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Kristin_Gail

Real-Time Kiln Advice (Kiln Curently Firing)

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Kristin_Gail    12

Thanks, Mark.

I can't believe you got sent to Hawaii for work!

In that most recent photo above, I've already increased the height of the bag wall and closed completely the two bottom layers. It's now four bricks high (first two firings it was one brick, last firing it was three). I, too, noticed in the photo (but hadn't in real life) the unevenness of the spaces on that top layer. I've now fixed that. And I like the sounds of a target brick better. 

 

This morning I put in two target bricks and took out the angled shelves. 

 

target_brick.jpg
Is this proper placement?  I've read people talking about the importance of the distance from the burner to the target brick, even by an inch, to the success of a firing.   The distance from the burner ports to the bag wall is approximately 9 inches.  The distance from the burner ports to the target bricks is about 4.25".

 

When I re-built the bag wall, I noticed a few spots between the first and second layers where the flame/soda had eaten straight through the bricks. Little round channels, four or five of them, less than a dime's diameter on the burner side, decreasing in size and some not all the way through on the other side.

 

It's going now.  Happily holding around 200°F.

 

Thank you again!

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JBaymore    1,432

WOAH!  Is that bagwall INSULATING FIREBRICKS???????  This last photo makes it look that way....at least to me.

 

The bagwall should be HARD FIREBRICKS...... high to super duty.

 

If those are IFB... they are trying their darndest to keep the heat energy concentrated in the firebox area.  So they do not become as good at being radiant heat sources to send some of theat energy into the stacking of ware.  Plus they will create excessive firebox temperatures, and deteriorate not only the kiln lining faster... but also the burner nozzles due to the higher level of radiant heat energy coming back out the burner ports (due to the high firebiox temps).

 

Bagwall brick spacing looks much better in that last photo.... might even be a bit too tight. I'd have a little wider opening in the bottom row (maybe 1/2" ) behind the targets.

 

I would have turned the target bricks at an angle so that the axis of the burner flame hits the corner to "split" at about a 45 degree angle. (Those should be hardbrick too.)

 

best,

 

.........................john

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Kristin_Gail    12

Yessir, those are soft bricks. Every single one of them - including the target bricks.

I keep saying, and thinking, and typing, to you guys, "I'm certain I'm doing something really, really wrong - something obvious - but have no idea what it is."

It sounds as though you've found it. Or at least one of the its.  Phew.  I'm thankful.

 

--

I turned off the kiln, will procure some hard bricks tomorrow (hopefully) when the refractory opens.

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neilestrick    1,381

Did we ever fix the issue with the damper having to be so closed down? I still feel like the chimney is too tall. Is there a way at this point to put a passive damper in? You just need to be able to pull a brick or two out of the chimney above the damper, to spoil the draft. That would allow you to test if the chimney draw is too strong, and see if you can get more control out of the damper.

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Kristin_Gail    12

Neil, I obviously know nothing about kilns.  But I've always felt the chimney was too tall - it just seemed logical to me, because I have to damper it down so far.  

 

I followed advice, though, from folks here and Marc Ward, and added a 36" pipe to the top before firing #3 (the last one, which this thread was initially about).  

 

During that firing, it did fire better (temp went up instead of down) with the passive damper - that is, the space above the damper (which is shorter than the damper slot) - left open.

 

But I don't know how I would take any bricks out of the chimney.  There's that one, directly across from the flue, that I can take out.  But none above the damper.

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JBaymore    1,432

You can use the clean out port below the damper as a passice damper also.  It'll work OK for testing.  Any cold air lwet into the chimney serves two functions to decrease the draft.  One... is the volume of the air itself.  Any air in there is gases that are not drawn from the kiln.  Two is the cooling effect that air has on the stack gases.... which decreases draft also (see below).

 

The normal progression for the damper of a firing is from fully open to almost closed on all fuel kilns.  The sizing of chimneys on natural draft type kilns tends to be based on the earlier stages of the firing, not the later stages when the flue temps are hottest. Technically they are almost always "too big" for the end of the firing.

