Making The Right Call
By Steve Fair
Tips for choosing the most effective engineered screen media
By Steve Fair
October 20, 2016 – It’s important for producers to use the best tools for the job. The right choice is especially important when choosing screen media for vibrating screens.
Many aggregates operations have used traditional products, such as woven wire cloth, for years with great results. But for operations experiencing high wear and frequent screen changeouts, it’s worth looking into engineered screen media. Materials such as polyurethane, rubber and perforated steel plates often handle heavy and abrasive materials better than woven wire. But operators need to know how to choose the best screen media for their operations.
The difference between using “good enough” screen media instead of the optimal screen media for the application can be unwanted downtime and expense. Consider three things when selecting the best engineered screen media for an application. First, look at all aspects of an aggregates operation and any challenges to increasing production rates and profitability. Second, look at the composition of the material going through the vibrating screen and consult an expert from a reputable company to match the best screen media to the application. Finally, learn to properly install and maintain the screen media.
Have a Look Around
The first step toward selecting the most productive screen media involves answering several questions. What material is being processed? Is the screen media reaching a suitable lifespan for the operation? And what sort of challenges are occurring with the current screen media?
Consider the types of materials going through the vibrating screen. Factors such as material size, weight and abrasiveness all come into play during the selection process. For example, screening gravel typically requires media with higher wearability to handle the material’s abrasiveness. Materials with top sizes as large as 10 inches, on the other hand, require more durable screens because of the constant high impacts.
Next, look at the vibrating screen itself and complete a vibration analysis. Some analysis systems are designed to safely monitor vibrating screen performance in real time and detect irregularities before small problems lead to diminished performance or bigger issues. In some cases the machine may be running perfectly, but changing the screen media can prevent screening irregularities and the resulting damage. Consider the three phases material goes through within the vibrating screen, from layered to basic to sharp. Producers can customize the screen deck with various types of screen media through each phase by accounting for open area and wear life to maximize productivity in each phase.
In the layered phase, as material of all sizes hits the screen deck, the media should handle a deep bed depth, high impact and a mix of coarse and fine particles. Material should stratify in the middle of the deck during the basic phase, and near-size and oversize particles should be at the top of the material being screened. Virtually all undersize material should have fallen through the screen media by the time it reaches the sharp phase at the discharge end, where near-size and oversize particles should be in direct contact with the media.
A vibrating screen operator should also examine wearability to determine whether media in the three phases is reaching maximum potential. If it seems like screen media has to be changed too often, consider switching to something more durable.
Next, look at the screening challenges. Examine discarded screen media for signs of problem areas, such as broken wires, wear areas, pegging or blinding. Common screening issues include premature wear due to heavy material along with large amounts of abrasive fines. Screening problems can cause carryover or contamination, resulting in unwanted material in the screened pile, or the added cost of re-screening. Also, broken screens mean costly unscheduled changeouts. All of these signs indicate there’s likely a better screen media option for at least one phase of screening, if not all three.
Screening a Solution
An operation can see increased maintenance costs and downtime as a consequence of using the wrong screen media. If a vibrating screen continues to operate while having issues with pegging, blinding, broken screens or screen media with incorrectly sized openings, the screened pile will likely be contaminated and might require re-screening. Perhaps the most costly problems are unscheduled changeouts. It takes about an hour to shut down a vibrating screen and change one screen media section. While at first glance, an hour may not seem like a long time, the lost production can result in thousands of dollars off the bottom line.
Engineered screen media, by itself or combined with woven wire cloth or self-cleaning screens, solves many common screening problems. The screens generally offer a longer service life than wire alternatives and their durable qualities address screen breakage from heavy bed depths. In addition, polyurethane and rubber resist premature wear from abrasive materials. Besides the longer service life, polyurethane and rubber engineered screen media dampen the noise level of screening when compared with metal screens. This allows for more operational hours in areas with decibel limits during certain times of the day.
