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First Firing of My Homemade Raku Kiln


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#41 Mark C.

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Posted 24 January 2013 - 01:45 AM

[quote name='Benzine' date='23 January 2013 - 11:18 PM' timestamp='1359001131' post='28387']
Thanks for those links Mark. What else would I need to complete the burner? A hose, regulator, some type of flow control? Much like electricity, gas frightens and confuses me.


You will need a regulator High Volume (harbor freight) a hose or flex gas line and a valve (ball valve I feel is a good choice) None of this costs much and is what all raku kilns need-think investment in fun.
Mark
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#42 Benzine

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Posted 24 January 2013 - 06:43 PM

[quote name='Mark C.' date='24 January 2013 - 12:45 AM' timestamp='1359009943' post='28392']
[quote name='Benzine' date='23 January 2013 - 11:18 PM' timestamp='1359001131' post='28387']
Thanks for those links Mark. What else would I need to complete the burner? A hose, regulator, some type of flow control? Much like electricity, gas frightens and confuses me.


You will need a regulator High Volume (harbor freight) a hose or flex gas line and a valve (ball valve I feel is a good choice) None of this costs much and is what all raku kilns need-think investment in fun.
Mark
[/quote]

What would you guess all of that costs, in total? Would I have to use plumber's dope, when putting it all together, or just Teflon tape?
"Anything worth believing, is worth questioning"

#43 Mark C.

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Posted 24 January 2013 - 06:50 PM

I would use a better quality pipe dope like rector seal with teflon (in mix) Not a big teflon tape fan-I was taught by a licensed plumber.
My guess is with burner 120$ -130$ tops
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#44 Benzine

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Posted 24 January 2013 - 11:08 PM

I would use a better quality pipe dope like rector seal with teflon (in mix) Not a big teflon tape fan-I was taught by a licensed plumber.
My guess is with burner 120$ -130$ tops


Excellent. My Dad, is actually a Master Plumber, so I will try to recruit him to help me construct the burner.

Should I adjust the port size as well?
"Anything worth believing, is worth questioning"

#45 Mark C.

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Posted 25 January 2013 - 12:22 AM

When you order the burner you specify which gas orfice you want-propane or natural gas-they are different . No other modification is needed-the orifice is threaded into burner and is brass.
Mark Cortright
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#46 Idaho Potter

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Posted 25 January 2013 - 05:47 PM

Benzine, my burner was set up by a propane supplier. It has a pilot light at the burner, plus a gauge at the tank end of the hose. It also doesn't look like yours, more like a Venturi so I get good oxy while burning. My intake opening is 4 inches square even with the fibre wrapped around edges, and the lid opening is 4" x 6" and I use a small 8 inch square shelf as an adjustable vent control.

Shirley

#47 Benzine

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Posted 22 September 2013 - 11:51 AM

Alright folks, I'm dragging up this topic from the depths of the forum, and dusting it off.

 

There's no sense in creating a new topic, when I already made this one, reduce, reuse, recyle, BE GREEN!.....

 

A little summary, so you don't have to read through the entire thread again.  I built a barrel style Raku kiln, from a steel garbage can, and ceramic fiber blanket.  It is fueled with a weed burner, though I don't recall the BTUs off the top of my head.  I have used it thus far on three occassions, to do four loads.  It works fairly well, with a couple minor issues, which I'll discuss below.

 

Anyway, I once again plan to do a Raku firing with my students.  Last year, the firing was a sucess overall.  The problem was, the kiln took too long to reach temperature, over an hour for the first batch, and nearly as long for the second.  Also, the temperature wouldn't get above 1700 F.  It just hung around 1600.  So, some of the glazes didn't quite get to maturity.

 

Previously, some have suggested that I use a damper on the exit flue.  I was also asked, about the size of both ports.  When building the kiln, I followed a couple sets of instructions, which said to make the ports four inches, which I did.  However, to protect the metal skin, of the barrel, I had the fiber blanket overlap that about a half inch all the way around.  So the ports ended up being about three inches of actual open space. 

 

Should I widen the ports?  I can cut the metal, to make it five inches, and leave the blanket to overlap a half inch, so the ports would actually be four inches, as I intended?  I am just hesitant, as once I cut the metal away, I can't add it back in.

 

Also, currently, the bottom of my kiln is just the fiber blanket.  Would it be a good idea to put a shelf, or kiln brick over top of that, so that my posts are more stable? 

For my prior firings, I actually used some soft fire bricks as my posts, because I thought the standard posts would be too wobbly on the soft bottom.  The bricks worked, but a couple of them have slightly cracked, from the stress.  So I'll probably get some proper posts, but want a more solid bottom.

