Tractor fuel tank, water tank, plastic products manufacturing rotomolding machine

MACHINES, MOLDS, MATERIALS

The principle of rotational molding of plastics isn’t complicated. Basically the process consists of introducing a known amount of plastic in powder, granular, or viscous liquid form into a hollow, shell-like mold, and then rotating that tool biaxially in an oven until the resin melts and coats the inside of the mold cavity. The tool is then cooled, and the part is removed from the mold. And that’s it. If you’re counting on your fingers, that’s a mere four steps: mold charging, mold heating, mold cooling, and part removal.

The equipment is a bit more complicated, and rotational molding machines themselves are made in a wide range of sizes. Rotomolding units normally consist of molds, an oven, a cooling chamber, and mold spindles. The spindles are mounted on an arm biaxially rotating the mold or molds, which provides a uniform coating of the plastic inside each mold as it’s heated. There are two types of turret rotational molding machines commonly used: independent-arm and fixed-arm. In fixed-arm turret machines, all of the arms — typically three — index at the same time. This requires that heating, cooling, and servicing operations must be done at the same length of time for each arm. Independent-arm machines, by contrast, provide process flexibility by allowing one arm to index while the other arms can remain stationary.

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