Keeping Vibrating Screens Lean, Clean and Green

Suppliers are finding ways to support the industry’s goals for energy reduction, materials conservation, process efficiency and the circular economy

By Russell A. Carter, Contributing Editor

Companies in the extractive industries sector generally have little or no control over the market price of their products. Consequently, the mining industry’s operational focus is on managing all aspects of production to achieve the lowest cost per unit at the highest rate of output. Vibrating screens have traditionally been used throughout the industry to help in this strategy by reducing the amount of waste material generated through processing, while contributing to the goal of achieving the highest product yield. That hasn’t changed, but as global demand for base metals, precious metals, battery metals and various types of industrial minerals shifts, sinks and surges in response to economic trends, screening technology needs to advance at a rate that keeps pace with evolving processing demands.

Some of those demands include the ability to classify increasingly complex or hard-to-handle ore, or to work in concert with ore-sorting systems to maximize the amount of sortable particles passing through while removing fines before they reach the sorter. The expanding use of HPGRs, for instance, and their tendency to product higher amounts of fines coupled with the trend among mine operators to seek physically smaller, more energy-efficient plant equipment, could amplify an ongoing challenge for screen equipment manufacturers to improve throughput without significantly increasing machine size. 

Meanwhile, quality standards for feed materials used in conventional processes such as iron and steelmaking are becoming more stringent regarding fines content and impurities as Direct Reduced Iron (DRI) facilities proliferate, and new flowsheets are being developed for processing battery-metal ores containing lithium, nickel, cobalt or graphite into high-grade concentrates. 

Some of these critical materials present tough classification problems. Screen equipment supplier Derrick Corp., for example, worked with a major graphite producer in Africa to classify flotation concentrate into distinct coarse and fine graphite flake products to maximize the plant’s financial return. The material is difficult to separate because of flake graphite’s fragile characteristics, frothy nature, and the presence of flotation reagents. Derrick said that after extensive testing, it was able to provide results that were satisfactory to the customer, which consequently purchased a two-stage wet screening system consisting of 8 primary and 4 secondary Derrick Stack Sizer high-frequency screening machines. 

An Essential Part

Screening technology tends to get lost in the shuffle as the industry’s fascination with transformative technologies – AI, electrification, automation, etc. – continues to intensify. However, the trends mentioned above are likely to ensure that vibrating screens will maintain their status as an essential part in the wheel of modern mineral production technology for the foreseeable future. One indication of a favorable outlook is supplier M&A activity within the sector, and screening equipment suppliers have definitely been active. Just in the past year or so:

A large Nordic process equipment producer announced plans to move its screening media production from the Midwestern US to Mexico, citing a need to improve product lead times and production capabilities by relocating to a facility that is optimized for the purpose. The new plant is expected to double the company’s previous production output of screening media.

In June, FLSmidth acquired the American company Morse Rubber. Based in Iowa, Morse manufactures and markets heavy-duty rubber products for mineral processing. The acquisition brings FLS additional advanced molding capabilities for rubber and composite mill liners, as well as screen media and various rubber and rubber ceramic wear components, to its existing service offerings.

Late in 2022, injection molded screening media producer Polydeck opened an expanded manufacturing facility at its Spartanburg, South Carolina headquarters, noting that the project was designed to provide room for additional growth for at least seven years or more.

Sandvik acquired Schenck Process (SP) Group’s mining business last year. The purchase gave Sandvik an established global provider of high-capacity screening solutions, with a strong aftermarket business that includes application support, screen refurbishment, product engineering design and manufacturing and digital support services. Main R&D and production sites are located in Australia, with additional production units in South Africa, Brazil and China. 

Sandvik also completed the acquisition of the South African-based company Kwatani, which makes screens, feeders, fine separators, drives and services. 

Kwatani recently announced that demand for its equipment has surged in recent months to record levels, with orders coming not only from South Africa and the southern African region but also overseas markets.

