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Stacking Help For Reduction Gas Firing


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do you have a picture of your kiln, flu, bag walls and burner ports from the inside? Think of it as a maze for the flame, but you have to know the character of the flame as well as the pull of the stack or chimney.Some kilns do better with a 9" post on the first level and some don't need that much space.Are you using target bricks at the end of the bag walls? Is this a downdraft? If so, un-uniform taller pieces can go on the top shelf.Handles should not hang over the the bag walls and firebox. Pieces can be stacked tightly to about a 1/4". Two-three fingers distance from the walls depending on the fingers..If you have two or more columns of shelves, stagger the heights.

 

 

 

Marcia

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Each kiln is different, but if your kiln fires nicely, you can load it just about any way you want. The only thing I would avoid is putting very short shelves at the very bottom and getting too close to the walls. But I've never had a problem with appendages hanging out over the bag walls as far as kiln performance is concerned. I've had the good fortune to fire dependable gas kilns over the years, and have always stacked them as tight as possible, with less than 1/8" between pieces. If it's designed properly, there will be good air flow through the kiln even if the stack is very tight. You do not have to be all that concerned about flame path like you do with a wood burning kiln.

 

In a downdraft kiln, the bag wall is designed to force the flame upward before it is pulled down and out the flue. The height and tightness of the bag wall will depend on the kiln. For a new homemade kiln it will take a couple of firings to figure it out. If the top runs cold, the bag wall is built higher.

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It ran hot on the bottom and cold on top. It looks like most of the heat and flames, found their way back to the flue after the first shelf. One piece had the glaze blown off one side where the flame path was highest. You said that if the kiln is designed well, stacking would not matter. That might be a very true commentary on my coversion kiln design.....it is very finicky, tempermental, and uneven....

 

I think I need to close the damper more too.

 

Why is a short shelf a bad idea on the bottom?

 

Jed

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Marcia, the kiln is a bit backwards. The burners are horizontal on either side of the exit flue. The flames hit the back of the kiln where they are deflected upwards. I stacked 2" posts with 1/4 airspace between posts acting as a bag wall for the first shelf.

 

The flame was forceful and not licking. I neeed to turn down the air I guess and let the kiln heat up more slowly.

 

The drawing is the same orientation as the kiln. I am sure it will cause lots of questions.

 

Jed

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Those little kilns are a whole different ball game. First, make sure the bottom shelf is high enough that air can move well down there. You'll probably have to go higher than 2". I would even try putting it at the top of the flue opening and putting the shelf tight against the wall above the flue opening. You could also try making a flue channel that runs under the bottom shelf, to about 4 inches from the opposite wall. Make sure there's adequate space around the edges of the shelves for air movement. You may find you need to go to a smaller shelf to give the kiln room to breathe. It's going to take a lot of experimentation.

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Are the target bricks slanted at 45 degrees to bounce the flame up? I have built double cross drafts before and they fired well.They were much bigger 40 and 60 cubic feet. I don't question the concept.

You need space for the flame to travel and you need to bounce it up. Are you using smaller shelves than you would if this were electric?

 

Marcia

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Are the target bricks slanted at 45 degrees to bounce the flame up? I have built double cross drafts before and they fired well.They were much bigger 40 and 60 cubic feet. I don't question the concept.

You need space for the flame to travel and you need to bounce it up. Are you using smaller shelves than you would if this were electric?

 

Marcia

Yes, I have slanted target bricks to redirect the flame upward when the flame reaches the distal wall.  I have 5" flame trough below the first shelf.  The flame travels about 16 " laterally before being deflected upward,  I also have  2 smaller target bricks at about 7" to deflect some of the flames upward along the lateral walls.  I think I will make a better bagwall along the back of the kiln to help direct the flames to the top of the kiln.  I'm thinking of placing  1/2" x 1/2' holes in the bagwall about every 4 " apart so some of the flames can get into each of the shelves.  Again, I am flying by the seat of my pants here.....  I'm still mourning the loss of not getting the Alpine 24 cubicfoot kiln recently.

 

Jed

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Whatever you do make the flame go up into the load way further as it just wants to go out the flue as its so close.You can make this happen with shelves bricks or both. The target bricks matter more than how you stack the pots on load. These small conversions are each a unique setup with yours being even more so.

Mark

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Like Marcia mentioned, if you're using normal size shelves for an electric that size, they're probably too big. If you've only got an inch or so around the shelves, they are probably trapping the air and heat at the bottom. Go to a smaller size or cut those down. Typical sprung arch gas kilns with 2 burners have fireboxes that are about 6" wide, then the bag wall, then a couple more inches before the shelf edge. That's a total of about 20" of open space in a kiln that usually has 24" wide shelves. Lots of breathing room. If I remember correctly my old gas kiln had 22 cubic feet of stacking space, and a total interior volume of 40+ cubic feet. So for your kiln to really fire properly, you're going to have a much smaller stacking area than you may have thought.

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Like Marcia mentioned, if you're using normal size shelves for an electric that size, they're probably too big. If you've only got an inch or so around the shelves, they are probably trapping the air and heat at the bottom. Go to a smaller size or cut those down. Typical sprung arch gas kilns with 2 burners have fireboxes that are about 6" wide, then the bag wall, then a couple more inches before the shelf edge. That's a total of about 20" of open space in a kiln that usually has 24" wide shelves. Lots of breathing room. If I remember correctly my old gas kiln had 22 cubic feet of stacking space, and a total interior volume of 40+ cubic feet. So for your kiln to really fire properly, you're going to have a much smaller stacking area than you may have thought.

I will cut the shelves down to 12" allowing about 2" on the sides. If the shelves are smaller than that, I won't have much stacking room left....sigh...

 

The next firing will be Sat.  Hopefully the airflow will be better with the changes..

 

Thanks guys

 

jed

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