Centrifugal casting is a manufacturing process that is used to produce parts with thin walls. This technique is generally used for cylinders or for stock parts in standard sizes that are not finalized products, unlike investment casting products produced through the technique of wax casting.
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Centrifugal casting produces high quality parts with uniform wall thicknesses because it has tight control over the material. The casting is fairly free from defects and any present impurities settle near the inner surface. Centrifugal casting allows for high production rates and does not have as much waste metal as do other processes. Metals such as iron, steel, copper, nickel or aluminum are the most common materials though glass or mixed materials are also possibilities. Parts produced through centrifugal casting are typically no more than 10 feet in diameter and 50 feet long with wall thicknesses ranging from a tenth of an inch to 5 inches. The outside surface is very fine while the interior may require machining to remove impurities and inclusions. The equipment used to produce the parts may have an axis to produce long thin cylinders or a vertical axis for rings. Typical parts made by centrifugal casting include pipes, boilers, pressure vessels, cylinder liners, sleeve valves and other cylindrical metal parts. It can also cast disks such as railway wheels or fittings for applications in which the grain and balance are important.
The process of centrifugal casting involves a long cylinder permanent mold that is mounted on rollers attached to a motor that continually rotates the mold around its axis at speeds from 300 to 3,000 rotations per minute. A ladle is used to pour molten metal into a pouring basin or directly into the mold. Centrifugal force is the force that causes substances to move away from their center of rotation and as metal enters the spinning tube, it is centrifugally thrown to the wall. This creates parts with even wall thicknesses and smooth outer surfaces. When the metal is cool and solidified the part is slid out, ready for further processing or machining. Most castings solidify beginning from the outside which may create structural zones such as the chill zone which forms almost instantly on the mold wall. The columnar zone is the intermediate layer with beneficial metallurgic properties. The equiaxed zone is the inside layer. The chill and equiaxed zones may be removed for certain applications where only the columnar zone is desired. Bimetallic pipes are formed when two different metals are poured in together. The varying densities and weights allow one metal to sink under the other, resulting in a pipe with the two metals in distinct layers.
