2018 Valentine’s Day Hot Metal Pour Part 1: The Detailed Process of Casting Iron

Happy New Year from Franconia Sculpture Park! In the dark, cold days of winter, we at Franconia look forward to the infusion of warmth and community that comes with our first big event of the new year: The Valentine’s Day Hot Metal Pour!

Welcome to the first of a two-part blog feature leading up to our annual Valentine’s Day Hot Metal Pour. As an iron artist myself, molten iron makes my heart skip a beat! In this post, I will focus on the process of casting iron and information on how you can create your own cast iron sculpture. My next post will focus on the lives of some of the professional iron artists behind our Hot Metal programs.

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This year the Valentine’s Day Hot Metal Pour will take place on Saturday, February 17th, from noon to 5pm in our outdoor studio known as the “work pad” which we transform into an outdoor foundry three times each year. The event is family-friendly, FREE, but donations are always welcome! A series of Community Mold Making (Scratch Block) workshops for all ages are being held in the weekends leading up to the pour, during which we welcome the public to become a part of the process and create your own mold for your own cast iron sculpture — Keep reading for more information on these workshops and how you can participate!

Where do we begin? Making a Mold

There are endless possibilities in metal casting, but each artist has to begin with some kind of form or “pattern” to be reproduced in the iron. This all depends on the subject matter and interests of the artist. Some iron artists work primarily with found or natural materials, while others create a pattern out of wood, foam, clay, 3D printed objects, wax, or other materials. Cast iron sculptures can be very detailed representations from life or completely abstract. Did you know there’s a stunning variety of approaches to the iron sculptures on exhibition at Franconia? Make sure to see our cast iron exhibition area next time you visit the park!

An artist’s chosen pattern needs to be draftable meaning that the artist maps out parting lines based on the angles of their pattern in a way that the artist can take a mold off of it in tightly interlocking sections that can be released, without the pattern getting stuck inside the hardened sand material that we use. At Franconia we focus on resin-bonded sand for making our iron molds. It’s a two-part system in which we mix fine silica sand inside a cement mixer with a Sil-Bind binder and a catalyst (hardener), that when combined will self-set in about 4 hours. The pattern to be molded is positioned on a bottom board with a flask or box constructed around it. Immediately after mixing, the sand and Sil-Bind mixture is tightly packed against the form inside the flask. Iron artists work quickly and carefully to capture all of the intricate details of the pattern’s surface before the sand mixture begins to set up in less than 20 minutes.

 

 

After all the parts of the sand mold have been created (this could be two, three, or hundreds of pieces!), all of the pieces are taken apart and the original pattern is carefully removed to create the negative space of the form that will be filled with iron. With drills and other tools, iron artists carve channels called sprues and gates into the hardened sand that become the pathways for the molten iron to flow efficiently into the mold to create a detailed, successful casting.

Before the pieces of a sand mold are re-assembled, a final bit of surface preparation happens with a solution called mold wash, which is a mixture of powdered graphite and denatured alcohol. This creates a carbon barrier against the sand and allows the iron toIMG_4705flow quickly and smoothly through the mold, capturing the best detail possible without burning too far into the sand. The mold wash is sprayed or brushed carefully onto the negative space of the mold and the alcohol is burned off before the pieces of the mold are re-assembled. Then the mold sections are securely bound back together with steel banding to preserve the negative space of the form and prevent iron from leaking out.

How can you become a part of the iron casting process?

At Franconia, we want you to create art with us, not just watch! We view all of our programs as opportunities to engage the community in hands-on art experiences and demystify the process of creating art. While media such as drawing or painting might be more commonly known, it is a rare treasure to have such a comprehensive and internationally-known program for cast iron art, right here in the East Central Minnesota part of the St. Croix River Valley!

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Varying slightly from the multi-piece sand molds that I’ve been describing, our community scratch block molds are one-piece “open-face” molds that are pre-formed in various sizes and shapes. At our Mold Making Workshops, Franconia artists will demonstrate the subtractive process of creating your scratch block sculpture, providing various carving tools and drill bits and guiding you through the process of creating your own design to be poured and finished by Franconia iron artists on February 17th.

To carve your own scratch block and create your own cast iron sculpture, attend one of our Community Mold Making Workshops! Workshops are filling up fast (last year’s workshops sold out completely!) so act fast and visit the event page to reserve your spot! Workshops will be held on January 27, 28, and February 3, 4, 10 & 11, with two workshops each day; either 10am to 1pm, or 2pm to 5pm. The workshops are free and molds are available to purchase in various sizes: $30 for small molds, $45 for medium molds, and $75 for large molds (credit card fees apply). Watch our scratch block video created by 2014 intern artist Dylan Redford on Vimeo for a demonstration of the process:

The Main Event!

To get ready for an iron pour, we spend time breaking down iron from old radiators and bathtubs as well as coke (a refined coal product… our dark and dusty fuel source)! The coke and iron has to be broken down with hammers into smaller but uniformly sized fragments (for iron, think tortilla chips, for the coke, think lime-sized!) in order for the furnace to run smoothly and efficiently. Some large, brick-sized chunks of coke are kept large like the size of bricks and are set aside to be used in the bottom of the furnace to help start or “burn in” the furnace.

 

The type of iron furnace that we operate is referred to as a cupolette, a smaller batch melting furnace with a lid, fabricated from a steel cylinder and lined with a high-temperature fibrous clay material called refractory (meaning it is resistant to heat). The bottom of the cupolette has a hinged door that can be closed when the furnace is filled and running and opened when the iron pour is over in order to clear out the center of the furnace. Before the pour, the bottom door of the furnace is closed and a special mixture of sand, clay, and vermiculite is packed into the bottom at a slight angle towards the spout. This is called bottom sand, which helps to seal the bottom of the furnace and provide a sturdy but removable platform for the melting iron to drip down into the well, or bottom chamber, of the furnace.

