Blowmolders looking for risks to their business from their peers also need to keep in mind the advances made in alternative processes, including rotational molding (rotomolding).

Cutting-edge rotational molding is utilizing the latest in material, mold, and process technologies to beat back competitive plastic-fabrication methods like blowmolding and thermoforming and even stake out new metal-to-resin conversion turf. Mark Kearns, a professor at the Queens University Polymer Processing Research Centre in Belfast, North Ireland, laid out 10 such projects in a presentation highlighting rotomolding innovation at the Rotoplas conference (Oct. 22-23; Rosemont Convention Center; Rosemont, IL). The parts highlighted ranged from tables to boat hulls to air ducts for jets, but consistent throughout was the application of advanced rotational molding methodologies like multilayer, multishot, foamed structures; polyethylene blends and micropellets for more complex, difficult-to-mold structures; internal air cooling; in-mold temperature monitoring; molded-in inserts; and inmold graphics, among others.

Bob Dunne, president of custom rotational molder Meese Orbitron Dunne Co. (MOD: Ashtabula, OH) is a practitioner of advance rotomolding; his company recently added a second Leonardo automated rotational molding system from Persico SpA (Nembro, Italy) to its domestic stable. In 2007, MOD became the first company in North America to purchase the automated Leonardo system, and when this second unit comes online in 2009, it will be the only company in North America operating two of the systems in different facilities.

A rotomolding veteran, Dunne sees two distinct groups within his processing community when it comes to new technology. “Rotomolders all over the world are a pretty clever and resourceful bunch,” Dunne says, “but there is definitely a split between the 'conventional' and 'technical' rotomolder. Some firms do slowly adopt the cutting-edge technology, but in my view, at this stage, they tend to be the exception. In most instances it comes down to many companies only seeing the short-term costs and not the potential long-term gains.”

Turning art to science

Dunne and Kearns see particular value in a number of mold-centered technologies now seeing increasing use in rotomolding. In terms of mold pressurization, where a tool is pressurized to help with surface appearance, Kearns still sees more adoption in Europe than North America. “The process is still not widespread,” Kearns says, “but we're definitely seeing more and more molders utilizing mould pressurization,” adding that it's most relevant to small, technical, high-specification products that require good surface appearance, need to be completely bubble/pin-hole free, and require tight tolerances.

Kearns sees a similar adoption pattern in internal mold cooling. “[Internal mold cooling] is definitely required and being used for products like multilayer complex foam moldings, because of the long cooling times,” Kearns explains, adding that he increasingly sees it used for very large tanks, with the biggest benefit coming in cycle-time savings. Kearns' department at Queens University is currently involved in a European funded study dubbed Micromelt that's investigating the benefits rotomolding can gain from internal water cooling and industrial microwave heating.

How roto stacks up

In weighing rotomolding's pros and cons as it relates to competitive technologies, Dunne lists low tooling costs, flexibility, and part consolidation as positives, but sees tolerances, wall-thickness variations, and shrinkage/warpage issues as potential negatives that can lead customers to blowmolding and injection molding. “There has been a history of products initially manufactured via rotomolding,” Dunne says “and as sales increase, blowmolding is then used.” In its case, Dunne says its machinery investments have helped answer some of the aforementioned concerns. “The Leonardo Machine has been of interest to a number of automotive companies,” Dunne says. “Particularly in multilayer (polyethylene/polyamide) fuel-tank applications, where wall thickness can be made very thin in comparison to conventional rotomolding.”

Beyond machinery technology, Kearns laid out specific instances where other advances helped rotomolders keep existing business, or in some cases, win new clients and even markets. Among the parts he highlighted in Chicago were a washer bottle for the Bugatti Veyron and Audi R8; an inmold label decorated waste-oil tank for fast-food use; roofing tiles with built-in vents; a triple-layer boat hull; a foam-filled table; an automotive pump housing; and air ducts that see use in Boeing 777 commercial and F-15 and F-18 fighter-jet aircraft.

In particular, Kearns sees rotomolding advances move the process and the parts it creates from the outside, and things like water tanks, to the inside, and highly aesthetic pieces, with innovation coming from the top and leading the way. “Innovation will not take place without inspirational leadership and powerful motivation,” Kearns explains. “An innovative rotomolding organization will have awareness of customer opportunities; ambitious and entrepreneurial leadership; the ability to generate and develop new ideas; and the availability of the necessary resources to achieve success.”—[email protected]