mudduck on sun 1 nov 09
I built and have been trying to learn to fire a gas kiln for about a =3D
year now. The kiln is built to Nils Lou's style of MFT, but it has an =3D
arch. It's is 45 wide X 45 deep and 50 from the car floor to the arch. =3D
The exit flue approx. 36 sq. inch, one full brick and double venturi =3D
with the fiber lined metal chimney. Burners are 2 Ransom B-4 high =3D
pressure on propane purchased from Mark Ward.=3D20
It takes me 11 hrs to fire to cone 10 using 42 gallons of fuel. I would =3D
really like to learn to fire the kiln a little faster and more efficient =
=3D
on the propane.=3D20
I get poor reduction on the bottom shelf, which sits on a brick laid on =3D
its side. So my first shelf is just above the flue opening. I hear of =3D
people having 4"flame coming from the bottom peep. As yet I haven't been =
=3D
able to get any flame from the bottom peep. The most I've pushed the =3D
damper in is 2 inches open. If I push the damper in any more the kiln =3D
seems to make a woofing sound and seems to stall or have very little =3D
temp. rise. As some have said I don't want to blow this thing up. And =3D
being self taught on firing I don't know what to change to get the =3D
reduction on the bottom shelf and save more fuel. I have an oxy probe =3D
inserted in the center of the door. During reduction I'm reading from =3D
.78 to .80. Reduction is good to heavy in the rest of the kiln just not =3D
on the bottom shelf.=3D20
The kiln fires even from top to bottom as far as the temp. goes, a =3D
little hotter in the back than front.
I've tried to include as much info that I can think of, hope I included =3D
enough.
I'd like to talk to someone about this. I talk much better than I type!!
Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net
Des & Jan Howard on mon 2 nov 09
Gene
I'll mess around with some figures from you.
The dimensions given are approx. 58cuft,
may not be setting space, but I'll go with it.
42 gal propane @ $1.45/gal, (Larry's quoted price)
=3D $60. Near enough $1/cuft gas cost. Jan figures min.
packing in 1cuft is 18 coffee mugs @ $18 each ($324)
or 2 medium salad bowls $85-95 each ($170-190),
all figures wholesale. Not bad for a buck.
If you've achieved your aesthetic goals you're laughing.
Des
mudduck wrote:
> It takes me 11 hrs to fire to cone 10 using 42 gallons
> of fuel. I would really like to learn to fire the kiln
> a little faster and more efficient on the propane.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
-32.656072 149.840624
Larry Kruzan on mon 2 nov 09
I wonder if you have a target brick in the flame path? One thing I did was
to place a hard brick at the end of the flame channel propped up at a 45
degree angle that (I think) help to force the flame upward, promoting
circulation.
You also don't mention if you are using a bag wall. I do not. BUT the three
bricks that are supporting the bottom shelves are on edge, in line with the
burner flame path, so some may argue that this forms a type of bag wall.
The figures that you give for the kiln size are about double my chamber
size. So the figure of 42 gallons of propane are pretty much the same per
cubic foot. Pretty good numbers overall with the exception of the firing
time.
There are several variables that come to mind that will affect the firing
time. Thermo-mass being one critical variable that could be a issue - the
hardest one to change and I'm not sure you would want to. Kiln shelves are
one thing to look at - are you using heavy silicon carbide shelves or the
light Nitrite Bonded shelves? Is you kiln made of IFBs or hardbrick?
The biggest trade off in dropping the time is fuel consumption. I could
blast my kiln to 2500 degrees in 3-4 hours but I doubt that the glazes woul=
d
look very good and I would use a lot of extra fuel doing it. That is not to
say that you could fire faster than you are and still get good results.
I'd give Marc Ward a call and ask him about your burners orifice size. You
might be able to change them to a larger size a get more heat out of them.
I've always found him very helpful.
Again, feel free to call me at 309-241-2950.
Best,
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of mudduck
Sent: Sunday, November 01, 2009 3:12 PM
To: Clayart@LSV.CERAMICS.ORG
Subject: Reduction-fuel saving
I built and have been trying to learn to fire a gas kiln for about a year
now. The kiln is built to Nils Lou's style of MFT, but it has an arch. It's
is 45 wide X 45 deep and 50 from the car floor to the arch. The exit flue
approx. 36 sq. inch, one full brick and double venturi with the fiber lined
metal chimney. Burners are 2 Ransom B-4 high pressure on propane purchased
from Mark Ward.
It takes me 11 hrs to fire to cone 10 using 42 gallons of fuel. I would
really like to learn to fire the kiln a little faster and more efficient on
the propane.
I get poor reduction on the bottom shelf, which sits on a brick laid on its
side. So my first shelf is just above the flue opening. I hear of people
having 4"flame coming from the bottom peep. As yet I haven't been able to
get any flame from the bottom peep. The most I've pushed the damper in is 2
inches open. If I push the damper in any more the kiln seems to make a
woofing sound and seems to stall or have very little temp. rise. As some
have said I don't want to blow this thing up. And being self taught on
firing I don't know what to change to get the reduction on the bottom shelf
and save more fuel. I have an oxy probe inserted in the center of the door.
During reduction I'm reading from .78 to .80. Reduction is good to heavy in
the rest of the kiln just not on the bottom shelf.
The kiln fires even from top to bottom as far as the temp. goes, a little
hotter in the back than front.
I've tried to include as much info that I can think of, hope I included
enough.
I'd like to talk to someone about this. I talk much better than I type!!
Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net
jonathan byler on tue 3 nov 09
I was having problems at one point with one of our gas kilns doing a
poor job during body reduction on the bottom rear shelf. I think I
found that the cause was the bottom area near the burners was actually
heating up too fast, causing the clay body to go gray instead of red,
and for copper reds down there to not reduce enough early on. I think
what was happening was that it was glowing hot there while the rest of
the kiln was too cold to put into reduction.
raising the height of the bag wall deflected the flames from that
spot. I think the problem might have been that the burners are not
pointed quite perfectly. either way, see if you can check for
hotspots and maybe solve your problem that way.
On Nov 3, 2009, at 7:40 PM, Paul Borian wrote:
> you could draw a line on the damper at the 2" open mark and very
> carefully
> push it in just a tiny bit more and see if that results in any
> flames out
> the lower peep holes. You could also try going slower through body
> reduction - i have done a lot of firings where it climbed just a
> little for
> an hour during body reduction, then i would let it climb normally
> after
> that. You said pushing the damper in more causes the kiln to stall -
> so you
> could try to find the delicate balance in between stalling and
> climbing
> just a very little bit.
> Also do you have the gas pressure turned all the way up? if not you
> may
> want to try increasing it, at least during body reduction.
> Paul
>
> ---------- Forwarded message ----------
> From: mudduck
> Date: Nov 2, 2009 7:08pm
> Subject: Re: Reduction-fuel saving
> To: blanketcreek@gmail.com
> CC:
>
>
>> Paul the pots on the bottom look just like they came out of the
>> electric
>> kiln. The clay is light tan with no reduction. Where as the pots in
>> the
>> rest of the kiln are a nice toasty brown.
>
>
>
>
>
>> Thanks!!
>
>
>> Gene
>
>
>> mudduck@mudduckpottery.net
>
>
>> www.mudduckpottery.net
>
>
>> ----- Original Message ----- From: "Paul Borian" blanketcreek@GMAIL.COM
>> >
>
>
>> To: Clayart@LSV.CERAMICS.ORG>
>
>
>> Sent: Monday, November 02, 2009 12:58 AM
>
>
>> Subject: Fwd: Reduction-fuel saving
>
>
>
>
>
>
>
>
>
>
>> as far as not getting reduction at the bottom - are the pots down
>> there
>
>
>> really coming out different than the ones in other parts of the
>> kiln? i
>
>
>> often do not get flames out the bottom spy hole but it does not
>> make a
>
>
>> difference in the finished product - they look the same down there as
>
>
>> anywhere else.
>
>
>
>
>
>> Paul
>
>
>
>
>
>> ---------- Forwarded message ----------
>
>
>> From: mudduck mudduck@mudduckpottery.net>
>
>
>> Date: Nov 1, 2009 4:11pm
>
>
>> Subject: Reduction-fuel saving
>
>
>> To: Clayart@lsv.ceramics.org
>
>
>> CC:
>
>
>
>
>
>
>
>
>
>
>> I built and have been trying to learn to fire a gas kiln for about
>> a year
>
>
>> now. The kiln is built to Nils Lou's style of MFT, but it has an
>> arch.
>
>
>> It's is 45 wide X 45 deep and 50 from the car floor to the arch.
>> The exit
>
>
>> flue approx. 36 sq. inch, one full brick and double venturi with the
>
>
>> fiber lined metal chimney. Burners are 2 Ransom B-4 high pressure on
>
>
>> propane purchased from Mark Ward.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> It takes me 11 hrs to fire to cone 10 using 42 gallons of fuel. I
>> would
>
>
>> really like to learn to fire the kiln a little faster and more
>> efficient
>
>
>> on the propane.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> I get poor reduction on the bottom shelf, which sits on a brick
>> laid on
>
>
>> its side. So my first shelf is just above the flue opening. I hear of
>
>
>> people having 4"flame coming from the bottom peep. As yet I haven't
>> been
>
>
>> able to get any flame from the bottom peep. The most I've pushed the
>
>
>> damper in is 2 inches open. If I push the damper in any more the kiln
>
>
>> seems to make a woofing sound and seems to stall or have very little
>
>
>> temp. rise. As some have said I don't want to blow this thing up. And
>
>
>> being self taught on firing I don't know what to change to get the
>
>
>> reduction on the bottom shelf and save more fuel. I have an oxy probe
>
>
>> inserted in the center of the door. During reduction I'm reading
>> from .78
>
>
>> to .80. Reduction is good to heavy in the rest of the kiln just not
>> on
>
>
>> the bottom shelf.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> The kiln fires even from top to bottom as far as the temp. goes, a
>> little
>
>
>> hotter in the back than front.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> I've tried to include as much info that I can think of, hope I
>> included
>
>
>> enough.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> I'd like to talk to someone about this. I talk much better than I
>> type!!
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>> Gene
>
>
>
>
>
>
>
>
>
>
>
>
>> mudduck@mudduckpottery.net
>
>
>
>
>
>
>
>
>
>
>
>
>> www.mudduckpottery.net
Janine in Tacoma on tue 3 nov 09
Hi Gene:
I am pretty new to gas firing as well, but your kiln is about the same si=
=3D
ze as=3D20
mine - the big difference is I have four burners (MR 75s). Cone 11 in 8 =
=3D
to 10=3D20
hours, depending on size of load - and could probably get there faster if=
=3D
I=3D20
tried. I'm burning natural gas, get nice efficient reduction from about =
=3D
Cone 06=3D20
to finish with gas at 2.5 to 3", flue closed half-way, with a final 15-30=
=3D
minute=3D20
oxidation at the end to even out top and bottom. Is there any way you co=
=3D
uld=3D20
add a couple of burners? I'm sure others have more knowledgeable opinion=
=3D
s,=3D20
but mine is that you're underpowered.
Happy to talk or correspond off-list.
Best of luck and cheers!
Janine
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