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 Materials

A: I have been looking around for matierals and found

• [ http://www.zircarceramics.com/] This is a really cool site that can make heater element segments and stuff.
• Local supplier : [ http://www.atlanticfirebrick.com/]
• Current EBAY options [ http://cgi.ebay.com/Fire-Brick-Refractory-high-temperature-brick_W0QQitemZ190078067831QQcategoryZ92150QQrdZ1QQssPageNameZWD1VQQcmdZViewItem]

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)

A: I like the idea of using perferrated stainless steel sheet ( lots of little holes in it ) as the outter 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.

Lid Insulation Fastners

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.

• Ceramic thread
• Silicon carbide bolts
• Ceramic bolts. Ceramic Bolts Link
  

The quartz thread scares me but it is very strong. I might be able to get some to play with but I would never trust it. The ceramic bolts can be gotten in the 3" long range for about $22 each.

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.

A: 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.

• Any possibility of getting a section of round very large pipe?---Anything off round is going to make the pleating of the fiber blanket a pain and heat loss radially assymetric. Possibly can you fab thin stainless sheet into a nice round tube? 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 if possible. 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.

A: No matter the shape or layout of the kiln, the rotating base under it will be the same. It will be 60" to 80" in diameter and made of steel. I will presume that we want to support 2000 pounds of kiln and mirror on it and will want to rotate it up to 20 rpm. This was how fast my little 9" f/1.5 epoxy test mirror was spinning when I made it. The larger mirrors will need to be spun slower but that is easy once the faster capability is setup.

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.