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Kath K

Kiln Not Reaching Temperature

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Re-posting under new topic name with updated information....

 

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. 

 

I use a Harco controller and is set to the same program for glaze firing. It controls the ramp rate.Temp only got to about between 850 - 920 deg celsius, trying to get to 1060 earthenware glaze temp. The controller shuts the firing down when it doesn't reach the rate after a long period trying.

 

I've cleaned the jets in my burners, turned out they were partially blocked, so the gas train is in pieces at the moment. Hopefully that may solve a big part of the problem.

 

I've had some great feedback, such as burner too close to port, kiln to close to wall, could be secondary air problem, shelves too close to wall trapping the air flow through the kiln, need to have a gap, maybe I should step the shelves. I'll definitely take these suggestions on board for my next firing when I put everything back together. Thanks to all.  Photo's of burner, flue and kiln packed attached.

 

post-2005-0-75559800-1446721090_thumb.jpgpost-2005-0-18322400-1446721145_thumb.jpgpost-2005-0-30572900-1446721163_thumb.jpg

 

 

 Am I going to ruin my work if I fire a 4th time? Any additional tips or advice appreciated.

 

Thanks again

 

K

 

 

 

 

post-2005-0-75559800-1446721090_thumb.jpg

post-2005-0-18322400-1446721145_thumb.jpg

post-2005-0-30572900-1446721163_thumb.jpg

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Seems strange to me that it could not reach 1080c but I don't know too much about gas kilns. Could something be stopping the burner turning up the power?

 

From that front pic you can see it is uneven. I think you want to try and stop the flame going up the left wall and out the top. Maybe you could stack the upper shelves touching the left wall? Not sure.

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The exit flue is in the top center? How big is the exit flue?

 

I'd say the burner is definitely too close to the port. With the kiln being that close to the wall, you're going to calcine the cement wall and weaken it.

 

Using that type of controller on a gas kiln is far from ideal. Gas kilns require constant pressure inside the kiln in order to maintain evenness, and the damper must be adjusted accordingly as the temperature increases. Cycling the gas on and off like and electric kiln just doesn't work very well at all.

 

Can you override the controller and fire manually?

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I was surprized to see that controller on a gas kiln. Everytime the main burner switches off cold air would just be sucked through the kiln.... added prob of poss cracking some of your ware

Another thing Neil, was that Kath's kiln did not seem to have a chimney attached directly to the kiln, even for a couple of feet...so what is the consequence of this?

What is stopping the flame deflecting off the top of the kiln and straight out the top exit?

My kiln had a single burner, which I never cleaned ever,flame passed along the floor in the same pattern, as Kath's , up to the roof of the kiln BUT it then went down thro the shelves and exited at the bottom of the kiln, close to the burner port. THus the bag wall like Kath's

How would you stop the flame scooting out of the kiln at the first pos opportunity in this case?

What make is the kiln Kath? Anyone you know fire in gas?

I'd be getting your gas man back, by pass the hardco controller and as Neil says firing manually, prob for glaze 6-8 hours max..... Need a thermocouple and meter, and of course cones.

I usd to fire with pilot, then fire up the main burner when temp got to about 200C but turn back the pilot to a minimum at this point otherwise my kiln would be too fast at the initial firing period.

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Yeh, orton has some advice on what length the firing should take.. about 3-6 hours.. so don't freak a the thought of babysitting, which you have to do more so with gas , for 10-12 hours as you stated in the other post.

Search firing with LPG which I presume you are using.

I'll try to find an article on this , was in an old 'Pottery in Australia" mag, but maybe I threw it out with the kiln..... too old, kiln, and too weak now to "man handle" the cylinders. Miss the gas.

And keep a log. DO you seal off the burner port when you finish firing? Not related to your question I know but there is little room there.... GO with getting g around the controller then see what a difference it makes. May get away with not moving the burner for your purposes.

