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IRON HERE AND THERE
Wesley Jacobs
2013
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Wesley Jacobs WCMT Report August 2013
Contents
Section Title
1. Abstract2. Aims & Objectives of Fellowship Trip
3. Fellowship Trip Itinerary
4. Iron Casting Overview (History & background to trip)
5. Findings: Continuous/Intermittent/Cupolette Furnaces
6. Observed technical improvements7. Recommended reading
8. Conclusions & recommendations
9. Glossary
10. Appendices
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1. Abstract
This report details the information gleaned on a Winston Churchill
Fellowship trip to the USA in March-April 2013.
It will eventually form the basis of a manual and comparison table
detailing the operation of cupola furnaces and their various forms
(Continuous, Intermittent & Cupolette). There is not a known
manual in UK for running a cupola furnace for casting iron
sculpture, and the practical experience gained on my Fellowship
trip along with recommended reading and observed technical
improvements will be of benefit to the small British iron art-
casting community.
The report does not detail the history of iron casting, which is in
itself another, extensive research project. It does highlight
however, best practice observed in the USA and charts some of
the changes and future challenges faced by contemporary iron
sculptors.
2. Aims & Objectives of the Fellowship Trip:
• Better understanding of intermittent furnaces
• Construction and operation of intermittent furnaces
• Experience of the running of symposia & open workshops
•
Practical experience of running a fine art foundry within a
university
• Understanding material limits and new product research
• New mould-making methods for iron & bronze casting
• Fuller understanding of equipment, processes and health-and-
safety around metal casting
• Relationship between Industry and Academia within iron art
casting
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• Work with and learn from practising sculptors using cast iron in
their work
After the Fellowship Trip:
• Modifying furnaces and assisting others to make or modify
furnaces
• Sourcing new products to maximise efficiency and quality of
castings
• Understanding of environmental impact and improvements in
iron casting to create best practice papers.
3. Fellowship Trip Itinerary:
• Attend Iron Tribe Exhibit, address delegates on 8th
March.
• Shadow and work with Sculpture Professor David Lobdell at
University of New Mexico.
•
Attend Tucumcari Iron Pour as crew member & observer• Observe and work with Gerry Masse at ‘Sculpture Trails’
(Solsberry, Indiana)
• Work with Jim Wade & Jeremy Colbert (University of Kentucky
at Lexington)
• Attend SLOSS ‘National Conference on Contemporary Cast Iron
Art’ as a delegate & crew member
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4. Iron Casting Overview
Iron Casting has been happening for thousands of years all over the
world, at the same points in history. Some continents advanced the
practice more than others, at various times - and investigation intothe smithing and/or production of metals has formed a foundation
for our current society and advancement into the technological age.
Iron is still the most important material that man wields.
The man credited with the most significant advancement in the
production of cast iron (and making of pots and other domestic
objects) was Abraham Darby I. A Staffordshire-born Quaker, he grew
up in a world of metal working, predominantly brass, in the Bristol
area. He was an inventive man who intelligently challenged pre-
conceived ideas about the mining of ores and the smelting of the ore
into metal. He had grown up with metal in his blood. His famous
experiments into the use of coke as a fuel began with melting brass.
The smelting of iron to extract the metal from the ore had, for
hundreds of years, used charcoal as fuel. The supply of charcoal was
becoming exhausted in the late 1600s, since trees were beingstripped away as the demand for the fuel grew. Darby bought an old
charcoal-fuelled furnace in the gorge at Coalbrookdale in Shropshire.
There was, in Coalbrookdale, a natural abundance of coal, iron ore
and limestone. Darby continued to experiment with coking coal,
which was a fuel available in abundance throughout England. Coke is
purified coal, manufactured by baking at extremely high
temperatures in coking ovens and then immediately quenching
before the coal fully combusts. This procedure eliminates impurities
found in coal and produces a fuel that burns hotter for longer.
His descendants, Abraham Darby II & III, continued the legacy he
began by commercialising cast iron as an everyday product (the
plastic of its time). As well as conceiving, engineering and making the
famous Iron Bridge in Coalbrookdale, they started to use cast iron to
make artistic objects in the form of fountains and statues.
The medium of cast iron is very versatile. The sculptural properties ofiron, when cast, are not too dissimilar to bronze - extreme detail can
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be achieved, the material has longevity and it is strong. Iron is,
however, difficult to wield because of the higher temperatures
required to melt it and because of its brittle state once cast.
By the middle of the nineteenth century, the foundry in
Coalbrookdale was the largest in the world and the company
continued making functional objects and art castings.
Two hundred years later, and two thousand miles away, several
sculptors in the USA became interested in having a more hands-on
experience of casting their own sculpture rather than sending their
work to commercial foundries to be cast.
One of these investigative sculptors was Julius Schmidt. If he wasunable to make what he envisaged because the tools or materials he
required did not exist in the art world, he looked for them in
industry, or made them himself. He was looking for a practical
method of casting iron sculpture which would not require the
equipment of a commercial foundry. His first adaptation from
industry to the backyard foundry was to make carved piece-moulds
using bonded sand, inspired by motor industry professionals he saw
casting engine blocks in this way.
Using scrap materials, he learned how to build a small cupola furnace
suitable for use in an artists’ workshop, whilst serving as Chairman of
the Sculpture department at Kansas City Art Institute 1955-59. From
then, cupola furnace building spread throughout art departments in
US universities and became an important part of the sculpture
teaching programmes. This eventually became what is known among
iron art casters as the US-led ‘Iron Pour Movement’. Since the late1980s, American professors have been coming to the UK to learn
more about the heritage of the iron casting process. In doing so, they
made connections with art colleges, universities and independent
establishments and shared their furnace-building and mould-making
techniques. This equipped UK sculptors to connect with the process
of making their own cast iron sculpture.
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My first introduction to art casting was as a student at Norwich
School of Art & Design. I had an experience of casting bronze during
an exchange trip to Kansas State University, where I met and worked
with Professor Daniel Hunt. Post-art school, I was invited as an
emerging sculptor to a cast iron workshop at the Museum of Steel
Sculpture (MOSS) in Ironbridge. I received more teaching and
experience during this workshop than I had at art school. It was a
crash course into iron casting and I discovered a love for our long
history as a nation of ‘makers’ and one-time leaders in industry. This
exciting week of hard graft, dirty, dangerous explosive processes was
one of the major life-changing events that catapulted my enthusiasm
to make and to learn as much as I could about casting and sculpture.In Oxfordshire, space became available to me to expand my studio
into a larger enterprise - so The Bullpen, a new business, was born.
