Everything you always wanted to know about casting… but were afraid to ask
Casting is a complex art and science that dates back several thousand years. So it’s not surprising that it has its own world of specialized terminology that’s quite foreign to the average OEM design engineer or purchasing manager.
That’s why we created this casting terms dictionary, to shed light on the most common terms you need to know to work effectively with a foundry to have your castings produced.
Castability: The ability to successfully make a casting from a customer’s design, using a hand-molded casting process that meets the customer’s requirements. Lawton frequently consults with our customers to design practical solutions to solve these problems, while still meeting their requirements.
Machinability: The ease of machining a casting. Material selection is a factor which can be characterized by hardness.
Gray iron: Gray iron is a type of cast iron that contains flakes of graphite in its microstructure. It is used for castings where the stiffness of the component is more important than its tensile strength.
Ductile Iron: Ductile iron has much more impact and fatigue resistance, due to the spheres of graphite that form with the addition magnesium.
Runner bars: Pathways that transport molten iron through the mold. As it gets close to the mold, it splits into ingates.
Ingates: The channels that transport molten iron from the runner bars into the mold cavity.
Riser: Also known as a feeder, the riser delivers molten iron to the top of the mold to fill in voids created as the metal cools, contracts and solidifies.
Molding sand: silica sand mixed with an acid and a binder that chemically reacts, creating a solid, concrete-like mold that can be used for casting.
Mold coating: Also known as a refractory coating, it’s applied over the top of a sand mold to prevent damage from the heat of the molten iron as it’s poured into the mold. It helps the mold maintain its shape until the molten metal cools.
Test bar: Typically, a separately casted sample of iron from the same pour as the casting. The sample piece is machined to standard specification that will be used to determine the mechanical properties of the iron.
Tensile strength: The test bar is pulled until it fractures. The maximum stress it withstands before fracturing is its tensile strength.
Yield strength: This test measures how much load stress the test bar can withstand before plastically deforms.
Brinell hardness: A standard testing practice used to determine the hardness of a casting, using a steel or tungsten carbide ball as an “indenter.” This test is performed to evaluate the resistance to deformation of the material.
Annealing: Heat treating a casting to soften the iron. Annealing alters the physical and sometimes the microstructural properties of the iron to increase its ductility and reduce its hardness. This makes it more workable.
Solidification modeling: A computer simulation of the flow rate and cooling properties of molten metal within the mold. It helps engineers design an optimal configuration of ingates to meet customer requirements.
Parting line: The line where the two halves of the mold separate.
Draft: A taper on the vertical sides of a mold or core box that permits the core or sand mold to be removed without damaging the sand.
Core: A metal or sand insert placed in a mold to shape the interior of the casting or section of it that cannot be shaped by the mold.
Core box: A wood or metal box manufactured in a shape cavity into which sand is packed. A core box is required to make a core.
Cope: The top half of a horizontally parted mold.
Cheek: The middle part of a three-part mold. Complex mold designs may contain undercuts and other design features that prevent the use of a single split in the mold. In other cases, it may be less costly to do a three-part pattern. In addition, using a cheek may eliminate the need for cores.
Drag: The bottom half of a horizontally parted mold.
Datum scheme: An exact point or location on the casting that is used as a reference in defining its geometry. It’s used to measure a casting to assess how closely it matches the customer’s design tolerances.
Slag: A by-product of melting iron. As iron is heated, impurities embedded in it rise to the top of the melt. They must be removed before making a pour. If they are not removed, they will create defects in the casting.
Hobs: A tool used to cut gears.
Ultrasonic testing: A type of testing that uses high-frequency sound energy to examine and measure castings. It is frequently used to detect flaws in ductile iron.
If you’re confused by any other casting terms, why not ask us?
Better yet, why not participate in one of our upcoming iron 101 master classes at our headquarters in De Pere, WI (near Green Bay). We look forward to chatting with you!