, and are more complex than I want to get into
here. They involve the flame path, the position of the flame fronts, and
the thermal gradients in the flows.
In a downdraft kiln, the stack port is low. It is possible for an
inversion to form, in which the flame front moves across to the stack port
without moving high. This is one of the functions of a bag wall, or a
vertically directed burner: to force a vertical flow.
Anyway, we now have the pressure profile more or less complete: The
pressure goes from atmospheric to below in the burners, then rises almost
to atmospheric inside the kiln, may rise above atmospheric in some parts of
the kiln, but exits the kiln to the stack in a region of low pressure. The
flow in the stack, and therefore in the kiln, is defined by the pressure
gradient in the stack. If it is high, the flow is large. If low,
small. Stacks are built to have a potentially large pressure gradient, and
therefore a large flow. This permits a high rate of burning and quick
temperature rise. How to regulate this? The damper does this by
introducing a lossy flow restriction. Lossy means that, unlike in a smooth
Venturi, the pressure on either side of the restriction is not the
same. The pressure behind the damper gate will be less than it is before
the gate, so it reduces the pressure gradient in the rest of the stack, and
therefore reduces the flow. Another way of looking at it is to say that
the damper controls the pressure in the kiln. The farther in the damper,
the higher the pressure in the kiln. Push the damper in too far, and you
may stall the kiln, and get a blowback at the burners. Pull it out too
far, and the burners will run lean, and not heat the air sufficiently. The
damper setting at the stack and at the secondary ports depends on the
burner setting.
To set up the kiln for firing, you need to set the burner gas rate to get
the proper heat for the temperature ramp you are trying to achieve. Then
you need to set the primary air to burn much of the gas in primary
air. Then, set the secondary dampers to give enough air to burn the rest
of the fuel. If you do this with the stack damper wide open, you will
undoubtedly have the kiln at negative pressure. That means it will be
sucking air through every crack, and will probably be in oxidation. The
ideal damper position is where the secondary air ports can be almost wide
open. Then the kiln will be balanced in pressure, just a bit below
atmospheric. It will be easy to control the atmosphere by small
adjustments of the stack damper.
When the kiln is drawing strongly, lots of secondary air will be drawn in
through the burner ports and also through any open peeps and cracks. So it
will be harder to develop a reduction atmosphere in this case, even with
strong fuel flow. When the damper is closed down, the kiln pressure will
rise slightly, and the secondary flow will be inhibited. The burners will
burn rich, and it will be easier to establish reduction. However, the
carbon monoxide will also find it easier to leak out of the kiln, so beware
of CO during reduction.
Having said all this, every fireman will have his or her own preferences
about just how to set up the burners and dampers. All that is really
happening is that the internal pressure of the kiln is being set sightly
higher or lower. You can successfully fire with the damper wide open, or
with it some way in. If the kiln was designed properly, the damper will
most often be perhaps a quarter to three quarters of the way in for most
firers.
That's the story on gas flow and pressure in a kiln. The design of the
proper rates of flow is another matter which will have to wait until
another evening.
Gavin
Gavin Stairs
Stairs Small Systems
921 College St., # 1-A
Toronto, Ontario, Canada M6H 1A1
phone: (416)530-0419 stairs@stairs.on.ca
Gavin Stairs on mon 1 nov 99
At 11:26 PM 31/10/99 , Dave Finkelnburg wrote:
...
> Your lengthy post below may confuse some folks who fire simple
>atmospheric, fuel kilns. If I may, I think the original idea was explain
>how too much fuel can stop a kiln from heating to the desired final
>temperature.
> To explain that, one needs to visualize a fixed flow of gas into a
>kiln. As the kiln heats up during the
>firing, the volume of the products of combustion from that gas will
>naturally increase because the water and excess air and oxygen are being
>heated. If carried too far, this increase in volume will eventually stall
>the kiln by preventing adequate air getting in with the fuel to burn it.
> Michael Rector did a good thing by describing this process, though as
>you point out, the wording may not have been exactly correct.
> The important point, which you obviously understand well, and all of us
>who fire fuel kilns need to remember, is this. A fuel kiln can "stall" just
>as effectively from too much fuel as from too little.
> Now if I could just do a better job of getting the same cones in my gas
>kiln down all at the same time..... :-(
Good point, Dave and Michael. I'm afraid I jumped at the thought of an
operating, open burner kiln being above atmospheric pressure at the ports.
Yes, the pressure balance may alter during firing, and not just once. At
the beginning, when the stack is cold, it may be very touchy, and hard to
get the flame going the right way. That's why fireplaces tend to be
smokey, and why old wood burning cook stoves have a cut off that allows the
smoke to bypass the oven, so you can get the chimney drawing without
smoking out the kitchen. Then when the stack begins to draw, the pressure
will drop, and continue dropping while the stack warms up. When that slows
down some, then the pressure may creep back up as the volume of the exhaust
air rises, because of being very hot.
I'm not sure that the volume of volatiles will have much effect. There may
be enough free water to have some effect early on, but the bound water and
other stuff is only a kiln volume or so, in glaze firing at any rate, and
shouldn't make much difference, I think.
In any event, there may need to be continuing adjustments, especially if
you are going for a firing time record. These can all be done at the stack
damper. It seems to me that, if you are not interested in fast firing, you
may find that these adjustments are minor, or may even be neglected
entirely, except when you want to reduce. It depends somewhat on the
individual kiln. Some kilns may automatically run in oxidation while
warming, and shift slowly to reduction at some point. You need to know
your own kiln.
I haven't thought too much about the optimization of firing profiles for
this kind of slow creep of operating variables. But I will. Design of a
kiln should take these things into account.
