Often just referred to as screens, vibrating screens work within a physical framework that vibrates so as to classify and separate materials by particle size during industrial material processing applications. The basic principle behind vibrating screen efficiency involves centrifugal force caused by an inbuilt imbalance in the driveshaft, which in turn separates materials according to particle size during processing. Consisting of a sieve or mesh surface, a vibrating mechanism and a damping device to regulate vibrations, the basic physics is similar to what occurs in landslides, in which solids flow like liquids.
A motor with an unbalanced weight on its driveshaft initiates the vibrations, generating centrifugal force. Using a mechanism attached to the screen’s side plate, this unbalanced weight connected to the driveshaft’s base causes the screen to vibrate. Screen efficiency depends on a number of factors, which include the type of material being processed and the application, along with the screen’s design. To fully understand the importance of vibrating screen efficiency in industrial applications, it’s important to first review how these screens operate.
An Overview of Vibrating Screen Efficiency
The concept of vibrating screen efficiency is measured by the total amount of material that filters through the screen’s holes, divided by the total amount of material processed. While screens made of fixed mesh have been used in material processing, their effectiveness is greater when they’re made to oscillate. These vibrations cause particles to hop upwards without sliding along the screen’s surface, with each jump providing a chance for material to pass through the screen’s holes. The vibratory screens cause particles to separate, classifying them by size against the screen’s mesh. Smaller particles fall through the mesh, while larger particles are discharged only once they reach the screen’s edge.
Different varieties of vibratory screens include:
- Banana: Named for its distinctive shape, the banana screener is utilized by coal and mineral processing for high throughput processing with a larger proportion of fine particles.
- Circular: Using a circular motion and providing consistent screening across the entire surface of the screen, circular vibrating screens work well for classifying both larger and smaller particles; these screens are used for processing aggregates as well as in quarrying and mining.
- Dewatering: Used to remove moisture from bulk materials, these screens help handle tailings in mining operations or in the processing of wet sand.
- Elliptical: Used to achieve better vibrating screen efficiency, elliptical screens are used by the mining and recycling sectors for more viscous or otherwise difficult-to-process materials.
- Grizzly: This type of screen removes oversized particles from materials prior to crushing; it’s used primarily in the recycling and mining sectors to augment crushing.
- High-Frequency: For finer particle separation, high-frequency screens are used in dewatering, mineral processing and similar applications.
- Inclined: Typically featuring an inclination between 15 to 30 degrees, these screens are often used for dry or wet screening for handling materials like gravel or sand.
- Linear: These use linear motion to convey material along a production line; linear vibratory screens are used in industries like mining, metallurgy and construction for materials with fine to mid-sized particles.
Regardless of how the machine is designed, there are basic principles behind how a vibratory screen works. Fine particles – often referred to as “undersized particles” or simply “fines” – fall through the screen’s mesh, while oversized particles slide to the edge of the screen. Vibrating screen efficiency is particularly important for the mining and mineral processing industries.
Factors That Influence Vibrating Screen Efficiency
A number of elements affect vibrating screen efficiency. Not only do factors like the angle of inclination, length and opening size of the screen influence the effectiveness of a screen during processing, but the condition of the material being processed also matters as well. Measuring vibrating screen efficiency is relatively straightforward, however, and simply involves calculating the proportion of particles that go through the screen against the total material being processed.
Factors affecting vibrating screen efficiency include:
- Feed rate: The rate at which material is fed into a material processing system affects the efficiency of vibratory screens. Lower feed rates lead to longer screening times, resulting in near complete particle separation as material passes through the screen, whereas higher feed rates cover screens quickly and in turn reduce efficiency.
- Moisture: Damp material can affect vibrating screen efficiency markedly, as surface moisture causes materials to agglomerate and plug the screen’s openings, which can easily occur with materials like clay or those that are similarly viscous.
- Open area: The proportion of open area in the screen’s material affects vibrating screen efficiency, with the ratio of openings within the screen compared to the total screening surface. Thus, the more areas through which material can pass, the greater the chance particles will have of passing through the screen.
- Particle shape: While materials with spherical particles require no special orientation, most coarser materials are irregularly shaped so have difficulty passing through a vibrating screen. Efficiency is hindered when too many irregularly shaped particles occur in a material.
- Particle size: Those particles that are considerably smaller than a screen’s aperture will easily flow through the screen, whereas those particles that are nearly the size of the screen will take more time to pass through. The larger the particles, the longer it takes for them to pass through the vibrating screen; efficiency of processing suffers when too many near size particles clog the screen’s openings and reduce the surface through which material can pass.
