Rotational molding
making hollow plastic objects in a heated mold
Rotational molding (BrE: moulding) involves a heated mold which is filled with a charge or shot weight of the material. It is then slowly rotated (usually around two perpendicular axes), causing the softened material to disperse and stick to the walls of the mold forming a hollow part. In order to form an even thickness throughout the part, the mold rotates at all times during the heating phase, and then continues to rotate during the cooling phase to avoid sagging or deformation. The process was applied to plastics in the 1950s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over time, improvements in process control and developments with plastic powders have resulted in increased use.
Rotocasting (also known as rotacasting), by comparison, uses self-curing or UV-curable resins (as opposed to thermoplastics) in an unheated mold, but shares slow rotational speeds in common with rotational molding. This kind of rotocasting should not be confused with centrifugal casting.
History
In 1855 a patent taken out by R. Peters in Britain documented the first use of a rotating mechanism producing "two centrifugal motions at right angles to each other" by means of beveled gearing, and heat. This rotational molding process was used to create artillery shells and other hollow vessels, the main purpose of which was to create consistency in wall thickness and density. In a U.S. patent in 1905, F.A. Voelke described a method including a polymer for the production of articles using paraffin wax.
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This entry incorporates text from “Rotational molding” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.