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Patrick

Used hard brick gas catenary arch kiln build

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Your 16ga chimney will be extremely hot and will most likely fail after just a few firings.. .  I'm speaking from experience on this one.  Mine would start to glow at about cone 5 on.   I had to extend a short brick chimney that transitioned to metal from a short 5ft to about 12ft. This got the metal above the kiln shed roof and out into the open air keeping it much cooler.  You could touch the metal part with a stick before I raised it and the stick would instantly burst into flames.

On a friend's kiln he had a short brick chimney then a light gauge metal extention. we were firing it and  at about cone 8 it failed and actually collapsed down into the brick section. It partially blocked off the exit flue and severely choked the firing until it melted away enough and we were able to finish.

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On 3/11/2019 at 5:53 PM, Russ said:

Your 16ga chimney will be extremely hot and will most likely fail after just a few firings.. . 

Thanks for the food for thought Russ.  Been chewing on it, and here's where I am at.  Any additional thought would be appreciated.

Let's say you're right and my cone 6 firings would soften it up enough to where it would sag - a possibility since it will be sticking out at about a 45 degree angle from the kiln, and not standing up straight.  I would be willing to bet a couple of pieces of 1" angle iron welded to the bottom corners running the entire length  and supporting the chimney from those pieces would keep it stable.  It seems to me that the piece of angle iron surrounded by air would not get close enough to temps high enough to soften.  I could be wrong, but I think that might keep it in one functional piece.

I initially thought about cutting small holes in the bottom to introduce cooler air, and then I remembered I would be mounting an oxygen sensor in there. Duh.

See image below and keep snide remarks private. ;) ... I know.  Just don't say it.

Red = sheet.  Green = supports/mounting points attached to not-yet-existing steel frame.  Blue = O2 sensor.

PITA? Maybe. Functional? I think so.

KilnFrontWallStackedChimney.jpg

Edited by Patrick

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18 minutes ago, liambesaw said:

That looks like an abstract painting of Jabba the hutt riding a red french fry like a witch on a broom.  

Why not use brick for the chimney?  The steel and whatnot seems like a royal pain.

First ... You are absolutely correct and I appreciate your vision! LOL!!!

Second. Slowly running out of brick (180 or so left out of 1000), and I'm milking the "forced air burners don't need a chimney" ideology.

... Jabba the Hut.  ... That's rich.

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I would not bother with a metal  chimney unless you line it with  ceramic fiber which is cheap.

You can use steel but not at the exit point as it's just to hot there.The flue gets incrediably hot and steel needs to be futher up and awway from that.

I have found that over the years  people try all kinds of things-tghis is one of those times.

I will not  try to talk you out of this but will add as Russ did I have seen steel fail before. 

If you are out of bricks use ceramic fiber as a liner in your steel area.

I use stainless steel in three of my gas kilns-two have the stack made from stainless after 8 feet of brick.

Start looking in slavage yards for stainless pipe-say 8 inch-that will hold up better than steel.You could drill holes and hold it with honemade buttons-see my post on making them

Keep us in the loop on the 1st fire I'm going to learn something new for sure, as you will

 

Yes I did heal up fine it took 8 weeks of no throwing-then some PT on my crushed hand-I went to SF for the hand workup.Light work during xmas season thensome time off.

Back to normal now-loading-throwing trimming today-usual day for me.

Edited by Mark C.

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4 minutes ago, Mark C. said:

Yes I did heal up fine it took 8 weeks of no throwing-then some PT on my crushed hand-I went to SF for the hand workup.Light work during xmas season thensome time off.

Back to normal now-loading-throwing trimming today-usual day for me.

Thanks for the pointers. Stainless did cross my mind.

Good to hear about you being back at it!

Edited by Patrick

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My second thought regarding the oxygen sensor was to use a IFB and a stainless steel tube on the rear wall, removing it from the chimney equation.  If I do that, I'll probably just set up some kind of "Don't go near here or you'll die like Liambesaw said" kind of barrier and let it exhaust straight out of the wall.

Edited by Patrick

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Hey Patrick   Ummmm  my vote is NOT to just let it exhaust out the back.   I'll revert back to the been there done that mantra..  mypotter friend (bless his heart) had the same wood roof joists as you do above his kiln. They were 3 or 4 feet above the arch of his kiln.    They charred after just the first firing... and he had a brick / metal chimney.  the charring was just from the radiated heat from the kiln!  Just imagine if he let the exhaust straight out the back how fast the fire department would of joined the firing party.  I used firebrick for about 6 feet then I switched to regular old red brick pavers till I was thru the roof then switched to a metal chimney.  The pavers were seconds and we're quite cheep... .25 cents each as I remember.    My metal chimney is actually hot water tanks welded together but as Mark said stainless steel would be by far preferable.  Go to a scrap metal place and ask them to keep their eye out for one.

