Brian Molanphy on tue 19 mar 02
thanks to vince pitelka and john baymore for detailed messages about shuttle
kilns.
1.one part of john's message leaves me confused.
john wrote: 'A typical car bed floor refractory layout that I use employs a
graded
> rating system. This lets you have a brick with a higher insulating value
>
> (but lower use rating) on the outer cold face surfaces....and a higher use
> rating (but lower insulating value) toward the hot face. ' and a few
> sentences later: 'The first layer that is sitting on the steel is often a
> layer of medium
> duty hard refractory brick, in the configuration called "thin splits". '
>
please explain what is use rating. i thought that medium-duty hard
refractory thin splits were low-insulating value, high-use rating.
2. has anyone tried a shuttle for a vapor kiln? would salt build-up
interfere with the seal? i see on john's webpage,
http://www.JohnBaymore.com/p0001347.htm, that he has built a hinged-door
soda. if this works ok, wouldn't a shuttle work ok too?
thanks, brian
John Baymore on thu 21 mar 02
Brian,
Sorry about the ambiguity..... let me see if I can clear that up for you.=
1.one part of john's message leaves me confused.
john wrote: 'A typical car bed floor refractory layout that I use employs=
a
graded rating system. This lets you have a brick with a higher insulatin=
g
value
(but lower use rating) on the outer cold face surfaces....and a higher us=
e
rating (but lower insulating value) toward the hot face. ' and a few
sentences later: 'The first layer that is sitting on the steel is often a=
layer of medium
duty hard refractory brick, in the configuration called "thin splits". '
please explain what is use rating. i thought that medium-duty hard
refractory thin splits were low-insulating value, high-use rating.
Use rating is the maximum continuous use temperature range that the
refractory is intended for use at. For IFB this is usually indicated in
degrees F........ 2000 F or 2300 F or 2600F or 2800 F....... and is usual=
ly
abbreviated to a shorter form such as a G-20 (2000F), G-23, G-26, G-28 an=
d
so on. Typically as the Use Rating if an IFB goes up, the insulating val=
ue
per inch of the material (the K value) goes DOWN. This is because
typically there are less little insulating air spaces in a given volume o=
f
brick material and more of the clay material that the brick is composed o=
f.
That is why a K-20 IFB typically weighs less than a K-26.
Hard refractory brick use a slightly different and more generalized ratin=
g
system...... such as low duty, medium duty, high duty, and super duty. T=
he
insulating value per inch of most hard refractorie is not all that
different.....one type to another. They are all pretty bad insulators >.
You also can find a PCE rating for hard brick. This stands for Pyrometr=
ic
Cone Equivalent. That means if you took the brick materials and made a
standard cone out of it...... what heat work it would take to deform it t=
he
usual way. In selecting appropriate hard firebrick fopr a particular
application.... you are usually looking at the composition of the
particular material as much as the "use rating". =
You can usually "get away with" medium duty hard firebrick in a cone 10
kiln....what we potters think of as "high duty" use......... but not in
really extreme locations. =
It is important to note here that a periodic kiln (typical potter's kiln)=
subjects refractories to thermal stresses that are not typical in the
typical industrial continuous tunnel kilns..... so the continuous use
rating of a refractory is not necessarily the ONLY factor to look at in
selecting a brick grade. Use of marginally rated refractories compromise=
s
kiln longevity. If you are building a short lived kiln.... you can get
away with stuff that you wouldn't do in a "lifetime" kiln . My
experience in kiln building is typically..... save money on materials
now....... spend MORE later to fix it .
I guess my comment in another spot in that last posting wasn't that clear=
as to WHY I utilized the hard brick splits on the cold face. A little
further along in that post I mention that the splits on the cold face are=
being used mainly for their structural strength to span the openings
between the 9 inch OC steel struts that form the ladder chassis frame. A=
nd
no need to use high duty there....... pretty cold . So they are not
being used for much insulating value.... that has already been done by th=
e
IFB layers above them. =
2. has anyone tried a shuttle for a vapor kiln? would salt build-up
interfere with the seal? i see on john's webpage,
http://www.JohnBaymore.com/p0001347.htm, that he has built a hinged-door
soda. if this works ok, wouldn't a shuttle work ok too?
The "secret" to the door seal for soda firing is first of all to use
Thermal Ceramics insulating firebrick for the soda kiln structure (good
resistance to soda), then to coat the BRAND NEW IFB with sprayed ITC 100
HT. Then just about every firing a THIN (thin, thin, thin) wash of alumi=
na
hydrate is painted onto the contacting points of the face to face door
seal. After firing, you clean off any "fuzzy deposits" that appear in th=
e
door seal area. At the first sign of any sticking between the two, the
offending area is LIGHTLY wet sanded, and the ITC in that spot is
refreshed. Then the alumina wash goes on again. Ongoing routine
maintenence is KEY to keeping this working. You also need to locate the
soda spray ports in such a manner that you are not in danger of spraying
directly onto the refractories in the door area. And make sure that the
people DOING the spraying are clued in to the whole deal .
A shuttle is a little trickier. Not because the above wouldn't work.....=
.
but because of the variables of the dripping of soda materials into the
floor area. To introduce the soda..... a super-saturated soda solution i=
s
sprayed into the kiln at temperature (with a stainless nozzle assembly). =
If done correctly, very little supersaturated soda/water ever reaches the=
floor refractories area. If done incorrectly....... it does. A heavy
spraying directly onto the refractories in the area where the car heat se=
al
is could cause the car to adhere to the kiln structure. Risky. =
Additionally....... eventually you get soda dripping off of the underside=
s
of the silicon carbide shelves unless you grind them all the time. This
too can cause a drip to seal tha car into the kiln. =
And CAVEAT EMPTOR......... any soda kiln lined with soft brick has a
limited life expectancy. The IFB self destructs. You can slow it down
with correct refractory selection and using ITC 100 HT....... but you CAN=
'T
stop it. That is the price of using IFB over hard brick. It is just
another kiln building design tradeoff. Eventually the door seal area wil=
l
have to be replaced as the overall lining deteriorates. In the case of a=
car heat seal..... the shifting of even a little refractories seals tha c=
ar
into the kiln. So you'd want to allow generous clearances on that
seal....... which itself opens another can of worms.
Not impossible...... but requires some real thought.
Hope this helped.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
"DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop =
August 16-25, 2002"
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