Rotational moulders are machinery that cost-effectively fabricate a wide variety of seamless, single part plastic products. They use a combination of high heat, rotation and metal moulds to create plastic constructions that may be as small as a water bottle and/or the size of a large storage tank. Industries served include medical, waste management, marine, automotive and packaging.
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Among the processes practiced by rotational moulders is rotomoulding, an alternative to thermoforming, blow moulding and injection moulding that is lower in cost but not as common because of the large size and initial investment in the machinery. Rotational 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, school, 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 rotomoulding process begins with the fabrication of the mould, which is made of either 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 rotational moulders: the rock and roll, clamshell, vertical rotational, shuttle and carousel machines. The rock and roll machines are composed of a single arm that holds one large mould, perhaps for a plastic tank. Clamshell machines are also single arm and considered small. This machine is heated and cooled in the same chamber. Vertical rotational machines are energy efficient and can fit into compact heating and cooling chambers. Shuttle machines transport the moulds from different heating and cooling areas. They are able to fabricate large amounts of products at once, but require much space to do so. Finally, carousel machines, which are the most common type, have several arms that may be in the heating or cooling chambers simultaneously. The cooling process takes about 20 minutes. Once the plastic has fully cured, the newly formed product is manually unloaded, which can prove difficult if the plastic has shrunk. If the part has openings, they must be cut out.
