Paul on mon 22 jul 02
Hello,
I am interested in hearing some reduction-firing schedules for those who use
forced air burners. Specifically, i am looking for advice on how much
adjustment is done with the primary air blowers during body reduction as
well as for the glaze reduction. I recently switched to forced air from
venturi burners, and only after making the switch did i find strong evidence
suggesting that the primary air intakes on venturi burners do not necessariy
need to be cut back in order to obtain a reduction atmosphere, due to the
relatively ineffecient nature of that type of burner. Thus, the reduction
can be obtained maily by moving the damper in.
So for forced air, since they are more effecient, does this mean one must
cut back the blowers on them to avoid oxidation; or is it possible to reduce
by leaving them open and working mainly with the damper? My inclination was
to cut back the air a little during body reduction, but then open back up
for the rest of the firing since it seemed kind of limiting to keep them
parly closed for the rest of the firing. So i tried this for the first glaze
firing but have not seen the results yet.
Any feedback would be appreciated. thanks!
Paul
KLeSueur@AOL.COM on tue 23 jul 02
I use forced air burners on my kiln. Each has an individual shut offf valve. My kiln is unique to Ann Arbor. It has no bag walls and no chimney. Three brick are left out of the bottom middle of the door to vent. Each burner has a flap that closes over the air intake. I drew marks at equal intervals and numbered them on each burner. When firing I have the burners in the full open position for oxidation. Half closed in #8. I use this setting for body reduction. For glaze reduction I close down to #9 position but also cut back on the gas.
I also put a valve on the main gas line to the kiln. It is positioned so that the lever is parallel to the wall. I drew equi-distant marks with a compass on the wall and numbered them. The lever has a wire attached to it so that when I open the valve it points to a number on the wall. I use it to controll gas flow to all four burners.
In this way I can control both the air and gas and measure the flow to each. Part of my firing notes read as follows:
Hour three- all burners on, gas #11, air full.
Hour five - begin body reduction, gas #11 air # 8
hour eight - begin glaze reduction, gas #10 1/2, air #9
This enables me to keep accurate records and make adjustments to increase or decrease the reduction and to slow the kiln down.
Kathi LeSueur
Working Potter on tue 23 jul 02
In a message dated 7/23/2002 12:57:56 AM Eastern Daylight Time,
paul@DOCRET.COM writes:
> So for forced air, since they are more effecient, does this mean one must
> cut back the blowers on them to avoid oxidation; or is it possible to
> reduce
> by leaving them open and working mainly with the damper?
>
I have a round aluminum disc, cut from flashing scrap, for my air control on
the blowers, held in place with a single screw on an ofset tab, set so this
disc can float over the opening in infinite increments to control intake of
the air.ADDITIONALLY, with a damper on my chimney and the option of opening
individual bricks in a bricked up door,that, I plan ,ahead, to be able to
remove for the purpose of additional options to control the air intake
aiding in the reduction and oxidation of the gas 45cuft sprung arch 2
forced air burners entering either side of the chimney.
Misty
Liz Willoughby on wed 24 jul 02
Hi Paul, I have a Bailey 24/18 cu ft kiln with forced air burners.
These burners have a metal flap over the fan section. There is a
separate knob that controls the fans in the burners. Before I go
into reduction the fan is on med. and the flaps are open 1/4 inch.
The damper is open. When I go into reduction I adjust the damper,
close the flaps, and turn the fan to low. I adjust the gas to
maintain the right "sound", and the right flame. I keep those flaps
closed to the end of the firing, and turn the fan to med. or high
after a period of 1 hour heavy reduction. The damper, fan, and the
amount of gas (propane) are adjusted for the amount of reduction that
I want. Testing for backpressure, looking at the flame going up the
chimney tells me if I am into good reduction.
Of course all kilns are different, and this is what works for me and my kiln.
Liz, where the weather is finally cooler and the moon is full.
>
>So for forced air, since they are more effecient, does this mean one must
>cut back the blowers on them to avoid oxidation; or is it possible to reduce
>by leaving them open and working mainly with the damper? My inclination was
>to cut back the air a little during body reduction, but then open back up
>for the rest of the firing since it seemed kind of limiting to keep them
>parly closed for the rest of the firing. So i tried this for the first glaze
>firing but have not seen the results yet.
>Any feedback would be appreciated. thanks!
>Paul
Liz Willoughby
RR 1
2903 Shelter Valley Rd.
Grafton, On.
Canada
K0K 2G0
e-mail lizwill@phc.igs.net
Tommy Humphries on thu 25 jul 02
Vince,
Some blower motors, I know that the ones that we use, are rated to run at a
specific speed in relation to the power drawn. If we restrict the air to
some of the blowers the motor will begin to overspeed due to lack of air
resistance to the cage...an hour or so of this overspeed and the circuit
breakers begin to pop. If your motors are designed as variable speed then
that might be the difference. I am not an electrician, so am not at all
fluent on what happens here...I can ask the 'lectritian at work for the low
down if you want.
Tommy
----- Original Message -----
From: "vince pitelka"
To:
Sent: Thursday, July 25, 2002 11:03 AM
Subject: Re: FORCED AIR/REDUCTION
> > > So for forced air, since they are more effecient, does this mean one
> must
> > > cut back the blowers on them to avoid oxidation; or is it possible to
> > > reduce
> > > by leaving them open and working mainly with the damper?
>
> Our forced-air downdraft at the Craft Center has those hokey, unreliable,
> imprecise blower rheostats, as did the Alpines when I was at
UMass-Amherst.
