Hank Murrow on mon 27 sep 04
On Sep 27, 2004, at 7:43 PM, Fredrick Paget wrote:
> Nowdays we could build a controller to handle it.especially since
> there are now, spiral cut Globar tubes that run on a much higher
> voltage / lower current.
>
> Hank , if I strike it rich, I will let you build one for me.
Hey Fred;
I can hardly wait to deal with the local Building Dept. on this! The
advantage of the spiral cut rods is that they are terminated at one
end, the current going down one side of the helix and running back up
the other, which is perfect for a lifting kiln. Very pricey, but
elegant. feed in a little H2 for reduction and you are home free, or as
near to it as you'll get. Good luck in the Lotto.
Cheers, Hank
murrow.biz/hank
Ron Roy on mon 27 sep 04
A friend of mine called and described a combination glowbar and gas kiln he
saw in Korea.
He seems to think this is the future.
Anybody got any experience with this technology?
What is the down side of using glow bars?
Thanks - RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jim Murphy on mon 27 sep 04
Hi Ron,
I've read about the new "Globar SD" SiC elements in Ceramic Industry
Magazine, but, these are of course "electrical". Don't know any specifics
about combining electric & gas in a furnace.
Here's a couple web references below - including Kanthal - regarding Globar
elements.
www.ceramicindustry.com/ci/cda/articleinformation/features/bnp__features__it
em/0,,132209,00+en-uss_01dbc.html
www.kanthal.com
Hope this helps.
Jim Murphy
Fredrick Paget on mon 27 sep 04
>A friend of mine called and described a combination glowbar and gas kiln he
>saw in Korea.
>
>He seems to think this is the future.
>
>Anybody got any experience with this technology?
>
>What is the down side of using glow bars?
>
>Thanks - RR
Whoa!What are we talking about here? Kiln elements or ignition devices?
--
From Fred Paget, Marin County, California, USA
fredrick@well.com
Hank Murrow on mon 27 sep 04
On Sep 27, 2004, at 10:07 AM, Ron Roy wrote:
> A friend of mine called and described a combination glowbar and gas
> kiln he
> saw in Korea. He seems to think this is the future. Anybody got any
> experience with this technology?
>
> What is the down side of using glow bars?
Dear Ron;
I investigated Glow Bars for possible use in my Doorless Fiberkiln. The
upside is a completely sealed kiln that may be reduced with a small
admixture of hydrogen gas fed to the chamber for exquisite atmosphere
control. The downside is pretty severe price penalty for the controls
to regulate the high voltage electricity they require.
Betty Feves lived and potted in eastern Oregon, and she had a glow bar
kiln. Also, they used to have one at Cranbrook.
I would love to outfit one of my lifting kilns with a glow bar system,
so I hope someone steps up to the plate to oreder one some day.
Cheers, Hank
murrow.biz/hank
David Hendley on mon 27 sep 04
----- Original Message -----
>
> What is the down side of using glow bars?
>
They can break, and they are very expensive to replace.
We had one at my college in the '70's (glowbar only, no
gas). It was a great kiln that could easily handle cone 10.
It weighed about 5 times more than a typical electric
kiln, with a heavy frame and 9" thick walls, producing
very cost-effective firings.
David Hendley
david@farmpots.com
http://www.farmpots.com
Wayne on mon 27 sep 04
Yikes!
Bad, BAD idea! Shame on them! Somebody smack those engineers in the
head with a large pot of kimchee! A METAL pot!
I have an AMANA gas stove/oven (1998 new). The burners on top use
the standard piezo-electric "click-click-click" lighters. No
electric needed. Work unless the burner gets wet.
One day the oven wouldn't light. The oven uses that miserable=20
(insert your choice of expletives here!) glowbar. The glowbar uses
a ceramic element that heats up, and is "sensed" as being hot enough
(bright enough!) by some type of optical sensor. If all goes well,
it senses, and turns the gas valve on, and the burner lights. The
sensor had failed, hence the oven wouldn't light.
(Manufacturers adopted this to eliminate pilot lights (allegedly to
save gas) while ensuring that normal morons, er, regular folk didn't
blow themselves to their final rewards. ("Duh...gee, why ain't the
oven comin' on? Turned it on about 15 minutes ago! Think I'll just
look inside with this here match, and....")
