Through his company, Rotokinetics LLC, Bill Sampsell is pushing the thermosets for rotational molding - mainly polyurethanes - with a special machine and molds, all designed to make detailed, low-volume parts profitably.
The firm, which builds Rotocaster-brand machinery, has turned out everything from detailed architectural parts to realistic trees for zoo displays, he said.
``This process allows us to do complicated parts beyond what a traditional, thermoplastic rotomolding machine can do, like a Corinthian capital,'' Sampsell said by telephone from Athens, Ga.
Most rotomolding uses thermoplastic resins, tumbled through molds in big ovens, then cooled before demolding. The single-station Rotocaster machines have no ovens. Instead, the reaction of the two-component polyurethane creates the heat to set up the parts, usually less than 200°F.
Parts continue to cure outside the mold.
Not having an oven allows the molder to fabricate its own molds from epoxy, vinyl ester and urethane rubber. A silicone rubber liner can duplicate intricate, complicated shapes. ``I can copy tree bark,'' Sampsell said. Traditional rotomolding is way too hot for those types of molds. The molds are inexpensive and can be made for fast turnaround on low-volume jobs - like the Spiderman figures Sampsell made a few years ago for Blockbuster video stores.
``We did 2,500 6-foot-tall Spidermen,'' he said. Another exotic part: a 7-foot bulldog for a local beer distributor.
Rotomolding technology from Rotokinetics also can make parts from gypsum with acrylic latex and melamine resin. ``You wind up with beautiful cast-stone parts that are hollow,'' Sampsell said. Applications include columns for fencing and parts for sweeping stairways made of concrete.
Rotocasters come in three frame sizes: 54 by 50 inches, 66 by 50 inches and 84 by 55 inches. The largest machine can support molds up to 650 pounds.
Molds are attached to a frame, which is moved into position on a wheeled cart.
Using a special feature called Power Load, the single arm drops down, attaches to the mold, then lifts back up into position. Both the arm and the frame turn during molding.
Sampsell said the fully programmable machine repeats movements exactly, even turning the opposite way. A rock 'n' roll feature can make odd-shaped parts.
``There is no machine that will automatically reverse itself without operator intervention,'' Sampsell said.