Rotomolding at a Glance
Rotational Molding, Rotocasting
From Wikipedia, the free encyclopedia
A heated hollow mold is filled with a charge or shot weight of material, it is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase. The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.
In 1855 R. Peters of Britain documented the first use of biaxial rotation and heat. This rotational molding process was used to create metal artillery shells and other hollow vessels. The main purpose of using rotational molding was to create consistency in wall thickness and density. In 1905 in the United States F.A. Voelke used this method for the hollowing of wax objects. This led to G.S. Baker's and G.W. Perks's process of making hollow chocolate eggs in 1910. Rotational molding developed further and R.J. Powell used this process for molding plaster of Paris in the 1920’s. These early methods using different materials directed the advancements in the way rotational molding is used today with plastics.
Plastics were introduced to the rotational molding process in the early 1950s. One of the first applications was to manufacture doll heads. The machinery was made of an E Blue box-oven machine, inspired by a General Motors rear axle, powered by an external electric motor and heated by floor-mounted gas burners. The mold was made out of electroformed nickel-copper, and the plastic was a liquid PVC plastisol. The cooling method consisted of placing the mold into cold water. This process of rotational molding led to the creation of other plastic toys. As demand and popularity of this process increased, it was used to create other products such as road cones, marine buoys, and car armrests. This popularity led to the development of larger machinery. A new system of heating was also created, going from the original direct gas jets to the current indirect high velocity air system. In Europe during the 1960s the Engel process was developed. This allowed the creation of large hollow containers to be created in low-density polyethylene. The cooling method consisted of turning off the burners and allowing the plastic to harden while still rocking in the mold. 
Rotational Molding:"A small industry"
The Rotational Molding Industry as a whole has under went very significant changes over the last several years. Many consolidations, mergers & acquisitions have taken place amongst the molders, material suppliers, mold makers and other Rotational Molding industry related vendors. Several years ago, the United States of America was home to nearly 500 separate Rotational Molding companies. Currently, there are less than 100 viable Rotomolding suppliers left in operation.
A large number of molders have been acquired by various holding companies throughout the globe. While many other molders have simply went out of business due to rising, uncontrollable costs. Many molders, who lacked in capability, innovation abilities or even customer service- also have either closed their doors or have become acquired through bank acquisitions. These consolidations, paired with the shrinking domestic resin supply have kept things interesting to say the least in Rotational Molding.
Library of Videos about Rotomolding, Rotationally Molded Products and more!
Thanks to the team at Granger Plastics in Middletown, OH for the video footge! We will constantly be adding new Rotational Molding videos on a regular basis!
Rotational Molding Products
Rotational Molding videos can be found at RotationalMolding.tv or at Rotational Molding Videos.
More Rotational Molding Videos coming soon!
Many of these videos display the types of high quality products that can be manufactured via the Rotational Molding process, the extreme durability of a Rotationally Molded product or the ease of use of a Rotomolded product.