Rotationally molded parts have to follow some restrictions that are different from other plastic processes. As it is a low pressure process, sometimes designers face hard to reach areas in the mold. Good quality powder may help overcome some situations, but usually the designers have to keep in mind that it is not possible to make some sharp threads used in injection molded goods.

Some products based on polyethylene can be put in the mold before filling it with the main material. This can help to avoid holes that otherwise would appear in some areas. This could be also achieved using molds with movable sections.

Another limitation lies in the molds themselves. Unlike other processes where only the product needs to be cooled before being removed, with rotational molding the entire mold must be cooled. While water cooling processes are possible, there is still a significant down time of the mold. Additionally, this increases both financial and environmental costs. Some plastics will degrade with the long heating cycles or in the process of turning them into a powder to be melted.

Material requirements

Due to the nature of the process, materials selection must take into account the following:

Due to high temperatures within the mold the plastic must have a high resistance to permanent change in properties caused by heat (high thermal stability).

The melted plastic will come into contact with the oxygen inside the mold—this can potentially lead to oxidation of the melted plastic and deterioration of the material’s properties. Therefore, the chosen plastic must have a sufficient amount of antioxidant molecules to prevent such degradation in its liquid state.

Because there is no pressure to push the plastic into the mold, the chosen plastic must be able to flow easily through the cavities of the mold. The parts design must also take into account the flow characteristics of the particular plastic chosen