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In rotational molding, the product is formed from liquid or powdered thermoplastic resin inside a closed mold or cavity while the mold is rotating biaxially in a heating chamber. To obtain this mold rotation in two planes perpendicular to each other, the spindle is turned on a primary axis, while the molds are rotated on a secondary axis (Fig. 14–1).
Rotational molding (also popularly known as rotomolding) is best suited for large, hollow products requiring stress-free strength, complicated curves, a good finish, a variety of colors, a comparatively short (or very long) production run, and uniform wall thickness. It has been used for products such as fuel tanks, furniture, tilt trucks, industrial containers, storage tanks, portable outhouses, modular bathrooms, telephone booths, boat hulls, garbage cans, light globes, ice buckets, appliance housings, and toys (Fig. 14–2). The technique is applicable to most thermoplastics but is most widely used with polyethylene.
Virtually unlimited design possibilities (parts as small as a golf ball to a 22,500-gallon agricultural tank).
Relatively low machinery cost.
Low tooling costs.
Strong outside corners in virtually stress-free parts.
Part finish from matte to high gloss.
Simultaneous processing of multiple colors.
Simultaneous processing of different parts.
Quick mold changes.
Possibility of molding in metal inserts.
Molded-in multicolor graphics.
Multilayer molding for chemical resistance or strength.
Double-walled parts molding for additional rigidity.
Possibility of minor undercuts.
Virtual 100% usage of material (no scrap).
KeywordsInjection Molding Golf Ball Parting Line Mold Rotation Boat Hull
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