In this establishment I set up a place to share, teach and draw artists
back into the workshop. I also wanted to excite and encourage artists
to brave the constraints of not having the skills to make their own
work, and to allow artists to have the freedom of creating in a safe &
encouraging environment together in a community. The first major
project run at The Bullpen was in collaboration with Daniel Hunt
from Kansas State University and Oxford Engineering - and ‘Belle’,
the UK’s first Continuous-flow cupola was designed, constructed and
operated with resounding success.
The iron casting processes used by artists/teachers who cast their
own work today are intensely physical. Whilst demanding strength,also allow adults of any age or ability to experience the freedom of
working together as a team. This teamwork is fundamental for the
successful operation of a cupola furnace for casting iron.
There is a grit and determination needed to see through the process
(which is repeated over and over for hours at a time):
From sand-mould making through to the organising of equipment,
the breaking up of iron and coke, the weighing out of these into
charges, the lighting of the furnace, continual charging of the
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furnace, operating the furnace, the tapping out of the iron into
ladles, ‘botting’ the furnace to refill it, to pouring the iron into the
moulds - and so it goes on.
Not many people know about this process, and to explain and
successfully communicate it to people is not easy. In many ways it
seems fitting that this process is used to make art, which is a non-
verbal expression of something. Iron is harder to wield than bronze -
it brings about a more industrial quality to the melting of the metal.
There is a more depth to the process of melting it, which somehow
adds to the narrative of the finished sculpture. The cast iron art
object made in this dangerous and exciting way is a reflection of the
quality and authenticity of its birth from the furnace, in a language offeeling, form and emotion.
5. Findings
Continuous/Intermittent/Cupolette Furnaces: A comparison
Before my Fellowship trip, I was familiar with the workings of one
form of cupola furnace since I am a furnace operator myself. I run a
Continuous-flow Cupola furnace for casting iron. There are variations
of cupola furnaces for iron casting that I observed and monitored on
my trip which have led to my creating a comparison table and basic
analysis of the running of each furnace. This forms the majority of my
findings.
Basic description of any cupola furnace:
Cupola furnaces have been in use since the late seventeenth century
and have hundreds of different designs. Modern day blast furnaces
that extract iron from ore are basically larger versions of a cupola.
The cupola is a metal melting machine, predominantly for the
melting of iron. It is a cylindrical steel structure with a 2-4inch
refractory lining that coats the inside.
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The cupola can be made in many different sizes, from small
backyard-size to the monumental size (filling whole building) used in
industry today.
The furnace is comprised of three main units: Well, Wind-belt and
Stack.
At the bottom of the well is a door that opens and closes, and above
the door about a foot or so up is the wind belt . This is attached onto
the outside of the cylinder, and it has an opening where a blower is
attached.
The wind belt has four holes called tuyeres that open up and go all
the way through the depth of the wind belt, through the shell of thecupola and its lining, into the open cylinder of the furnace.
Just above the base door and below the wind belt is an opening
called a tap hole, which is a 2 inch hole that goes all the way through
into the furnace. Around the tap hole is a spout where the iron is
channelled out.
Further along to the left or right of the tap hole is a slag hole, from
which the slag on top of the molten iron will be siphoned off and
trickle out.
Spark arrester
Stack
Windbelt
Blower pipe
Well
‘Belle’, The Bullpen’s Continuous-flow cupola furnace
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Above the windbelt is a cylindrical stack reaching approximately 3-4
feet in height. This too is lined with refractory 2-4” thick.
Charges are weighed amounts of metal, coke and limestone that are
added to the furnace so the metal is continually in contact with the
fuel that melts it. The limestone in the charges acts as a flux (taking
impurities out of the liquid metal and making it more fluid) and it
also protects the collected pool of iron from oxidising. In the well,
large chunks of coke are positioned. They are super-heated by a
burner using forced air and propane to approximately 1500oC. Once
that coke bed is burning, the charges of coke, metal and limestone
are added. The burner is removed, and then air is forced around thewindbelt, fuelling the coke consumption and melting the iron at the
same time.
The three types of furnace designs used to cast iron (in the art
communities in which we operate) are a Continuous Cupola, an
Intermittent Cupola and a Cupolette. These furnace designs have
been in use since the 1950s and have gained popular appeal among
students, tutors and sculptors.
Continuous Furnace (Technical):
A Continuous-flow cupola is a uniquely designed cupola. Not many
exist, and they are rarely seen or used for casting iron in the iron-art
world. With this style of furnace the molten iron runs up and out of
the spout (as in a teapot) into pre-heated ladles, all in one
continuous flow whilst charges are added. Rather than having aspout that is plugged in between ‘taps’, a continuous furnace has a
siphon-type design within the spout construction. The spout is only
plugged during the burn-in of the furnace. Once a full well is
obtained, it is unplugged and a continuous stream of iron flows out
and is not stopped until the production of castings is complete.
On a Continuous, burn-in is achieved by using a forced-air and
propane burner that is put into the burn-in/drain port (which is to
the right of the spout). The burn-in/drain port should be centred 3”
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from the spout hole and 3” from the well unit, and the hole is 2”
wide.
Preparing the Continuous Cupola:
The furnace is positioned with legs attached and importantly levelled
with a spirit level. Then the bed sand is laid.
Stack
Windbelt
Tuyeres
Spout
Refractory lining
Bed sand
Well
Legs
Stack
Refractory lining
Windbelt
Tuyeres
Well
Spout
Bed sand
Burn-in drain port
Slagger
Cross section 1
Cross section 2
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To lay the furnace bed, the bed sand should come to just below the
spout inlet and the burn-in/drain port to form a well of a slightly
concave slope. The back of the slope rises to just below the tuyere
opposite the spout.
The pool is created by the slope that funnels the molten iron to
collect in the dip of an angled slope of sand. The iron is pushed up
towards and above the botted spout, and it rises up towards the slag
hole.
