Chris Hogg on wed 10 mar 99
I missed the beginning of this thread, but Emily, desperate in Texas,
was having trouble with firing her 11 cu.ft. Olympic updraft gas kiln. I
am a hobby potter in the UK and have been using a small 4 cu.ft. Olympic
kiln (1827G) on propane for over 15 years very successfully, but I had a
lot of difficulty in the early days. I don't remember all the symptoms
in detail, but I do remember poor reduction even with lots of orange
flame at the vent, when all the books talked about blue flame. The
burners were also rather noisy, with a sort of whistle.
The fault lay with the burners. On my kiln, these are Bunsen burner
types, with a short threaded burner tube and an adjustable primary air
inlet plate beneath. The problem was that the flame was burning at the
jet, not on the top of the burner tube where it should be. It wasn't too
bad at very low gas pressures, but as soon as I increased the pressure,
the flame popped back down to the jet. No amount of adjusting the gas
pressure or varying the primary air would correct it.
An article in Ceramic Review by Andrew Holden on his Power Kiln
(May-June 1984, p.18-20) described home-made burners with wire gauze
over the ends of the burner tubes. I got some stainless steel sieve
mesh, about 1/16 inch aperture, cut small pieces about 1 inch square,
and pushed them up inside the burner tubes right to the top. This
prevented the flame striking back to the jet and gave much better
combustion and control.
However, the gauze in the burner tube did decrease the open area of the
tube, limiting the amount of primary air the could be drawn in
underneath. I replaced the tubes by what I believe plumbers in the UK
call a 'nipple'. It's a short length of pipe, threaded on the outside at
each end, for connecting together pipes of different diameters. The
nipples I used had a 3/4-inch hole at one end and a 1-inch hole at the
other. The narrower thread was an exact match for the body of the burner
assembly. A larger kiln may have bigger fittings. They were made of
black iron (cast iron?) and I got them in my local building supplies
shop. I cut larger pieces of stainless steel gauze and wired them over
the outside of the top end of these tubes. Everything now works well,
with quiet blue flames on the burners, and a blue flame at the vent in
reduction.
I have now removed the plates on the primary air adjusters, so that I
run with maximum primary air all the time. I control reduction only by
restricting the vent, which limits the amount of secondary air coming in
around the burner ports. Operating a gas kiln in this way, helps to
prevent too much heavy sooting when reducing at low temperatures, say
around 15000F.
In any updraft kiln, there is a level or plane of neutral pressure
between the top and the bottom. Above this plane, there is a slight
positive pressure in the kiln, which forces the exhaust gas out through
the vent and spys. Below the neutral plane, there is negative pressure,
which draws the secondary air in through the burner ports. As the firing
proceeds, you need more air to burn the increased amount of fuel to
achieve higher temperatures. This means that the neutral plane tends to
rise in the kiln.
I don't ever get too big a flame from the lower spy-hole: seldom more
than 1-inch, with perhaps a 3-inch flame from the top spy. The flame at
the lower spy is blue and often difficult to see. At about 20000F,
pressure at the lower spy is neutral with no movement of air or gas
either into or out-of the kiln and the flame is no longer present: the
neutral pressure plane is then just at the level of the spy. You can
check it with a smoking taper to see which way the smoke is drawn.
If I have the top vent closed up too much, the temperature stops rising
and even falls, as not enough air is being drawn in to burn the gas and
generate heat. Control is quite sensitive to the vent setting. A digital
pyrometer is almost essential: I don't know how I would have managed
without mine. If I have the vent open too wide, the point of oxidation
on the lower shelves rises higher in the kiln as more air is admitted.
The bottom shelf always goes oxidising when firing to the highest
temperatures. It's an inevitable consequence of this type of kiln
design. The secondary air coming in doesn't mix immediately with the gas
from the burners, so there is always an apparent excess of air at this
point. You just have to work with it.
Lastly, you might just check that the jets on your burners are the
correct size for propane and the size of kiln you have. How? The
handbook should tell you the size, and I just measured the diameter of
the jet hole using a ruler with fine graduations on it. A hand lens may
help, but the holes are not so fine as to be unmeasurable.
