p&q university lesson 8- screening : pit & quarry
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.
vibrating screen working principle
When the smaller rock has to be classified a vibrating screen will be used.The simplest Vibrating Screen Working Principle can be explained using the single deck screen and put it onto an inclined frame. The frame is mounted on springs. The vibration is generated from an unbalanced flywheel. A very erratic motion is developed when this wheel is rotated. You will find these simple screens in smaller operations and rock quarries where sizing isnt as critical. As the performance of this type of screen isnt good enough to meet the requirements of most mining operations two variations of this screen have been developed.
In the majority of cases, the types of screen decks that you will be operating will be either the horizontal screen or the inclined vibrating screen. The names of these screens do not reflect the angle that the screens are on, they reflect the direction of the motion that is creating the vibration.
An eccentric shaft is used in the inclined vibrating screen. There is an advantage of using this method of vibration generation over the unbalanced flywheel method first mentioned. The vibration of an unbalanced flywheel is very violent. This causes mechanical failure and structural damage to occur. The four-bearing system greatly reduces this problem. Why these screens are vibrated is to ensure that the ore comes into contact will the screen. By vibrating the screen the rock will be bounced around on top of it. This means, that by the time that the rock has traveled the length of the screen, it will have had the opportunity of hitting the screen mesh at just the right angle to be able to penetrate through it. If the rock is small enough it will be removed from the circuit. The large rock will, of course, be taken to the next stage in the process.
Depending upon the tonnage and the size of the feed, there may be two sets of screens for each machine.
The reason for using two decks is to increase the surface area that the ore has to come into contact with. The top deck will have bigger holes in the grid of the screen. The size of the ore that it will be removed will be larger than that on the bottom. Only the small rock that is able to pass through the bottom screen will be removed from the circuit. In most cases the large rock that was on top of each screen will be mixed back together again.
The main cause of mechanical failure in screen decks is vibration. Even the frame, body, and bearings are affected by this. The larger the screen the bigger the effect. The vibration will crystallize the molecular structure of the metal causing what is known as METAL FATIGUE to develop. The first sign that an operator has indicated that the fatigue in the body of the screen deck is almost at a critical stage in its development are the hairline cracks that will appear around the vibrations point of origin. The bearings on the bigger screens have to be watched closer than most as they tend to fail suddenly. This is due to the vibration as well.
In plant design, it is usual to install a screen ahead of the secondary crusher to bypass any ore which has already been crushed small enough, and so to relieve it of unnecessary work. Very close screening is not required and some sort of moving bar or ring grizzly can well be used, but the modern method is to employ for the purpose a heavy-duty vibrating screen of the Hummer type which has no external moving parts to wear out ; the vibrator is totally enclosed and the only part subjected to wear is the surface of the screen.
The Hummer Screen, illustrated in Fig. 6, is the machine usually employed for the work, being designed for heavy and rough duty. It consists of a fixed frame, set on the slope, across which is tightly stretched a woven-wire screen composed of large diameter wires, or rods, of a special, hard-wearing alloy. A metal strip, bent over to the required angle, is fitted along the length of each side of the screen so that it can be secured to the frame at the correct tension by means of spring-loaded hook bolts. A vibrating mechanism attached to the middle of the screen imparts rapid vibrations of small amplitude to its surface, making the ore, which enters at the top, pass down it in an even mobile stream. The spring-loaded bolts, which can be seen in section in Fig. 7, movewith a hinge action, allowing unrestricted movement of the entire screening surface without transmitting the vibrations to the frame.
