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Kiln Vent Operation

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I built a kiln vent.  For ease of construction I am using the bottom peep hole for exhaust instead of drilling holes in the bottom of the kiln.  I think the peep hole was to big on its own.  I took a hollow peep plug and drilled four holes through the end tip.  The kiln vents through these.  The end of the vent, 6" expandable aluminum, fits snugly against the side of the kiln.  It is held in place with wire from the two plugs above it.  This all works great.  No odor at all during firing.

 

Prior to the using the vent my kiln always fired one cone hotter on the top shelf than the bottom.  I was thinking the vent would help even out this difference.  It hasn't.  After two bisque firings, the top shelf is still one cone hotter than the bottom.  I am glaze firing today.  I have several glazes that are cone 5 only.  They will blister at cone 6.  So I make sure this glaze is in the bottom shelf only.  I put my more flexible glazes in the middle and top.

 

Question:  Could this temp difference simple be an element issue?  I have never had to change my elements.  At this time I am OK with the temp difference due to the different glaze temps.  But in the future what can I do the get more even temps.  I want to try some controlled cooling firings.  I am worried how these will turn out.

 

I appreciate any help offered.

 

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Unevenness in single zone kilns is common. There's more heat loss out the lid and floor than in the middle, so they often use 'graded' elements to compensate, where the very top and very bottom elements run hotter than those in the middle. This doesn't always fix the problem, though, so you have to pay attention to how you load the kiln. While it's easiest to load smaller pots at the bottom and big pots at the top, it's not the best for even firings. Since the bottom of your kiln is running cold, you should pack it looser, with taller pots. Also make sure you have a shelf on the bottom about an inch off the floor. It will provide additional insulation (and protect the floor of the kiln from glaze drips). Pack the kiln tightest in the middle, and fairly tight at the top, too. It wouldn't hurt to check your elements, too, and make sure they're all still good. Use a multi-meter to check the resistance. But if your kiln has always fired that way, it's probably not the elements.

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I'm sorry to hear the vent didn't even things out, I have similar problems with a similar kiln and have tried everything to get it to fire more evenly. I was hoping a factory made downdraft vent would help. Stacking taller pieces more lightly in the bottom didn't change the cones. I can be a full cone cooler in the bottom. The amps are correct, there is a shelf 1" off the bottom, the elements are new, the relays are also, it has fired unevenly from day one and after new parts a few years into use.

I want to do some more complex glaze development and really would like a way to get more even firings. Sorry to hear the home made vent didn't help. Would the factory made give better results?

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I have a envirovent system and my kiln's floor is still a cone cooler, I have a dual pyrometer set up that I use to manually even out the firing at the end.   I am looking at buying a kiln  with heat in the floor but I haven't researched how this works with a envirovent system.  My 45 year old small Paragon gave out yesterday and I was told by my kiln guy that it is to old and crumbly to repair again.  My 1027 Skutt is also on the down hill slide I thinks it's about 25 years old.  I have decided to get a one new kiln that's medium in size and replace both of them.   Denice

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I wouldn't have thought a vent would make much difference as they only extract enough for a small negative pressure. That and I believe kilns heat much more with radiation and conduction than convection. 

 

You can't suck the radiation to the bottom of the kiln.

 

"All objects give out and take in thermal radiation, which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits. Infrared radiation is a type of electromagnetic radiation that involves waves. No particles are involved, unlike in the processes of conduction and convection, so radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun, although it is 150 million km away from the Earth"

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Thanks everyone for all the help.

 

I should of waited to open the glaze firing today before posting.  The first firing I did with the vent was a cone 05 bisque.  Yesterday I did a glaze firing to cone 6.  Usually this works as the top fires to a cone hotter.  Well, the top was at about a six and a half with the 6 cone all the way over with the tip bent.  The bottom was cone 6 with just the tip touching the shelf.  I ran on medium ramp to 700 F then switched to fast ramp for the rest of the firing.  If this is repeatable then I should be able to program in a cone 5 firing and all work good.  As is was, 2/3 of the firing is going into the trash.  Most of my glazes can not go beyond cone 5 1/2.  I checked the kiln every hour during the firing.  The kiln vent was working very well till about 1600.  I started to smell a small amount of fumes.  I think it was due to the kiln expanding and being to tight.  I gave a little pressure up on the lid for about 30 seconds and the smell dissipated.  I may need to add a small hole in the top of the kiln to let more air flow.  I will do another glaze firing before I take any further action.   It is killing me to have to throw out so much work.  It seems like the bigger the kiln, the bigger the problems.

