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151. The process of rotational molding

Rotational molding was an innovation of the 1940s, but wasn't widely used until the development of better technology that made the process faster. In addition, new polymer and plastic molds entered the marketplace and were well suited for rotational molds. This method of plastic molding has several advantages over some other techniques that result in higher prices for products and a less environmentally friendly process.

The first step in producing a lightweight and affordable polyethylene (plastic) product is to create custom molds. This is usually done using a computer software program capable of creating 3D images. The mold is most often made of aluminum because the lightweight material is easier to handle than some other metals although it may be a bit more costly. Machinists get to work tooling the mold from the product design. Once the mold is done, the rest of the process is in the hands of the plastics manufacturer where the rotational molding is done.

As the aluminum quickly heats up, the resin melts and continues to coat the inside of the mold. The time the mold spends spinning and heating is critical to the quality of the product. In the past it was up to the rotational mold experts to judge when a mold was ready to remove from the oven and cool. Today, sensitive instruments gauge the air temperature in the mold, improving quality control.

Fans are often used to help the mold cool. Unlike some other mold methods - such as injection molds - the cooling of the aluminum causes the mold to shrink slightly away from the interior of the mold. This allows easy removal of the largest products, such as water tanks. The product is then carefully inspected by the rotational manufacturer and, if it meets all specifications, is shipped to the customer.