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Rotational Molding

Rotational molding is a manufacturing process for producing hollow plastic parts. It is also known as rotomolding or rotocasting. Rotomolding uses heat and rotation on two axes to form plastic parts. The plastic used in the process is usually polyethylene in liquid, powdered or granulated form. Heat is applied to melt the plastic and form a layer against the mold as it is rotated  Often, the hollow part of the mold is rotated at varying speeds to ensure the plastic particulates or liquid melts and forms evenly. A long cooling process involving fans ensures that the part solidifies properly to prevent any structural defects.

Rotomolding creates parts that lack weld lines or joints. The process wastes very little material. Leftover polymer is often re-used to make additional parts. While the manufacturing time is longer than other methods, molds are relatively inexpensive and quick to produce. Rotomolding is much slower than injection molding, but large parts are significantly cheaper than other types of molding. Most molds can be used repeatedly.

Some examples of uses include: 

  • Plastic tanks
  • Traffic cones
  • Helmets

Rotomolding Design Considerations

  • Because of the nature of the materials (see our Materials page) used, parts can come in a variety of colors and with permanent designs or graphics, which can be applied either during or after the production process.
  • Shapes must be relatively simple.