Just my 2 cents.

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have been following this since the beginning but i have no experience that might help.   except for using insulated stainless chimney sections on the fireplaces and woodstoves in two of the houses i lived in.   the sections come in 2 or 3 foot lengths and screw together.    have been trying to remember the brand name but it has escaped the filing system in my head and is flying around somewhere in space.    just remembered it, METALBESTOS!

if you do a brick chimney to start and at some reasonable point change to this stuff, would that work for going through the metal roof?  i took mine through a wooden chimney on one house and used the steel chimney with an insulated sleeve through the floor and roof above in the second.  

will post this now so i don't lose it and check the internet for the brand name.  

edit    well, things have changed significantly since the last one i did in 1990.    i did find something that looked a little like the one i used, it is called Dura-vent.  i do not think it would be as good as the one i used.  mine was very heavy and rated to be used with only 2 inch clearance from combustibles.   i put it into a 2 foot by 2 foot square wood shaft and its outer dimension was 1 foot.  the inner flue was 8 inches, i think. 

Edited by oldlady
add

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The kind of stainless I have for stack material came from pulp mills-its a heavy wall about 3/16 and is super heavy. single thinkness not the double walled thin stove pipe used in wood stove piping. 1/8 would work well to.I bought it by the # and it is spendy-lasts a lifetime and is hard to work with. You can cut it -torch is best-it can be welded  as well.It can be ground  down as well.I looked for long while before finding mine.We no longer have a pulp mill . Brewerys use stailess but its all small stuff.

My big kiln has 12 inch diameter my salt kiln has 8 inch

I have seen it glow red with zero effects.It will never rust or change.

Edited by Mark C.

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On 3/10/2019 at 7:41 PM, Patrick said:

Lastly, I have been nostalgically building a monitoring system out of a raspberry pi 3 b+, an arduino uno, two adafruit  max31855 thermocouple boards, two 18.5" K-type thermocouples, and a bosch 12028 automotive oxygen sensor. 

You should add a rotary actuator with a gas valve and make it automated :D I did a very basic program after firing and recording what the voltage needed to be every 15 min. No safety but saved turning it up a smidge every 15min.

 

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On 3/16/2019 at 7:01 AM, High Bridge Pottery said:

You should add a rotary actuator with a gas valve

Have a particular model/type/source in mind? I ain't above tryin' anything once. ;)

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On 3/16/2019 at 7:01 AM, High Bridge Pottery said:

You should add a rotary actuator with a gas valve and make it automated :D I did a very basic program after firing and recording what the voltage needed to be every 15 min. No safety but saved turning it up a smidge every 15min.

 

I've never had to turn up a gas kiln that often. Every hour or so works fine.

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A quick photo update.

A QUESTION: does anyone have a recommendations on pilot burner orifice sizes? I am planning on using a 1/32" opening controlled via needle valve.  What are your thoughts?

To do this weekend:

(1) Learn how to put together CSST (Corrugated Stainless Steel Tubing) and hook up burners.

(2) Wire up blowers. I purchased male plug ends that will light up when powered. I figured this would make baby sitting easier. (Do I have electricity? etc.)  I know they make valve and solenoids for this.  At some point I will probably install them, but not now.

(3) Plumb in pilot tubing.  Fabricate a pilot flame deflector thingy and modify it until I like it.

(4) Down stack the front wall and crank up all 4 burners to figure out what's what.  I need to mark my blower inlet flaps so I can have some semblance of predictability/control.  Also get an idea of where my WC gauges are at during certain flame behaviors, etc.

What I DON'T like:

(1) My burner mounts.  Everything is very adjustable right now.  When I get the hang of it, I will probably weld most it and add some diagonal braces as well.

(2) My exhaust hole. I will fab up something so I don't get medium-well each time I want to look at my gauges. ... Jabba the Hutt riding a french fry... LOL!!

Hope you guys are well.

OBTW: The front wall support has 4 rods on the bottom that fit into 4 holes on the angle iron it is sitting on (read: easily removable).  I will then attach the front and back wall across the top sides of the kiln.  That's why it is leaning out - the rods are holding it in place.  The front burners will stay put when the wall is down stacked, ergo the funky cut out on the left and right bottoms on the frame.