Emily, I hope this helps solve your problems. If you want a detailed
description of my firing schedule, e-mail me.
Chris.
Stephen Mills on fri 12 mar 99
Can I as a supplier stick my nose in here. We were among the first to
supply Olympic Gas Torch Kilns in the UK via Harrison Mayer who were
importing them at the time. We initially had problems of the type Chris
describes. We subsequently discovered that the reason for this problem
looks like being peculiarly British. Propane Gas in the UK is supplied
as High Pressure cylinders able to run up to 30 lbs per square inch.
Olympic gas Kilns are I designed to run off domestic type low pressure
supplies i.e around 60 millibars max either Propane or Natural (methane)
Gas just by changing the jet size. This is a hell of a lot lower than 30
psi. Fix a low pressure gas regulator onto the input and all is
controllable!
Steve
BPS
Bath
UK
In message , Chris Hogg writes
>----------------------------Original message----------------------------
>I missed the beginning of this thread, but Emily, desperate in Texas,
>was having trouble with firing her 11 cu.ft. Olympic updraft gas kiln. I
>am a hobby potter in the UK and have been using a small 4 cu.ft. Olympic
>kiln (1827G) on propane for over 15 years very successfully, but I had a
>lot of difficulty in the early days. I don't remember all the symptoms
>in detail, but I do remember poor reduction even with lots of orange
>flame at the vent, when all the books talked about blue flame. The
>burners were also rather noisy, with a sort of whistle.
>
>The fault lay with the burners. On my kiln, these are Bunsen burner
>types, with a short threaded burner tube and an adjustable primary air
>inlet plate beneath. The problem was that the flame was burning at the
>jet, not on the top of the burner tube where it should be. It wasn't too
>bad at very low gas pressures, but as soon as I increased the pressure,
>the flame popped back down to the jet. No amount of adjusting the gas
>pressure or varying the primary air would correct it.
>
>An article in Ceramic Review by Andrew Holden on his Power Kiln
>(May-June 1984, p.18-20) described home-made burners with wire gauze
>over the ends of the burner tubes. I got some stainless steel sieve
>mesh, about 1/16 inch aperture, cut small pieces about 1 inch square,
>and pushed them up inside the burner tubes right to the top. This
>prevented the flame striking back to the jet and gave much better
>combustion and control.
>
>However, the gauze in the burner tube did decrease the open area of the
>tube, limiting the amount of primary air the could be drawn in
>underneath. I replaced the tubes by what I believe plumbers in the UK
>call a 'nipple'. It's a short length of pipe, threaded on the outside at
>each end, for connecting together pipes of different diameters. The
>nipples I used had a 3/4-inch hole at one end and a 1-inch hole at the
>other. The narrower thread was an exact match for the body of the burner
>assembly. A larger kiln may have bigger fittings. They were made of
>black iron (cast iron?) and I got them in my local building supplies
>shop. I cut larger pieces of stainless steel gauze and wired them over
>the outside of the top end of these tubes. Everything now works well,
>with quiet blue flames on the burners, and a blue flame at the vent in
>reduction.
>
>I have now removed the plates on the primary air adjusters, so that I
>run with maximum primary air all the time. I control reduction only by
>restricting the vent, which limits the amount of secondary air coming in
>around the burner ports. Operating a gas kiln in this way, helps to
>prevent too much heavy sooting when reducing at low temperatures, say
>around 15000F.
>
>In any updraft kiln, there is a level or plane of neutral pressure
>between the top and the bottom. Above this plane, there is a slight
>positive pressure in the kiln, which forces the exhaust gas out through
>the vent and spys. Below the neutral plane, there is negative pressure,
>which draws the secondary air in through the burner ports. As the firing
>proceeds, you need more air to burn the increased amount of fuel to
>achieve higher temperatures. This means that the neutral plane tends to
>rise in the kiln.
>
>I don't ever get too big a flame from the lower spy-hole: seldom more
>than 1-inch, with perhaps a 3-inch flame from the top spy. The flame at
>the lower spy is blue and often difficult to see. At about 20000F,
>pressure at the lower spy is neutral with no movement of air or gas
>either into or out-of the kiln and the flame is no longer present: the
>neutral pressure plane is then just at the level of the spy. You can
>check it with a smoking taper to see which way the smoke is drawn.
