Engineering & Mining Journal

SEP 2017

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Page 51 of 99

SCREENING MACHINES 50 E&MJ • SEPTEMBER 2017 mounts and body brackets, simplifying and accelerating maintenance and bear- ing changeouts for operators. The split-bucket rubber mount in- cludes a two-piece body bracket, which allows operators to remove the side arm and bucket in one piece. Prior to these improvements, in order to remove the side arm, workers were required to dis- connect the rubber mounts along with re- moving 15 bolts. Now, a crew can remove the side arm and split-buckets from the screen as a whole assembly — reducing the number of bolts removed to eight. Metso's new UltraFine screen utilizes a modular design with up to 10 individ- ual screen decks nested together into a single vibrating assembly. It is a high-fre- quency vibrating wet screen designed for applications requiring separation from 0.075 mm to 1 mm, and is claimed to be a viable alternative to hydrocyclones for low-capacity plants or for operations with heterogeneous materials. UltraFine Screens can also be used in conjunction with hydrocyclones in a two-stage classi- fication circuit. The unit incorporates a patent-pend- ing feed splitter box to ensure the feed is evenly distributed across the complete width of each screen deck. According to Metso, this machine arrangement deliv- ers double the screening area relative to other fine screen technologies in a much more compact overall assembly. The smaller footprint contributes reduced building and infrastructure cost and thus reduces the capital cost to implement this technology. Depending on the configu- ration of the unit, the feed slur- ry reports to a splitter box and the resulting sub-streams flow through hoses to the screen feed inlets — one for every two decks. Each of these streams is further split to evenly feed across the en- tire width of each of the screen decks. Each screen deck uses two-side tensioned panels of poly- urethane screening media cloth with the appropriate aperture size to achieve the desired separation. Each screen deck also has a sep- arate underpan and overflow col- lection point. The corresponding streams are combined into one discharge point for the oversize and one for the undersize. Mixing Art and Science Selecting the correct screening media for an application begins with a broad choice — wire cloth, synthetic materials or rub- ber — and often then quickly evolves into a myriad of options involving details that range from aperture size to surface config- uration. As Polydeck, a U.S.-based suppli- er of screening media products, suggested in a recent blog post, the design, manu- facture and selection of screening media can be a mixture of art and science. According to Polydeck, the most im- portant exercise when selecting screen media is taking stock of the entire screen- ing circuit. This will help determine the best materials to be used, as many factors are impacted on this evaluation alone. Wire cloth, polyurethane and rubber have significant differences. Polyurethane has higher abrasion, cut and tear resistance, and is used mostly in wet applications. It can be made in a higher hardness rat- ing, and it has better load bearing ca- pacity than rubber. Rubber is favored in dry applications and offers excellent an- ti-blinding characteristics at lower (soft- er) durometer. Both polyurethane and rubber are significantly less noisy to oper- ate than steel screen media and modular screen panels offer the greatest control in meeting product specifications because of their ability to customize the deck sur- face in 1-ft increments. For customers who prefer wire cloth, Polydeck said its recently introduced Metaldex AR500 steel media provides the wear life of abrasion-resistant steel along with the open area of wire cloth, bundled in a modular design. The weld- ed wire insert is embedded in a poly- urethane border that allows for secure attachment to the company's versatile PipeTop II stringer system. Because Metaldex's pin-style fas- tenings fit seamlessly on the PipeTop II stringer system, Metaldex panels can be used side-by-side with Polydeck Polydex or Rubberdex modular screen panels. Metaldex's open area is claimed to be equal to or greater than wire cloth with the same aperture and wire diameter. Sandvik noted its new WX6500 all-rub- ber screening media "sorts like steel, lasts like rubber," offering the same accuracy as wire mesh at 2-mm to 32-mm separa- tions along with 10 times the product life. According to Sandvik, the thinness and flexibility of the material prevents the blinding and pegging associated with wire mesh; and because it blinds and pegs less, customers can avoid frequent media inspections. In order to achieve a "perfect fit" only two dimensions are needed — length and width of the screen deck. Mapping the Deck Metso now offers ScreenPlanner, a web- based software package that allows users to plan or "map" the configuration of one or more screen decks, and by entering various types of data such as modular media panel arrangements, parts lists, application details and notes on wear points and other observations, create an historical diary of the screen's operational life as well as generate reports on wear status and parts to order. Metso's web-based ScreenPlanner software allows users to design modular-media deck configurations and track wear patterns, among other features.

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