Rotational Moulding - The Facts
Rotational moulding is a technique of manufacturing, both economically and a limitless range of plastic objects in all shapes and sizes. Rotational moulding differs from other processing methods in that the heating, melting, shaping and cooling stages all occur after the polymer is placed in the mould, therefore there is no pressure applied during forming.
The concept behind rotational moulding is to have a hollow mould, each designed to a specific requirement. Using a rotational moulding machine, powdered plastic is placed into these moulds and placed inside the machine where the temperature is raised to the appropriate level and then rotated in two axes. The mould itself rotates through 360° while the whole machine oscillates in one or two planes. The result of this combined operation is to melt the plastic and gradually cover the inside of the mould, to form the appropriate shape.
Rotational moulding is the most cost effective process compared to blow moulding, vacuum forming, GRP moulding and fabrication and is ideal for shaping complex customised mouldings. The rotational moulding process is suited for the production of small as well as large volume productions, the main advantage being that the mould costs are low. The material most often used in rotational moulding are 'Polyethylene' and 'Polypropylene'.
Advantages of rotational moulding:
- Stress-free products
- Minimum design
- Low mould costs
- Economically produced large products
Materials used in rotational moulding:
- Polythene (low density)
- Polypropylene
- Ethylene Vinyl Acetate
- Polyvinyl Chloride
Typical examples of rotational moulding:
- Manhole inspection chambers
- Slides and climbing frames
- Children's playhouses
- Canoes and kayaks
- Rainwater tanks
- Diesel fuel tanks
- Traffic cones
- Pallets
Rotational moulding process explained:
- Plastic is introduced to a mould in powder form up to the mass required for the product.
- The mould is then closed and passed into an oven chamber, where it is heated to a temperature typically 220°C and 400°C. Whilst in the oven chamber it is rotated both on its vertical and horizontal axis.
- As the mould rotates and heats up, the mass of powder within begins to melt and adheres to the inner surface of the mould. The rotation and heating continues until an even layer of plastic is achieved over the mould. The mould is then taken out of the oven whilst still rotating and moved into a cooling chamber.
- Cool air is directed at the mould but in some cases water jets are used to cool the mould. When the plastic inside the mould has become solid, the mould is removed from the cooling chamber. The plastic component is then removed and allowed to finish the cooling process unrestricted by the mould.
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or email info@trifibre.co.uk for further details.
