John Baymore on mon 25 oct 99
------------------
(clip)
I turned on the kiln at 9 am and full-blasted by 11 am. By midnight,
feeling as exhausted as if I'd been heating it myself....well, maybe it was
a couple margaritas....I shut it all off. I think it reached cone 3??? as
my cone 5 glaze had melted but was pitted.
(snip)
Joanne,
Diagnosing such things from a distance with little information to go on is
highly difficult at best, and I am going to assume that the conversion kit
folks have the correct orifices (not too big nor too small) in the burners.
I may have one thought that comes from your comment above using the terms
=22full-blasted=22 and the fact that the glaze was =22pitted=22, and what is=
a
highly COMMON problem exhibited by many new fuel firers.
Try firing the kiln with LOWER settings of the gas pressure going into the
burners. Seems counter intuitive....but it may be an issue here. Often
people try to push the kiln by adding a lot of gas into the matter.... but
the gas only helps if it can combust IN the chamber. In a small kiln
..........such as your electric conversion.....it is often problematic to do
this. If it is not combusting it is creating strong reducing conditions
and exiting the chamber unburned. The strong reducing conditions could be
preventing you from realizing enough BTU's inside the chamber to offset the
total losses (with exit gases, thru walls, etc.)....... and hence, no
climb.
Also the size of the opening at the exit flue is important and is a
variable that you are not used to dealing with in electric firing.
Generally speaking it'll decrease in the number of square inches open as
the firing progresses. A small change here can have a big impact on the
atmospheric conditions in the chamber (from strong oxidation to strong
reduction) and the amount of gases escaping (along with heat) from the
kiln. Play with the size of the opening with the damper, particularly
when the kiln seems to stall. Often opening it a tiny bit will cause the
kiln to climb....even though that seems counterintuitive also. If you are
firing reduction, generally speaking, a small amount of flame present at
the exit flue is good....... a huge amount is not.
(snip)
the interesting part is that by 8 am the kiln was cool. Perhaps I need
insulation????
(slip)
The electric to gas conversion will not counter the fact that electric
kilns are typically notorouisly underinsulated. They also are generally
small in physical size with a high ratio of surface area (outer heat
exchange surface) to thermal mass (the load of pots, furniture, and kiln
structure itself)....so they tend to cool very fast even when electric
fired. This is something you will have to either accept or deal with at
some point........... but I don't think it is the root of the problem in
getting to temperature. It is important to note that the slow rate of
cooling in a LARGE gas kiln has as much to do with the look of =22gas =
fired=22
pots as does the effects of the reduction firing.
Because you now have some whopping large holes into (burner ports) and out
of (flue) the kiln chamber that the electric kiln folks never intended....
the possibility of cold air flow during the cooling cycle really compounds
this cooling problem. When you shut down, take great pains to seal the
exit flue well to prevent a draft continuing to flow in the chamber. Also
if it is at all possible, fashion some burner port covers to close off
those ports so that radiant heat is not leaking from them ....as well as
cold air coming in. Thinly sliced insulating fire brick can be fashioned
to do this. (Don't just stuff loose fiber in there...... bad habit to get
into....fiber is nasty stuff to get into the air.)
(slip)
I suppose i should coat the inside with itc100....do I wrap the outside
with wool and chicken wire?
(snip)
Coating the inside with ITC should help a little bit with the distribution
of heat in the chamber...... which will also result in a little more being
retained. Changing the emissivity of the inner hot face should improve the
cold face temperature.... so decreasing the heat loss a tiny bit. So yes,
that will help a tad, is not all that expensive, and is easy to do. Follow
the directions=21=21=21=21=21
Be careful in just wrapping any kind of insulation around the outside of
the kiln. By putting insulation there you are making what was the old
outside surface of the kiln get hotter. This may cause some critical
components to get so hot they deteriorate. Stainless will take pretty high
temperatures..... but there are many grades of stainless and not all
connectors and fasteners used are necessarily stainless. You may want to
unjacket the kiln before adding such insulation..... but this gets
complicated.
Be careful handling refractory ceramic fiber. The dust is not great stuff
to breathe. Get a MSDS before using it and read it carefully. If you do
decide to use it........ cover it once it is in place with a hard
air-setting coating like thinned Greenpatch 421 (no sense wasting the more
expensive ITC 100 HT on a cold face =3Cg=3E).
Don't go into the =22increase insulation thing=22 until you have spent some
time learning how to fire a fuel kiln. It is likely that your problem is
adjustment of the balance between gas, primary air, and damper that is the
culprit here...... not the insulation. Firing a fuel kiln involves a
number of variables that are a little different than the typical low,
medium, high (and maybe a lid closure) of the manual electric kiln. have
faith......... you WILL figure this out. Tons of people do. See if you
can find a local potter who fires with gas to come over and watch what you
are doing. That person can probably help you immensely.
Hope this is of a little help.
BEst,
.......................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
Joanne Van Bezooyen on tue 26 oct 99
Hi John,
Thank you for SO MUCH information. I can't believe how much I am learning from
you all!
Firing with less gas pressure so it fully combusts is a new possibility for me
to experiment with and I can see where that can make sense. I hate to waste
anything....let alone gas fuel.
Making close-off shutters for the secondary air to close up at shut-down so
cooling is slower makes good sense, too. I knew to close the damper with
bricks. I will forget about the extra insulation at this point
With all the harmful dust particles that can be in a potter's breathable air,
has anyone experimented with cigarette filters up your nostrils for
protection? The idea seemed funny to me, but then, it also makes sense, huh.