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Anatomy of an iron cupolette

After the bottom sand is packed, large pieces of coke called bed coke are arranged in the bottom of the furnace, and a propane torch is positioned through the tap spout of the front of the furnace. A powerful electric blower is connected to the wind belt (the wider ring that circles around the middle of the furnace). The blower forces air into a spiral inside the furnace, increasing oxygen and accelerating the internal temperature. The propane torch is lit and used for at least two hours or until the bed coke is hot enough to be able to sustain the internal heat just by the air of the blower.

When the artists operating the furnace determine it is hot enough to start melting iron, one artist ascends the staircase to the charging platform while another opens the lid and a bucket or two of smaller “charge” coke is added (the lime-sized pieces!). Then two 50-pound buckets of iron (100 pounds total) are poured in at timed intervals so that the iron fills flush with the very top of the furnace. The temperature inside an iron furnace reaches close to 2700 degrees!

IRON_5Think of the inside of the furnace sort of like a percolator… As the iron begins to melt, it drips down through the spaces in between the coke and fills the bottom of the furnace. (This is why the size and shape of the iron and coke are so important!) There are four small windows called “tuyeres” surrounding the wind belt of the furnace where artists can peek into the inside of the furnace to monitor what’s happening inside.

Tapping Out

When the falling drops of iron are no longer visible through the tuyeres, we know that the iron has finished melting into the bottom well of the furnace. This usually takes 15 to 20 minutesIMG_1820 depending on the furnace. A pour team comprised of at least three artists take their places in front of the furnace with a metal vessel called a ladle that has a refractory liner and has been pre-heated. Two artists carry the ladle on either end, while one artists stands in front of the tap spout of the furnace to “tap out” or chisel out the bott (clay plug) with a pointed steel rod, allowing the molten iron to flow into the ladle. The molten iron taps out between 2400 and 2500 degrees!

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The pour team carries the 100 pounds of molten iron (plus the weight of the ladle itself) across the pour floor and carefully fills each mold, including the visiting artist molds and all of the scratch block sculpture molds made by community members!

The FSP/UMN Connection

The Valentine’s Day Hot Metal Pour as well as our Community Collaboration Hot Metal Pour programs occurring annually in August have formed a wonderful partnership with the University of Minnesota Art Department Foundry, providing transformative community art experiences for students outside of the traditional studio classroom. This year the pour is once again organized by lead artist Tamsie Ringler, a Franconia board member and artist as well as term assistant professor of sculpture and foundry at UMN, and myself Amber White, Franconia Program Assistant and former UMN Foundry Teaching Assistant. The UMN Foundry students spend the weeks leading up to the pour helping to prepare the furnaces, tools, and materials indoors at the UMN Foundry. The weekend of February 17th, students and other community artists will ignite the park with their energy, braving the elements and providing the expertise that it takes to have a safe and successful pour.

 

What about weather?

Iron artists are no strangers to extreme temperatures! A winter iron pour is the ultimate fire and ice experience, and in order to combat the cold and take extra care with our furnaces, we operate two smaller furnaces for the winter Valentine’s Day pour as opposed to the larger furnaces that you might see during the August Community Collaboration Hot Metal Pour. We light basic wood fires inside the furnaces the night before the pour to help keep them warm and dry overnight, then we stagger the start of the furnaces to ensure the first one is up and running hot before starting the next. With two furnaces running, we also have a backup just in case one of the furnaces chills out.

Franconia iron artists have decades of experience and many are known and respected internationally. UMN students who are newer to the process are given expert instruction in mold making and pouring procedures throughout the semester, and every pour begins with a safety meeting. All precautions are taken to ensure that the molds are poured smoothly and successfully and everyone remains safe. All tools and ladles have to be pre-heated using the heat of the furnace to prevent steam bursts and to keep the iron as hot as possible throughout the pour. Cold iron is bad news! Iron and water also don’t mix, so molds are kept dry and free of moisture. Artists wear full personal safety gear including leather boots, aprons, chaps, spats (foot coverings), gloves, and jackets along with safety glasses and hard helmets with face shields.

 

But wait! We aren’t done…

Even though the melting and pouring of iron is often the most exciting and spectacular part of the casting process, there is a ton of work left to finish a cast iron sculpture. Iron artists can spend weeks carefully excavating their sculptures from the sand, grinding off the sprues and gates, and finishing the surface with a patina, paint, or other treatment. Cast iron sculpture can be exhibited on its own or be welded, drilled, and combined with all sorts of other materials.

IMG_0887After our community-designed scratch blocks are poured, Franconia artists pop them out of the sand blocks, quench them in water with tongs to be sure they have cooled, and use angle grinders with grinding discs or wire wheels to smooth any sharp edges and clear any remaining sand from the surface of your design. We work swiftly to make sure you can take home your iron casting on the same day of the pour! After taking your cast iron tile sculpture home, you can decide whether to let it rust naturally, seal it, paint it, and display it in endless ways.

Stay tuned for our next post about the life of an iron artist, featuring several of our Franconia iron artists! Check out this heartfelt love letter to iron for a warm-up, produced by John and Michael McMenamin:

Mark your calendars and register today for one of our Mold Making Workshops to create your own cast iron sculpture. We’ll see you at the park February 17th!!

 

This activity is funded, in part, through a grant from the East Central Regional Arts Council through an appropriation from the Minnesota State Legislature with money from the State’s general fund. Thank you!

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Covia (Unimin) Corporation’s generous donation of 48,000 pounds of silica sand each year since 2005 has contributed to the energy, inspiration, and growth of Franconia and ensures this vibrant arts sanctuary is available to all. Thank you!

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