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November 2006

Equipment Spotlight

Vibratory Screens

—View a list of manufacturers at the bottom of the page

When it comes to low-cost, reliable separation of differently sized particles in a stream of recyclable materials, few solutions can outperform vibratory screens. Using the combined forces of gravity and mechanical agitation, many vibratory screeners move streams of material down horizontal or sloped screening decks featuring apertures of graduated sizes. Particles then either fall through the apertures to hoppers or conveyor belts below or are ejected from the end of the screening deck. In another approach, circular vibratory screeners use rotary vibrating action to push particles through screen apertures. The screens themselves differ as well. Vibratory screeners may use wire mesh, perforated metal sheets, disc screens or fingers to segregate particles by size.

Applications for vibrating screens are found in many different industries. In recycling, they help to separate construction and demolition debris, divide scrap tire particles, segregate wood chips, break up municipal solid waste, sort out auto shredder residue, recover sand from foundry waste and divide plastic and metal particle streams by size, among other uses. Vibratory screening equipment selection depends on a number of factors, including the size and shape of particles, throughput rate, moisture content and more.

At The Cleveland Vibrator Company in Cleveland, Ohio, screeners may be air-powered using a reciprocating piston or electromechanical drives. General sales manager Jack Steinbuch says recycling applications for Cleveland Vibrators exist at foundries, where screens are used to recycle sand employed in the metallurgical process. Plastics recycling operations employ Cleveland Vibrator screens to filter streams of ground plastic materials. “We do a lot with the plastics recycling guys,” he says.

For recycling, Cleveland’s EMS electromechanical screeners are the most popular units. These employ two rotary electric vibrators, one rotating clockwise and the other rotating counterclockwise. The vibrating rotors produce a linear vibration force which is placed at an angle designed to go through the center of gravity of the screening body, Steinbuch explains. Material lifts from the screening deck and moves forward propelled by gravity. “That has proven to be a very reliable motion to separate material by particle size,” Steinbuch says. Coarser material is lifted from the screen deck by the vibratory force and moves forward, while finer material gets closer to the screen deck and eventually falls through.

Cleveland’s design allows the machines to be installed in areas with less headroom because there is no need to have a large hopper under the equipment. “It’s a little simpler to work with, and very easy to install,” Steinbuch says.

Plastics recyclers typically employ EMS machines equipped with 24 by 48 inch screen decks. These vibratory screeners sell for approximately $10,000. Larger machines, up to 48 by 96 inches, are priced at approximately $20,000. Steinbuch says one advantage of their approach is that the electric vibrators employ no belt drives or other mechanical linkage, so they are reliable and easy to maintain. “The biggest issue for us has been lower maintenance,” Steinbuch says.

Action Equipment in Newberg, Oregon, offers its Taper-Slot and Vibra-Snap screens for a variety of screening applications. The Taper-Slot is used for materials with particle shapes and sizes that would tend to plug a conventional screener, says President Andrew LaVeine. Construction and demolition, scrap tires and wood waste often incorporate particle sizes and shapes that are tough for many screens to handle, he says. Particles that are oblong in shape, for example, tend to plug screen apertures.

Many applications employ multiple screeners, using Taper-Slot screeners with larger aperture screens for larger particle sizes and Vibra-Snap screeners for finer material streams. “That’s a machine that’s suited for screening very small particle sizes with moisture content,” LaVeine says of the Vibra-Snap, which can work with particle sizes down to 1 or 2 millimeters.

Action’s patented finger design used on the Taper-Slot makes for a highly rigid screen deck and provides for more accurate screening and less catching. The Vibra-Snap takes a different approach, with a non-rigid screening deck made up of a tensioning and relaxing polyurethane panel. “It’s like a trampoline,” LaVeine says. The Vibra-Snap deck moves a few inches, rather than the much smaller distance typical vibratory screen decks move. “It’s really a specific machine for nasty, icky smaller aperture screening, LaVeine says. “There’s no way to bind a Vibra-Snap screen aperture.”

Vibra-Snap screeners are priced at approximately $50,000 for a model with a 4 by 10 feet deck. Double-deck models may cost up to $200,000. Taper-Slots are general custom designs with up to 20-foot screeners and costs vary widely, LaVeine says.

Recycling is not a major application for vibratory screeners, but it is significant. According to Steinbuch, “We do a little in recycling, but not as much as other markets. We do a lot in the recycling business with our vibratory feeders to bring material to an eddy current or something taking material from the shredder. That is primarily in auto-shredding.”



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