Mining Mirror May 2017 - Page 29

Mining in focus If a vibrating screen continues to operate while having issues with pegging, blinding, broken screens, or screen media with incorrectly sized openings, the screened pile will likely be contaminated and might require re-screening. composition of the material going through the vibrating screen and consult an expert from a reputable company to match the best screen media to the application. Finally, learn how to install and maintain the screen media properly. Asking the right questions The first step towards selecting the most productive screen media involves answering several questions. What material is being processed? Is the screen media reaching a suitable lifespan for the operation? What sort of challenges are occurring with the current screen media? Fair advises that an operation needs to consider the types of materials going through the vibrating screen. Factors such as material size, weight, and abrasiveness all come into play during the selection process. For example, screening gravel typically requires media with higher wearability to handle the material’s abrasiveness. Materials with top sizes as large as 25cm, on the other hand, require more durable screens because of the constant high impacts. Next, Fair says, look at the vibrating screen itself and complete a vibration analysis. Some analysis systems are designed to safely monitor vibrating screen performance in real time and detect irregularities before small problems lead to diminished performance or bigger issues. “In some cases, the machine may be running perfectly, but changing the screen media can prevent screening irregularities and the resulting damage,” says Fair. Operators should consider the three phases material goes through within the vibrating screen, from layered to basic to sharp. Producers can customise the screen deck with various types of screen media through each phase by accounting for open area and wear life to maximise productivity in each phase. In the layered phase, as material of all sizes hits the screen deck, the media should handle a deep bed depth, high impact, and a mix of coarse and fine particles. Material should stratify in the middle of the deck during the basic phase, and near-size and oversize particles should be at the top of the material being screened. Virtually all undersize material should have fallen through the screen media by the time it reaches the sharp phase at the discharge end, where near-size and oversize particles should be in direct contact with the media. A vibrating screen operator should also examine wearability to determine whether media in the three phases is reaching maximum potential. If it seems as if screen media has to be changed too often, Fair says a company needs to consider switching to something more durable. “Next, look at the screening challenges. Examine discarded screen media for signs of problem areas, such as broken wires, wear areas, pegging, or blinding. Common screening issues include premature wear due to heavy material, along with large amounts of abrasive fines. Screening problems can cause carryover or contamination, resulting in unwanted material in the screened pile, or the added cost of rescreening. Also, broken screens mean costly unscheduled changeouts. All of these signs indicate there’s likely a better screen media option for at least one phase of screening, if not all three,” says Fair. He concludes by saying that if traditional screen media isn’t working and unscheduled changeouts are eating into profits, it might be time to consider a polyur