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The exit flue is in the top center? How big is the exit flue?

 

I'd say the burner is definitely too close to the port. With the kiln being that close to the wall, you're going to calcine the cement wall and weaken it.

 

Using that type of controller on a gas kiln is far from ideal. Gas kilns require constant pressure inside the kiln in order to maintain evenness, and the damper must be adjusted accordingly as the temperature increases. Cycling the gas on and off like and electric kiln just doesn't work very well at all.

 

Can you override the controller and fire manually?

 

The exit flue is in the top center? How big is the exit flue?

 

I'd say the burner is definitely too close to the port. With the kiln being that close to the wall, you're going to calcine the cement wall and weaken it.

 

Using that type of controller on a gas kiln is far from ideal. Gas kilns require constant pressure inside the kiln in order to maintain evenness, and the damper must be adjusted accordingly as the temperature increases. Cycling the gas on and off like and electric kiln just doesn't work very well at all.

 

Can you override the controller and fire manually?

The exit flue doesn't sit top center, it sits to the right so the opening is not above where the burner feeds in. It is about 12 inches long. I usually leave it fully open at the start.

 

Interesting about the constant pressure, the cycling of the gas on and off is supposed to maintain the the ramp rate, if the ramp rate slows, the burner kicks in to get it back up there. I thought that kept pressure in the kiln. As you can tell, I'm only a novice and didn't realise it doesn't, I am learning all the time, thanks. In saying that, I have had good firings in the past, where it cuts in and out, but no two firings are ever the same. Frustrating.

 

I have cleaned my jets, they were partially blocked, so everything is in pieces at the moment. I probably won't get it going for a few more weeks, but I am taking everything I have learned on board when I do.

 

I think I can override the controller to fire manually, but really not too confident in doing this. Then again, with all the time, babysitting, and adjusting I might as well be doing it manually..

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Seems strange to me that it could not reach 1080c but I don't know too much about gas kilns. Could something be stopping the burner turning up the power?

 

From that front pic you can see it is uneven. I think you want to try and stop the flame going up the left wall and out the top. Maybe you could stack the upper shelves touching the left wall? Not sure.

My gas jets were partially blocked, so I think that is part of the problem.

 

There is an opening at the bottom of the kiln inside where the flame is drawn to and then goes up the flue, so it is not built to go straight out the top. Thanks for the suggestion though.

 

I will try restacking, I think there may not be enough gaps for the flame to circulate freely and is a bit stifled...not sure either!...

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I was surprized to see that controller on a gas kiln. Everytime the main burner switches off cold air would just be sucked through the kiln.... added prob of poss cracking some of your ware

Another thing Neil, was that Kath's kiln did not seem to have a chimney attached directly to the kiln, even for a couple of feet...so what is the consequence of this?

What is stopping the flame deflecting off the top of the kiln and straight out the top exit?

My kiln had a single burner, which I never cleaned ever,flame passed along the floor in the same pattern, as Kath's , up to the roof of the kiln BUT it then went down thro the shelves and exited at the bottom of the kiln, close to the burner port. THus the bag wall like Kath's

How would you stop the flame scooting out of the kiln at the first pos opportunity in this case?

What make is the kiln Kath? Anyone you know fire in gas?

I'd be getting your gas man back, by pass the hardco controller and as Neil says firing manually, prob for glaze 6-8 hours max..... Need a thermocouple and meter, and of course cones.

I usd to fire with pilot, then fire up the main burner when temp got to about 200C but turn back the pilot to a minimum at this point otherwise my kiln would be too fast at the initial firing period.

Mine exits at the bottom too, it can't go straight out the top. The pilot stays burning when the main burner goes off.

 

Not sure of the brand, it was a rebuild by my kiln guy years ago, may have been a portakiln? not sure, no brand on it. He set it up originally for my mother many years ago, then about 5 years ago he set it up for me with the controller. Mum had it worked out doing stoneware temperatures manually. I'm not as clever as my mum was that's why I got the controller! 