 

Any extra help/ input will be appreciated. 


"Anything worth believing, is worth questioning"

#48 JBaymore

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Posted 22 September 2013 - 12:04 PM

One of the biggest issues I see with people using this kind of relatiovely primitive kind of setup and "stalling out" is.... ..... get ready for it......... turn the burner......... are you ready........... DOWN.

 

If the burner is set way too high, what you are doing in the chamber is putting in a lot of cold entrained primary air along with the cold expanding propane gas (not yet combusting)........ and a good portion of the combustion of that mix is happening (if at all) outside the actual chamber. 

 

It doesn't climb as fast as you want... and you tend to add more fuel (which entrains more air).  Making the issue worse.

 

Another issue on getting to temp is using too much "damper"...... in the assumption that it is controlling heat losses.   Yeah... it does.  BUT.... and it is a big but...... on these inefficient burner setups (the absolute BEST venturi burners ... the VERY expensive ones ... can only entrain about 75-80% primary air)....... you are not getting good areation of the mixture.  So the rest is coming as secondary air.  This is induced by the tiny draft that the kiln structure is creating.  If you damper it down to control the heat losses... you are also decreasing the secondary air at the same time.  Which is likely necessary for you to ever burn the gas to start with.  Net result.... still stalls.

 

Without seeing the kiln in operation ....can't play doctor.  But keep this all in mind.

 

best,

 

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


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#49 Benzine

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Posted 22 September 2013 - 12:30 PM

John, I'm going to go ahead and ask you to keep all of your "science" out of this discussion. Just tell me which deity to sacrifice a rabbit to, in order to ensure a successful firing, and I'll be on my way.......

I have actually tried to keep myself from cranking the burner up. After my first firing produced quite a bit of carbon, I was told that too much gas, not enough air, was probably the problem. So with my later firings, I moved the burner back from the port, and waited longer, before turning up the burner.
Your post makes a lot of sense, and is definitely something I didn't think of.

Would a photo of my set up help you diagnose Doctor, or would it have to be one of them "Moving Pictures"?
"Anything worth believing, is worth questioning"

#50 JBaymore

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Posted 22 September 2013 - 02:06 PM

A rabbit won't do.  You need the relatively rare albino jackalope.  Oh... and it has to be betweeen 1 year and 2 years old.  Once you have one, let me know.... I'll give you further instructions on how to handle the next steps.

 

best,

 

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


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#51 Benzine

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Posted 22 September 2013 - 08:23 PM

A rabbit won't do.  You need the relatively rare albino jackalope.  Oh... and it has to be betweeen 1 year and 2 years old.  Once you have one, let me know.... I'll give you further instructions on how to handle the next steps.

 

best,

 

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

Hmmm....Deal! 

 

I'm slightly skeptical of the specifications, but at least you didn't tell me it was a snipe.  I'll only fall for that twelve times....


"Anything worth believing, is worth questioning"

#52 JBaymore

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Posted 22 September 2013 - 08:28 PM

Snipes only work for wood kilns... not gas kilns.

 

best,

 

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


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Professor of Ceramics; New Hampshire Insitute of Art

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#53 dave the potter

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Posted 23 September 2013 - 11:58 AM

First get an adjustable regulator for the propane tank(try propane company, farm supply, hardware store).Add a gauge that has a 20 to 30 PSI scale. This will allow you to get more or less propane w/o having to monkey around with the orifice. Use a piece of fiber or old kiln shelf to adjust the vent (flue) where the hot gas exits at the top. Make sure there is plenty of secondary air coming in around the burner. Open the regulator until you can barely detect flame coming out the top, then turn the regulator back until the exhaust is clear. If the kiln gets hot, great! If not you can close the exit flue some.. Just remember the initial load can take considerably longer than subsequent ones. Adjusting BTU's up or down and how much flow there is should get you to a reliable firing.



#54 wadar

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Posted 23 September 2013 - 07:02 PM

Regardless of the type of burner you use you must have enough space at the inlet port to allow it to draw sufficient secondary air for efficient combustion. if your burner is 2.5" in diameter make the port 4.5", or 1" all around. This will allow plenty of area. Since you are bringing in cold propane and relatively cool air you must also allow for an exit flue of at least that area, since the exhaust gases have expanded in combustion.This means that the exhausted fuel  requires more area to flow out of the kiln.You can't really force the exhaust out by putting more fuel/air in. if you were using a blower or if you had a chimney that would help, but with your set up you need a flue opening of say 5'5". Then use a piece of fiber tied to some wire mesh for a damper.

