OiltoDiesel
04-28-2006, 05:20 PM
I hope this explains how I think we can build an inexpensive burner that will work very well for us.
First a little history:
In the past Ceramic Fiber made from compressed fibers of Alumina and Silica blanket was the only really lightweight refractory material available. We have always known it to be rather nasty stuff to work with, and as a result of personal experience have always stressed the need for protective clothing and the use of Respirators as opposed to the rather ineffectual dust mask. Within the last few years Ceramic Fiber has been re-classified as a Grade 2 carcinogen, thus putting formally into the public arena what many of us have long suspected. This re-classification (and the threat of it) forced the makers of low thermal mass insulation material to try to come up with a ?safe? alternative; the result is a needle-compressed blanket composed of a form of Calcium-magnesium-silicate. There are several manufacturers, but at the time of writing the best performing "safe" blanket is made by Thermal Ceramics, the makers of Triton Kaowool, and is known as Superwool 607 Max. This has a working temperature rating of 2300 degrees Fahrenheit. Although this blanket is rated as safe, the dust it creates will still make you cough, so it is advisable to wear a proper respirator, not one of those rather ineffectual dust masks.
The original Alumina-Silica blanket is still available, and for certain high-temperature applications is still the best material.
Building Portable Kilns out of Ceramic Fiber can be great fun. The lightness and flexibility of the material in its pre-fired state, coupled with its undoubted thermal efficiency, means a kiln can be built that you can keep in the garden shed, and bring out only when you want to fire, rather than have a permanent edifice on your plot.
Simple fiber kilns can be built on any framework from chicken wire to a steel drum or what-have-you, because its lightness means it has no need of a heavy supporting structure.
The kiln I shall outline is a simple updraft type based on a cylindrical format. This is because they are the easiest for the beginning kiln builder to start with. The more complex down draft types are very well covered in several books currently available.
I strongly recommend the use of a good quality respirator or anti-toxic-dust mask, well covering clothing, and rubber gloves at all stages of construction, whichever blanket you use. Both are capable of irritating sensitive skins, and both will make you cough. Wearing protective clothing and a respirator is optional, based on your own judgment, when using "safe" fiber. I would consider its use mandatory when using Alumina silica blanket!
For firing these kilns I am working on the basis of using propane gas and any good plumber's torch or weed burner which will deliver at least 19KW (67000 btu). (I don?t have any experience with the Beckett Burner but it too will probably work). This will handle up to 4 cu.ft gross capacity and should fill the bill. This keeps it simple, effective, reasonably priced, and is readily available throughout the country. Four feet of high pressure hose and a good variable regulator. This will deliver up to 25psi of gas, far more than most of us will need. This burner is obviously very powerful, but it can be turned down to a candle flame. I prefer to be over gunned when firing as it does give you the option of speed when needed.
Before we start building kilns there are two questions to ask #1 How wide the burner port? & #2 How wide the flue? I don?t propose to go into lot?s of complicated calculations, I can?t anyway!, suffice to say you should make the burner port approximately 3" diameter which is 1/2" bigger than the burner and gives, according to my calculations, an area of just under 4 3/4", I then add 60% of that, giving me a flue area of just over 7 1/2" which I use as my minimum size. I always start off with two bits of brick over part of the flue to restrict the exit a bit. The above seems to work well for kilns from .8cu ft to 4cu ft so it's a formula that we should probably stick with.
Before you start building your kiln there is one piece (or pieces) you will need to make: Buttons to hold the fiber to the walls and the roof. I plan on making a lot of these and will make them available to all interested.
http://www.oiltodiesel.com/oiltodiesel/Image1.JPG
#1 Disc cut out of scrap stoneware clay (well grogged) with a 1 1/2" diameter cutter. A pinch of clay applied to the back & a hole cut through.
#2 You can make them like this but the holes in the front create a heat path through the fiber which is ultimately destructive and corrodes the wire holding it.
#3 A short length of Nichrome wire is looped through the hole in the button and taken out through the fibre and the Kiln wall and bent over to hold it in place.
You won?t need a great number, space them about 8"-9" apart and stagger them.
The bottom half of the kiln will only need them in a circle just below the rim.
The lid will obviously need more support.
CONSTRUCTION
#1 Oil drum. If it has a separate lid drill at intervals around the rim and fix with self tapping screws or pop rivets. Cut a slice out of the drum so that the internal height is 2' (610mm) PLUS the thickness of the blanket you are going to put in the lid and base. Then subtract about 1 1/2"(37.5mm) to give you a compression joint between the lid and base. You should wind up with a finished internal height of 27" before lining.
http://www.oiltodiesel.com/oiltodiesel/Image2.JPG
Measure the circumference of the drum, add about an inch (25mm) to that and measure off a piece of blanket to that length. Lay it out flat and cut lengthways; one strip for the lid, one for the base.