- Screen angle: Depending upon the positioning of a vibrating screen, efficiency can be affected by the angle at which particles meet the screen’s surface. This largely depends on the angle at which the screen lies, as the more inclined a screen is, the narrower the opening and thus the fewer particles pass through. Horizontal screens are as a result generally a more efficient option.
- Vibratory intensity: When materials meet the surface of a screen, vibrations should be enough to ensure apertures aren’t blinded or pegged, though not excessive enough to throw particles too far away from the screen’s surface. Generally, the higher the feed rate, the higher the vibration rate should be.
Normally, separating coarser particles will involve using lower speeds that cause less oscillation, while finer materials require greater speed and more oscillation to screen. To help determine vibrating screen efficiency, it’s important to look at the best aperture size at both the feed and discharge ends, along with the depth for the material bed.
Tips to Maximize Vibrating Screen Efficiency for Industrial Applications
While vibrating screen efficiency is affected by the above factors, it’s also important to understand how exactly to deal with them. Though 100 percent efficiency is rather illusive in material handling applications, for many industries a 90 percent efficiency rating is normally considered outstanding. However, it often requires a careful balance to maximize screening efficiency while also producing as little contamination as possible within the material being processed.
Aperture & Screen Size
Depending on the material being processed, the size of the apertures may matter more. It’s essential as well to consider congestion along the screen’s surface to ensure that particles will pass through without clogging the holes. Additionally, the size of the screen may be a factor, with longer screens providing increased residence time through which material can pass through the screen.
If vibrations are too fast or slow there’s a greater likelihood material won’t pass through properly. The angle at which the screen’s surface inclines should also complement the focus and frequency of these vibrations.
How material is fed will affect a vibrating screen. Efficiency will suffer if particles get through that aren’t properly sized or separated. This may indicate the flow of the feed is too fast, or else the distribution of material is inappropriate for the application. As material is fed into the machine, it’s a good idea to watch whether any product is expelled from the screen or is otherwise thrown upwards while feeding, which indicates the amount of material being fed is too high. For the most part, vibratory screens should feed into the impact area or feed box and should spread all the way across the surface to maximize the screening area.
A key aspect of vibrating screen efficiency involves ensuring screens are maintained properly. Any machine requires regular inspection and maintenance, so it’s imperative to have a preventive maintenance plan. This will help avoid unplanned downtime that interrupts production. It’s also important to regularly clean the screen to remove contaminants or product that may be blocking the screen’s apertures so material can get through. Screens should also be replaced as per the manufacturer's recommendations, or if damaged to the point that they no longer work as they should. Properly tensioned screens are also important to ensure maximum energy is imparted to the particles.
Benefits of Optimizing Vibrating Screen Efficiency
The benefits of ensuring vibrating screen efficiency are worth the effort. Vibratory screens are an integral part of many industrial systems for mineral processing, mining, pelleting wood, recycling and solid waste management, as well as for the chemical, food, pharmaceutical and other industries. As such a versatile piece of equipment, ensures their optimal operation comes with multiple benefits.
Some benefits that result from pursuing vibrating screen efficiency include:
- Benefiting sustainability programs through reduced emissions, and energy consumption waste.
- Cutting operational costs through the simple and streamlined design of modern vibratory screens, which consume less energy.
- Enhancing the quality of materials produced during processing, especially in the mining and mineral processing sectors.
- Increasing screening efficiency, especially for higher throughputs often results in backflows and blinding of screen openings with other screening methods.
- Lowering upfront investment when compared to other types of industrial screening.
- Reducing maintenance expenses and resulting downtime, as modern designs have fewer parts and typically only the screen needs to be replaced.
To ensure the highest vibrating screen efficiency, material handling solutions should always follow best practices when working with vibratory screens, particularly when it comes to maintaining them.
Best Practices to Follow When Using a Vibrating Screen
By paying careful attention to best practices regarding maintenance, a manufacturer can guarantee a long and productive life for any vibratory screens within its material handling system.
To ensure the highest vibrating screen efficiency, best practices should include:
- Inspecting installation: Poorly aligned screens can distort aperture size/ shape. Improper hole size can result in inaccurate separation.
- Proper clearances: For optimal vibrating screen efficiency, there should be sufficient clearance on each side of the machine, normally about two feet (about 61 cm) on each side, to allow the operator to adjust screen tension and inspect the screen, along with its components.
- Sampling lubricant: Burnt, viscous or contaminated grease will reduce lubrication and lead to bearing failure.
- Properly lubricating: Manufacturers provide guidelines for lubricating a vibratory screen to maintain its efficiency, which entails ensuring the machine is level when serviced, using the correct amounts and types of grease, changing it at regular intervals and keeping stored lubricant clean.
