Cleaning up Their Acts

Much standard equipment exists to help plastics recyclers filter out undesirable materials from molten polymer; but, when contaminant levels are high, there is often a penalty for using such equipment—reduced output and downtime. And in some cases the plastic scrap is so highly contaminated that even the most effective melt filtration systems cannot render them recyclable. As a result, one fewer raw material stream is available to the recycling company.

A new melt filtration system addresses these problems, opening the door to additional sources of raw material while eliminating downtime and operator intervention. The Fimic self-cleaning screen changer—developed in Italy and sold in North America exclusively by ADG Solutions, Fairfield, Conn.—has enabled two companies specializing in plastics recycling to reduce downtime by 30 percent and to run materials they previously could not process. Both ABC Polymers Inc., Stone Mountain, Ga., and KW Plastics, Troy, Ala., have reported successful recycling of plastics with high levels of contaminants, such as paper and paperboard, without constant operator intervention since incorporating this new technology.

Common Approaches
Mounted at the end of a reprocessing extruder, a screen changer filters contaminants from molten plastic before it is pelletized. One standard type of screen changer uses slide plates for quickly replacing screens on which contaminants have accumulated. At high contaminant levels, these systems can be ineffective because of the labor involved in continuously changing screens. In addition, the screen packs cannot be reused, so frequent changes significantly increase the cost of production.

The buildup in extruder back-pressure as contaminants accumulate on the screens of standard equipment also causes three other problems:

1. Reduced throughput;
2. Plugging of the vents through which volatiles and moisture are released; and
3. Broad swings in pellet dimensions, since the pelletizer downstream of the screen changer continues operating at a constant rate, while the extrusion rate varies with back-pressure.

Another standard system uses so-called back-flush filters to clean away contaminants, but with high loadings, particularly of paper and cardboard, the contaminants can blind the screen and can cause the system to be in a perpetual back-flush mode, with huge volumes of material potentially purged from the system and wasted.

As an automatic, self-cleaning system, the Fimic screen changer is designed to avoid these problems. The self-cleaning cycles are subject to PLC (programmed logic controller) control. In each cycle, as molten polymer enters the screen changer, contaminants accumulate on the hard-faced stainless steel screen plate. The buildup continues until back pressure reaches a preset level. This actuates a rotating blade, which sweeps the screen and purges the contaminants through a central discharge port. Typically the screen does not need to be touched or changed more often than every week or two, depending on the material being processed.
 

ABC Polymers: Saving on Material Cost
Based near Atlanta, ABC Polymers has been recycling plastic scrap since 1974. The company recycles more than 250 million pounds of plastics annually, with a customer base throughout Asia and the Americas.

In a reprocessing line that includes the Fimic plastics recycling equipment, ABC runs chiefly low- and linear-low-density polyethylene (LDPE and LLDPE), though it also has used the line to recycle polypropylene (PP) and polystyrene (PS). Typically the source material is stretch wrap, bubble wrap and foam used for packing and shipping. Contaminants, up to 3 percent, may consist of labels, paperboard and plastics, such as nylon cords or PET strands, whose higher melt temperatures result in filter-clogging "unmelts."

Jeramy Daniels, president of ABC Polymers, says, "Previously it was not economical for us to run this type of material, given the need to wash and dry it before processing, clean away buildup from a conventional screen changer every few minutes and lose a significant amount of good material with every purging. The Fimic system has reduced our total cost for using the material by 25 to 30 percent."

KW Plastics: Opening a Door to New Resource Materials
Founded in 1981, KW Plastics is a leading recycler of post-consumer and post-industrial plastics and the largest producer of custom-engineered compounds based on recycled PP copolymer, with plants in Troy, Ala., and Bakersfield, Calif. Applications for its injection-molding compounds include automotive components, batteries, containers and industrial caster wheels.

In four reprocessing lines featuring the Fimic plastic recycling system, KW Plastics runs primarily PP scrap, including rigid parts, woven and nonwoven fabrics, fibers and film. Typical contaminants in the material stream are labels, paper, cardboard and non-PP unmelts, such as PET and nylon.

"We wash all materials before processing them, but some materials are virtually impossible to get clean enough for conventional screen changers," says company co-owner Kenneth Campbell. "The Fimic system has opened the door to new source materials for us. The beauty part of the system is that it has a huge 24-inch-diameter screen and its operation is completely automatic."
 

Proven Performance
The patented Fimic screen has a 20-year track record in overseas installations. Prior to ADG Solutions becoming the North American importer of the system, only a few units had been sold in the United States, purchased directly from the Italian firm Fimic Officine Meccaniche SAS, based in Padua.

The Fimic screen changer is designed to be able to handle plastic scrap containing up to 3 percent loadings of paper, labels or cardboard without a slowdown or stoppage of the process. Even contaminants measuring nearly 1 inch in diameter do not pose a problem. The self-cleaning action is designed for efficiency, with purgings averaging less than 2.5 pounds per cleaning cycle and minimal discharge of good material along with contaminants.

Besides paper, the system can handle other contaminants, such as metal foil, wood, textile fibers and unmelted plastic. Four models are available, with screen diameters from 12.5 to 25 inches and throughput capabilities from 1,200 to 6,000 pounds per hour. Replacement screens and blades are readily available. The working life of a screen is typically two weeks.

For ABC Polymers and KW Plastics, ADG Solutions also supplied Pawcatuck, Conn.-based Davis-Standard's Ram Stuffer reclaim extrusion systems and worked with the companies to design their installations. ADG is the exclusive North American distributor for Davis-Standard's reclaim and compounding systems.

The author is president of ADG Solutions, a plastic recycling equipment supplier headquartered in Fairfield, Conn. He can be contacted at sandy@adgs.net.