[IMG]http://www.oiltodiesel.com/oiltodiesel/Image3.JPG [IMG]http://www.oiltodiesel.com/oiltodiesel/Image4.JPG [IMG]
#2 Line the base first, then the sides. For the sides, lay the fiber in a loose star shape (above right), butt the two ends together, then push the inner folds in towards the wall in the direction of the arrows so that the butted ends are in compression. Smooth the fiber down with a rolling pin or a piece of plastic pipe. Lay strips of thin plastic sheet over the already installed fiber, and repeat the operation to lay in the second layer, removing the plastic sheet when you've finished. If you want the Kiln to be capable of 2300 ? 2400 deg F, you will need two layers of 1 inch (25mm) fiber, with a layer of 1/2 inch (13mm) sandwiched in between.
NOTE: Remember to stagger the blanket joins to prevent heat leaking out to the casing.
Next put the base piece of shelf in and cut the burner hole just above the base shelf, drill the sides at intervals just below the rim and secure the fiber to the walls with eight buttons. Don?t pull them so tight it looks like a leather armchair as the blanket will tear on its initial shrinkage.
Cut the hole for the burner then cut the blanket like a star and fold the ends out. You can either glue the ends down or wire them down, tricky, but easier to renew when worn. N.B put the wire loops in place before you cut the blanket. If you want something longer lasting for the burner and/or flue ports see "Flue and Burner block alternatives" later on in this leaflet.
#3 The lid is assembled like the base. The flue hole is cut first and the loops put in place before any blanket is put in. Use eight buttons around the rim, and four around the flue vent. If you use the brick alternative you will only need two buttons in the roof.
NOTE: For the flue I recommend a rectangular hole rather than a round one, as the circulating flame will have to change direction to exit the kiln, so the rectangular hole acts as a form of passive baffle and keeps more of the heat in. A round vent will allow the already circulating fire to continue unhindered out of the kiln producing a cold spot at the top of the kiln.
FINAL JOB spray the inside with RIGIDISER (W), or Kaowool hardener, using a garden hand spray. This puts a hard skin about 2mm thick on the surface of the fiber, which although brittle, prevents the flame from the burner tearing up the kiln wall and reducing it to dust. So it's good for the kiln, your pots, and your lungs! Rigidiser (w) is colored blue (which burns out) so that you can gauge how much you have put on. Kaowool hardener has no coloring matter in it, so I suggest the addition of a bit of food coloring so that you can see where you have sprayed.
When firing the kiln, always angle the burner as shown. The flame spirals up around the pots, and then reluctantly out of the flue vent. If you point the torch straight in, the fire more or less avoids everything in its hurry to get out, resulting in a very uneven firing.
First a little history:
In the past Ceramic Fiber made from compressed fibers of Alumina and Silica blanket was the only really lightweight refractory material available. We have always known it to be rather nasty stuff to work with, and as a result of personal experience have always stressed the need for protective clothing and the use of Respirators as opposed to the rather ineffectual dust mask. Within the last few years Ceramic Fiber has been re-classified as a Grade 2 carcinogen, thus putting formally into the public arena what many of us have long suspected. This re-classification (and the threat of it) forced the makers of low thermal mass insulation material to try to come up with a ?safe? alternative; the result is a needle-compressed blanket composed of a form of Calcium-magnesium-silicate. There are several manufacturers, but at the time of writing the best performing "safe" blanket is made by Thermal Ceramics, the makers of Triton Kaowool, and is known as Superwool 607 Max. This has a working temperature rating of 2300 degrees Fahrenheit. Although this blanket is rated as safe, the dust it creates will still make you cough, so it is advisable to wear a proper respirator, not one of those rather ineffectual dust masks.
The original Alumina-Silica blanket is still available, and for certain high-temperature applications is still the best material.
Building Portable Kilns out of Ceramic Fiber can be great fun. The lightness and flexibility of the material in its pre-fired state, coupled with its undoubted thermal efficiency, means a kiln can be built that you can keep in the garden shed, and bring out only when you want to fire, rather than have a permanent edifice on your plot.
Simple fiber kilns can be built on any framework from chicken wire to a steel drum or what-have-you, because its lightness means it has no need of a heavy supporting structure.
The kiln I shall outline is a simple updraft type based on a cylindrical format. This is because they are the easiest for the beginning kiln builder to start with. The more complex down draft types are very well covered in several books currently available.
I strongly recommend the use of a good quality respirator or anti-toxic-dust mask, well covering clothing, and rubber gloves at all stages of construction, whichever blanket you use. Both are capable of irritating sensitive skins, and both will make you cough. Wearing protective clothing and a respirator is optional, based on your own judgment, when using "safe" fiber. I would consider its use mandatory when using Alumina silica blanket!
For firing these kilns I am working on the basis of using propane gas and any good plumber's torch or weed burner which will deliver at least 19KW (67000 btu). (I don?t have any experience with the Beckett Burner but it too will probably work). This will handle up to 4 cu.ft gross capacity and should fill the bill. This keeps it simple, effective, reasonably priced, and is readily available throughout the country. Four feet of high pressure hose and a good variable regulator. This will deliver up to 25psi of gas, far more than most of us will need. This burner is obviously very powerful, but it can be turned down to a candle flame. I prefer to be over gunned when firing as it does give you the option of speed when needed.
