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Gas kiln won't heat up above 650C/1200F


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#21 Mark C.

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Posted 04 May 2013 - 02:50 PM

I think your burner is way to small for this kiln-
maybe get a bigger one or several more of these .
You need to more BTUs to fire this hotter.

Is the hole in the front on top the exhaust hole?If so then a small chimney may help.
Mark
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#22 glinum

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Posted 05 May 2013 - 04:11 AM

Mark, I agree that the burner is too small. I think I'll have to buy a bigger one. Or maybe I can have two of the same size? Is it ok to fire two burners from the same tank? I worry that the pressure will split between two burners and it won't give any difference. Maybe I have to get two burners and two tanks?

I just did a test and boiled 1liter of water with fully open burner. It took 4m30sec. Can I estimate burner BTU with this information? We don't use BTUs here because we use metric system, so I don't really know how to calculate and convert it.

#23 bigDave

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Posted 05 May 2013 - 10:54 AM


Or maybe I have to switch to woodworking...

Hang in there. It sure looks cool, youve got that going for you..LOL

You are actually helping those of us that will try this in the future. Doesnt Simon use two Weed burners ?

Keep trying, fiddling with it...everybody does woodworking, but only a chosen few make fire in the backyard

#24 Mark C.

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Posted 05 May 2013 - 09:14 PM

Mark, I agree that the burner is too small. I think I'll have to buy a bigger one. Or maybe I can have two of the same size? Is it ok to fire two burners from the same tank? I worry that the pressure will split between two burners and it won't give any difference. Maybe I have to get two burners and two tanks?

I just did a test and boiled 1liter of water with fully open burner. It took 4m30sec. Can I estimate burner BTU with this information? We don't use BTUs here because we use metric system, so I don't really know how to calculate and convert it.


The tank will freeze up if its to much draw-You can run water or cover it in water to help.
As far at BTUs thats for British Thermo Units and you can do a web search on conversions-not sure why we use them here in the states.
I use a burner like that for wasps nests and the like. It just looks to small for that size kiln.
I think two would work a lot better . That kiln looks plenty well insulated and should fire fast with the right burners.
Mark
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#25 glinum

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Posted 07 May 2013 - 10:37 AM

bigDave, thank you for the encouragement, it really helped, especially about the chosen ones!
So the next day I decided to decrease the kiln inner volume by putting a fiber wall about 2/3 from the front lid and cut the shelf on half. And I didn't put too many pieces in there. So I noticed that the temperature climbed much quicker than before. I got to 500C/932F in about two hours, but then again it just stucked. So I thought what if I somewhat close the top hole. I used some pieces of fiber and and made the hole about 7cm, while it was 10cm. I also closed bottom hole a little. To my surprise the temperature started to climb! I also tried different burner positions and noticed that it should not be too far out, just about inlined with the entrance. So in about 2.5 hours I got to 700C/1292F. Then it stuck again so I closed the top hole even more and it started to climb! In another 2 hours I got to 850C/1562F. And it seemed like a limit because no tweaks I tried helped.
Anyway I was so happy even with this result Posted Image The pieces were glowing orange, what a joy Posted Image

So the conclusion is the holes should not be big and the pieces should not be packed to tightly. I think there's some perfect proportions for the holes I'll have to find.

The next day I went and bought a bigger burner with side holes. I also wanted to buy a splitter to be able to connect two burners, but couldn't find it. I removed the wall in the kiln and reverted to original volume. Everything went fine, but at 800C/1472F it stucked. So I inserted the burner more in the hole (it was about 2in away) and it climbed to 850C/1562F and wouldn't climb any more.

Maybe the shelf is making problem? It's actually an insulation board and it doesn't heat up like a special kiln shelf should.


Mark, you are right, I know about the tank freezing, I put it in a water container and added hot water there.

Attached Files

  • Attached File  glow.jpg   38.54KB   14 downloads
  • Attached File  820.jpg   141.91KB   14 downloads


#26 INYA

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Posted 09 May 2013 - 03:17 AM

That is really sad to hear!
What was the temperature outside? I think I wrote before that my firing was depending on that very much. I could never imagined that for example 20 C difference (in outside temp) makes such a huge difference in firing. For example at summer evening (cca 17C I think) I could not get it over 1000-1100C
The problem is that every little thing makes a big difference. I noticed that when something blocked the progress it was time to make changes. I am trying to say that when you saw that you are not getting above 600 C it would be better to stop and not waste any more gas.

as marcia wrote:
see if you get a pull of a draft with a lit newspaper torch by your burner port. This is important since you are using a natural draft and no forced air.<br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; font-size: 12.727272033691406px; line-height: 19.09090805053711px; background-color: rgb(250, 251, 252);">

have you tried that?


