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Rotational Molding Comes Of Age As Product Developers Understand Its Strengths, Seek Low Initial Cost
Sept. 28th, 2005
By Robert Dunne
Now that product design and development engineers better understand rotational molding's impressive range of inherent strengths compared to even a few short years ago, they have been confidently specifying the process in ever greater numbers. After stellar growth during the mid-1990's, the rotational molding industry appeared to reach its peak by 2001 as the toy industry moved overseas and the 9/11 recession rippled through the economy, according to Dr. Peter J. Mooney of Plastics Custom Research Services, Advance, NC. Today, after a modest recovery, more than 1,700 rotational molders operate worldwide and tallying the annual tonnage of material used is now done in billions in the Americas alone, according to a 2003 report from the Association of Rotational Molders.
Rotational molding delivers consistent wall thicknesses, sturdy corners and structural strength even with complex, hollow and multi-wall parts in odd shapes and configurations. Its ability to seamlessly achieve nearly any shape in tight tolerances provides product designers with the flexibility to create exactly what they envision without compromising their designs. These advantages have established rotational molding as the obvious choice for producing chemical and fuel tanks, bulk containers, kayaks, carts, housings, point-of-purchase displays and other products. A diverse range of materials including nylons, metallocenes and cross-linkable polyethylenes may be rotationally molded, in addition to the more commonly used polyethylenes, polypropylenes and PVC. A host of additives for meeting FDA requirements, fire resistance and controlling static are also available. Since the process relies solely on heat and smooth rotation for melting and forming (without high pressures), the mold doesn't have to withstand the pounding required of injection molding and other processes. That's why rotational molding tooling often costs 50 - 80% less than a comparable tool used for injection or blow molding. This low initial cost minimizes the risk in bringing new products to market and often makes producing small quantities cost-effective, compelling reasons for product developers to consider rotational molding. This advantage vs. other materials has driven experienced rotational molders to become skilled in recognizing opportunities to convert existing products from metal, wood and fiberglass into plastic. Multiple parts and components are often redesigned into a single, rotationally molded part delivering increases in strength and structural integrity while eliminating assembly steps and secondary operations. As the cost of steel continues to rise along with the cost to assemble fabricated metal parts and its shortcomings vs. plastic become more apparent, these conversions will become even more prevalent. Further, each conversion yields a product that likely will never again be produced with anything but plastic.
But as rosy as the picture appears, the industry is facing a series of issues that threaten to derail the very cost and quality benefits that have driven its growth. And these hurdles arise at a time when the process has finally earned acceptance as a viable partner in product development.
Raw material costs in the United States, for example, have increased by more than 50% over the last 18 months. The natural gas used to power rotational molding machines has increased by more than 220% over the last 36 months. Freight has not only increased markedly due to fuel surcharges but its dependability has plummeted as railroads experience delays due to shortages in rolling stock and track congestion and trucking companies wrestle with driver shortages. Foreign competition is a growing concern for US-based companies as approximately 33% of the world's rotational molders are based in Asia. Though some produce inferior knock-offs of established products, their low costs are even undercutting the already low cost of American rotational molding. Costs are increasing throughout the entire operation yet many rotational molders are being strangled by medium and long term contracts that restrict their ability to pass these costs on to their customers. Certainly, injection molders, extruders and other processors suffer many of the same cost increases, but due to the more limited palette and supply of materials available to begin with and the lack of clout with a smaller number of suppliers, rotational molders have been disproportionately impacted. As overall costs increase, twin sheet thermoforming and other processes become more viable even in areas that have become obvious places for rotational molding.
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