This is helped by the shape of the sloped sand-bed that is packed
tightly into the body of the furnace.
Bed sand recipe:18kg/40lb kiln-dried silica sand
8kg/18lb powdered bentonite clay
2 handfuls of fine sawdust
Mix with enough water to form a slightly tacky consistency (using a
spray-bottle).
Once mixed, the consistency should mean that if it is formed into a
ball it will hold its shape and can be split apart and separate into two
halves cleanly. If too much water is added, this will bind the sand and
clay together too strongly and will increase difficulty when removing
the bed at the end of the pour.
Once the bed has been laid, the bed coke has to be added. The
largest chunks of coke 4’’ or larger need to be carefully positioned in
the well, keeping in mind where the burn-in port is. A channel made
of coke pieces needs to be placed around where the forced air andpropane come in through the burn port. There needs to be space for
the flame of the burner to come into the well of the furnace in a y-
shaped motion. Above this channel of coke there needs to be more
coke of the same size, packed tightly and rising up into the well. This
will reach up to the top of the tuyeres with the stack not added at
this point. A gap is needed and coke pieces should not block the
tuyeres.
Approximately 25-30lbs/11-13kgs of coke is required to fill the well.
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To test if the bed coke is strong and compact enough once the bed is
laid, a heavy crew member can climb in and stand on the coke bed to
see if it moves. This adds pressure that will force the coke into
position, and when the bed is secure, the stack can be fixed into
place.
A well & stack seal compound needs to be added to the refractory in
the well to create a seal that joins the stack to the well below it.
Well & stack seal compound recipe:
2 parts bentonite to 1 part silica sand
Mix with water to a wet-clay consistency
A paintable slip is made from the compound which is painted onto
the refractory of both the well and the stack. Sausage shapes are
made out of the compound and added around the well seam. Then
the stack is ready to put in place, so it is lifted on and eased into
position. The weight of the stack pushes down on the compound and
seals the bond between the well and the stack.
Following the positioning of the stack, the upper bed coke is added.These pieces of coke need to be about an inch smaller in diameter
than the bed coke. Again, as with the well, these should be tightly
packed together but leaving just enough room for the flame and heat
to rise up through the coke bed evenly. The upper bed needs to rise
up in the stack to about 12” above the bed coke level. At this stage, it
is time to burn-in.
Running the Continuous cupola:
The burner is lit and pushed into the burn-in port, with tuyere covers
open and the blower off. The burn-in takes approximately an hour.
Continual observation of colour inside the furnace is paramount at
this stage - the furnace operator is looking for an even orange to
yellow colour in the coke all the way up through the well to the top
of the upper bed.
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When this is achieved, a steel pole with a flat base is used to ram
down through the stack and into the well to compress some of the
consumed coke. Usually the bed drops, and if/when it does, more
pieces of coke are added to keep it at 12” above the tuyeres.
When this extra coke is burning, the furnace is ready to go to blast
(i.e. adding forced air through the windbelt). At this stage the blower
is attached with the burner still in place. The blast is switched on and
there will be an automatic increase in temperature. The furnace
crew will continue to keep the burner in place for about five minutes
with the blast still on. The charge crew should be ready to start
adding the charges and the furnace operators ready to take the
burner away, to add the sand and bott mix to the spout, and plug upthe burn-in port.
The burner is taken away, the blower is switched off and then
charges are added all the way up to the top of the stack.
To plug the burn-in drain port speedily, sand is forced into the hole
to block as much as possible. Then a small cylindrical plug made from
used resin-bonded-sand approximately 2”round is used to push into
the burn-in port as snugly as possible. A slip made from diluted bott-
mix should be painted on to the outside of the plug and burn-in drain
port, to which a bott can be affixed with force, therefore sealing up
the well entirely.
At this stage, whilst the charges are still being added and the burn-in
drain port has been sealed, the spout should be filled to the top with
dry silica sand. Then a slip wash is painted onto the spout opening
and a bott is shoved with force into the top of the spout, covering up
the sand channel.All tuyere covers should then be closed, and blast switched onto full.
Within 3-5 minutes it should be possible to see the first droplets of
iron dripping past the tuyeres. Iron sparks should appear from the
slag hole, indicating that iron is being melted above it.
In approximately five minutes there will be a full well of metal. Slag
will be coming out of the slag hole, and here the furnace operator
will be watching for when a stream of iron starts to come out. It is
sometimes difficult to see the difference between slag and iron at
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this stage; but the iron is a much brighter white and is more fluid
than the slag.
When the well is full, the spout needs to be tapped (unplugged). The
furnace operator will call for the ladle crew, who will get into
position, putting their pre-heated ladle directly underneath the
spout. The furnace operator takes a thin, heated steel rod and picks
off the bott on the spout. The next step is critical: once the bott is
removed, the rod is then plunged downwards into the spout
(following the direction of the interior spout angle) and immediately
pulled out with a twist, in order to release the sand and draw up the
molten iron. This should be done in one movement. If the rod is not
hot and it takes too long, it can push the sand too far back into thefurnace or create a cold shut, meaning iron could cool at the point at
which it needs to flow up the spout. This means the furnace would
have to be switched off and drained of its molten iron and the whole
process begun again another day.
Once iron is flowing out, the ladle is pulled up off the ground and put
onto the ladle-holders on the furnace legs. It will take a few minutes
for the flow of iron to find its own rhythm, and it might sputter a bit
to begin with. Eventually it will settle down. The first pot of iron may
take 7-10mins to fill. As it is the first tap, the iron will be cooler than
subsequent pots. This will be directed to a mould that needs cooler
metal, or some operators might pour the iron into ingot moulds. As
the ladle is taken away to be poured, the furnace operator calls for
another ladle crew who are waiting to come in and take over from
the previous crew. The furnace continues to run and finds its rhythmwith the help of the operator. Heat will continue to increase in the
furnace, and the iron will be pouring into ladles faster and hotter.
As the furnace is running, constant checks need to be made on it.
