Jump to content

Homemade Gas Updraft Kiln, Not Enough Temperature Any Help :)


laythss

Recommended Posts

Hello everyone,  I am new to this form, and new to kilns. last week i started trying to make an updraft gas kiln, and it seems i hit a wall that i need some help with. 

 

Setup :

Kiln inside size : 9" x 18" height 15" 

first shelf @ 6"

Bricks used : Firebricks/ refractory bricks 9x2.5x4.5

** Dry stacked **

Gas : LP

Temperature : K type thermocouple sensor  (0-1300 c ) 

positioned at 9" height on the sidewall and sticking out 1.25"

(https://www.amazon.com/gp/product/B00UWVZAY8/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1)

 

The problem :

I cannot get the kiln to go more than 1200 degrees 

 

Trials :

1- With heat source positioned flush with inside wall, two top bricks open. Temperature rises to 500 f within 5 minutes and then within 10 minutes to 600 degrees. From then on temperature will stay between 600-700 degrees even after 45 minutes. adjusting the gas flow at times helps get it to temperature. 

 

2- Continuation  of 1 : top bricks closed... temperature drops fast to 400 degrees and with adjusting the gas down to accomodate less oxygin i can bring it back up to 600-650 

 

3- Same as 1 but after 30 minutes i started opening up holes in the bricks by sliding them apart without burning myself to make more air holes... the more holes i open the higher the temperature got.... reached max 1200 f 

 

4- same as 1 with burner positioned 2" outside of the Kiln. same max temp as 1 

 

From what i am seeing and from the amount of carbon in the kiln after so few firings, i think i have too little oxygen in the kiln. It is my first attempt to make a kiln and from all the pictures and videos i saw i didnt see holes in an upward drift gas kiln, other than the peek holes, which i tried to make but it only increased the temperature upto 900 f. 

 

Do i have to make holes all over the kiln for oxygen?  is the kiln design just wrong? is it too small ? i really cannot figure out what is the next step i should try, or just redo the whole thing with a different design. ANy help is very much appreciated. 

Here are some pictures of the project. 

 

Thanks in advance,

Layth

 

image1.jpeg

 

image2.jpeg

 

image3.jpeg

 

image4.jpeg

Link to comment
Share on other sites

Are you saying you don't have an exit flue? All kilns need an exit flue. Heat has to move through the kiln, with enough air to feed the combustion. You shouldn't have any carbon buildup, especially at low temps. I can't really tell what's going on from your photos, but I would recommend getting a kiln building book to learn about how to build one properly. There are certain 'rules' to follow if you want it to work.

Link to comment
Share on other sites

Not enough info here for us

It looks like this is made from fireplace bricks not high fire bricks that have names stamped on them.

Also soft bricks not hard bricks will give you a much better insulated kiln. All your heat is going into the hard brick which will suck it up.

Your exit looks like there is not enough air flowing thru as it all cartooned up.

I suggest a book on kiln building.

Those wood clamps will fail when this lid gets hot  just so you know.

Link to comment
Share on other sites

It is difficult to know what the photos show. What are you using as a guide for your design?

Marcia

Trials :

1- With heat source positioned flush with inside wall, two top bricks open. Temperature rises to 500 f within 5 minutes and then within 10 minutes to 600 degrees. From then on temperature will stay between 600-700 degrees even after 45 minutes. adjusting the gas flow at times helps get it to temperature. 

 

burners should be a little removed from the OUTSIDE wall to pull in secondary air. 

 

2- Continuation  of 1 : top bricks closed... temperature drops fast to 400 degrees and with adjusting the gas down to accomodate less oxygin i can bring it back up to 600-650 

Where is a flue and damper. Could your draw a schematic layout?

 

 

3- Same as 1 but after 30 minutes i started opening up holes in the bricks by sliding them apart without burning myself to make more air holes... the more holes i open the higher the temperature got.... reached max 1200 f 

 

you need a better draft system

 

 

4- same as 1 with burner positioned 2" outside of the Kiln. same max temp as 1 

 

From what i am seeing and from the amount of carbon in the kiln after so few firings, i think i have too little oxygen in the kiln. It is my first attempt to make a kiln and from all the pictures and videos i saw i didnt see holes in an upward drift gas kiln, other than the peek holes, which i tried to make but it only increased the temperature upto 900 f. 

