Aggregate material is separated into sizes through the use of screens. In most crushed-stone operations, this process occurs after the shotrock has been processed by a primary crusher. The role of screening in the processing flow is to size and separate material ahead of secondary and tertiary crushing circuits, and/or to size and separate material in preparation for final product stockpiling. The bottom line is that crushers produce the material; screens separate the material; and screening efficiency affects the operations overall performance.
Screening is both art and science. The art of screening lies in the meticulous fine tuning, tweaking and synchronizing of screen setups within a near-limitless number of applications. Its science is stratification. In other words, the vibration of the screen deck agitates the material causing it to stratify, allowing the larger particles to remain on the top deck and the smaller particles to fall through the openings of the screening surface. Screening efficiency is calculated as the percentage of the undersize materials passing through the openings divided by the percentage of undersize in the feed. For example, if a screen is only 75 percent efficient, then 25 percent of the material within the desired product range is being rejected with the oversize material.
Vibrating screens must be properly selected and designed, or they will be the biggest bottleneck within an operation. Todays trend is toward larger screens to increase capacity within larger plants. While most producers want more tons per hour across the screen, the key to optimum screening is maximizing capacity without losing efficiency. This may involve a good amount of trial and error, as there are many operating parameters to consider.
Maximum screening efficiency results from proper adjustments in speed, stroke, rotation (or throw) direction and angle of inclination. Each of these parameters affects one of the most important facets in screening proper depth of bed.
As feed material is a mixture of varying sizes, oversize material will restrict the passage of undersize material, which results in a build-up, or bed depth, of material on the screen surface. Bed depth diminishes as the undersize material passes through the screen openings. For efficient screening, the material bed should not reach a depth that prevents undersize from stratifying before it is discharged. The industry rule of thumb is this: Depth of bed (in dry screening) should not exceed four times the opening size at the discharge end of the screen. Consequently, with a -in. opening, the depth of bed at the discharge end should not exceed 2 in.
Loading screens too heavily is a common practice, and one that leads to a carryover problem and less screening efficiency. Operators should consider these four parameters to fine tune screening performance.
Increasing speed has its trade-offs. Greater speed may decrease depth of bed, but also increases the G-force, which decreases bearing life. Using the proper opening size for the desired particle separation, along with increased speed, will leave a minimal percentage of desired product size in the oversize. Alternatively, combining increased speed with a slightly larger opening size may allow a percentage of oversize in the desired product specification.
Increasing stroke delivers a higher carrying capacity and travel rate, while reducing plugging, blinding and enhancing stratification. However, it can create some inefficiency when lightly loaded decks lead to material bouncing. Generally, coarse separation requires increased stroke and less speed, while fines separation needs less stroke and higher speed.
Rotation direction can dramatically impact incline screen performance. Running counter flow, or uphill, increases material retention time and action on the screen, potentially giving the particles more opportunity to find an opening and ultimately increasing efficiency. Direction of rotation has little effect on a linear-type horizontal screen.
Increasing the angle of inclination causes faster material travel, which can be advantageous in certain dry screening applications. Although, there may be a point where too much incline will hinder efficiency as fines may roll over the media rather than pass through. Consider adjusting both linear and triple-shaft horizontal screens for inclination as well. One can realize some gain in capacity, rate of travel and productivity by adding some incline to the horizontal screen.
There are a limited number of applications where a horizontal screen is more suitable than an incline screen. These may include portable applications or plants where proper clearance for an incline is not available or applications with heavy water use, such as a dredge-fed screen.
An incline model is less prone to plugging and uses gravity to reduce its energy and horsepower requirements. There are differences in rate of travel between an incline and horizontal unit. At 45 to 50 ft. per minute (and at a specific tonnage), a horizontal screen will experience diminished capacity due to a greater depth of bed. Alternatively, on a 20-degree incline and at 70 to 75 ft. per minute travel rate, an incline screen will deliver up to 25 percent more capacity than a linear-stroke horizontal machine. Unlike the latter, the circular motion of an incline screen results in less stress to the vibrating frame.
Most of the processes for separation and classification consume large amounts of water. Different types of machinery and equipment have been developed to recover the water used for processing and to produce a final product that is easy to transport and store. One such device is a dewatering screen.
The purpose of the dewatering screen is to remove the water content down to 14 percent or less so the material can be conveyed and stacked. Dewatering on a vibrating screen produces a dense, compact filter cake that moves to the screen deck. Polyurethane and profile wire are the best media options for dewatering screening.
Typically, the screen deck is minus-3 degrees (negative slope). The filter cake traps smaller particles and allows water to pass through to the screen deck openings. Dewatering in mineral processing is normally a combination of the sedimentation and filtration methods. The bulk of the water is removed in the first one-third of the machine by sedimentation. This thickening of the material produces a pulp of 55 to 65 percent solids by weight. Up to 80 percent of the water can be separated at this stage. Filtration of the thickened pulp then produces a moist filter cake of between 80 and 90 percent solids. Filtration is the process of separating solids from liquid by means of the porous filter cake that retains the solid but allows the liquid to pass.
Specifying the right screen involves making sure the manufacturer understands the production goals and is supplied with complete application data, which includes information such as tons per hour, material type, feed gradation and top particle size, particle shape, application type (wet or dry), type of screen media and deck opening, and the method of material feed. Armed with accurate information, the manufacturer can customize the screen setup for maximum performance. For example, with a known feed gradation, the manufacturer can analyze the loading on each deck. If a deck has a heavier depth-of-bed ratio relative to the opening, that deck may be specified at a steeper angle than an accompanying deck. Therefore, one might have an incline screen at 20 degrees on the top deck, and up to 24 degrees on the bottom deck where its more heavily loaded.
Plugging happens when near-size particles become lodged, blocking the openings. Solutions may include increasing stroke, changing media wire diameter or opening shape, using urethane or rubber media, and adjusting crusher settings.
