There are many variations, but most consist of a horizontal cylinder with a tangential hole for a gas burner. The casing can be any steel container, gas bottles are the most popular. There are 3 types of lining:
- Ceramic Fibre Blanket: High thermal efficiency but very short lived.
- Firebricks: Very inefficient and slow to heat up.
- Insulation castable: Robust and thermally efficient and fast heating. The most popular material is Hollocast 1, because of the great ease of installation and high quality and simplicity.
Place the cylindrical casing upright on a piece of cardboard. Find a tin or pipe smaller than your desired I.D. Wrap SFK cardboard (smooth one side, corrugated the other) around it to get the desired diameter. Insert a pipe tangentially through the casing into the SFK, to form the burner hole.
Calculate the volume of Hollocast 1 required:
(O.D. in mm ÷ 200)² X ∏ = area in dm² - (I.D. in mm ÷ 200)² X ∏ = area in dm² Cross section area in dm²
X height in mm ÷ 100 = volume in litres. X density of 1,5 = Kg of Hollocast 1 powder
Mix the Hollocast 1 powder with water, (about 4,4 litres/ 20Kg bag) until it starts to flow slowly. Pour it into the gap between the SFK cardboard and the casing. It will set and get warm in about an hour. You can strip the core as soon as the Hollocast gets warm. You can start heating immediately, with a small gas flame. If you hear steam hissing, turn down the flame, as you are approaching a steam explosion.
Borax drips and damages the refractory lining. The cheap and easy solution is to place a ceramic tile on the floor and replace it every time it is saturated.