Rotomolding

Rotomolding, or rotational molding, is a manufacturing process for producing hollow plastic parts. In the process, a hollow mold is filled with polymer resin, typically thermoplastic pellets or powder. The mold is heated and simultaneously rotated about two perpendicular axes inside an oven. As the mold turns, the softened polymer coats the interior surface, building up a hollow part with a relatively uniform wall thickness as the material melts and adheres to the mold.

After the desired melt has formed, the mold is cooled while still rotating, allowing the part to solidify while maintaining its shape. The mold is then opened and the finished part is demolded. The process avoids high pressure and can accommodate complex geometries, producing large, seamless hollow components.

Materials and equipment used in rotomolding are designed for thermoplastics such as polyethylene (HDPE, LDPE, MDPE), polypropylene, and PVC, among others. Molds are typically made of steel or aluminum, sometimes with interior coatings to ease release. Equipment includes a heated oven, a two-axis rotating frame (turntable and arm system), and a cooling system. Process parameters—such as heat time, rotation speeds, and cooling time—control wall thickness and part quality.

Advantages of rotomolding include the ability to produce large, complex, hollow parts with relatively low tooling costs and good impact resistance. Common applications are water and chemical storage tanks, chemical drums, camping gear, kayaks, playground equipment, and automotive or industrial components. Limitations involve longer cycle times, moderate dimensional tolerances, and material limitations compared with other plastics processes. Rotomolding has evolved with automation and improved mold coatings, expanding its industrial and consumer uses.