KilnBackBurner1.jpg

KilnFrontBurner1.jpg

Edited by Patrick

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@Patrick No idea on the pilot orifice. I've always just used water heater pilots. Start with the 1/32", you can always drill them out larger if needed.

It may just be the angle of the photo, but it looks like your burners are too close to the ports. They should be pulled back from the outer wall a distance roughly equal to half the diameter of the burner tip. That'll keep them from getting too hot and degrading, leave room for the pilots, and allow secondary air draft through the ports.

With power burners, you should really have solenoids on the gas line, so if the power goes out the gas will shut off. Otherwise, when the blowers go out you'll be pumping raw gas through the kiln and you'll have a huge flame coming out the flue. I've seen a kiln shed catch on fire that way. Even 5 minutes without watching the kiln could result in your shed burning.

I hate the round flaps on blowers. They don't sit tight against the blower body, and it's difficult to accurately measure what percentage of air is open. Take off the flaps and use magnetic business cards. Better seal, easy to measure.

I'm wondering if your upper burner ports are going to act like the flue opening and have back pressure out them. 

Definitely rig up something to protect the front burners from the flue opening.

It's good to see progress!

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I also think the burner tips are to close to kiln-so move them back a tad

I'm with nNeil on the hieght of the back burners-whats the thinking to so high up?Hopefully you will nit get back pressure from those opening acting like a flue exit.

When fire is over you will need to plug these holes otherwise it will make for an exit draft and your do not want that.

As Neil says the exit flue heat is going to cook your burners-You need to insulate them from the flue,you really need a flue extension.

Edited by Mark C.

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patrick,   been thinking about your chimney.   found something you might like to read.   search for "Lowell Baker Potter"  and you will get several items.  read the one that says ''castables" and it will take you to a 1981 copy of ceramics monthly.   on page 96 there is an article with recipes.    interestingly, a few pages before that article is one about making a castable catenary kiln in Fiji, i think it was, left the page  and hope i remembered it correctly.  that castable kiln uses portland cement as an ingredient.   wonder how it stood the test of time.

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Got 4 pilots made. Opted for a straight flame and bent bracket instead of straight bracket and a flame deflector.  I'll just hose clamp it to the burner until I figure out whether or not I still have to fiddle with it.  Since I used a 1/32" hole for the gas orifice, I used two 5/32" holes for air in the side of the pilot tube (to get the 10:1 air to gas ratio for good combustion)... HERE'S THE FUNNY PART - Then I realized I completely forgot all the geometry I learned.  The area of a 1" diameter hole (3.14 inches squared) is larger than two 1/2" diameter holes (each is .79 inches squared - 1.58 inches squared total).  I figured out you need 2 holes that are each 71% of the diameter of the large one to get the same area.  Sigh.  ... If you, like me, are not a "math person" and didn't get the above, picture this:

Imagine a 1 inch circle. It's 1 inch from the left side of the circle to the right side of the circle.

That would mean it is 1/2 inch from the center of the circle to either side, right? So you could fit two 1/2" circles side by side inside a 1 inch circle, and it would not take up all the area of the 1 inch circle. ... That's the best I got to explain it.

Soooo, I am glad I made them with the holes on the side. I can always drill them out larger. But since I am also using a needle valve to feed them, I could also just not dump that much gas to them.

We shall see.

 

EDIT ADDITION: (A big thanks to Fred Sweet for sending me a PM to help me save face regarding how I don't do math well.  Below, I have posted his correction. ... See. Told ya so.  You guys are great!)

####

Patrick-

You math is wrong in your posting. Remember that the area of a circle is:  Pi x R squared.

The  radius of a 1” circle is  0.5 inch, which when squared = 0.25 which you multiply Pi. This gives you an answer of 0.79 square inches.

The radius of a 0.5 inch circle is  0.25inch, which when squared = 0.0625 which you multiply Pi. This gives you an answer of 0.1963 square inches. Since you have two of them, the combined total of two .05 inch circles would be 0.3926 square inches.

Therefore, if you round off the numbers, you’ll find that the area of a 1” diameter is approximately three times as large as a 0.5” diameter circle. 

Does this make sense? You did your calculations using the 1” and 0.5” as radii. That’s where your error is.

Regards,

Fred

####

KilnPilotBurner.jpg

Edited by Patrick

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When you fire this monster could you let us know how much gas is used?

I used to have a large cat like this and it sucked up gas like the Heindenberg.

Th other thing is are you going to connect the two steel walls together so they do not spread? Hopefully thats a yes -It looks like a top attachment could be easy to slip in.

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