Blinding occurs when moisture causes fine particles to stick to the surface media and gradually cover the openings. In this case, changing stroke and increasing speed may help. Also, if changing the screen media does not improve the situation, consider ball trays or heated decks. Ball trays incorporate rubber balls into pockets beneath the screen cloth. As the machine vibrates, the balls strike the media to free collected material. Heated decks have an electric current in the wire that heats and dries material, so that it easily knocks itself loose as the screen vibrates.
Carryover occurs when excessive undersize particles fail to pass through the openings. Solutions may involve changing stroke, speed or reversing screen rotation; changing wire diameter or the shape of the opening to increase open area; changing the angle of inclination; changing feed tonnage; controlling feed segregation; and centering feed on the screen.
Vibration analysis, the acquisition and analysis of data regarding the vibrational characteristics of the machine, is one of the tools for ensuring optimum vibrating screen performance. Vibration analysis collects data on parameters such as natural frequencies, displacements and stroke amplitude, and the operation of bearings and gears. It typically involves using a hand-held analyzer connected to a series of accelerometers. The analyzer electronically records the vibrational data. This data can be immediately examined on the analyzer or downloaded onto a computer for a more detailed analysis.
Tests are conducted both at the factory and in the field. Baseline readings are taken at the factory on every machine while they are on the test stand for quality control. More readings should be taken shortly after start-up once the machines are operational in the field. Readings should be taken while the machine is empty and when it is fully under load. They should also be taken any time a speed or stroke change is made, when significant screen media changes occur, when applications change, and importantly, when and if there are any major support tower upgrades or rebuilds.
Vibration analysis benefits from the additional technologies of impact testing and operating deflection shape (ODS) analysis. Impact testing is used to determine natural frequencies that could cause issues at run speeds, or would require structural changes. A baseline reading is taken on each machine at the factory and is used to confirm the accuracy of engineering models. ODS analysis is used to animate and check new equipment and new concepts, while also confirming engineering models for accuracy. ODS identifies how a machine moves in actual operation and at specific frequencies. The analysis compares mode shapes to determine the most effective structural modifications to the machine.
At the primary stage, large scalping screens remove fine material before the feed enters the primary crusher, helping to protect the crushers wear parts from abrasive stone or sand material that has already been sized. Without scalping, the primary crushers liners wear faster, requiring more frequent changes and maintenance downtime.
Following the primary-crushing stage, screens with two or three decks and different opening sizes separate the aggregate material into different size categories with conveyors transporting the sized material for further crushing or stockpiling as a saleable product. Usually this screening is accomplished through dry screens. Wet screens may help to remove debris from material before stockpiling, as clean stone is often required for concrete and asphalt specifications.
Depending on the process stage, the material to be screened is fed to the screen from an intermittent-feed loading device like a wheel loader or from a continuous-feed device like a hopper or a conveyor. The screen box uses shafts with counterweights or exciters to cause the material bed to vibrate. Through the vibration, larger particles work their way to the top of the material bed, while the smaller particles make contact with the screening surface.
Because they are inclined, circular-motion screens provide a high travel rate. They generally accept a continuous feed very well. Screens using circular motion are best suited for larger material, as finer material tends to blind on this style of screen. Also, wet, sticky material does not screen well with this type of screen, unless water spray is also used.
Linear-motion horizontal screens typically generate less blinding and pegging of material on screen media because their straight-line motion, with high G-forces, can both dislodge material and convey it forward across the screen. This motion can be more effective than circular- or elliptical-motion screens, resulting in a high-efficiency screen that also operates at a fairly high speed. The operator is able to better control the material travel rate across the screen, further improving screening efficiency. Linear-motion screens also benefit producers through a lower installed cost because they require less headroom than circular- or elliptical-motion screens.
Elliptical-motion horizontal screens offer some of the efficiency of linear-motion screens and the tumbling effect generated by inclined circular-motion screens. They also work to speed material travel rate at the feed end, while slowing it at the discharge end. However, this type of screen does not exert the high G-forces that linear-motion screens do.
There are formulas to help select screens based on many factors, including feed tonnage, screening area and desired efficiency. There are enough variables involved in the formula that it is best to work with manufacturers who understand the complete parameters of the application.
It is important that the manufacturer knows the feed method, size, gradation, moisture content and rate. Existing equipment and mounting structure, total plant production needs and efficiency requirements are also part of the equation. Manufacturers can help to specify not only the best screen unit for the application, but also the best screen media.
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 its most basic definition, screen media can be described as a surface with openings on a vibrating screen deck that allows undersized particles to pass through, and oversized particles to carry over. A vibrating screen can have anywhere from one to four decks, with each deck having a different sized opening, or mesh, for the separation of various particle fractions. Every application is a unique screening challenge, and thus the type of screen media selected is critical for success.
Screen media is a replaceable wear surface that can be made up of one or more removable panel sections on a single deck. There are a vast number of screen media configurations based on material types, aperture sizes and styles, fixing systems and surface features, to name a few. 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.
To get the best possible screen media solution, 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 products 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 is there? Does the material need to be washed? Is noise a concern?
The two most important factors for 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 tradeoff between the two in designing the configuration of screen panel openings. In general, wire cloth will provide the maximum open area 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 (such as 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 and the 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 with one offered at a fraction of the cost. Therefore, cost per ton of material processed is a more accurate gauge of the cost of screen media.
Screen media originated with the steel options of wire and plate. Now, the choices include wire, perforated and flame-cut plate, polymers (polyurethane and rubber), and hybrid media. Heres a closer look at each of those options.
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 its own application benefits. Stainless steel, for example, is beneficial for corrosion prevention and is effective as an anti-blinding solution.