The gauge to know the correct air blast is going into the furnace to
keep it at optimum combustion is to look at the colour of the slag. As
it comes out of the furnace, the slag is a gloopy stream that cools as
it drips down and forms a glasslike consistency. Pieces can be picked
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up with tools to study its colour: a matt, flat black indicates that too
much air is being put into the furnace. This means the melt zone is
being pushed too far up the stack and needs to be brought back
down, so airflow is lessened in order to bring it back down or an
extra coke-only charge is added. The ideal colour in the slag is a
glossy black. By tweaking the air more, a grey-green colour can be
achieved, and then the furnace is running at its optimum and cannot
combust any more efficiently.
The Continuous cupola needs two people running and observing the
furnace, keeping the tuyeres open and free from any cooling iron, so
a continual blast of air is evenly distributed into the furnace. The slaghole also needs to be kept clear so that the slag can flow out freely.
The two operators continue to work the furnace with steel rods,
making sure that the rods remain hot and only opening up the
tuyeres when absolutely necessary (to remove blockages or cooling
iron around the edges of the tuyeres where the blast is entering the
furnace and it is always cooler). They never open up more than one
tuyere at a time because that leads immediately to more loss of
heat. During the operation, breaks are required every now and then,
so a backup crew is brought in.
The mould captain is in charge of where each ladle is to go, to know
how much iron is needed to fill the moulds, and how much iron is in
each ladle. The mould captain is in constant communication with the
pour crew, to feed them the information about where to pour and
also with how much force to pour the metal into the mould.
Towards the end of the pour, the mould captain needs to be
aware of how many moulds remain empty and how many charges
are left in the furnace. If s/he calculates that there is enough iron left
in the collected ladles to fill the remaining moulds, s/he should then
communicate to the charge master to stop adding charges. The last
ladle crew is positioned in front of the burn-in drain port. Other
furnace crew should get ready to take the blower and equipment out
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of the way of the furnace. Water buckets and/or hosepipes should
be made ready. The blast can now be switched off and all the
electrics should be taken away. The furnace operator will ensure that
the tuyere covers are opened and then take a hammer and long
chisel to chip out the burn-in drain port. The ladle crew will collect
the remaining molten metal from the well (which may be as much as
40lb/18kg) to take it away and pour into the last remaining mould or
ingot moulds.
At this stage, the bottom door of the furnace needs to be opened.
The contents of the furnace (its initial sand bed laid at the beginning
and all the contents above it) need to be immediately evacuated
before it cools. A team of people with rods/bars should dislodge thismaterial by ramming up and under the furnace through the open
bottom door as fast as possible. When the contents comes rushing
out at speed, the crew need to be especially careful to watch out for
any molten metal and slag or white-hot coke pieces. This mass of hot
material should be immediately quenched with the buckets of water
thrown on in rotation.
The pour is complete.
Intermittent Furnace (Technical):
On an Intermittent cupola, the tap hole and spout are completely
different to those on a Continuous cupola (see the following cross
section diagram). The tap hole is plugged with a clay bott, which
seals the molten metal safely inside the furnace whilst it collects in
the well unit. With this style of furnace the molten iron runs up tothe slag hole, slag comes out of the hole and this is the indicator that
there is a full well of iron to be ‘tapped out’ into pre-heated ladles.
Preparing the Intermittent Cupola:
If the furnace requires patching or re-lining, see Appendix 1. To lay
the bottom, bott mix is used to build a gasket seal (as for the
Continuous) around the lining of the furnace to the door. Thisreduces the chances of seepage and bottom sand leaking out.
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Simple Bott Mix Recipe:
25lb/11kg fire clay
50lb/22kg silica/sand
48oz/1.3kg bentonite
1-2lb / 0.5-1kg of paper pulp
(The paper pulp can be soaked toiletry tissue mixed to a mash.
Sprinkle it in bits through the bott mix. Alternatively cellulose
insulation made from ground up newspaper distributes more evenly
in the mix)
The bott should be firm but not dry.
Ensure the bott mix is firmly tamped around the door.Pour in dry sand, moulding sand or all-purpose sand (but avoid any
with clay) up to 1 ½” below tap hole. The bed should slope up from
the tap hole to the back side of the furnace as you look into the tap
hole, at least 2” above the bottom of the tap. The steeper the slope
of the bed, the higher the head pressure will be (affecting with what
force and speed the metal comes out of the tap).
A rod with a flat disc can be used as a tamper. The bott mix on top ofthe sand bed should be gently tamped down, until nicely uniform
Cross section of intermittent cupola
Stack
Refractory
Windbelt
Tuyeres
Slaggers
SpoutBed sand
Legs
Tap hole
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with a slope up to the back side of the well. Sometimes the material
will stick to the bottom of the tamper (pulling up what has just been
tamped down) - this is called a ‘cookie’. A graphite wash should be
put onto the tamper. If it keeps sticking, more dry sand should be
sprinkled onto the bott mix on top of the sand bed in the well.
It is important to have dry sand so that when the furnace drops
bottom it does not lock up (leaving a solid bed to punch out) and
there will be no jamming.
Pieces of bed coke measuring half the diameter of the furnace (e.g.
6-8” pieces) can be positioned in a triangle inside the well. For the
next layer, it is necessary to ‘turn’ the triangle, and again on the nextlayer and so on. Even with 4 pieces of coke the layers will rotate so
that air pockets are created. This structure is also stable so it cannot
collapse during combustion. See Appendix 2.
Usually the furnace operator keeps positioning bigger pieces of coke
4-5” diameter or the biggest pieces available. Coke should be laid
progressively, and should not get too small too fast in the melt zone
at the windbelt and just above it. Coke can be layered 9-10” abovethe top of the tuyeres and left there. At this stage, the furnace can
be burned-in.
Running an Intermittent Cupola:
Burning-in: the furnace operator lights a flame-thrower (propane &
air burner) close to the tap hole and then slides it up just inside thetap hole and puts bott mix around the outside to seal it and to burn-
in the bed.
Burn-in time for a 14-18” furnace is usually about an hour. The
furnace operator looks for colour on top of the coke. The bed has
been laid all the way up through the melt zone, and burn-in is
required to get colour all the way to the top of the upper bed coke.
When the upper layer is burning a yellowy-orange colour that is thetime to ‘go to blast’. When burning in, it is important to keep the
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slaggers open so everything stays hot, unless all the slaggers are
going to run. Slaggers that are not going to be used should be closed.
