ROTATIONAL MOULDING
Process
This method is also referred to as Rotamoulding or Rotomoulding. It is used to produce hollow plastic products. Post moulding operations enable the production of more complex products. It differs from other moulding methods in that the melting and moulding stages occur after the polymer is placed in the mould and no external pressure is applied.
There are four main stages:
Charging the mould – A predetermined amount of polymer powder is placed in the mould. Once the mould is dosed it is then placed into an oven.
Heating and Fusion – In the oven the mould rotates around two axes tumbling the powder. The rotation speed is relatively low (<20 revolutions per minute). As the mould becomes hotter the powder melts and sticks to the inner wall of the mould building up an even coating over the entire surface.
Cooling – After sufficient time to evenly distribute the molten polymer the mould is cooled using either air or water, or a combination of the two. The polymer solidifies to the required shape.
Demoulding – When the polymer has cooled sufficiently to retain its shape the mould is opened and the part removed.
Materials
Low and Linear Low Density Polyethylene, Polypropylene, EVA and PVC.
Products
Manhole inspection chambers
Water tanks
Fuel tanks
Canoes and kayaks
traffic cones
pallets
Children’s slides and playhouses
Advantages
Large mouldings can be produced economically
Minimum design constraints
No weld lines
Stress-free products
Comparatively low mould cost (moulds can be fabricated, cast or machined)
Disadvantages
Relatively long cycle times means higher part costs
May need more than one mould to achieve the required output
Material costs relatively high
Labour intensive