Three tractor-trailers recently completed hauling Poly Processing Co.'s Ferry RS-430 rotational molding machine to the company's plant near Stockton, Calif. Sixty-four feet long and 35 feet wide, with an oven 35 feet wide, high and deep, the machine was purchased from another molder in the western United States who had used it to make eight 90-gallon trash barrels at a time.
Poly Processing will use it to make 4,000-gallon containers, to be used as agricultural and chemical storage tanks. The machine's advantage is its four independent arms, allowing nearly continuous production, said Guy Carrow, Poly Processing's manager for research and develop-ment.
``You always have a mold ready'' to fill with resin and move to the oven with the four-station machine, he said.
The carousel also allows better use of labor, as workers are not slowed by waiting for an individual molding process to be completed, he said.
It is the second such carousel-type, multistation molding machine for Monroe, La.-based Poly Processing, with the first installed at the company's headquarters plant.
In all, Poly Processing has nine rotomolding machines at its plants in California, Louisiana and Winchester, Va., with the largest able to mold a 14-foot diameter, 16-foot tall, 16,000-gallon tank, also in the California plant, Poly Processing President Jerry M. France said.
Poly Processing is the rotational molding division of privately held Abell Corp., also based in Monroe. According to France, the company traces its roots back 25 years in the agricultural chemicals storage business, to a company named Ouachita Fertilizer Co. As Ouachita grew, it needed to find alternatives to storing chemicals in corrosion-prone metal containers and began making plastic ones. That operation, in turn, grew to be Poly Processing, which he described as a sister operation to Ouachita.
Sales for the rotomolding operation were $29.8 million in 1994, up 11 percent from 1993's $26.4 million. Total company sales in 1994 were about $69 million. About 215 of Abell's 350 employees work in rotomolding.
Carrow said one of the rotomolder's specialties is the employment of cross-linked polyethylene, which serves to better produce large tanks that not only have walls of uniform thickness - a major advantage of rotational molding in the first place - but excellent strength characteristics as well.
``Cross-linking'' involves the use of a thermally activated agent in a low viscosity resin - a resin that can easily fill a mold and assure uniformity of the formed structure's wall thickness.
When heated, however, the agent acts to increase the molecular weight of the resin, which gives it qualities of high stress crack resistance and good ``hoop stress'' during the rotomolding process that is far greater than the resin's original capability.
``It produces a tougher tank,'' Carrow said.
Cross-linking leads to another unique accomplishment for Poly Processing - it is the only rotational molding company receiving a ``Classified'' rating from Underwriters Laboratories Inc., for providing XLPE storage tanks meeting ULs drinking water storage component standards. Some states require that any container used in a water plant be UL certified, Carrow said.
Drinking-water standards are only one set of UL approvals given to Poly Processing, France said. UL approvals also have been received for more than 40 other chemicals, he said.
Although the company has been issued UL approval based on its own tests, UL sends ``follow up'' field representatives to make unannounced visits to factories to ``observe and countercheck production controls used in the manufacture'' of products it certifies.