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Subject Author Date
Raku Red Deer 05-10-2007
Posted by Red Deer on May 10, 2007, 9:19 am
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Hi Everyone,
I got a portable raku kiln a while back and I haven't been able to get
good results.
I was using a 17 pound propane tank which kept freezing up so I got a
100lb tank yesterday and it just seemed not to get hot enough. I'm
wondering if the kiln is in-
sufficent. It's a Bracker brand. It came as a kit with the flame
coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a
shelf,etc. The kiln itself is a large trash can lid with hardware
wire attatched lined with a stiff fiber blanket. Has anyone had
experience with this kind of kit? Thanks,
Sandi


Posted by Clayboy on May 10, 2007, 11:06 am
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> Hi Everyone,
> I got a portable raku kiln a while back and I haven't been able to get
> good results.
> I was using a 17 pound propane tank which kept freezing up so I got a
> 100lb tank yesterday and it just seemed not to get hot enough. I'm
> wondering if the kiln is in-
> sufficent. It's a Bracker brand. It came as a kit with the flame
> coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a
> shelf,etc. The kiln itself is a large trash can lid with hardware
> wire attatched lined with a stiff fiber blanket. Has anyone had
> experience with this kind of kit? Thanks,
> Sandi

Hi Sandy,

If your tank is freezing, then put it in a large container of water.
This will keep the pressure up. The 100 lb tank should have no
pressure problems. It is not the size of the tank that determines the
heat. It is the burner. What temp are you trying to get to. I fire
a garbage can style raku kiln that I built and I have no problem
getting up to temp. I can go easily to 1800 F in 20 to 25 minutes. I
am using a 20 lb tank of propane as my fuel. My burner is rated at
100,000 btu, but 50,000 should still get you up to temp. Is there
enough air getting into the kiln for full combustion? Too little air
around the burner and it won't matter what size tank or burner you
have, you just will not get enough heat.

Gene


Posted by Dewitt on May 11, 2007, 8:36 am
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wrote:

>Hi Everyone,
>I got a portable raku kiln a while back and I haven't been able to get
>good results.
>I was using a 17 pound propane tank which kept freezing up so I got a
>100lb tank yesterday and it just seemed not to get hot enough. I'm
>wondering if the kiln is in-
>sufficent. It's a Bracker brand. It came as a kit with the flame
>coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a
>shelf,etc. The kiln itself is a large trash can lid with hardware
>wire attatched lined with a stiff fiber blanket. Has anyone had
>experience with this kind of kit? Thanks,
>Sandi

I'm guessing the problem is the opposite of what you suspect. Not too
little gas, but too much. And too little air. It's a common problem
when firing raku kilns - especially when the system does not have a
regulator to control the gas pressure which most grass burner systems
don't. Flames shooting out the top of the kiln look impressive, but
don't help heat the ware.

The best thing I can suggest is to have someone who has experience
firing raku kilns assist you with the first couple of firings. Some
things are easy to demonstrate but hard to explain. . .

If that's not possible, try firing slower with less gas pressure. Pull
the burner back 1" from the burner port so that air is entrained in to
the flow. For the first 2/3rds of the firing, there should be no
visible flames coming out of the exhaust port. For the last part of
the firing, there should be no more than about 4" of flame coming out
of the burner port. When flames are shooting a foot or two out the
top of a raku kiln, then combustion is occurring outside the kiln
where the heat is wasted.

Also, since you likely don't have a pressure regulator, you'll need to
listen to the sound your burn makes so you can manually adjust the gas
flow as pressure drops off in the tank - though with a 100 gallon tank
the pressure drop should be minimal.

deg

Posted by STEPHEN MILLS on May 11, 2007, 6:56 pm
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It may well be that you are putting much too much heat into it:
beg, borrow, or buy a thermocouple and pyrometer if you haven't got one, and
starting with the smallest flame possible on the Burner, increase it only
enough to get a steady rise in heat, for example about 150oC per hour.
Stuffing too much heat into it uses up all the free air in the kiln,
resulting in a heavy reduction which will prevent any increase in heat! The
old kiln firer's saying: "More equals less" applies in full here.
You will learn by experience how fast you can go


> Hi Everyone,
> I got a portable raku kiln a while back and I haven't been able to get
> good results.
> I was using a 17 pound propane tank which kept freezing up so I got a
> 100lb tank yesterday and it just seemed not to get hot enough. I'm
> wondering if the kiln is in-
> sufficent. It's a Bracker brand. It came as a kit with the flame
> coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a
> shelf,etc. The kiln itself is a large trash can lid with hardware
> wire attatched lined with a stiff fiber blanket. Has anyone had
> experience with this kind of kit? Thanks,
> Sandi
>
>



Posted by Red Deer on May 11, 2007, 7:31 pm
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wrote:
> It may well be that you are putting much too much heat into it:
> beg, borrow, or buy a thermocouple and pyrometer if you haven't got one, and
> starting with the smallest flame possible on the Burner, increase it only
> enough to get a steady rise in heat, for example about 150oC per hour.
> Stuffing too much heat into it uses up all the free air in the kiln,
> resulting in a heavy reduction which will prevent any increase in heat! The
> old kiln firer's saying: "More equals less" applies in full here.
> You will learn by experience how fast you can go
>
>
>
>
>
> > Hi Everyone,
> > I got a portable raku kiln a while back and I haven't been able to get
> > good results.
> > I was using a 17 pound propane tank which kept freezing up so I got a
> > 100lb tank yesterday and it just seemed not to get hot enough. I'm
> > wondering if the kiln is in-
> > sufficent. It's a Bracker brand. It came as a kit with the flame
> > coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a
> > shelf,etc. The kiln itself is a large trash can lid with hardware
> > wire attatched lined with a stiff fiber blanket. Has anyone had
> > experience with this kind of kit? Thanks,
> > Sandi- Hide quoted text -
>
> - Show quoted text -

Thank you all for great information. I'm thinking now I shouldn't
turn up the gas as far as it will go. Also there was a gentle breeze
when I fired and flames were shooting out the hole where the weed
burner goes in and looked like it could come back up the gas hose.
Thank you again.
Sandi


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