Jump to content
Sign in to follow this  
jrgpots

Single Firing In A 3.5 Cf Gas Conversion Kiln.

Recommended Posts

jrgpots    231

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

Share this post


Link to post
Share on other sites
jrgpots    231

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

Share this post


Link to post
Share on other sites
neilestrick    1,381

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.

Share this post


Link to post
Share on other sites
jrgpots    231

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

Share this post


Link to post
Share on other sites
jrgpots    231

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

Share this post


Link to post
Share on other sites
jrgpots    231

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.

Share this post


Link to post
Share on other sites
Tyler Miller    331

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.

Share this post


Link to post
Share on other sites
JBaymore    1,432

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

 

best,

 

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

Share this post


Link to post
Share on other sites
jrgpots    231

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

Share this post


Link to post
Share on other sites
JBaymore    1,432

6. This was not a failure.

 

Jed,

 

Very true and a very important lesson for all.

 

best,

 

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

 

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

Share this post


Link to post
Share on other sites
Mark C.    1,808

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

Learn from the experience.

Mark

Share this post


Link to post
Share on other sites
jrgpots    231

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

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×