Perforated and flame-cut plate screens are a good alternative for secondary screening and are 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 is available in different durometers and more frequently applied in wet applications 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. Open-cast thermoset polyurethanes have superior wear-life performance over injection-molded urethanes, primarily due to the slow-curing manufacturing process, which creates stronger molecular bonds in the material. Polyurethane panels are often found in a modular configuration for ease of installation and replacement. However, there are large cable-tensioned polymer screens that are better suited for aggressive, high-impact applications.
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 combine 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 buildup, and to gain greater sizing accuracy.
Rubber generally offers the longest wear life of any screen media in the most difficult and aggressive scalping applications. Rubber panels are effective in reducing noise levels by up to 9 decibels when compared with steel media, which is about a 50 percent reduction as recorded by the human ear.
Hybrid screens come in several different types that maximize open area and wear life. Urethane-encapsulated wire offers the advantage of urethane screen media (wear life and noise reduction) without the need 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 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 and 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 its important to check the installation at each shift to ensure the screens are secure and in place. One check at start-up and one at shutdown will be far less costly than unplanned downtime.
Modular polymer screens (stringer system and individual panels) generally have a higher initial cost per square foot compared with wire screens. However, in addition to the wear life benefits, modular panels are 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 was worn. Modular systems offer greater ease of installation (without any pins or bushings), and are better engineered for retrofitting applications.
Wear life for any type of media is largely determined by its mass the diameter of the wire or the thickness of the urethane. The media must be heavy enough to handle a given top-size material and peak feed rate. Synthetic screens (rubber or urethane) will wear far longer often more than 10 times longer than wire cloth or plate screens.
When working with wire cloth, workers typically detect excess wear when a hole is blown through the cloth, allowing oversize material to contaminate product stockpiles. Consequently, it is common to assume that the same wear pattern and result will happen with synthetic media but that is not so. Operators tend to look for a hole to weld or repair rather than looking at the actual gradations. Frequent quality-control sampling to detect sudden or gradual specification changes is the most effective method to monitor the wear life and condition of synthetic screen panels.
With modular synthetic panels, the maintenance crew can catch any wear issues early by conducting a sieve analysis. This involves examining the particle distribution of a representative sample of material, which is expressed in the percentages of a particle size group passing through or being retained on standard testing sieves. For example, if production is slightly off on a number-one sieve, the crew should start gauging its screens and checking for any wear. After this routine maintenance, they simply take a few minutes to change out a modular panel or two, and they are up and running again.
Note that polyurethane and rubber panels are available in different durometers, which is a measure of surface resistivity or the resistance of plastics toward indentation. Media manufacturers may use the Shore-A scale in selecting plastic and rubber compounds for screen panels the higher the number, the harder the material.
An aperture is an individual opening in the screening surface. Synthetic media panels are manufactured in a wide range of opening types and sizes. Both polyurethane and rubber media panels are offered with either square (the most common type), slotted, zigzag, slotted zigzag and round openings. For example, zigzag openings reduce or eliminate plugging or pegging, which is a condition where near-size particles wedge or jam into the screen openings, preventing the passage of undersize material. Round openings are highly effective in primary scalping operations to minimize plugging or pegging.
Depending upon specification requirements, decks can be composed of panels with varying opening sizes and/or types. Note that solid (with no openings) rubber or polyurethane panels can be installed at the feed end of a screen deck where heavy wear is experienced. Or, solid panels can be used as a discharge lip.
Special surface features, such as dams, skid bars and deflectors can be used to enhance performance. When produced by an injection-molding process, these features can be molded into the surface as part of the original panel construction. This seamless integration of surface feature to panel allows greater strength and longer life versus that of a laminated-on feature.
For example, dams are used in wet applications to slow material and increase washing efficiency. Skid bars are effective in scalping applications to keep oversize material off the screen panel surface, while reducing wear. And, deflectors help redirect material toward the middle of panels.
Sorting aggregate to specification piles requires accurate screen openings and high open area for optimum production capacity. Synthetic polyurethane or rubber media panels offer these characteristics, while increasing wear life over that of conventional wire cloth media. Note that for damp material typically prone to blinding, natural rubber panels are often recommended as they retain open area even in very sticky materials.
Wet sizing (usually with sprays) often increases a screens efficiency. Polyurethane media panels deliver greater wear life in this application. Rinse screens are part of the final wash to clean aggregate products prior to sale. Polyurethane media panels are a good fit for rinsing applications as they offer long service life and are available in a wide range of opening characteristics and sizes.
Dewatering involves draining the maximum amount of moisture out of a sand product or waste fines, while retaining as much solid material as possible. Manufacturers offer dewatering panels in a variety of openings from 0.1 mm (about 140 mesh) to 2 mm. Typically the panels have a heavier steel skeleton structure to withstand the very heavy bed depths and high G-forces of the application.
Efficiency is gauged by product throughput or product yield. It is the ratio of the percentage of material passing through the screen surface to the percentage of undersize material in the feed that is available to pass through.
Some assume that wire cloth offers greater open area versus synthetic media. However, when considering maximum open area, it is important to understand that the percentages of open area listed in conventional wire cloth media catalogs are based on all the openings in a section of the screen. Yet, a good portion of those openings are blocked by bucker bars, crown rubber, clamp rails and center hold-downs, causing actual open area to be compromised by as much as 40 percent.
In the case of synthetic media, the open area is sometimes calculated by ignoring the border. In many cases, the traditional synthetic screen panel has a large border or dead area around the perimeter that often is not taken into account, and thus the open area percentage is overstated. To avoid the specification of undersized vibrating screens, open area needs to be calculated by taking the total number of openings in the screen panel, and determining the percentage of actual open holes versus the complete surface of the panel itself. End users should compare the open area between two different screen panel brands of the same aperture by merely counting the number of holes on each screen panel.
While the use of synthetic screen media definitely reduces maintenance labor, it does not eliminate it. Producers may wish to specify and stock certain modular synthetic screen panels that can be used in multiple applications as operations may be able to get a useful life out of a panel in one location, and then move it to another application where it will function for a period of time.