To blast, the burner is taken out, the tuyere covers are closed, and
the furnace is run on blast for a few minutes. It is important to leavethe tap hole and all slaggers open and blast for at least four minutes
to make sure the tap hole is hot before the charge crew start
charging. (If the furnace is charged when the tap hole is cold, there is
the risk of a cold tap throughout.)
Tap holes can be made 2 ½ - 3“ because the bott can be partly or
fully knocked out when it is being tapped, so the stream can be
controlled and it is easier to clean out quickly if does freeze up. Thespout on the tap hole should be angled steeply (wide with high sides)
to reduce splash from the spout. A short spout means metal is likely
to arc up and out in a ‘rooster-tail’ fashion out of the spout, never
actually touching it. A large, wide spout will contain the initial
forceful flow of iron pouring out of the furnace and will channel it
safely into the ladle. If the spout is positioned fairly high up with high
sides, it also means more room for positioning the ladle underneath.
During the pour, the furnace operator will again measure where the
coke is in furnace - if it has sunk, it can be ‘buffered’ (by putting in
another layer of coke until it is above the 9-10” and letting it burn
down a little bit) before charging is resumed.
Charges should be layered coke first then iron. The weight of the
coke charge should measure 4” deep in volume. See Appendices 3 &
4. Charge coke sizes should be 1/10 of the internal diameter of the
furnace.
An 18” intermittent furnace requires 7 ½lbs/3 kg coke to 52lbs/24kg
of iron. A 16” continuous furnace runs on 5lbs/2.3kg coke to
50lbs/22.5kg of iron.
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With an Intermittent cupola, iron will come out of the well first (as
opposed to waiting for slag to show first on the Continuous). As soon
as there is a stream of iron flowing out of the tap hole and spout (not
just a few drops - there will be a trickle, then a stream), the furnace
should be botted up.
The size of bott that is needed is determined by the volume of the
furnace. If running a furnace likely to tap out 250lb or 100kg at one
time, a fairly big bott is required. When running a small furnace
tapping out only 50lbs/23kg or so, little botts of about 4” diameter
are required. (A 16-18” furnace takes botts of 6” diameter).
The bott can be formed into a cone so that it can be forcibly shovedupwards into the tap hole and leave a big mushroom shape on the
outside. The furnace operator will tap it down to form a mound that
sticks to the face of the furnace as well as the spout.
The furnace operator needs to ensure there are no gaps around
where the bott has been positioned- if the furnace starts leaking,
more bott will be put around the tap hole.
Metal in a Continuous cupola will come up the spout and into theladle, but in an Intermittent cupola, the slaggers are used to judge
time and volume. See Appendix 5. Furnaces larger than 14” diameter
will have multiple slaggers as well as small and large ladles
depending on the crew and how many moulds there are to pour.
Whilst the furnace is being charged and the metal is being collected
in the well, the furnace operator is looking for slag to come out of
the slaggers. It will run down out of the furnace and that indicatesthere is a full well because slag sits on top of the iron. When it is time
to tap, if the slaggers are on either side of the furnace, they should
be botted up before tapping out (or there is a greater risk of burns
because the pour crew will be near the slaggers).
As the slag runs out of the slagger, it is best to leave it to flow out
and not directly poke straight at the slagger. The operator should
remove slag if needed by coming at the furnace from the side andnot poking directly into the hole of the slagger. This helps to
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maintain the lifespan of the refractory lining on the inside of the
slagger and keeps the temperature of the slagger consistently hot.
When iron is running out of the slagger in a thick stream (the iron
being brighter than the slag and a lot more fluid) the furnaceoperator will call for the ladle crew, and bott the slagger up. This
saves metal and retains heat, whilst preventing the feet of the pour
crew from being exposed to molten slag and iron coming out of the
slagger.
To tap out an intermittent cupola, a tap-spike is used (steel bar with
a chisel on one end and a point on the other). The furnace operator
carefully uses the chisel-end to ease out all the bott from around the
tap hole leaving what only remains inside the hole. A faint yellow
glow can sometimes be seen in the remaining bott sealing the
furnace. If the bott mix is made correctly, the furnace operator can
gently tap through it, piercing the bott material and releasing the
iron out of the furnace and into the pre-heated ladle. When tapping
out, care should be taken to ensure the tap spike is not driven downbecause this can create a hole into the bed. The furnace operator
must tap upwards at the same angle as the bed sand has been laid.
The spout should be the same angle as the sand bed, so that angle is
a gauge of where the bed is.
The flow of iron exiting the intermittent furnace at tap-out is very
different to the flow of iron exiting a continuous cupola. The
intermittent furnace releases all of the metal collected in the well atone time. This is a fast flowing, large volume of molten iron that can
be reactive to the surroundings as it pours out.
Once the furnace has been tapped and the metal is drained and
taken away, the slagger should be opened again.
When the furnace has been run many times, the operator will be in a
better position to gauge the time it takes to get a full well (how long
it takes to get to the first slagger, then the second slagger etc). If the
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coke is the same size, burn-in time is the same and initial blast and
blast pressure is consistent, the furnace will give its operator all the
information s/he needs to know what the ‘average’ is for that
particular furnace. Once the furnace operator has this information
s/he will know how long to keep the slaggers botted, to keep the
furnace sealed up until the well is full.
Dropping the bottom of an intermittent furnace requires a final tap
to get all the metal out. The furnace operator will wait for the entire
pour crew to clear away equipment from the furnace area. Leaving
the tap hole open will release lots of slag and some metal will still beflowing out. When the area is cleared, the blower can be turned off-
blast and the tuyeres opened.
At this stage, the furnace operator will open the furnace bottom
door and the dry sand bed should fall straight out if it has not been
disturbed. The pour is complete.
Cupolette Furnace (Technical):
The cupolette is derived from the cupola. From the 1970s onwards,
artists and engineers began modifying cupola designs and arrived at
the concept of shortening the stack and attaching a lid onto the
shortened stack, forming the cupolette. The main distinguishing
feature of the cupolette is its lid, which reflects heat from the
burning bed below back down into the chamber of the furnace again.
The lid serves the same purpose as the stack for the cupola, creating
pressure on the coke and confining the combustion to the melt zone.
