Process Overview
The rotational moulding process starts with a good quality mould that is placed in a moulding machine that has a loading, heating, and cooling area.
Several moulds may be placed on the machine at the same time. Pre-measured plastic resin is loaded into each mould, and then the moulds are moved into the oven where they are slowly rotated on both the vertical and horizontal axis. The melting resin sticks to the hot mould and coats every surface evenly. The mould continues to rotate during the cooling cycle so the parts retain an even wall thickness.
Once the parts are cooled, they are released from the mould. The rotational speed, heating and cooling times are all controlled throughout the process.
Design Advantages
Rotational moulding offers design advantages over other moulding processes. With proper design, parts that are assembled from several pieces can be moulded as one part, eliminating expensive fabrication costs.
The process also has a number of inherent design strengths, such as consistent wall thickness and strong outside corners that are virtually stress free. If additional strength is required, reinforcing ribs can be designed into the part.
Rotational moulding delivers the product the designer envisions. Designers can select the best material for their application, including materials that meet FDA requirements. Additives to help make the part weather resistant, flame retardant, or static free can be specified.
Inserts, threads, handles, minor undercuts, flat surfaces that eliminate draft angles or fine surface detail can all be part of the design. Designers also have the option of multi-wall moulding that can be either hollow or foam filled.
Cost Advantages
When cost is a factor, rotational moulding has the advantage over other types of processes as well. In comparison to injection and blow moulding, rotational moulding can easily produce large and small parts in a cost effective manner. Tooling is less expensive because there’s no internal core to manufacture. Since there is no internal core, minor changes can be easily made to an existing mould.
And because parts are formed with heat and rotation, rather than pressure, moulds don’t need to be engineered to withstand the high pressure of injection moulding.
Production costs for product conversions are reduced because lightweight plastics replace heavier, often more costly materials. This makes rotational moulding as cost effective for one-of-a-kind prototypes as it is for large production runs.