Rotational moulding, also known as rotomoulding, is a versatile plastic manufacturing process used to produce large, hollow plastic parts. Unlike injection moulding or blow moulding, this method uses finely powdered plastic resin that is heated and rotated in a mould to coat its interior evenly.
The process takes place on a rotational moulding machine, with the most common type being the carousel machine. These machines enable efficient production and are ideal for custom plastic moulding, such as the specialised components manufactured by Contact Plastics.
Rotational moulding sits in the middle of the plastic manufacturing spectrum in terms of cost and production volume. Here's why it is a popular choice for many industries:
Moderate mould costs – Cheaper than injection moulding but more expensive than compression or dip moulding.
Mid-range production output – Typically around 20 moulded parts per 24 hours per mould.
Rotational moulding is a precise, multi-step process designed to create high-quality, hollow plastic parts. Here's how it works:
Stage 1: Loading the MouldAt the loading station, the mould is opened and a pre-measured amount of powdered plastic (polymer) is placed into the mould cavity. This step ensures consistent material distribution and correct final product weight. |
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Stage 2: Sealing and Transfer to OvenThe mould is closed using clamps or bolts, ensuring a tight seal. The machine's carousel arm then moves the mould into the heating station (oven), where the next stage begins. |
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Stage 3: Heating and RotationInside the oven, the mould is heated while rotating on two axes. This even rotation ensures the polymer melts and adheres uniformly to all interior surfaces of the mould. |
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Stage 4: Cooling PhaseAfter heating, the mould is moved to the cooling station. It continues to rotate while large industrial fans rapidly cool the exterior, allowing the melted plastic to solidify evenly inside the mould. |
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Stage 5: Final Cooling and RotationAs cooling continues, two-axis rotation helps maintain consistent wall thickness and prevents deformation. The part begins to harden within the mould cavity, readying it for safe removal. |
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Stage 6: Unloading and InspectionOnce fully cooled, the mould returns to the loading station. Operators open the mould and remove the final part, inspecting it for proper curing, shape accuracy, and material integrity. At this stage, the mould may also be cleaned and prepared for the next production cycle. |
Rotational moulding offers several unique benefits, making it ideal for manufacturing tough, durable plastic products:
Rotomoulded parts typically have thicker walls than injection or blow-moulded parts. This gives them excellent UV resistance. For example, Contact Plastics manufactures rotomoulded water barriers that withstand harsh South African weather and remain intact after 8+ years on the road.
Unlike injection moulding, rotomoulding allows for complex, hollow shapes. A good example is the Contact Plastics hose reel cabinet, which features a 4mm thick wall and a large hollow body – a design not feasible with injection moulding.
Rotomoulded parts can undergo post-production processes like:
Drilling
Assembly
Printing
Lacquering
Foam filling for added strength
This flexibility makes it ideal for custom and functional designs.
In Part 2 of our rotational moulding blog series, we’ll explore the different types of moulds used in rotomoulding and how to choose the right mould for your product design and production needs.
