Centrifugal Casting

Centrifugal casting or rotocasting is a casting technique which has application across a wide range of industrial and artistic applications:

Processes

• It is used as a means of casting small, detailed parts or jewelry. An articulated arm is free to spin around a vertical axle, which is driven by an electric motor or a spring. The entire mechanism is enclosed in a tub or drum to contain hot metal should the mold break or an excess of metal be used. Single use molds are prepared using the lost wax method. A small amount of metal in a crucible (a sort of ceramic pan) next to the mold is heated with a torch. When the metal is molten the arm is released, forcing (by centrifugal force) the metal into the mold. The high forces imposed on the metal overcome the viscosity, resulting in a finely detailed workpiece. A similar advantage is obtained by vaccum casting.
• For industrial casting of small parts using poured hot metal, a disk shaped mold is contained within a rotating drum, and molten metal is poured into the center.
• It is applied to the fabrication of large telescope mirrors, where the natural curve followed by the molten glass greatly reduces the amount of grinding required. Rather than being cast by pouring glass into a mold an entire turntable containing the peripheral mold and the back pattern (a honeycomb pattern to lighten the finished product) is contained within a furnace and charged with the glass material used. The assembly is then heated while spun at slow speed until the glass is liquid, then gradually cooled over a period of months.
• Also known in the glass industry as spinning, this process is similar to that used for metals. The centrifugal force pushes the molten glass against the mold wall, where it solidifies. (This cooling process takes anywhere between 16 to 72 hours depending on the impurities or volume of material.) Typical products made are TV picture tubes and missile nose cones.

Applications:

• This process is commonly used to shape glass into a spherical object such as a marble.
• In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3000 rpm) as the molten metal is poured. The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.