I have a little kiln made with soft brick sides and a fiber top that reaches temp just fine and the burner port is roughly twice the size of the burner and he exit flue is roughly twice the size of the burner port. I use the fiber/wire mesh as a damper so I can reduce if I want to. is, The point is, imho, you need to get more air in and more exhaust out for your kiln to work properly.

Hope this makes sense,

good luck with it,

Bill



#55 Idaho Potter

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Posted 23 September 2013 - 08:26 PM

My first load usually takes about an hour, second is about 40 minutes, after that (kiln is hot by this time) subsequent firings take 15 to 20 minutes.  Another thing is if the day is cool - cold, have a propane heater on top of another propane tank and keep your glazed pots very warm.  I know, everyone says stack next load on top of kiln, NOT GOOD IF YOUR KILN ONLY OPENS FROM THE TOP.  Too much shifting of pots,  I use an old card table next to a propane heater--works fine.

 

I can't help you with all the science discussed, because I play it by ear--literally.  I have marked the knurled knob so I know where to set the propane for the first setting.  First load, I leave it there for 20 - 30 min, then turn it up according to how the roar sounds.  Can't describe it, it's just one of those things you get to know.  I only do two turn ups of gas and keep an eye on the glaze glossing which tells me when it's ready to pop the top. 

 

If you're ever in Idaho, stop by and take a listen.

 

Shirley

 

edit:  Meant to also say that I use three soft kiln bricks to balance my shelf (fiber under those bricks and kiln bricks under fiber with hard bricks under those).  My kiln measures 20" dia. by 24" height--including space below shelf.  Over the years, I've decided I'd rather fire smaller loads because frequently I'm the only one doing the firing and pose-reduction.  I can only keep track of limited number of things.  Don't multi-task as well as I once did.



#56 Benzine

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Posted 23 September 2013 - 10:14 PM

Thanks for all the advice folks.  I'll be giving it another shot here in a few weeks, and I'll let you know how it goes, post alterations. 

 

So I'll widen both ports, and sacrafice at least one albino rabbit, and we'll see if that works.


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#57 mom23inmo

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Posted 23 September 2013 - 11:41 PM

I'd sure love to see some pics of how your work came out. :)  I'm working on my own kiln as well.



#58 Benzine

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Posted 26 September 2013 - 08:36 PM

I'd sure love to see some pics of how your work came out. :)  I'm working on my own kiln as well.

I've only fired the kiln three times.  I took a picture, of my first vessel, and I'll see if I can locate that picture.  The second firing, was all student work, and the the third was a couple small items, I made for gifts, then gave away. 


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#59 Benzine

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Posted 20 October 2013 - 08:58 PM

Alright, so I widened both the burner port (4"), and flue (5").  My burner head is 2", so I have much better air flow around the burner head now. 

 

I plan to do another firing next weekend, to see how this affects my firings, hoping it doesn't stall out as it has in the past.

 

One things, that I don't believe I've asked previously, how close to the exit flue, can the wares be?  It should still be fairly hot all the way to the inner lid of the kiln correct?


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#60 MichaelP

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Posted 21 October 2013 - 11:00 AM

First get an adjustable regulator for the propane tank(try propane company, farm supply, hardware store).Add a gauge that has a 20 to 30 PSI scale. This will allow you to get more or less propane w/o having to monkey around with the orifice. Use a piece of fiber or old kiln shelf to adjust the vent (flue) where the hot gas exits at the top. Make sure there is plenty of secondary air coming in around the burner. Open the regulator until you can barely detect flame coming out the top, then turn the regulator back until the exhaust is clear. If the kiln gets hot, great! If not you can close the exit flue some.. Just remember the initial load can take considerably longer than subsequent ones. Adjusting BTU's up or down and how much flow there is should get you to a reliable firing.

Dave,

 

Do you use the regulator to adjust the weed burner output (while keeping the needle valve of the burner fully open) or it makes sense to keep the regulator at some setting (the highest?) and regulate the burner by the needle valve?

 

I'm at the planning stages of making a racu kiln (most likely, a converted old electric kiln), and am going to use my 500,000 BTU weed burner although I understand it could be on overkill for a 4-5 cu ft chamber. By the way, will a 0-30 PSI  regulator/gage sufficient for 500K BTU or I should go for a 0-60 PSI one?

 

Thanks.

 

Mike

 

EDIT: I checked some references and spoke to a couple of people. Red Dragon 500,000 btu weed burner needs optimal pressure of 30 psi (and the permissable working range is up to 90 psi), so I guess I'll go with a 0-60 psi regulator to have a healthy margin. I can always dial below 30 psi if needed.

And using the needle valve to regulate the flame while keeping the regulator at a set point was another recommendation,






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