John Rodgers on mon 14 feb 00
I have never seen a discussion of envelope kilns on the list before. Has
anyone ever thought of the difference between car kilns and envelope
kilns?
Nils Lou designed a 90 cu ft MFT Envelope Kiln for me back about 1989/90
for my studio in Alaska. The goal was to have a kiln without a moving
floor, in which to fire delicate porcelain figurines. The greenware
figures were very easily broken with the least jiggle, so the stationary
floor was the answer.
A car kiln is designed so the car or cart is the floor of the kiln, is
mobile, and with its load of shelves, ware and door on one end are
rolled along tracks to open and close the kiln. The stationary part of
the kiln consists of two side walls, a roof or top and the rear wall,
where the burner ports and the exhaust port are located.
An envelope kiln is designed as a box with the floor and the rear wall
as one piece, and as in the car kiln, the rear wall has the two burner
ports and the exhaust port in it. The floor and its attached rear wall
are stationary. Imagine, if you would, the letter "L" laying on its
side, with the long side laying along the floor, and the short side
sticking straight up. That is the profile appearance of the floor and
end wall of an MFT envelope kiln. The envelope is built on a "U" shaped
frame of channel iron, with wheels attached. The two sides and back wall
of the envelope are mounted on the "U"shaped frame and support the flat
top. Thus the envelope.....!
Stacking the two types of kilns is the same, but the advantage of the
envelope kiln over the car kiln is that once the kiln is loaded , the
ware never moves thus eliminating the risk of jiggling something and
upsetting the ware or shelves. With the envelope on it track and wheels,
all that you need do is push the envelope over the stacked ware on the
kiln floor, tighten the locks, and fire away.
The original MFT envelope kiln built at my shop had sheet metal sides
with welded buttons on the inside to hold the fiber block insulation
that was used at that time. If I build another one, I will build a steel
frame with expanded metal grillwork for the walls and ceiling, and use
wide-sheet refactory fiber for the insulation. This would make the whole
thing much lighter and more efficient.
Otherwise, the car kiln and the envelope kiln perform the same.
Just thought I would mention an alternative to the traditional MFT car
kiln.
The 90 cu ft size seems to be about the size limit for the MFT. I have
seen pictures of much larger envelope kilns for industry, but they were
all updraft burner types with many burners mounted in the floor, not the
sidewalls, as in the MFT.
For delicate work, where breakage is a constant problem, the envelope
MFT may be the answer.
John Rodgers
Birmingham, AL
Hank Murrow on tue 15 feb 00
>----------------------------Original message----------------------------
>I have never seen a discussion of envelope kilns on the list before.Snip___
>The original MFT envelope kiln built at my shop had sheet metal sides
>with welded buttons on the inside to hold the fiber block insulation
>that was used at that time. If I build another one, I will build a steel
>frame with expanded metal grillwork for the walls and ceiling, and use
>wide-sheet refactory fiber for the insulation. This would make the whole
>thing much lighter and more efficient. Snip__, John Rodgers
***Dear John; If you plan to fire that proposed kiln in reduction,
I would seriously question the use of expanded or perforated metal for the
shell. The reason is that hot gasses will be driven by backpressure through
the fiber lining and onto the steel. This will cause warpage and early
demise of the kiln. I've seen it, and I've testifed in court about this
construction in relation to reduction fires. Another problem that
fiber-lined kilns are subject to is condensation of water vapor onto the
inside surface of the steel. I use 16 Gauge stainless steel sheet to build
a shell that will resist such corrosion. Enjoyed hearing about the kiln
Nils designed for you, Hank in Eugene
John Rodgers on mon 28 feb 00
Hi, Hank.
Enjoyed your comments re: the kiln but I was a little confused by what you said.
To clarify my own experience, let me say that I have at least 6 friends who have
the same type construction as mine was.....that is a sheetmetal envelope with a
refractory lining for insulation.....and they fire their kilns in recuction
typically about every three weeks. This has been so for a number of years. As
far as I know, none have had any problems with the design, in terms of
backpressure of gasses through the fiber to the kiln wall and resulting
corrosion or burnout.
If memory serves, on the job I just came off of, we used an MFT car kiln, and
the stationary kiln envelope was constructed of steel frame with expanded metal
over it, and refractory fiber attached. The fiber inside of the kiln had been
sprayed with ITC100. It gave no trouble at all.
John Rodgers
Birmingham, AL
Hank Murrow wrote:
> ----------------------------Original message----------------------------
> >----------------------------Original message----------------------------
> >I have never seen a discussion of envelope kilns on the list before.Snip___
>
> >The original MFT envelope kiln built at my shop had sheet metal sides
> >with welded buttons on the inside to hold the fiber block insulation
> >that was used at that time. If I build another one, I will build a steel
> >frame with expanded metal grillwork for the walls and ceiling, and use
> >wide-sheet refactory fiber for the insulation. This would make the whole
> >thing much lighter and more efficient. Snip__, John Rodgers
>
> ***Dear John; If you plan to fire that proposed kiln in reduction,
> I would seriously question the use of expanded or perforated metal for the
> shell. The reason is that hot gasses will be driven by backpressure through
> the fiber lining and onto the steel. This will cause warpage and early
> demise of the kiln. I've seen it, and I've testifed in court about this
> construction in relation to reduction fires. Another problem that
> fiber-lined kilns are subject to is condensation of water vapor onto the
> inside surface of the steel. I use 16 Gauge stainless steel sheet to build
> a shell that will resist such corrosion. Enjoyed hearing about the kiln
> Nils designed for you, Hank in Eugene
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