Kiln-Design-Details

Kiln Schematic

F: The general scheme of the kiln is shown in the sketch to the right. Its a very cheap and quickly built design. Pleat refers to pleating made with alumina-silicate kiln blanket material. The toilet paper roll of fiber blanket in the lid will be supported by the steel of the stock tank. We will have to use a high temperature hanger of some time to support it. This possibly could be the same wire we use for the heating elements as it seems to retain some structure at 2100 degrees. However this must be verified as the total lid insulation could run upwards of 100 lbs.

F: I anticipate that the insulation thickness should be on the order of 1 foot minimum in all locations.

Possible Kiln Material Suppliers

• atlanticfirebrick.com-Atlantic Firebrick Notes Local supplier :
• zircarceramics.com heating elements This is a really cool site that can make heater element segments and stuff. ---(FR) I talked with these people several years ago. Their stuff is a bit pricey. Talked to them about the cylindrical fiber board as an option for the kiln tube body.
• Ebay Brick AuctionCurrent EBAY options
• Thermal Ceramics Surplus material page - Has fiberboard. Possibly we could fashion some sort of beam affair underneath the kiln blanket in the lid?
• Harsco.com - Black Beauty Coal Byproducts
  
  
• Shuttle-Tiles
  
• Tile-Recipe-Notes

Why build and not buy a Kiln

• A: I found a place that makes kilns. Large Fusing Kilns This might be the way to go. ----VERY expensive fiberboard. I've looked at these. Not the best fit. I weeded this idea a long time ago (FR)

Lots of reasons not to buy the kiln.

• --wrong shape= less even annealing due to non radially symmetric layout
• --not enough insulation
• --not really meant for doing 2100 for long periods of time
• --cost would be probably upwards of 10,000 or more for our specs.
• --we can get just what we want by doing it ourselves. If we ever need a second one it will be relatively cheap and very quick to fab

I have a friend with this sort of kiln. Its great for slumping / fusing. But the term fusing means more like gluing 2 pieces of glass together.

They're meant for a 1/2 - 1 day run.

We're going to be running 2 months minimum.

Lid Insulation Fastners-Possible Solutions

A: I started looking at ways to hold the insulation up against the steel frame that makes the roof of the kiln. There are a few choices.

• 1a-Ceramic thread ( 40 lb tensile )This stuff is pretty light weight. I think we will skip it in favor of the yarn version of the same thing. [ http://www.3m.com/market/industrial/ceramics/pdfs/sewing_thread_10.04.pdf]
  
• 1b-Ceramic yarn ( 140 lbs tensile )[ http://www.3m.com/market/industrial/ceramics/pdfs/roving_yarns.pdf] The ceramic thread scares me a bit but it is very strong. The sample has arrived and it is very cool. About like heavy kite string or like a heavy fiberglass strand. It is pink but that will burn off at around 400C. It is supposed to hold its strength to 2200 F so I will be testing it along with the 12" of sand under the test kiln.
  
• 2-Silicon carbide bolts ( no clue on finding these )
  
• 3-Ceramic bolts [ http://www.superiortechceramics.com/standard/bolts_washers.shtml] These come in many diameter and pitch and about 3" long max. They are about $22 each in 1/4" -20 by 3" long. They are good to 3000 F degrees and we would only need 20 of them to carry the weight of the insulation in the roof. They could be used in conjunction with ceramic stand offs and stainless steel bolts to give the 12" of blanket depth needed.
  

(FR)-I'm not convinced yet on the ceramic bolts. Seems costly and I sense there is probably another way to do it.

• We can possible fire our own and then have the right length. I think phlocast 30 cast into an I shape would probably do the trick. The anchor point of the lower should be internal to the blanket thus if it cracks it will be retained by the insulation rather than dropping down into our glass.
• Another idea would be to use kiln furniture of the right size. It can be obtained in fairly long lengths and I've never seen one shatter due to heat/cool stress. We could use a diamond bit and drill holes in it to place a ceramic cross piece in it to form the I shape.

• Ceramic Fiber Rope - a knot on both ends would be simple! Would need a ceramic washer of some sort but sounds alot cheaper than bolts! I have an email in to see if it has any tensile strength

Ceramic Fiber Rope Site This site also mentions rope with inconel in it. I'm not familiar with inconel properties. Any ideas here?

• We could possibly put a band around the outside of the toilet paper roll and put it in tension enough to make the whole affair structural???