>
>If I have the top vent closed up too much, the temperature stops rising
>and even falls, as not enough air is being drawn in to burn the gas and
>generate heat. Control is quite sensitive to the vent setting. A digital
>pyrometer is almost essential: I don't know how I would have managed
>without mine. If I have the vent open too wide, the point of oxidation
>on the lower shelves rises higher in the kiln as more air is admitted.
>The bottom shelf always goes oxidising when firing to the highest
>temperatures. It's an inevitable consequence of this type of kiln
>design. The secondary air coming in doesn't mix immediately with the gas
>from the burners, so there is always an apparent excess of air at this
>point. You just have to work with it.
>
>Lastly, you might just check that the jets on your burners are the
>correct size for propane and the size of kiln you have. How? The
>handbook should tell you the size, and I just measured the diameter of
>the jet hole using a ruler with fine graduations on it. A hand lens may
>help, but the holes are not so fine as to be unmeasurable.
>
>Emily, I hope this helps solve your problems. If you want a detailed
>description of my firing schedule, e-mail me.
>
>Chris.
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Chris Hogg on sun 14 mar 99
Steve, I hear what you say (read what you write?), and there may well be
a UK dimension to using Olympic kilns, but surely no-one runs their kiln
directly from a propane cylinder! I certainly don't. I have always had a
regulator that drops the bottle pressure to 37 millibar (approx. 15"
water gauge), and after a further drop through the control tap, the gas
pressure in the burner manifold is typically 0-10 millibar (say 0-4"
water gauge). That's well within your figures, but I still had problems
with my burners.
Incidentally, I see that in my original posting, the 'degrees' symbol
came out as an extra zero, making all the temperatures appear a factor
of ten too high. I don't really fire to 20000F, even in my Olympic!
Chris.
In message , Stephen Mills writes
>----------------------------Original message----------------------------
>Can I as a supplier stick my nose in here. We were among the first to
>supply Olympic Gas Torch Kilns in the UK via Harrison Mayer who were
>importing them at the time. We initially had problems of the type Chris
>describes. We subsequently discovered that the reason for this problem
>looks like being peculiarly British. Propane Gas in the UK is supplied
>as High Pressure cylinders able to run up to 30 lbs per square inch.
>Olympic gas Kilns are I designed to run off domestic type low pressure
>supplies i.e around 60 millibars max either Propane or Natural >(methane)
>Gas just by changing the jet size. This is a hell of a lot lower than 30
>psi. Fix a low pressure gas regulator onto the input and all is
>controllable!
Stephen Mills on mon 15 mar 99
Chris,
A lot do, High Pressure burners are the norm in my experience, most part
time potters over here have relatively small Kilns, powered straight off
the bottle with an adjustable regulator attached to it in fact the only
low pressure kit we've ever sold was for natural gas, not low pressure
propane.
Steve
Bath
UK
In message , Chris Hogg writes
>----------------------------Original message----------------------------
>Steve, I hear what you say (read what you write?), and there may well be
>a UK dimension to using Olympic kilns, but surely no-one runs their kiln
>directly from a propane cylinder! I certainly don't. I have always had a
>regulator that drops the bottle pressure to 37 millibar (approx. 15"
>water gauge), and after a further drop through the control tap, the gas
>pressure in the burner manifold is typically 0-10 millibar (say 0-4"
>water gauge). That's well within your figures, but I still had problems
>with my burners.
>
>Incidentally, I see that in my original posting, the 'degrees' symbol
>came out as an extra zero, making all the temperatures appear a factor
>of ten too high. I don't really fire to 20000F, even in my Olympic!
>
>Chris.
>
>In message , Stephen Mills writes
>>----------------------------Original message----------------------------
>>Can I as a supplier stick my nose in here. We were among the first to
>>supply Olympic Gas Torch Kilns in the UK via Harrison Mayer who were
>>importing them at the time. We initially had problems of the type Chris
>>describes. We subsequently discovered that the reason for this problem
>>looks like being peculiarly British. Propane Gas in the UK is supplied
>>as High Pressure cylinders able to run up to 30 lbs per square inch.
