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In somewhere between 1940 and 1950 in the USA, the rotational moulding process was developed for a small number of plastics but its popularity did not take off because it was regarded as a slow process. In the past few years, however, process control improvements and plastic powder developments have resulted in a very large increase in its use.
When the Plastics were introduced to the rotational molding process in the early 1950s. One of the first applications was to manufacture doll heads. The machinery was made of an E Blue box-oven machine, inspired by a General Motors rear axle, powered by an external electric motor and heated by floor-mounted gas burners. the cooling method consisted of placing the mold into cold water. This process of rotational molding led to the creation of other plastic toys. In the ancient period of time the heated hollow mold is filled with a charge or shot weight of material, it is then slowly rotated causing the softened material to disperse and stick to the walls of the mold so that it should come out easily. Maintaining the thickness throughout the part the mould was use to rotate continuously to avoid any sought of defromation and sagging of the mold in the cooling phase. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.
As demand 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 the creation of large hollow containers to be created in low-density.
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.
There are various types of rotational moulding machine are used by the manufacturers. They are:
- Rock and roll machine
- Clamshell machine
- Vertical or up & over rotational machine
- Shuttle or swing arm machine
- Carousel machine