“The current level of business is the best we’ve ever seen since the company was founded nearly 50 years ago and every month now is turning out to be a record month,” said Jan Schoepflin, general manager–Sales & Service at Kwatani. 

He said Kwatani is currently producing around 60 machines a month. “To keep pace with demand, we’ve rented additional factory space to complement the 17,000 m² we already have.” As part of Sandvik Rock Processing Solutions, Kwatani also been able to outsource some production to other Sandvik factories overseas, including Sandvik’s Indian factory.

One of Kwatani’s current orders involves delivery of more than 70 screens and associated equipment to a large copper mining operation in Central Asia. This is the largest order in Kwatani’s history and probably the largest single-screen order ever to be won by a screen manufacturer based in Africa. “We’re expecting another large order from this region shortly – it won’t be quite as big but will still be very substantial,” said Schoepflin.

Kwatani also cited two other large contracts in southern Africa, one for a major platinum mine in South Africa and the other for a zinc project in the DRC. Both projects are in the construction phase.

Multotec, another South African company, just opened a new manufacturing facility in the Brazilian state of Minas Gerais to better serve the regional mining sector. The facility will largely be devoted to screening media, using compression molding for production of rubber screen panels and hand-casting polyurethane (PU) panels. 

The company said the facility now has the capacity to produce 15-20 metric tons of elastomers per month and plans are in place to increase its manufacturing capability for both injection and compression molding.

Making Them Better

In addition to expanding their product portfolios, market presence and production capacity, screening equipment suppliers are finding ways to improve the performance and cost-effectiveness of their offerings. At one end of the spectrum, this can include design tweaks to existing models, such as McLanahan’s skid-mounted, containerable version of its UltraDRY dewatering screen; or modifications to the basic elements of a screen, demonstrated by Allgaier’s process for manufacturing corrosion-resistant screen cloths with service life increased by a factor of 2 to 3. The improvement is the result of a gas-based wire treatment process featuring precise control of temperature, pressure, gas composition and duration of exposure. 

Application flexibility is another selling point. Tema Isenmann, for example, points out that it has many screening media products that are stand-alone, but also offers products that work best in systems. One of those product systems is their pin & leg panel system.

Two types of pin & leg systems are available, serving different machine panel sizes. Modular open-cast polyurethane pin & leg panels are compatible with all 1 x 1-ft and 1 x 2-ft systems. The injection molded pin & leg panels are compatible with 1 x 1-ft systems.

These panels and systems can be used for a variety of functions, according to the company. The high-flow systems offer reduced margins for an increased open area, and the solid pin design helps with quick and easy installation and removals. Both are suitable for all screening applications, from wet sliding materials to dry abrasive wear. 

Manufactured in various durometers, pin & leg systems are available in H-sleeve, round sleeve, and other pinning options. The panels are custom-made, with integral steel frames, and are 30 mm to 70 mm thick, depending on the application. The systems can be retrofitted to any existing pin-type fastening system, eliminating the need for modification of the original screening deck.

In some cases, a third-party design solution can benefit both the OEM and the end user. Bearing manufacturer NSK, for example, worked with a screen manufacturer that was having problems consistently mounting bearings in their shaker box assemblies. In addition, the manufacturer was looking for opportunities to reduce costs and improve the overall performance of their products. NSK engineers offered a solution that comprised a unitized bearing assembly that could simply be bolted to the machine frame without individually assembling the bearings, seals and lubrication components.

Some of the advantages offered by the NSK solution included a high-strength SG iron housing, full labyrinth and contact seal; a pre-greased assembly that was ready to fit with bearing-location features and was customer regreasable; overall vibration and noise level reduced by 50-60%; and improved ease of installation that reduced the manufacturer’s in-house costs by a six-figure sum annually.

Real-time condition monitoring of screen status and performance is an emerging product category with several screen OEMs offering the service. Sandvik, for example, is promoting Schenck’s CONiQ, an advanced motion sensor system that uses wireless and synchronized 3D motion sensors installed at various points on a machine to provide monitoring of the screen’s full motion. The sensors, according to Schenck, are magnetically mounted and thus can be installed in just a few minutes, and are powered by batteries with sufficient capacity for a year of operation. The system can generate a slow-motion, 3D wireframe video of screen motion, providing a powerful visual tool that can help detect problems and even reveal potential opportunities for performance optimization.

