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 mould, but shares slow rotational speeds in common with rotational molding. This kind of rotocasting should not be confused with centrifugal casting.
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. Development led to G.S. Baker's and G.W. Perks' process of producing hollow chocolate Easter eggs in 1910. Rotational molding had developed further when R.J. Powell made mention of the commonly used ratio of 4:1 between major and minor axes of rotation at slow rotation speeds. His patent covered this process for molding hollow objects from plaster of Paris in the 1920s. These early methods using different materials directed the advances in the way rotational molding is used today with plastics.
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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.
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. Plastics typically are made through human industrial systems.
Molding (American English) or moulding (British and Commonwealth English; see spelling differences) is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. This itself may have been made using a pattern or model of the final object. A mold or mould is a hollowed-out block that is filled with a liquid or pliable material such as plastic, glass, metal, or ceramic raw material. The liquid hardens or sets inside the mold, adopting its shape.
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