Kiln Help

[kjharris]

Hoping to get some help from Tomhumf, Mark C or any of our other converted electric to gas kiln users.  I've been using mine for several years now in an updraft configuration and as expected it fires unevenly so I'm finally getting around to adding a proper chimney. I've reshaped my burner opening  and put brick at a 45 degree angle along the side and added a square shelf on it's side to better direct the gas and shield the pieces on that first shelf. I've attached a few pictures of what I'm working with. In one of them I've outlined in sharpie where I may cut out my flue, I'd appreciate any feedback on which of the two locations may work better. The octagonal shelf in the picture is a placeholder, I've got another one that I'll cut to size and cover the rest of the gap there. I'm thinking I should cut more off of each side as well, only about an inch away from the wall at the current size. 

[Mark C.]

So the deal with any downdraft kiln is to keep the heat/flame in the chamber for as long as you can to heatwork the load.

Since your burner in on the right side (floor lever is great ) the flame will want to race towards the flue to get out.

The theory is get the flame up and thru the load before it exits the flue. I do not think you have enough blockage to keep the flame going up and over the load .

More bag wall (meaning higher-way higher ) That flame /heat will just jump over the low shelve and brick and go under the bottom shelve out the flue.

I like the floor level flue with the sharpie and the octogon shelve -but that shelve can be a lot wider to the right side(to much empty space)

you need to rasie the bag wall (shelve up at least 1/2 the kiln height  or more)- to keep the flame/heat from racing to the flue. The brick  wall also needs to come way up. Think of the flame as water teryin g to get out the flue.

You do not have enough blockage yet for that flame

No matter what these kilns fire uneven and you will need to learn to glaze for this.

Also get those old coils pulled out before they become a  mess.

reconfigue and take some more photos for us.

 

[liambesaw]

How are you going to make a chimney? Internal?

It looks like you're planning on cutting the brick and putting the chimney on the outside of the kiln?

Be careful if it's going to be external, not sure the stainless jackets holding the kiln together will be able to handle that much heat.

 

[Min]

Really good detailed plans for converting an electric to a downdraft here. The author, Boris Robinson, has an article in the April 2020 Ceramics Monthly. 

[kjharris]

54 minutes ago, Mark C. said:

More bag wall (meaning higher-way higher ) That flame /heat will just jump over the low shelve and brick and go under the bottom shelve out the flue.

I like the floor level flue with the sharpie and the octogon shelve -but that shelve can be a lot wider to the right side(to much empty space)

you need to rasie the bag wall (shelve up at least 1/2 the kiln height  or more)- to keep the flame/heat from racing to the flue. The brick  wall also needs to come way up. Think of the flame as water teryin g to get out the flue.

You do not have enough blockage yet for that flame

No matter what these kilns fire uneven and you will need to learn to glaze for this.

Also get those old coils pulled out before they become a  mess.

reconfigue and take some more photos for us.

Thanks so much, that's exactly the thing I needed to know. The bag wall was where most of my concern was. I'll get the coils pulled before the next attempt. Thanks a lot for the advice. About half an hour after I posted this I scored a few thousand pounds of refractory brick for 100$ so I may end up doing something else entirely but I'll post an update after I pick it up tomorrow. If it looks like I'll be building one from scratch then I'll really need some help. 

[kjharris]

33 minutes ago, Min said:

Really good detailed plans for converting an electric to a downdraft here. The author, Boris Robinson, has an article in the April 2020 Ceramics Monthly. 

Thanks a lot, I have referenced that and would have put an angle on my burner and gone in from underneath but I wasn't quite that handy when I first converted it. 

[kjharris]

40 minutes ago, liambesaw said:

How are you going to make a chimney? Internal?

It looks like you're planning on cutting the brick and putting the chimney on the outside of the kiln?

Be careful if it's going to be external, not sure the stainless jackets holding the kiln together will be able to handle that much heat.

 

Yeah that's the plan, I'll cut out only the portion of steel that I need to for the opening which will be lined with some soft fire brick so it should be ok.

[liambesaw]

8 minutes ago, kjharris said:

Yeah that's the plan, I'll cut out only the portion of steel that I need to for the opening which will be lined with some soft fire brick so it should be ok.

But the stainless sandwiched between two layers of soft brick will still get too hot, maybe extend the chimney out a little away from the side of the kiln?

[Sorcery]

Everything I read or watched about an external chimney turned out poorly.

I went with that design Boris outlined and even got quick emails back when asking him questions.

I swear you can witness how the draft inducer begins to take effect when it starts glowing, and it seems to automatically jump the Degree/hr at that point between about 1500 and 1700F, which works perfectly to near hands free get you over the 2k hump.

With no stainless cutting necessary, it is a super easy build.

I got mad firing notes, and some pics on Boris' thread here.

Sorce

[Sorcery]

What size is this?

Is that chimney not going to cover your therm hole?

Sorce

[kjharris]

22 hours ago, liambesaw said:

But the stainless sandwiched between two layers of soft brick will still get too hot, maybe extend the chimney out a little away from the side of the kiln?

Ah I gotcha,  yes It'll be extended out at least a few inches from the side.

[kjharris]

12 hours ago, Sorcery said:

Everything I read or watched about an external chimney turned out poorly.

I went with that design Boris outlined and even got quick emails back when asking him questions.