Gavin
Michael Rector on wed 3 nov 99
How wonderful to find that there are people in this world that know more about
firing kilns than I do and able to explain things. This is great; I wish that I
had joined this list three years ago. At first I felt a little embarrassed when
I looked at my mail after four days and found so much discussion of my response
to Joanne. I could have explained the phenomenon of stalling without including
a poorly thought out physical explanation for it. I have often been frustrated
by poorly thought out, oversimplified, and at times wildly inaccurate
information that I have found in many books written for ceramic artists, so this
contributes to my embarrassment when I think that I could have avoided my error
by opting out of a non essential part that I knew I did not fully understand.
However my error clearly contributed to the mission of this list by generating
useful and interesting discussion. I am gladdened by this. Thanks to you all
for your contributions and thanks especially to Dave Finkelnburg for backing me
up and clarifying my point.
BTW Dave, I have found that stalling the kiln helps to even it out. In firing
updrafts I have noticed that when conditions are close to a stall the kilns fire
evenly but slowly eating up a lot of time. At the other extreme when the kiln
temperature rises rapidly there is a tendency for to be very uneven so one ends
up spending a lot of time soaking to even it out. Somewhere in between there is
a happy medium where the kiln temp. rises briskly and evenly, and the total
firing time often ends up being less than either extreme. I don't know if I am
telling you anything new, but it occurs to me that thinking about in these terms
might help in finding that happy medium.
I do not have enough experience with downdraft kilns to know if they have
similar tendencies. I would be interested to hear from those who fire downdraft
kilns on this topic. In the few fires I have done, I have noticed that when
damper is fairly wide open there is often a cold area in the lower front, and if
one closes the damper a bit this area tends to catch up fairly rapidly.
So there is an example of explaining a phenomenon without offering any physical
explanation. Now it is high time for me to learn more physics, or perhaps just
relearn all that I have forgotten from my geology student years.
Michael
Dave Finkelnburg wrote:
> ----------------------------Original message----------------------------
> Gavin,
> Your technical knowledge always amazes me! Wow, you have a great grasp
> of a lot of the fundamentals!
> Your lengthy post below may confuse some folks who fire simple
> atmospheric, fuel kilns. If I may, I think the original idea was explain
> how too much fuel can stop a kiln from heating to the desired final
> temperature.
> To explain that, one needs to visualize a fixed flow of gas into a
> kiln. As the kiln heats up during the
> firing, the volume of the products of combustion from that gas will
> naturally increase because the water and excess air and oxygen are being
> heated. If carried too far, this increase in volume will eventually stall
> the kiln by preventing adequate air getting in with the fuel to burn it.
> Michael Rector did a good thing by describing this process, though as
> you point out, the wording may not
> have been exactly correct.
> The important point, which you obviously understand well, and all of us
> who fire fuel kilns need to remember, is this. A fuel kiln can "stall" just
> as effectively from too much fuel as from too little.
> Now if I could just do a better job of getting the same cones in my gas
> kiln down all at the same time..... :-(
> Good potting!
> Dave Finkelnburg enjoying another sunny day in Idaho
> dfinkeln@cyberhighway.net
>
> -----Original Message-----
> From: Gavin Stairs
> To: CLAYART@LSV.UKY.EDU
> Date: Saturday, October 30, 1999 11:03 AM
> Subject: Re: cold conversion kiln
>
> ----------------------------Original message----------------------------
> At 13:47 1999.10.28 , you wrote:
> >----------------------------Original message----------------------------
scott lykens on thu 4 nov 99
how much gas do you use?
ie how close to full throtle do you run her?
you just might have way too much fuel
>From: Burt Cohen
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.UKY.EDU
>Subject: Re: cold conversion kiln
>Date: Mon, 25 Oct 1999 13:27:12 EDT
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>----------------------------Original message----------------------------
>Hi Joanne: I think that the first solution to your problem of achieving
>temperature is to find a potter who works with gas to take a look at your
>set up. It is probably very simple/ Clayart is a lousy medium to
>troubleshoot kiln problems.(My opinion) You have a few requirements to
>advance temperature.-first- enough fuel-, ie enough gas (as well as
>pressure) factors here are size of tank size of orifice on burner # of
>burners in relation to the kiln size. Second-amount of air- at burner
>(primary) coming into kiln (secondary) as well as the size of the chimney.
>Lastly the kiln itself- But I tend to think that isn't your problem because
>everything else being equal a good combustion system can usually overcome
>even poorly insulated kilns-
>ITC ain't gonna help you!
>Sorry just had to say that
>Yours-
>Burt Cohen
>-----Original Message-----
>From: Joanne Van Bezooyen
>To: CLAYART@LSV.UKY.EDU
>Date: Saturday, October 23, 1999 8:06 PM
>Subject: cold conversion kiln
>
>
> >----------------------------Original message----------------------------
> >disappointed again.
> >
> >yesterday, I shortened the kiln (removed a ring) and sealed up some
> >leaky cracks. I turned on the kiln at 9 am and full-blasted by 11 am.
> >By midnight, feeling as exhausted as if I'd been heating it
> >myself....well, maybe it was a couple margaritas....I shut it all off.
> >I think it reached cone 3??? as my cone 5 glaze had melted but was
> >pitted.
> >
> >the interesting part is that by 8 am the kiln was cool. Perhaps I need
> >insulation???? Can any of you recommend something? I suppose i should
> >coat the inside with itc100....do I wrap the outside with wool and
> >chicken wire?
> >
> >this may be a lesson in
> >"I-should-a-bought-a-new-kiln-in-the-first-place-as-it-would-a-been-cheaper
>".
> >
> >Joanne in Tucson Arizona
> >
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