Hank Murrow on mon 30 aug 10
Dear Jonathan;
I'll have a crack at this. I have built some 50+ brick kilns and tend to =
=3D
imagine that a flat roof is best for turbulence, if you can make the =3D
roof long-lasting. So the Minnesota flattop has an advantage in my mind =3D
going in, though I have never built one, just fired them.
If your burners are on two sides, as in many European designs, then I =3D
favor arches which spring from burner side to burner side, in the =3D
expectation that this configuration will create turbulence before gases =3D
travel down into the flue-trough under the shelves. I have built both =3D
ring arches and tied arches in perhaps 2 dozen of these kilns. The =3D
mixing, particularly if the arch can be keep shallow, is the same for =3D
both types.
Also within my building experience are that cross-draft kilns, mostly =3D
for salt, that fired well & even, providing that I used a salt brine =3D
solution to salt the kiln, even if the chamber was 4 or 5 cones apart =3D
before salting. The H2O seems to soak up firebox heat and give it up to =3D
the rear of the chamber before leaving...... at least, that's how I read =
=3D
the results. The arch sprung from the firewall to the chimney side in =3D
each case.
My own Doorless Fiberkiln design has a very shallow rise(4" across 40" =3D
span) from all four sides and behaves much as a flat roof does except =3D
that the shallow rise seems to 'lock in' the fiber modules =3D
securely(never had a failure in several thousand fires on a dozen or =3D
more kilns). And the flame-retention tips(16) emanate from all four =3D
sides, almost guaranteeing evness of both reduction and heat.
See: http://www.murrow.biz/kiln-and-tools.htm
The anagama, and variations on the noborigama present opportunities and =3D
challenges of their own, as a search of kiln images will turn up. I love =
=3D
the directional and variable effects of such fuel firing and prefer a =3D
flame shaped design, sometimes referred to as a 'beached whale'. =3D
Not-too-wide firebox of about 7 feet in length, followed by an doubly =3D
enlarged space tapering down to the chimney entry at the rear, with a =3D
shallow rise from firebox to chimney entrance. Not the most efficient =3D
design, but one that yields the pots I have been after in the last 15 =3D
years or so. These are mildly side-stoked during the final third of the =3D
firing. Train-kilns seem to be gaining ground lately, which counter all =3D
of these preferences..... so "your mileage will vary".
Please report how it turns out for you after twenty or so fires.
I love to fire my kiln-design, solo and for any period that I deem suits =
=3D
the ware....... & I love the anagama and its crew, taking shifts, making =
=3D
meals, reading poetry during the night or after meals as 'dessert', The =3D
wait until we all rendezvous for the unloading: it does not get any =3D
better than that for me. The best thing is that I get to do both, solo & =
=3D
group, easy & difficult, dirt cheap & beyond extravagant.
Makes a potter ecstatic, IMHO.
Cheers, Hank
On Aug 30, 2010, at 4:29 PM, jonathan byler wrote:
> Which is better: a roof arch that arches in the same direction as the
> general flame path, or a roof that arches perpendicular to flame
> path? I have mostly seen downdraught kilns with the roof arch
> perpendicular to the flame inputs, and crossdraught types with the
> roof arch parallel to the flame path (like the sanderson's bourey box
> klin in jack troy's "woodfired stoneware and porecelain"). I
> understand that the perpendicular arch in most downdraught kilns is
> supposed to cause more turbulence resulting in a more even heat
> distribution. would this not also be desirable in a crossdraught
> design? or would this turbulence interrupt the very directional flame
> path and subsequent marking of the pots that is considered desirable
> in the crossdraught design?
>=3D20
> is the reason the downdraught kilns tend to heat more evenly because
> the length of the flame path from firebox to exit flue is roughly the
> same all around, whereas the flame path in a cross draught kiln heats
> the pots closest to the firebox faster and the ones closest to the
> flue slower? I understand that an anagama or other very long kiln
> tends to have multiple fireboxes to rectify this. is this a big deal
> when dealing with a relatively short ware chamber that is more of a
> cube in cross section?
>=3D20
> -jon
jonathan byler on mon 30 aug 10
Which is better: a roof arch that arches in the same direction as the
general flame path, or a roof that arches perpendicular to flame
path? I have mostly seen downdraught kilns with the roof arch
perpendicular to the flame inputs, and crossdraught types with the
roof arch parallel to the flame path (like the sanderson's bourey box
klin in jack troy's "woodfired stoneware and porecelain"). I
understand that the perpendicular arch in most downdraught kilns is
supposed to cause more turbulence resulting in a more even heat
distribution. would this not also be desirable in a crossdraught
design? or would this turbulence interrupt the very directional flame
path and subsequent marking of the pots that is considered desirable
in the crossdraught design?
is the reason the downdraught kilns tend to heat more evenly because
the length of the flame path from firebox to exit flue is roughly the
same all around, whereas the flame path in a cross draught kiln heats
the pots closest to the firebox faster and the ones closest to the
flue slower? I understand that an anagama or other very long kiln
tends to have multiple fireboxes to rectify this. is this a big deal
when dealing with a relatively short ware chamber that is more of a
cube in cross section?
-jon
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