Selecting screen media for your application

Every aggregate producer wants higher capacity, lower costs per ton, less downtime and, in turn, more uptime. With that said, choosing the proper screen media for a given application is the key to delivering screen sizing accuracy and maximum throughput, which also greatly impacts the performance of upstream and downstream equipment in a process.

There are a vast number of screen media configurations available based on material types, aperture sizes and styles, fixing systems and surface features. As a result, manufacturers are constantly striving to differentiate their products by varying these specifications to dial in a functional and often customized solution for producers.

In order to ensure that the best possible screen media solution is provided, it is imperative that the producer supplies the manufacturer with complete and accurate application data up front. Vibrating screen inside box dimensions, a particle size distribution, moisture content and desired final product(s) are some of the minimum requirements to properly select screen media.

Further questions that should be asked of the producer include:
◾ Is it a wet or dry screening process?
◾ Will blinding or plugging be a problem?
◾ How abrasive is the material?
◾ Will there be much impact on the screening surface?
◾ What is the top size and the bottom size feed to the screen deck?
◾ How much screening area do I have?
◾ Do I need to wash the material?
◾ Do I need to be concerned about noise?

In general, the two most important factors to an aggregate producer, as it relates to screen media selection, are the screen panel life expectancy and open area. Producers should examine the issue of maximum open area versus maximum wear life – there has to be a trade off between the two in designing the configuration of screen panel openings.

In general, wire cloth will provide the maximum open area benefits with a sacrifice to wear life, and the reverse is true for polymer screen media. However, recent and ongoing developments in material compounds and hybrid solutions (eg., urethane-encapsulated wire) have helped to expand the spectrum of this “sweet spot” and enable producers to enjoy more of the best of both worlds.

Ultimately when making a decision on screen media the producer needs to consider the benefits realized or overall costs over the life of the media panel. A panel with a higher upfront cost may provide significant wear life or throughput benefits, compared to one offered at a fraction of the cost.

Therefore, an important metric for producers should be cost per ton of material processed. This is a more accurate gauge of the cost of screen media to a producer.

Screen media selection

Screen media material choices include wire; perforated and flame cut plate; polymers (polyurethane and rubber); and hybrid media. Screen media originated with the steel options of wire and plate. However, with the emergence and innovation of polymers over time, producers have realized cost per ton benefits of these materials.

In comparison to wire cloth, there is often a sacrifice to open area, but the added wear life, ease of installation and noise reduction benefits of polymer media may create added-value for a producer. Polymer screen media is often recommended if the producer is changing out wire cloth more than five times a year as a result of wear.

◾ Wire cloth: Wire cloth is the best option for an operation with frequent media change outs as a result of varying product specifications. The most common wire cloth options are high carbon, oil tempered and stainless steel wire, each with their own application benefits.

Stainless steel, for example, is beneficial for corrosion prevention and also effective as an anti-blinding solution. The different opening styles in wire also have their own application benefits to meet the producer’s needs – square, rectangular, long slot, etc.

Rectangular slots, for example, increase throughput and reduce plugging and blinding, but compromise sizing accuracy.

◾ Perforated and flame cut plate: Plate screens are a good alternative for secondary screening, and available in various steel types and hardness. Plate screens are ideal on top- and middle-deck applications for impact and abrasion resistance.

Steel plates have seen recent improvements in quality with options available all the way up to the 400- to 500-Brinell range (a measurement of the hardness of the steel plate), providing for longer wear life and durability.

◾ Polyurethane: Polyurethanes are available in different durometers, and more frequently applied in wet applications, or where water is added or the feed is in slurry form. Urethane is also the best choice for dewatering screens.

Polyurethane does have its place in dry applications, as well, with the development and improvement of material compounds and chemical formulations. Polyurethane panels are often found in a modular configuration for ease of installation and replacement; however, there are also large cable-tensioned polymer screens, for example, better suited for aggressive high-impact applications.

◾ Rubber: Rubber media is ideal in dry, high-impact applications and can often be offered in place of plate screens, depending on the nature of the feed. Modular rubber systems have been found to be effective in combining the
benefits of modular screen panels with the durability of rubber impact screens in a high open area design.

Rubber screen media may also be recommended in a wet screening application such as where a plant is processing only natural sand and gravel. As well, self-cleaning rubber screens are used in fine, sticky or near-size material applications to prevent blinding from fines build-up, and to gain greater sizing accuracy.

◾ Hybrid screens: There are a number of different types of hybrid screens that seek to maximize open area and wear-life benefits for a producer. Urethane-encapsulated wire allows producers to take advantage of the benefits of urethane screen media (wear life, noise reduction) without having to convert to a modular deck, and without great sacrifice to open area.

Another common hybrid screen combines wire held in place with rubber or urethane strips for greater wear life and an optimal flexing action during screening to prevent plugging or blinding.

Screen media installation

Screen media is attached to a deck frame in any number of ways. Proper installation, which includes tightening or tensioning the screen surface against the supporting frame, is integral in prolonging the life of the screen.

This is applicable both for modular screen panels that are hammered into place on some types of stringer systems, or tensioned panels that are tightened against a clamp rail with rubber pads beneath the screen creating a tensioned crown.

Improper screen installation is the biggest cause of premature failure on a deck, and therefore it’s important to check the installation at each shift to ensure the screens are secure and in place. One check at start-up and/or shutdown will be far less costly than unplanned downtime.

Modular polymer screens (stringer system and individual panels) are generally more costly upfront on a square footage basis in comparison to wire screens. However, in addition to the wear life benefits, modular panels are also smaller and safer for operators to handle.

They allow for selective change out of individual worn panels, as opposed to a complete wire cloth panel that would need to be changed out if one section of it was worn. More innovative modular systems offer greater ease of installation (without any pins or bushings), and are better engineered for retrofitting applications.

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Information for this article courtesy of Weir Minerals.