My kiln is much simpler (and it fired to 1250 C at least 30 times, but it was summer), the air just has to go up and not around... the newspaper torch could tell you if you have enough air.
The chimney is not a good idea in my opinion. Before you quit.. maybe try a hole on the upper side of the barrel (in the metal). The thing is small and the temperature will be high enough everywhere.


OH another thing- you might not have enough insulation or the shelf is positioned to low (it could suppress the fire). I am having more room under.
Maybe it is just a combination of all those reasons.
I would try different solutions:
- first the newspaper torch (if that is ok then ...)
- firing in a warmer room or a warm day (this will tell you about the insulation)
- then the upper hole
.......................

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#27 glinum

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Posted 10 May 2013 - 01:23 PM

Hallelujah! Posted Image Posted Image
I finally sorted it out. The reason was quite simple - I had to throw away the pressure reducer. For some reason I thought it's not ok to run a burner without it, but I talked to another Ukrainian potter who uses similar setup and he said he runs it without the reducer.
Posted Image


So no other tweaks were actually necessary if I got rid of it on my very first firing. The burner size was ok, the holes were ok, the flu, the draft etc. were ok.
I climbed to 1040C/1900F in about 8 hours and the burner was only 70-80% open, so I believe I could easily climb to 1250C/2280F if I wanted. But I was firing earthenware so 1040C/1900F was just fine.
When I opened the burner some more the reduction flame ran out the top hole. That is so exciting! Posted Image I didn't actually need it for bisque firing, but now I know I can do reduction firing if I want.

Check out the video.

Here is the picture of the fired pieces I made this morning.
Posted Image

I have some questions about color changes but will post it later in a separate topic.

This is what happened to the shelf:
http://imageshack.us...b/16/shelfq.jpg
Probably it will live a few more firings and then I'll buy some good kiln shelf, because this one is not.

So this topic is now in resolved status http://ceramicartsda...ult/biggrin.gif
Thanks to everyone who tried to help, I really appreciate this.

Andrey

#28 INYA

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Posted 13 May 2013 - 10:47 AM

I did not know you were useing reductor...

there is no reductor on my burner :)

happy for you
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#29 Marcia Selsor

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Posted 13 May 2013 - 10:51 AM

I am happy for you too.
Marcia

#30 Mart

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Posted 01 June 2013 - 03:24 PM

Yes, I am going to build one. Is it OK if I use the "weed burner" (I think it's used also for fixing/building special type of roofs) burner they sell in hardware stores?

#31 Mart

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Posted 04 June 2013 - 01:51 AM

I finally found a business, that sells ceramic fiber blankets.
They have few different options available:
50 mm thick (~ 2") for 1260 C (2300 F)
and
50 mm (~ 2") thick for 1430C (2606 F)

They also have it 25 mm thickness and for the same temperatures.

What do you recommend? 25 or 50mm?

#32 Marcia Selsor

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Posted 04 June 2013 - 11:36 PM

Thicker is better in most cases. better insulation, less fuel consumption.

Marcia

#33 JLowes

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Posted 10 June 2013 - 12:49 PM

Although this instance is resolved, I thought I would throw in a picture of my raku kiln. Sorry I don't seem to have a better view to show you. This was loosely based on a design by Daryl Baird shown in a Pottery Making Illustrated article titled Raku Lite from the July/August 2007 issue.

It uses 1-inch (2.54 cm) inwulation and one weed burner from Harbor Freight. The base is insulating fire brick on expanded metal, framed with angle iron, and some inexpensive plastic casters under. The outside of the chamber is expanded metal lathe such as used for plastering, or backing tile base. It gets to temperature quickly, but one must start with the burner in, or close to, the burner port and gradually move it back as temperature and gas flow increase. It will get to temperature faster than I fire it, but 45 minutes of slow climb is what I prefer. I block the exhaust port partially with a piece of kiln shelf early on to retain heat as an adjustable damper. I use a 20 pound tank and no regulator.

I fire Western raku, naked raku, ferric fuming in foil, and carbon fuming with great results from all.

JohnAttached File  Saturday Rakuing.jpg   108.52KB   8 downloads




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