Long story short: it cost me $147.50 to replace the glowbar
"assembly" (And I get a break because we clean our appliance tech's
house). The assembly has failed once every two years, requiring yet
another trip out to replace it...three trips so far, at $150 a pop!
AND, if you don't have electric, it just can't be bypassed. Forget
the oven then. At least we can still light the burners on the top.
All this to save about $12 a year in propane? Sheesh!
Would I buy another? Do I need to ask that question? It would be
cheaper to buy another stove. Pilot lights work...every time, all
the time. Stay away from those damn glowbars.
Sorry for the rant,
Wayne Seidl
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Monday, September 27, 2004 1:08 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Glowbars and gas kiln???
A friend of mine called and described a combination glowbar and gas
kiln he
saw in Korea.
He seems to think this is the future.
Anybody got any experience with this technology?
What is the down side of using glow bars?
Thanks - RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Marcia Selsor on mon 27 sep 04
I only have experience with glowbars, but the technology seems like it
would work since the "elements" are silicon carbide and would not
corrode in a reduction atmosphere.
The down side is this. One student at Southern Illinois University
fired the glowbar kiln firing home made bricks..a solid load. Glowbars
work on radiant heat. This solid mass firing proved too much for the
glowbars and ruined them. The instructor was really upset. It was a
fairly new kiln. I think they are very expensive elements.
Marcia Selsor in Montana.
On Sep 27, 2004, at 11:07 AM, Ron Roy wrote:
> A friend of mine called and described a combination glowbar and gas
> kiln he
> saw in Korea.
>
> He seems to think this is the future.
>
> Anybody got any experience with this technology?
>
> What is the down side of using glow bars?
>
> Thanks - RR
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> _______________________________________________________________________
> _______
> 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.
>
David Hendley on mon 27 sep 04
----- Original Message -----
>
> Whoa!What are we talking about here? Kiln elements or ignition devices?
>
Wayne & Fred ~ we are talking about silicon carbide kiln "elements".
David Hendley
david@farmpots.com
http://www.farmpots.com
Jim Murphy on mon 27 sep 04
Ron,
Did some more thinkin'.
I DO recall reading somewhere [American Ceramic Society Bulletin perhaps
???] about industrial "tunnel kilns" firing both with gas and with electric
SiC elements.
I believe these tunnel kilns use "gas" for most stages of firing where they
may use "reduction" if they desire. The ware moves through the tunnel and
finally enters a controlled "cooldown zone".
I think electric [Globar SD] SiC elements are used in the controlled
cooldown zone region of the tunnel kiln.
Best wishes,
Jim Murphy
Hank Murrow on mon 27 sep 04
Dear Wayne; The Glow Bars Ron and I are referring to are waaaay more
expensive than the tiny ones you describe, and are made of SiC, and are
big (for my Doorless Fiberkiln they were 40" long and 1.5" diameter).
An entirely different animal, and industrial in nature.
cheers, Hank
murrow.biz/hank
On Sep 27, 2004, at 10:24 AM, Wayne wrote:
> Yikes!
> Bad, BAD idea! Shame on them! Somebody smack those engineers in the
> head with a large pot of kimchee! A METAL pot!
>
> I have an AMANA gas stove/oven (1998 new). The burners on top use
> the standard piezo-electric "click-click-click" lighters. No
> electric needed. Work unless the burner gets wet.
> One day the oven wouldn't light. The oven uses that miserable
> (insert your choice of expletives here!) glowbar. The glowbar uses
> a ceramic element that heats up, and is "sensed" as being hot enough
> (bright enough!) by some type of optical sensor. If all goes well,
> it senses, and turns the gas valve on, and the burner lights. The
> sensor had failed, hence the oven wouldn't light.
>
> (Manufacturers adopted this to eliminate pilot lights (allegedly to
> save gas) while ensuring that normal morons, er, regular folk didn't
> blow themselves to their final rewards. ("Duh...gee, why ain't the
> oven comin' on? Turned it on about 15 minutes ago! Think I'll just
> look inside with this here match, and....")
