Engineering & Mining Journal

JUN 2014

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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settings, where changes to the speed or stroke could provide the solution. Another common problem is uneven load- ing over the width of the screen, or feed seg- regation, in which case changes to the feed- ing arrangement is the solution. It is also important to remember that making adjust- ments to the crusher may also help. In reali- ty, there is often very limited benefit in chang- ing the properties of the screening media before the feeding arrangements and screen settings have been optimized. Our teams often run into "screening problems" that have other causes than the screening media. Perkins: "Performance problems arise from improper installation of the panels on the machines. Derrick is developing mech- anisms that mitigate this problem. However, with such a large installed base worldwide of older technology, coupled with the long life of the machines, this is an ongoing training hurdle for the natural turn-over experienced by most operators." McElvenney: "The most common prob- lem that we see is screens being fed with too much coarse material as a result of mill discharge cyclones being overloaded and 'roping.' This results in the screen receiv- ing slugs of coarse material and subse- quently flooding." Leblond: "A large percentage of the woven wire media in use break because of poor installation that is itself a result of a lack of know-how on proper practice. Since 2008, Major Wire and its authorized dealers have given a simplified screen maintenance seminar to more than 6,000 operators to teach best practice in the installation of ten- sioned screen media on shaker screens." Naday: While modular panels are sim- ple and easy to install and remove, diffi- culties caused by untrained contractors doing maintenance are seen. Sometimes panels are left in operation after they have failed, causing costly repairs, and some- times the installation is done incorrectly. Easton: The greatest difficulties arise when particular screening technologies are misapplied. For example, using a high- energy vibratory screen on material that is very friable can cause significant attrition and particle-size degradation, leading to losses as well as plugging. Often in miner- al applications, the need to classify mate- rial by particle size is superseded by the need to classify on particle density. If size classification techniques are attempted when both size and density classification are required, the results can be disastrous. Sibley: "Over a long period, we have observed that screening machines are not correctly maintained or setup for the screening duty they are being utilized for. We frequently find that the amplitude and speed are not appropriate to the cut size, and the 'g'-forces are incorrect for effective stratification and screening efficiency. 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