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Diy Kiln Vent


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#21 MichaelP

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Posted 03 November 2014 - 10:28 PM

..would such an addition in my situation be overkill?

IMHO, it would. Just consider how many potters never used one. :)

 

Certainly, it will have a positive impact: especially, on more even heat distribution throughout the chamber. So if you have a problem with uneven firing, by all means, try it. Otherwise, I doubt that you'll notice any real difference. But this is just my humble opinion.



#22 docweathers

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Posted 15 February 2015 - 01:11 PM

Attached is a picture of a cheap in "envirovent" that I built for my km 1227 Skutt. It slides underneath the kiln and the little spring pushes it up against the bottom of the kiln to form a seal. Enough cool air leaks around this interface to keep the exhaust gases cool. I use the rheostat to control how much suction it produces. The whole thing cost about $40 With all new parts from the hardware store.,

 

I'm not sure how much suction I really need but I tested by holding a butane barbecue lighter flame above a quarter inch diameter hole in the lid.(Courtesy of the prior owner of the kiln). If the flame is strongly pulled into the whole I assume that's enough suction, but I'm not sure. Advice on this point would be appreciated.

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#23 JBaymore

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Posted 15 February 2015 - 01:26 PM

Docweathers,

 

As long as you have negative pressure with the kiln fully loaded and running, indicated by the fact that stick incense smoke or your butane lighter flame is being pulled into the kiln at every possible opening, then you are fine at a certain level. 

 

This does not tell you if you have too MUCH air flowing..... and are wasting heat energy in warming air being exhausted that is not necessary to either pick up materials being given off the wares or to allow reactions needing oxygen to go to completion.

 

Technically for maximum efficiency the amount of flow would be different at different parts of the firing....... but in practical usage...... a one-size-fits-all vent setting is what is usually used.

 

If you smell anything in the room during a firing... then the flow is not high enough.  If the chamber is under negaticve pressure.... nothing flows into the room air.

 

best,

 

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


John Baymore
Professor of Ceramics; New Hampshire Insitute of Art

Guest Professor, Wuxi Institute of Arts and Science, Yixing, China

Former President and Past President; Potters Council
 

http://www.JohnBaymore.com


#24 docweathers

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Posted 15 February 2015 - 01:52 PM

John

 

Theoretically, what would be the difference in flow necessary during different stages of firing.


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#25 Cavy Fire Studios

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Posted 15 February 2015 - 04:06 PM

Okay, I have a homemade vent. It's a metal box with a dryer tube that goes into another metal box and out the window. I have an on/off switch for the fan. :) My Uncle Martin was a contractor for a bajillion years and he made it for me. ♥ John kinda has me worried now, though...My bisque is STANKY. I mean, phewie! Smells like burned squash. Does that mean Fred isn't getting enough negative air flow? Am I suffocating my ware? OR MYSELF?!

I have wee bunnies and a guinea peeg (other than myself) in the living room with my kiln, so if he was leaking toxic gasses, wouldn't my tiny babes show signs of illness? They're much more fragile than I am...
Guinea piggin'. Can you dig it?
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#26 Grype

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Posted 15 February 2015 - 10:09 PM

If your smelling stuff, then your vent isn't working properly. That is 100% for sure. Unless you have some type of window crack, the seal is bad or something where it could be blowing back in. What John said about negative pressure is the key, if your vent is sucking enough, then nothing should go out of the kiln cracks because more is being sucked in with force than going out. 

 

I had to tweak my box several times before I got rid of any smells. I had it too low, then went too high, now its just right... Took me several firings to get it right.


- Joseph   /   Every firing is a test. One day I will pass.


#27 LeeU

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Posted 15 February 2015 - 10:39 PM

Uh oh........now I am worried. My kiln is about to be wired up, with a vent kit installed. The kiln is on a large back porch that was previously just screened in (large panels of screening in wood framing) and is now covered from the inside with super heavy duty vinyl sheeting-the kind that outdoor restaurant patios use.  I will have cement board under the kiln and it will be in a corner position placed about 24" from the metal trailer wall and the outside "wall" (screen covered with the all-weather plastic sheeting). There is a door that can be left open as well. Do I need to worry about the vinyl sheeting around the porch? I can move the kiln to the middle of the space if I have to. The "room" is about 14 x 16. 


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#28 Mark C.

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Posted 15 February 2015 - 10:45 PM

Vinyl melts-how far away is it exactly?? 24 inchs??-You could always prop a piece of cement board in front of the vinyl. 2 feet is a long ways if thats what you have.

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#29 Mug

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Posted 16 February 2015 - 09:56 AM

I think what John was saying was, when you bisque the water and volitals are burnt off, it would need a little more draw at the beginning and not as much tward nil the end.



#30 JBaymore

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Posted 16 February 2015 - 11:16 AM

At certain points in the firings ... depending on WHAT you are firing....... there are materials that require oxygen to be present.  If it is not present in sufficient volume... then those reactions do not take place properly.  So at the time WHEN those reactions are happening.... you need enough airflow to supply all that is needed.  At certain times...... certain fumes / gases are being created... at those times you need to have enough flow to capture all of them and exhaust them.

 

At other times pretty much nothing is getting generated or is requiring oxygen ..... and at those times... any airflow is only having the function to convectively help with heat transfer.  Since electric kilns are mainly radiative transfer devices...... this flow is of minimal use.

 

A huge percentage of issues that show up in the finish firing (glaze firing) actually are caused by issues happening in the BISQUE firing that are causing them.  People just think they are finish firing problems... because they show up then.

 

The "stink" mentioned is likely sulphur dioxide leaking out of the kiln.  Certainly not good for you...... but by the time is it in the seriously lethal range... it will drive you out of the kiln room/studio. 

 

But it can be a "marker" telling you that other things you CAN'T smell are getting out into the room too.

 

best,

 

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


John Baymore
Professor of Ceramics; New Hampshire Insitute of Art

Guest Professor, Wuxi Institute of Arts and Science, Yixing, China

Former President and Past President; Potters Council
 

http://www.JohnBaymore.com





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