 

Unfortunately I don't know anyone that fires in gas, let alone the setup I have. I need to put my feelers out there. I'm putting off getting the kiln guy back until I really have too, he is so expensive. He can be helpful and not helpful at the same time. I'm sure I will have to at some point, he is the only one I around my area that I know of.

 

I'll put everything back together in the next few weeks, taking all this great help on board when I re fire.

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Yeh, orton has some advice on what length the firing should take.. about 3-6 hours.. so don't freak a the thought of babysitting, which you have to do more so with gas , for 10-12 hours as you stated in the other post.

Search firing with LPG which I presume you are using.

I'll try to find an article on this , was in an old 'Pottery in Australia" mag, but maybe I threw it out with the kiln..... too old, kiln, and too weak now to "man handle" the cylinders. Miss the gas.

And keep a log. DO you seal off the burner port when you finish firing? Not related to your question I know but there is little room there.... GO with getting g around the controller then see what a difference it makes. May get away with not moving the burner for your purposes.

I keep a log, every hour, time, temp, target, pressure, bit slack on damper settings because I make little adjustments all the time recently. I know, I should but I forget.

Wow, that would be the best thing if I could fire in that time. I'll check that website. I have some Pottery in Australia mags, really old ones, I'll have a look in those too.

No, I don't seal off the port after firing.

I would like to give it one more go I think with the controller, using my new found knowledge, to see what happens. If I still get no joy, then I will try manually. You will see me back with a new topic then!..

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I use a controller on my kiln but never shut the gas completely off.  This may be impossible to do on your kiln but if you can control it manually without starting and stopping a burner than it can also be done  automatically and will follow a traveling setpoint.

David

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Go for it Kath, go around the controller,

Seal off the damper and port after you turn off at the  end.

YOu have a thermocouple or some device  o measure temp?

Roughly

Aim at 100 deg/hour for 1st couple of hours My kiln : from memory pilot only to 200deg.  turn back the pilot to minimal

Main burner on , very low PSI  0.5 ish for me.

Turn up gradually.

Then when kiln is 600deg  you can go much faster, esp in a glaze. feet up after 5-6 hours max.

Fibre kilns cool fast so block the port as well as closing damper fully at the end.

Port being so close to the kiln may mean you get a little reduction , depends on your kiln really. But at t heat temp  and speed prob not..

I MISS my gas kiln.

Discovered I'm a contro; freak after many years :wacko:  about to fire ,well in the next few weeks... my new electric which has a controller on it, hmmm I won't be able to fiddle athe end of firing as I am prone to..... or knowing the glazes know I can turn off just that little bit early/late depending on what I've got in there........

Can I over ride a controller??

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I use a controller on my kiln but never shut the gas completely off.  This may be impossible to do on your kiln but if you can control it manually without starting and stopping a burner than it can also be done  automatically and will follow a traveling setpoint.

David

Thanks David

 

Not sure if I can do this. It is programmed to reach a temp at a rate per hour as follows:

 

Stage 1 - 50 deg per hr to 150 deg

Stage 2 - 120 deg per hr to 980

Stage 3 - 60 deg per hr to 1060

Stage 4 - soak 25 mins 

 

once it reaches the ramp rate required the main burner cuts out (pilot continues) until the ramp drops and cuts back in...when going well..

 

How do you prevent yours starting and stopping?

 

K

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it sounds like you have everything under control, but ill add my 2 cents and hope that it is additional information that is useful. if you have successfully fired the kiln in the past then i think the setup should be ok, i have both updraft kiln and down draft, the up draft kiln will not have a chimney stack, if i have not fired a kiln for a while the burners will collect insects dust and spider webs and need to be cleaned, if you are firing off lpg the tank needs to be of a volume that will provide sufficient vapor delivery to match the BTU demand of the kiln, if the tank is almost empty it will ice up and also cause problems reaching temp, if firing off natural gas there will be a minimum # inches residual of gas pressure needed at the burners to meet the cone rating for the kiln. 

