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Benzine

First Firing of My Homemade Raku Kiln

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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....

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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.

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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

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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.

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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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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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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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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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The adjustable regulator is used so that you can have the burner on full and still be able to adjust the flow of gas.  My setup is a 100lb propane tank connected to a Ransome burner through a ball type gas valve. The gas comes through the regulator which I usually have set at 10 psi. The valve is mostly for shutting the gas flow on or off except the 1st cycle where I use the valve to turn the burner up in gradual steps. From the valve the gas goes through the orifice which is a fixed size(sorry, I don't remember the size and the kiln is not where I am but I can get that later).  This sequence determines the BTU value of the burner.  500K BTU sounds like a lot for Raku but that would be a maximum output under ideal conditions so the regulator combined w/the orifice size really determine the output of the burner.

 

I hope this is not overly detailed. I have used many different Raku kilns and burners but they all work on the same principle.

I will get the orifice size for my burner so we can do the math but this weekend it is camping with the sun-in-laws and the grandchildren so it will be a few days.

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Alright folks, so I've done a couple more firings, since I've widened both ports.

 

I did one this past Monday, to test the kiln, for the firing I would be doing with my students this Friday. 

It went well.  The glazes reached maturity, and in a good amount of time.  The wares themselves, aren't exactly where I wanted them, but that was due to my rushing the reduction, not because of the kiln.

 

So this afternoon, my Art club did our second annual firing.  Last year's firing went well, but the kiln stalled, and some of the glazes didn't mature.  The students still had fun though.

This year, the kiln gods smiled upon us.  The kiln performed beautifully, the glazes reached maturity, and we had some great reduction.  The students were super psyched with the results, but sad, that I wouldn't let them take them home, until after they've been in the display case a while. 

 

We actually did two firings, and the second one took almost no time at all, due at least in part, to the port modifications. 

 

I've got one more firing to do this weekend, as we didn't have time to fire all the student's projects.  So I will do those, and possibly even my couple pots, that didn't reduce in the way I wanted earlier in the week.

 

Good times.

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I hope this is not overly detailed. I have used many different Raku kilns and burners but they all work on the same principle.

I will get the orifice size for my burner so we can do the math but this weekend it is camping with the sun-in-laws and the grandchildren so it will be a few days.

Thanks Dave. Take your time.

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