Scaling up screening performance

Screening is a critical part of most mining and aggregates operations, often determining the final product’s gradation and quality as well as playing a vital role in ensuring production and throughput rates. Its efficiency directly impacts overall cost-effectiveness and operational performance. Prioritising decisions about screening equipment, media and operational factors can significantly reduce costs, enhance uptime, and optimise results. Even so, screening often receives less attention than crushing or other processing equipment selection.

Four steps to screening success

Screening involves separating materials through screens or meshes to achieve uniformity in gravel, sand and crushed stone for further processing or direct use. The four key considerations when choosing and using screening equipment and media are:

• Preparation: collecting data for better decisions.
• Equipment: choosing the right screening equipment.
• Media: selecting the optimal screening media.
• Operations: ensuring long-term screening performance.

Preparation: collecting data for better decisions

The best place to start is by gathering and analysing information about the screening operation you plan to set up. Although the resources available for this step will vary according to the size and maturity of your business, it is always worth properly exploring the technologies available to support your decision-making process.

Figure 1. Physical trials, process simulations and lab tests can all play a role in selecting the right screen and media.

Process simulation

By allowing virtual testing instead of physical trials, process simulation tools can save time and resources later on. They can help you select the best equipment for specific materials and production goals and predict how adjustments in set-up or equipment selection would affect performance, such as production capacity, throughput and product gradation, as well as operational costs. For example, Metso’s Bruno software saves time and resources by identifying the best equipment for specific materials and production goals.

Lab tests

Run independently or used to confirm the results of a process simulation, lab tests can also play a valuable part in designing effective screening solutions for mining and aggregates. By providing critical data on material properties and behaviour, they make it possible to tailor screening processes and equipment to specific requirements. Lab tests are available for a range of applications, such as dry fine screening, wet fine screening, and traditional wet or dry screen testing. The results from the lab tests can be used to guide your decisions on screen type, aperture size and shape, screen deck configuration and material handling.

Equipment: choosing the right screening equipment

The wide array of screening equipment can be overwhelming, but you can narrow down your options by asking a few critical questions.

Figure 2. There is a wide range of screening equipment that is best suited to aggregates production.

Mining or aggregates?

Since mining operations are characterised by high tonnage and 24/7 usage, they require heavy duty machines that can be relied upon to keep going between planned shutdowns. Key priorities are high availability and capacity, as well as ease of maintenance and availability of wear parts. Some examples of screening equipment designed to support the high capacity and mechanical availability required for mining operations are conventional inclined and horizontal screens, box exciter banana screens, dewatering screens, and high-frequency screens. Each one has a different stroke pattern (circular, linear or elliptical motion) to fit a specific application.

If your screening solution is intended for aggregate production, the equipment will typically be operating for eight hours per day, rather than round the clock. With less heavy use, your screens will last longer, so wear and tear will be a lower priority. For aggregates, we therefore generally recommend horizontal equipment that has a low and compact profile and gives high quality separation efficiency.

Figure 3. Applications typical of mining or large quarries often require stationary screening equipment able to handle the high production rates.

Stationary or mobile equipment?

Stationary screening equipment is ideal for high-production mining applications since it can handle large volumes, integrates well with other equipment, and offers high precision production with lower long-term maintenance costs. Mobile equipment, on the other hand, is more suitable for aggregate production due to portability, lower initial investment, flexibility and minimal set-up time.

Wet or dry materials?

Screening sticky, high-moisture materials is challenging, often requiring water for processing. However, environmental regulations and rising water costs have prompted the development of sustainable innovations like Metso’s Banana Screen Efficiency (BSE) and Efficient Screening (EF) technologies. Combining banana/multi-slope screens, elliptical motion, and flexible rubber media makes it possible to effectively screen sticky materials with minimal or no water.

Media: selecting the optimal screening media

Once you have chosen your equipment, the next thing to consider is the selection of the ideal screening media. While there is no universal solution to solve all your potential screening challenges, the right choice can have a positive impact on media lifetime and screening performance. Below are some things to think about when making your selection:

Application-specific media

As a general rule, polyurethane media is more suitable for wet applications whereas rubber media is more suitable for dry applications. Sometimes the specific application will narrow down your options even further. For example, scalping applications require thick and durable media, guiding you firmly towards the selection of thicker rubber materials with smaller open areas.

Balancing wear life versus costs

Is cost or wear life your top priority? Synthetic media gives a long wear life and is easy to switch out when worn. However, wire cloth is preferred in some regions since it carries less upfront costs in most cases the downside being that it also wears out faster, which can lead to a higher overall cost of operation if changeouts are too frequent.

Fire risk

Rubber and polyurethane are quite flammable materials, and fires caused by welding incidents or similar can pose serious threats including health hazards for your operators and lost production for your business. In areas that are susceptible to fire, you can significantly reduce the risks by choosing fire-retardant rubber screening media.

Figure 4. Selecting the right screen media can have a positive impact on both media lifetime and overall screening performance.

Modular Media

Ideal for mining operations with variable ore types, modular media enables the quick replacement of damaged panels and easy adjustments. However, it may not suit applications demanding maximum throughput due to reduced open areas.

Ease of maintenance

Changing out worn screening media can be time consuming and risky. Modular media (see above) allows you to replace individual panels as needed. You can also reduce the hazards involved in replacing screening media by choosing, for example, Metso’s hammerless attachment system, which not only improves safety, but also reduces change-out time, leading to higher uptime and productivity.

Pegging and blinding

Pegging occurs when particles become wedged in the screen apertures, particularly in near-size material that matches the aperture size, whereas blinding happens when fine or sticky material builds up on the screen surface, blocking apertures and reducing efficiency.

The good news is that your choice of screening media can significantly reduce the risks of pegging and blinding. For example, flexible polyurethane or rubber screening media have smooth surfaces and elastic properties which reduce the chances of particles becoming stuck. And once again, modular media can also be beneficial as it allows the use of different types of panels in sections of the screen where pegging or blinding is most likely.

Operations: ensuring long-term screening performance

Once your operations are up and running, it’s time to consider how to achieve the best screening performance and ensure the longest lifetime for your screening assets. Smooth, efficient operations depend on ongoing maintenance, monitoring, and adherence to recommended operating parameters.

Maintenance

The most obvious aspect to consider is maintenance, parts of which have already been covered above. Scheduled maintenance is critical to ensure the longevity and efficiency of equipment, prevent unexpected breakdowns and maintain safety standards. Shutdowns should be scheduled at regular intervals, depending on the size and type of operation you are running.

Monitoring

Why not take advantage of digital monitoring software to keep track of the health of your equipment and establish optimal maintenance frequency?

Remote monitoring tools such as Metso Metrics for screens is one example, enabling real-time monitoring of equipment health, optimising performance, and helping you better plan maintenance activities. Wireless, Bluetooth sensors provide data on strokes, bearing temperatures, and other parameters and, in the case of deviations, alerts are sent to your personnel.

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