Rotomoulding is an alternative to thermoforming, blow molding and injection molding, and although it is lower in cost, this process is not as common because of the complex and large machinery required for the fabrication process.
Roto moulders produce many different parts and products for the food and beverage processing, medical, pharmaceutical, waste management, marine, sporting goods, recreation, toy, packaging, materials handling, automotive, plumbing and construction industries.
They are composed of a series of moulds, an oven, a cooling chamber and large mould spindles that are mounted on a rotating axis. The roto molding process begins with the fabrication of the mould, which is made either of stainless steel or aluminum.
Depending on the complexity, they are either welded or die cast. Aluminum moulds are thicker, since it is a softer metal. The polymer resin, in the form of fine powder, is poured into the mould. The spindles begin rotating in two directions into the oven chamber.
Under high heat, the plastic melts and evenly coats the inside walls of the mould. To cure, the moulds are then taken to a cooling chamber.
There are several different types of roto moulders, and they include rock and roll, clamshell, vertical rotational, shuttle and carousel machines. Rock and roll machines are composed of an arm that holds a large mould.
Clamshell machines are also single-arm configurations and are considered small. Vertical rotational machines are energy efficient and can fit into compact heating and cooling chambers. Shuttle machines move the moulds from different heating and cooling areas.
They can fabricate large numbers of products at once, but require a lot of operating space. Finally, carousel machines, which are the most common type, have several arms that can be in the heating or cooling chambers simultaneously. The cooling process takes about 20 minutes.
Once the plastic has cured, the newly formed product is unloaded manually, which can be difficult if the plastic has shrunk during the process. Parts that emerge from roto moulders, if they are intended to have holes or openings, must be sent for additional processing like cutting and surface finishing.