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Rotational Moulding

A process of moulding thermoplastics, ideal for the production of medium and large hollow items. Typical products suitable for rotational moulding, sometimes called rotomoulding, include tanks and containers, kayaks, garden products and furniture - the list is endless!

As with all processes and materials, it is important to weigh up the advantages against the disadvantages. For the design engineer it is important to have a basic understanding of the parameters of rotomoulding and its limitations. However, this is where the expertise of Rota Design comes in, guiding you through the pitfalls and capitalising on the positive benefits where appropriate.

A great advantage of rotational moulding to consider is the relatively cheap tooling costs especially in comparison to injection and blow moulding. A low initial investment provides an entry point for lower volume production with much faster time to market. Diversity of products and overall production cost in the rotomoulding industry are positive factors which make for many exciting and innovative products.

Tooling may be fabricated, cast or machined from solid and since moulds in general are not pressurised, tooling costs are extremely cost effective.

A disadvantage of rotational moulding is the relatively long cycle times and hence production output. It is essential therefore, to calculate the most cost-effective process given the volume of business against the tooling, overheads and material costs.

Rotationally moulded products may be simple or complex in shape and include features such as strengthening ribs, inserts of brass or steel, moulded threads, holes, textured and engraved surfaces.

The process provides a extremely uniform wall thickness even at corners and sharp angles. In comparison, blow moulding tends to stretch the molten plastic and the finished product has inherent stress and thus, locations where failure may occur in service.

The rotational moulding process has a limited range of mouldable polymers available which is a slight disadvantage to many designers. Polyethylene is the most commonly used material for rotomoulding but to its advantage it is extremely versatile.

In summary, therefore, large products may be produced without incurring high start-up costs. The fact that production rates are relatively slow is offset by the fact that you don't have to make millions of parts before the tooling costs are recovered.

Below is a simulation of the rotational moulding process with kind permission from the British Plastics Federation. Rota Design is a member of the British Plastics Federation.