>
> Long story short: it cost me $147.50 to replace the glowbar
> "assembly" (And I get a break because we clean our appliance tech's
> house). The assembly has failed once every two years, requiring yet
> another trip out to replace it...three trips so far, at $150 a pop!
> AND, if you don't have electric, it just can't be bypassed. Forget
> the oven then. At least we can still light the burners on the top.
>
> All this to save about $12 a year in propane? Sheesh!
> Would I buy another? Do I need to ask that question? It would be
> cheaper to buy another stove. Pilot lights work...every time, all
> the time. Stay away from those damn glowbars.
>
> Sorry for the rant,
> Wayne Seidl
Hank Murrow on mon 27 sep 04
On Sep 27, 2004, at 11:03 AM, David Hendley wrote:
> Glo Bars can break, and they are very expensive to replace.
> We had one at my college in the '70's (glowbar only, no
> gas). It was a great kiln that could easily handle cone 10.
> It weighed about 5 times more than a typical electric
> kiln, with a heavy frame and 9" thick walls, producing
> very cost-effective firings.
Coming down through the roof of my lifting design, they would be very
effective, if expensive, and the whole kiln (28 cu ft) would weigh
around 1500 pounds. 800# for the pad and 700# for the lifting part.
Since the kiln would have 8" fiber walls and be completely sealed, it
would retain the efficiency of the kilns you describe. I have had the
engineers do an energy analysis on electricity usage, and in Oregon, it
comes out to $12 per firing for Cone 10 over 20 hours (I like long
fires...... glazes like 'em too), reduction or oxidation.
Cheers, Hank
murrow.biz/hank
Fredrick Paget on mon 27 sep 04
>----- Original Message -----
>>
>> Whoa!What are we talking about here? Kiln elements or ignition devices?
>>
>
>
>Wayne & Fred ~ we are talking about silicon carbide kiln "elements".
>
>David Hendley
OK Just so we keep them straight. Silicon carbide kiln elements were
trade marked
"Globar "not glow bars. The glow bars are those finicky gas oven lighters.
There is a student at SanFrancisco State University who contacted me
last week about one of these old Alpine Globar kilns. They have one
there at State and he is going to try to resurrect it. He wanted to
know if I knew of an instruction manual for the kiln with the wiring
diagram.
Let me know and i will pass it on to him if anybody can come up with
one or a reference??
He says he is an E.E. student (Electrical Engineering) so I gave him
a few pointers and he is off and running.
There used to be one of these at San Jose State College (before it
became University) in Herbert Sanders lab. There is a picture of it
in his book. Also there was one I knew about in the 1950's at a
pottery called Skyline pottery on the road on top of the coast range
mountains near San Francisco.
The big draw back besides expense with those was the very low
voltage, high current that those solid rods consumed and the fact
that they changed with age so a stable setting was impossible. The
current had to be adjusted with a special, big, heavy transformer and
switch, to get the heat level you needed.
Nowdays we could build a controller to handle it.especially since
there are now, spiral cut Globar tubes that run on a much higher
voltage / lower current. Contemporary Kilns in Novato here in Marin
County makes some industrial furnaces using these. The owner had a
little working model in his office of one for exhibit at trade
shows, that ran plugged into 120 volts.
Those old Alpine Globar kilns would go to cone 16, I understand, and
reduction does not harm the Globar element.
Hank , if I strike it rich, I will let you build one for me.
Fred
--
From Fred Paget, Marin County, California, USA
fredrick@well.com
Ron Roy on tue 28 sep 04
Thanks Jim,
A bit more information about that kiln - they take it up to around 800C
with the glow bars - then start adding some gas to get reduction - not a
lot. Seems electricity is cheaper to fire with there than fosil fuels. Lots
of mountains and rivers to generate power.
The main reason I am asking is - what effect does reduction have on glow bars.
What we are talkig about here is an electric kiln with gas introduced for a
reducing atmosphere.
RR
>I've read about the new "Globar SD" SiC elements in Ceramic Industry
>Magazine, but, these are of course "electrical". Don't know any specifics
>about combining electric & gas in a furnace.