This results in a very quick batch-melting furnace.
There is no large stack to attach to the well, and no need to pre-heat
the coke and iron inside the stack. This also adds to the speed of the
melt and ease of operation.
The cupolette is easy to manage and can be charged with the
amount of metal needed at one time and requires fewer people torun it. It is not reliable however, for large scale production pours.
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Preparing the Cupolette:
Most cupolettes are built as one complete furnace, rather than three
different sections to be attached to one another.
Setting up the cupolette is relatively simple. The furnace is levelled. A
bott mix is made and the door is sealed with this mix and the dry
silica bed sand is added. The slope of the bed sand and laying the bed
coke is the same as for the intermittent cupola. A piece of wood
should be placed on the bed in front of the tap hole to prevent the
bed being blown away by the torch flame during burn-in. Large
pieces of coke are positioned to create a tunnel inside the well just
behind the tap hole so that the burn-in flame penetrates into the
middle of the coke bed. The height of the stack and lid design will
determine the position of the coke above the tuyeres.
Running the Cupolette:
Burning-in: as for the intermittent cupola, the furnace operator lights
a flame-thrower close to the tap hole and then slides it up just inside
the tap hole and puts bott mix around the outside to seal it and to
burn-in the bed.
The burn-in time I experienced at Iron Tribe and Tucumcari in NewMexico was between 1-2 hours. See Appendix 6.
Cross-section of cupoletteLid
Refractory
Short stack
WindbeltTuyeres
Spout
Bed sand
Slagger
Tap hole
Legs Bottom door
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The furnace operator looks for colour on top of the coke during burn-
in. Because of the shorter stack, this is easy to access and observe. It
is important to keep the lid, tuyeres and slaggers open so everything
stays hot. The fire is quickly drawn up the short stack because the lid
is open.
When the upper layer is burning a yellowy-orange colour (and the
entire bed of coke is burning) the furnace operator will organise the
crew to go to blast. The air is turned on and the furnace is run on
blast for five to ten minutes. The coke bed height is adjusted if
needed, and then charges of iron can be added. See Appendix 7.
The time is noted when the first charge is added. The cupolette lid is
opened for charging and then immediately closed again. The charges
for a cupolette are larger than cupola charges and the coke is not
weighed but continually added to keep the coke at around 4” above
the height of the bed.
Iron should be dripping down behind the tuyeres in about five
minutes after the first charge. If iron is showing sooner than five
minutes the bed height is not high enough, and if it is showing later
than six minutes the bed is too high. The bed height needs to be
adjusted accordingly and then the furnace should be botted up once
a steady stream or iron is running out of the tap hole.
After about fifteen or twenty minutes the well should be full of iron.
The slag hole is opened just beforehand to ascertain if slag is at the
slagger level and flowing easily. The furnace is botted up when iron
starts to flow out (as with the cupola this is the indicator for the
furnace operator that the well is full and the crew should prepare for
the furnace to be tapped).
The cupolette is tapped out in the same way as the intermittent
cupola, and the process is repeated until all the moulds are filled.
Once the moulds have all been poured, switching off and opening
the bottom door is the same as for the intermittent and continuous
cupolas. The pour is complete.
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6. Observed technical alternatives for UK iron casters
-In various foundries in the USA, I observed the use of shop-bought
‘No Nails’ to glue cups onto pour spouts. This is a cheaper and moreinventive way than using sodium-silicate based foundry core glue.
-I observed foundry men not using core glue to join the cope and
drag (i.e. two parts of the moulds). No glue was used to put together
mould pieces thus preventing moulds from popping and seepage.
-Ceramic shell mixers were inexpensive small paddle-mixer motors
with a long paddle situated in the ceramic slurry, put on timer switch
(five minutes on, five minutes off scenario). This resulted in low
equipment prices rather than industrial slurry mixers, highly efficient
for small batches and cost effective to run with low electric costs. It
is also safer than having the mixer running constantly.
-In the USA workshops I observed resin-bonded-sand mould making
using the equivalent product to that used in the UK - less space was
used around the original pattern. Rather than using a 3” thick mould
around the pattern, a 1 ½-2” thick mould was used. This would result
in lower material and energy costs for making moulds.
-On a large production pour, I observed the use of large bull ladles on
moveable gantries to contain a large ‘tap’ which could then be
siphoned off into smaller ladles to be poured into moulds. This
meant just one large tap and therefore fewer sparks, spills and metal
splash on furnace crew.
-Refractory thickness on the inside of furnaces was observed to be
only 2” thick on several successfully running furnaces. I was also
interested to see the use of ceramic fibre, coated in ceramic shell for
lining steel ladles. These were used for multiple pours and were
extremely light and manoeuvrable.
-Burners & blowers connected to burner ports are too close to the
heat. It is advisable to have an outsource blower with a pipe away
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from heat, propane, sparks and dust. It also makes the burner setup
more stable.
7.
8.
‘Dante’ - New Mexico Highlands
University 18” id cupolette
‘Scooby-Doo’ - New Mexico Highlands
University 14” id cupolette
Jeremy Colbert’s 16” id cupola
University of Kentucky
Jim Wade’s 18” id cupola,
University of Kentucky
The furnaces pictured below are those
encountered on the Fellowship trip:
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9. Recommended reading
Title Author Publisher
Date
Highlights
Casting Iron C. W. Ammen TAB Books
inc. 1984
Measurements for
building cupolas &
equipment, practical
diagrams
The Complete
Book of Sand
Casting
C. W. Ammen TAB Books
inc. 1979
Detailed
comprehensive
discussion of sand
casting
Iron Melting
Cupola Furnaces
For The Small
Foundry
Stephen Chastain Stephen D
Chastain
2000
Measurements &
practical diagrams for
building cupolas (Non-
art based)
Metal Casting
Appropriate
Technology in
the Small
Foundry
Steve Hurst ITDG 1996 Good generally
informative book on
casting, mould-making,
furnace construction
(Art-based)
Foundrywork for
the Amateur
B. Terry Aspin Argus Books
Ltd, first
published
1984
Basic but interesting
information on
crucible iron casting
The Iron & Steel
Industry
W.K.V. Gale David &
Charles Ltd
1971
Glossary of all terms
relating to iron and
steel casting
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10. Conclusions/comparisons:
Having been taught to cast iron with a continuous cupola, over the
past seven years I have facilitated large scale Iron Pour events. It has
required a tremendous amount of man-power, materials and energy.Teaching and training crew-members has been a long and difficult
process. It has always been my desire to seek alternatives for smaller
batch-melting, to experience different ways of achieving the same
end result and to have more iron casting options available to me as a
tutor and as a sculptor.
