Sandy Miller on tue 5 jul 05
John, Mel, Vince, Liz ....................
Yes, we are a cheap bunch but some are new to clay. EDUCATION! I own two Cress Kilns, 3" IFB and one with a nifty controller. I have been firing over 18 years with one of these kilns. They look and fire great, I take care of them. They are firing more than off. I did my homework on these kilns, it was the best I could buy at the time. I would like to upgrade so this conversation is very timely. When I found out there was "other" clay available I tried it..............$80 to ship test clay to my studio, no free lunch.......cost was more, boxes weighed less but I did the math and it cut my production time and made better pots. I am now paying for the clay and loving this clay and telling other potters about my experience with this clay.
When I started out and many folks on this list are starting out, entry level prices are a must. My first kiln was a tiny little paragon that held 24 mugs but it allowed me to fire at home. This list is invaluable for education so keep talking...... I'm listening, we are all listening...........Right now I would rather have thicker IFB and fiber insulation than a controller.
My raku kilns are double walled and could probably go to ^10. I don't think I could build my own electric kiln but wish I could................hmmmmmm the next step...............
thanx to everyone who has contributed to this post!!
Sandy Miller
www.sandymillerpottery.com
So hot in Ohio this summer I may have to spray myself with ITC........would that be 100?
Maurice Weitman on tue 5 jul 05
Michael Wendt wrote:
>Be sure to add insulation to the outside of the lid and to the
>inside of the base as well.
Hello, Michael,
I've been thinking of adding insulation to the lid on my electric,
but I've heard/read that it'd be better to add the fiber to the
inside of the lid. I've forgotten the reason(s) given, but I think
it had something to do with not wanting the lid's bricks to get too
hot by trapping heat against it's top.
There are complications to having fiber on the inside, of course.
Aside from having to "button" it, either you'd lose that space (if
only the inside portion of the lid were covered) or the lid hinge
apparatus would have to be adjusted if the entire lid were covered.
(But it would form a tighter seal at the lid while a normal brick lid
would warp, right?)
And since my kiln has elements in the floor, if I were to add
insulation to the bottom, I'd have to add it to the outside... messy
at best, no?
And isn't it true that not much benefit would be derived by adding
insulation to the floor?
What do you think?
Thanks.
Regards,
Maurice
Michael Wendt on tue 5 jul 05
Sandy,
You can add two or three wraps of Kaowool around the outside of an existing
kiln. It would work best to have a new jacket made for the kiln and it might
require the twisted end connectors on the new elements to be a little
longer, but such a project would cost a fraction of the cost for a new kiln
and extend the brick life considerably too.
If you are not a metal worker, go to a local heating and air-conditioning
contractor. They can cut, bend a form a new jacket that will allow the
additional insulation.
Be sure to add insulation to the outside of the lid and to the inside of the
base as well.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Sandy wrote in part:
I would rather have thicker IFB and fiber insulation than a controller.
My raku kilns are double walled and could probably go to ^10. I don't think
I could build my own electric kiln but wish I could................hmmmmmm
the next step...............
thanx to everyone who has contributed to this post!!
Sandy Miller
Michael Wendt on wed 6 jul 05
Maurice,
The main reason to add fiber to the outside of the lid rather than the
inside is you can cover the Kaowool on the outside with metal very easily.
Just get a large sheet of cardboard and lay it on the lid. Trace it and then
draw rectangles at each flat the size needed to cover the edges of the
Kaowool when they are bent down and still allow a small overlap so that the
cover can be screwed to the lid band. Take that to your local sheet metal
shop and have them cut and bend it from 28 or 30 gauge galvanized or
stainless if you prefer.
Adding insulation to the outside also increases brick life because it is the
high temperature differential across brick that gradually cracks it.
As to the powered base... if the bottom of the kiln is bare brick, adding
insulation on the outside is as easy as blocking the kiln up 2.5" where you
put your posts and putting 3" of kaowool everywhere else.
Just my take on it.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Maurice wrote:
There are complications to having fiber on the inside, of course.
Aside from having to "button" it, either you'd lose that space (if
only the inside portion of the lid were covered) or the lid hinge
apparatus would have to be adjusted if the entire lid were covered.
(But it would form a tighter seal at the lid while a normal brick lid
would warp, right?)
And since my kiln has elements in the floor, if I were to add
insulation to the bottom, I'd have to add it to the outside... messy
at best, no?
And isn't it true that not much benefit would be derived by adding
insulation to the floor?
What do you think?
Thanks.
Regards,
Maurice
John Baymore on thu 7 jul 05
And isn't it true that not much benefit would be derived by adding
insulation to the floor?
This is a very common thought amongst potters..... but it is not exactly
based in the science of it all.
"Everyone" knows that heat rises...... so the bottom of the kiln does not
need as much insulation. Problem is, this concept is not true. A hot gas
when suspended in a colder gas will rise (the hot air baloon effect) ...
and this "truth" which we learn experientally through life gets
extrapolated to kilns. So we make the further assumption that it is
the "HEAT" rising.
Basic laws of thermodynamics say that heat energy moves from areas of
higher concentration to areas of lower concentration. Relates to basic
entropy. Prove this to yourself.
Take a metal knife. Dip it in cold water for five minutes. Dry it off.
Hold it horizontally on one end and use a propane torch to heat the other
end. Time how long it is before you have to drop it . Put it in the
water again. Now repeat this with the knife held vertically and your hand
on the bottom. It will be (within a VERY slight variance...see below) the
same time. Ditto any other position.
Conductive and radiative heat transfer knows no "direction". Convective
transfer is another story.....but does not come majorly into play when
deciding wall insulation values. It DOES affect HOW kilns fire though.
So if the hot face of the IFB on the floor of the kiln is at 2300 F and
the hot face of the IFB on the roof of the kiln is at 2300 F, and the
materials of the floor and roof are the same....... the same amount of
heat energy will pass through the IFB section.
The driving force for the exact heat transfer is the Delta T...
differential in temperature between the hot face and the cold face of the
refractories. If you do not allow heat to disapate off the cold face of
one of the IFB sections..... the heat transfer thru the wall is less.
This can account for a VERY SLIGHT difference in heat loss off the typical
kiln roof when compared to the floor which often is configured to not
disipate heat to the surrounding air as easily. The walls typically
disipate more heat to the surrounding air due to natural upward convection
flow...and so have a slightly higher heat loss due to a slightly lower
cold face temp. But the magnitude of all of these differences is pretty
negligable.
Countless generations of potters kilns have been built with underinsulated
floors based on the "experiential" knowledege that "heat rises"... and
then things have to be done to compensate for the colder bottoms .
SO if you decide that you need X inches of insulation in the roof or
walls... you should put that in the floor too.
best,
................john
JBaymore@compuserve.com
http://www.JohnBaymore.com
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
"Please use compuserve address for direct communications."
Snail Scott on fri 8 jul 05
At 11:50 AM 7/7/2005 -0400, John B wrote:
>...if you decide that you need X inches of insulation in the roof or
>walls... you should put that in the floor too.
Definitely! Heat doesn't rise unless there's an
unevenness in temperature, and convection to carry
the air about - neither likely in an evenly-heated
kiln full of stuff.
I added an extra floor to my electric kiln (actually
the lid off my old kiln), and I lay fiberboard on
the lid during firing. This seems to have evened out
my firings quite a bit. And with all that bottom
insulation, I was able to shorten the stand enough
to make the rim height 2" lower - enough to make
loading a lot easier. I blame the demise of the
original floor (at least in part) on years of
leaning on the rim to load.
-Snail
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