 

As I remember for ease of constructiuon you used a 9" x 9" cross section for the flue.  That is a large XC for that size kiln.  So you will tend to have 'excess draft'.  But with those cheapie MR burners... you do need a lot of secondary air entrainment.... so that is a good place to be on the potential draft.  But that means that the dampe will be very closed near the end of the firing.  And touchy to adjust. 

 

The amount of draft created by a chimney is directly proportional to the temperature of the gasses contained within the stack, and in particular to the temperature of the gasses at the exit point of the flue.  It is also connected to the cross-section of that vertical flue. And the last piece major of this is the volume of the total column on hot gases in that flue.  Ther is also the factor odf the smoothness of the sutrface of the interior of that flue...... but that is minor compared to the other aspects.  They are all interrelated factors.

 

You have a "supercharger" on your kiln engine.  You'll have to learn to use it accurately.

 

As to the amount closed the dampe might be........

 

For example, on my 40 cubic foot gas kiln, when the kiln is near the end of a cone 9 firing, the damper is open about an area of 9" wide by 1 1/2" deep.... or an area of about 13 1/2 square inches.  A change of 1/8" at that point in the firing will make a huge difference in the kiln atmosphere and the climb rate.

 

It is not much different on the two student built 60 cubic foot gas kilns with forced air burners at the college. Or on the 35 cubic foot Baily at the college.

 

Hope this helps.

 

Glad I caught the soft brick issue.  THAT alone will make a HUGE difference.  Diagnosing this stuff from afar via written word and pictures is SO hard.

 

best,

 

.......................john

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Mark C.    1,800

I was going to Hawaii on my own for a vacation.

I volunteered to help out as a visiting artist during some classes at a small art center that I knew about from another trip-then was asked to do the salt kiln conversion and teach how to fire it. That turned into a job-I did this for free and at turned out very well.It was fun .They will be doing their own fire soon.

 

Take Johns advice on the hard bick and target bricks.

Mark

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Kristin_Gail    12

A friend who's building a wood-fired glass-blowing furnace (which apparently is an anomaly?) just gave me twelve of his high-fire hard bricks.  As he passed them my way, he told me not to use them right now - they're wet from being out in the rain.  

 

To dry them, then, would I just candle the kiln, vented, overnight, after building the new bag wall (with the kiln still loaded full of pottery)?

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TJR    359

 

I am thinking that your secondary air is way too much. This is the dial on the back of your burners. Crank it way in to about 1/4 inch, or the thickness of a pencil.

 

That shutter is primary air... not secondary.

 

So that is three changes all happening simultaneously for a test.  Too many variables changed for one test to read what is what.

 

I'd need video for a lot of the aspects of the kiln to say more very effectively.

 

The "blue" on the burners sounds like a good sign.  At least they are able to entrain some primary air.  That gives you some control.

 

The about 1" open (are you sure about that) on the damper sounds potentially plausible now that you have some primary air available.  You will find that changes of 1/8" on a kliln that size will make a differencde in the atmosphere and climb rate.

 

FYI...... Letting air into the chimney has the same effect on the kiln draft as closing the damper.

 

Make a change and wait at least 10-15 minutes to evaluate what it is doing.  Don't be changing things every 5 minutes.

 

best,

 

..............john

 

Sorry, John. I meant to say primary air.

T.

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TJR    359

Replace the soft brick bag wall with hardbrick. You want six inches from the kiln wall on the left to the bag wall. The target bricks may be in the way. Do they prevent the flames from going under the work?

TJR. Looks too crowded for combustion.

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TJR    359

Your top shelf post in the middle should be placed above another post. You have no support there.That shelf could crack and fail.

Tom.

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neilestrick    1,381

 Looks too crowded for combustion.

 

I mostly disagree. I've fired little kilns with tight fireboxes like this before without any trouble. I wouldn't change anything there yet.

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JBaymore    1,432

 

Looks too crowded for combustion.

 

I mostly disagree. I've fired little kilns with tight fireboxes like this before

 

 

Looks too crowded for combustion.