John Baymore wrote:
> ----------------------------Original message----------------------------
> ------------------
> (clip)
> I turned on the kiln at 9 am and full-blasted by 11 am. By midnight,
> feeling as exhausted as if I'd been heating it myself....well, maybe it was
> a couple margaritas....I shut it all off. I think it reached cone 3??? as
> my cone 5 glaze had melted but was pitted.
> (snip)
>
> Joanne,
>
> Diagnosing such things from a distance with little information to go on is
> highly difficult at best, and I am going to assume that the conversion kit
> folks have the correct orifices (not too big nor too small) in the burners.
>
> I may have one thought that comes from your comment above using the terms
> "full-blasted" and the fact that the glaze was "pitted", and what is a
> highly COMMON problem exhibited by many new fuel firers.
>
> Try firing the kiln with LOWER settings of the gas pressure going into the
> burners. Seems counter intuitive....but it may be an issue here. Often
> people try to push the kiln by adding a lot of gas into the matter.... but
> the gas only helps if it can combust IN the chamber. In a small kiln
> .........such as your electric conversion.....it is often problematic to do
> this. If it is not combusting it is creating strong reducing conditions
> and exiting the chamber unburned. The strong reducing conditions could be
> preventing you from realizing enough BTU's inside the chamber to offset the
> total losses (with exit gases, thru walls, etc.)....... and hence, no
> climb.
>
> Also the size of the opening at the exit flue is important and is a
> variable that you are not used to dealing with in electric firing.
> Generally speaking it'll decrease in the number of square inches open as
> the firing progresses. A small change here can have a big impact on the
> atmospheric conditions in the chamber (from strong oxidation to strong
> reduction) and the amount of gases escaping (along with heat) from the
> kiln. Play with the size of the opening with the damper, particularly
> when the kiln seems to stall. Often opening it a tiny bit will cause the
> kiln to climb....even though that seems counterintuitive also. If you are
> firing reduction, generally speaking, a small amount of flame present at
> the exit flue is good....... a huge amount is not.
>
> (snip)
> the interesting part is that by 8 am the kiln was cool. Perhaps I need
> insulation????
> (slip)
>
> The electric to gas conversion will not counter the fact that electric
> kilns are typically notorouisly underinsulated. They also are generally
> small in physical size with a high ratio of surface area (outer heat
> exchange surface) to thermal mass (the load of pots, furniture, and kiln
> structure itself)....so they tend to cool very fast even when electric
> fired. This is something you will have to either accept or deal with at
> some point........... but I don't think it is the root of the problem in
> getting to temperature. It is important to note that the slow rate of
> cooling in a LARGE gas kiln has as much to do with the look of "gas fired"
> pots as does the effects of the reduction firing.
>
> Because you now have some whopping large holes into (burner ports) and out
> of (flue) the kiln chamber that the electric kiln folks never intended....
> the possibility of cold air flow during the cooling cycle really compounds
> this cooling problem. When you shut down, take great pains to seal the
> exit flue well to prevent a draft continuing to flow in the chamber. Also
> if it is at all possible, fashion some burner port covers to close off
> those ports so that radiant heat is not leaking from them ....as well as
> cold air coming in. Thinly sliced insulating fire brick can be fashioned
> to do this. (Don't just stuff loose fiber in there...... bad habit to get
> into....fiber is nasty stuff to get into the air.)
>
> (slip)
> I suppose i should coat the inside with itc100....do I wrap the outside
> with wool and chicken wire?
> (snip)
>
> Coating the inside with ITC should help a little bit with the distribution
> of heat in the chamber...... which will also result in a little more being
> retained. Changing the emissivity of the inner hot face should improve the
> cold face temperature.... so decreasing the heat loss a tiny bit. So yes,
> that will help a tad, is not all that expensive, and is easy to do. Follow
> the directions!!!!!
>
> Be careful in just wrapping any kind of insulation around the outside of
> the kiln. By putting insulation there you are making what was the old
> outside surface of the kiln get hotter. This may cause some critical
> components to get so hot they deteriorate. Stainless will take pretty high
> temperatures..... but there are many grades of stainless and not all
> connectors and fasteners used are necessarily stainless. You may want to
> unjacket the kiln before adding such insulation..... but this gets
> complicated.
>
> Be careful handling refractory ceramic fiber. The dust is not great stuff
> to breathe. Get a MSDS before using it and read it carefully. If you do
> decide to use it........ cover it once it is in place with a hard
> air-setting coating like thinned Greenpatch 421 (no sense wasting the more
> expensive ITC 100 HT on a cold face ).
>
> Don't go into the "increase insulation thing" until you have spent some
> time learning how to fire a fuel kiln. It is likely that your problem is
> adjustment of the balance between gas, primary air, and damper that is the
> culprit here...... not the insulation. Firing a fuel kiln involves a
> number of variables that are a little different than the typical low,
> medium, high (and maybe a lid closure) of the manual electric kiln. have
> faith......... you WILL figure this out. Tons of people do. See if you
> can find a local potter who fires with gas to come over and watch what you
> are doing. That person can probably help you immensely.
>
> Hope this is of a little help.
>
> BEst,
>
> .......................john
>
> John Baymore
> River Bend Pottery
> 22 Riverbend Way
> Wilton, NH 03086 USA
>
> 603-654-2752
> JBaymore@compuserve.com
> John.Baymore@GSD-CO.COM
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