Grey Casting

Grey Casting

Like most iron alloys, grey iron, which is the particular iron used for grey casting, is composed of 95% iron by body weight. Grey alloys, however, have the additional requirements of between 2.1 and 4% carbon and 1 to 3% silicon. After being heated in an electrical inductive or cupola blast furnace, these materials are cooled at specific rates to create graphite. Flakes or spheroids of graphite are what give these particular alloys their name as the deflection of these inclusions produces a grey appearance along fractured surfaces. These microstructure components are also linked to the specific physical, chemical and mechanical properties of grey iron castings such as high thermal conductivity and wear resistance. Other properties include low melting point, resistance to deformation and energy dissipation all of which vary depending upon the specific elemental structure of the alloy in use. Regulatory bodies provide standardized grading for easy consideration and iron foundry specialists can provide helpful insight into grey casting capacities.

Iron foundries provide several different methods for grey casting. Virtually every one of these involves the creation of a mold into which molten iron is poured. Controlled cooling then solidifies the materials into a newly formed part that is ready to be removed or ejected. One of the most common techniques for accomplishing this is die casting. This involves the use of reusable molds which bear the impression of the desired part or piece. These molds can produce complex parts at high production rates and are used in many mass manufacturing operations. Centrifugal casting can likewise be used for mass production, though only cylindrical products such as pipes and tubes are created in this way. The molds for this type of casting are rotated at high speeds along a central axis as the liquefied grey iron is poured into the cast. Products manufactured in this way have a fine grained outer surface with even dispersion. Sand molding is one of the most economic processes that is easily accomplished, but more popular when only small numbers of identical components are required. The two part mold cavity used in sand casting is fully disposable after use as it is composed of synthetic or natural sand, the choice of which depends upon the accuracy needed and the desired surface finish. Often finishing techniques such as sanding, grinding or deburring are required with this and other molding processes which tend to leave residual artifacts on the outer surface of the part.