>>Olympic gas Kilns are I designed to run off domestic type low pressure
>>supplies i.e around 60 millibars max either Propane or Natural >(methane)
>>Gas just by changing the jet size. This is a hell of a lot lower than 30
>>psi. Fix a low pressure gas regulator onto the input and all is
>>controllable!
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
George Nagel on mon 4 oct 04
I have an olympic updraft gas kiln I'm having problems with. I'm firing to cone 10 using an oxygen probe along with a cone pack, using the schedule that the oxyprobe recommends (around 300 degrees per hour). Cones 8 to 10 are going down ahead of their temp. reading on the probe. When I shut off the gas at cone 10 using the cones I get blistering and dry, what looks like underfired, glazes. If I keep firing on up, including a soaking period I'm still get some isolated blistering. Am I correct in thinking that I need to stay with the higher temp. and soak longer?
This kiln has three burners. They recommend spreading the shelves so there's a half inch space going up the middle of the kiln. I was told I'd get more even results if I put a small piece of shelf over the middle burner deflecting the flame to the side. Any thoughts on which would give me more even results?
Thanks for any help. George
sdr on tue 5 oct 04
George, what size is your kiln? Olympic makes several.
The smallest one is the most difficult to deal with, uneven
heat being the problem. My suggestion is to really slow
down the early part of the firing, to even out the heat.
Also, temp probes are never accurate; you must use
cones to figure out where your hot/cold spots are.
Place cones here/there all over the shelves, and note
on your next firing which are at the proper stage.
Try placing your half-shelves at different levels, leave
a goodly gap in between at the center, slow the early
part down, give the glazes time to mature. You might
also place a shelf over the top layer of pots, to help
trap heat that otherwise rushes out the top vent.
You might also just check your glazes, in case of a
mixing error.
regards
Dannon Rhudy
----- Original Message -----
From: "George Nagel"
> I have an olympic updraft gas kiln I'm having problems with. I'm firing
to cone 10 using an oxygen probe along with a cone pack, using the schedule
that the oxyprobe recommends (around 300 degrees per hour). Cones 8 to 10
are going down ahead of their temp. reading on the probe. When I shut off
the gas at cone 10 using the cones I get blistering and dry, what looks like
underfired, glazes
Paul Vernier on tue 5 oct 04
On Mon, 4 Oct 2004 21:07:18 -0700, George Nagel
wrote:
>I have an olympic updraft gas kiln I'm having problems with.>Thanks for
any help. George
>
A quick search of the archives will get you several postings that myself
and
others have posted on taming the Olympic Torchbearer. Not that we have been
completely succesful. Even firings yes. Even reduction ?? Learn to fire
this one and you will have a lot of knowledge to apply to your next kiln.
Paul
Santa Cruz, CA
Fara Shimbo on wed 6 oct 04
Hi, George,
I have an Olympic Torchbearer, probably the same kiln or at
least the same type of kiln that you do. I fire it to cone
9 or 10.
I don't have an oxyprobe, just a pyrometer. I always fire
by cones. I'd like to get an oxyprobe someday because I've
found that up here in the mountains, the kiln (runs on propane)
is always slightly reducing, no matter what I do. The result
of this is that anything that comes into contact with, or just
too close to, the flame may blister or boil.
I know one's supposed to use only half shelves in the kiln but
I get my best results with one full shelf on the bottom, supported
by three-inch posts. Anything on top of that can be packed
however you like, but a flame coming right up the middle seems
to be very damaging to my wares.
Curiously, some of the clays I use will blister in the electric
kiln but not in the gas. Southern Ice is the worst; I don't use
it now. But so long as you keep stuff out of the direct path
of the flame the kiln works great.
Fa
--
=============================================================
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=============================================================
Steve Mills on wed 6 oct 04
Fire slower, a LOT slower; like 180 to 200F per hour (I prefer the
former). Give the glazes time to melt properly!