 

lastly you should have no problem re-firing as many times as needed as long as the clay has not been taken all the way to maturity. the higher the cone the more this is an issue. once you have taken the cay to its rated temperature re-firing to maturity can be successful an additional thin coat of new glaze i find is helpful, but you are at a much higher risk of cracks. additional firing of work fired to maturity at lower temperatures in later firing is also not usually a problem.

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Kath, im not necessarily saying you should apply more glaze to your pieces, I'm firing at a much higher cone rating and as you said you work did not reach maturity. a trick i was taught along the way to help when you need to reglaze a piece that is already fired is to put it in the microwave on high for a minute, this will do two things, it will heat the piece so the re-dip (spray,brush) in glaze will dry thicker faster and somehow the surface of the fired piece is more receptive to the application of fresh wet glaze.

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Go for it Kath, go around the controller,

Seal off the damper and port after you turn off at the  end.

YOu have a thermocouple or some device  o measure temp?

Roughly

Aim at 100 deg/hour for 1st couple of hours My kiln : from memory pilot only to 200deg.  turn back the pilot to minimal

Main burner on , very low PSI  0.5 ish for me.

Turn up gradually.

Then when kiln is 600deg  you can go much faster, esp in a glaze. feet up after 5-6 hours max.

Fibre kilns cool fast so block the port as well as closing damper fully at the end.

Port being so close to the kiln may mean you get a little reduction , depends on your kiln really. But at t heat temp  and speed prob not..

I MISS my gas kiln.

Discovered I'm a contro; freak after many years :wacko:  about to fire ,well in the next few weeks... my new electric which has a controller on it, hmmm I won't be able to fiddle athe end of firing as I am prone to..... or knowing the glazes know I can turn off just that little bit early/late depending on what I've got in there........

Can I over ride a controller??

Well Babs....had my gas train re-fitted by a gas plumber today, so I know it is nice and safe (and way less than half the price of the original guy). I asked about it being too close to the wall and the burner too close to the port. He thought all was OK. He was really helpful, told me how I can clean jets in the future without removing the whole kit and kaboodle. He discovered the solenoid that controls the pilot was faulty so the pilot won't turn off at the end of the program, so I will need to turn the gas off manually. This is a new problem, it was working last firing, but I can work around this easily until i decide to replace the solenoid.

 

So.... I fired it up at about 1:30pm today, had to give the controller another go....changed the program a little as below:

 

Stage 1 - 50 deg per hr to 150 deg

Stage 2 - 200 deg per hr to 980 (was 120 per hour)

Stage 3 - 60 deg per hr to 1050 (was 1060, cones have made it evident that it is firing hotter than controller shows)

Stage 4 - soak 25 mins 

started at 2psi ended at 3.5psi

 

and....you wouldn't believe it, I didn't, it went perfectly to schedule...finished at 6:30pm....5hrs!!! maybe because I ramped up stage 2 as I knew it had made it through 3 times already. Probably should change stage 2 back to 120 per hr next glost, 

 

Long story short.....one happy girl today!!! Seems it was partially blocked jets after all! Will see results tomorrow, fingers crossed, either way, happy it is back to normal.

 

Hope your firing with your new electric kiln went well, and you could control yourself with the controller!!!

 

Thanks once again

 

K

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it sounds like you have everything under control, but ill add my 2 cents and hope that it is additional information that is useful. if you have successfully fired the kiln in the past then i think the setup should be ok, i have both updraft kiln and down draft, the up draft kiln will not have a chimney stack, if i have not fired a kiln for a while the burners will collect insects dust and spider webs and need to be cleaned, if you are firing off lpg the tank needs to be of a volume that will provide sufficient vapor delivery to match the BTU demand of the kiln, if the tank is almost empty it will ice up and also cause problems reaching temp, if firing off natural gas there will be a minimum # inches residual of gas pressure needed at the burners to meet the cone rating for the kiln. 

