The secondary motion of the Armaflex screen sections effectively handles the clumping effect created by dust suppression systems.

In the last year or so, Polydeck Screen Corp. has introduced three new products that have proven to be very popular in prep plants. Polydeck specializes in the manufacture of screening panels using injected molded polymers. The three new products are the Armadex line of bolt-down rubber panels, and the polyurethane VST and Cutter screen panels. Each offers plant operators a way to improve performance and, in some cases, reduce operating costs.

At the center of all this activity is Steve Parsons, one of Polydeck’s regional managers who services customers in the heart of coal country. With more than 30 years of experience, Parsons is also heavily involved in the company’s ongoing R&D efforts serving as one of Polydeck’s product managers, recommending, developing and testing new designs and innovations. He not only understands the screen manufacturing process, he also benefits from the one-on-one interaction he has with dozens of plant superintendents, all of whom have different issues. “Each prep plant has to deal with site specific conditions and most of the improvements that we’ve made as a company are the result of a direct response to one of our customers’ needs,” Parsons said. As part of the company’s continuous improvement philosophy, Polydeck heavily invests in ongoing R&D, he explained, developing and improving products through prototyping, testing, and evaluation.

The injection molding that Polydeck uses exclusively to produce its rubber and polyurethane screen panels requires specific skills and equipment. The venting process for instance, according to Parsons, has to be perfect. “During the injection molding process, the raw polymer is heated and mechanically mixed in a chamber and then forced out under high pressure into a cooled mold,” he said. “When the polymer is introduced to an injection-molded dye, it’s critical that all of the air escapes, leaving 100% polyurethane or 100% vulcanized rubber. This produces a clear, crisp, sharp aperture achieving size tolerances that can’t be attained from cast molding. The poured casting process uses a liquid reducer that must evaporate, which creates distortion from shrinkage. As it dries, the liquid dissipates and the product deforms. If injection molding is done correctly, it produces a consistently sharp product. We have some very talented manufacturing engineers that have perfected this process.”

Injection molding has other advantages as well, such as the ability to mold in surface features. The company’s new Cutter panel for example, uses surface features and very small apertures specifically designed for heavy-media recovery. “The enhancements on this panel improve drain rates,” Parson said. “It has a cutting edge that is tilted into the flow similar to the cutting action on a triple-blade razor.” Polydeck introduced it to the market about two months ago after over a year of design and testing.

Their product testing usually involves several types of coal. The grind of the coal creates different shapes or fragments that vary by region, Parsons explained. The shapes can be flat slabs or pyramids, and each presents a different set of problems for the screen deck. “The flat particle will pass a long slender slot, while the pyramid shapes can get caught in the aperture like little pegs, so each has to be handled differently. The best way to identify these issues is through a good screening analysis,” Parsons said.

Another new screen media that the company has developed that also features molded surface features is the VST screen panel. This design incorporates slots at opposing 45? angles ,creating a zig-zag flow which should yield a higher retention time and allow more time to drain. “Sometimes the material flow is so rapid, the aperture is not recognized. Unless the energy can be slowed, water will carry through the process,” Parsons said. “The material washes off the end instead of falling through the holes. By enhancing the