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Spheroidal Graphite Iron Features
Spheroidal graphite iron is also known as ductile iron. Ductile iron's composition uses graphite spheroids within the iron's matrix, as opposed to graphite flakes found in other iron choices, such as gray iron. The spheroid matrix creates a more-flexible iron consistency, resisting impact compared to other irons.
Porosity
During casting, the molten ductile iron moves from a heated container to the intended mold shape. However, the iron's transition from the container to the mold can cause porosity within the final cooled cast. Porosity occurs when air or gas bubbles become trapped within the iron's consistency. As a result, the casting has voids that compromise its overall structural integrity, regardless of the molded shape. Many iron casting businesses control the overall casting air atmosphere through vacuums for preventing porosity. Also, the iron's movement from the container to the mold must have as little turbulence as possible for avoiding porosity voids.
Shrinking
As molten ductile iron cools within a mold, the entire casting shrinks by approximately 5 to 10 percent of the total volume. As a result, surface casting defects appear, such as gouges or extrusions, compromising the casting's quality. Many manufacturers use flexible molds, allowing the iron to shrink without sticking to the mold's inner surface. Another solution to shrinking is creating a uniformly thick iron part. The casting cools evenly across its composition, producing less stress and preventing large-scale shrinkage.
Microstructure
The casting's final microstructure, or visual surface grains, may reflect defects in the casting process. The iron may appear patchy. Uneven casting cooling creates an unappealing aesthetic look. The final casting may require annealing, or heating, to repair the unsightly microstructures. However, this type of iron surface grain may be difficult to repair.