August 1, 2014
by Kerry Clines, Contributing Editor
Screening 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 modifying 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 efficiency 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 aggregate industry. Flexibility keeps the media from blinding and pegging, which means more efficient screening and less downtime for cleaning the screens. Most of the major screen media suppliers now offer some type of flexible 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 separation 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 material? How is the material being fed into the screens? What percentage of fines 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 figure out what combination of screens and screen media will work best for their unique operation.
Metso Mining and Construction’s Lokotrack ST2.8 track-mounted scalping screen is designed to take on sticky, wet feed, even when high capacity production is a requirement. It includes a brand new high-stroke screen, which is said to provide the highest stroke on the market. Metso says it also offers more screening area on the second deck than other mobile screens in the same size range. The high eccentric throw improves material separation while a large screen surface helps to ensure precision on fine separation. The new unit is also a low-emission machine designed to minimize operating noise and reduces fuel consumption by 25 percent.
Metso Mining and Construction | www.metso.com
Deister Machine Co.’s BFO-11224-EX2 Mine-Duty Screen offers the next generation in machine size and production output. The 12-foot by 24-foot, horizontal, single-deck unit is said to deliver day-to-day reliability and high-volume capacities in a variety of hard rock mining and mineral processing applications. The unit features the Deister EX Series of geared exciters, which are designed to create the force output required to drive large screens. Geared exciters feature all-steel components, specially coated bearing inner races to deter wear on shafts, and shafts that are case-hardened and ground for minimal wear.
Deister Machine Co. | www.deistermachine.com
The 893 mobile screener, from Terex Finlay, boasts an aggressive forward-facing modular configuration screen box with a 20- by 6-foot top deck and an 18- by 6-foot bottom deck. Depending on application, the hydraulic adjustment can be used to vary the working range angle from 14 to 18 degrees. The top deck can be fit with a variety of media, including mesh, punch plate, bofor bars, and tines. The bottom deck can be fitted with mesh, punch plate, and cascade fingers. A 44-inch apron feeder and hydraulic gearbox drive are standard. The hopper has a 13.1 cubic yard capacity. Powered by either a Tier 3 Cat C6.6 or Tier 4 interim Cat C4.4 engine, it is also equipped with three hydraulically folding discharge conveyors for maximum stockpiling capacity and rapid set up and tear down times. The plant has a capacity of 800 tons per hour.
Terex Finlay | www.terex.com
Major Wire Industries Ltd. introduces modular deck crown adapters for modular decks. The adapters allow operators to convert a flat screen deck into a crowned deck on pin- and grooved-type screen decks. The adapters were developed for operators with flat screen decks who were limited to using modular type screen media, but wanted to use the company’s Flex-Mat 3 media.
Major Wire | www.majorwire.cc
With a compact, efficient design, Midwestern Industries’ Model MR-7 Screener is engineered for conveyor-type installations. The double deck allows materials to be separated from an approximately 1-inch opening on the top deck to a 1/8-inch separation on the bottom deck. The 48-inch-wide by 84-inch-long unit comes with 2 horsepower, 230/460-volt, three-phase, 60-cycle, 1,750 rpm motor, V-drive components, and belt guard and conveyor installation carriage members. The unit can be made from stainless steel or carbon steel with corrosion-resistant coatings.
Midwestern Industries | www.midwestind.com
Powerscreen’s Warrior 2100 features its exclusive triple-shaft technology, which, along with a 16- by 5-foot screen box and amplitudes and accelerations of over 5/8 inch and 6 g, respectively, offers efficient throughput, especially in sticky material. Economy was top-of-mind in the screen’s design, which lowers fuel consumption through a lower engine running speed of 1,800 rpm and enhanced hydraulics. Available media options include bofor grizzly, finger modules, punch plate, and new 3D punch plate for scalping, screening, and recycling. Adjustable speed, stroke, and timing are said to enhance versatility and performance in aggregate applications. Conveyors feature high stockpiling heights, a chassis riser and telescopic side conveyor option, a screen box raise function, and the ability to raise the collection conveyor. A chute design with feeder under-tray slide-out minimizes spillage and material buildup around the machine.
Powerscreen | www.powerscreen.com
Deister’s exciter vibrating mechanism is designed for use with large, linear-stroke screens and feeders. The company says multiple units can be positioned in series and linked by flexible shaft couplings to provide exceptional B-10 bearing life in conjunction with aggressive G-force. Innovative seal, shaft, and bearing designs are said to make the unit rugged and easy to maintain. The exciter mechanism can be driven by V-belts or a direct-drive flexible shaft.
Deister Machine Co. | www.deistermachine.com
Elrus says its compact 6- by 12-foot three-deck screen plant was designed with an emphasis on increasing plant efficiency, reducing size and weight, and reducing the overall cost of ownership. It incorporates two screening sections on each deck, offering the benefits of both horizontal and inclined screening. The primary high-angle panel at the feed end results in rapid fines removal, while the secondary lower-angle panel results in accurate sizing and stratification.
Elrus Aggregate Systems | www.elrus.com
The new Terex Cedarapids V Series horizontal screens are said to increase production and handle applications not possible with trraditional horizontal screens. They combine the high G-force ElJay oval stroke motion with variable slope operation to handle larger deck loads. The design features more steel in the ‘rock zone’ to improve durability. The screens have several patent-pending features to boost production. The screens install up to 10 degrees in 2.5-degree increments to suit the application. A patent-pending vibration damper system offers low maintenance, while a patent-pending optional bottom deck deflector boosts efficiency.
Terex Mineral Processing Systems |www.terex.com