What Is Rotational Moulding? A Guide to the Process

Rotational moulding, often shortened to rotomoulding, is a manufacturing process used to produce hollow, seamless plastic parts. It is the process behind everything from water tanks and chemical containers to playground equipment and road barriers. It is also our core process at Francis Ward, where we have manufactured rotomoulded products in the UK since 1986. If you are researching how to manufacture a hollow plastic product, this guide explains how rotational moulding works, what it does well, and the kinds of parts it suits.

What is rotational moulding?

Rotational moulding (or rotomoulding) is a manufacturing process that produces hollow, seamless plastic parts. Powdered plastic is placed inside a hollow mould, which is heated and slowly rotated on two axes. The plastic melts and coats the mould walls evenly, then cools to form a single, one-piece part.

Because the part is formed against the inside of the mould rather than forced in under pressure, rotational moulding produces stress-free parts with consistent wall thickness and no joins or weld lines. This makes it well suited to large, durable items that need to hold their shape and stand up to demanding conditions. It is the process we use to manufacture our own range of IBCs, drums and roll cages, as well as bespoke parts made to our clients’ own designs.

How the rotational moulding process works

The process follows four main stages.

1. Loading. A measured quantity of polymer, usually in powder form, is placed into one half of the mould. The mould is then closed and secured.

2. Heating. The mould moves into an oven and begins rotating slowly on two perpendicular axes. This biaxial rotation tumbles the powder across every internal surface as the heat builds, so the plastic melts and gradually coats the mould walls in an even layer. The rotation continues throughout, which is what gives the finished part its uniform thickness.

3. Cooling. The mould leaves the oven, still rotating, and is cooled using air, water spray, or a combination of the two. Controlled cooling helps the part hold its shape and reduces the risk of warping.

4. Unloading. Once the plastic has set, the mould is opened and the finished part is removed. The mould can then be loaded again for the next cycle.

The slow, low-pressure nature of the process is central to its character. It is not the fastest way to make a plastic part, but it produces robust, hollow components that many other processes cannot match.

Materials used in rotational moulding

Polyethylene is by far the most common material in rotational moulding, available in low, medium and high-density grades to suit different strength and flexibility requirements. Other polymers can also be used, including polypropylene, nylon and PVC, depending on the demands of the application.

Material choice can be tailored to specific needs such as impact resistance, temperature stability, chemical resistance, colour and UV resistance. Additive technology also allows for specialist grades, including fire-retardant, anti-static and anti-microbial options. At Francis Ward, we can match a polymer to your application and incorporate recycled content where it is suitable, which supports waste reduction without compromising on performance.

The advantages of rotational moulding

Rotational moulding offers several benefits that make it the right choice for particular products:

• Seamless, one-piece parts. With no welds or joins, there are no weak points where a part is most likely to fail or leak.
• Uniform wall thickness. Biaxial rotation distributes the material evenly, including into corners and complex shapes.
• Low tooling cost. Because the process works at low pressure, tooling can be made in sheet steel or cast or machined aluminium, which is considerably cheaper than the hardened tooling required for high-pressure processes.
• Large part capability. The process can produce sizeable items in a single piece, which would be difficult or costly by other methods.
• Design freedom. Features such as moulded-in inserts, double walls, textures and graphics can be built into the part.
• Durability. Rotomoulded parts are hard-wearing and well suited to outdoor, industrial and multi-trip use.

Common applications and products

Rotational moulding is used across a wide range of industries. Some of these products form part of our own range at Francis Ward, while many more are made across the sector, which shows the versatility of the process. Common applications include:

• IBCs, tanks and silos for storing and transporting liquids, powders and granules, including containers for dangerous and hazardous goods
• Seamless, heavy-walled rotomoulded drums for chemicals and multi-trip use
• Roll cages for distribution and logistics
• Agricultural tanks, troughs and equipment
• Septic tanks, drainage chambers and water treatment products
• Street furniture, playground equipment and traffic management products
• Buoyancy and offshore components
• Kayaks, canoes and other watercraft
• Wheelie bins, waste containers and material handling bins

Several of the products above, including our IBCs, drums and roll cages, are part of our standard range, and we also manufacture bespoke products to a client’s own design. If you have a product in mind, our contract rotational moulding service covers the full process, from design and tooling through to production.

Is rotational moulding right for your product?

Rotational moulding is an excellent fit for hollow parts, large items and lower to medium production volumes, where its low tooling cost is a real advantage. It is less suited to very high-volume runs or parts that need extremely tight tolerances or fine surface detail, where a process such as injection moulding may be more appropriate.

The best way to find out is to discuss the part with a manufacturer who runs more than one process and can advise you objectively. At Francis Ward, our technical team can review your design, recommend the right approach, and support you from initial concept through tooling and into full production.

Frequently asked questions

What is the difference between rotational moulding and rotomoulding? There is no difference. Rotomoulding is simply a shorter, informal name for rotational moulding.

What materials can be rotationally moulded? Polyethylene is the most common, in various densities. Polypropylene, nylon and PVC can also be used, along with specialist grades such as fire-retardant and anti-static materials, and recycled polymers where suitable.

Why is rotational moulding tooling cheaper than injection moulding tooling? Rotational moulding works at low pressure, so the tooling does not need to withstand the high forces involved in injection moulding. Moulds can be made from aluminium or sheet steel, which lowers the cost considerably.

Is rotational moulding suitable for low volumes? Yes. Its low tooling cost makes it a practical choice for prototypes, small batches and medium production runs, as well as larger volumes.

How large can rotationally moulded parts be? This depends on the manufacturer’s equipment. At Francis Ward, we can rotationally mould products up to 4.5 metres.

Talk to us about your project

If you are considering rotational moulding for a new product, or looking for a contract moulder to take on an existing design, our team can help. Send us a drawing, a specification, or an outline of what you need, and we will advise you on the best route to manufacture. Discuss your rotational moulding project or call us on 01274 707030