Engineered screen media is versatile. It allows operators to solve different problems or address unique situations by ordering customized panels. Some screen media manufacturers, for example, offer dual durometer screens with softer polyurethane on the top layer and more rigid polyurethane on the bottom. This combination works well for hard-hitting applications requiring openings greater than two inches, and, especially when used with tapered openings, helps eliminate pegging and blinding by allowing larger particles to better screen or reject near-sized particles. Some screen media manufacturers address high-impact applications and improve wear life by supplying screens with solid areas to withstand the heaviest of materials. Engineered media’s versatility addresses not only the material’s composition, but also its temperature. Manufacturers can create polyurethane products to withstand high-heat applications, such as when screening silica after running it through a drying drum. Operators can also ask for additionally customized screen media for unique and challenging applications.
A Lot to Choose From
Manufacturers create engineered screen media out of several different types of materials, such as polyurethane, rubber and perforated plates. Polyurethane offers a long lifespan and durability. Look for a polyurethane screen media manufacturer who blends their own material and who pours their polyurethane open cast rather than injection-moulded. The open cast process takes about nine hours to complete and typically lasts about 1.5 to two times longer than injection-moulded products. In addition, open cast polyurethane permanently hardens when cured to maintain its chemical properties, so it resists wear and tear. Injection-moulded screens, though faster to manufacture, can soften when the temperature rises during screening, resulting in less wear life. Engineered screen media is made with thicker material for increased durability, but this results in less open area. This is ideal for screening many small aggregates materials or for decks with mixed media. Hybrid screens are an option that combine woven wire with polyurethane to achieve open area closer to wire cloth but with four to six times longer wear life while weighing less than woven wire. Other polyurethane screens achieve additional durability with thicker wire to hold up to deep bed depths, large top sizes and wide bar rail spacing. There are misconceptions that polyurethane is strictly for dry applications, whereas there are others that it is only for wet applications; in fact it works well in both. Look for rubber screen media when screening material with a top size larger than 12 inches, or when an application requires an opening bigger than 4 inches. Manufacturers can create rubber screens thicker than polyurethane for improved durability. The screens also dramatically reduce noise, handle high-impact applications and resist abrasion.
Consider perforated steel plates for heavy-duty operations that require a large amount of open area. Some manufacturers customize each plate’s thickness to a customer’s application and can create almost any size opening. The screens should be manufactured with tapered openings to resist pegging. Many perforated plates come in different abrasion-resistance levels, so be sure to choose a plate appropriate for the application.
After determining the best combination of materials, open area and opening size and shape, think about how the screen media will be installed. If a vibrating screen has a cambered deck, switching to a modular system can cost $5,000 to $15,000. Look for a manufacturer that offers tensionable screen sections that hook for a cambered deck to eliminate the need for a costly deck conversion. This allows an operator to test the media on a vibrating screen with no additional costs or commitment, as well as the option to blend engineered media with woven wire cloth or self-cleaning screens. Engineered screen media products also come in modular panels for flat decks.
Also be aware that engineered screen media is often heavier than woven wire cloth, so the weight of a vibrating screen may change.
Calling a screen media expert is a fast way to assess an operation and find the most effective screen media choices for an operation’s specific needs. Look for a company that offers certified technicians with years of experience in vibrating screen media selection and maintenance. Some manufacturers not only offer consultations to help an operation find the best combination of screen media but also provide on-site training to make sure the entire team knows how to properly install it to maximize wear life.
Ask the manufacturer to do a vibration analysis before and after installing the engineered screen media to ensure everything runs correctly. It’s a good idea for producers to complete an inspection of screen media weekly. Inspect square holes carefully. Wear becomes apparent if the openings in engineered media begin to round. Also make sure tensioning remains correct by checking screen tension weekly. Look for a manufacturer that provides ongoing support, too. Find a company that follows up to make sure the screen media works well once in use.
Steve Fair is the Tyler engineered media manager (Haver & Boecker).