A Role in Recycling

One area in which screens will undoubtedly be gaining market momentum is metal recycling, as evidenced just recently by Rio Tinto’s announcement of an agreement with Giampaolo Group, a large North American metal management businesses, to form a joint venture to manufacture and market recycled aluminum products. Rio Tinto will acquire a 50% equity stake in Giampaolo Group’s wholly-owned Matalco business for $700 million subject to usual closing adjustments.

Matalco is a producer of recycled aluminum billet and slab products. It operates six facilities in the United States and one in Canada, with the capacity to produce approximately 900,000 metric tons of recycled aluminum per year. Rio Tinto will be responsible for sales and marketing of Matalco products following a transition period after completion of the transaction.

As other mining companies also widen their production horizons to include increased metal scrap recycling, related technologies such as intelligent sorting and selective separation equipment will draw attention. Screens designed specifically for recycling will be required, and manufacturers such as General Kinematics or Spaleck, among others, will continue to refine their existing recycling screen designs as demand grows for improved classification of recyclable materials such as metal shredder residue.

For example, General Kinematics’ original Finger-Screen has proven to be highly successful in many recycling applications that are prone to problems inherent in other types of screening media. The two-mass, low horsepower design has few moving parts, and the units’ tapered finger designs and unique cam-out surfaces and staggered positions help to prevent material bypass. Finger-Screens were initially offered in standard sizes with widths up to 72 in. (1800mm) as well as custom sizes; but the company’s Finger-Screen 2.0 is now available in larger standard and custom sizes as well.

According to General Kinematics, Finger-Screen 2.0 provides more energy, faster travel rate, and a higher lift for challenging materials. Unlike rotary trommels, which aerate materials, cause blinding and need daily cleaning and maintenance, Finger-Screen 2.0 separates materials based on 3D sizing with minimal blinding and minimal housekeeping. When used as the primary screen, Finger-Screen 2.0 provides the initial size separation which scalps off any potentially destructive contaminants, allowing the rest of the downstream equipment to operate effectively.

Recyclability of polyurethane (PU) and rubber screen media is another area of interest. Rigid cast polyurethane single-layer screen panels often have an insert made of metal that enables the screen to retain its form under repeated shocks. In dual-layer screens, the base layer itself gives the screen its structural rigidity and is made from cast PU with a high degree of hardness, so there is no need for a metal insert. The top layer is made of lower-hardness cast PU that is engineered for high resistance to wear and tear.

Currently, once any of these screens are worn out, they find their way into landfills or are incinerated. Screens with metal inserts are particularly hard for mining companies to recycle mechanically. For these screens, going without a strong insert is not feasible because the screen itself must deliver tear and abrasion resistance, which would be lost if its stiffness had to be increased. This makes creating a single recycling stream for mining screens a challenge. Recyclable media panels were first introduced over a decade ago, but Covestro, a global supplier of high-tech polymer materials, recently highlighted a process it has developed for “closing the loop” of a circular production process resulting in new screen media production from old. 

The company said its Baulé Granules processing unit allows users to incorporate pellets produced by the module as fillers in newly cast PU. The module is claimed to work seamlessly with many of Covestro’s existing Baulé machines and allows for the mixing and metering of filled components into cast polyurethane production.

To replace the metal insert in screens, Covestro tested and validated a new PU pultruded insert that delivers high stiffness and rigidity. In parallel, the company said its Desmodur MDQ75164 is the material of choice to significantly increase the wear resistance of the PU screens themselves, extending the lifetime of the components. 

This result is an all-recyclable solution for mining screens that creates a single recycling stream for the reuse of waste material. At the end of their useful life, single-layer screens with the new composite insert can be reused as a granulate input for the bottom layer of new dual-layer cast PU screens.