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help needed evening out my kiln temp differences


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#1 shoshi

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Posted 23 January 2013 - 01:10 AM

Hello,
I have an Olympic torchbearer gas kiln model 2827G. It's a basic updraft with 4 venturi burners and I fire it manually using cones and a pyrometer with 2 leads to monitor the temperature. I've used it for bisque and oxidation glaze firing-both low and high up to cone 10. The problem has always been the temp difference between the bottom and the top shelves. There is usually around 100 degrees celsius difference (sometimes more) with the top being hotter. I've tried packing the top denser than the bottom with some success. I also tried moving my shelves to act as saggers with the hope it would redirect the flame. That made the bottom even cooler and I aborted that firing until I could rearrange the shelves back to usual configuration. The longer I fire it, the less difference there is but the longer the top shelf is at a mature temperature so it can end up over fired and the bottom under fired. Does anyone else have this problem with this kind of kiln? Any ideas on how to solve this?
Thanks

#2 Mark C.

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Posted 23 January 2013 - 03:00 AM

This is the way with updrafts. The idea is to slow the heat/flame down so that it evens up temp wise. That is do not let it get out easy and fast.
First I suggest a small thin top shelve stacked under the exit flue with just an inch and 1/2 or two from the lid top. This slows down the flow.
Second stack the bottom so the flow is broken and slow-try to think about how the heat/flame travels up and divert it thru the load.
Because you are in oxidation mode the heat just flies out so try and divert and slow it down. I would pack the bottom tighter and make sure your shelves are all 1/2 shelves and staggered as well as put a small top shelve near the exit flue. try this and you will see some change

My updraft fires with 6 burners on the bottom has a hotter bottom and a cold top always-I slow the flow down with a small 8x10 shelve stacked close to the flue but not obstructing it.
Its always a cone or more off top to bottom.
I load the hot glazed pots in bottom and the cool glazed ware on top and it works well.
PS mine is a reduction fired which also slows down and even things up better I think temp wise. When it oxidizes it flies and gets more uneven.
Mark
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#3 OffCenter

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Posted 23 January 2013 - 07:45 AM

Hello,
I have an Olympic torchbearer gas kiln model 2827G. It's a basic updraft with 4 venturi burners and I fire it manually using cones and a pyrometer with 2 leads to monitor the temperature. I've used it for bisque and oxidation glaze firing-both low and high up to cone 10. The problem has always been the temp difference between the bottom and the top shelves. There is usually around 100 degrees celsius difference (sometimes more) with the top being hotter. I've tried packing the top denser than the bottom with some success. I also tried moving my shelves to act as saggers with the hope it would redirect the flame. That made the bottom even cooler and I aborted that firing until I could rearrange the shelves back to usual configuration. The longer I fire it, the less difference there is but the longer the top shelf is at a mature temperature so it can end up over fired and the bottom under fired. Does anyone else have this problem with this kind of kiln? Any ideas on how to solve this?
Thanks


With that kiln you're just going to have to accept the fact that, while there are things you can do (mainly slowing down the firing) that will help even out the firing, there is always going to be a difference in temp between the top and bottom. So, just get all zen about it and embrace the difference--cone 10+ glazes at top, cone 10 in center, cone 9 in bottom.

Jim
E pur si muove.

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#4 shoshi

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Posted 23 January 2013 - 05:01 PM

This is the way with updrafts. The idea is to slow the heat/flame down so that it evens up temp wise. That is do not let it get out easy and fast.
First I suggest a small thin top shelve stacked under the exit flue with just an inch and 1/2 or two from the lid top. This slows down the flow.
Second stack the bottom so the flow is broken and slow-try to think about how the heat/flame travels up and divert it thru the load.
Because you are in oxidation mode the heat just flies out so try and divert and slow it down. I would pack the bottom tighter and make sure your shelves are all 1/2 shelves and staggered as well as put a small top shelve near the exit flue. try this and you will see some change