 

Do i have to make holes all over the kiln for oxygen?  is the kiln design just wrong? is it too small ? i really cannot figure out what is the next step i should try, or just redo the whole thing with a different design. ANy help is very much appreciated. 

Here are some pictures of the project. 

 

What is the size of the interior? And what type of burner? You need a chimney.

 

 

Marcia

Link to comment
Share on other sites

Thank you all for your reply…

 

Today i changed somethings in the kiln as well as making it smaller and reached 1850 according to the sensor in the kiln (not sure how much i trust that thing though), 

this weekend i will buy some cones and make some peeking holes, and get my welding glasses ready and see what cone i am really firing at. 

 

I still am confused about some things, and hope i can get more feedback and info from you 

 

@Marcia

-In regards to the flue/damper, from what I read in couple of articles, on an unpdraft kiln, it is nothing more than an opening at the top. So I assumed that right. Today I just readjusted that and made a flue that is 1 foot high and 4.5†x 7.5†dimension.

 

-Still what bothers me is the size is way bigger than what it should be according to this site :

“The chimney passage must not be restricted and the sizing should be checked carefully first. A rough rule-of-thumb ratio is one square inch of flue area to 8,000 BTU's of maximum gas inputâ€

http://www.combust.com.au/ceramics/kiln/kiln.htm

Maybe my burner is oversized for the kiln size, I am still a bit confused about the calculations I made earlier, and trying to see if I made some mistake along the way.  

 

-In regards to the damper, I am really not sure where to use that on the flu since any reduction in whole size is bringing temperature lower, but I can use a brick for now to restrict the flue if needed.

 

- "a better draft system" â€¦ is it possibly the problem that the heat circulating inside is being “stuck†instead of exiting through the flue and causing problems? Since usually I see the burners in updraft systems to be coming from underneath pointing vertically, whereas I have mine at floor level pointing horizontally towards the back wall of the kiln.

 

- I just changed the size of the interior and made it smaller. 9†x 9†x13†(dimensions without flue) = 0.61 cu ft

The burner is MR-750 Venturi Burner – Propane from aardvarkclay with an orfice size of #38

 

@Neilestrick 

thank you for your reply, but after further reading i believe the smoke was due  to too much gas and too little air and from what i understand this can happen at any time, please let me know if i understood that wrong. 

- yes there was a hole for air to go out, so it was not totally closed, but it was just a hole not a flue...now I changed it  to a flue.

-the venturi burner I bought is for propane.

-in regards to weather the burner can heat up the size and type I have, I am a bit confused but i think the answer is yes. I did the calculations, and from what I understand I need 10370 BTU/HR to reach cone 06 in 6 hours in a hardbrick kiln.

http://www.potterswithoutborders.com/2012/07/lpg-burner-calculations/

and the burner I am using does way more than that if the figures on the chart are BTU/hr

http://www.axner.com/mr-750venturiburner.aspx

Maybe I have too big of a burner or I am reading the output wrongly. am i doing this right ?

 

@Mark C  

- From my understanding you can build with hard firebrick as well , it is not as efficient but doable.

http://www.potterswithoutborders.com/2012/07/lpg-burner-calculations/

-Assuming what I have is hard firebrick , it was called refractory firebrick from the guy who gave it to me. I don’t have access to soft firebrick where I am, and I was trying to see if I can get the design right, before going and spending a lot of  money on making one.

The clamps as u said are not the best way of doing this, but again they are not a permanent solution, it is just for testing, and they have held at temperatures 

Thank you all for your reply…

Thank you all for your reply…

 

Today i changed somethings in the kiln as well as making it smaller and reached 1850 according to the sensor in the kiln (not sure how much i trust that thing though), 

this weekend i will buy some cones and make some peeking holes, and get my welding glasses ready and see what cone i am really firing at. 