If the media supplier has provided a diagram of the deck layout, post it as a reference tool for the maintenance crew. This is especially important if the deck layout is made up of different panel types and opening sizes. This will ensure that the correct layout is maintained as panels are replaced and will ensure that the deck design remains accurate for the given application.
Portable screening plants are a major part of the business for aggregate producers, road builders and contractors. Any of these operators can tell you how important quality screeners are to a business, but whats right for one operator may lead to production issues for the next.
From small, highly customized design modifications to the overall type and size, there are a multitude of factors to sift through. Selecting the right screener takes time, research and clearly outlined goals for the operation. Here are six key considerations.
Analyze everything from output capacities to business goals before buying. The first thing to do is size the equipment to match the operation. This is not an option. Understanding the application and materials will help determine the ideal production, capacity and number of end-size products. The screen must be aligned with the goals of the operation.
Next, fully understand the companys goals and projected sales to determine what size screen is needed. For example, if an operation can sell 500,000 tons per year, its screens need to sort nearly 42,000 tons per month. If the screen is in operation two days each week (about eight days each month), 10 hours each day, the operation will require a machine capable of screening around 525 tons per hour. A screen that processes 300 tons per hour would limit profits and cap growth potential. A machine with a potential output of 900 tons per hour would come with extra expenses and no added value.
Scalping and screening have several main differences. Standard screens are often considered finishing screens because theyre capable of producing specific-sized end products. Operators can adjust the speed of the feeder belt to help produce a clean, sized, finished product. These units typically have two or three screen decks and are ideal for use in sand and gravel pits, on asphalt jobs and in quarries.
Scalping screening plants are built to handle the toughest materials but are not as precise as standard screening plants. Material is fed directly onto the screen. Scalpers are ideal for sorting materials before crushing, processing scrap metals and recyclables, and to extract rock from dirt on construction sites.
Hopper size is typically 12-ft. wide with an option to upgrade to a 14-ft. wide. Those extra 2 ft. can capture more product and prevent spillage. The size of the hopper is perhaps most pertinent when pairing the screener with the loading machine, especially when using a large wheel loader.
A tipping grid or live head can be added to a screener above the hopper for additional sizing. While they perform a similar duty, they are very different. A tipping grid is essentially a hinged grid that blocks larger materials from entering the hopper. This is an affordable option but can become a chore, particularly in wet or dirty applications where the tipping grid may become plugged frequently.
A live head is essentially a vibrating screen that attaches to the hopper and is ideal for heavy-duty, dirty, wet and sticky applications. The unit can be used for two purposes: to scalp dirty material off and eliminate the need for manual cleaning, or to size material going into the machine so operators can produce an additional sized product.
While these are generally very efficient, operators should know that screeners with 14-ft. hoppers would not be used to the full potential. A typical live head measures 12 ft., making 2 ft. of the hopper unusable.
Apron feeder versus belt feeder is another key element to evaluate, as different products vary in durability. The standard belt feeder is perfect for sand and gravel operations, but is likely to tear or break when working with metal, large rock or extremely abrasive material. An apron feeder, which is essentially a belt made of metal, is durable and can handle nearly anything an operator throws at it.
Stockpiling offers little mystery. The higher the stockpile, the less time it will take operators because theyll be able to run for longer periods without having to move material. Even an additional 8 to 10 in. of stockpile height can make a significant difference.
Aside from all the proper adjustments and operating parameters required to gain the most in screening efficiency, the need for good preventative maintenance practices is a must for longer-lasting screens and reliable performance. Here are eight key components to a solid maintenance program.
Establish an oil-sampling program. Although a commonly overlooked practice, a regularly scheduled oil sampling is an operators best insurance against catastrophic component failure and costly downtime. The valuable insights provided by samplings such as detecting a worn bearing allow operations to schedule maintenance downtime around periods of prime production. Scheduled sampling and analysis establishes a baseline of normal wear and can help indicate when abnormal wear or contamination is occurring. Oil that has been inside any moving mechanical apparatus for a period of time reflects the exact condition of that assembly. Thats because oil is in contact with mechanical components as they wear, trace metallic particles enter the oil. These particles are so small that they remain in suspension. Particles caused by normal wear and operation will mix with the oil. Any externally caused contamination also enters the oil. Identifying and measuring these impurities, indicates the rate of wear as well as any excessive contamination. Importantly, an oil analysis will also suggest methods to reduce accelerated wear and contamination.
Employ recommended lubrication practices. Always consult the owners manual for the manufacturers recommended lubrication practices. Install the correct amount of oil, and use the recommended type of oil. Change the oil at the proper intervals, making sure that the oil in storage is clean and that clean containers are used to transport the oil. Make sure that the machine is completely level so that oil does not pool at the low side of the machine.
Maintain proper belt tension. Belt tensioning must be right on target for optimum screen performance not too loose and not too tight. Ideally, the belts should only be tight enough so as to not slip during start-up. If necessary, use a belt gauge to set the correct tension. If belts squeal during start-up or operation or whip excessively this may indicate insufficient belt tension.
Over-tightened belts can cause serious damage such as pulling the vibrating frame out of square with the support frame. Operating in this twisted position introduces stresses that may lead to spring failure, metal fatigue, or cracking and broken welds. This twisting affects stroke amplitude and character, which then affects material flow and screening efficiency. Over-tightened belts also put an extra load on the mechanism bearings and may tear up motors and motor bases. Additionally, to prevent drive belts from slipping, flopping or coming off, keep belts and sheaves clean and properly aligned. Inspect sheaves for wear, and if the grooves are worn, replace the sheave.
