adding firebrick to fiber-lined kiln

Adding fiber is the way to go, as far as insulating efficiency. Where are the elements? A good start would be to put 2" of fiber on the floor. Put a few IFB on that fiber to support your kiln shelves.

OK. Sounds like a smaller kiln. Maybe 1 or 2 rows high of heavy fire brick will give more hot mass that will radiate the heat over a period of time. Depending on the size of the kiln maybe even a couple of bricks will work. Of course your warm-up time will be longer.

Fiber has a much greater insulating value than any firebrick.

FYI, not good to wrap anything on the outside of the kiln.

What type of kiln do you have? How big are the pieces you are making? If you are making beads, they don't need nearly as much attention to ramp down as larger pieces. When I make beads or marbles, usually I put the last bead in and wait about 5-10 minutes and just turn the kiln off and let it ramp down on its own (which takes about 6 hours to get to room temperature). I have never had any problem with annealing stress using this method.

I don't believe you can shut off a fiber lined kiln, as it will ramp down far too fast. My intention is to ramp down slowly to at least 700 degrees before turning the kiln off. I'm trying to minimize that hour of getting from 950 to 700, as I sometimes have to run out without prior notice and would like to simply shut down. My comfort level with leaving the kiln unattended, even with the digital controller, is nil. That's why I'm trying to add firebrick to slow down the temp drop when I shut off the kiln.

Hence the reason for putting a couple of heavy firebrick in the kiln for added thermal mass.

Pick up a cheapo set point controller and TC on ebay and wire in a redundant overtemp interrupter. That way you can have peace of mind when you leave.

The kiln I use is not fiber lined, but it is quite small (9" square bottom, about 12" high). You still haven't said how large your kiln is. If it is large enough, you can just stack fire bricks in it to make an internal shell. Leave a hole to put your beads in and then put a brick in to fill the hole when you are ready to quit. This should slow the ramp down quite a bit. Other then the small Paragon QuikFire kilns, I have never seen a fiber based kiln. If it is one you built yourself, it would probably be just as easy to make a firebrick kiln as it would be to change this one. Have you ever fired the kiln empty and logged the ramp times to see how fast it would fall? The ramp down may be slower than you think. And remember, you said you were doing beads, not large objects, there is a whole different dynamic with small objects due to their scale.

It's a Fusebox II, the inside dimensions are 14" wide, 9½" deep, and 5½" high. And yes, I test fired the kiln and documented it -- here's what happened in the first hour:

1:06 PM temp 968 Turn off 1:20 PM temp 748 1:35 PM temp 654 1:50 PM temp 588 2:05 PM temp 532

It just drops too fast to turn it off. I need it to drop at no more than

225 degrees per hour until it gets to 700 degrees or so.

Thanks -- I definitely am going to plan on putting a brick inside on the left. The right side has the thermocoupler and I'm afraid it will throw off the controller, but maybe I'm wrong. For some reason, I thought it was not OK to put anything on the outside, am I wrong?

No. You are correct.

Well, kind of a bummer, but when I added a sizeable firebrick to the left side of the kiln and did another test of temperature drop when shutting the kiln at 968 degrees, there was no discernable difference. I'm disappointed, but I guess the firebrick additions will not make enough of a difference. Oh well.

Are you adding insulating firebrick or heavy firebrick? Heavier brick may make more of a difference.

Check into redundant OT protection. Then you can leave the kiln on for the complete cycle.