>
>Here's a couple web references below - including Kanthal - regarding Globar
>elements.
>
>www.ceramicindustry.com/ci/cda/articleinformation/features/bnp__features__it
>em/0,,132209,00+en-uss_01dbc.html
>
>www.kanthal.com
>
>Hope this helps.
>
>Jim Murphy
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Joyce LEE on tue 28 sep 04
ok
----- Original Message -----=20
From: Wayne=20
To: CLAYART@LSV.CERAMICS.ORG=20
Sent: Tuesday, September 28, 2004 10:50 AM
Subject: Re: Glowbars and gas kiln???
My apologies to the list. I saw "Glowbar" and not "Globar" in Ron's
original post. Two different animals. Wasted a totally good rant
.
Wayne Seidl
slinking off to help ol' Blue eyes load her kiln and look at cones
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of David
Hendley
Subject: Re: Glowbars and gas kiln???
> Whoa!What are we talking about here? Kiln elements or ignition
devices?
>
Wayne & Fred ~ we are talking about silicon carbide kiln "elements".
David Hendley
david@farmpots.com
http://www.farmpots.com
=
_________________________________________________________________________=
_____
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.
Hank Murrow on tue 28 sep 04
On Sep 27, 2004, at 11:20 PM, Ron Roy wrote:
>
> A bit more information about that kiln - they take it up to around 800C
> with the glow bars - then start adding some gas to get reduction - not
> a
> lot. Seems electricity is cheaper to fire with there than fosil fuels.
> Lots
> of mountains and rivers to generate power.
>
> The main reason I am asking is - what effect does reduction have on
> glow bars.
>
> What we are talkig about here is an electric kiln with gas introduced
> for a
> reducing atmosphere.
The Glo Bars love a reduction atmosphere. It is simpler to just bleed
in a little Hydrogen from a small bottle for reduction when ever you
want it. More effective.
Cheers, Hank
murrow.biz/hank
Joyce LEE on tue 28 sep 04
ok
----- Original Message -----=20
From: Jim Murphy=20
To: CLAYART@LSV.CERAMICS.ORG=20
Sent: Tuesday, September 28, 2004 12:40 PM
Subject: Re: Glowbars and gas kiln???
Ron Roy at ronroy@CA.INTER.NET wrote:
<adding some
gas to get reduction - not a lot. ... What we are talking about here =
is an
electric kiln with gas introduced for a reducing atmosphere.>>
Thanks Ron,
I sure got that one backwards. I feel humbled ["greatness" must surely =
be
just around the corner]. In the future, I'll skim through industrial =
kiln
design articles "more slowly".
<glow
bars.>>
All SiC elements will react (oxidize) with the furnace atmosphere and
degrade over time. "Porosity" and "Average Grain Size" appear to be =
key in
engineering newer longer-life Globar SD (recrystallized SiC) elements =
per
the following quote from Kanthal's website:
"Porosity and average grain size are the two main features that =
determine
the life and performance of recrystallised silicon carbide heating =
elements.
The new Kanthal Globar SD elements are less porous than other Kanthal
elements and have a relatively large grain size. These features reduce =
the
total surface area of silicon carbide that is exposed to the furnace
atmosphere, and this reduces the rate of resistance increase over =
time."
Hope this helps Ron.
Best wishes,
Jim Murphy
=
_________________________________________________________________________=
_____
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.
Earl Brunner on tue 28 sep 04
Aren't the Glowbars silicon carbide? Shouldn't be any affect at all.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Monday, September 27, 2004 11:20 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Glowbars and gas kiln???
Thanks Jim,
A bit more information about that kiln - they take it up to around 800C
with the glow bars - then start adding some gas to get reduction - not a
lot. Seems electricity is cheaper to fire with there than fosil fuels. Lots
of mountains and rivers to generate power.
The main reason I am asking is - what effect does reduction have on glow
bars.
What we are talkig about here is an electric kiln with gas introduced for a
reducing atmosphere.
RR
Ron Roy on tue 28 sep 04
Thanks again Hank - RR
>On Sep 27, 2004, at 11:03 AM, David Hendley wrote:
>
>> Glo Bars can break, and they are very expensive to replace.