Prevent material buildup. Accumulation of dust and stone around moving parts is one of the largest single causes of part failures, particularly for pivot motor bases, support springs, roller bearings and the vibrating frame. Impact between the vibrating frame and accumulated material may lead to tower vibrations as well as potential side sheet and support deck cracking. Note that sheaves and belts are susceptible to material jumping over the side sheets and causing damage. Where possible, use stationary skirt plates or rubber flaps to deflect airborne material. Its also important to avoid material buildup in bins, hoppers and transfer points.
Maintain proper screen media support and tensioning. Uniform tension must be maintained on the screen surface to prevent whipping and to maintain contact between the screen surface and the bucker-up rubber on the longitudinal support bars. Improper tensioning may cause severe damage to costly screen media. Also, do not operate a vibrating screen with screen cloth or other screen media sections removed as this will accelerate wear on the support frames and the longitudinal support bars.
Inspect for wear. Inspect cross members for signs of premature wear especially in wet-screen applications where wear is accelerated. Cover and protect the cross members, decking and housing tubes with rubber or urethane liners to extend their life. Prior to installing screen media sections, make sure they are appropriately square and flat so that they will seat properly on the longitudinal support bars.
Monitor spray systems. Use the required number of spray nozzles and make sure they are open and fully operational. Maintain the proper water volume and pressure. Avoid spraying perpendicular (at 90 degrees) to the screen surface as this may result in a rapid deterioration of the screening surface. The spray should strike the screening surface at approximately 45 degrees. Nozzles can be positioned to spray against or with the flow of material. This choice depends upon the desired washing/rinsing efficiency and material properties. For most applications, a pressure of approximately 40 lbs. per square in. at the nozzles is desired.
Operate with proper clearances. Maintain adequate clearances around stationary structures, and never allow vibrating frames to hit stationary structures. Wherever possible, provide a minimum of 24-in. side clearance on each side of the machine. This enables the operator to adjust screen-cloth tension and check the units condition and operation. Allow sufficient clearance in front of the screen at the discharge end, or in the rear at the feed end, for replacing screen sections. Set the clearance at least 1 ft. longer than the longest screen panel. Maintain a minimum vertical clearance of at least 5 in. between the vibrating frame and any stationary structures such as the feed hopper or discharge chutes and bins. Avoid providing places for dust and stones to accumulate and interfere with the movement of the vibrating frame.
In the mineral processing area, the trommel screens(aka. Rotary drum screens) and vibrating screens are both widely used screening & classification equipment. But whats the difference between the trommel screens and vibrating screens, and how to choose the most suitable screens for your mineral processing application? Or even how should we choose the right screening equipment for specific mining conditions?
Thorough we all may know that they are both are widely used screening equipment, but the different working methods and principles also mean the difference in output, as well as the types of materials suitable for screening processing.
Vibrating screens are screened using the exciting force generated by a vibrating motor and belong to vibrating screens. Commonly used mine vibrating screens include circular vibrating screens and linear screens.
The trommel screen is another screening form. During the screening process, the equipment will not vibrate, but generally, the motor and reducer drive the drum to rotate through the bearing. The material in the drum passes through the screen from high to low due to the rotation of the drum. And it is successfully screened out, so the trommel screen belongs to a type of rolling screening.
trommel screen: It is a cylinder. The outer surface of the cylinder uses one or more layers, or several sections of screens to increase the screening specifications. The volume of the trommel screen is generally large, mainly including motors, reducers, drum devices, screens, and machines. It is composed of a frame, a sealing cover, and an inlet and an outlet. A steel ring must be added to the drum device to prevent the trommel screen from deforming.
The roller device is installed on the frame obliquely. The motor is connected with the roller device through a coupling through a reducer, and drives the roller device to rotate around its axis. When the material enters the drum device, due to the tilt and rotation of the drum device, the material on the screen surface is turned and rolled. The qualified materials (products under the screen) are discharged through the outlet at the bottom of the rear end of the drum, and the unqualified materials (on the screen) The product is discharged through the discharge port at the end of the drum.
Using the vibration motor as the vibration source, the material is thrown up on the screen while moving forward in a straight line. The material enters the inlet of the screening machine evenly from the feeder, and produces several kinds of screens through the multi-layer screen. The upper and lower objects are discharged from their respective outlets.
The screen surface is fixed on the screen box, and the screen box is suspended or supported by springs. The bearing of the main shaft is installed on the screen box and is driven by the pulley to rotate at high speed. The eccentric counterweight plate is installed on the main shaft and generates centrifugal inertia force with the rotation of the main shaft, so that the screen box forms an approximate circular orbit vibration.
The trommel screen can be divided into single-layer, double-layer and three-layer vibrating screens according to the number of layers of the screen. This vibrating screen is also similar, according to the number of screen surface layers can be divided into single-layer, double-layer, three-layer and four-layer vibrating screen.
The vibrating screen is a screening equipment with a vibrating motor as the vibration source, so the screening accuracy is high. The trommel is a high-output screening equipment, and the screening accuracy is not as high as the vibrating screen.
For the trommel screen, the material is turned over and rolled in the drum, so that the material stuck in the sieve hole can be ejected to prevent the sieve hole from being blocked. For the circular vibrating screen, the material moves in a parabolic circular trajectory on the screen surface, so that the material is dispersed as much as possible to improve the materials bounce force, and the material stuck in the screen hole can also jump out, reducing the hole blocking phenomenon.
Vibrating screen and trommel screen have their own working methods and screening principles. Some raw materials can be screened through them. However, for different sites and different material requirements, suitable screening machines should be selected to achieve better screening results.
Screening or sieving is one of the crucial processes in any of product manufacturing or process industry. Industrial screeners scalps, grade, sift, de-dust and do numbers of screening activity to provide quality to the final product. Failure of Vibro Sifter can have an adverse effect on the whole processing unit which will lead to production loss. A broken mesh screen can push product manufacturers into reprocessing of the material or even scrap/discard the product due to inaccurate sizing or contamination.
