Market data: the key to selecting the correct screening system lies in end market demand.

Designing an appropriate screening system for a C&D recycling operation hinges on a number of factors, such as the type of material to be processed, the amount of throughput you hope to achieve and your mobility requirements. However, the ultimate factor is often the specifications of the end product you wish to produce and the market demand in your area.

"It depends so much on the material characterization that you have and the size cut you are trying to make," Bill Guptail of General Kinematics, Crystal Lake, Ill., says. General Kinematics produces vibratory process equipment.

BEFORE BUYING. "I really believe that before you can think about equipment on a C&D facility, you'd better know what your end markets are," Guptail adds. If a company expects to market wood, he says, "you want to make sure that you are able to present a wood product that is recognizable--no lead paint, no treated lumber. That's really critical. If it's concrete, or if it's demolition material and it has a lot of brick, you have to see what the maximum piece size is [in your area]."

Bruno Lagace, manager of application engineering for Erin Systems, Portland, Maine, also stresses the importance of the material's characteristics. "First of all, the recycler needs to know exactly what he is going to screen." He says recyclers should consider the size and density of the raw product, maximum particle length, the presence of wrappable materials and whether the material is comprised of new construction debris or demolition debris.

"The recyclers who are looking to achieve a high percentage of recycling will want the screen to maximize screening of fines, but will also want the screen to do a segregation of the material in order to present a steady flow to the pickers," Lagace says.

Scott Jable of Lubo USA, Stamford, Conn., the exclusive U.S. and Canadian distributor of Lubo Screening & Recycling Systems manufactured in The Netherlands, also says starting with end products is key in designing an appropriate C&D screening system. In addition to determining the marketable end products for your area, Jable points out that the material's incoming condition is also an issue. "Is it very much a mixed C&D product? Are there only two products that you are looking to separate? The inbound stream plays a part in that as well," he says.

Steve Cohen, president of The Screen Machine, Reynoldsburg, Ohio, says that after the product mix has been determined, C&D recyclers should consider the manner in which they will feed the machine. "Are they going to feed it with all excavator, a front-end loader or another conveyor, because that will determine the size of the hopper," he says. The Screen Machine makes portable aggregates screening and crushing equipment.

"The next decision that a customer has to make is whether or not he wants the machine to be on wheels, on tracks or stationary," Cohen says. "The wheeled ones need to be pulled, so they are not nearly as portable. Where, with a track machine, you can literally screen and move continuously," he adds. "A wheeled machine, it wouldn't be practical to move more than once a day."

C&D recyclers should ,also consider the need for primary sizing when designing appropriate screening systems for their operations.

PRIMARY PROCESSING. "The primary screen is often the most difficult thing to get correct," Jable says. "The problem with most primary screening techniques is that they don't allow for a big enough screening size.

"For instance," Jable continues, "if your screen can only go up to an 8- or 12-inch screening size ... that means that everything else 8 or 12 inches and larger generally goes to a sorting line. That's a lot of material." Jable instead suggests using a screen to remove pieces measuring fewer than 18 or 24 inches, reducing the amount of material on the manual picking line. "If your screening size it too small on your primary screen, your pickers are overwhelmed, and you don't get high throughput or high quality end products."

"I feel the way to handle C&D is with a primary sizing unit," Guptail says. "Primary sizing is important to make the fines material more easily recovered in automated equipment."

Lagace also notes the importance of removing fines. "You do not want 30 percent to 40 percent of the material on that belt to be fines," he says. "On top of that, if you screen with a fingerscreener, you will have natural segregation of material, and your picker will be able to be more effective since the flow of material will be of the same thickness all along the picking line."

Manual screening using picking lines, therefore, remains an important part of the process. "I believe that fully automatic sorting of C&D would be very hard to achieve since the C&D by nature is non-homogeneous and is really tough to sort," Lagace says.

Jable notes that the trend toward automation is still real. "With the high cost of labor, everyone is trying to automate as much as they possibly can; but, again, you want to be sure the automation is justifiable," he says.

CONVEYING CONCERNS

The effectiveness of screening equipment often has to do with the way in which material is presented. This is where conveying equipment comes into play.

"We look at C&D as a heavy-duty application," John Poplawski of Hustler Conveyor, St. Charles, Mo., says. Hustler Conveyor manufactures a full line of conveyors as well as trommels and magnetic separation equipment. "Normally, what we do is either go with a steel-belt conveyor with a 7/16 plate. Normally what we do for baler feeds and applications of a lighter duty is use 1/4 inch."

To make the conveyors more durable, Hustler reinforces the belts every 9 inches at the pitch, Poplawski says. "Basically what it does is add another support member."

The piano-hinged belt Hustler manufactures is solid so dirt and debris will not build up and it features bigger flights, or slats driven on the outer edges of the conveyor by a drive chain. It is also hinged every 2 inches for durability. The double-beaded apron conveyor offers better containment of materials and easier maintenance, Poplawski says.

Bill Guptail of General Kinematics, Crystal Lake, Ill., says apron conveyors are often used on the feed system. When working with more finely sized material, how you present it to the screening equipment becomes more important, he says. "An apron will go up a little steeper."

"One of the neat trends of machines now coming out is they all have conveyors that are built on to them," Steve Cohen, president of The Screen Machine, Reynoldsburg, Ohio, says. "No longer do you need to haul the crusher, the screening plant and two or thee conveyors." In addition to durability, conveyors need to be set up quickly to reduce an operation's downtime, he says.

"If customers want to be able to sit in one place and run for several days, then they are going to need to bring a separate conveyor that is very long--an 80- or 100-foot stacker," he says. "But the whole idea of these machines on tracks is that you can make windrows. They key is instead of getting a long conveyor and stockpiling into a really high single pile, you can move the machine along and make smaller piles."

GETTING EQUIPPED

Visit our equipment spotlight at www.cdrecycler.com for information on C&D processing and support equipment.

The author is associate editor of Recycling Today and cab be contacted via e-mail at dtoto@Recycling Today.com.