One, two, or three vibrators, depending on the length of the screen, are mounted across the frame and are connected through their armatures with a steel strip securely fixed down the middle of the screen. The powerful Type 50 Vibrator, used for heavy work, is shown in Fig. 7. The movement of the armature is directly controlled by the solenoid coil, which is connected by an external cable with a supply of 15-cycle single-phase alternating current ; this produces the alternating field in the coil that causes the up-and-down movement of the armature at the rate of thirty vibrations per second. At the end of every return stroke it hits a striking block and imparts to the screen a jerk which throws the larger pieces of ore to the top of the bed and gives the fine particles a better chance of passing through the meshes during the rest of the cycle. The motion can be regulated by spiral springs controlled by a handwheel, thus enabling the intensity of the vibrations to be adjusted within close limits. No lubrication is required either for the vibrating mechanism or for any other part of the screen, and the 15-cycle alternating current is usually supplied by a special motor-generator set placed somewhere where dust cannot reach it.
The Type 70 Screen is usually made 4 ft. wide and from 5 to 10 ft. in length. For the rough work described above it can be relied upon to give a capacity of 4 to 5 tons per square foot when screening to about in. and set at a slope of 25 to 30 degrees to the horizontal. The Type 50 Vibrator requires about 2 h.p. for its operation.
The determination of screen capacity is a very complex subject. There is a lot of theory on the subject that has been developed over many years of the manufacture of screens and much study of the results of their use. However, it is still necessary to test the results of a new installation to be reasonably certain of the screen capacity.
A general rule of thumb for good screening is that: The bed depth of material at the discharge end of a screen should never be over four times the size opening in the screen surface for material weighing 100 pounds per cubic foot or three times for material weighing 50 pounds per cubic foot. The feed end depth can be greater, particularly if the feed contains a large percentage of fines. Other interrelated factors are:
Vibration is produced on inclined screens by circular motion in a plane perpendicular to the screen with one-eighth to -in. amplitude at 700-1000 cycles per minute. The vibration lifts the material producing stratification. And with the screen on an incline, the material will cascade down the slope, introducing the probability that the particles will either pass through the screen openings or over their surface.
Screen capacity is dependent on the type, available area, and cleanliness of the screen and screenability of the aggregate. Belowis a general guide for determining screen capacity. The values may be used for dried aggregate where blinding (plugged screen openings), moisture build-up or other screening problems will not be encountered. In this table it is assumed that approximately 25% of the screen load is retained, for example, if the capacity of a screen is 100 tons/hr (tph) the approximate load on the screen would be 133 tph.
It is possible to not have enough material on a screen for it to be effective. For very small feed rates, the efficiency of a screen increases with increasing tonnage on the screen. The bed of oversize material on top of the marginal particlesstratification prevents them from bouncing around excessively, increases their number of attempts to get through the screen, and helps push them through. However, beyond an optimum point increasing tonnage on the screen causes a rather rapid decrease in the efficiency of the screen to serve its purpose.
Two common methods for calculating screen efficiency depend on whether the desired product is overs or throughs from the screen deck. If the oversize is considered to be the product, the screen operation should remove as much as possible of the undersize material. In that case, screen performance is based on the efficiency of undersize removal. When the throughs are considered to be the product, the operation should recover as much of the undersize material as possible. In that case, screen performance is based on the efficiency of undersize recovery.
These efficiency determinations necessitate taking a sample of the feed to the screen deck and one of the material that passes over the deck, that is, does not pass through it. These samples are subjected to sieve analysis tests to find the gradation of the materials. The results of these tests lead to the efficiencies. The equations for the screen efficiencies are as follows:
In both cases the amount of undersize material, which is included in the material that goes over the screen is relatively small. In Case 1 the undersize going over the screen is 19 10 = 9 tph, whereas in Case 2 the undersize going over is 55 50 = 5 tph. That would suggest that the efficiency of the screen in removing undersize material is nearly the same. However, it is the proportion of undersize material that is in the material going over the screen, that is, not passed through the screen, that determines the efficiency of the screen.
In the first cases the product is the oversize material fed to the screen and passed over it. And screen efficiency is based on how well the undersize material is removed from the overs. In other cases the undersize material fed to the screen, that is, the throughs, is considered the product. And the efficiency is dependent on how much of the undersize material is recovered in the throughs. This screen efficiency is determined by the Equation B above.An example using the case 1 situation for the throughs as the product gives a new case to consider for screen efficiency.