The mesh is the most important part of the screening process. An improper weaving of mesh wire will result in wire breakdown which can affect the overall processing time. Also, the inaccurate opening of the wire mesh due to improper mesh weaving will lead to an inaccurate particle size of the products.
Breaking or tearing of mesh wire is a common challenge to most of the manufacturers. Sieving and screening with broken mesh are never advisable because it can lead to incorrect sizing of particle size which will result in product recall from the market. The pharmaceutical drug manufacturers are facing a major challenge of getting faster approval on medicines from USFDA due to incorrect particle size distribution and product contamination which can be achieved with precise and accurate manufacturers of screening mesh.
There are many reasons that play role in breaking of the wire mesh, but with proper maintenance and knowledge the manufacturers can increase the life of mesh screen and eventually decrease the overall operating costs of the organization.
4.Product Feed: Always feed the product material at the center of mesh screen frame to achieve accurate sizing and screening of the material due to proper distribution of the material across the screen
5.Mesh Bending: The most known and common reason behind mesh bending or loose mesh is over feeding of the material. The continuous over feeding of the material will lead to high pressure on the mesh cloth and when it reaches its durability level, it tends to curve/turn downwards. This will result in low throughput and improper screening of the material.
To avoid such situation the manufacturers should install material hopper with the flow control arrangement system. A flow control system will have a sliding frame which allows you to adjust the flow rate of the product.
Due to continuous vibration, the mesh frame can bend/turn from the edges/corner due to inaccurate mesh clamping. The production engineer or the machine operator should check the rubber gasket regularly because a broken rubber gasket can lead to breakage of the mesh screen which eventually increases production loss and high operating costs for the organization.
WSM VIBRATING CONVEYORS AND SCREENS ARE USED IN A WIDE VARIETY OF APPLICATIONS, FROM SIMPLE TRANSFER CONVEYORS, TO HIGH CAPACITY SCREENING OF PARTICLEBOARD FURNISH, TO SEVERE DUTY CHIPPER INFEED UNITS.
Energy-efficient, natural frequency design utilizes power springs to reduce horsepower requirements and operating costs. Heavy-duty construction for reliable, long operating life with less downtime and horsepower.
Optional steel coil springs for severe duty conveyors. Coil springs are heat-treated for long wear life. Optional fiberglass springs (not shown) are made of uni-directional fiberglass for lighter duty applications.
With the ability to move high volumes of material using just minimal horsepower, our Vibrating Screens & Conveyors to orientate and level material as it conveys, reducing any surges to down screen equipment.
To discover the full range of options that come with our WSM Vibrating Screens & Conveyors, simply complete the contact form to receive your Free Product PDF. Questions? A member of our support staff will contact you.
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Screens can be considered the cashbox of the operation, because while crushersmake the gradation, screens make the specification. Material must go through or over a specified size to end up in the right pile. Unlike the crushers, Vibratory Screens cannot produce material; they can only size material that is already reduced to the product sizes. Vibratory Screens allow crushers to achieve maximum performance by sizing the material feed to the crusher and efficiently removing the finishing product from the circuit as it is produced.
Vibratory Screens can be subdivided into Inclined and Horizontal style screens. Today's screens come in widths from 4-12' wide and from 8-32' long. Screens are normally sized so that the length is 2.5 times the width. The width of a screen will determine the maximum carrying capacity of the screen deck, while the length of the screen will determine the overall efficiency of the deck.
McLanahan Vibratory Screens are engineered with ASTM A572 Grade 50 steel side plates. With a tensile strength of 65,300psi (65ksi), these side plates have a 45% higher yield strength than A-36 steel, which can withstand up to 36,000 psi (36ksi) of stress before it begins to drastically deform. A fully bolted construction reduces/eliminates cracking due to stress risers in the steel caused by welding. Worn components can be quickly replaced without cutting.
McLanahan Vibratory Screens are built with an integrated feed box and are able to withstand heavier loading and larger material in the feed end without worrying about bolts loosening or structural failure.
McLanahan Vibratory Screens feature robust side plate stiffening. Formed plates are bolted to side plates to form a rigid support grid along the length of the side sheet. Independent cross members can be pulled individually and relined in a clean work bay versus on a screen tower, and reduce the need for heavy and wear prone X-bracing. Cross members are on 4' centers to allow more clearance for personnel to access the decks. Replacement cross members come shorter in length and with machined/matched shims to allow for easy installation in areas with limited clearance.
Structural tubing gives the producer a variety of size options and allows you to replace only the worn tubes, not the complete deck frame. A sacrificial weld plate installed on top of the tubes allows stringers and bucker bars to be welded in without welding directly to the tube.
The performance of a screen is affected by four variables: eccentric throw, frequency (rpm), angle of adjustment and throw direction. By manipulating these variables, the operator can dial in the screen to match the application and material.
Eccentric ThrowEccentric throw is the radius of the screen box. Generally, the greater the throw, the more aggressive the screen action will be. Consequently, the smaller the throw, the less aggressive the screening action. Keeping this in mind, the operator can set up the operation with a heavy throw for heavier or larger materials, or a smaller throw to create a sifting action more suited for finer separations.
FrequencyThe frequency of the screen is measured in the number of revolutions per minute the screen makes. In conjunction with the eccentric throw, a lower frequency allows for a more aggressive screen action for larger material and cuts, while a higher frequency is used for smaller material and cuts.
Angle of AdjustmentThe angle of the screen plays a large factor in its overall performance as well. A flatter screen angle will provide a longer retention time of material on the deck and more probability that a particle will fall through the opening. As the angle is increased, the retention time is decreased.
ThrowIt may be advantageous to run the throw of the screen uphill. The goal is to increase the retention time on the screen, as well as change the orientation of the particles to the screen opening. The reverse action does not hurt the screen and is usually used in finer screening application, but be cautious not to increase the bed depth too much.
