In the past, large, hollow tanks symbolized rotational molding. While tanks are still made by this process, rotational molding has made great strides in capabilities and offers distinct advantages over other processes.
In fact, rotational molding is undergoing tremendous worldwide growth as designers are becoming aware of its advantages. The current annual growth of rotational molding is about 15 percent in North America and Europe; 80 percent in Australia; and about 25 percent worldwide.
Innovative designers are pushing the boundaries of the process, creatively approaching both new and conversion products. The process offers designers many options, some of which are exclusive to rotational molding.
With proper design, parts manufactured as several pieces using other processes can be rotomolded as one part, eliminating expensive fabrication costs.
The process also has a number of inherent design strengths, such as consistent wall thickness and strong, virtually stress-free outside corners.
Another contributing factor to the growth of the industry is the fact that rotational molding is cost-effective. Because parts are formed with heat and rotation, rather than pressure, molds don't need to be engineered to withstand the high pressure of injection and blow molding.
Since there is no internal core to the mold, minor changes can easily be made to an existing mold.
But as the industry grows, so do the demands placed on it. In order to meet them, suppliers are improving existing materials and equipment. Resin suppliers recently introduced a resin that produces parts with a solid skin and a foam core in one shot. The material is a blend of two polyolefins that separate during the molding process. One makes the outer skin, and the other makes a foam backing up to 6-7 inches thick.
Resin manufacturers are also developing metallo cenes, which will give molders a cycle time reduced by as much as 30 percent due to the relatively low melting point of the resin.
Machinery manufacturers have improved efficiencies as well. Machines today offer improved energy consumption with a higher production rate.
To aid in the development of new technology and improved efficiencies, the Association of Rotational Molders is sponsoring research projects at Queen's University of Belfast, Northern Ireland; University of Massachusetts in Lowell, Mass.; and Brigham Young University in Provo, Utah.
Frederick is executive director of the Association of Rotational Molders in Oak Brook, Ill.