My updraft fires with 6 burners on the bottom has a hotter bottom and a cold top always-I slow the flow down with a small 8x10 shelve stacked close to the flue but not obstructing it.
Its always a cone or more off top to bottom.
I load the hot glazed pots in bottom and the cool glazed ware on top and it works well.
PS mine is a reduction fired which also slows down and even things up better I think temp wise. When it oxidizes it flies and gets more uneven.
Mark




Thanks a lot! I'll try your suggestions
Shoshi



#5 shoshi

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Posted 23 January 2013 - 05:02 PM

Thanks a lot! I'll try your suggestions.
Shoshi

#6 docweathers

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Posted 23 January 2013 - 10:12 PM

As a result of the above discussions, I have just decided to mix some clone7 glazes for the top of my 2728G.

Larry

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#7 Diz

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Posted 24 January 2013 - 10:52 AM

Good Morning,

I too have a Torchbearer (2831) and have fought those temperature differences between top and bottom. I only do cone 10 reduction in my kiln and after many firings am beginning to gain ‘some’ control. Hopefully my suggestions will be of some help, although while working to even the temp I am also fighting to maintain some reduction within my kiln.

In addition to the shelf baffle within 2” of the underside of the lid, I also placed my bottom shelf on 5” posts. I use ½ shelves throughout my kiln and between the ½ shelves forming the bottom shelf, there is a 1” gap between these shelves. This 1” gap continues between the shelves all the way up to the baffle shelf even if ½ shelves are somewhat off-set. The top shelf layer, below the baffle shelf, I make the opening between the ½ shelves only ½”. (So try to make the shelves forming this final shelf somewhat level in order to be able to place your baffle shelf level.)

Make sure that you have the correct size shelves. Originally I had the wrong shelves and that created additional problems. I now have shelves that are 24” on the long side.

You need to divert some of the flame to flow below your bottom shelf. I have created a baffle on 2 of the burners (in opposite corners on the diagonal of the base) using kiln posts. My 1” shelves sit on 5” posts and the baffle is created by putting a 3” kiln post on each side of the port with another kiln post lying across the 3” posts. This lays as tight to the kiln wall as you can and still sits a bit under the shelf so the flame is directed under the bottom shelf from 2 burners while the other 2 burners shoot flames up the inside wall.

I also created a greater ‘draw’ of air by creating a chimney from excess firebricks. I place 4 bricks to surround the port in the lid and then I place a broken shelf on top of this so I can regulate the amount of air escaping the kiln. This is important with my reduction but this port is partially closed early in the firing and the kiln will still be in oxidation. So by trapping some of the heat you can use that heat to manage temps within the kiln.

I hope some of this will be of help to you. All these things have combined to make my firings much better. I have had firings where top and bottom are within 15 degrees but they are rare. Knowing my glazes I place certain glazes on the top and bottom shelves that I know will work if the temp is a bit off.

Although I have a double pyro in the kiln, cone plaques influence my final decision as to when the firing is over.

Good luck! This kiln creates frustration and I would not recommend it to anyone. Olympic has given little help – their usual response has been “Keep trying, you just about have it”. Thank goodness for Mike at Continental Clay!! He is a font of information and willing to share.

Diz

#8 OffCenter

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Posted 24 January 2013 - 12:35 PM

Good Morning,

I too have a Torchbearer (2831) and have fought those temperature differences between top and bottom. I only do cone 10 reduction in my kiln and after many firings am beginning to gain ‘some’ control. Hopefully my suggestions will be of some help, although while working to even the temp I am also fighting to maintain some reduction within my kiln.

In addition to the shelf baffle within 2” of the underside of the lid, I also placed my bottom shelf on 5” posts. I use ½ shelves throughout my kiln and between the ½ shelves forming the bottom shelf, there is a 1” gap between these shelves. This 1” gap continues between the shelves all the way up to the baffle shelf even if ½ shelves are somewhat off-set. The top shelf layer, below the baffle shelf, I make the opening between the ½ shelves only ½”. (So try to make the shelves forming this final shelf somewhat level in order to be able to place your baffle shelf level.)

