Jump to content


Photo
* * * * - 3 votes

Real-Time Kiln Advice (Kiln Curently Firing)


  • Please log in to reply
162 replies to this topic

#21 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,432 posts
  • LocationGrayslake, IL

Posted 17 April 2014 - 07:02 PM

Definitely use target bricks. It will help with a lot of issues. If the reduction was uneven, it should fix itself once you get good pressure in the kiln. If you've got pressure out top and bottom spy holes, then you're more likely to have even distribution of the reduction. Did you do an actual body reduction period around cone 08, where you put it into reduction and stall out the temperature for about 45 minutes?


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#22 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 18 May 2014 - 05:31 PM

Hey, guys.  I'm looking at another firing of this kiln tomorrow, and am attempting to review and implement your advice.  My guess is I'll be back here tomorrow ...

 

Marcia, the kiln was horribly loaded last time, very very loose and even empty the top 10" or so.  I've done much better this time.  Not perfect - It's very tight all the way to about 4" from the top, then loose (as I ran out of pots of that height or shorter).

 

Neil, I was using the pyrometer instead of cones to judge when to reduce - shooting for reduction from 1623°F - 1850°F.  (Using cones for the end of the firing, though, of course.)

 

The fellow who visited with his ceramic students - he suggested I make the bag wall even taller, and tighter.  Also, when I mentioned target brick, he suggested using a tall piece of kiln shelf, spanning the width of the kiln, propped up at an angle against the bag wall, to deflect the flame.  I did this with three different pieces of kiln shelf, overlapping each other.  I should probably take a photo ... 

 

bag_wall_target.jpg

 

Are you guys rolling your eyes at this, or have I possibly done something to help?  I hope.



#23 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,624 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 18 May 2014 - 05:43 PM

For me I would put in those target bricks and tighnen the bag wall just a bit .That load looks way to loose I would also do as Marcia suggested put the tall stuff in the back-the flame will just pass thru that open tall stuff as you saw. You want it to get restricted by the load and be forced thru it.

How about a postitive brick stop under the middle of floor so flames have to go to the rear to get out.Thats betwwen a& b shelve underneath them?

Pack the load tighter next fire-think like a flame and force it to flow where you want it to go.

Take a look at that salt load I stacked in Molokai workshop thread under education-this was a 1st time fire and it worked as good as it can get.

I packed that load as tight as I could with student works which tend to be all over the board in sizes.

It looks like you got some keepers-maybe more reduction as well next fire.

Mark


Mark Cortright
www.liscomhillpottery.com

#24 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 18 May 2014 - 05:53 PM

Mark, you're saying it was too loose in the pictures on Page 1, the other firing, right? Or do you mean the photo I just posted is still too loose?  Besides the top shelf, 4-5" from the top (which those tester things are on), the rest of the kiln is pretty darn close.  A couple open spots on top of large plates, etc., but otherwise 1/4" or so between most pots.  (I just realized it's closer to 1/2" between pots right there at the front of that shelf, except for that bottle on its side. So now I think you're talking about this photo.  Damn it, I thought it was tight.  I guess it isn't.)

 

I'm having a difficult time finding the photos of the salt kiln you mentioned.  Can you help me find the thread?

 

I love the idea of a brick between the bottom two shelves.  Completely logical.  I'll have to try it next time, though.  Just spent all day loading this thing - would take an awful lot to get me to unload and re-load it.

 

I can, however, still tighten up the bag wall more - and am very open to switching the big shelf deflectors to some sort of target brick.



#25 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,624 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 18 May 2014 - 07:27 PM

My comments where not on your most recent photo

but now that I have seen that I would add the target brick as it breaks up the flame -the shelves just push it up where as the target brick splits the flame into many.Just put a brick on end in front of flame path where your shelves are-I would take them out-myself as your flame dis go up last fire you said.

The bag wall on right side has a larger gap  on a few bricks-I would even that out-you could add a few more loose bricks to that bag wall if you want it to go higher?maybe a soap  brick or two?

Mark

 

heres that salt fire a few weeks ago

http://community.cer...nth/#entry58763


Mark Cortright
www.liscomhillpottery.com

#26 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 19 May 2014 - 04:46 AM

Thanks, Mark.

I can't believe you got sent to Hawaii for work!

In that most recent photo above, I've already increased the height of the bag wall and closed completely the two bottom layers. It's now four bricks high (first two firings it was one brick, last firing it was three). I, too, noticed in the photo (but hadn't in real life) the unevenness of the spaces on that top layer. I've now fixed that. And I like the sounds of a target brick better. 

