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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JUNE 2014 • E&MJ; 73 www.e-mj.com S C R E E N S wire, giving up to 50% more higher-quality production," Leblond said, adding that Flex-Mat 3 produces up to twice as much as polyurethane or rubber media for users looking for more tons per hour. Les Naday, mining industry manager for Polydeck Screen Corp., said there has been some improvement in wear resistance and durability because of new formulations that have become available for rubber and polyurethanes. These formulations have proved to be beneficial in specific cases, he said, emphasizing the way in which manufacturers can now tailor their screen media products to meet individual opera- tions' requirements. For FLSmidth, the company's general manager for screen media, David Sibley, also pointed out that while investigation into improved materials for the manufac- ture of polyurethane screen panels is ongo- ing, none of the many materials tested in the last few years has demonstrated quali- ties over and above the material currently in use. In addition, the use of high-quali- ty spring-steel frames has enabled modular screen media to achieve a much higher "open area," with percentages of up to 55%, while reducing the installed mass. The company has also introduced hybrid modular polyurethane panels using different types of screen media such as wire screens, perforated material and wedge wire to bring different characteris- tics to modular screening. Screening specialist for Tenova Delkor, Rhett McElvenny, looked at materials used in linear belt screens. "The screening medium used for the linear belt screens has historically been a woven polyester mono-mono construction," he said. "Some duties can use polypropylene cloths. However, these pose tracking problems, particularly on larger machines. Some duties may also use metal link mesh as the screening medium, but these are quite specific to a particular duty." Screen Media Design Having asked the experts about screen media developments, E&MJ; extended this to the design of screening media. Have there been any noticeable changes in this area, such as the wider use of modular designs? Naday (Polydeck): Modular media has taken hold in mining applications, allowing the mixing of various duties to meet main- tenance cycles. Most large mines take advantage of modular panels' flexibility as well as their safe and easy installation and removal. LeBlond (Major Wire): Around the world, large mining operations use poly- urethane or rubber while smaller opera- tions are largely using woven wire. Easton (WesTech): "Specialty screening products differ significantly from tradition- al vibrating products in that the material being screened does not necessarily have to move across the screen surface. This opens a much wider range of possible materials and configurations that can be used for screening media. "For example, WesTech's linear screen utilizes a moving belt of screen fabric with flexible roving, allowing the media to wrap around return drums. The fact that the media moves to the discharge eliminates the need for the material itself to slide and wear on the media surface. This configura- tion also allows for easy cleaning of the media in the return cycle, eliminating peg- ging and plugging issues." Sandvik: More and more customers are realizing the benefits of modular media: easy to handle, fast installation and mould- ed holes with a relief angle. This prevents problems with pegging. McElvenney (Tenova Delkor): The media have not changed greatly; the medi- um is a woven cloth and the aperture deter- mines the cloth model used. "Tenova Delkor has increased the size of the actual screening device in the past five years from 25-m 2 units to 32 m 2 and more recently, to a 40-m 2 machine," he said. Perkins (Derrick): The company is com- mitted to manufacturing urethane panels for exclusive use on screening machines designed and manufactured by ourselves. There is a strong relationship between the performance of the panel and the machine it is installed on. "We believe that this is truly a situation where one-plus-one is greater than two, so to speak." Sibley (FLSmidth): "In most new process plants, screening machines are being sized according to the open area and use of mod- ular screen panels. Further to this, we have developed and supplied our BPS (Bolted Pin System) polyurethane modular screen pan- els, where the unique design gives a superi- or open area and reduced installed mass of the panels on the screen decks." The advantage of a higher open area and lower installed mass adds to the screening efficiency and the effective con- sumption and use of input energy. In addi- tion, the BPS panel-fixing method has proved to be user-friendly for plant mainte- nance staff, with less plant downtime for routine deck replacement, Sibley said. Common Screening Problems E&MJ; next asked each of the respondents about any specific problems they see on a regular basis that arise from operators not using appropriate screening practice. Sandvik: It is important to take the whole process into consideration when problems occur on a screen. Sometimes there is a lack of process knowledge, and adjustments are done on the screening media instead of maybe making changes at the crusher settings, chutes or feeders. When a screen is not performing, it is important to really understand the underly- ing reason for the problem. An example might be if there is a problem with through- put, where material is not being screened out and just keeps recirculating. Having the knowledge to do a proper study to identify the real problem is key here. Even if the problem is shown to be on the screen, the actual cause might be somewhere else. Just making changes to the screening media when it comes to hole sizes and thickness could lead to an end- less road of changes that don't really solve the problem. The cause of the poor screen- ing might instead be non-optimal screen FLSmidth's screening experts point out that the company's use of high-quality spring-steel frames allows modu- lar screen media to achieve a much higher 'open area' while reducing the installed mass. EMJ_pg72-77_EMJ_pg72-77 6/3/14 3:06 PM Page 73