Make sure that you have the correct size shelves. Originally I had the wrong shelves and that created additional problems. I now have shelves that are 24” on the long side.

You need to divert some of the flame to flow below your bottom shelf. I have created a baffle on 2 of the burners (in opposite corners on the diagonal of the base) using kiln posts. My 1” shelves sit on 5” posts and the baffle is created by putting a 3” kiln post on each side of the port with another kiln post lying across the 3” posts. This lays as tight to the kiln wall as you can and still sits a bit under the shelf so the flame is directed under the bottom shelf from 2 burners while the other 2 burners shoot flames up the inside wall.

I also created a greater ‘draw’ of air by creating a chimney from excess firebricks. I place 4 bricks to surround the port in the lid and then I place a broken shelf on top of this so I can regulate the amount of air escaping the kiln. This is important with my reduction but this port is partially closed early in the firing and the kiln will still be in oxidation. So by trapping some of the heat you can use that heat to manage temps within the kiln.

I hope some of this will be of help to you. All these things have combined to make my firings much better. I have had firings where top and bottom are within 15 degrees but they are rare. Knowing my glazes I place certain glazes on the top and bottom shelves that I know will work if the temp is a bit off.

Although I have a double pyro in the kiln, cone plaques influence my final decision as to when the firing is over.

Good luck! This kiln creates frustration and I would not recommend it to anyone. Olympic has given little help – their usual response has been “Keep trying, you just about have it”. Thank goodness for Mike at Continental Clay!! He is a font of information and willing to share.

Diz


This makes my suggestion that after doing a few obvious thing to improve the firing you have to stop fighting it and accept the fact that your kiln is never going to give you the control and options you desire. If you want to fire a kiln that lets you control the fire and control the evenness of the temp then you have to build or buy a well-designed kiln. If you want to fire a Torchbearer then you have to accept it for what it is--a big, hot toy. But, that's not necessarily a bad thing. You can play with toys. I love using mine for saggar firings.

Jim
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#9 docweathers

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Posted 25 January 2013 - 05:31 PM

Good Morning,

I too have a Torchbearer (2831) and have fought those temperature differences between top and bottom. I only do cone 10 reduction in my kiln and after many firings am beginning to gain ‘some’ control. Hopefully my suggestions will be of some help, although while working to even the temp I am also fighting to maintain some reduction within my kiln.

In addition to the shelf baffle within 2” of the underside of the lid, I also placed my bottom shelf on 5” posts. I use ½ shelves throughout my kiln and between the ½ shelves forming the bottom shelf, there is a 1” gap between these shelves. This 1” gap continues between the shelves all the way up to the baffle shelf even if ½ shelves are somewhat off-set. The top shelf layer, below the baffle shelf, I make the opening between the ½ shelves only ½”. (So try to make the shelves forming this final shelf somewhat level in order to be able to place your baffle shelf level.)

Make sure that you have the correct size shelves. Originally I had the wrong shelves and that created additional problems. I now have shelves that are 24” on the long side.

You need to divert some of the flame to flow below your bottom shelf. I have created a baffle on 2 of the burners (in opposite corners on the diagonal of the base) using kiln posts. My 1” shelves sit on 5” posts and the baffle is created by putting a 3” kiln post on each side of the port with another kiln post lying across the 3” posts. This lays as tight to the kiln wall as you can and still sits a bit under the shelf so the flame is directed under the bottom shelf from 2 burners while the other 2 burners shoot flames up the inside wall.

I also created a greater ‘draw’ of air by creating a chimney from excess firebricks. I place 4 bricks to surround the port in the lid and then I place a broken shelf on top of this so I can regulate the amount of air escaping the kiln. This is important with my reduction but this port is partially closed early in the firing and the kiln will still be in oxidation. So by trapping some of the heat you can use that heat to manage temps within the kiln.

