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Mudrunner88

Kiln Malfunction During Glaze Firing...can I Re-Fire?

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My kiln malfunctioned before reaching peak temperature. I was glaze firing stoneware at cone 6 and the witness cones indicated the temperature didn't even reach cone 5. Can I re-fire to cone 6? Or is all lost?

 

If I can re-fire, do I need to re-glaze the pieces?

 

Hope someone has had experience with this. Thank you!

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Thanks Neil. The glaze hasn't crawled but the colours are wrong. Should I fire as is, or add more glaze? Some pieces aren't as opaque as usual but I haven't under fired before so I don't know if that's to be expected.

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Thanks Neil. The glaze hasn't crawled but the colours are wrong. Should I fire as is, or add more glaze? Some pieces aren't as opaque as usual but I haven't under fired before so I don't know if that's to be expected.

Just replace the cones and re-fire as is. Should work great.

TJR.

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We've had this happen before. Sometimes the results are a little different than normal, like if you took brownies out of the oven for a few minutes then put them back in. But I definitely agree about refiring as usual. Let us know how it goes!

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I've had 3 glaze firings in a row not reaching temperature. I have refired 3 times, glazes still not quite matured. Thinking of giving it one more go....will my pots eventually be ruined?? I'm trying to get to cone 04, I have not had this sort of problem before. My gas burners may need a clean, that will be my next problem..

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Each attempt, I've made adjustments to the air and gas pressure, with little difference in the result, you are right.

 

It is a downdraft gas kiln, about 600mm square (24"). Last firing, the pilot was only a little candle flame and the main burner sounded a little fluffy. I turned the needle valve for the pilot, no difference. When I put something over one of the little holes around the neck of the pilot, it got bigger. I'm thinking they might need a clean, really not sure how to go about this.

 

Prior to these last few firings I hadn't used the kiln in over 1 year and these firings have been OK. I probably would only fire 2 or 3 times a year normally. The burner setup was replaced 5 years ago. Unfortunately I have no photo of the kiln itself, but have attached a .pdf of the gas and controller setup.

 

Gas Kiln controller.pdf

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A picture of the whole kiln would help, too. I'd like to see the exit flue, bag wall, damper, etc.

 

I agree with babs that the burner is too close to the port. And the whole thing seems to be way too close to the wall from a safety standpoint.

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A picture of the whole kiln would help, too. I'd like to see the exit flue, bag wall, damper, etc.

 

I agree with babs that the burner is too close to the port. And the whole thing seems to be way too close to the wall from a safety standpoint.

I'll try and get a pic of the whole kiln and a measurement from the wall. It's in my father's shed, plan to drive over there today.

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is this kiln located in australia?  the Harco brand kiln is made in austraila, maybe they have a technical person who can help with the problem.

Yes, and it is the Harco. I've had the guy that installed it checking it out (not cheap). He advised to re-fire, adjusting the pressure and damper settings before worrying about whether the burners need a clean. He doesn't seem to think it is the controller.

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A picture of the whole kiln would help, too. I'd like to see the exit flue, bag wall, damper, etc.

 

I agree with babs that the burner is too close to the port. And the whole thing seems to be way too close to the wall from a safety standpoint.

I'll try and get a pic of the whole kiln and a measurement from the wall. It's in my father's shed, plan to drive over there today.

 

The kiln is 6 inches from the wall. I've attached some more photos.

 

The jets have now been removed from the burners, pilot was mostly clogged the main partly clogged. Blew air through them with a bike pump, that seems to have cleared it (I think). When you look through the hole up to the light, you can just see something that looks like a hexagonal pattern gauze. I've been told I can use a special gas prick to clean properly. So everything is in pieces now...

post-2005-0-68779200-1446367189_thumb.jpg

post-2005-0-82931200-1446367212_thumb.jpg

post-2005-0-32079700-1446367268_thumb.jpg

post-2005-0-24310500-1446367231_thumb.jpg

post-2005-0-87944800-1446367300_thumb.jpg

post-2005-0-09631200-1446367324_thumb.jpg

post-2005-0-68779200-1446367189_thumb.jpg

post-2005-0-82931200-1446367212_thumb.jpg

post-2005-0-24310500-1446367231_thumb.jpg

post-2005-0-32079700-1446367268_thumb.jpg

post-2005-0-87944800-1446367300_thumb.jpg

post-2005-0-09631200-1446367324_thumb.jpg

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What is the flame doing during the firing?

That burner is soooo close to the port or what ever that hole is called.

If the damper is not adjusted properly, with that burner blocking up the secondary air that would reduce the draw......