Generally, manufacturers of screening units of one, two, or three decks specify the many dimensions that may be of concern to the user, including the total headroom required for screen angles of 10-25 from the horizontal. Very few manufacturers show in their screen specifications the capacity to expect in tph per square foot of screen area. If they do indicate capacities for different screen openings, the bases are that the feed be granular free-flowing material with a unit weight of 100 lb/cu ft. Also the screen cloth will have 50% or more open area, 25% of total feed passing over the deck, 40% is half size, and screen efficiency is 90%. And all of those stipulations are for a one-deck unit with the deck at an 18 to 20 slope.
As was discussed with screen efficiencies, there will be some overs on the first passes that will contain undersize material but will not go through the screen. This material will continue recirculating until it passes through the screen. This is called the circulating load. By definition, circulating load equals the total feed to the crusher system with screens minus the new feed to the crusher. It is stated as a percentage of the new feed to the crusher. The equation for circulating load percentage is:
To help understand this determination and the equation use, take the example of 200 tph original or new material to the crusher. Assume 100% screen efficiency and 30% oversize in the crusher input. For the successive cycles of the circulating load:
The values for the circulating load percentages can be tabulated for various typical screen efficiencies and percents of oversize in the crusher product from one to 99%. This will expedite the determination for the circulating load in a closed Circuit crusher and screening system.
Among the key factors that have to be taken into account in determining the screen area required is the deck correction. A top deck should have a capacity as determined by trial and testing of the product output, but the capacity of each succeeding lower deck will be reduced by 10% because of the lower amount of oversize for stratification on the following decks. For example, the third deck would be 80% as effective as the top deck. Wash water or spray will increase the effectiveness of the screens with openings of less than 1 in. in size. In fact, a deck with water spray on 3/16 in. openings will be more than three times as effective as the same size without the water spray.
For efficient wet or dry screeningHi-capacity, 2-bearing design. Flywheel weights counterbalance eccentric shaft giving a true-circle motion to screen. Spring suspensions carry the weight. Bearings support only weight of shaft. Screen is free to float and follow positive screening motion without power-consuming friction losses. Saves up to 50% HP over4- bearing types. Sizes 1 x 2 to 6 x 14, single or double deck types, suspended or floor mounted units.Also Revolving (Trommel) Screens. For sizing, desliming or scrubbing. Sizes from 30 x 60 to 120.
TheVibrating Screen has rapidly come to the front as a leader in the sizing and dewatering of mining and industrial products. Its almost unlimited uses vary from the screening for size of crusher products to the accurate sizing of medicinal pellets. The Vibrating Screen is also used for wet sizing by operating the screen on an uphill slope, the lower end being under the surface of the liquid.
The main feature of the Vibrating Screen is the patented mechanism. In operation, the screen shaft rotates on two eccentrically mounted bearings, and this eccentric motion is transmitted into the screen body, causing a true circular throw motion, the radius of which is equivalent to the radius of eccentricity on the eccentric portion of the shaft. The simplicity of this construction allows the screen to be manufactured with a light weight but sturdy mechanism which is low in initial cost, low in maintenance and power costs, and yet has a high, positive capacity.
The Vibrating Screen is available in single and multiple deck units for floor mounting or suspension. The side panels are equipped with flanges containing precision punched bolt holes so that an additional deck may be added in the future by merely bolting the new deck either on the top or the bottom of the original deck. The advantage of this feature is that added capacity is gained without purchasing a separate mechanism, since the mechanisms originally furnished are designed for this feature. A positivemethod of maintaining proper screen tension is employed, the method depending on the wire diameter involved. Screen cloths are mounted on rubber covered camber bars, slightly arched for even distribution.