I hope some of this will be of help to you. All these things have combined to make my firings much better. I have had firings where top and bottom are within 15 degrees but they are rare. Knowing my glazes I place certain glazes on the top and bottom shelves that I know will work if the temp is a bit off.

Although I have a double pyro in the kiln, cone plaques influence my final decision as to when the firing is over.

Good luck! This kiln creates frustration and I would not recommend it to anyone. Olympic has given little help – their usual response has been “Keep trying, you just about have it”. Thank goodness for Mike at Continental Clay!! He is a font of information and willing to share.

Diz


Have you ever tried having alternate layers of shelves touching alternate outside walls so that the flame is forced to travel back and forth between shelf layers? Or maybe having alternate layers of shelves touching the outside walls with a large gap between the shelves then the next layer touching in the center with a larger space between the outside of the shelves and the inside wall of the kiln?

I have not tried these ideas , but before I do I wanted to see if such ideas were part of your experiments. Does anyone else have any idea what would happen with such strategies?


Also, what specifically is it about updraft kilns that cause greater temperature differences.

Larry

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#10 R Fraser

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Posted 25 January 2013 - 08:03 PM

I was firing the same kiln I bought used a couple of years ago and heard the same advice about restricting the exit to add slight back pressure and even out the temp etc. I did get a slightly more even reduction in one firing using a "baffle shelf" just below the exit of the top of the kiln but could not reproduce the result. I did note the kiln was extremly sensitive to ambient conditions, even a light breeeze made the process very uncertain. I also called Olympic and even though it was bought used they were very gracious and tried to help me get the results I wanted. I burned alot of fuel trying to find a happy place with that kiln and never did feel that I had it quite right as I never had any consistency from one firing to the next. I do know a studio potter who can get her updraft torchbearer kiln to work for her, but I do not know how. More than one person told me I just needed to get know the kiln and its idiosyncracies and where it was hot and cool and what shelves I could count on reliably reducing. What no one could tell me was how much I would spend in fuel during this learning process. I burned through at least ten 100 pound propane cyllindars and produced some dissapointing ware & had pretty much given up on cone 10 reduction firing. Then, I went to a weekend workshop with Simon Leach in Pa last summer and he had converted the same kiln to downdraft and was getting very interesting and reproducable results. When I came home I made a base out of hard brick that had 2 flame paths for a pair of MR750 burners on high pressure propane and a central exit channel for the chimney. I made a 9 foot brick chimney and plugging the top of the kiln and I fired it as a down draft kiln for several firings with better control over the chamber atmosphere and pretty even reduction. I named it the "DeathStar". In the end I was down to less than 1/2 cone difference top to bottom (seveal firings were even top to bottom) and I was pretty happy, but in the conversion lost some usable space for stacking ware, and it was a fuel hog. So this summer I built a 22 cuft kiln out of used IFB and could not be happier! I do have a torchbearer for sale now...
The image is from the last firing done in the converted Olympic before I took it down to make way for Kiln 2.0 Cone 10R with nice even reduction for a blood red copper red accent.

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#11 Diz

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Posted 26 January 2013 - 03:34 PM

I have tried alternating the shelf layers out to touch the wall and next layer touching in the center, continuing the in & out up the layers until the baffle about 1-2" under the lid. I have been getting much better consistency with the 1" open channel up the center. Another thing I did was adjust each of the gas pipes so that their top edge was 1/2" below the bottom of the base.

This kiln is VERY touchy and every change in gas, lid or port opening/closing has to be done by a tap to the handle/brick. I find that my best firings seem to be the day before a storm and the worst days to fire are hot, humid days.

Since I have implemented the changes my firings have been far more successful in 2012 - far better than previous years - no refires of pieces and little wasted gas. My firings average about 13 hours.

Regarding eveness of temp throughout the kiln - do not expect temp to rise evenly throughout the kiln. I find that the bottom is usually hotter until midway thru the firing and then it flips to top hotter and then thru dampering the top port I work to even out the temps. I have double pyros in the kiln so I can see temp rise, stall or drop and if a tap sends the temp the wrong way, a reverse tap does not necessarily correct the problem. The Torchbearer came with its own set of gremlins (and we do not get along).

