Rotational molding, rotomolding, or rotocasting is a production process to form hollow parts of limitless size. This is a cost-effective method to produce large plastic parts. Resins are added into a mold that’s heated and rotated slowly, both vertically and horizontally. The simultaneous heating and rotation distributes and fuses the resin on the inner surfaces of the mold. The result is a product that contains seamless parts with a uniform wall thickness with more material in corners to absorb shocks and stresses where they occur most.
Rotational molding has had a place in industry since the 1940’s. The materials prior to 1961 were limited to vinyl plastisols in liquid form and were used primarily in the manufacture of novelty items such as artificial fruit, mannequins, children’s toys, and hollow display items. What is new in rotational molding in recent years relates not to plastisols but to powdered resins of about 35 mesh which have triggered improvements in equipment design and the overall technology, making this technique among the major plastics processing methods of today.
In 1961, the first polyolefin powder, a low-density polyethylene, was publicly demonstrated to the rotational molding industry. Polyetheylenes remain one of the most popular materials for rotomolding, because of the process ability, broad range of properties, and low cost. Major thermoplastic raw material suppliers have investigated specially formulated powders for rotational molding, including polypropylene, nylons, polycarbonate, rigid polyvinyl chloride and others. These powders can be foamed or reinforced with fiberglass. In addition to the raw material suppliers, many rotational molders also have used custom grinding services or have their own in-plant grinding capabilities which have also enlarged the material selection for this process.