Engineering & Mining Journal

SEP 2017

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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SCREENING MACHINES 48 E&MJ; • SEPTEMBER 2017 www.e-mj.com In the mechanical world, a machine that shakes is often a machine that breaks. That's not the case in mineral processing, where thousands of vibrating screens cur- rently in operation are expected — and engineered — to shake, vibrate or oscil- late continuously shift after shift, provid- ing predictable and reliable dewatering and particle-separation performance. Shakiness in machinery can usually be attributed to imbalance or structural weakness, and although screen manufac- turers commonly use out-of-balance me- chanical arrangements to impart motion to the screen deck, in actuality, screens must adhere to Newton's Third Law re- garding balance of forces — for every action, there is an equal and opposite re- action — in both design and operation to provide consistent performance and avoid self-destruction. In fact, mineral-process- ing screen technology in general is a bal- ancing act of sorts, with suppliers stack- ing new designs, improved materials and increasingly sophisticated monitoring and analysis services against their customers' desires for higher capacities, less mainte- nance and lower consumables costs. Among the many factors that can alter a working balance in any given screen application are changes in par- ticle size and shape, material densi- ty, moisture content, and particle size distribution. When the balance point shifts to one extreme or another, higher operating costs or lower production gen- erally follow. Restoring the balance after a shift in any of these factors may be as simple as changing the type of screen media used, or as complex as changing from one type of machine to another. Whatever the solution, the screen is likely operating at less-than-optimum performance, or not at all, until the kinks are worked out — sometimes sim- ply by trial and error. It can be an ex- pensive process in terms of lost output and equipment costs, and one that pro- ducers are anxious to avoid. Fortunate- ly, screen equipment suppliers such as Metso, FLSmidth, Sandvik, McLanahan, Polydeck, KPI-JCI, Telsmith, Weir, Der- rick, Deister, and Multotec offer a stag- geringly large selection of products and configuration options to meet just about any application challenge. E&MJ; recently surveyed the product portfolios of several major suppliers to identify new items and services that bol- ster customer prospects for maintaining the crucial balance between screen per- formance and steady production. Getting It Right Screen machine designs and updates rep- resent the manufacturer's effort to opti- mally balance weight, strength and overall stiffness — too much weight requires too much force, not enough mass can result in a flimsy machine, for example — along with the need to minimize opportunities for fatigue cracking at joints and other vul- nerable points. Maintenance access, ma- chine footprint and headroom, and other installation considerations also play a ma- jor part in design decisions. Computer-aid- ed design and analysis has been of great value in refining machine design. Weir, for example, has used Finite Element Analysis in its design effort since 1992, enabling it to incorporate a steady stream of improve- ments in screen mass and strength. McLanahan Corp.'s MAX line of in- clined vibrating screens, introduced last year, also illustrates how suppliers are re- fining their designs to meet user needs. McLanahan's MAX production line man- ager, Jeff High, provided E&MJ; with a list of design details focusing on reliability and improved maintenance efficiency. The MAX line, offered in sizes and configurations ranging from 5 ft x 16 ft to 8 ft x 24 ft in triple-, double-, and single-deck models, was designed to pro- vide maximum headroom between decks, making maintenance and media change- outs more convenient. From a structural standpoint, MAX screens are fabricated with A572 Gr. 50 plate (45% higher yield strength than traditional A36 plating) for maximum strength. Side plates are a fully bolted construction to reduce and eliminate cracking due to stress caused by weld- ing — also making it easier to change out worn components without cutting. Screening the Options A look at what's new in products and services designed to improve vibrating screen value and performance By Russell A. Carter, Contributing Editor Flexible and delivered as a roll, Sandvik's WX6500 all-rubber screening media weighs only a third as much as wire mesh, making it easy to move around site and work with, according to the company.

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