> I always set them on medium, and I do not touch them for the entire
firing.
> All adjustments are done with the swinging air shutter over the blower
> intake.
>
> Some people hesitate to use an air shutter because they assume that the
> blower motor is working harder when you partially cover the air intake,
but
> that does not seem to be the case at all. If anything, it actually seems
to
> be easier on the blower motor when the intake is partially covered. Just
> listen to the motor. When you partially cover the intake, it speeds up
> rather than slows down. If it was placing a greater load on the motor,
the
> motor would slow down.
>
> But back to your question, I always do both. I adjust the damper AND
adjust
> the blower intake shutters. It is a fine balance, and every kiln is
> different. You will have to experiment to get the right balance for your
> kiln.
> Good luck -
> - Vince
>
> Vince Pitelka
> Appalachian Center for Crafts
> Tennessee Technological University
> 1560 Craft Center Drive, Smithville TN 37166
> Home - vpitelka@worldnet.att.net
> 615/597-5376
> Work - wpitelka@tntech.edu
> 615/597-6801 ext. 111, fax 615/597-6803
> http://www.craftcenter.tntech.edu/
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
vince pitelka on thu 25 jul 02
> > So for forced air, since they are more effecient, does this mean one
must
> > cut back the blowers on them to avoid oxidation; or is it possible to
> > reduce
> > by leaving them open and working mainly with the damper?
Our forced-air downdraft at the Craft Center has those hokey, unreliable,
imprecise blower rheostats, as did the Alpines when I was at UMass-Amherst.
I always set them on medium, and I do not touch them for the entire firing.
All adjustments are done with the swinging air shutter over the blower
intake.
Some people hesitate to use an air shutter because they assume that the
blower motor is working harder when you partially cover the air intake, but
that does not seem to be the case at all. If anything, it actually seems to
be easier on the blower motor when the intake is partially covered. Just
listen to the motor. When you partially cover the intake, it speeds up
rather than slows down. If it was placing a greater load on the motor, the
motor would slow down.
But back to your question, I always do both. I adjust the damper AND adjust
the blower intake shutters. It is a fine balance, and every kiln is
different. You will have to experiment to get the right balance for your
kiln.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@worldnet.att.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
vince pitelka on fri 26 jul 02
> Some blower motors, I know that the ones that we use, are rated to run at
a
> specific speed in relation to the power drawn. If we restrict the air to
> some of the blowers the motor will begin to overspeed due to lack of air
> resistance to the cage...an hour or so of this overspeed and the circuit
> breakers begin to pop. If your motors are designed as variable speed then
> that might be the difference. I am not an electrician, so am not at all
> fluent on what happens here...I can ask the 'lectritian at work for the
low
> down if you want.
Thanks Tommy. I am referring to the small squirrel-cage blowers found on
Alpines and on the Harry Dedell/Marc Ward power burners. With those ones it
does not seem to be a problem at all to regulate the primary air by use of a
swinging shutter over the intake.
I think that this depends on the kind of air impeller. Vane-type blowers
such as are found on vacuum cleaners or on some larger industrial power
burners will bog down if you restrict the intake, but that does not seem to
be the case with most squirrel-cage blowers.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@worldnet.att.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Tommy Humphries on fri 26 jul 02
I don't know about those little blowers much...the instance I was referring
too was when I was building a spray booth and needed a good exhaust fan.
The maintenance department came lugging up an old 40" squirrel cage blower
they had removed from the hammer mill some time back...way too big for the
job, but we just had to hook it up, don't you know. Sucked the pots right
off the turntable the first time it was run, probably moving 20,000 cfm
through a 40x50" booth. Choking down the intake to the fan created the
overspeed situation I was talking about. Of course this was a 240 3 phase
motor rated at I think 3 hp...originally used to blow the clay from the
hammer mills up to the top of the holding silos, 100' up :^)
Later,
Tommy
----- Original Message -----
From: "vince pitelka"
To:
Sent: Friday, July 26, 2002 12:30 AM
Subject: Re: FORCED AIR/REDUCTION
> > Some blower motors, I know that the ones that we use, are rated to run
at
> a
> > specific speed in relation to the power drawn. If we restrict the air
to
> > some of the blowers the motor will begin to overspeed due to lack of air
> > resistance to the cage...an hour or so of this overspeed and the circuit
> > breakers begin to pop. If your motors are designed as variable speed
then
> > that might be the difference. I am not an electrician, so am not at all
> > fluent on what happens here...I can ask the 'lectritian at work for the
> low
> > down if you want.
>
> Thanks Tommy. I am referring to the small squirrel-cage blowers found on
> Alpines and on the Harry Dedell/Marc Ward power burners. With those ones
it
> does not seem to be a problem at all to regulate the primary air by use of
a
> swinging shutter over the intake.
>
> I think that this depends on the kind of air impeller. Vane-type blowers
> such as are found on vacuum cleaners or on some larger industrial power
> burners will bog down if you restrict the intake, but that does not seem
to
> be the case with most squirrel-cage blowers.
> Best wishes -
> - Vince
>
> Vince Pitelka
> Appalachian Center for Crafts
> Tennessee Technological University
> 1560 Craft Center Drive, Smithville TN 37166
> Home - vpitelka@worldnet.att.net
> 615/597-5376
> Work - wpitelka@tntech.edu
> 615/597-6801 ext. 111, fax 615/597-6803
> http://www.craftcenter.tntech.edu/
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
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