 

I mostly disagree. I've fired little kilns with tight fireboxes like this before without any trouble. I wouldn't change anything there yet.

 

 

without any trouble. I wouldn't change anything there yet.

 

 

Ditto.

 

best,

 

..............john

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Kristin_Gail    12

Replace the soft brick bag wall with hardbrick. You want six inches from the kiln wall on the left to the bag wall. The target bricks may be in the way. Do they prevent the flames from going under the work?

TJR. Looks too crowded for combustion.

TJR - in the photo you're referring to (the last one posted), the burner ports are at the bottom. The holes you see on the right/left of the target bricks are not for burners. They're for wood (which I don't plan to use).

 

There are nine (9) inches between the kiln wall at the bottom (burner ports) to the bag wall.

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Kristin_Gail    12

Tomorrow we hope to find a way to cut the bricks for the bag wall.

 

Then I'm thinking of doing a quick video tour of the whole kiln, just to make sure I haven't thoroughly confused y'all with the photos.

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Kristin_Gail    12

I'm beginning to get the idea that perhaps I should ask for help *before* I build something, instead of asking for help when the something doesn't work.  So.  Here's how I plan to build the new hard brick bag wall.  

 

bag_wall_plan.jpg

 

To the right of each layer are numbers I was shooting for - the top number is the total number of inches of space between bricks across the layer.  The bottom layer is the total number of brick inches across the layer.  

 

The top layer is off by 1/2", but the cuts won't be perfect.  I can choose the smaller 4.5" bricks for that layer.

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neilestrick    1,381

For the target bricks I would put a brick standing straight up with the narrow side facing the burner ports. The idea is that the flame hits the brick and splatters out all over. If you set it in at an angle it will just ramp flame upward. It may be sticking into the firebox a bit far that way, so if possible cut it lengthwise, or set it into the bag wall so it doesn't stick out quite so far.

 

You can cut those bricks with a masonry blade on a circular saw. The dust will do bad things to your saw so don't use a good one. Wear a mask and eye protection.

 

I think you're over thinking the bag wall. You are not going to want to cut that many bricks. It does not have to be perfectly symmetrical and even. A few gaps here and there are fine and will do the job. I would keep the bottom layer gap free.

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Mark C.    1,800

I agree on asking before the fix is needed-its a lot easier on you and your gas bill.

 

On that thought-Tom brings up a Great point thats that stilts/Posts need to be above one another

Thats a basic practice in all posting in all kilns at all temps and your top shelve shows not much line up with stilts underneath it?-so in the future put the stilts one on top of each other with the shelve in between-otherwise you are just asking for problems-cracks or failures on shelves

 

As far as a bag wall I'd just cut some bricks in 1/2 with a wet or dry diamond saw-you can cave man this with a brick chisel as well but the breaks are rough which really will not matter as a bag wall.Just use full and 1/2 bricks and ,maybe a few 1/3 bricks

I think you are over thinking all the dimensions-if you have a brick saw you cuold cut a few bricks into 1/3s to mix it up.

Cutting hard brick is a far cry from soft brick cutting

Cut only what you need per layer-lay it out with my above options and cut less.

Mark

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Kristin_Gail    12

I didn't think much with the first one. I just cut some bricks and set them in there.

 

My husband works in the landscape industry - he was just going to take the bricks with him to a job site today and cut them there; figured it would be quicker than other options. Because he'd be away from the kiln, I thought I'd see how things would stack up first, as I couldn't make any adjustments while building.

 

Because I did have comments about tightening up the bag wall, evening out spaces, back on page 2 - so I thought it better to show y'all first. Someone also mentioned (John?) having 1" gaps in the bag wall on the bottom layer, behind the target bricks. But now I'm reading different?

 

Marc Ward had mentioned having 10% of the first layer be gaps, 20% of the second layer, 30% of the third. What I have now is pretty much what's in the drawing, which is certainly not following these guidelines.

 

Oh yes, and on the shelves - I ran out of the rectangle shelves that stack nicely atop one another and had to use half-rounds on the top. I can't fix that, but I can try harder to get two of the three supports to line up.

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