The Rotomold Process

The Rotomolding or rotational molding plastic process produces large hollow parts or components of virtually any size or shape. In rotomolding, plastic resins is poured into the open cavity of a 2 or more part mold. The exact type and amount of resin is dictated by the part’s predetermined “recipe” based on the desired wall thickness and other characteristics.  The mold or tool is then closed and bolted shut creating a tight seal. The tool is attached to one of the arms of the rotational molding machine. Typically, each arm of the rotomold machine can hold multiple molds of similar size.

The rotational molding machine has three stages… loading and unloading, gas ovens generating high temperature, and a cooling station. Once the open mold is loaded and closed, the machine’s arm is moved into the gas oven. The arm articulates spinning the mold using centrifugal force to melt and evenly spread the resin throughout the mold and into the corners. The mold will spin for 90 seconds to a couple minutes as the recipe stipulates. The molds then move into the cooling chamber and continue to spin while they’re cooled either with air of cold water. The rotomolding process is completed when the mold shifts back the worker’s platform, is opened, the part is removed, and then the mold is again filled closed and bolted shut ready for another cycle.

Parts produced through the rotomold process all contain a seem where the two or more sides of the mold come together.  A well designed part will hide or locate the seem in a non-critical or inconspicuous area. Rotationally mold parts are often used in air or water tight applications like flotation devices, tanks, rain barrels, road barriers, and more.