Thinking ahead: matching conveyors to the recycling task can require a lot of thought by plant designers and operators.

Sometimes, a conveyor belt is simply a conveyor, moving cargo or material forward. But recyclers have also become experts at using an array of conveyors that double as screeners and separators to make purer secondary commodities.

Known by many names, these machines can make recyclers more profitable while also conveying material efficiently through the production process.

What they can offer is the best of both worlds--a way to move material through a recycling plant while also automatically doing some of the work.

ACROSS THE BOARD. The use of screening devices that also move (or convey) material through a facility is found in every segment of the recycling industry, from scrap metals and paper plants to residential material recovery facilities (MRFs) and mixed C&D plants.

The potential of such devices can be seen in the re-design of many MRFs, where systems using the same number or (often) fewer manual sorters now handle commingled streams that in theory should be a lot more difficult to separate.

While early MRF configurations consisted of picking stations set alongside flat, moving conveyors, automated screening has increasingly changed the layout of these facilities.

Trommel screens--which separate primarily by size--were deployed initially in some MRFs (and are still used in some facilities) to roust out broken glass.

But an amazing variety of screening devices are now deployed at MRFs, especially those considered single-stream plants that separate mixed recyclables collected in a compactor truck.

One recent plant system designed by Van Dyk Baler Corp., Stamford, Conn., for a customer in Canada included several disc screens, which deploy rapidly spinning hard rubber discs that propel some material forward while allowing other items to fall between the discs and below to another waiting conveyor belt.

According to Van Dyk Baler, the single-stream system is slated to process more than 40,000 metric tons per year of residential recyclables collected in the city of Winnipeg.

The system uses one Lubo Starscreen to positively sort old corrugated containers as well as a Double Deck French Banana Starscreen with air jets intended to positively sort old newspapers (ONP) collected in the commingled stream. Additionally, a Glassbreaker Starscreen is part of the new system to help ensure glass remains separated from the paper grades.

Like MRFs, mixed C&D facilities are asked to produce several marketable commodities from a jumble of incoming material. Equipment makers and recyclers of this stream continue to experiment with a variety of screening conveyors arranged in different orders to produce the cleanest products possible.

At the Madison Materials facility operated by Ware Disposal in Santa Ana, Calif., the mixed stream can include a mixture of scrap lumber and drywall; pieces and trimmings of siding, pipe and wiring; trash generated at construction and demolition sites; pieces of concrete, brick and block rubble; carpet and padding; and scrap pallets.

After larger objects are picked out by a hydraulic material handler operator using a grapple, material is loaded onto a steel-belted conveyor made by Ptarmigan Machinery, San Antonio, and then heads to a vibrating finger screen made by General Kinematics, Barrington, Ill.

The finger screen is designed to send materials 4 inches in size and larger in one direction while smaller material drops through. The smaller material runs by a Dings magnet that picks up marketable ferrous material and then to a General Kinematics de-stoner, another moving screen that uses air knives to separate dirt and wood chips from rock. The rock- and metals-free material is then marketed as a mulch product.

Currently, Madison Materials is using conventional conveyors combined with 14 manual sorters to procure marketable products from the 4 inches and larger stream. Other C&D recyclers, however, use more automation than what is found in the Madison Materials facility.

The expanded use of metals shredders has prompted the greater use of conveyors, feeding and screening devices in scrap processing facilities. Ferrous Processing & Trading (FPT), Detroit, operates several shredders in Michigan, Ohio and Florida. Some post-shredder material from the company's Detroit shredders is shipped to a highly automated sorting facility in nearby Warren, Mich., known as SLC Recycling.

At the SLC facility, the first post-shredder step involves a trommel used to take out dirt and fines. The metallic fines falling through the trommel are sold as a lower grade melting material, while the larger materials move on to the next steps of the sorting system.

Eddy current separators are deployed at the individual shredder yards as well as at the SLC facility. Conveying lines leading away from the trommel and, eventually, to a sand-flotation system, also run past a Steinert eddy current that further purifies the nonferrous stream, removing plastics, rubber and other organics.

FORWARD MARCH. Beyond the screening roles, conveyors are still often used to accomplish the task they are most closely associated with--moving material from point A to point B.

In the recycling and solid waste industries, this can involve the movement of much greater amounts of material than one might find in a warehouse, where evenly spaced boxes might be the objects being conveyed.

On the tipping floors of some recycling plants, "live floors" are being used more commonly. These moving metal slats are also used on truck trailer floors to help offload material with less manual assistance. On its Web site, Keith Mfg. Co., Madras, Ore., identifies several recycling market applications for its Walking Floor[R] line of products.

At MRFs, bins and bunkers with live floors "are ideal for storing material until it is needed," the company notes. The activated slats, which can be made of aluminum, steel or a combination of the two metals, will bring material forward to be pushed onto a pit conveyor or otherwise handled by an appropriate loading vehicle.

Keith trailer floors used in the recycling market can unload a variety of materials, including whole or shredded tires, aluminum or tin cans, wood debris, green waste, paper sludge, auto fluff and compost, according to the company.

Disc screens, fingerscreens, vibratory feeders, trommel screens and live floors notwithstanding, traditional conveyors still deserve a mention for their role.

And even traditional "move-it-forward" conveyors come in an array of sizes and styles, meaning recyclers have to make careful choices even for this type of material handling equipment.

The Web site (www.usconveyor.net) of U.S. Conveyor Technologies Manufacturing Inc., Mackinaw, Ill., divides its product line into several segments, including vibratory conveyors and trommels, but also several types of belt conveyors.

The company's belt conveyors are subdivided into several categories: flat belts, radial stackers, troughers, steel belts and flat rollers. These conveyors are all designed to meet the needs of different segments of the scrap metal, foundry and C&D recycling industries, market segments that are the primary focus of the conveyor manufacturing firm.

If variety is the spice of life, recyclers can look forward to shopping from a flavorful menu of products when outfit ring their plants with conveyors.

The author is editor of Recycling Today and can be contacted via e-mail at [e-mail].