Enough softening occurs with hot-working methods for metals to recrystallize. The mechanical process of working metal deforms it in such a way that the coarse crystallinity of its ingot-cast state becomes progressively fragmented and rearranged so the crystalline structure is refined, creating a smooth, dense product. Hot-working methods include pressing into shape between forging dies, or rolling, passing the metal through pairs of flat or grooved heavy rollers. Bars, shapes, plates, sheets, and strips are formed by hot rolling.
Cold working occurs at such temperatures and rates that no recrystallization occurs, but the working increases tensile strength, the amount of pulling force an object can take before it breaks and decreases ductility. Cold working processes include drawing, extruding, pressing, and stamping. In the extrusion process, used most often for aluminum, semi-molten metal is forced through a die, which is a mold or shape. This can create continuous shapes, such as window frames. Cold drawing is used to make wire or tubing, drawing the metal through a series of dies to reduce its cross-sectional area until the final shape is obtained.
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In the casting process, the final form of the metal is created in a foundry with a mold of the desired shape. Molten metal is poured into the mold and allowed to solidify. The metal shape can then be machined, etched, or carved for design variety. Sand molds are prepared from a mixture of moistened sand and clay, packed over a wood or metal mold. Objects cast in sand molds can be solid or hollow. Although sand casting is the traditional casting method, others include plastic mold casting for nonferrous metals, composite mold casting for alloyed aluminum, and investment (lost wax) casting, creating permanent reusable molds. Die casting is used for lower-melting-point, nonferrous metals that are forced into the molds under pressure.
Expanded metal is open mesh formed by slitting metal sheets. Metal mesh fabric is made by weaving or welding strips or wires of metal into a sheet that ranges from rigid to flexible. Perforated metal sheets have holes in various shapes and sizes that are stamped out of the sheet of metal. Industrial steel plates have pressed or stamped raised patterns.
When used for components of building structure, steel is produced in several standard metal shapes. I-beams are designed to place the material where most of the strength is needed, with flanges at the top and bottom, and a thin connecting element, thus the standard “I” shape. A “W” shape refers to a wide flange. Other shapes used in construction include C-shapes, angles,