Kiln Evenivity

[Larry Lunsford]

I just got back from Bert’s kiln building workshop. After contemplating my navel for a while, my thoughts wandered to kiln evenivitee-tee-tee-tee (is that a word or a bird call?). Burt’s design calls for an element that is a straight strand of nichrome that zig-zags to cover the surface of the lid. The zigs are spaced 1â€

[Don Burt]

You might throw-in a couple columns and coefficients to account for the heat reflection or absorption off-of the sides and lid. A spot close to a fire brick will have a different evenivity profile. I'm not certain what the technical term for that concept is...I know when a firebrick or fiber board is on the kiln shelf, the technical term is baffle-n-go, but I never took calculus.

[Bert Weiss]

Larry

Your calculations are all well and good. Try pricing out the 2 element systems and get back to us. I believe that you will find that the straight wire nichrome costs about half as much as a kanthal coil and quartz system. Mullite rods falling somewhere closer to quartz than straight nichrome.

Are coiled elements somewhat easier? Yes they probably are, but to my thinking, the lower cost along with the even heat they throw out makes them my choice.

[Lauri Levanto]

Looks fine Larry
- when you make coasters.
Draping deeper pieces gives you a set of ther
variables, however. D is no longer constant.
Slumping into a mold and especially casting
adds a few variables, especially the heat
capacity of the mold material

-and uneven loss of heat thru the floor(in shadow)
and top with radiatin elements close to it.

That is why I ordered my kiln with side elements, too
and keep the shelf higher than the lowest side elements.

The Czech "bezemoth" pictured in the BE catalog
has a similar arrangement.

-lauri

P.S. While talking about kiln design,
top or side door or belljar type?

[Pam Kissel]

WOW!! very interesting posting. All I know is.........well really nothing, however, I have found that in my evenheat coffin kiln I have to put my shelves above the side elements....I use 6" post. I am still having troubles getting an even fuse (aka bubbles from shelve) but I am still trying and I find all of this discussion about heat transference interesting..........tell me more.

[charlie holden]

One thing that complicates the calculation is that the IR doesn't radiate just straight down. Parallel element's radiation overlap each other. Many of the better large, commercial, fiber, bell kilns, like the ones from the Czech Republic, which use coiled elements, in tubes on the ceiling and one along the bottom front and rear walls, space the ceiling element further apart in the center of the ceiling and closer together near the walls. I don't know if they follow a formula or if they are just building from experience. In any case, walls seem to soak up heat, or at least they define the edge where there is no more overlap of IR from the next element along the row.

As far as coiled versus single wire elements, there's no doubt that single wire will provide more evenivity. But that doesn't mean that it is enough more even to offset the additional labor it takes to hang that much wire. Quartz tubes are so easy and fast that I won't do it any other way.

ch

[charlie holden]

One thing that complicates the calculation is that the IR doesn't radiate just straight down. Parallel element's radiation overlap each other. Many of the better large, commercial, fiber, bell kilns, like the ones from the Czech Republic, which use coiled elements, in tubes on the ceiling and one along the bottom front and rear walls, space the ceiling element further apart in the center of the ceiling and closer together near the walls. I don't know if they follow a formula or if they are just building from experience. In any case, walls seem to soak up heat, or at least they define the edge where there is no more overlap of IR from the next element along the row.

As far as coiled versus single wire elements, there's no doubt that single wire will provide more evenivity. But that doesn't mean that it is enough more even to offset the additional labor it takes to hang that much wire. Quartz tubes are so easy and fast that I won't do it any other way.

ch