chloride (PVC) plastisol. The cooling method consisted of placing the mold into cold water. This process of rotational molding led to the creation of other plastic toys. As demand for and popularity of this process increased, it was used to create other products such as road cones, marine buoys, and car armrests. This popularity led to the development of larger machinery. A new system of heating was also created, going from the original direct gas jets to the current indirect high velocity air system. In Europe during the 1960s the Engel process was developed. This allowed large hollow containers to be manufactured in low-density polyethylene. The cooling method consisted of turning off the burners and allowing the plastic to harden while still rocking in the mold. In 1976, the Association of Rotational Moulders (ARM) was started in Chicago as a worldwide trade association. The main objective of this association is to increase awareness of the rotational molding technology and process. In the 1980s, new plastics, such as polycarbonate, polyester, and nylon, were introduced to rotational molding. This has led to new uses for this process, such as the creation of fuel tanks and industrial moldings. The research that has been done since the late 1980s at Queen's University Belfast has led to the development of more precise monitoring and control of the cooling processes based on their development of the “Rotolog system”. Equipment and tooling Rotational molding machines are made in a wide range of sizes. They normally consist of molds, an oven, a cooling chamber, and mold spindles. The spindles are mounted on a rotating axis, which provides a uniform coating of the plastic inside each mold. Molds (or tooling) are either fabricated from welded sheet steel or cast. The fabrication method is often driven by part size and complexity; most intricate parts are likely made with cast tooling. Molds are typically manufactured from stainless steel or aluminum. Aluminum molds are usually much thicker than equivalent steel molds, as it is a softer metal. This thickness does not much affect cycle times because aluminum's thermal conductivity is many times greater than steel's. Owing to the need to develop a model prior to casting, cast molds tend to have additional costs associated with the manufacturing of the tooling, whereas fabricated steel or aluminum molds, particularly when used for less complex parts, are less expensive. However, some molds contain both aluminum