The Fellowship Trip enabled me to have the experience of observing
and participating in the running of different furnaces to comparealternative options. I was also able to acquire skills and techniques
that I will be able to put into practice in my studio-foundry, The
Bullpen. As a result of the trip I wish to complete, with my recent
new knowledge, the building of an intermittent cupola with a lid that
can be added when a cupolette option is required.
An intermittent cupola requires fewer crew members than a
continuous. It is quicker to set up, but also requires substantial spaceto operate. It does, however, allow furnace operators to tap the
furnace only once if a small pour is required (e.g. few moulds),
without having the complicated and time consuming burning-in,
spout procedure and shutting-down of a continuous cupola. Having
the option of a lid that can be swapped in (to turn the cupola into a
cupolette) will provide many more options to facilitate small batch-
melting for one-off commissions and may be possible to run with
only three or four crew members. This will mean that inexperienced
crew and additional participants can be trained in a more controlled
manner.
The continuous cupola requires a large crew to operate, and this is
not always readily available or cost effective. It also requires many
moulds to be filled, since it produces so much molten iron which
needs to be used or it is not worth running. It is complicated and
time-consuming to set up and also requires a lot of space both in
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terms of the pour area (mould line) and wider cordoned off area for
visitors to be able to watch. It needs an additional safe operating
area to enable two ladles to be continually heated. There is so much
to monitor constantly (not least health and safety) and it is
complicated to run with inexperienced crew.
By having an optional lid facility, the furnace can be run as a
cupolette with even fewer people operating it. This will give The
Bullpen the opportunity to transport a furnace to almost any
location, meaning the outreach work will affect and benefit more
people across the UK.
The Fellowship trip enabled my observation of furnaces in academic
institutions with students and artist-tutors working together to
create sculpture. See Appendix 8. If a setting such as The Bullpen
could offer students and artists the opportunity to work on a
selection of different furnaces, their creative practice and production
levels could be increased and their experience widened.
So few art students in the UK have the prospect of working in iron at
all, that non-academic settings are prevailed upon to deliver this
unique opportunity. The Bullpen can now offer one-off casting of
commissions with a smaller furnace and the control of small batch-
melting as well as large-scale workshops using a continuous cupola.
For artists in the small iron community in the UK who occasionally
collaborate to run a furnace for the casting in iron of their sculpture,
there will now be more opportunities to meet specific needs and
individual requirements, as well as future large funded projects.
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Comparison Table - Iron Furnaces
(16” refers to the internal diameter of the furnaces with which I
gained experience before and during the Fellowship trip)
16” CONTINUOUS 16” CUPOLA 16” CUPOLETTE
Most
appropriate
for
Large production
pour
Medium-large
pour
Small-medium
pour
Space/arearequired
High ceiling/covered area
High ceiling/covered area
Covered area
Number of
moulds to
pour
Large number Medium Small-medium
Number of
crew requiredMinimum 15 Minimum 6 Minimum 4
Experience of
crewMinimum 8 Minimum 6 Minimum 4
Length of time
of pourMax 4 hours Max 4 hours Max 7 hours
Time taken to
set up & burn-in
5- hours 2-3 hours 1 hour
Burn-in time 1 hour 1 hour 1-2 hours
Fuel economy Fair & efficient Fair Good
Quality of
castingsGood Good Fair-good
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Questions about the Future of Iron Art Casting:
The research I would like to undertake following the Fellowship tripis in the following areas:
• The Culture of iron casting and its accessibility for students and
artists - how more people can have access to it across the UK
• Making equipment safer and more accessible for
transportation. See Appendix 9.
• Cupola furnaces built specifically to run on coke, a material that
is now not being produced in this country (resulting in thenecessity of overseas shipments and other problems). There
are not enough people in the UK to investigate/research
running a cupola with other fuels and these alternatives have
to be found soon or cupola art casting will become redundant
and other melting procedures sought (e.g. induction furnaces)
• Detailed information about the history of the modern-day
cupola used in the UK
•
Why iron art casting is not taught on sculpture courses in theUK as it is in the USA
• Closer links with industry to be formed and relationships being
mutually beneficial. See Appendix 10.
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11. Glossary:
Refractory lining - heat-resistant material made from high alumina content
ceramic mix
Coke - purified coal
Slag - the molten limestone that is added in the charge to the furnace forms
slag on the iron.
Charges - weighed amounts of coke, iron & limestone
Windbelt - steel cylindrical section that wraps around the outside of the well
where air is forced in, which then enters the furnace through the tuyeres
Stack - Refractory lined cylinder that sits on top of the well containing coke andiron charges
Well - Bottom third of the furnace where molten iron is collected
Tap hole - Where burn-in takes place and iron is released out of the furnace
Tuyeres - Two-inch openings into the body of the furnace through which air
(blast) is added, feeding oxygen to the coke bed to maintain combustion
Tuyere covers - come out of the windbelt and have a tuyere cover which can be
opened or closed giving the furnace operator access to maintain the melt zone.They are also used as a viewing port to see how the furnace is working
Ladles - steel containers lined with refractory which take the molten metal
from the furnace and pour it into moulds
Slag hole / Slagger - the hole where the slag come out of the furnace
Spout - where the iron comes out of the furnace (made from refractory
material built around the tap hole)
Tap/Tapped out - when the furnace is opened up to release an amount of
molten iron into ladles
Melt zone - the area from the bottom of the tuyeres to just above the where
the iron melts
Bott - sand, clay and water mix used to make a ball to plug holes in the furnace
(tap hole, slaggers etc)
Burn-in- forced air and propane burner inserted in the furnace to set light tothe coke bed.
