IRON HERE AND THERE

Wesley Jacobs

2013

Wesley Jacobs WCMT Report August 2013

Contents

Section Title

1. Abstract

2. 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 improvements

7. Recommended reading

8. Conclusions & recommendations

9. Glossary

10. Appendices

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

• 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

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 into the 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 being stripped 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 of iron, when cast, are not too dissimilar to bronze - extreme detail can

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 was unable 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 late 1980s, 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.

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

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 of feeling, 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.

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 the cupola 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

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 the windbelt, 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 a spout 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”

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

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 and propane 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.

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.

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 up the 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

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 the furnace 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 rhythm with 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

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 slag hole 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

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 this material 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 to the 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. This reduces the chances of seepage and bottom sand leaking out.

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 of the sand bed should be gently tamped down, until nicely uniform

Cross section of intermittent cupola

Stack

Refractory

Windbelt

Tuyeres

Slaggers

Spout Bed sand

Legs

Tap hole

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 next layer 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” above the 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 the tap 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 the time to ‘go to blast’. When burning in, it is important to keep the

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 leave the 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. The spout 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.

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 shoved upwards 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 the ladle, 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 indicates there 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 and not poking directly into the hole of the slagger. This helps to

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 furnace operator 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 down because 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 at one 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

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 be flowing 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 to run it. It is not reliable however, for large scale production pours.

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 New Mexico was between 1-2 hours. See Appendix 6.

Cross-section of cupolette Lid

Refractory

Short stack

Windbelt Tuyeres

Spout

Bed sand

Slagger

Tap hole

Legs Bottom door

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.

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 more inventive 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

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:

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

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 compare alternative 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 space to 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

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.

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/area required

High ceiling/ covered area

High ceiling/ covered area

Covered area

Number of moulds to pour

Large number Medium Small-medium

Number of crew required

Minimum 15 Minimum 6 Minimum 4

Experience of crew

Minimum 8 Minimum 6 Minimum 4

Length of time of pour

Max 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 castings

Good Good Fair-good

Questions about the Future of Iron Art Casting:

The research I would like to undertake following the Fellowship trip is 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 the necessity 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 the UK as it is in the USA

• Closer links with industry to be formed and relationships being mutually beneficial. See Appendix 10.

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 and iron 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 to the coke bed.

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 plate over the top of it (a kiln shelf or ceramic fibre blanket piece can also be used).

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 the properties 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.

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 and burned 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.

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.