iandol on thu 29 nov 01
Dear Raphael,
Though I have not built this design of kiln I have seen the same =
principles used with a Salt Glaze Kiln and the following notes are based =
upon that experience. Daniel Rhodes design featured as Fig 185 has a Sub =
Floor Flue and a Supra or Floating Hearth.
The Floating Hearth must be raised on posts to allow burnt gas access to =
the flue exit at the base of the chimney.
The area past these posts or props must be equal to, or greater, than =
the area of the exit from the kiln. There should also be an equal area =
between the edges of the tiles or shelves which form the Floating Hearth =
and the Bag Walls. These areas should also be equal to or greater than =
the sum of the areas of the fireports.
For example, if the area of the exit to the chimney base is one square =
foot or 144 sq ins and the floating floor is three feet long, these gaps =
must be at least two inches wide and high. (2*36*2 =3D 144).
In the design Fig 184, the flames from the fire ports farthest from the =
flue exit will tend to be drawn in that direction instead of vertically =
upwards and over the bag wall. In Fig 185 flames are prevented from =
taking this short cut by the floating hearth which should abut directly =
onto the back wall above the flue exit without a gap. It is for this =
reason that D. Rhodes suggests leaving gaps between the bricks of the =
bag wall in Fig 184, allowing flames to be drawn directly onto the ware. =
Adjustments can be made to the space between the floating hearth and the =
floor beneath to restrict the flow of gas close to the flue exit if the =
end farthest from the chimney seems to be firing cooler.
About ten years ago I built and 4=BD cu ft fibre kiln and used the =
notion of a raised hearth and an undershot flue to ensure good =
circulation and better heat distribution.
So in answer to your questions <hinder?>> I believe it a good design, that it certainly assists in =
evening out the distribution of heat and that it is one of the better =
designs available for the exhausting of burnt fuel provided the ratios =
and proportions of the fire ports, the pathways and the flue exit are in =
good order.
My best regards to you,
Ivor Lewis. Redhill, South Australia.
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