I swear you can witness how the draft inducer begins to take effect when it starts glowing, and it seems to automatically jump the Degree/hr at that point between about 1500 and 1700F, which works perfectly to near hands free get you over the 2k hump.

With no stainless cutting necessary, it is a super easy build.

I got mad firing notes, and some pics on Boris' thread here.

Sorce

I would have loved to go in from the bottom when I first made it. It's already so small inside though so that's why I'm opting for an external chimney. 

[Bill Kielb]

12 hours ago, Sorcery said:

Everything I read or watched about an external chimney turned out poorly.

I went with that design Boris outlined and even got quick emails back when asking him questions.

I swear you can witness how the draft inducer begins to take effect when it starts glowing, and it seems to automatically jump the Degree/hr at that point between about 1500 and 1700F, which works perfectly to near hands free get you over the 2k hump.

With no stainless cutting necessary, it is a super easy build.

I got mad firing notes, and some pics on Boris' thread here.

Sorce

1500 - 1700 degrees? What rate do you fire and are you firing in reduction? Just curious.

[Sorcery]

7 hours ago, Bill Kielb said:

1500 - 1700 degrees? What rate do you fire and are you firing in reduction? Just curious.

The bottom of the "chimney/ flue wall/ kiln shelf/ draft inducer" begins to "glow" at about 1550F, and without looking at my notes, is fully red by 1700, maybe hotter. 

I love this design (not that I've tried another) because it seems capable of any rate at any temp. I got it down to 30F/hr between 800F and 1200F. Up to 600F/hr through mom critical points. Though I don't use that, as it seems too inefficient on gas.

The Firing I noted, what I felt was a rate jump due to the draft inducer, it was running about 120F/HR then boosted itself to about 200F/ HR. The reason it was noted, is because I was (In learning) needing to bump the gas up a tiny bit, every now and then to keep it at 120F, then all of a sudden I didn't have to bump gas. With nothing having changed, I kind of ...."hmmmm...draft inducer?" ...and noted it orange hot.

I was calculating rate like every 5 minutes on the first 2 firings, so I can learn, with temps written down between 7 times a minute...and every 5 minutes. 

I fired the first in Oxidation. Second in Reduction, and third in a heavier reduction.

Single firing, I used Stephen Hill's reduction schedule, staying in Oxidation till about 1900F.

That's where this kiln gets interesting part 2!

At about 1850F with the damper closed to roughly equal to the input hole, I noted "auto-reduction", at 50F short of 1900F, I just smiled and thanked the Kiln gods. Didn't bother trying to adjust for the 50F.

I had coppers red, yellow ochre celadons blue, and my regular clay body pretty AF! So I reckon the reduction was good.

The oxidation fire was Oxidized too.

As far as tools go, I'll use a rock as a "field hammer", since I believe in convenience. I also refuse to shop at Harbor Freight because I respect the value of a good, and the right tool.

This kiln....is certainly good, and the right tool!

Sorce

 

[Sorcery]

8 hours ago, kjharris said:

I would have loved to go in from the bottom when I first made it. It's already so small inside though so that's why I'm opting for an external chimney. 

Sure!

I considered cutting internal bricks back to allow for more internal chimney space. Reckon a half inch or so of brick left might be enough to keep a hot chimney. Perhaps, if you are building stationary, which I highly recommend, you can cut the SS from behind the internal chimney to put fiber or other brick, but still get the draft inducing internal chimney benefits.

I would also consider a sideways design.

I recently fired my baby Raku kiln which is sideways to cone 6 temps. That one ...hands off 200F the whole 8hour firing. It's updraft but I reckon we can think up a downdraft design.

 

Sorce

[neilestrick]

With gas kilns (and probably with electric kilns, too, although it's not as evident since you're not running them manually), there's a point at which the bricks have absorbed enough heat that you start to get some noticeable return on your investment as they become saturated with heat. In grad school we had a slow cooling gas kiln, made for firing shino glazes, that was great for doing this. The walls were built with 9" of hard brick interior, and 9" of soft brick exterior. The kiln was fired quite slowly so that the hard brick absorbed as much heat as possible, so when the kiln reached temp and you turned it off, it would take days to cool. There was a point where the bricks became saturated and started to return heat, and it would rocket up in temp. A friend of mine accidentally hit cone 14+ because it spiked while it was soaking at a high temp.

Most kilns will throw themselves into reduction around 1800F with a slight adjustment to the damper, and without any adjustments to the burners, especially when using venturi burners. The fact that you're experiencing both of these phenomena shows that your kiln is behaving like a real kiln! Congrats!

It's nice that we have a repeatable design for these little kilns that actually works. People have struggled with these conversions for years.

[Sorcery]

I put a couple thicker than usual peices in today.

Last time I fired my little sideways raku joint, I blew up a thick one. Thicker than these, and that heats faster than this bigger one, still, I planned on turning off the burner a couple times around 200F to be safe.

My wares on top were reading 240F on the IR.

And the Baso turned off. Lit it again, off again.

She's telling me to obey what I was doing.

Had Beer and threw her salt this time. Payed a little more respect than usual. 

It's these kind of things that make me ...think?..KNOW they are spirited!

Going to all 10 this time!

After we get going again!

Love this game!

 

Sorce

[kjharris]

I had the bricks delivered today, there are 400-500 of them. Anyone have a recommendation for good kiln building books?