Keep It Clean

When processing plastics, either the post-industrial variety or those from post-consumer programs, size reduction plays an integral part of the process. However, this necessary step is also a vulnerable one, as it has the potential to introduce contaminants and unshreddables to the plastic materials being processed, according to David Kaplan of Maine Plastics, Zion, Ill.

"In a hot market, you can get away with more," Kaplan says of contamination. "In soft markets, it just screws up the load."

In plastics recycling operations, the old adage, "Cleanliness is next to Godliness," holds true. Therefore, recyclers must be certain to thoroughly clean all of their their processing equipment when switching the types of plastics they are processing as well as the color of the material they are running through their equipment to realize the optimum value for their material and to keep their customers happy.

DEEP CLEAN. "Make sure you keep the grinder really, really clean," Kaplan says. For Maine Plastics, thorough cleaning can mean hours of disassembling equipment to access the hard-to-reach crevices.

Jase Traylor of Jet Polymer Recycling (JPR), Rainsville, Ala., outlines the cleaning process employed at the company’s plant. First, he says, rigid materials are removed by hand from all of the conveyors, including the sorting conveyor, shredder in-feed conveyor, shredder discharge conveyor and granulator in-feed conveyor. All conveyor belts and sidewalls are then blown thoroughly using high-pressure air and vacuumed to ensure that there is no cross contamination. "All belts and sidewalls are inspected by technicians for any remaining contaminants," Traylor says.

The screens of the shredder and granulator are also cleaned by hand, blown with high-pressure air and vacuumed. "The granulator’s and shredder’s internal parts are all hand cleaned, blown thoroughly clean and vacuumed," he says. Contaminants are freed from the rotary shaft of the shredder, which is then also blown clean and vacuumed. Finally, JPR’s technicians inspect all machine components to ensure maximum decontamination, Traylor says.

This leaves the surrounding work area, which is swept and the resultant material discarded. "The entire area is visually inspected to ensure no contaminants are left behind," he says.

"The final step is a purging run of plastic to ensure that the new material being processed is completely dominant in the system before being placed in the final shipping container," Traylor adds.

When processing varying colors of a material, Kaplan says its best to start with clear and natural materials, which are the most valuable, before moving on to white and then black material. "If you get a little white in the black, it’s not bad," he says, adding that the reverse, however, is not good.

Equipment layout also plays a role in reducing contamination in a processor’s finished product

IN THE DESIGN. At JPR, which offers toll processing services to manufacturers, a sorting/picking conveyor brings incoming material to the shredder. Traylor says, "This allows two to three people to sort the material and remove any contaminants before it reaches the first step in the grinding process. After being sorted and all physical contaminants

"After the shredding phase, the material runs over a series of high-power magnets that remove both ferrous and nonferrous metals," Traylor says.

Finally, the material enters the grinder, where it is processed into granules of uniform size that will be stored until the generator requires the material.

Not all incoming material must be processed through the shredder originally, however. "For small or lighter material we receive, it is usually not necessary to run the material through a shredder prior to the grinding phase," Traylor says. "The shredder is mainly for heavy, bulky material that would damage or compromise the blades of a granulator if they were run directly through it."

Kaplan also says that pre-shredding material is not always necessary. "You wouldn’t necessarily shred bottles or parts if they were small enough, but you could shred purgings and baled material."

Kaplan adds that shredders can be difficult to clean and stresses that a recycler should look for a shredder designed for ease of access to facilitate the cleaning process.

Jeff Taylor of Sterling-Hempstead Shredder Systems, Forest, Va., says two-stage size reduction is also a function of volume when dealing with post-industrial material.

Maine Plastics’ Kaplan echoes this sentiment, saying, "You don’t want to run a couple hundred pounds of material through a shredder."

Taylor says, "When scrap volume is high and/or the parts being processed are difficult for a granulator to process, a primary shredder benefits the size-reduction system by feeding the granulator a smaller, more consistent and even flow of material. The shredder becomes the metering device that allows the granulator to operate at its peak efficiency and, at the same time, reduces the maintenance cycles."

However, when processing post-consumer material, Taylor says, at minimum an operation will need a de-baler, sorting conveyor, a shear-type shredder for primary size reduction, a trommel to remove loose dirt, a granulator and possibly a wash line for final cleaning. He says companies also could opt for something like Sterling-Hempstead’s Elutriator, which enables the removal of dirt and fines by separating materials of various densities using air.

Taylor adds that Sterling-Hempstead operates a 4,000-square-foot research and development test facility that includes two elutriation systems for testing customer materials.

JPR has two grinders that can be used in conjunction with its shredder or alone. "This allows us to connect one granulator with the shredder and use the other granulator for the smaller material that does not require pre-shredding," Traylor says.

JPR operates a Vecoplan shredder for initial size reduction, which is linked to a Cumberland grinder. An Avian grinder stands alone.

"Depending on customer specification, we can create particles anywhere from ¼ to ½ an inch. For the most part, however, we run a 3/8-inch granulator screen."

After the grinding phase, Jet Polymer Recycling conveys material to a cyclone, "where dust and fines are carried up, and the finished product falls down through the cyclone into its final shipping container," Traylor says.

Some operations may opt to pelletize their granulate, which would be the final step in the process. "By nature, granulate is not uniform in size and contains dust in many cases," Taylor says. "This causes different melt temperatures and can create flashes (uneven surfaces or "poc" marks in the finished material) in the end product.

"Also, when using color compounds with granulate, you often times have swirls in the finish because it does not blend as well," Taylor says.

Pelletizing the regrind, however, produces a more consistent product because the color compounds and additives are blended with the regrind during extrusion, Taylor explains.

When shopping for equipment, Jet Polymer Recycling’s Traylor cautions that, "in the end, you get what you pay for." He suggests choosing a supplier with a proven track record that offers a factory warranty and parts program as well as good mechanical and technical support.

"It’s also a good idea to visit other sites that run similar equipment you might be looking for and just talk to the people who actually run the equipment day in and day out and see what they think about it," Traylor says. "There is no substitute for experience with a piece of machinery."