Each firing presents its own challenges but in the past year my level of frustration has dropped. At times I wished I had the 'college learning' about ceramics so I could understand all the chemistry involved with firing and glazes - instead my lack of book learning is accompanied by persistence.

Thank goodness for potters who are so willing to share their successes and failures so we can learn from each other.

Diz

#12 docweathers

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Posted 26 January 2013 - 06:05 PM

What is your theory about this " I did was adjust each of the gas pipes so that their top edge was 1/2" below the bottom of the base." Does this mean that you sawed-off each pipe?

I too have no training in the arts. As the Beatles said "I get by with a little help from my (pottery) friends"

I do appreciate your sharing your experiences and experiments with the torchbearer.

larry

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#13 docweathers

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Posted 26 January 2013 - 11:54 PM

There are many companies that make kilns that look very similar to the Olympic torchbearers. Is the large temperature variation from top to bottom unique to some design issue with the Olympic or is it common to all similar kilns? If this is unique to the torchbearers, what is the critical difference between it and the look-alikes

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#14 OffCenter

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Posted 27 January 2013 - 08:22 AM

There are many companies that make kilns that look very similar to the Olympic torchbearers. Is the large temperature variation from top to bottom unique to some design issue with the Olympic or is it common to all similar kilns? If this is unique to the torchbearers, what is the critical difference between it and the look-alikes


That must be something new. I thought Olympic was the only company making that design. What other companies make them?

Jim
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#15 docweathers

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Posted 27 January 2013 - 02:30 PM

You are right. I was misinformed. Olympic is the only one making such a kiln. Thanks for the correction

Larry

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#16 Diz

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Posted 27 January 2013 - 05:25 PM

I did make adjustments to the length of the pipes . 2 of the pipes had to be a bit longer, one was right length and the other I cut a bit. I placed a 1/2" thick board under the openings in the base and made my measurements up to the board and then calculated/adjusted the correct length to be properly seated in the burner. It did seem to make a difference when I got everything changed around.

Diz

#17 docweathers

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Posted 27 January 2013 - 06:08 PM

What is your theory of the "correct length" and how does that make a difference in what?

Larry

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#18 Diz

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Posted 27 January 2013 - 11:13 PM

When you look at the venturi burner, the short gas pipe is seated down into the top of the mixing chamber. When the pipe is properly seated it should extend up to 1/2" below the base of the kiln. (I used a 1/2" board to sit on top of the pipe and barely touch the underside of the kiln floor.) The burner system is attached to the square metal kiln base, but in its construction (at least for mine) the 4 venturi burners were not a uniform distance from the floor/base of the kiln. Therefore I had to measure each pipe length separately being sure to figure in the amount of the pipe that was seated in the mixer. I would suggest that you do one pipe at a time, fitting it, and then use that pipe to aid in deciding the correct length of the next pipe (perhaps just a bit longer, or shorter, or glory be - there are 2 the same length!).

Hope this helps. The easiest part of the Torchbearer is unpacking it and putting it together - the hard part is the tweaking of all its parts. But I am making headway and for that I am happy.

Diz

#19 docweathers

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Posted 27 January 2013 - 11:23 PM

I have one of the old, but instill good condition, six burner torchbearers. all six of my burner tubes are about a half-inch below the base of the kiln. so I think I will be spared this ritual. I will be applying all of your other tweaks. Thanks for saving me doing the experimentation myself. I too have a dual probe pyrometer, so I will be able to keep track of the temperature differences.

One thing I also have that may provide some guidance is an oximeter made from a Ford fuel injection oximeter. The thing works pretty well and is easy to make.

Larry

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#20 Mark C.

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Posted 27 January 2013 - 11:42 PM

One thing I also have that may provide some guidance is an oximeter made from a Ford fuel injection oximeter. The thing works pretty well and is easy to makeHow about giving us the build details on this?Mark
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