Before we start building kilns there are two questions to ask #1 How wide the burner port? & #2 How wide the flue? I don?t propose to go into lot?s of complicated calculations, I can?t anyway!, suffice to say you should make the burner port approximately 3" diameter which is 1/2" bigger than the burner and gives, according to my calculations, an area of just under 4 3/4", I then add 60% of that, giving me a flue area of just over 7 1/2" which I use as my minimum size. I always start off with two bits of brick over part of the flue to restrict the exit a bit. The above seems to work well for kilns from .8cu ft to 4cu ft so it's a formula that we should probably stick with.
Before you start building your kiln there is one piece (or pieces) you will need to make: Buttons to hold the fiber to the walls and the roof. I plan on making a lot of these and will make them available to all interested.
http://www.oiltodiesel.com/oiltodiesel/Image1.JPG
#1 Disc cut out of scrap stoneware clay (well grogged) with a 1 1/2" diameter cutter. A pinch of clay applied to the back & a hole cut through.
#2 You can make them like this but the holes in the front create a heat path through the fiber which is ultimately destructive and corrodes the wire holding it.
#3 A short length of Nichrome wire is looped through the hole in the button and taken out through the fibre and the Kiln wall and bent over to hold it in place.
You won?t need a great number, space them about 8"-9" apart and stagger them.
The bottom half of the kiln will only need them in a circle just below the rim.
The lid will obviously need more support.
CONSTRUCTION
#1 Oil drum. If it has a separate lid drill at intervals around the rim and fix with self tapping screws or pop rivets. Cut a slice out of the drum so that the internal height is 2' (610mm) PLUS the thickness of the blanket you are going to put in the lid and base. Then subtract about 1 1/2"(37.5mm) to give you a compression joint between the lid and base. You should wind up with a finished internal height of 27" before lining.
http://www.oiltodiesel.com/oiltodiesel/Image2.JPG
Measure the circumference of the drum, add about an inch (25mm) to that and measure off a piece of blanket to that length. Lay it out flat and cut lengthways; one strip for the lid, one for the base.
[IMG]http://www.oiltodiesel.com/oiltodiesel/Image3.JPG [IMG]http://www.oiltodiesel.com/oiltodiesel/Image4.JPG [IMG]
#2 Line the base first, then the sides. For the sides, lay the fiber in a loose star shape (above right), butt the two ends together, then push the inner folds in towards the wall in the direction of the arrows so that the butted ends are in compression. Smooth the fiber down with a rolling pin or a piece of plastic pipe. Lay strips of thin plastic sheet over the already installed fiber, and repeat the operation to lay in the second layer, removing the plastic sheet when you've finished. If you want the Kiln to be capable of 2300 ? 2400 deg F, you will need two layers of 1 inch (25mm) fiber, with a layer of 1/2 inch (13mm) sandwiched in between.
NOTE: Remember to stagger the blanket joins to prevent heat leaking out to the casing.
Next put the base piece of shelf in and cut the burner hole just above the base shelf, drill the sides at intervals just below the rim and secure the fiber to the walls with eight buttons. Don?t pull them so tight it looks like a leather armchair as the blanket will tear on its initial shrinkage.
Cut the hole for the burner then cut the blanket like a star and fold the ends out. You can either glue the ends down or wire them down, tricky, but easier to renew when worn. N.B put the wire loops in place before you cut the blanket. If you want something longer lasting for the burner and/or flue ports see "Flue and Burner block alternatives" later on in this leaflet.
#3 The lid is assembled like the base. The flue hole is cut first and the loops put in place before any blanket is put in. Use eight buttons around the rim, and four around the flue vent. If you use the brick alternative you will only need two buttons in the roof.
NOTE: For the flue I recommend a rectangular hole rather than a round one, as the circulating flame will have to change direction to exit the kiln, so the rectangular hole acts as a form of passive baffle and keeps more of the heat in. A round vent will allow the already circulating fire to continue unhindered out of the kiln producing a cold spot at the top of the kiln.
FINAL JOB spray the inside with RIGIDISER (W), or Kaowool hardener, using a garden hand spray. This puts a hard skin about 2mm thick on the surface of the fiber, which although brittle, prevents the flame from the burner tearing up the kiln wall and reducing it to dust. So it's good for the kiln, your pots, and your lungs! Rigidiser (w) is colored blue (which burns out) so that you can gauge how much you have put on. Kaowool hardener has no coloring matter in it, so I suggest the addition of a bit of food coloring so that you can see where you have sprayed.
When firing the kiln, always angle the burner as shown. The flame spirals up around the pots, and then reluctantly out of the flue vent. If you point the torch straight in, the fire more or less avoids everything in its hurry to get out, resulting in a very uneven firing.