In countries with low-grade orebodies and relatively high labor costs, such as Canada, the U.S. and Sweden, the small, low-tonnage mining operation has virtually disappeared. In those countries, the industry has shifted to high-tonnage, lowgrade operations, which require larger equipment with a low operating cost and high throughput.

Emerging economies like Brazil, Russia, India and China require large quantities of raw minerals such as iron ore and copper to feed their growing global and local demands. Fueled by the growth of these emerging markets, a global boom in metals and energy prices has been sparked. To meet this demand, high-tonnage operations have become the norm and now dominate in countries like Australia, Peru and Chile where major ore reserves are located.

Whether it is low-grade or high-grade ore being extracted from the earth, the focus has shifted to high-tonnage operations. The common denominator is that mine operations are looking for higher output while lowering costs. As a result, there is even greater importance placed on integrated processing solutions or comminution packages, including screening technology. Once a secondary design consideration, screen technology now plays a significant role in mineral processing operations.

Typical screen applications include:

• Grizzly screens for coarse material separation;

• Large capacity double-deck combined scalping and sizing screens for closed-circuit, secondary crushing circuits;

• Fine separating sizing screens operating in closed circuit with high-pressure grinding rolls; • Linear motion horizontal screens for SAG mill discharge;

• High-frequency sizing screens for coarse material recovery from cyclone overflows; and

• High-frequency dewatering screens.

In addition, some mine operations opt to locate smaller screens throughout a plant for specialty applications such as tramp metal removal.

Larger-tonnage plants that deploy new high-pressure grinding rolls have created a new technical challenge for vibrating screen suppliers. To meet the needs of both large primary grinding mills and large secondary cone crushers, screen sizes have been increased beyond the standard 4-m screen width. As manufacturers have increased screen sizes to accommodate higher throughput, they have also focused on increasing screen media life and simplifying replacement procedures.

There are several important criteria to consider when evaluating screening technology, including separation effectiveness, equipment durability and overall maintenance costs. The wrong screen can completely disrupt the operating efficiency of a plant. When an improper selection of a screen occurs, operators are forced to compromise the production and cost targets of other equipment in the plant.

For example, a cone crusher’s operating cost can be as much as 50% higher if fines are not adequately removed prior to crushing. Besides the added operating cost, the cone crusher will be forced to reduce its crushing effectiveness to prevent mechanical damage caused by the packing of the newly created fines and the fines that entered the crusher from the screen oversize. In the case of SAG mills, a poorly selected SAG mill discharge screen can adversely affect both the cone crusher processing critical size material and the feed size to the downstream grinding mills. In both cases, production is lost and in the case of the cone crusher, mechanical reliability can be compromised.

The challenge facing manufacturers of screening technology is to design systems that vibrate larger and heavier screens without sacrificing ease of operation and maintenance.

The interdependence of the individual components of a mill circuit requires that all unit processes are optimized and aligned for maximum capacity, efficiency and utilization. By carefully designing and integrating equipment, capital investments can be minimized without compromising productivity or increasing maintenance costs to ensure the continued efficiency of mine operations around the world. O’Bryan is global product manager–screening technology for Weir Minerals (www.weirminerals.com).

