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Kiln vent- Do I need one?


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#1 clay lover

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Posted 14 April 2012 - 10:02 AM

I have a Skutt 1027, sits outside under a BIG covered shed, not anywhere near me when firing, lots of breeze blowing past. So fumes aren't an issue.

Recently I have been having some problems with getting even cones when firing a load that is made up of different shapes than I usually do, and therefore different loading patterns. I've been considering adding a vent to help with this.
My question is; Have you addd a vent after firing without one, and how did it change your firings ?

Do people that do a lot of low , say 2-3" tall, forms better off with a vent, or do they use taller kiln posts than the form calls for to get circulation?
Does a vent change your firing schedule, or the ammount of electricity used? Make elemants last longer?

I du pull every other peep out when firing a glaze, and usually get good color and even cones without the vent.

#2 Chris Campbell

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Posted 14 April 2012 - 10:42 AM

I have the same kiln ( with computer controls ) and it is vented but I still had issues with even firing top to bottom. I solved this by holding for ten minutes at the top temperature and then following a controlled cooling program. Fires very evenly this way and if you have the computer, I would try it before buying a venting system.

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#3 neilestrick

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Posted 14 April 2012 - 10:44 AM

The vent may help to even out your firing slightly, but I don't expect it to solve your problems. Skutt claims that unevenness can be cut almost in half. In their tests a 79 degree difference top to bottom was reduced to 45 degrees. Firing times will increase by a few minutes, and firing cots will increase by a few cents. How the load is stacked will ultimately have a greater impact. I would try to load the kiln tighter in the middle, looser at the bottom.

If you're ever in the market for a new kiln, get one with zone control. It won't matter how you load it. My 20 cubic foot electric has no cold spots.
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#4 clay lover

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Posted 14 April 2012 - 12:48 PM

Chris, I'm doing pretty much what you are doing, with a longer hold at peak. I've been fine since Skutt ponied up with the new mother board, it was defective from the get go.
Last firing, I had some much taller pieces and rather than use 14" posts in the bottom, which gives me the willies, I decided to do 7" pieces on the bottom shelf, a shelf on top of that with 3" post, some plated in there, and then from the thermocouple up to the lid, 8 tall slender pieces, not tight packed. The cones were over fire by 1 cone in the 14" top layer, a hot ^7,and the bottom didn't reach ^5. Any suggestions as to why that happened? The bottom shelf was about what it usualy and usually does ^6 fine.

Could all the air spae in the top 14" including the thermocouple, change what the thermocouple read and decidied to do?

As long as I use moderate spacing, all shelves between 5" and 8", it fires very evenly.
What should I do in the furture with the occactional shelf of 'Talls' ? Keep them in the bottom and ignore the wiggly 2 or 3 shelves on top of it?

Neil, I won't be buying anything soon. I have been told by Skutt that their bottom and top rings fire hotter to help with eveness.

#5 Chris Campbell

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Posted 15 April 2012 - 04:10 PM

I always have weird loads so I load each row of shelves at right angles to the ones below when I can ... When I can't I try to mix up the two sides since I have half shelves. I think a lot open space at the top and a tighter pack below was a challenge for your system.

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#6 JBaymore

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Posted 15 April 2012 - 05:01 PM

One of the things that a local pickup vent system does for an electric kiln is to get some oxygen flowing through the unit.

This can be particularly important in tightly stacked bisque firings, where reactions have to happen that need oxygen to take place. The defects cause by this lackl of oxygen do not show up until the glaze firing.....so people assume it is the glaze firing that is the problem.

So the vents are doing more than venting fumes and evening out the kiln a bit by improving convective heat transfer.

If you are handy with tools and fabricating things...... you can build one far cheaper than the commercial units. But if not...... well...... you'll have to buy one.

best,

...............john
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#7 icyone

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Posted 15 April 2012 - 11:53 PM

I get steady firing on all shelves after installing fan. Used to be a good amount of difference.

Mostly use 4" or higher posts and still get even temps when using up to 10" posts. However I get a little hotter on shelves that use a shorter post in center of kiln so I always use at least a 5" one on the middle one where my thermocouple is

I have all plugs sealed as per the (orton) fan instructions.

My times are always consistant now no matter how full or loose the load 7 hours and 50ish min when before it would fluxuate up to 40 min difference depending on how packed it was.

#8 Arnold Howard

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Posted 16 April 2012 - 04:25 PM

Chris, I'm doing pretty much what you are doing, with a longer hold at peak. I've been fine since Skutt ponied up with the new mother board, it was defective from the get go.
Last firing, I had some much taller pieces and rather than use 14" posts in the bottom, which gives me the willies, I decided to do 7" pieces on the bottom shelf, a shelf on top of that with 3" post, some plated in there, and then from the thermocouple up to the lid, 8 tall slender pieces, not tight packed. The cones were over fire by 1 cone in the 14" top layer, a hot ^7,and the bottom didn't reach ^5. Any suggestions as to why that happened? The bottom shelf was about what it usualy and usually does ^6 fine.

Could all the air spae in the top 14" including the thermocouple, change what the thermocouple read and decidied to do?

As long as I use moderate spacing, all shelves between 5" and 8", it fires very evenly.
What should I do in the furture with the occactional shelf of 'Talls' ? Keep them in the bottom and ignore the wiggly 2 or 3 shelves on top of it?

Neil, I won't be buying anything soon. I have been told by Skutt that their bottom and top rings fire hotter to help with eveness.


How far away was the nearest shelf to the thermocouple?

How densely packed was the bottom 7"?

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com

#9 neilestrick

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Posted 17 April 2012 - 01:55 PM

I have been told by Skutt that their bottom and top rings fire hotter to help with eveness.


Yes, the very top and very bottom elements run hotter to compensate. They call it 'graded' elements. Lots of kin manufacturers do this, some to the extent of having 3 or 4 different types of elements in one kiln. But how you load the kiln can wipe out any advantage this gives.
Neil Estrick
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#10 Arnold Howard

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Posted 17 April 2012 - 02:12 PM

[/quote]Yes, the very top and very bottom elements run hotter to compensate. They call it 'graded' elements. Lots of kin manufacturers do this, some to the extent of having 3 or 4 different types of elements in one kiln. But how you load the kiln can wipe out any advantage this gives.
[/quote]

That is good advice.

These elements are also called "tuned" elements. When replacing them, be sure to install the correct element for each kiln section. The T/B (top/bottom) elements must not be mixed up with the M (middle) elements.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com




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