Rotational Moulding
Rotational molding, also called rotomolding or rotational casting, is a thermoplastic processing method for producing hollow parts, from the most simple to the very complex.
The principle of rotational molding of plastics is simple. Basically the process consists of introducing a known amount of plastic in powder, granular, or viscous liquid form into a hollow, shell-like mold. The mold is rotated and/ or rocked about two principal axes at relatively low speeds as it is heated so that the plastic enclosed in the mold adheres to, and forms a monolithic layer against, the mold surface. The mold rotation continues during the cooling phase so that the plastic retains its desired shape as it solidifies. When the plastic is sufficiently rigid, the cooling and mold rotation is stopped to allow the removal of the plastic product from the mold. At this stage, the cyclic process may be repeated. The basic steps of (a) mold charging, (b) mold heating, (c) mold cooling, and (d) part ejection are shown in Figure Fig. Rotational Moulding Materials Currently polyethylene, in its many forms, represents about 85% to 90% of all polymers that are rotationally molded. Crosslinked grades of polyethylene are also commonly used in rotational molding. PVC plastisols make up about 12% of the world consumption, and polycarbonate, nylon, polypropylene, unsaturated polyesters, ABS, polyacetal, acrylics, cellulosics,
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