Stratification and SeparationTwo main operations have to occur for material to be screened: stratification and separation. Stratification is the process of larger sized material rising to the top of the bed, while smaller particles go to the bottom of the bed. Separation is the process by which particles introduced to the screen opening either fall through the opening or do not. Stratification must occur before separation can take place.
The separation probability is a function of the ratio between the size of the screen opening and the size of the particle. If the ratio is large in other words, the particle is much smaller than the opening there is a high probability the particle will fall through. If the ratio is small the particle is close in size to the opening then the probability is low that it will fall through.
Motion on a Vibratory Screen is produced with a combination of amplitude (stroke) and frequency (speed). The goal is to allow the particle to see as many openings as possible as it travels down the screen, but never see the same opening twice. Large screen openings for large cuts can be achieved with high amplitude and low speed. For small screen openings for finer cuts, the opposite is true: low amplitude and high speed.
Many producers have experienced a variety of problems that point to a screen deck that was improperly selected. It's wearing too fast. Its plugging (material getting stuck in the screen opening) or blinding (screen opening clogged by sticky material). The noise level is too high.
Many factors affect the overall efficiency of the screening process. Selecting the proper media for the application will be a big factor toward success. Wire cloth is the most widely used screen surface. Technological advances make it easier to consider other types of screen media.
The type of media chosen will depend on material abrasiveness, impact, material size, moisture content, cost-effectiveness and noise level. Wire cloth may be the lowest initial cost media, but the most cost-effective for anoperation will be the one that meets the specific application.
Rubber screens are a good choice for scalping decks in a dry, high-impact application. Rubber is very durable and can withstand the impact of the larger feed material hitting the deck. In a dry secondary application, a rubber screen can provide a long life, even in abrasive feed material.
FLEX-MAT vibrating wire screens will provide more spec product at a lower operating cost, while delivering more wear life and eliminating blinding, pegging and clogging issues.
When using static screening media (woven cloth, polyurethane or rubber panels, etc.), the only vibration is induced by the screen box which typically vibrates with a range of 500-1,000 strokes per minute. FLEX-MAT high-vibration wire screens have individual wires that vibrate independently at a high-frequency of between 6,000-10,000 strokes per minutes.
MAJOR ensures optimum wire quality and consistency at all times by developing, (through its own specifications and internal laboratory quality controls), the best recipe for a wires chemical content to optimize all factors, and by using the most advanced patented wire-making process, MAJOR also only uses the highest quality of stainless steel wires with the highest tensile strength, available in Type 304 and Type 316.
This process is the ultimate way of improving the molecular structure. The rod is heated first and then cooled at a controlled temperature to optimize the molecular structure before being drawn through a conic die.
Open area varies with the screening media type and affects the tonnage or volume of material that can be processed on a screen deck. On screen boxes with multiple decks, the relation of open area and material gradation between the decks is an important efficiency factor that needs to be balanced.
Its flat surface offers 100% of surface wear, compared to only the upper knuckles of woven screens, which results in the even wear of its wire, maintaining the opening within the given specification for a longer time. Polyurethane panels however, lose opening specification after a certain percentage of wear due to the slight V shape of the opening.
Designed to provide high-performance on all decks for a wide range of materials, FLEX-MAT screens provides the highest-efficiency level of self-cleaning capacity for higher throughput, reduced downtime as well as maintenance and replacement costs.
Players in the industrial automation and equipment industry continue to face an environment that remains hyper-competitive. Evolution in end-user demand is influencing players in the industrial automation and equipment landscape to optimize their manufacturing process. Sluggishness in the oil & gas industry, muted growth in automotive sales, and stagnancy in the agriculture sector have posed challenges to players in the recent past.
With the increase in oil rigs and natural gas projects being quoted, various companies are making reinvestments, to either cater requirement of preventative maintenance or for generating a better ROI. Investing in infrastructure development remains a top priority for the industrial automation and equipment companies, with improvements in energy- and operational-0efficiency gaining center stage.
XploreMR utilizes robust methodology and approach to arrive at market size and related projections. The research methodology for this report is based on 3 dimensional model. We conduct about 45-60 min duration detailed interviews with product manufacturers; apart from this we also collect market feedback from industry experts. To validate this data, we interact with senior panel members having more than 10 years of experience in relevant field. The panel members help in validating the findings and fill the gaps if any. In addition, we leverage on our existing pool of information, paid database and other valid information sources available in public domain. Usually industry interactions extend to more than 50+ interviews from market participants across the value chain.
XploreMR collects data from secondary sources including company annual reports, association publications, industry presentations, white papers, and company press releases apart from these we leverage over paid database subscriptions and industry magazines to collect market information and developments in exhaustive manner. After being done with desk research, detailed questionnaire and discussion guide is formulated to initiate primary research with key industry personnel; the discussion aims at collecting key insights, growth perspectives, prevalent market trends and quantitative insights including market size and competition developments. Both of these research approaches help us in arriving at base year numbers and market hypothesis.
In this phase, XploreMR validates the data using macro and micro economic factors. For instance, growth in electricity consumption, industry value added, other industry factors, economic performance, growth of top players and sector performance is closely studied to arrive at precise estimates and refine anomalies if any.
Data analysis and projections were made based on proprietary research frameworks and statistical analysis, which was further validated from industry participants. These frameworks include Y-o-Y growth projections, macro-economic factor performance, market attractiveness analysis, key financial ratios, and others.
For public companies we capture the data from company website, annual reports, investor presentations, paid databases. While for privately held companies, we try to gather information from the paid databases (like Factiva) and based on the information we gather from databases we estimate revenue for the companies. In addition, the team tries to establish primary contact with the companies in order to validate the assumptions or to gather quality inputs.
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DUBLIN--(BUSINESS WIRE)--The "Vibrating Screen Global Market Insights 2021, Analysis and Forecast to 2026, by Manufacturers, Regions, Technology, Application, Product Type" report has been added to ResearchAndMarkets.com's offering.
