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48Cuf Gas Kiln Help


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#41 Ben

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Posted 15 August 2013 - 07:53 PM

You know Mart,

You will get more flies with honey....

And you'll be more likely to get someone to follow your top quoting preferences if you reword your instructions.

I find your remark "extremely" objectionable and annoyingly off topic. 

You added nothing to solving the problem at hand as this is not an internet ettiquette discussion forum nor topic.

 

 

Looks like "Eeny, meeny, miny, moe" wil give the final answer to a young kiln builder :)

Fantastic indeed

 

BTW, it is EXTREMELY annoying when you "top quote" ;)

 

Please use:

 

quoted text

 



#42 neilestrick

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Posted 15 August 2013 - 09:28 PM

The burner ports and flue openings must be sized properly, and the methods listed thus far work well. However secondary air is also affected by the draw of the exit flue as well. If the chimney is too short, there won't be enough draw to bring in the secondary air or do an effective job exhausting air in general. How tall is the chimney?


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#43 Mart

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Posted 16 August 2013 - 04:30 AM

 

Looks like "Eeny, meeny, miny, moe" wil give the final answer to a young kiln builder :)
Fantastic indeed
 
BTW, it is EXTREMELY annoying when you "top quote" ;)
 
Please use:
 

quoted text

 


You know Mart,
You will get more flies with honey....
And you'll be more likely to get someone to follow your top quoting preferences if you reword your instructions.
I find your remark "extremely" objectionable and annoyingly off topic.
You added nothing to solving the problem at hand as this is not an internet ettiquette discussion forum nor topic.

 


FTFY (Fixed That For You)
I'll use larger smileys next time, when drawing attention to a simple, logical and also useful net etiquette.

I agree, this is off-topic so lets get back to the burner port holes.

Working back from the exit flue size via kiln capacity in cubic shoes... toes... no.. feet, gives very different results as shown before.

1. Add the total inlet flue areas (ports) to find the exit flue area.

 

Start from 4. and 3.

2. A rule of thumb for exit flues is 2 1/2 sq. in. per cf kiln space.

3.42*2.5=8,55inc2 - 55.16 cm2(divide that by number of burners and I get 55.16/2=27.58 and sq2 from 27.58=5.25x5.25 square opening or circular opening diameter 59,2 mm.

I can not fit my burner in to that burner port because it's outside diameter is 60 mm

3. I find that 7,000 btu burner input requires 1 sq. in. exit flue area, regardless of the burner system used A kiln requiring 1,000,000 btu burner input will need an exit flue of143 sq.in., or 12"x12".

54720/7000=7,82 - 50,44 cm2 is smaller than 1 and will not work for burner port.
 
Finding the BTU's one needs (from another book)
4. for cone 10, 6-8 h firing) 16,000*kiln size in cf 3,42*54720=54720


Even this will be too small for the burner port:
If I am going to take the result from 3 2 (27.58) and add it to the area of my burner (28.27). This will give me a space around the burner with area 27.58.
Final diameter for the burner port will be: 28.27+27.58= 55.85 cm2 or a circular hole with a diameter of 8.43 cm

Sounds like those equations work for larger kilns an not small, less that 5 feet3



#44 neilestrick

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Posted 16 August 2013 - 03:02 PM

The math for computing the inlet and outlet size is the same regardless of the size of the kiln, whether 10 cubic feet or 100. Yes, there is a point at which the burner ports cannot be smaller than a certain size, but having ports that are a little oversized won't affect things all that much. That's why there's a damper on the flue. Problems only arise when the ports are too small, or way too large.

 

I've read this thread several times, but I still have a lot of questions. Many photos of the setup, inside and out, would really help a lot!


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#45 gianda

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Posted 19 August 2013 - 08:11 AM

Thanks guys, for all the support and help...

 

As said in my last post, problem has been solved... :)

 

Overall, I think that i was a combination of problems... Undersized burners to start with, burner ports to continue, exit flues maybe, and during the last firing, after finishing the gas on the two small burners, the temp started rising like crazy on the two new larger burners alone  from 1184 to 1215 in 8 minutes... ( 1 deg, C every 15 seconds. which at high temps is pretty good as far as my experience goes.) The final temp reached, after the gas on the larger burners run out too was 1235. which was reached in 12 minutes or so...

 

Looking at this, I feel pretty confident that I should be able to get to cone 10 at the next firing...

 

Here a sum up of the changes done for ref.

 

2 Large burners using 35mm iD SS pipe with 60mm dia burner head and 1.8mm orifice. Burner ports of 75x75mm square.

2 small burners using  25mm iD ss pipe with 45mm dia burner head and 1.2mm orifice. Burner ports of 60mm dia.

Exit flue is 7"x4.5"

Kiln size is 3'x3'x4'depth chamber.

