Cleveland — Gareth McDowell thinks it's time for rotational molding to step up — to multilayer molding, new materials, more demanding high-tech parts, and closed-loop process control based on precise control of temperature inside the mold.
Rotomolding, simply put, is too inefficient, McDowell told attendees at the Society of Plastics Engineers' Rotational Molding Conference. “I think we need to get there, to take rotomolding to the next level,” he said in a keynote speech June 7 at the Cleveland conference.
McDowell said the rotomolding industry needs to launch a coordinated effort to boost technology, perhaps by naming a special committee.
He asked: Why can't rotomolding turn out parts for cars? “I'm dreaming of more than tanks and kayaks,” McDowell said.
McDowell is a director of a British company, 493K Ltd., which developed technology for monitoring temperature and pressure in the rotomolding industry.
He identified some reasons that rotomolding is getting held back.
One is over-reliance on single-layer parts. Some molders are doing multilayer, with methods such as drop boxes, but McDowell said you don't know if the box actually opened or not until you open up the mold to remove the finished part. The drop box also adds cycle time and cost, and requires people with years of experience to operate it properly, he added.
The key, McDowell said, is being able to accurately measure temperature. His idea is technology to access the mold in the oven, unhindered by the high heat of rotomolding.
On the materials front, rotomolders have long lamented the industry's overreliance on polyethylene, which McDowell called a forgiving, “safe” material that has a wide processing window. He said he's not knocking PE, “but it hasn't actually been promoted as an engineering plastic.”
Why not a wider range of materials like polypropylene, nylon, polycarbonate, fluorocarbons, polyester and polystyrene? That brings up the need for improved process control inside of the mold. “If you're going to run anything beside polyethylene, please keep close temperature control,” he said.
Rotomolding also needs to have double-sided molds, to bring heat and cooling to both sides of the plastic part. More use of internal air cooling would help.
Vent pipes also are an issue. “We need to step it up and get to the point where we can open and close our vents during the cycle,” he said.
Another item on McDowell's wish list: Rotomolding machines with no arms in the oven, only the mold. Right now, the process heats and cools steel on the arms, an inefficient way to do it, he said.
“At the very least, insulate the arms,” he said.
McDowell also said current rotomolding machinery technology does not control the wall thickness closely enough. I would like to see encoders on all the arms, as well as software that allows you do dial in rotation speed, temperature and other parameters to the machine runs closed-loop and fully automatic.