 

This morning I put in two target bricks and took out the angled shelves. 

 

target_brick.jpg
Is this proper placement?  I've read people talking about the importance of the distance from the burner to the target brick, even by an inch, to the success of a firing.   The distance from the burner ports to the bag wall is approximately 9 inches.  The distance from the burner ports to the target bricks is about 4.25".

 

When I re-built the bag wall, I noticed a few spots between the first and second layers where the flame/soda had eaten straight through the bricks. Little round channels, four or five of them, less than a dime's diameter on the burner side, decreasing in size and some not all the way through on the other side.

 

It's going now.  Happily holding around 200°F.

 

Thank you again!



#27 JBaymore

JBaymore

    Moderator

  • Moderators
  • 2,809 posts
  • LocationWilton, NH USA

Posted 19 May 2014 - 07:41 AM

WOAH!  Is that bagwall INSULATING FIREBRICKS???????  This last photo makes it look that way....at least to me.

 

The bagwall should be HARD FIREBRICKS...... high to super duty.

 

If those are IFB... they are trying their darndest to keep the heat energy concentrated in the firebox area.  So they do not become as good at being radiant heat sources to send some of theat energy into the stacking of ware.  Plus they will create excessive firebox temperatures, and deteriorate not only the kiln lining faster... but also the burner nozzles due to the higher level of radiant heat energy coming back out the burner ports (due to the high firebiox temps).

 

Bagwall brick spacing looks much better in that last photo.... might even be a bit too tight. I'd have a little wider opening in the bottom row (maybe 1/2" ) behind the targets.

 

I would have turned the target bricks at an angle so that the axis of the burner flame hits the corner to "split" at about a 45 degree angle. (Those should be hardbrick too.)

 

best,

 

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


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#28 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 19 May 2014 - 08:13 AM

Yessir, those are soft bricks. Every single one of them - including the target bricks.

I keep saying, and thinking, and typing, to you guys, "I'm certain I'm doing something really, really wrong - something obvious - but have no idea what it is."

It sounds as though you've found it. Or at least one of the its.  Phew.  I'm thankful.

 

--

I turned off the kiln, will procure some hard bricks tomorrow (hopefully) when the refractory opens.



#29 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,432 posts
  • LocationGrayslake, IL

Posted 19 May 2014 - 09:14 AM

Did we ever fix the issue with the damper having to be so closed down? I still feel like the chimney is too tall. Is there a way at this point to put a passive damper in? You just need to be able to pull a brick or two out of the chimney above the damper, to spoil the draft. That would allow you to test if the chimney draw is too strong, and see if you can get more control out of the damper.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#30 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 19 May 2014 - 09:19 AM

Neil, I obviously know nothing about kilns.  But I've always felt the chimney was too tall - it just seemed logical to me, because I have to damper it down so far.  

 

I followed advice, though, from folks here and Marc Ward, and added a 36" pipe to the top before firing #3 (the last one, which this thread was initially about).  

 

During that firing, it did fire better (temp went up instead of down) with the passive damper - that is, the space above the damper (which is shorter than the damper slot) - left open.

 

But I don't know how I would take any bricks out of the chimney.  There's that one, directly across from the flue, that I can take out.  But none above the damper.



#31 JBaymore

JBaymore

    Moderator

  • Moderators
  • 2,809 posts
  • LocationWilton, NH USA

Posted 19 May 2014 - 09:58 AM

You can use the clean out port below the damper as a passice damper also.  It'll work OK for testing.  Any cold air lwet into the chimney serves two functions to decrease the draft.  One... is the volume of the air itself.  Any air in there is gases that are not drawn from the kiln.  Two is the cooling effect that air has on the stack gases.... which decreases draft also (see below).

 

The normal progression for the damper of a firing is from fully open to almost closed on all fuel kilns.  The sizing of chimneys on natural draft type kilns tends to be based on the earlier stages of the firing, not the later stages when the flue temps are hottest. Technically they are almost always "too big" for the end of the firing.

 

As I remember for ease of constructiuon you used a 9" x 9" cross section for the flue.  That is a large XC for that size kiln.  So you will tend to have 'excess draft'.  But with those cheapie MR burners... you do need a lot of secondary air entrainment.... so that is a good place to be on the potential draft.  But that means that the dampe will be very closed near the end of the firing.  And touchy to adjust. 