- Preventing buildup: When dirt, dust, old products or other contaminants accumulate around moving parts, it affects vibrating screen efficiency and can eventually lead to failure of components like belts, pivot motor bases, roller bearings, support springs and even the vibrating framework.
- Proper belt tension: As part of the drive system, belts should be tight enough not to slip but loose enough not to squeal when in operation; the belt must be correctly aligned, for which a belt gauge can help ensure the correct tension.
- Appropriate screen support: A uniform tension needs to be sustained across the screen’s surface to keep contact between the rubber on the support bars and the screen’s surface to prevent severe damage to the screen.
- Regular inspections: The cross-members will show accelerated wear that can negatively affect vibrating screen efficiency and performance, so should be checked regularly, along with the screen’s drive system and support structure.
- Protecting screen: To extend the life of a vibratory screen, it’s important to cover housing tubes, decking and cross-members in order to protect them from wear.
- Cleaning screen: Keeping the screen’s panel free of material will help optimize efficiency, but this should be done according to the manufacturer’s recommendations so as not to damage components within the equipment.
- Logging maintenance: Every maintenance activity should be logged, with the date and work performed listed so as to better schedule other maintenance activities.
Maintenance is critical for achieving optimal vibrating screen efficiency. As with any industrial equipment, vibratory screens should be installed correctly, inspected consistently, kept clean and lubricated properly, with all maintenance activities logged properly.
Common Mistakes to Avoid
While it’s important to follow best practices when dealing with a vibrating screen, efficiency can also be affected by improper use of a vibrating screen. Efficiency can be affected negatively by simply neglecting to keep the screen clear of material buildup, for example.
Other common mistakes to avoid to maintain optimal vibrating screen efficiency involve:
- Allowing too much vibration results in damage to the vibrating screen; efficiency suffers when screens are improperly installed, misaligned or unbalanced.
- Failing to or incorrectly adjusting settings like frequency or amplitude of vibrations can lead to decreased vibrating screen efficiency and performance.
- Failing to safeguard against abrasive materials can damage the screen unnecessarily.
- Ignoring safety provisions poses a real danger to operators, as the risk of injury or worse accidents could result from improper grounding or failure to wear personal protective equipment.
- Neglecting to replace missing or damaged parts like bearings or springs will result in malfunctions that can lead to equipment failure.
- Not sufficiently training operators of vibrating screens may affect efficiency, as operators without proper training often don’t understand best practices for operating and maintaining vibratory screens properly.
- Overloading too much material onto the screen causes stress to the screen that can cause a premature breakdown.
- Utilizing an unsuitable screen for an application could affect production, as it might not have the ability to handle the throughput necessary or its apertures may allow oversized particles through.
It’s also important not to operate vibrating screens without their media, as this puts unnecessary wear on the support frames and bars.
Future Trends and Developments in the Field of Enhancing Vibration Screen Performance
While screening has been used for a variety of applications since ancient times, the vibratory screen only came into existence in the late 19th century. Even though the technology isn’t new, it’s still being improved upon. Innovations in screen technology continue to be made in a multitude of different industries. Here are just a few trends and developments seeking to enhance vibrating screen efficiency.
Structural Solution for Heavy Loads of Asphalt
The asphalt sector requires vibrating screens that can handle heavy loads. The screens used in the industry need to separate and select either an aggregate of stones and pebbles or the constituent parts of powders by particle size. This innovative design doesn’t change the basic geometry seen in conventional screens but rather allows a screen that’s dimensionally similar to provide greater structural resistance at load amplitudes and frequencies higher than those to which it’s normally exposed.
Vibration Analysis for the Construction Industry
The idea of analyzing vibrations may seem like a throwback to 20th-century vibes, but tools that monitor and then analyze vibrations in real time offer a means by which to fine-tune vibrating screen efficiency in the construction industry. Using smart devices and analytics software, data can be sent from sensors monitoring vibrations to smartphones, tablets, computers or even cloud-based servers. These systems both calculate and communicate acceleration, deviations, orbit and other vibratory data in real time. Some more advanced systems can even store and utilize historical data to predict performance and make recommendations on when to schedule maintenance tasks.
Solving the Problem of Grain Loss
The processing of crops requires high-quality equipment that often involves using a vibrating screen. Efficiency in the agricultural sector seeks to reduce waste, and a device that combines a vibratory screener with a centrifugal fan helps with grain recovery. While vibrating screens have been used for separating grains from husks, conventional screens find it difficult to separate trapped grains within the husk. Though there are other methods and machines used for separating grain from husks, vibrating screens are less likely to accrue impurities in the raw product. The combination of the fan and the screen helps prevent grain loss.
To learn more about vibrating screen efficiency and how we can help, contact the experts at Prater Industries.