Banana screens use a multi-slope design to quickly and efficiently separate fines from oversize particles. Angling for the Best Approach The author updates E&MJon matters of specific screening requirements, usage trends and Weir Minerals’ strategy for serving its screen-market customers. Weir Minerals specializes in linear-motion screens. What benefits do these type of screens offer, and for which specific applications do they offer the most benefit when compared with screens that use circular or elliptical motion? A linear-motion screen action is needed whenever the screen approaches an angle where material must be both dislodged and mechanically advanced forward on the screen with minimal or no benefit of the incline to assist in moving material or keeping material from pegging in the screen openings. The clearest illustration of a linear motion benefit is when the material must be conveyed up the screen at a negative angle, as is common with Enduron dewatering screens. For screens with angled inclines of less than 10° (which includes most banana screens with multiple inclines or slopes) a linear motion exciter is required. Linatex—now Enduron—screens have been popular for use in dewatering applications for many years. Have you seen increased interest from customers for these types of screens, given the industry's increased focus on water conservation, reduction of energy costs, tailings management, etc.? Dewatering screens used in combination with hydrocyclones and centrifuges are in even greater demand. On the environmental front, any project that encompasses the use of water must consider water recovery as a key aspect of their long-term environmental plan. Permit requirements that demand a return of a mined or processed minerals resource to its original state less the mineral, cannot leave behind a large tailings pond that did not exist prior to the minerals activity without objections from the regulatory agencies. So today, we see a much stronger trend for dewatering screens of increasing size to meet hightonnage demands of large mining operations. Banana or multi-slope screens are used in many mineral applications ranging from diamonds to iron ore. What are their principal advantages? Banana screens have decks arranged to provide a two-prong attack to the screening activity. As shown in the diagram, the first stage is the steep angle of inclination (usually inclined 30°-35° from horizontal) that causes the material to immediately stratify due to rapid shearing. Once this stratification occurs, 60%-70% of the screening required is accomplished in these high incline areas along the first third of the screen length. The middle third of the screen (usually inclined 10°-20° from horizontal) removes the next 20%-30% of material and the last third (usually inclined 10° or less from horizontal) performs final finishing, with almost all the separation action a result of linear-motion, mechanical agitation. In applications where coarse, heavy rocks are processed, the initial high-velocity screening angle is reduced to 25° , as there is no benefit to rapidly stratifying coarse particles at the feed end of a banana screen. In addition to providing customers with equipment packages that can handle high tonnages, what products, services and technologies can Weir Minerals offer to give customers better plant availability, space or energy savings and improved materials handling capabilities? Weir is currently introducing new products in many fronts to reduce wear, ease maintenance and lower costs. Current new developments include a wide range of new wear metals and new elastomer (rubber and urethane) products that will last up to 50% longer than what is currently in common use in the market. Whether it is material handling, comminution or separation—if the material being processed is wear-intensive, Weir has new solutions and continues to develop new solutions to help our customers lower their costs and increase uptime. Weir continues to focus on providing the most economical solution tailored to the needs of the industry served.

Outdoor testing: Supporting the custom engineering concept is an outdoor endurance testing station to evaluate new vibratory drives and screen designs under
real-world conditions.

Custom-engineered drives are already being manufactured at Martin Engineering locations in the U.S. and China, and as the business grows, the firm plans to supply them from all eight of its business units around the world. “Global manufacturers need to be able to count on worldwide availability of customized solutions like these,” said Vice President of Operations Robert Nogaj. “This approach is part of our evolving global business strategy to tailor solutions for specific customers and applications.”

“The target market for these new services is any manufacturer that supplies vibratory equipment of virtually any kind,” Nogaj added. “If an OEM has a unique need for a drive that hasn’t been (or couldn’t be) designed before, or if there’s a design for a machine that they could not find a drive for, now there’s a cost-effective resource for developing them.”

Martin Engineering is targeting continuous-duty applications that often require explosion-proof construction and multiyear reliability, backing the products with the industry’s first three-year warranty, plus three additional years on bearings and electrical parts. A key to the new technology is its global availability, as the company will be able to manufacture custom designs in any of the countries in which the firm does business. Customers will benefit from regional engineering, manufacturing and service in virtually any location.

“There are many suppliers who provide off-the-shelf solutions, and we will continue offering conventional vibrators in a wide range of sizes and force outputs,” Nogaj said. “But for the builders of next-generation equipment, we can now deliver design options that engineers have never had before. Instead of being limited to an offthe-shelf vibrator, manufacturers can specify the exact sizes and parameters they need to suit new and emerging designs.”

Nogaj said the designs are likely to find utility in high-frequency vibratory screens, sizing equipment, dewatering operations and other vibratory equipment.

While traditional designs will remain a cornerstone of the company’s family of vibration products, the company is now able to custom-engineer the size and shape of the drives, torque curves, weight and many other features, in both electrical and mechanical units. “This will allow OEMs to build equipment that hasn’t been available in the past,” Nogaj said. “Rather than being handcuffed into using the stock designs that are on the market now, they can order the exact vibrator properties, profile and output that they need.”

