Rotomolding manufacturers explain about the historical development process of rotomolding!
Rotational molding, as used by rotomolders, involves a heated hollow mold that is filled with a charge or injection weight of material and then slowly rotated (usually about two vertical axes) to disperse and adhere the softened material to the mold walls.
To maintain a uniform thickness across the part, the mold is always rotated at all times during the heating phase and also avoids sagging or distortion during the cooling phase.
The process was applied to plastics in the 1950s, but was rarely used in the early years because it was a slow process on small amounts of plastic. As time passed, improvements in process control and the development of plastic powders have led to a significant increase in use.
In contrast, rotational casting (also known as spin casting) uses self-curing resins in unheated molds, but has a slower rotation speed in rotational molding. In high-speed centrifugal casting machines, self-curing resins or white metals are utilized and should not be confused with spin casting.
In 1855, R. Peters in England recorded the first use of biaxial rotation and heating, a rotomolding process used to make metal cannonballs and other hollow containers, using rotomolding for the primary purpose of maintaining consistent wall thickness and density.
In 1905, FA Voelke used this method to hollow wax products in the USA. This led to the manufacture of hollow chocolate eggs by GS Baker and GW Perks in 1910.
Rotational molding techniques were further developed and RJ Powell used this process for molding plaster of Paris in the 1920s. These early methods using different materials led to the development of the way rotational molding is used with plastics today.
In the early 1950s, plastics were introduced into the rotomolding process. One of the earliest applications was the manufacture of doll heads, a machine made from an E Blue box oven inspired by the rear axle of a General Motors car, powered by an external electric motor and heated by a floor-mounted gas burner.
The molds are made of electroformed nickel-copper and the plastic is liquid PVC plastisol . The cooling method consists of placing the mold in cold water. The process of rotomolding led to the creation of other plastic toys. As the demand and popularity of the process increased, it was used to produce other products such as road cones, boat buoys and car handrails.
This popularity led to the development of large machines and the creation of new heating systems, from direct gas injection streams in the beginning to the current indirect high-speed air systems.
In Europe in the 1960s, the Engel process was developed. This allowed the manufacture of large hollow containers from low density polyethylene. The cooling method consisted of turning off the burner and allowing the plastic to harden while still rocking in the mold.
In 1976, the Association of Rotational Molds (ARM) was founded in Chicago as a global trade association. The association's main goal was to raise awareness of rotomolding technology and processes.
In the 1980s, new plastics, such as polycarbonate, polyester and nylon, were introduced into rotomolding. This led to new uses of the process, such as the creation of fuel tanks and industrial molded goods.
Since the late 1980s, research conducted at Queen's University Belfast has been based on the development of the "Rotolog System", which has led to better monitoring of the cooling process.
