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Single Firing In A 3.5 Cf Gas Conversion Kiln.

ramp speed

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#1 jrgpots

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Posted 17 May 2014 - 01:10 PM

I am anxious to test fire my electric to gas conversion kiln. It is a small 3.5 cf kiln. I have two burner. I want to try a single fire with bone dry greenware taken to cone 7.

Here are my problem.

1. Thermocoupler has not yet arrived in the mail, so it will be hard to judge ramp speed and temp.
2. I don't know how fast the thing will heat up.

So, I have thought about using 1 burner for the first 1-2 hours at 1 psi pressure with the lip cracked, then close the lid for a second hour, maintaining the single burner. After 3 hours, start the second burner and increasing the pressure to 3 psi until the cones bend.


Wrong? right?, too fast?, too slow? At any rate, this firing is nothing but guesswork.

Jed

#2 jrgpots

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Posted 17 May 2014 - 01:18 PM

The temp 1 hour into the firing is 200 degree F a bit fast. I propped the lid a little wider.

#3 neilestrick

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Posted 17 May 2014 - 02:11 PM

1psi may or may not be too fast. Run it as slow as you can for the first few hours to avoid explosions. Paper smolders at around 400F so you can use that as a judge early on.


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#4 jrgpots

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Posted 17 May 2014 - 04:04 PM

3 1/2 hours into firing, turned on second burner. Waiting for the red glow.

Sorry for the blow-by-blow tracking of a simple firing. I'm just excited....a little.... OK, really excited.

Jed

#5 Biglou13

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Posted 17 May 2014 - 06:16 PM

I'm excited also please post results!
Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

The true sign of intelligence is not knowledge but imagination.
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#6 jrgpots

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Posted 17 May 2014 - 07:44 PM

I had a small hiccup that set me back. Ran out of propane. I had to take a short break to get more fuel. So, I'm 4 1/2 hours into firing...orange glow. My guess it is at about cone 08-07. I estimate 2 more hours of the dragon's breath before cone 7.

Looking through the peep hole I see no explosions....

Jed

#7 jrgpots

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Posted 17 May 2014 - 10:59 PM

After 9 hours the kiln never got up to cone 5. One of the burners started to cut out.

I guess I will need to insulate the kiln with kaowool and improve my burners.....sigh. Maybe I'll just buy them...I'm tired.

#8 Tyler Miller

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Posted 18 May 2014 - 01:13 AM

Jed, I've got a very different burner setup than you, but I find that sometimes with venturi burners you can overdo it with the propane and you not only freeze out your tank, but also cool the kiln with too much fuel.  I was having a hard time reaching cone 6 for a while.  Firing for what seemed like forever, and getting nowhere fast.

 

I did a crazy experiment a few times to figure things out.  I racked up a cones 07, 05, 04, 1, 3, 4, 5, 6, 7, 8.  I didn't use a pyrometer.  I just fired up slowly through all the cones and I found that I could reach cone 6-7, with a MUCH lower psi than I thought I needed. On my current setup, I have the burner assembly from a 500K Btu weed burner, then the little factory needle valve (I think that's the right term, maybe ball valve? it's late), then a redhead psi regulator at the tank.  I set the redhead at 1-2 psi for the initial heat with a slack yellow flame, needle valve nearly closed.  I then use the needle valve to slowly ramp up to the point where I can't get a bigger flame (2/3-3/4 open), then I start bumping up the psi on the redhead until about 8.5-9.5 and then I coast into cone 6-7.  Usually it happens a little faster than a coast, though.  The needle valve only partially open seems to speed up the flow of the propane to the burner and gives me a better mix.  I have no doubt I could reach cone 9-10, I just haven't tried.

 

I'm not sure if this will help your setup or not, but I thought I'd share.  Good luck on the next run.  I hope it works out.



#9 JBaymore

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Posted 18 May 2014 - 07:11 AM

Tyler has hit the core of what the inexperienced fuel-firer often encounters. Less is often more.

 

best,

 

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


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#10 jrgpots

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Posted 18 May 2014 - 08:57 AM

Thank you. I think you nailed it. Also I had uneven heat. The bottom shelf melted a cone 5 glaze, but the top didn't get higher than cone 2.

Lessons learned:
1. I need a top shelf as a ceiling to trap trap heat.
2. I need to figure out a better stacking model.
3. Less fuel.
4. Work on the burners.
5. Insulate the outside of the kiln.

6. This was not a failure.

Jed

#11 JBaymore

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Posted 18 May 2014 - 09:10 AM

6. This was not a failure.

 

Jed,

 

Very true and a very important lesson for all.

 

best,

 

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

 

"Clay is long.... life is short."


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#12 Mark C.

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Posted 18 May 2014 - 07:33 PM

Like rocket launching the 1st few do not make it all the way.

Learn from the experience.

Mark


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#13 jrgpots

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Posted 18 May 2014 - 10:38 PM

I tore down the burner today. They didn't seems to have as much roar as other burners I have made in the past. I thought I had placed .035" MIG welding tips in them as gas injectors. That would have given me 14,500 BTU @ 3 psi and 25,138 BTU @ 9 psi on each burner. Assuming an 88% effeciency on the burners, I would need 42,000 BTU for my 3.5 cf kiln. That should have been just right. These numbers are from The Kiln Book, Third Edition by Frederick Olsen pg 196-197.

But, I had placed MIG tips of size 0.023". The resulting BTU output was 6,267 BTU @ 3 psi and 11,442 BTU @ 10 psi. This explains why I had to crank up the pressure to 10 psi, froze the tank, and never reached my goal of cone 7.

So, I will be changing the MIG tips to 0.035" and retest the burners.

Sorry for the extended rant, but there may be another DIYer who could use my mistake to his/her advantage.

Next firing will be in 2 weeks.

Jed




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