This report describes the global market size of Vibrating Screen from 2016 to 2020 and its CAGR from 2016 to 2020, and also forecasts its market size to the end of 2026 and its CAGR from 2021 to 2026.
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ResearchAndMarkets.com Laura Wood, Senior Press Manager [email protected] For E.S.T Office Hours Call 1-917-300-0470 For U.S./CAN Toll Free Call 1-800-526-8630 For GMT Office Hours Call +353-1-416-8900
The advent of the vibrating screen has greatly saved labor costs and production costs, so how to choose vibrating screen accessories so that the vibrating screen can truly meet the production requirements of high quality and high efficiency?
The vibrating screen is composed of a vibrating motor, a screen, a grid, a bearing, a bouncing ball, etc., most of which are vulnerable parts. No matter which damage will affect the screening effect and efficiency of the equipment, these parts are replaced frequently, which requires The user of the vibrating screen selects the appropriate spare vibrating screen accessories:
1. Choosing the vibration source of the vibrating screen accessories-the vibrating motor is the core component of the vibrating screen, that is, the vibration exciter. The size of the exciting force is determined by the size of the vibrating screen, the characteristics of the material, and the processing capacity. The weight and processing capacity of the screening machine are different, so the size of the vibration motor is also different. If the exciting force is too large, the vibrating screen may crack due to the excessive exciting force. On the contrary, if the exciting force is too small, the treatment effect will not be achieved, and the phenomenon of material accumulation and network blocking may occur.
Second, how to choose vibrating screen accessories filtration-the screen is an indispensable accessory for the vibrating screen, and it is the part that directly contacts the material. Generally, the material of the vibrating screen is 316L, 316, 304. According to the different materials to be screened, different screens should be selected. 316L (316) is used for the screening of acid, alkali or food and medicine, and 304 can be used for screening materials without special requirements.
The bearing is the support point of the vibrating motor or the exciter. It is one of the most critical components in the vibrating screen equipment. Its main function is to support the mechanical rotating body, reducing the friction coefficient and rotation accuracy during the operation of the vibrating screen. Therefore, pay attention to the following points when selecting bearings:
Fourth, select the vibrating screen accessories cleaning device-bouncing ball The bouncing ball plays a role in clearing the blocked materials in the vibrating screen. Bouncing balls are divided into sizes: 10, 15, 20, 25, 28, 30, 40. Classified by material: rubber: used for screening general materials; silica gel: more elastic than rubber, good wear resistance, and not easy to fall off. Usually suitable for the screening of food, medicine and other materials. For more details, please email or SNS contact.
Rotary motion of the motor change into the horizontal, vertial and inclined sports through the installation of the ends of the weight on the vibration motor, and then transfer the motion to the surface of the scr...
The linear vibrating screen is driven by double vibrating motor, when two vibrating motors do synchronous and reverse rotation, the excitation force generated by its eccentric block. In the direction parallel to ...
ZSG high efficiency mining vibrating screen is designed for high level screening of granular and powdered material, it's a common screening equipment that frequently used at blast furnace discharge, coking plant ...
DZG series high frequency vibrating screen features of high frequency, low amplitude and low noise, it's ideal for screening & filtering of powder, granule, pulp or slurry material in food, pharmaceutical, chemic...
1.We are factory and be able to give you the lowest price than market one; 2.Our products have been exported to over 80 countries and widely used in global mining and construction industry; 3.we have a prof...
Henan Sand Gravel Vibration Vibro Screen Manufacturer Industrial Screens Sieve Shaker Machine Industrial Screens (Sieve Shaker Machine) isofmultilayerandhighefficiency.Theeccentricshaftvibrationexciter...
Product Description Sediment dry screening unit dewatering vibrating screen be customized Brief introduction Base on lower water content sand is well needed and sold in market, we do research and manufacture a se...
Tumbler screen, which uses a operating principle of slow acceleration and a longer residence time on the mesh surface area, is ideal for multi-stage separation of fines, lightweights and difficult to screen mater...
* ALL MODELS ARE COMING WITH ELECTRIC MOTOR, MOTOR BASE AND ACCESSORIES * ALL MODELS DO NOT INCLUDE STEEL STRUCTURE SUPPORT AND STANDS. * DOVE RESERVES THE RIGHT TO MODIFY THE SPECIFICATIONS AT ANYTIME, WITHOUT PRIOR NOTICE.
DOVE laboratory will assay your ore samples rapidlyand analyze your raw materials and recommend the most efficient processing plant according to the ore specifications, minerals composition, and ore assay results, and your project size and the geologic and topographic conditions of your mine.
WE HIGHLY RECOMMEND FORWARDING SOIL SAMPLES OF YOUR MINE TO US FOR ANALYSIS, IN ORDER TO DESIGN AND RECOMMEND THE MOST EFFICIENT PROCESSING PLANT, TAILOR MAID TO YOUR MINE REQUIREMENTS, FOR HIGHEST PRODUCTION RECOVERY.
Erimaki produces different types of screens, including circular vibrating and direct discharge screens; rectangular, static, rotary and tumbler screens. Productivity and professionalism in screening and separation has been the companys philosophy for over thirty years.
Thanks to the simple adjustment of counterweights on the motor axis and the three-dimensional vibration they generate, the circular vibrating screens allow to sieve, classify, dedust and filter a very wide range of products, achieving good results even with fine products. The vibrating motion of the screen runs both horizontally and vertically and can be adjusted in both directions.
The vibrating screens are characterized by the possibility to easily and quickly change the vibrating movement and, consequently, the behaviour of the material to be sieved. By installing an inverter, it is possible to change the vibration speed, assuring flexibility of use, with both solid and liquid products. Thanks to the simple construction, the screens can be quickly disassembled for cleaning or mesh replacement.