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Rotomolding Equipment The equipment used in rotational molding is relatively simple but has many variations (Figure 13). The most common type of rotomolding machine is a multiple-spindle or carousel machine (Figure 14). Carousel machines are usually wheel-shaped. The spindles, each carrying a a group of molds or a single large mold, are mounted on a central hub and driven by vari- able motor drives. Most carousels have the freedom to rotate in a complete circle. The carousel consists of a heating station or oven and a cooling sta- tion. In many cases, the carousel also is equipped with an enclosed chamber and a loading and unload- ing station. The shuttle-type machine (Figure 15) is used most often to rotomold larger parts. A frame for holding one mold is mounted on a movable bed. Incorporated in the bed are the drive motors for turning the mold biaxially. The bed is on a track that allows the mold and the bed to move into and out of the oven. After the heat- ing cycle is complete, the mold is moved into a non-enclosed cooling station. A duplicate bed with a mold is then sent into the oven from the opposite end. The clamshell (Figure 16) utilizes an enclosed oven that also serves as the cooling station. This machine uses only one arm and the heating, cooling and loading/unloading sta- tions are all in the same location. Other types of equipment include “open-flame” and “rock-and-roll.” The newest type of rotomolding equipment is the Wytkin Composite Mold Technology (CMT), which utilizes a mold that is electrically heated and air cooled to produce the part (Figure 17). Heating Stations Most rotomolding ovens are fired by natural gas, using blowers to distribute heat throughout the chamber. Some ovens have the capability to be heated by oil or propane gas, but natural gas is the preferred method. Normal oven temperatures are 400° to 850°F (270° to 454°C). Ovens must be well insulated to minimize heat loss. Hot-air convection is the most com- monly used heat source, although hot-liquid conduction and infrared radiation are also used. Figure 13. Schematic of a system used to obtain mold rotation in two perpendicular planes MOLD HOLDER HINGE SPIDER SECONDARY AXIS OF ROTATION CLAMP PARTING LINE UPPER AND LOWER MOLD HALVES SPINDLE FIRST DRIVE CONNECTED TO INNER SHAFT PRIMARY AXIS OF ROTATION SECOND DRIVE CONNECTED TO SPINDLE Figure 14. Carousel type machine OVEN LOAD-UNLOAD STATION COOLING STATION 10 MOLDSPDF Image | A Guide to Rotational Molding Equistar
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