An important component in the decision to offer custom-engineered vibration is Martin Engineering’s extensive new R&D capabilities in the CFI. For example, the firm has recently added four massive, spring-mounted 10,000-lb test blocks specifically for development and trial of new vibrator designs.

Indoor test block: The massive 10,000-lb (4,545 kilo) test block in the Center for Innovation is used for
the development and trial of new vibration designs.

“This kind of capability is intended to serve the OEM who has vibration needs that are presently unmet,” said Global Vibration Development Manager Brad Pronschinske. “It will be a huge competitive advantage for manufacturers trying to develop new products, giving them a design freedom that wasn’t possible before.”

Martin Engineering’s new capabilities also include sophisticated dynamometer testing that allows the company to map the shape and values of an electric motor’s torque curve. “The dyno testing helps us analyze existing designs, but it also means that customers can come to us to obtain a specific torque curve,” said Pronschinske. “That can be an extremely valuable asset for new product development, and until now it’s been a service that has been nearly impossible to find without investing huge amounts of money.”

Further supporting Martin Engineering’s commitment to the custom engineering concept is an endurance testing station located outside the CFI, where engineers can evaluate new vibratory drives and screen designs on any of five different shakers. A similar station at the company’s China facility also features two shakers. “The outdoor test stations are intended to duplicate tough, realworld operating conditions,” Pronschinske added. “The setup at CFI has one shaker design with a four-pole drive unit that can develop as much as 10 Gs of force, helping us to engineer the highest quality, longestlasting vibrators in the world.”

Martin Engineering will offer an extensive range of designs and features for specific applications, including explosionproof models, vertical shaft units, flangemounted designs and even low-profile vibrators that can be incorporated as part of a support structure. “This capability allows us to take a huge leap beyond the conventional four-footed designs that dominate the market today,” Pronschinske said.

As in most sectors of mineral processing technology, an underlying philosophy of particle separation science is that “there’s always room for improvement.” It’s a driving force that’s nowhere more apparent than in the constant flow of new ideas related to screen-machine and media design in processing of ores, slurries and tailings. Here’s a quick sampling of what’s new—and effective—in the commercial market.

Metso has introduced a new, highenergy elliptical-motion horizontal screen, which it says will provide increased uptime and safer maintenance, while delivering up to 25% more screening capacity compared with a conventional screen of the same size. The model ES screen machine features two unbalanced shaft lines that rotate in opposite directions, generating a high-energy elliptical motion with a selfsynchronizing principle. There are no mechanical timing devices, gears, belts or oil leakage, which together with the reliable grease lubrication system, should keep downtime and maintenance to a minimum. The unit also offers up to 50% more space between the decks compared with similar flat screens, for easier, safer and more comfortable access for maintenance. The standard deck frame of the screen is preconfigured to handle both modular and tension screening media with minimal interruption and can be easily converted to handle the media of choice.

Making Fines Pay
At the other end of the particle size spectrum, Deister Machine Co. has developed a new Ultra-Fines Recovery (UFR) system, designed to recover ultra-fine particles in mill tailings and enable mining operations to eliminate or greatly reduce the need for maintenance-intensive settling ponds. Deister describes the UFR as a cost-efficient alternative to plate filter presses, allowing producers to create a dry tailing or silt product that can be stockpiled prior to removal, or used as a saleable product.

Metso’s ES elliptical-motion horizontal screen.


Deister Ultra-Fines Recovery system.


Major Wire Flex-Mat 3 Modular panels.


Polydeck Armadex bolt-down rubber panels.

The Deister UFR System is capable of recoveries from 350-400 mesh, and at feed capacities from 1,500–3,500 GPM (5700–13,250 l/min). It utilizes a radial distribution manifold for even distribution of solids to all cyclones. The system’s reverse slope vibrating screen is available in sizes up to 7-ft wide and 12-ft long (2.13 x 3.65 m), with solids capacities up to 70 t/h.

The UFR system’s cyclones are available with a variety of liner and body materials. Victaulic connections allow flexibility and ease of maintenance. Optional Duck Bills can be attached to the cyclone apex with siphon control to accommodate variable feed solids conditions. The sump is constructed with reinforced walls and vertical columns.

A sloped bottom plate promotes even solids flow to the pump inlet and an automatically adjusted makeup water valve protects the pump. Several pump configurations are available, mounted on a steel frame base pad.

