Rotational molding is a three-stage, no-pressure, plastic molding process that provides an economical manufacturing method for producing large or small seamless, lightweight, stress-free, one-piece, hollow plastic parts. Rotational molding differs from all other processing methods in that the heating, melting, shaping, and cooling stages all occur after the polymer powered resin is placed in the mold, and that no external pressure is applied during the entire process.

Process Overview

The rotational molding process starts with a quality mold that is placed on one of the arms of the rotational molding machine and consists of three stages: loading-unloading stage, heating (oven ) stage, and controlled cooling stage.

Several molds may be placed on the machine at the same time. Pre-measured plastic resin is loaded into each mold. The molds are then moved into the oven where they are slowly rotated on both the vertical and horizontal axis. The melting resin begins to coat the internal surface of the heated mold evenly, which allows the operator to control the wall thickness.

Once the parts are cooled, they are released from the mold. The rotational speed, heating and cooling times are all controlled throughout the process.

Rotational molding offers design advantages over other molding processes. Starting with a proper design, parts that are assembled from several pieces can be molded as one part, eliminating expensive fabrication costs.

The process has a number of strengths, including consistent wall thickness and strong outside corners that are virtually stress free. Reinforcing ribs can be added for additional strength.

As a result, rotational molding delivers the product the designer envisioned. Designers can select the best material for their application, and additives can be added to provide additional product features such as weather resistance, flame retardant, or static-free.

When cost is a factor, rotational molding offers considerable advantages over other processes. When compared to injection and blow molding, rotational molding can easily produce large and small parts in a cost effective manner. Tooling is less expensive since there is no internal core to manufacture.

Production costs for product conversions are reduced since lightweight plastics replace heavier, more costly materials. Rotational molding is ideal for one-of-a-kind prototypes as well as larger production runs.