Rotational moulding is a technological process that can be used to manufacture hollow bodies in one piece, without the need for welding.
Thanks to this technology, it is possible to obtain pieces that are free from internal stresses and with a uniform thickness.
It is possible to mould very large articles, with highly complicated contours in a variety of colors and materials. The technique can also be used for co-moulding processes, where different types of moulds are used simultaneously to create finished products with a variety of surface finishes.
The investment costs in terms of equipment are much lower than those of other plastic product manufacturing technologies.
At present most of the production is carried out using linear and crosslinked polyethylene such as PVC, polypropylene, polyamide, polycarbonate.
What sets this technology apart is that the mould can be moved on two different axes: one in a fixed direction, and one variable.
This guarantees that the polymer comes into contact with all the internal surfaces of the mould, which, when heated, melt the polymer so that it adheres to them, covering them completely. In this way, the polymer, which is loaded in powder form, is melted one layer at a time, until the finished piece is created.
Since the mould is rotated slowly, the polymer is not applied to its internal surfaces by the action of centrifugal force, but simply by being melted when it comes into contact with the heated surfaces.
The rotational moulding cycle may be divided into four easily explained phases:
The mould is loaded with the desired quantity of powder of the chosen colour
The mould is heated for about 20 minutes at approximately 250 °C, and rotated according to the programmed primary and secondary rotation sequences.
The mould is cooled for about 20 minutes by means of air and water, while continuing to rotate in accordance with the programmed primary and secondary rotation sequences.
The mould is opened, the finished piece is removed, and the procedure is repeated, starting from phase 1.