I'll leave this to the experts.

Watch for flammable debris lodging as it seems to be on the burner system.

This kiln has fired for you previously?? set up like this?

Is there no chimney on the top of the kiln?? Or have you dismantled this?

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What is the flame doing during the firing?

That burner is soooo close to the port or what ever that hole is called.

If the damper is not adjusted properly, with that burner blocking up the secondary air that would reduce the draw......

I'll leave this to the experts.

Watch for flammable debris lodging as it seems to be on the burner system.

This kiln has fired for you previously?? set up like this?

Is there no chimney on the top of the kiln?? Or have you dismantled this?

Having the gas controller connected, the main burner cuts in and out, according to the ramp rate set on the controller. The pilot stays on. Because it is struggling to reach temp this is not happening as regularly as it should. When it gets to around 500-600 deg Celsius, the main burner just stays on, trying to get to temperature, then shuts down at around 800 - 900.

 

I didn't even think about the burner being too close, that could be contributing to the problem, thanks for that thought...however, yes I've done quite a lot of successful firings with this set up. There is a big open door a couple of feet from the kiln and a small open window above and the shed door open for plenty of ventilation.

 

I only noticed that leaf when I took the photo, 'cause it's zoomed in. I will watch for that in the future as well, thanks.

 

The third photo shows the chimney, this goes up through the roof of the shed.

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Kath, does the chimney sit flush on the top of the kiln,? And you can dampen the draw at this point? Is this where you use your damper?

Haven't fired in gas for a long time, my prob with a single burner gas was to regulate the lower firing stages so that it would creep up slowly enough . I did not have a computer controlled firing thingie.

Hopefully some one else will help you . Nothing has been changed between firings?

Can you change the ramping o f he controller to accommodate so it gets to temp.

How long is your firing schedule?

Is the regulator at the gas bottle functioning?

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Kath, does the chimney sit flush on the top of the kiln,? And you can dampen the draw at this point? Is this where you use your damper?

Haven't fired in gas for a long time, my prob with a single burner gas was to regulate the lower firing stages so that it would creep up slowly enough . I did not have a computer controlled firing thingie.

Hopefully some one else will help you . Nothing has been changed between firings?

Can you change the ramping o f he controller to accommodate so it gets to temp.

How long is your firing schedule?

Is the regulator at the gas bottle functioning?

The chimney sits above the kiln and yes I use the damper bricks to adjust the air at the flue opening.

I got the controller thingie :) to control the rate of temperature rise and make it easier for myself, cause I am definitely no expert. I stay with the same programs on the controller, I have a bisc program and a glaze program. Last attempt I did ramp it up to reach 980, didn't make it. Firings are usually 10-12 hours. Gas regulator on the bottle is working.

 

I'm pretty convinced now main problem is the jets. They have been taken out, looked through, pilot almost completely blocked, the main partially blocked. Gave them a blast with a bike pump and they are all but clear now. Need another blast with something stronger next go.

 

I reckon it is a combination of this and struggling to get secondary air around the burner as you suggested. Even though firings were good before now, maybe they could be better if the burner wasn't so close to the port. Trouble is, the kiln is fixed in one place with the chimney through the roof. I'll see what happens when I give it another go. You have helped me a lot, got me thinking, thanks Babs!.

 

Kath

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Just to let you know, the pattern I am seeing when magnified, I think is still a bit of grit on the wall of the jet...optical illusion I think. Will give it a blast with something stronger. Hopefully that will do the trick. Because the chimney goes up through the roof, unfortunately I can't move it out from the wall. There is a large open door a couple of feet away and plenty of ventilation, it was set up this way many years ago (by the supplier) when my mother was firing it. Hope it is OK...

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Kath maybe repost this under new post. re gas kiln not reaching temp.

Looking at the shelf set up and not being able to see your full kiln pic 5 , I used to have to leave a gap between the shelves, down the middle of the kiln to allow the flame to travel back to the outlet which was at the bottom of my kiln. i.e the flame slides off the sloping brick,travels up to the top of the kiln, deflects down around your pots and then escapes. If our shelves are smack together to the edges of your kiln and together across the kiln where is the flame path?

Again I'm no expert at all but just thinking thro why.

YOur flame leaves your kiln at the top? so what is stopping it leaving the kiln pretty rapidly thus not really touching your pots or heating your kiln interior?

10-12 hours for a kiln this size to reach cone04 is really not good. IMHO

repost and see if your dilemma comes to the attention of some of the gurus. Its hiding under a false heading at the mo.

Good luck, I feel your pain.

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