Rotomolding finally gets some respect.

Rotational molding is the fastest growing plastics process in the U.S. It has ballooned by at least 10% per year during this decade, says design consultant Glenn Beall, president of Glenn Beall Plastics Ltd., Libertyville, Ill. Rotomolded products now top $1.3 billion in U.S. sales volume, according to some estimates.

"It's an unbelievable success story," Beall says. He credits three factors: Breakthroughs in processing and materials technology, the emergence of rotomolding product designers, and global support from the Association of Rotational Molders (ARM) in Oak Brook, Ill.

Size matters

ARM estimates total North American rotomolding material consumption at 420 million lb in 1997 and predicts that figure will grow to 695 million lb in 2000. The number of plants is estimated to be 500 to 700. In Beall's view, rotomolding's small size - relative to the 94-billion-lb U.S. plastics industry - explains why the process hasn't gotten much attention before now from major industry groups, such as the SPE and SPI. "The same is true in other parts of the world," says Beall. ARM not only fills that gap but has been joined by rotomolding groups in Australia and the U.K. It has 470 member companies worldwide, and draws as many as 750 attendees to its two annual meetings.

Beall, who was inducted into ARM's Rotational Molding Hall of Fame last year, says the ARM conferences exhibit a more open exchange of information between competitors than he sees in other plastics organizations. "The rotomolding industry has come to realize the benefits of sharing technical information," he says.

Joint efforts for progress

Basic research and development - too expensive for individual rotomolding firms - has been achieved by pooling money from many small companies. ARM has funded scientific research at Queens University in Belfast, Northern Ireland, which has yielded reports on cooling-time reduction and bubble elimination, as well as on tools for process diagnostics.

Breakthroughs have also occurred outside of the university. Beall says ovenless mold technology and larger, faster machines mark some of the more important technical introductions. Other recent advances are the first infrared closed-loop process-control device, single-shot foam/solid multi-layer structures, metallocene polyolefins for rotomolding, recycling of crosslinked resins, automated mold-filling devices, and a current project that places a camera and light source inside a mold to observe the process.

Parts are getting more sophisticated, too. A vacuum floor-sweeper frame made of PE by Pawnee Rotational Molding Co., Maple Plain, Minn., took the International Plastics Industrial Product Design Award at the 1998 SPE ANTEC. "That part replaced 120 metal parts, had the color molded in, and was 50% lighter. Many people who saw that complex part could not believe it was rotomolded," says Beall.

Meanwhile, SPE's major Polyolefins XI conference, held last month in Houston, was the first such meeting to have a session on rotomolding, Beall says. "SPE now wants to educate OEMs and product designers about the capabilities of rotomolding."

Fewer surprises

It hasn't been easy getting this far, says Patrick Long, president of ARM and a recent inductee into the Rotomolding Hall of Fame. He is also president of Formed Plastics Inc. in Carle Place, N.Y., which has been rotomolding since 1961 and was one of 13 firms that plunked down $250 each to form ARM in 1976.

Long remembers earlier days when materials and processing were not so reliable. In the late '60s, Formed Plastics was rotomolding lighting globes of cellulose acetate butyrate, which could explode if the processing temperature rose too high. Then polycarbonate came in the early '70s. It made stronger globes but had to be processed 50-70 [degrees] F hotter than butyrate. On one fateful day, Long remembers, "We were making a run of white butyrate globes. At lunchtime, we changed shifts. The man coming on thought we were running polycarbonate. He couldn't tell because you can't see the difference between the two materials in powder form. When he put the molds in the oven, the butyrate exploded. We decided we would never run that material again."