Lo rotational molding - also known as rotomoulding – is a technology for processing plastic materials at low pressure and high temperature, based on the adhesion of plastic materials to rotating hollow moulds.

Rotational molding is used for the production of hollow bodies, which do not require subsequent welding and assembly phases and are practically tension-free.

The phases of the rotational molding process

Production of bells for paper collection

Le phases of a rotational molding process are the following:

• loading the mold with polymeric material, mostly in fine powder, but also in granules or liquid form;
• the mould, once loaded and closed, is heated (for example in an oven) and rotated along one or two axes, so that the polymeric material introduced into it can adhere to the walls of the mold itself, taking on its shape. It is very important to correctly manage the times of this heating and rotation phase: if heated for too long, in fact, the polymeric material could degrade; on the other hand, too short times could have the consequence of obtaining a plastic material that is not sufficiently homogeneous;
• cooling of the mold, always rotating, so that the polymer solidifies assuming the desired shape. Rotation is suspended when the polymer material has hardened sufficiently. In this phase, the polymeric material shrinks, which facilitates the subsequent phase of extracting the product from the mold. In this phase, a change in the apparent density of the polymer also occurs;
• the mold is then opened and the resulting piece is extracted.

Advantages of rotational molding

It is a niche technology in a certain sense competitive with other polymer processing technologies, such as injection moulding, blow moulding, or thermoforming, compared to which it can offer some advantages.

• simplicity and functionality,
• eliminating the need to resort to finishing operations,
• relatively low production of waste,
• process flexibility with the possibility of producing small batches at acceptable costs,
• relatively economical manufacturing of moulds,
• low costs of improved machinery, molds and accessories,
• applications are continually increasing.

Applications of rotational molding

It is a technology used mainly to produce small batches of mostly large-sized products, such as large containers, barrels, underground tanks, tanks for the storage of chemical substances, fuel tanks, oil tanks, tanks, water purification tanks, dustbins, bins and bell production for paper collection. Given its characteristics, this technology is also used for production of products for the most varied fields of application: armchairs, furniture parts and furnishing items, lamps, automotive components, medical and healthcare products (stretcher parts, medical kit boxes, oxygen facial masks), tools for agriculture and gardening, the toy industry and leisure items (parts of dolls, rocking horses, balls, toy houses), details of pleasure boats, details of floor polishers, tool boxes, manhole covers, and other items.