When to choose rotomolding

Every manufacturing process has particular advantages and disadvantages. In the world of plastics, rotational molding is an excellent method of producing large parts inexpensively in low-to-moderate volumes over short production runs. When considering a project for rotomolding, review the following criteria:

- Estimated annual usage runs between one and 15,000 units.

- The desired part is hollow or can be molded in halves and cut apart after forming.

- The components are large, typically more than 2 lb.

- Tooling and mold costs must fall between $2,000 and $40,000.

- Lead time is short, typically between four and eight weeks.

The process itself involves placing granular, powdered plastic resin (or liquid resin in some cases) inside a cold mold. This mold is the shape of the final part, and it's placed inside an oven where it is rotated biaxially to distribute the powdered resin over the entire interior surface of the mold.

As the oven warms to between 300 and 700F, the heat warms the steel or aluminum mold. Resin touching the inside walls of the mold melts and sticks to the surface, and the process continues until all the resin is melted. Then the mold is water- or air-cooled to cause the resin to harden.

The most popular material for rotomolding is polyethylene, though PVC, fluoropolymers, polypropylene, and other materials can also be used. Foaming residents and advanced engineered resins are increasing in popularity, and should expand the opportunities for rotomolding into more product areas.