Deister also introduced two innovative options for use on mine-duty screens. Its new Exciter Vibrating Mechanism is designed for use with large linear-stroke screens and feeders. Multiple units can be positioned in series and linked by flexible shaft couplings. Innovative seal, shaft and bearing arrangements provide a rugged unit that is easy to maintain, according to the company—especially when combined with the Deister System Saver Oil Filtration System. Removable external counterweight slugs allow for easy output force adjustment over a wide speed range. The Exciter Mechanism can be driven by V-belts or direct drive flexible shaft.

Another option for large screens is Deister’s Isolation Base, which incorporates a secondary set of support springs, as well as shock absorbers that further isolate the forces generated by the vibrating screen frame from the stationary structure. The base, according to Deister, also is useful in reducing the size and complexity of the support structure under and around the vibrating screen.

Modular Media Meets the Challenges
Montreal-based Major Wire Industries now offers a wide variety of Flex-Mat 3 Modular screen media panel locking systems that increase overall screening production without costly screen box modifications. These locking systems, including Pin & Leg, Pin & Leg Maxi, Pin & Sleeve, Grooved, Step, Snap C, Snap P and Snap 2K, are claimed to fit virtually any existing screen box. Snap- and step-type panels are available in 1- x 2-ft (305- x 610-mm) sizes, while the pin- and grooved-type panels are available in both 1- x 1-ft (305- x 305-mm) and 1-x 2-ft sizes. All locking systems fit competitive dimensions as well. They install using the same fastening systems as traditional polyurethane and rubber panels and are available in both stainless steel wire and Major Wire’s proprietary OptimumWire. Flex-Mat 3 Modular panels replace existing polyurethane and rubber panels wherever throughput is compromised, such as at the discharge ends when throughput is critical.

South Carolina, USA-based Polydeck noted that high performance, extreme duty screening applications consistently provide challenges for traditional modular screen media. Wire cloth wears out quickly and modular synthetic media may be only marginally effective in dealing with the volume and weight of feed material. Bolt-down rubber has often proved to be an effective solution for these extreme duty applications.

The company is now offering Armadex rubber bolt-down screen sections. Armadex sections are made with Binary Injection Molding (BIM) technology, which is a proprietary Polydeck manufacturing method. This type of injection molding puts a premium gum rubber blend under extreme pressure in a staged sequence to produce high-quality bolt-down rubber media.

The process, says the company, creates a longer wearing screen section with the lowest dollars-per-ton investment. In addition, the BIM process allows customization options not available in traditional bolt-down screen media. Among available options in the Armadex line are square, slotted, round and custom aperture shapes; various aperture sizes that can be configured to optimize wear life versus open area for a specific application; sections that fit any existing frame configuration; and customizable bolt hole and aperture locations, allowing section designs that protect screen cross members and control wear rates in feed zones.

‘Old Reliables’ Produce Profits
Although the marketing spotlight naturally gravitates to new or improved products, the application of tried and true screen equipment and techniques often provides significant—and highly cost-effective—operational improvements.

Derrick Corp., headquartered in Buffalo, New York, USA, has focused on fine-screening applications in mining for decades, but has developed products for other screening tasks as well. Derrick can provide numerous examples of how incorporating units of its plant-proven fine-screening products into comminution circuits that use traditional setups can result in better performance. For instance, after a U.S.-based iron ore plant added 24 of its Multifeed screens with 150-micron polyurethane panels to the primary grinding circuit, the plant increased line production by more than 30%, reduced power consumption per ton by 24% and obtained the same product grade—but at a coarser grind.

The Multifeed screen is no newcomer to the industry—Derrick patented it in 1977 and it is the direct predecessor to the company’s popular Stack Sizer wetscreening unit.

The company also has heavily invested in perfecting its line of fine-screening polyurethane media. In another example, an iron ore producer operating a spiral plant to recover fine, liberated hematite from tailings installed Derrick 45-mesh polyurethane screen panels ahead of the spirals to remove coarse silica from the feed. The spirals were then tuned to recover more iron in the 40- to 200-mesh range at the same grade. This process improvement resulted in an additional 500,000 t/y of fine concentrates.