Assessing screen media options

Reviewing the pros and cons of polyurethane and high-vibration screen media

Screen media is often an afterthought for mineral processing operations. In the car world, an equivalent would be tires. When purchasing a new vehicle, buyers are often focused on larger, “flashier” components such as the exterior, engine, or the latest electronic bells and whistles over more “standard” parts such as the tires. However, just as tires are essential to a vehicle’s overall performance, so too is screen media for machinery in the mining industry.

Tires come in different varieties, like screen media. Beyond standard wire screens, many operations choose between polyurethane and high-vibration woven wire. Each has its strengths and weaknesses depending on application. Weighing polyurethane and high-vibration screen media against application, durability, efficiency, and maintenance can illuminate which one is the best choice for production needs.

The actual cost behind cost per tonne

Price is often a motivating factor when choosing between screen media options, but the full story of productivity cannot be summed up by just looking at either screen media panel cost or the cost of production per tonne. Much like a scale, the output amount must be weighed against the quality of the product.

Because of its durability and longer wear life, synthetic media such as polyurethane is often selected as a lower-cost option, since it requires fewer replacements than high-vibration screens. Its durability is also effective when used to handle high-impact material screening such as dewatering or when processing large amounts of minerals with little risk of pegging or blinding.

However, polyurethane panels trade durability for less open area and are much more rigid, therefore relying on the vibrating screen to do most of the work. The static movement of the screens limits vibration to 800-900 cycles per minute, which can decrease throughput and invite blinding and pegging with finer minerals. In comparison, high-vibration screen media has as much as 50% more open area than polyurethane, which allows more material to be sized accurately in less time. This result is achieved through the high frequency of its wires (8,000 to 10,000 cycles per minute) that adds to the vibration of the screen box to speed up material separation and passing. This performance requires more changeouts of screens because unprotected woven wire breaks more easily than polyurethane. The trade-off to more frequent replacements is that the increased screening action improves material throughput, virtually eliminates pegging and clogging across the top and bottom decks and yields a better-quality product. With high-vibration screen media, a higher investment upfront can lead to greater production gains down the road.

It should also be noted that while polyurethane screens currently outlast wire products, this gap has been closing. The inclusion of polyurethane strips within the design of high-vibration wire boosts its durability without sacrificing open area. This addition means that high-vibration panels can withstand harsher screening conditions with the most abrasive materials.

In some applications, the strengths of polyurethane and high-vibration screens can complement one another. In cases where the top deck receives heavy material with a high impact and requires a longer wear life, using a synthetic screen would be best. Once the polyurethane has taken the impact and the material is spread out more easily on the lower deck, a high-vibration screen can be used to overcome the limitations of the open area of the synthetic screen and produce more throughput. One industry case study reveals the benefits of such a pairing. An operation running polyurethane panels on the top deck and woven wire screens on the bottom decks experienced diminished throughput because of the low open area as well as poor material stratification and pegging and blinding issues. Replacing the middle deck with a high-vibration panel tripled its operational life, eliminated pegging and blinding, and resulted in a 200% increase in production volume.

Is silence always golden?

Many synthetic panels are made up of soft polyurethane, which means that they can be up to 10-db quieter than wire screens. Lower noise levels reduce occupational noise exposure for plant personnel and the associated potential for hearing damage.

One downside, however, is that less noise can mask underlying performance and maintenance issues. Tears in the panel are not visible, which means performing quick visual checks for them is not feasible. Also, these tears can lead to larger, less precise openings over time and therefore out-of-spec, potentially contaminated material coming through. Operators are only alerted to an issue when performing an assessment of the panels or when the opening is large enough that the material starts to flap when in motion. At this point, the quality of material may have already been significantly impacted. In contrast, while it is noisier, high-vibration screen media only requires a visual check each shift to assess any issues.

In one industry case study, an operation screening salt materials was only changing out its polyurethane screen media every eight months, but they noticed the panels passing out-of-spec minerals. Switching to high-vibration panels not only solved the issue but also eliminated pegging and extended the changeout time to two years.

A tailor-made approach

There is no one-size-fits-all when it comes to screen panels and fit. Sizing that is even a fraction of an inch off can have tonnes of impact in terms of quality screening. While polyurethane panels come in a variety of options for different screening needs, custom-designed high-vibration screen media can often ensure a perfect fit and more precise screening.

Whereas some custom high-vibration options are suitable for high-impact, heavy-material applications that still need a good amount of open area, others are ideal for low-impact, finer, or more sticky material. Despite their different uses, each custom-fit option is designed to strike the right balance of wear resistance, throughput, and blinding and pegging resistance to meet processing demands.

When ordering screen media, operations should look for a reputable manufacturer that uses first-class materials and a thorough manufacturing process to ensure that they are receiving the best possible product to achieve the strongest possible results. Whereas global supply chain issues may lead to some manufacturers cutting corners and using less than stellar materials in their wire, others are uncompromising in the composition of the final product they deliver to their customers.

Bottom line

Just as drivers need high-quality tires that offer excellent tread for enhanced traction and safety, so too do mining operations need high-performing screen media that provides higher throughput alongside reduced downtime, maintenance, and replacement costs.

When making the best purchasing decision for your operations, added value should replace cost per tonne. At the outset, polyurethane may seem like a cheaper alternative to many premium high-vibration wire products. In the longer term, customized high-vibration screens offer a more cost-effective and high-yield solution.

It may also be that a combination of both options can help you to maximize production while retaining quality. Partnering with an OEM-certified technician is a cost-effective first step towards identifying problems and solutions and selecting the screen media that fits the application and the distinct phases of screening in your operation.

Serge Raymond is a product specialist at Major Screens.

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