ENGINEERING TECH TIPS | 2 MAY 2025

Rotational Molding

Tech Tips from Our Engineers at Bamberger Amco Polymers

History & Introduction

Rotational molding, also known as roto molding, is a process that produces seamless, hollow, single- or double-walled parts. This is achieved by heating a powdered resin in a hollow mold while slowly rotating it. When the molten material is cooled, the resin solidifies into a finished part.​

From antiquity to the modern day, the rotational molding process has continued to evolve and improve. The basic concept was used by the Egyptians for the production of ceramics. Hundreds of years later, the Swiss used it to make hollow chocolate eggs. By the 1920s, an R.J. Powell patent specifically mentioned the common ratio between the major and minor axes of rotation for molds used in the production of Plaster of Paris. ​

The Roto Molding Process

• First, a homogenous powder (measured manually or automatically) is loaded into a mold; this is typically a 35-mesh powder. The amount of powder used determines the part’s actual wall thickness. ​
• The mold itself is usually made of cast aluminum or a fabricated steel sheet. Molds are evenly coated or sprayed with release agent before the powder is poured in.​

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