ROTATIONAL MOLDING PROCESS OVERVIEW In Rotational molding, liquid or powdered thermoplastic resin is formed inside a closed mold or cavity while the mold is rotating biaxially in a heating chamber. To obtain mold rotation in two planes perpendicular to each other (providing even distribution of the resin), the spindle is turned on a primary axis, while molds are rotated on a secondary axis. Rotational Molding (also popularly known as Rotomolding) is best suited for large, hollow products requiring seamless construction (for strength), complicated curves, a good finish, a variety of colors, and uniform wall thickness. The process has been used for products such as water tanks, storage tanks, industrial containers, outdoor chairs and benches, road barriers, portable outhouses, modular bathrooms, garbage cans, telephone booths, boat hulls, light globes, ice buckets, appliance housings (carpet and vacuum cleaners), and toys. The technique is applicable to most thermoplastics but is most widely used with polyethylene. There are essentially six basic steps in rotational molding; mounting the tool, loading resin, molding and curing, cooling, unloading the part, and final finish. 1. Tools are mounted on large spindles that will rotate during the heating process. 2. In the loading stage, powdered plastic is charged (material loaded) into the hollow mold. The mold halves are then clamped shut and moved into an oven where the loaded mold spins biaxially. 3. In the oven, heat penetrates the mold causing the plastic to become tacky and stick to the mold surface. Heating is done in a gas-fired hot-air oven. Because the mold continue to rotate while being heated, the plastics gradually become distributed on the mold cavity walls through gravitational force (centrifugal force is not a factor). As molten plastic flows through a bend in the mold, it slows producing a slight build up (which adds extra strength) in every corner. As the cycle continues, the polymer melts completely, forming a homogeneous layer of molten plastic. 4. When the parts have been formed, the molds move to a cooling chamber where cooling is accomplished by a cold water spray and/or forced cold air and/or liquid circulating inside the mold. The mold continues to rotate during the cooling cycle so as to ensure that the part does not sag away from the mold surface, causing distortion. 5. (Commercial Dryer Casing Shown here) The mold is then opened and the parts are removed. This can be done manually or by using forced air or mechanical means to eject the part. In final finish, parts are trimmed, and drilled to Nalpak's specifications. 6. The Tuffpak is then shipped to a local facility where the wheels, straps, locks and other finishing touches are completed.