Steve
Bath
UK
In message , George Nagel writes
>I have an olympic updraft gas kiln I'm having problems with. I'm firing =
>to cone 10 using an oxygen probe along with a cone pack, using the schedu=
>le that the oxyprobe recommends (around 300 degrees per hour). Cones 8 t=
>o 10 are going down ahead of their temp. reading on the probe. When I sh=
>ut off the gas at cone 10 using the cones I get blistering and dry, what =
>looks like underfired, glazes. If I keep firing on up, including a soaki=
>ng period I'm still get some isolated blistering. Am I correct in thinki=
>ng that I need to stay with the higher temp. and soak longer?
>
>This kiln has three burners. They recommend spreading the shelves so the=
>re's a half inch space going up the middle of the kiln. I was told I'd g=
>et more even results if I put a small piece of shelf over the middle burn=
>er deflecting the flame to the side. Any thoughts on which would give me=
> more even results?
>
>Thanks for any help. George
--
Steve Mills
Bath
UK
George Nagel on thu 7 oct 04
Hi Fara, Thanks for writing. Most of the response I'm getting is that eith=
er a full shelf on the bottom or something deflecting the flame is suggeste=
d. Not sure why Olympic recommends allowing the free path up the middle, I=
'm just guessing that maybe it helps circulation through the ware. Otherwi=
se the flame and heat path is mostly up the walls? I've had some problem w=
ith uneven firing which seems weird for such a small kiln. I've been using =
a small piece of kiln shelf as a type of bag wall just below the bottom she=
lves over the center burner to deflect the flame. I'm thinking I'm going t=
o try just placing the shelf piece on top of the bottom shelves to deflect =
the flame, but still keep the shelves slightly spread thinking maybe it wil=
l allow more circulation through the kiln. (I've heard about people having=
problems with uneven reduction.) The main glazes that are blistering and =
not coming out well are shino glazes now. I'm curious about what your firi=
ng schedule looks like. So, if you don't mind and get a chance let me know=
. thanks, George
-----Original Message-----
From: Fara Shimbo
Sent: Oct 6, 2004 5:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: olympic kiln firing
Hi, George,
I have an Olympic Torchbearer, probably the same kiln or at
least the same type of kiln that you do. I fire it to cone
9 or 10.
I don't have an oxyprobe, just a pyrometer. I always fire
by cones. I'd like to get an oxyprobe someday because I've
found that up here in the mountains, the kiln (runs on propane)
is always slightly reducing, no matter what I do. The result
of this is that anything that comes into contact with, or just
too close to, the flame may blister or boil.
I know one's supposed to use only half shelves in the kiln but
I get my best results with one full shelf on the bottom, supported
by three-inch posts. Anything on top of that can be packed
however you like, but a flame coming right up the middle seems
to be very damaging to my wares.
Curiously, some of the clays I use will blister in the electric
kiln but not in the gas. Southern Ice is the worst; I don't use
it now. But so long as you keep stuff out of the direct path
of the flame the kiln works great.
Fa
--
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
___________________________________________________________________________=
___
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.=
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George Nagel on fri 15 oct 04
Fara, Seems like I've solved the blistering problem. Slower fire, soaking, and firing down. Have trouble with good glaze reduction. Had any experience with that with this kiln? George
-----Original Message-----
From: Fara Shimbo
Sent: Oct 6, 2004 5:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: olympic kiln firing
Hi, George,
I have an Olympic Torchbearer, probably the same kiln or at
least the same type of kiln that you do. I fire it to cone
9 or 10.
I don't have an oxyprobe, just a pyrometer. I always fire
by cones. I'd like to get an oxyprobe someday because I've
found that up here in the mountains, the kiln (runs on propane)
is always slightly reducing, no matter what I do. The result
of this is that anything that comes into contact with, or just
too close to, the flame may blister or boil.
I know one's supposed to use only half shelves in the kiln but
I get my best results with one full shelf on the bottom, supported
by three-inch posts. Anything on top of that can be packed
however you like, but a flame coming right up the middle seems
to be very damaging to my wares.
Curiously, some of the clays I use will blister in the electric
kiln but not in the gas. Southern Ice is the worst; I don't use
it now. But so long as you keep stuff out of the direct path
of the flame the kiln works great.
Fa
--
=============================================================
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=============================================================
______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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