Centrifugal Casting
Centrifugal casting entails pouring a measured quantity of molten metal into a mold that is then rotated rapidly. The rotation of the mold forces the molten metal outward to give intimate contact between the metal and the mold. Spinning is continued until all the metal poured into the mold has solidified. Pouring must be done quickly to prevent chilling and laps. There are three standard types of centrifugal casting methods in general use:
True centrifugal easting, where the mold is rotated about its own axis without using a central core. If the mold is partially filled, a hole appears along the center of rotation of the casting, the diameter of the hole being determined by the amount of metal used. The weight of casting produced to that of metal poured approaches I: I.
Semi-centrifugal casting, where central cores are used to give irregular shapes to the central hole. A measured amount of metal is poured so the mold space between the core and the outer wall is filled completely. Proper design of the mold is essentia] so that directional solidification of the metal is retained. Sand or plaster cores are usually employed. Differentially heated or cooled outer molds may be needed to control the direction of solidification.
Centrifuged casting, where irregular shapes can be obtained that would not be possible if the parts were rotated on their own axes. In this process a number of molds are arranged about a central sprue like the spokes of a wheel. Molten metal is fed into the castings through radial gates. The process is similar to semicentrifugal easting, except that several castings are produced at once, and the molds are not spun on their own axes. Directional solidification is a problem in this process, but it can be solved by proper location of the castings, proper gating, and mold temperature control.
Process Data
Centrifugal casting molds may be made of a variety of materials, including steel, cast iron, sand, and graphite. Various wall coatings can be used, such as a mixture of graphite and sodium silicate in water.
Most aluminum casting alloys suitable for other processes can be used for centrifugal casting. The alloys should be poured at about 100°F less than with static casting. Alloys with short solidification ranges are preferable to those with wide freezing ranges.

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