>> We had one at my college in the '70's (glowbar only, no
>> gas). It was a great kiln that could easily handle cone 10.
>> It weighed about 5 times more than a typical electric
>> kiln, with a heavy frame and 9" thick walls, producing
>> very cost-effective firings.
>
>Coming down through the roof of my lifting design, they would be very
>effective, if expensive, and the whole kiln (28 cu ft) would weigh
>around 1500 pounds. 800# for the pad and 700# for the lifting part.
>Since the kiln would have 8" fiber walls and be completely sealed, it
>would retain the efficiency of the kilns you describe. I have had the
>engineers do an energy analysis on electricity usage, and in Oregon, it
>comes out to $12 per firing for Cone 10 over 20 hours (I like long
>fires...... glazes like 'em too), reduction or oxidation.
>
>Cheers, Hank
>
>murrow.biz/hank
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on tue 28 sep 04
Thanks again Jim - RR
>Did some more thinkin'.
>
>I DO recall reading somewhere [American Ceramic Society Bulletin perhaps
>???] about industrial "tunnel kilns" firing both with gas and with electric
>SiC elements.
>
>I believe these tunnel kilns use "gas" for most stages of firing where they
>may use "reduction" if they desire. The ware moves through the tunnel and
>finally enters a controlled "cooldown zone".
>
>I think electric [Globar SD] SiC elements are used in the controlled
>cooldown zone region of the tunnel kiln.
>
>Best wishes,
>
>Jim Murphy
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jim Murphy on tue 28 sep 04
Ron Roy at ronroy@CA.INTER.NET wrote:
<gas to get reduction - not a lot. ... What we are talking about here is an
electric kiln with gas introduced for a reducing atmosphere.>>
Thanks Ron,
I sure got that one backwards. I feel humbled ["greatness" must surely be
just around the corner]. In the future, I'll skim through industrial kiln
design articles "more slowly".
<bars.>>
All SiC elements will react (oxidize) with the furnace atmosphere and
degrade over time. "Porosity" and "Average Grain Size" appear to be key in
engineering newer longer-life Globar SD (recrystallized SiC) elements per
the following quote from Kanthal's website:
"Porosity and average grain size are the two main features that determine
the life and performance of recrystallised silicon carbide heating elements.
The new Kanthal Globar SD elements are less porous than other Kanthal
elements and have a relatively large grain size. These features reduce the
total surface area of silicon carbide that is exposed to the furnace
atmosphere, and this reduces the rate of resistance increase over time."
Hope this helps Ron.
Best wishes,
Jim Murphy
Wayne on tue 28 sep 04
My apologies to the list. I saw "Glowbar" and not "Globar" in Ron's
original post. Two different animals. Wasted a totally good rant
.
Wayne Seidl
slinking off to help ol' Blue eyes load her kiln and look at cones
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of David
Hendley
Subject: Re: Glowbars and gas kiln???
> Whoa!What are we talking about here? Kiln elements or ignition
devices?
>
Wayne & Fred ~ we are talking about silicon carbide kiln "elements".
David Hendley
david@farmpots.com
http://www.farmpots.com
Bob Masta on wed 29 sep 04
A couple more points about silicon carbide "Globar"-type
elements. On the plus side, they last a long time if
they are treated right. Depending on type, they are
rated at 5000 to 9000 hours before the resistance
increases 50%. I don't know how long it takes to go
another 50%, but the elements in my little kiln are from
a very old (1950's?) Burrell industrial test furnace that
were at about 100% when I got it.
I think the value for the money is probably pretty high.
I've never seen a price list, and elements are apparently
all custom made. But in buying elements for my new kiln
I had a chance to get some prices. The old elements had
a 10 inch hot zone (plus the cold ends that pass through
the kiln walls), and these were quoted in the $50 range
each. But longer elements only seemed to go up by maybe
a dollar per inch above that.
SiC elements are very low resistance, about 1 ohm per
foot for 0.75 inch diameter rods. That means you need
high current at low voltage, which is why older setups
like mine used massive transformers. And they don't like
sudden current inrush or rapid temperature increase, so
the transformers were adjustable. Nowadays this can be
done electronically with the equivalent of a giant lamp
dimmer that chops up the incoming voltage, but there is
still that high current problem. High current means high
losses and thus high heating in the solid state
controller devices, which is *not* where you want it.
