Rotational molding, also referred to as rotomolding or rotational casting, is one of the fastest growing plastics processing methods today.
The rotational molding process uses melted plastic to form a desired product. The mold is placed on a biaxial rotation (i.e. rotation on two axes) and rotated until the melted plastic covers all parts of the mold to produce the desired hollow plastic product.
Rotational molding techniques can be used to make hollow items of any size, open or closed, and of any desired shape.
In recent years, rotomolding techniques have been developed extensively. On the production line, this process can now compete with, or outperform blow molding, injection molding and thermoforming. In many cases, pieces virtually impossible to fabricate by any other processes can be produced by rotomolding.
Equistar produces a range of Microthene® high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) powders, as well as Petrothene® HDPE and LLDPE resin pellets for the rotational molding market.
Benefits and Applications
Rotational molding permits production of a countless number of fully or partially closed items. Design versatility of rotationally molded pieces is almost unlimited.
Some typical applications for which rotational molding is particularly suited include the following:
- Commercial, industrial and agricultural storage tanks ranging in size from five to 22,000 gallons
- Containers for packaging and material handling
- Variety of industrial parts, including covers and housings, water softening tanks, tote bins
- Numerous under-the-hood and in-the-cab automotive parts
- Hobby horses, pool tables and any other small or large toys with complex shapes
- Baby cribs, balls, dolls and doll parts
- Display window mannequins and other hollow display figures of all sizes
- Playground equipment and sporting equipment, such as golf carts, footballs, juggling pins, helmets, dumbbells, golf tee markers, canoes and kayaks
Rotomolded parts are also used in portable outhouses, battery cases, light globes, vacuum cleaner and scrubber housings and garbage containers. Other applications include furniture, game housings, surf boards, traffic barricades and display cases.
Properties
The rigidity or flexibility of an item is controlled by the properties of the resin used and by the wall thickness of the molding.
The main differences between rotational molding and other plastics molding techniques, such as blow and injection molding, are as follows:
- Resin powder is used instead of pellets.
- The resin melts in the molds instead of being forced under pressure into the molds in a molten state.
- The mold has a biaxial rotation.
- Rotomolding molds are less expensive because of their simplicity.
- Operating pressures are relatively low, allowing molds to be made from less expensive materials