What is Rotational molding?

Rotomolding, also known as rotational molding, is a plastic manufacturing process that allows for the production of large, hollow parts with complex geometries, without the need for pressure. Unlike injection molding or extrusion, plastic rotomolding uses heat and bi-axial rotation to evenly distribute molten material along the inner walls of a mold, resulting in lightweight, durable parts with uniform wall thickness.

The process starts with a hollow metal mold—typically made of aluminum or steel—that is loaded with a pre-measured amount of plastic powder, such as polyethylene. The mold is sealed and placed inside an oven, where it rotates simultaneously on two perpendicular axes. This rotational molding of large parts ensures even melting and coating of the material throughout the mold. Once the plastic is fully melted and distributed, the mold is gradually cooled and the finished part is removed.

A key advantage of rotomolding is the ability to produce seamless, one-piece parts with excellent impact resistance and consistent thickness. Inserts, reinforcement areas, or surface textures can be integrated during the process, eliminating the need for post-molding assembly steps.

Plastic rotomolding is widely used across industries such as agriculture, urban furniture, automotive, marine, construction, and water treatment. Typical products include storage tanks, chemical containers, trash bins, outdoor furniture, kayaks, playground equipment, and large technical components. The process is also ideal for custom, low-volume production where durability and design flexibility are priorities.

One of the main technical benefits of rotomolding is that it is a pressure-free plastic manufacturing method. This reduces tooling costs and mold wear. However, cycle times are longer than in pressure-based processes, as heating, rotation, and cooling require controlled thermal management. As a result, rotomolding is better suited for medium or low production runs where tooling flexibility outweighs cycle time.

Product quality in rotomolding depends on several variables: polymer type, powder particle size and flowability, oven temperature, rotation speed and cycle duration, and cooling conditions. Careful control of these parameters ensures even material distribution, prevents defects such as bubbles or warping, and maintains repeatability across parts.

At companies like Plásticos Lezo, with expertise in multiple plastic processing technologies, plastic rotomolding is offered as an alternative for projects where injection molding is not viable due to size, geometry, or production volume. Combined with other techniques, rotational molding of large parts becomes a versatile tool to develop functional, durable solutions for various industrial sectors.

In summary, rotomolding is an efficient, flexible process that allows pressure-free plastic manufacturing—ideal for large, hollow, and high-strength parts. Thanks to rotational molding of large parts, custom, seamless products with excellent performance and finish can be produced, making it a key technique in plastic manufacturing.