 

The amount of draft created by a chimney is directly proportional to the temperature of the gasses contained within the stack, and in particular to the temperature of the gasses at the exit point of the flue.  It is also connected to the cross-section of that vertical flue. And the last piece major of this is the volume of the total column on hot gases in that flue.  Ther is also the factor odf the smoothness of the sutrface of the interior of that flue...... but that is minor compared to the other aspects.  They are all interrelated factors.

 

You have a "supercharger" on your kiln engine.  You'll have to learn to use it accurately.

 

As to the amount closed the dampe might be........

 

For example, on my 40 cubic foot gas kiln, when the kiln is near the end of a cone 9 firing, the damper is open about an area of 9" wide by 1 1/2" deep.... or an area of about 13 1/2 square inches.  A change of 1/8" at that point in the firing will make a huge difference in the kiln atmosphere and the climb rate.

 

It is not much different on the two student built 60 cubic foot gas kilns with forced air burners at the college. Or on the 35 cubic foot Baily at the college.

 

Hope this helps.

 

Glad I caught the soft brick issue.  THAT alone will make a HUGE difference.  Diagnosing this stuff from afar via written word and pictures is SO hard.

 

best,

 

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


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#32 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,624 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 19 May 2014 - 10:10 AM

I was going to Hawaii on my own for a vacation.

I volunteered to help out as a visiting artist during some classes at a small art center that I knew about from another trip-then was asked to do the salt kiln conversion and teach how to fire it. That turned into a job-I did this for free and at turned out very well.It was fun .They will be doing their own fire soon.

 

Take Johns advice on the hard bick and target bricks.

Mark


Mark Cortright
www.liscomhillpottery.com

#33 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 19 May 2014 - 10:49 AM

No, no.  Just let me think you were paid to go to Hawaii.  It's more fun that way.



#34 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,624 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 19 May 2014 - 12:58 PM

I turned down a stipend pay that way they could not fire me.

Mark


Mark Cortright
www.liscomhillpottery.com

#35 Kristin_Gail

Kristin_Gail

    Advanced Member

  • Members
  • PipPipPip
  • 195 posts

Posted 20 May 2014 - 10:09 AM

A friend who's building a wood-fired glass-blowing furnace (which apparently is an anomaly?) just gave me twelve of his high-fire hard bricks.  As he passed them my way, he told me not to use them right now - they're wet from being out in the rain.  

 

To dry them, then, would I just candle the kiln, vented, overnight, after building the new bag wall (with the kiln still loaded full of pottery)?



#36 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,624 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 20 May 2014 - 12:36 PM

I see no issues with that.

Mark


Mark Cortright
www.liscomhillpottery.com

#37 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,432 posts
  • LocationGrayslake, IL

Posted 20 May 2014 - 01:39 PM

Should work. Those bricks are not super porous, so they shouldn't have all that much water in them.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#38 JBaymore

JBaymore

    Moderator

  • Moderators
  • 2,809 posts
  • LocationWilton, NH USA

Posted 20 May 2014 - 03:36 PM

Ditto

 

best,

 

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


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#39 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,153 posts
  • LocationCanada

Posted 20 May 2014 - 03:39 PM

 

I am thinking that your secondary air is way too much. This is the dial on the back of your burners. Crank it way in to about 1/4 inch, or the thickness of a pencil.

 

That shutter is primary air... not secondary.

 

So that is three changes all happening simultaneously for a test.  Too many variables changed for one test to read what is what.

 

I'd need video for a lot of the aspects of the kiln to say more very effectively.

 

The "blue" on the burners sounds like a good sign.  At least they are able to entrain some primary air.  That gives you some control.

 

The about 1" open (are you sure about that) on the damper sounds potentially plausible now that you have some primary air available.  You will find that changes of 1/8" on a kliln that size will make a differencde in the atmosphere and climb rate.

 

FYI...... Letting air into the chimney has the same effect on the kiln draft as closing the damper.

 

Make a change and wait at least 10-15 minutes to evaluate what it is doing.  Don't be changing things every 5 minutes.

 

best,

 

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

 

Sorry, John. I meant to say primary air.

T.



#40 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,153 posts
  • LocationCanada

Posted 20 May 2014 - 03:45 PM

Replace the soft brick bag wall with hardbrick. You want six inches from the kiln wall on the left to the bag wall. The target bricks may be in the way. Do they prevent the flames from going under the work?

TJR. Looks too crowded for combustion.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users