 

I still am confused about some things, and hope i can get more feedback and info from you 

 

@Marcia

-In regards to the flue/damper, from what I read in couple of articles, on an unpdraft kiln, it is nothing more than an opening at the top. So I assumed that right. Today I just readjusted that and made a flue that is 1 foot high and 4.5†x 7.5†dimension.

 

-Still what bothers me is the size is way bigger than what it should be according to this site :

“The chimney passage must not be restricted and the sizing should be checked carefully first. A rough rule-of-thumb ratio is one square inch of flue area to 8,000 BTU's of maximum gas inputâ€

http://www.combust.com.au/ceramics/kiln/kiln.htm

Maybe my burner is oversized for the kiln size, I am still a bit confused about the calculations I made earlier, and trying to see if I made some mistake along the way.  

 

-In regards to the damper, I am really not sure where to use that on the flu since any reduction in whole size is bringing temperature lower, but I can use a brick for now to restrict the flue if needed.

 

- "a better draft system" â€¦ is it possibly the problem that the heat circulating inside is being “stuck†instead of exiting through the flue and causing problems? Since usually I see the burners in updraft systems to be coming from underneath pointing vertically, whereas I have mine at floor level pointing horizontally towards the back wall of the kiln.

 

- I just changed the size of the interior and made it smaller. 9†x 9†x13†(dimensions without flue) = 0.61 cu ft

The burner is MR-750 Venturi Burner – Propane from aardvarkclay with an orfice size of #38

 

@Neilestrick 

thank you for your reply, but after further reading i believe the smoke was due  to too much gas and too little air and from what i understand this can happen at any time, please let me know if i understood that wrong. 

- yes there was a hole for air to go out, so it was not totally closed, but it was just a hole not a flue...now I changed it  to a flue.

-the venturi burner I bought is for propane.

-in regards to weather the burner can heat up the size and type I have, I am a bit confused but i think the answer is yes. I did the calculations, and from what I understand I need 10370 BTU/HR to reach cone 06 in 6 hours in a hardbrick kiln.

http://www.potterswithoutborders.com/2012/07/lpg-burner-calculations/

and the burner I am using does way more than that if the figures on the chart are BTU/hr

http://www.axner.com/mr-750venturiburner.aspx

Maybe I have too big of a burner or I am reading the output wrongly. am i doing this right ?

 

@Mark C  

- From my understanding you can build with hard firebrick as well , it is not as efficient but doable.

http://www.potterswithoutborders.com/2012/07/lpg-burner-calculations/

-Assuming what I have is hard firebrick , it was called refractory firebrick from the guy who gave it to me. I don’t have access to soft firebrick where I am, and I was trying to see if I can get the design right, before going and spending a lot of  money on making one.

The clamps as u said are not the best way of doing this, but again they are not a permanent solution, it is just for testing, and they have held at temperatures 

Thank you all for your reply… and here are some drawings of how it looks like ... (i didnt include the clamps but they are still there for now)

post-80112-0-42070600-1477025131_thumb.gif

post-80112-0-16905300-1477025132_thumb.gif

post-80112-0-46836300-1477025132_thumb.gif

Link to comment
Share on other sites

I have fired Olsen and Alpine updrafts. Olsen has the burners underneath. Alpines had them coming in from the sides. BOTh had damper systems on top of the kiln.

I think you may need enough room in the kiln for proper combustion of the burner. The Chamber may be too small. I sounds like a test kiln.

Marcia

Link to comment
Share on other sites

BTU per cubic foot.

 

9" hard brick

Cone 10 - 10,000 to 16,000

Cone 6 - 8,000 to 13,000

 

The 9" means a 9" thick wall if I remember correctly so if we can hopefully estimate double that for the 4.5" then you only need 25-30,000 btu. The problem is you can put that much gas into the kiln but you can't burn it to get heat out of it. Not enough space or air. Two smaller forced air burners could do it. I have always wanted to try a kiln this small and thought Bunsen burners that you use in science labs could be a good start.

Link to comment
Share on other sites

  • 4 weeks later...

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.