Super drums: coex takes on the toughest jobs.

Multi-layer drums can be stronger and have better barrier properties. They can also make use of recycled material, and save on additive costs. No wonder blow molders think they're going to be big.

Multi-layer blow molded drums of 30- to 55-gal size were hard to find as little as four years ago. Today, both of the top U.S. makers of plastic drums are going multi-layer, and at least three smaller firms are joining the action. Total installed capacity is estimated at more than 1 million coextruded drums annually. Though that's a small portion of the roughly 12 million plastic drums made domestically each year, multi-layer capacity appears set to expand by at least one-third next year.

Customer driven

What prompted this wave of interest in coextruded drums are higher expectations by drum buyers. Shippers of chemicals and food products are looking for greater stacking strength, ESCR, and barrier properties. "We have pushed the limits of what a single material can do for us," says Tim Knaus, product general manager for Russell-Stanley Holdings Inc., Bridgewater, N.J., one of the country's largest drum makers. It will install its first three-layer drum machine early next year. "I think a coex structure will be more expensive, but we are chasing performance, not lower cost."

As Knaus hints, drum makers are experimenting with a variety of materials to team up with workhorse HMW-HDPE. Although much of the work on coex drums is highly proprietary, processors reveal that candidates include modified HDPE, amorphous nylon, EVOH, PP, and other olefins and engineering resins. Layers of glass- or mineral-filled resin to increase stiffness and strength are also being considered.

Some customers are asking for drums whose linings won't interact with sensitive contents. That's why Fluoroware Inc., Chaska, Minn., decided to phase in three-layer drums and phase out its monolayer program. Thomas Brown, manager of chemical containers strategic business, explains that Fluoroware's drums transport high-purity chemicals used by the micro-electronics industry. "They specify purity in parts per trillion of trace contaminants," Brown says. In a monolayer structure, uv stabilizers and other additives could present contamination problems, he notes. "A multi-layer structure allows us to keep the additives in an outer layer - away from the chemicals."

Major chemical companies want recycled resin in drums as part of their environmental stewardship programs, says Harley Cramer, v.p. and general manager of U.S. Coexcell, Inc. in Maumee, Ohio. This subsidiary of Walbro Corp. was formed in 1994 expressly to make three-layer drums with a center layer (typically 30-40% of total thickness) made of recycled drums. "We are in markets we couldn't get without recycle," says Cramer.

Greif Bros. Corp. of Delaware, Ohio, a leading drum producer, is using coextrusion for product enhancement but also sees potential for recycling used drums into new ones through coex technology. Taking back empty drums would relieve the customer of the chore of disposal, says Jerry Geyer, director of new product development. He expects the market for multi-layer drums to grow by double digits annually over the next few years.

U.S. Coex- cell is exploring opportunities for increasing barrier properties through coextrusion. Cramer also sees potential to save money for customers who use fluorination barrier technology. Because pigments can inhibit fluorination, keeping pigments out of the inner layer can reduce the level of fluorine treatment needed, Cramer says.

Given all these incentives, it's no surprise that the line-up of current players in coex drums includes both of the nation's largest drum makers: Russell-Stanley has ordered its first three-layer continuous-extrusion machine from Krupp Kautex. Greif Bros. is already running at least three multi-layer machines - one three-layer accumulator-head model from Rikutec and two Kautex continuous-extrusion models that have three- and seven-layer capability.

Smaller drum makers taking the plunge into coextrusion include Fluoroware, which started up a three-layer continuous-extrusion machine from Bekum this past summer. U.S. Coexcell has two three-layer accumulator-head machines from Johnson Controls Inc.'s Plastics Machinery Div. (now called Uniloy Milacron). Schutz Container Systems Inc., North Branch, N.J., is also in the process of acquiring multi-layer capability.

(Other drum makers - Polyethylene Containers, Van Leer, Vanguard Container Corp., and Hoover Materials Handling Group - say they have no current plans for multi-layer products.)

Two routes to coex

Although multi-layer drum production started out with accumulator-head machines, there are signs that the market may shift toward continuous-extrusion technology. Greater parison and wall-thickness control, improved layer uniformity, and faster cycle times are cited as advantages of continuous extrusion by sources at Bekum America, Krupp, and Uniloy Milacron.

"We found a number of limitations in our 10 years of study of accumulator heads," says John Antonopoulos, president of Krupp Plastics & Rubber Machinery, which has extensive experience with blow molding multi-layer fuel tanks. "You cannot get as thin a layer of EVOH or of tie layer, nor as uniform flow, and there can be greater shot-to-shot variation." He notes that fast parison push-out creates control problems with multi-layer accumulator heads, while slower push-out lessens the problems but adds to cycle time. Antonopoulos says that with continuous extrusion, "You can use a wider viscosity range between different materials because of the smoother flow of the polymer layers. With the accumulator head, you must use a narrow range of viscosities."

Krupp supplies accumulator-head machines only for monolayer parts. For drums of two to seven layers, Krupp Kautex offers the CP 120 continuous-extrusion unit. It can be supplied with two 92-ton clamps to double the output of a single clamp at only 65% higher cost.

Antonopoulos and other machine builders say use of a Parison Wall Distribution System (PWDS) is a must for producing multi-layer drums. The PWDS reportedly yields a far more accurate radial profile of the parison on a continuous-extrusion unit than it does with an accumulator head because of the longer time to extrude the parison. "You can run the parison program more precisely over a two-minute extrusion than with the 10-second parison drop of an accumulator head," says Antonopoulos.

Bekum's Gary Carr, product manager for container machinery, says PWDS is used in its continuous-extrusion system principally to adjust material thickness at the top and bottom of the drum - areas that are usually the thickest during the molding cycle. "PWDS is employed at discrete points during parison drop. It compensates for collapsing the parison by imparting ovality in the tooling at a defined time and stroke thickness," he says.

Bekum's BA 220 M continuous-extrusion machine is used by Fluoroware to make 55-gal drums. Whereas accumulator models have a stationary clamp, this machine has a moving horizontal clamp that permits continuous extrusion of the parison. Bekum also offers two-layer technology for making 275-gal intermediate bulk containers (IBCs).

Uniloy Milacron's first multilayer drum machines were accumulator-head models, but the firm has now developed a continuous-extrusion model to produce small multi-layer or mono-layer drums up to 15 gal. Jim Potter, product development and applications manager, says the new BW-40 machine has a unique mold carriage that moves horizontally on linear bearings, as well as a special part-gripping system and three-station cooling for faster cycles

Rikutec (Richter Kunststoff-technik) of Germany supplies GBM series single- and dual-head machines for making drums with up to five layers. Because the molds are so large and heavy, the Rikutec system leaves the clamps stationary and shuttles the extruders and head on a platform from mold to mold. Rikutec, represented here by Gould & Eberhart has a special coex head that can operate either continuously or discontinuously.

RELATED ARTICLE: More Than One Way to Recycle

U.S. Coexcell turned to coextrusion in 1994 because it was then the only available means of recycling used drums into new ones. The U.S. Dept. of Transportation (DOT) would not certify the safety of using recycled resin in monolayer drums for transporting hazardous chemicals.

Now that has changed. As a result of a petition from the Plastic Container Institute, New City, N.Y. (headed by Greif's Jerry Geyer), the DOT established a new regulation last month that will allow transport of chemicals in monolayer drums that contain up to 100% recycled material.