About Rotational Moulding
The process starts with specially formulated resins such as plastisols, polyethylene, polycarbonate, acetate butyrate, polyamide, elastomers, polyurethane, polypropylene, ethylene vinyl acetate, and fluorocarbons. Cutting-edge advancements are being made with cross-linked polyethylene and nylon.
Rotational moulding, also known as rotomoulding is a technique for creating hollow plastic products. For certain liquid vinyls, the term slush moulding is also used. This method stands out due to its low residual stresses and cost-effective moulds. It’s particularly unrivalled when it comes to producing large, one-piece hollow objects over 2 cubic metres. While rotational moulding is renowned for manufacturing tanks, it’s also versatile enough to produce complex medical devices, toys, leisure craft, and visually striking point-of-sale products.
Explore Professor Roy Crawford’s quick guide to rotational moulding for more insights..
Design
Rotational Moulding makes a huge range of products possible. With good design, quality construction and even decoration, parts are fit for purpose, aesthetically pleasing and made to last!
Machinery
There are a variety of machines used in rotomoulding with purpose built moulds to develop the necessary parts. It can also include different fittings & inserts in the product design.
Materials
Rotational moulders currently use several different materials for rotational moulding however most of the products made using the process use polyethylene in a powder form.
Sustainability
Rotomoulding makes an immense contribution to the environmental sustainability through rainwater harvesting and its intrinsic recyclability.
How It Works
Design
Exceptional rotomoulded products begin with exceptional design. Our unique low-stress part formation process ensures material flows seamlessly around the mould, making early-stage design crucial. Skilled designers leverage this process to enhance strength, functionality, and aesthetics. Rotomoulding often employs computer-aided design (CAD) and finite element analysis (FEA) to guarantee parts are fit for purpose, perform efficiently, and last their intended lifecycle. Want to dive deeper into designing for rotational moulding? Explore our Designer’s Guide to Rotational Moulding by Glen Beall or browse our selection of rotomoulding books.
Explore our Designer’s Guide to Rotational Moulding by Glen Beall or browse our selection of rotomoulding books.
Fill
The process begins by placing the material, ground into powder or granules, into a hollow or shell-like mould. Various materials are utilised in rotomoulding chosen based on the desired attributes of the final product. Materials can be selected for their strength, rigidity, flexibility, surface finish, chemical resistance, and other properties. A skilled rotational moulder can provide a range of materials to suit your product needs and help you access high-quality moulds to ensure the best possible outcome. Discover more about rotomoulding materials here.
Heat & Rotate
Almost all rotational moulding involves using heat to sinter or partially melt the material within the mould. This can be achieved through various methods and machinery. Open flame techniques involve rotating the moulds over an open flame, while other machines use ovens to rotate the moulds inside. Some machinery heats the moulds directly. Although less common, room temperature vulcanising materials are also available and don’t require heat to form parts. Parts are rotated on one or two axes during the process, ensuring even coverage of the mould walls to create the desired part. These rotations can be programmed to create walls of varying thickness, depending on the end product's requirements. The material must be heated sufficiently to eliminate bubbles and form a solid part. For more details about the machinery and moulds used in rotomoulding, follow this link.
Cool
The final stage of the process involves removing the part from the mould and allowing it to cool properly. As most plastics change during cooling, controlling this phase can enhance the strength and other features of the final product. Cooling can be achieved through ambient air circulation around the mould, spraying the mould with water, or using a very fine mist. Cooling in rotomoulding is a specialised area; for more in-depth information, consider purchasing our ARMA Guide to Cooling.
Release
Once cooled to the optimal temperature, the rotomoulded parts are removed from the mould. They often continue cooling after removal and may need to be placed on special frames to ensure precise final parameters. This stage is when value-adding typically occurs, ranging from simple trimming to the addition of various fixtures, fittings, graphics, or decorations to complete the final part. If you're intrigued and want to learn more, check out the detailed information above on the rotomoulding process.
