Aggregates Manager

August 2014

Aggregates Manager Digital Magazine

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Page 31 of 43

S creening is considered one of the most important parts of aggregate production. Without proper screening, aggregate producers would end up with a pile of material in all different sizes that couldn't meet department of transportation, or any other, specs. Screens and screen media have changed and improved. Manufacturers have spent a lot of time on research and development to meet the needs of their customers, helping them increase production levels, decrease maintenance requirements, and improve the quality of their products. According to Ed Sauser, product manager for Terex Minerals Processing Systems, there are several things trending in screening today. One of these trends is to make the screen products more user-friendly so they require less downtime for maintenance and replacement. This can help reduce the cost of ownership for producers. Another trend in screening is the incorporation of vibrator mechanisms to shake the screen box. By mod- ifying the motion of the stroke, particle separation can be improved. There are three basic types of motion that screen boxes use today. The oldest and most simple stroke is a circular motion, which is most commonly used on an incline screen where gravity helps move the material down the sloped screen. Then there's a linear stroke where the screen shakes back and forth in a straight line. This motion is more aggressive than the circular motion and can be used on both incline and horizontal screens. The third type of motion is the oval stroke where the screen box moves in an elliptical motion, rather than a circular motion. This is the most aggressive of the three strokes and is becoming more popular because of its higher effi ciency rate. The aggressive shaking tends to keep the screen cloth cleaner, which reduces blinding and pegging. When used on an incline screen, the elliptical motion throws the material almost straight up initially, which helps drive the material through the screen. "There has been a lot of development with the oval stroke," Sauser says. "Manufacturers are trying to incorporate the motion into a lot of different screening products." Flexible screen media, such as Flex-Mat and Z-wire, is another trend that is becoming more prevalent in the ag- gregate industry. Flexibility keeps the media from blinding and pegging, which means more effi cient screening and less downtime for cleaning the screens. Most of the major screen media suppliers now offer some type of fl exible screen media and are developing new products using that technology. Then, there's the debate about which type of screen media should be used — wire or synthetic. Wire screen media has been around for a long time, but over the past decade, the quality and design of synthetic screen media has greatly improved and has gained acceptance in the industry. Synthetic screen media offers greater durability, and may offer better consistency in material separa- tion and sizing. Wet material tends to work better with synthetic screens, where dry material works well with wire screens. There are many things to consider when choosing the right screens and screen media. What type of material is being screened? How much moisture is in the ma- terial? How is the material being fed into the screens? What percentage of fi nes is in the feed? These, and other factors, should be considered when determining the right screening system to use. However, the most important step producers can take is to work with their supplier to fi gure out what combination of screens and screen media will work best for their unique operation. creening rends T S Screening Supplement in by Kerry Clines, Contributing Editor

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