Chimney height is 5'

 

I can post pics of the kiln for further reference, but as of now, after building my first kiln,  if I had time I would rip down everything but the chimney and floor and rebuild it from scratch... ( well... lots learned from building this first one) and waiting for the next one...

 

Also here i India materials are really cheap and saved a lot of $ by building my own kiln instead of asking someone to do it for me... ( here there are not many real professional companies that build them anyways...) All in all, my time not counting in the equation I have spent to build the kiln 80,000INR which in $ is about 1330$...

 

Carborundum shelves 1'x2'x1" come at roughly 40$

One 7 meter roll of high temp. 1470 deg C fiber costs about 35$

High alumina bricks 0.56$ a piece

Iron comes at little less then 1$/KG so the frame including welding and all set me back 250$

 

 

ANYWAYS, one never stops learning!

 

here the pic of the large venturi built from SS off the shelf parts for 15$ each...

 

 

 

 

And here some pics of the pots that came out of the firing @ 1235Deg C.  some glazes melted really well... some others not...

Some others might have needed a thicker application....

P.s. the pottery went through 2 firings !!!  hence the cracks on some of them... first firing @ 1125  and second firing at 1235.

 

 

Attached Files



#46 Ben

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Posted 19 August 2013 - 08:38 AM

Thanks guys, for all the support and help...

 

As said in my last post, problem has been solved... :)

 

Overall, I think that i was a combination of problems... Undersized burners to start with, burner ports to continue, exit flues maybe, and during the last firing, after finishing the gas on the two small burners, the temp started rising like crazy on the two new larger burners alone  from 1184 to 1215 in 8 minutes... ( 1 deg, C every 15 seconds. which at high temps is pretty good as far as my experience goes.) The final temp reached, after the gas on the larger burners run out too was 1235. which was reached in 12 minutes or so...

 

 

 

I have highlighted a small piece of text that is worth noting because I think it exactly pinpoints the problem. After the 2 small burners were shut off the kiln took off. If you made no other adjustments besides shutting off the 2 small burners I think that they are not mixing in enough air.

I'd try a firing using only the two newer burners and see how even you can get the temperature. If that doesn't work replace the 2 older ones with burners like the other two new ones and give another try.

 

You don't want the temp to rise that quickly. You are trying to do a specific amount of heat work on the pots/glazes in the kiln and time is a component of heat work. If the temp rises too fast, the glazes may not melt completely and the clay may not become totaly mature

 

 

The pots are great BTW. The brushwork is fantastic.



#47 gianda

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Posted 19 August 2013 - 09:44 AM

 

Thanks guys, for all the support and help...

 

As said in my last post, problem has been solved... :)

 

Overall, I think that i was a combination of problems... Undersized burners to start with, burner ports to continue, exit flues maybe, and during the last firing, after finishing the gas on the two small burners, the temp started rising like crazy on the two new larger burners alone  from 1184 to 1215 in 8 minutes... ( 1 deg, C every 15 seconds. which at high temps is pretty good as far as my experience goes.) The final temp reached, after the gas on the larger burners run out too was 1235. which was reached in 12 minutes or so...

 

 

 

I have highlighted a small piece of text that is worth noting because I think it exactly pinpoints the problem. After the 2 small burners were shut off the kiln took off. If you made no other adjustments besides shutting off the 2 small burners I think that they are not mixing in enough air.

I'd try a firing using only the two newer burners and see how even you can get the temperature. If that doesn't work replace the 2 older ones with burners like the other two new ones and give another try.

 

You don't want the temp to rise that quickly. You are trying to do a specific amount of heat work on the pots/glazes in the kiln and time is a component of heat work. If the temp rises too fast, the glazes may not melt completely and the clay may not become totaly mature

 

 

The pots are great BTW. The brushwork is fantastic.

 

 

Hi Ben,

 

thanks for the compliments, well, the 4 small old burners wouldn't reach temperature, while the two large ones seam to be doing the work just fine...

What I'll try next firing is to use the small burners alone for the first 4 hrs because at low pressures they seem to be doing just fine and the temp rises nicely and steadily... for the last 4 hrs ( 600deg onwards,) I'll shut those 2 off and replace them firstly with 1 single large new burner and then add an extra one when the temperature raise seems to have slowed down a little.

Hopefully it'll work!

 

P.s.  When the 2 small burners went off, I plugged the holes and left only the two single burners to do the work.



#48 Biglou13

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Posted 19 August 2013 - 08:49 PM

5' chimney. For natural draft I think needs to be taller? I'm to sleepy to dig out books.

Have you looked into forced air burner?
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#49 Biglou13

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Posted 20 August 2013 - 08:57 PM

Olsen's formula that 3 x dp(downward pull) + (hp(horizontal pull)
divided by 3) = height of chimney

Looks like your chimney is short. Which results in inadequate draft. Looks like you need 13 foot chimney. Taller is better just damper it.
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