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Rotational Moulding

Overview

Rotational moulding (often referred to as Rotamoulding or Rotomoulding) is a process used for producing hollow plastic products. By using additional post-moulding operations, complex components can be produced enabling the process to compete effectively with other moulding and extrusion practices.

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Overview

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 no external pressure is applied during forming.

This provides the following advantages:

Economically produced large products
Minimum design constraints
Stress-free products
No polymer weld lines
Comparatively low mould costs

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A range of Rotamoulded Tanks

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EXAMPLES OF ROTAMOULDED
PRODUCTS

The Process

The Rotational Moulding process is essentially split into four operations:

Charging Mould

A pre-determined amount of polymer powder is placed in the mould. With the powder loaded, the mould is closed, locked and loaded into the oven. The powder can be pre-compounded to the desired colour.

Heating & Fusion

Once inside the oven, the mould is rotated around two axis, tumbling the powder – the process is not a centrifugal one. The speed of rotation is relatively slow, less than 20 rev/min. The ovens are heated by convection, conduction and, in some cases, radiation. As the mould becomes hotter the powder begins to melt and stick to the inner walls of the mould. As the powder melts, it gradually builds up an even coating over the entire surface.

Cooling

When the melt has been consolidated to the desired level, the mould is cooled either by air, water or a combination of both. The polymer solidifies to the desired shape.

Unloading/Demoulding

When the polymer has cooled sufficiently to retain its shape and be easily handled, the mould is opened and the product removed. At this point powder can once again be placed in the mould and the cycle repeated.

Typical Materials Used

Polyethylene (Low Density)
LDPE, LLDPE

Polypropylene
PP

Ethylene Vinyl Acetate
EVA

Polyvinyl Chloride
PVC

Typical Products Produced

Manhole inspection chambers
Rainwater tanks
Slides and climbing frames
Diesel fuel tanks
Childrens playhouses
Traffic cones
Canoes and kayaks
Pallets

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We are grateful to Balmoral for their assistance in the preparation of this processes page. For more information click here. Alternatively email tanks@balmoral.co.uk directly.