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12. Appendices/case study examples:
Appendix 2
April 2013 - National Conference on Cast Iron Art at SLOSS Furnaces, Alabama
Laying the bed in the cupola was done the night before the pour. I had not seen
this done before, and observed that it helped with timings on the pour day and
led to a calm crew atmosphere and the furnace operator could concentrate on
other things on the pour day. The sand bed and coke bed also were settled
overnight.
Appendix 1
30th
March 2013 - Jim Wade of University of Kentucky described how he fires the
refractory inside his furnace:
When lining the furnace, he uses a 2” liner. Once the liner has been rammed into
the well and the stack, and the refractory has become leather-hard, he then
pours dry silica sand into the bottom of the well. He places charcoal briquettes
on top of this and pours on lighter fluid, letting the briquettes burn for a while to
get some heat in the furnace. Then he switches over to small bits of wood, slowly
building up to something like a campfire. He uses a heavy steel plate as a lid to
lay over the stack leaving a third or so open (and the slaggers and tuyeres also
open). This will trap the heat and cure the top of the stack. Depending on time,
sometimes after the campfire, he will eventually get a flame all the way through
the entire furnace (using shipping pallets for their vertical slats to burn all the
way down the furnace liner). He may even get a flame-thrower and put it in the
tap hole and burn that for a while. Alternatively, the coke bed could be laid,
burned-in and made to go to blast, running only on coke and blast. Curing the
pour-spout is also very important, whatever it is lined with. The campfire can
extend to that, followed by a flame-thrower close to the spout with a steel plateover the top of it (a kiln shelf or ceramic fibre blanket piece can also be used).
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Appendix 3
Jim Wade, tutor at University of Kentucky suggested a helpful way of working out
amount and positioning of coke for laying the bed in the furnace:
*A cardboard mock-up of the well (the same internal diameter of the furnace) is
placed on the workshop floor. The coke can be positioned inside it for furnace
crew to get used to what it looks like and practice laying the bed.
Appendix 4
26th
March 2013 - Jim Wade, tutor at University of Kentucky suggested a helpful
way of working out the amount of coke needed for a charge:
A cardboard ring the size of the internal diameter of the furnace should be placed
on the workshop floor. It can be filled with coke to see how it looks at 4” deep.
This amount of coke should then be weighed, and used as the gauge to measure
all the charges.
Appendix 5
30th
March 2013 - Jim Wade of University of Kentucky described monitoring
combustion in the well:
Some furnace operators leave the bott in the slagger and poke a small hole in it.
That way, the flame that comes out of the hole can be monitored to see if it is
yellow, green or blue. (Blue shows that it is oxidising and will break down theproperties of the metal). A ‘reducing flame’ will take oxygen from anywhere it
can and it will take it from the liner, and will wear out the inside of the furnace
quickly. Oxygen needs to be kept in the metal, not taken it away from other
materials inside the furnace to continue combustion. A neutral flame between
light orange-greenish is required, which means a neutral atmosphere. To monitor
this, the small hole through the bott into the slagger gives a fine flame coming
out from which the atmosphere of combustion can be gauged. Changing air-
intake will increase or decrease an oxidising or reducing flame. Damper on
blower can micro-adjust until you get the flame right.
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Appendix 6
Saturday March 9th
2013 - Iron Tribe Production Pour: my first experience of
participating in an iron pour run only with cupolettes, and two at a time.
A 16” cupolette and an 18” cupolette both running simultaneously. Approximately
200 moulds in sand and ceramic shell to be poured, with approximately 100
people from all over the mid-west of the USA participating. Small pour area was
crammed, claustrophobic and chaotic - but as all iron pours find their rhythm, the
pour was completed successfully with all moulds poured and everyone involved
was able to do something. I was a pour crew member and found communication
and direction by the mould captain very good and reassuring. I also enjoyed using
ceramic fibre and ceramic shell lined ladles as they were much lighter than the
ladles I was used to.
Appendix 7
March 15th
2013 - Tucumcari Iron Pour at Mesalands Community College.
Two furnaces in operation; a 16” cupolette and a 14” cupolette.
Started burning-in the 14” cupolette (‘Scooby-Doo’) at 12 midday with Professor
David Lobdell and another crew member. Burning-in went well and blast went on.
A good flame was exiting the cupolette. Twenty minutes in, with metal added,
the flame and colour was being lost (as seen through the tuyeres). Cold metal was
exiting the tap hole. We concluded there was too much air, and so tried to
decrease the airflow to bring the melt zone back down again. After two hours of
trying to pull the melt zone down, an oxygen lance was ignited and put into the
tap hole to try and clear out the cold metal. The remaining coke inside the
furnace was rammed down and the burner was placed in the slag hole andburned in for another hour to try and get the bed coke up to temperature again.
When this was achieved the furnace was back on blast with less air. The changes
had rectified the problem but the pour had lasted for nine hours. It was good to
experience a furnace malfunanction and how to rectify the problems. It would
not have been possible to rectify this problem in a cupola and continuous cupola.
There being only three crew members and the problems we faced made the pour
exhausting and dangerous. With more crew in place it would have been physically
less challenging.
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Appendix 8
April 9th
2013 - National Conference on Cast Iron Art at SLOSS Furnaces, Alabama
Whilst preparing for the pour at SLOSS it was interesting to observe the alumni of
the University of Kentucky being drawn back to assist with furnace preparation
and the pouring of metal. They acted as tutors to the students and were keen to
represent the institution that they were once part of. They were crucial to the
running of the furnace.
Appendix 9
University of Kentucky’s furnace and equipment were designed and built by
Jeremy Colbert. He designed a portable gantry that was collapsible and
transportable, and once erected became the lifting equipment for constructing
the furnace and for hoisting the large ‘bull ladle’. It was interesting to observe the
packing and transportation of a complete foundry unit in one trailer. The large
bull ladle was built to help contain large taps, enabling furnace operators to be in
less contact with molten metal.
Appendix 10
April 12th
2013 - National Conference on Cast Iron Art at SLOSS Furnaces,
Alabama
At SLOSS, I observed the unique culture of iron casting in industry connected to
art. Each used the other to promote awareness and education as well as
enjoyment and passion. SLOSS used the art community to promote its iron
casting heritage in a visual way. The artists used the history and surroundings as
inspiration and context for their artistic expression.