You don't want to use a simple on-off "infinity" control
like on standard electric kilns, since those produce too
much current surge when the elements are cold. (I'll
share my controller design with the group when I get it
finished.)
Oh, yeah. You need monster cables to connect these
elements without losing power to heating the cable at
these high currents. These are typically flat aluminum
braid that look like big car battery ground straps. They
wrap around the ends of the bars and are held in place
with spring clips. You want to keep these cables
short. I don't know what modern installations use for
cable insulation; mine use what appears to be heavy woven
asbestos cloth. (Shhh! Don't tell Homeland Security
I have a potential terrorist weapon here!)
You might think about putting a number of elements in
series to get a higher total resistance and thus a lower
current for any given power. The problem is that
elements don't all age at the same rate. If the
resistance of one starts to increase, it will end up with
more of the power, which will of course cause further
acceleration of its resistance increase. Big operations
can keep an eye on this and keep all their old elements
to try to find a match with the remaining series elements
when one is replaced, but it sounds like a lot of messing
around. Probably easier to just have a couple in series
and expect to replace them together.
One other issue is that the hot zone of an element must
not be too close to anything reflective, like kiln brick.
So you can't tuck these into grooves in the wall like
regular wire elements. There must be a space at least as
big as the diameter of the bar. For my 0.75 inch bars,
that means the bar reaches 1.5 inch from the wall.
That's a big loss of space in a small kiln, but it's also
a concern because you really don't want to have anything
bump it when it's hot, nor have glaze drip onto it.
Luckily (?) my kiln is so small that I can't really do
much that could be called "stacking", but I'd guess you'd
have to be pretty careful in a bigger kiln.
Just my two cent's worth...
Bob Masta
potsATdaqartaDOTcom
Hank Murrow on thu 30 sep 04
On Sep 30, 2004, at 10:11 PM, Ron Roy wrote:
>
> The first kiln shelves I ever had for my gas kiln were silican carbide
> -
> heavy mothers - 1 inch thick - I don't think the alumina shelves were
> even available back then.
>
> Those sheves "grew" - got thicker in the center over time - in other
> words- became slightly rounded.
>
> Does anyone have an explanation about why - I thought it was the
> reduction ???
Dear Ron;
The Norton/St.Gobain engineer says that it happens from oxidation. The
SiC stepped posts I bought from Ferro started out at 28" in length. Now
after 260 fires they measure 28.75" in length. 3/4"! Supposedly, the
Advancer materials do not do this.
Cheers, Hank
murrow.biz/hank
Ron Roy on fri 1 oct 04
Hi Earl,
The first kiln shelves I ever had for my gas kiln were silican carbide -
heavy mothers - 1 inch thick - I don't think the alumina shelves were even
available back then.
Those sheves "grew" - got thicker in the center over time - in other words
- became slightly rounded.
Does anyone have an explanation about why - I thought it was the reduction ???
RR
>Aren't the Glowbars silicon carbide? Shouldn't be any affect at all.
>
>Earl Brunner
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
steve harrison on sat 2 oct 04
> Those sheves "grew"... I thought it was the reduction ?
Hi Ron Roy,
I've experienced that phenomenon with some of my silcarb shelves.
I think that it is not so much the reduction, but the opposite, it is
the oxidation.
Some of those old silcarb shelves had the silcarb granules bonded
together with a glassy matrix, the whole shelf having a brown glassy
look.
During any oxidation phase, especially at higher temperatures, some of
the carbon would oxidise from the silicon carbide granule and pass out
to the atmosphere through the glassy bond matrix, causing the glassy
phase to foam up a bit, just like adding silcarb powder to a glaze.
Hence the shelves got slightly thicker over many firings.
Best wishes
Steve Harrison
Hot & Sticky Pty Ltd
5 Railway Pde
Balmoral Village
NSW 2571
Australia
http://ian.currie.to/sh/Steve_Harrisons_books.html
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