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Plastics Processing: Casting

Casting is a process most frequently used in the production of clear acrylic sheet or film.

Sheet casting may be accomplished by either a batch or a continuous process.

Batch Casting
In the batch cast, a plastic syrup is placed between two glass plates, then oven-cured for 12-16 hours. The process is slow, but results in high-optical-quality sheets with much smoother surfaces than would otherwise be possible.

Continuous Casting
Continuous casting involves flowing the syrup between polished stainless steel belts which cure the material during a journey through 10-15 individually temperature-controlled zones in an oven. This results in higher product throughput and more precise thickness control than batch casting. Due to the large space and equipment costs of this type of casting, it is not currently used very widely in the U.S.

Film Casting
Film casting is accomplished by extruding a resin melt through a wide slot die and onto a chill roll where it is set and cooled prior to being wound on rolls for transportation, storage, or further processing. While cast film is superior to blown film in terms of output, clarity, and uniformity, it doesn't have the strength of blown film; and its process involves considerably more waste.