• Alumina-Boria-Silica Fibers 3m High Temp Thread pdf

High Temp Thread Product Line Summary

• Harbison Walker Inswool blanket brick units description: The CSW Module system is a module using a 304 stainless steel “U” channel and two rods that runs through the blanket.

Edge Capture
We could capture one edge of the fiber blanket in compression after the style of cheap notebook binders. The U clip would require a good thermal junction made to the lid so there would be adequate heat transfer to ambient to maintain a low temperature. There would be enough load carrying capacity to support the layer captured and a layer either side. It would require something approaching uniform distribution on the lid but would be much cheaper and might be more effective than other methods mentioned so far.

Fiber Board

It will be more like sewing thru a dense styrofoam than anything else I can think of.

Stainless Steel Usage Note

304 Stainless is good for continious use at 950C ( 1750 F ). Stainless steel can be used up to 1100C ( 2010 F ) but that is the annealing temp so it will start to get soft at these temps. Its probably best to limit metal temperature exposure to less than 500 deg F for kiln longevity. Note the location of the stainless on the fiber blanket modules is on the chill side of the block. They are meant to be mounted in such a fashion that the stainless backing much below 1000 in the same way the stainless tube of my duncan 1029 kiln is. The skin of my kiln is keep below 500 Deg F by exposure to convective air flow. With 12 inch insulation its likely the surface of the kiln will not get smoking hot like my duncan 1029.

Vacuum kiln note: We can probably rely on kiln skin temps to stay low in a regular kiln. In a vacuum kiln we would have to make sure any part we want to limit the temperature of is in direct contact with the outer skin of the vacuum chamber.

Stainless Steel instead of Stock Tank

A: I like the idea of using perferrated stainless steel sheet ( lots of little holes in it ) as the outer shell walls of the kiln. That would reduce the weight of the steel structure and cut down on the mass of steel that gets hot. As the walls only have to hold in the sand loads and the insulation, the perforated sheet will be strong enough. As far as the lid goes, I have a large sheet of stainless steel ( 0.65" thick ). Once I know the shape of the structure and what we are using for insulation in the lid I can fabricate the structure for the lid.

• (FR)-Agreed!-Nice to have access to stainless capability!

Kiln Body Tube

AA: The galvanized feed bucket idea is cute but I was thinking of steel sheet and welding up the outside walls of the kiln. By mixing angle iron and flat plate I can make any structure cost effectivly and strong. I was thinking that 8 or 10 sided would be close enough to round.

FR: Go with 10 sided. 8 would not be enough. Jig it up so no one corner gets stuck overbudget in the distance from the interior diameter of the insulation. That's the same as the standard large kilns and its pretty space efficient. We will have to modulate the thickness of the kiln blanket pleat to make a round interior. This will most easily be done if we have a round tube of the correct diameter to stick inside your fabricated 10 sided kiln tube structure as a jig apparatus.

• By simply allowing for some minor amount of compression in the pleating of the tube the whole thing will hang together almost on its own due to the wedge effect. Also the heating elements are going to be hung off of this pleat. Therefore its essential to have equal spacing from kiln wall to mold outer wall. This idea is an almost direct rip of the ceramic fiber module shown in the photo on the right. Thus some precedent has already been set with using this style of insulation.

AA: Actually, round is not that bad of an idea now that I think of it. This is really just a big hoop with pleeted insulation on the inside. I will sketch up a design and see if it suits you.

Kiln Body Tube Specs Summary

• stainless steel
• 10 sided or round
• 2 feet tall to match the 2 foot widths of the standard commonly available kiln blanket - do sanity check on this - we need sufficient to cover the stack up of: 1) leveling sand 2) mold 3) glass pile

Kiln Elements

• There will be non-coiled linear kiln elements in the ceiling, walls and floor of the kiln.
• Kiln elements will require no coiling. Due to the size we can lay the wire in linearly in a fashion depicted by the photo on the left.

Why old kiln method was discarded

The second photo on the right in included to illustrate by firebrick is impractical. At 140 brinks it would be a good dose of money and very hard to deal with. Cost ~500 USD would be high. In the end due to varying thickness of the mold bottom we would be required to cover it with sand also to do mold leveling. Therefore the brick idea was discarded in favor of using a "toilet paper" roll of fiber blanket. This works not only on the bottom but on the lid of the kiln also. The only other option for the lid would be fiber board. That could run in the thousands just to get enough insulation thickness.