651-778-3300 Mon - Fri 7:00am - 3:30pm 867 Forest Street, St. Paul, MN 55106
Gray, ductile, and austempered ductile iron castings up to 250lbs.
ASTM A536, SAE J434, ASTM A48, SAE J431

Casting process

Core production for iron components

Cores define the internal space inside iron castings while the mold defines the outside shape of the casting.

Northern Iron & Machine produces cores using two processes. The phenolic urethane process is performed on an IMF Disco 3500 and a Simpson ABC 6 system. Shell cores are produced on Redford shell machine systems.

Both processes require the use of a core box die. The die creates a negative impression of the desired core shape. Our cores are primarily made of silica sand, similar to how molds are made.

But unlike molds, when using the phenolic urethane process for making cores, a three-part binder is mixed with sand and blown into the core box via compressed air.

By comparison, shell cores are produced somewhat the same as phenolic urethane cores, but the sand is mixed with a resin that reacts to heat. During the manufacture of shell cores, the die is heated, and the sand mixture is blown into the core box. The heat causes the resin to harden and the core to cure.

After a core has been produced, it may be coated with a core wash and then sent through a forced air oven for curing. The core wash process improves the surface finish of the final casting while preventing undesirable iron penetration into the mold.

During mold production, the cores are set in place prior to setting the two mold halves (cope and drag) that are closed.

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Molding operations

Northern Iron & Machine has two high-capacity automated molding lines. Both produce green sand molds using a pattern, a containment vessel, pressure and high-quality green sand.

The green sand is comprised of silica sand and Bentonite clay premix which serves as a binding agent. Green denotes the presence of moisture in the sand. Strict process controls ensure that the composition and moisture content of the green sand is kept within defined limits. For highest quality, the mold is not dried or baked.

The green sand casting process packs sand into a flask that surrounds a positive impression of the casting to be produced. This positive impression is known as a pattern. It includes runners, gates and risers that distribute the molten metal when pouring begins. The pattern is made from a durable material and built to exacting tolerances.

The rectangular or square compacted sand container, with the negative impression of the casting and various runners, is known as a mold. The mold is manufactured in two halves known as the cope and drag. While the cope and drag are separate components of the mold, filters, exothermic risers, and cores are added to the drag side of the mold. Then the cope is rotated downward facing and the drag is positioned beneath it so that the two halves of the mold can be placed together for pouring.

This process may vary depending on the equipment used. In some cases, castings may require a core be placed in the mold before closing. Cores are hardened pieces of sand specially shaped to form the internal surfaces or complex external surfaces of the iron casting and are produced using different processes.

Prior to pouring the molten material, a large weight is placed on top of the mold. This prevents the buoyant force of incoming molten material from separating the cope from the drag side of the mold.

Northern Iron’s largest molding line is an Osborne 30 square line. It has mold flasks that measure 30 x 30 x 12 inches deep. The pattern for it are mounted on two separate plates. The top flask is called the cope and the bottom half is called the drag.

Northern Iron’s newest molding line is Disa system which uses a match plate pattern and produces molds that measure 20 x 24 x 8 inches. With match plate patterns, the two halves of the pattern are mounted on opposite sides of the same plate. Using this match plate pattern, the Disa system makes both halves of the mold simultaneously.

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Melting and pouring

We use three 1500kw induction furnaces to melt a combination of scrap steel and iron returns. These furnaces are capable of melting 45 tons per shift. These furnaces operate within a range of 2750 to 2800 degrees farenheit

During the melting process, various elements are added to the furnace to keep the chemical composition of the iron within the specified limits for the particular grade that’s being poured.

After the proper chemical composition has been achieved, the furnace is “tapped”. During the tapping process the entire furnace is tilted forward and the molten iron is poured into a Tundish or transfer ladle.

Throughout the process, slag (impurities) are removed using a coagulant for concentrating the impurities and a slag spoon for their physical removal.

All cast iron and steel have elemental iron (symbol Fe) as their main component. The primary difference between iron and steel is carbon content, with steel having a much lower carbon content when compared with cast iron. Though we produce iron that conforms to a variety of specifications, the iron we pour can be broadly classified as one of two types for cast iron.

Grey iron – this is a basic type of iron that has the carbon distributed throughout its matrix in flake form.
Ductile iron – the carbon in this type of iron is distributed in nodules that are spread throughout the micro-structure of the iron.

During the production of ductile iron, magnesium is added to the bottom of the Tundish ladle. Iron is then tapped into the Tundish ladle on top of the Magnesium. The resulting reaction causes the carbon to coalesce into nodules spread throughout the micro-structure of the iron. This results in greater ductility.

Molten iron is moved in a transfer ladle from the furnaces to the individual pouring ladles.

At this point one of our foundry personnel pour the iron into each individual mold.

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Iron casting finishing

Once the iron casting has solidified, a solid part along with a series of runners and risers known as sprue are contained in the mold.

At this point, the weights and jackets are removed from the mold and then the mold is subjected to a shaking process that separates the sand from the part. A minimum shakeout time is maintained to produce the correct as cast structure. This newly separated sand is sent through a reclamation process for reuse.

Next, the sprue is separated from the casting with a hydraulic wedge. The removed sprue, like the sand, is recycled for reuse in future melts.

Following sprue removal, castings are processed through an abrasive shot blaster that removes any remaining sand and also cleans the casting.

The casting then receives a series of grinding operations to remove any excess material (parting lines, gate connections, and core flashings).

The completed casting is now ready for stacking in a shipping container.