Leland G. Hall on mon 26 jan 04
Hello,
I certainly can't help with all your questions, but perhaps some of them:
Yes, you might be better off with two smaller kilns, though I know that
some folks fire raku kilns that size with good results,
You might try closing the third burner port, and having the flue out the
top,
I think you indeed need to lose the hardbrick floor. Just stack a layer or
two of soft. If you coat the new soft brick floor entirely with ITC it
will last longer.
Many folks have had poor results with pyrometers in gas RAKU kilns. The
flame in contact with the therocouple seems to give eratic results. I have
experimented with various placements of the probe to acheive better
accuracy. I think that placing the probe OUT of the direct flame path will
give you better results.
The relationship between intake and flue must balance. Just tweak it
untill it works. There is probably a formula, but I don't know it. But
close that third burner port, and flue out the top. Hope some this helps,
Good luck,
Leland Hall
Before The Wheel Enterprises
Raku Pottery and Sculpture
La Pine, OR, USA
The above is in response to what follows
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
"The raku kiln is approx. 4=92 dia 4=92 h. It has 2 venturi burners operat=
ing
off of a large residential
propane tank (about 6=92 long)
There are 3 burner openings--6=94 sq., but only 2 are used and the middle
one left open.
The shelf is located only 4=94 from brick floor and we only fire 4-7 small
pots at a time.
I recently noticed that the kiln floor is simply one layer of hard brick
set into the ground
with no soft brick or wall.
THE PROBLEMS: I have not been doing the firings but the raku kiln master
reported the following:
With a pyrometer reading of 1795 the pots were not even red when removed.
The pyrometer was
located directing across from the burners, in the top 1/3 of kiln.
Personally I did 4 saggar test fires, based upon the way I learned from
Linda and Charlie Riggs,
and even though pyrometer reading was 1700-1750 the pots never reached
temperature and all
were shades of grey. (sorry Linda). I took them home and refired in my
own electric kiln
successfully.
QUESTIONS:
(1) Is it possible that the psi on the large propane tank is set too low
and the flame is therefore
not producing enough heat? What psi do you raku people use.
(2) Doesn=92t the hard brick floor cause a loss of heat ? Would it be bette=
r
to lay in a medium
or soft brick floor and short wall? How would you recommend construction
of a base so we older
folks don=92t have be down on our bellies. How do youse guys set it up.
(3) Since the interior volume is so much larger than what we fire at the
studio, would it be
better to have 2 smaller kilns instead of one so huge?
(4) Anyone in the Tucson area who could come and check this out for us.
Your suggestions for ways to solve this problem and also any simple
information on constructing
a raku kiln will be most appreciated."
BobWicks@AOL.COM on tue 27 jan 04
In terms of temperature in Raku fireing I always go by the color of the
project and the inside of the kiln. You must have a peep hole to do this. Also in
terms of oxygen versus reduction firing, I also go by the color. If the
flame comes out the flue as blue flame you definitely have oxygen fire. It it is
yellow or orange it has less oxygen. I would definitely close the 3 rd burner
port. There should be enough secondary air coming in the other two burner
ports to support good fire. It would not hurt to raise the lowest shelf so it
is at least 4 inchyes above the flame entering the kiln. this will allow the
flame to circulate and give a more even fire.
Good Luck.
Bob Wicks, Prof. Emeritus
HACC
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