 

lastly you should have no problem re-firing as many times as needed as long as the clay has not been taken all the way to maturity. the higher the cone the more this is an issue. once you have taken the cay to its rated temperature re-firing to maturity can be successful an additional thin coat of new glaze i find is helpful, but you are at a much higher risk of cracks. additional firing of work fired to maturity at lower temperatures in later firing is also not usually a problem.

Hi 1515art

 

Thanks for your information, everything is helpful and I am grateful. Turns out it was a partial blockage in the jets, i only fire about 3 times a year. Re-fired to temp today in 5hrs!! couldn't believe it. I use LPG thanks for that advice.

 

I'll be opening the kiln tomorrow, fingers crossed for survival...thanks for the reassurance.

 

I didn't re-glaze anything, but will keep your advice for the future. I haven't tried warming in the microwave to re-glaze, will give it a go if needed. My little tip... I have used hairspray on my pots before re-glazing and that has worked for me too!

 

Appreciate your 2 bobs worth! I think I did have everything under control after all, should trust my own judgement sometimes but am definitely no expert and need to ask the experts to be sure.

 

Thanks again

 

K

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know nothing about firing a gas kiln so if what i suggest sounds silly, just laugh.  have had experience with bugs getting inside a vent.  can the opening to your jets accept a cork to prevent a future problem?  if you only fire a few times a year, the rest of the time should they be covered with a plastic bag?

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know nothing about firing a gas kiln so if what i suggest sounds silly, just laugh.  have had experience with bugs getting inside a vent.  can the opening to your jets accept a cork to prevent a future problem?  if you only fire a few times a year, the rest of the time should they be covered with a plastic bag?

You know what, I reckon that's a great idea! I could bag the burners between firings, that will help somewhat. I also found out the blockage can be a carbon build up, not much I can do about that, but your idea will definitely help! Thanks!

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Looking at your firing schedule, I would

po. be aiming at 100deg /hr to 200C.t

then 150 to about 950

then slower to the top.

 

The first stage depends on the ware, your load looked like mugs and smallish stuff so they should take the 100 /hr rise. to 200C

Well done you I am having a beeech with new Kiln, read the post" How far should a controller be from the kiln....." That controller is not me!

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Looking at your firing schedule, I would

po. be aiming at 100deg /hr to 200C.t

then 150 to about 950

then slower to the top.

 

The first stage depends on the ware, your load looked like mugs and smallish stuff so they should take the 100 /hr rise. to 200C

Well done you I am having a beeech with new Kiln, read the post" How far should a controller be from the kiln....." That controller is not me!

Yes, maybe should have stuck with my original settings at least. I thought I could speed it up a bit in 2nd stage considering this was the 4th go. Not a good idea... about 30% of the load was OK the rest not so good at all. Every piece had some pinholing, some were peeling, some glazes were wrinkled the works! I expected failures so that's OK. Main thing is....on the positive side....kiln is working properly now!!!

 

Will try your schedule suggestion next time I think.

 

BTW my controller sits up on a shelf on the wall, about 1 metre from the kiln. Good luck with your new kiln, I'm sure everything will work out. Will check your post.

 

K

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The glaze "effects" may have ben due to the many prefirings this stuff went thro prior to this firing. A poster called Celia had similar effects after her kiln stuck at a low temp for some time, maybe search that,  your stuff is the stuff that went thro 3 weird firings, right? That would have had something to do with the crawling and wrinkling.

Pinholing can be caused by different stuff even , most often prob., by your bisque cycle.

Anyway one thing at a time, Kath.

Kiln working, next, change glaze cycle, maybe before that check info on bisque firing. Lots written here about that.

Glad your're on your way.

B

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