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A vent will not even out a firing unless it's only very slightly uneven. The only way to ensure even firings is to modify the load as I described above (which still may not do the job), or to get a kiln with zone control. More thermocouples = even firings. Most brands offer zone control as an upgrade (Skutt, Paragon, etc.), L&L has it as a standard feature. It's well worth the money to have it.

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Neil,

 

I can see how this should be true, but this was the 22 firing in this kiln.  This was the first firing ever that I saw the bottom shelf reach the programed cone. I'm going to throw a bunch of small test pots and see what happens.  First show is in two weeks, not sure I'm going to make it.

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Claylover I have a dual Envirovent system, my little test kiln is the only one that is vent less.  I'm going to remove a ring from the Skutt and keep using it until I find a deal on a new kiln or the Skutt breathes it's last breath.  I have ran across some deals the last several years but past them up I just have to be patience.    Denice

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Further firing test on hold. Sliced open my thumb. No throwing for awhile.

What I do when that happens is use super glue. Once the blood stops glue it shut. You can start throwing in 5 minutes after glue sets.

reglue when it opens later. They do this in emergency rooms daily with super glue.

I used some today on my finger cracks.

Mark

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Hmmm. I would have to take out 4 internal stitches and six external to squirt it in. I will keep that in mind for the next time. The glue couldn't sting anymore than it already does. Thanks for the suggestion mark.

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Since you already have stitches (not mentioned before in post)I would use the lock tight gell super glue over the external stitches . The internal ones will dissolve away and gell super glue water proofs the cut for a few hours at a time before peeling off. If you can stand the pain this will work.I have been in that situation before myself.

Mark 

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Thanks for the idea Mark. I already add a tube of the superglue to my studio tool box. Eight days since the cut. Still not throwing. I cut through the side of my thumb down to the bone. My whole thumb is still swollen and throbbing. It has worked out though. Two of my kids developed pneumonia (third one got up sick this morning) so I wouldn't have been in the studio anyway.

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Update on latest firing. Went perfect. Around 1900F I noticed the kiln lid had lifted up what seemed like more than usual. I could feel a good flow of air near the crack and see the bricks glowing inside. I thought that maybe to much air was being sucked in and effecting the temp. So I placed several large kiln post on top of the lid causing it to sit a little more snug. I can't help but wonder if this excessive amount of room air was causing the kiln to over fire and fire unevenly.in this firing the top and middle cone where the same and the bottom one half cone cooler.I plan to put the post on the lid again next firing. I will also check the lid hinge. It may be out of whack from moving.

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Wouldn't it be easier to add zone control to the kilns that don't fire evenly enough?  I have 3 electric kilns and have made them into zone control myself and am very pleased with the way they fire.  The Bartlett  V6-CF series 700 controller has the capability for up to 3 zone control built into it, you need the code to change to zone control, plus parts.  Euclids sells everything you need. Another control problem is due to the open end type K thermocouple which is getting contaminated, it may be cheap but not that reliable.  Omega makes a much better high temperature enclosed high response type K T/C,  I get at least 125 or more firings from this type.

David

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David, thanks for the suggestion. I had thought zone control was only for very large kilns. I will look into it. Right now I don't have money to consider it but can always look forward to Christmas. Firing again tonight. New glazes making me very anxious about outcome.

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David, thanks for the suggestion. I had thought zone control was only for very large kilns. I will look into it. Right now I don't have money to consider it but can always look forward to Christmas. Firing again tonight. New glazes making me very anxious about outcome.

It is not that expensive, 1 or 2 thermocouples some wiring, the relays are already there so reconfigure controller to zone control ,  If it is a Skutt talk to Mike.

David 

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David, thanks for the suggestion. I had thought zone control was only for very large kilns. I will look into it. Right now I don't have money to consider it but can always look forward to Christmas. Firing again tonight. New glazes making me very anxious about outcome.

It is not that expensive, 1 or 2 thermocouples some wiring, the relays are already there so reconfigure controller to zone control ,  If it is a Skutt talk to Mike.

David 

 

 

Bingo. It's really pretty cheap, especially considering the benefits of doing it. Which is why it should be standard equipment on all new kilns. It would prevent a lot of headaches for consumers and Skutt's tech help (or any other manufacturer that doesn't provide zone control as standard). The manufacturers pay less than $10 each for thermocouples, and wiring it differently would cost next to nothing. The controller can already do it. There's no reason for it to be optional.

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