Fredrick Paget on thu 5 apr 07
Globar kilns were in use here in USA back in the 1960's . There was a
Globar kiln made by Alpine. That company is long out of business and
the assets acquired by a new outfit that have no recollection of
those days. There are still a few of these old Globar kilns around
like dinosaur skeletons. Most are not in working order. Thery would
reach cone 16.
The Globar element is not like your trusty Kanthal element. You can't
just plug it in. It takes special electrical conditioning equipment
to fire it. The bulk Globars had a very low resistance so a low
voltage at high current was used supplied by a very large
autotransformer. It was all manual control and since the resistance
changes as the Globars age the settings on the autotransformer
switch are different .
Kiln design had to be different since the Globars are long straight
rods, they have to be mounted in a straight line. The ends sticking
out of the insulated kiln so that heavy wires can be clamped on to
the ends (which are metalized to provide electrical contact).
I have seen a newer type of Globar that is a hollow tube with a
spiral cut through to the hole in the middle. This gives a form that
has the shape of a spring but is not 'springy' indeed it is quite
rigid. But it does give a straight element that is of higher
resistance because the length is long and the cross section is small.
It will run on higher voltages and lower current. It does need some
form of power electronic control to take care of the changing
resistance with temperature and age.
I have been told by the man who ran Contemporary Kilns in Novato,
California, near here that a real nice potters kiln could be built
with these spiral Globars for about $10000 . That was 10 years ago
so the price might be double by now.
There are other kinds of elements yet that are used in high
temperature industrial furnaces. One is Moly disilicide. I don't know
much about them . They are in the form of a long thin rod formed into
a hairpin loop. I sort of wonder it those Japanese kilns have
elements of this material as the large cross section of the element
Lee illustrated on his Blog would have a very low resistance if it is
Kanthal and would run at a pretty low voltage. Of course the Japanese
electrical service is at 100 volts and maybe they have enough length
in the element to run on 100 volts. Maybe one of our Japanese
readers could clarify this?
Fred Paget
--
Twin Dragon Studio
Mill Valley, CA, USA
Bonnie Staffel on sat 7 apr 07
Hi Fred,
When I studied at Cranbrook in 1951/52 they had a very large globar =
kiln. I
don't recall the name of it. It fired my glazes beautifully and when I =
did
the same at home, there was no comparison. One of my glazes came out in
such a special way that Maija Grotell even commented that it was the =
most
beautiful glaze she had ever seen. Wow, that was something. However, =
when
I did the same glaze in my electric kiln, instead of the rich browns and
beige colors, mine came out dark gray and beige. At that time I also =
did
all my glazing on raw clay as we were charged by the cubic inch, and =
being
somewhat poor, I was able to save money that way. Nothing ever broke. =
I
believe it was a very slow firing. =20
There was always the possibility of these globars being broken if =
bumped. I
remember they were expensive to replace. Also available was a very =
small
Revelation Kiln that students could fire by themselves. Catherine Choy =
was
a student at the same time and I recall she was always experimenting in =
that
one. Sorry to say, she passed away early in her career after leaving
school.
When I was teaching in Denmark, they had a huge electric kiln with very
heavy thick coiled wires. I didn't inquire as to what they were made of =
but
I sure did want one of those kilns as it had a tunnel in the floor in =
which
one could introduce slender wood sticks or candles for reduction. It =
was
also a three-phase kiln. They were manufactured in England at the time =
and
most all the potters I met had this kiln in various sizes. =20
I purchased a kiln made by the Reduction Production Company back in the =
70's
and it had a drawer in the floor of the kiln where you could put =
charcoal to
introduce a reduction atmosphere. The floor hole was covered by a pair =
of
split shelves. The coils were also thicker and wound around an inch in
space. I had great reduction results with this kiln for a while but the
controls started to fail and the company itself went into bankruptcy so =
was
not available for repairs. However, when I left Charlevoix to go to NC, =
I
gave the kiln to a friend and it is still in operation for his bisque
firing. =20
Thanks for bringing these memories back to mind.
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Introduction to Wheel Work
Charter Member Potters Council
( Arial) on sun 8 apr 07
I have fired a glowbar kiln but that newly reworked kiln[new bars] is now
dormant and the designer has passed on and the program is no longer at that
site but the kiln may still be there.
Margaret
************************************** See what's free at http://www.aol.com.
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