Standard screens are furnished with suspension rod or cable assemblies, or floor mounting brackets. Initial covering of standard steel screen cloth is included for separations down to 20 mesh. Suspension frame, fine mesh wire, and dust enclosure are furnished at a slight additional cost. Motor driven units include totally-enclosed, ball-bearing motors. The Vibrating Screen can be driven from either side. The driven sheave is included on units furnished without the drive.
The following table shows the many sizes available. Standard screens listed below are available in single and double deck units. The triple and quadruple deck units consist of double deck units with an additional deck or decks flanged to the original deck. Please consult our experienced staff of screening engineers for additional information and recommendations on your screening problems.
An extremely simple, positive method of imparting uniform vibration to the screen body. Using only two bearings and with no dead weight supported by them, the shaft is in effect floating on the two heavy-duty bearings.
The unit consists of the freely suspended screen body and a shaft assembly carried by the screen body. Near each end of the shaft, an eccentric portion is turned. The shaft is counterbalanced, by weighted fly-wheels, against the weight of the screen and loads that may be superimposed on it. When the shaft rotates, eccentric motion is transmitted from the eccentric portions, through the two bearings, to the screen frame.
The patented design of Dillon Vibrating Screens requires just two bearings instead of the four used in ordinary mechanical screens, resulting in simplicity of construction which cuts power cost in half for any screening job; reduces operating and maintenance costs.
With this simplified, lighter weight construction all power is put to useful work thus, the screen can operate at higher speeds when desired, giving greater screening capacity at lower power cost.
The sting of the positive, high speed vibration eliminates blinding of screen openings.
The sketches below demonstrate the four standard methods of fastening a screen cloth to the Dillon Screen. The choice of method is generally dependent on screen wire diameters. It is recommended that the following guide be followed:
Before Separation can take place we need to get the fine particles to the bottom of the pile next to the screen deck openings and the coarse particles to the top. Without this phenomenon, we would have all the big particles blocking the openings with the fines resting atop of them and never going through.
We need to state that 100% efficiency, that is, putting every undersize particle through and every oversize particle over, is impossible. If you put 95% of the undersize pieces through we in the screen business call that commercially perfect.
aggregate screen problems and slutions | quarry screening equipment
Aggregate screen is one equipment in the quarry crusher plant which is used to screen the gravel size. After a long period of use, the aggregate screen cant start, the vibration is big or unstable. How to solve these problems? This article shares the aggregate vibrating screen problems and solutions.
First, we see if theres a problem in the power or the motor. If it is a motor failure, it replaces new motor parts is ok. The vibrating screen working assembly line is composed of centralized control lines. When some components are damaged, it needers to replace the new components in time. Sometimes the voltage is unstable, and the starting voltage is lower than the rated voltage value, so it is easy to be faulty. Therefore, it is necessary to ensure voltage stability in the working process of the vibration screen.
The aggregate vibrating screen uses the vibrating principle of the vibration exciter to screen the materials. The screening equipment cant start when the trouble with vibration exciter and it cant a normal operation. We should need to ensure a good lubrication state when the vibrator exciter working. If the lubricating oil thickens, solidifies and agglomerates, it will not have the proper lubrication function. So it is necessary to timely check and replaces the appropriate lubricating oil.
Check if the vibrating screen equipment itself is out of order. Due to the material supply flow of vibrating screen changes, such as more than the prescribed value of feeding, the material on the screen surface will form a blockage. When the material accumulated to a certain amount, the working load of the vibrating screen becomes larger, which leads to the failure of starting up. To deal with such problems is to clean the screen to ensure that the screen can be screened smoothly.
The vibrating motor is the part that provides exciting force for the equipment. If the motor power and model do not match or too large, there will be a large jump, displacement and other phenomena in the use of the process. And if the user adjusts the exciting force of the motor to increase the output or screen precision, it will cause the problem of intense vibration if the exciting force exceeds the rated range. If it needs to adjustment, we should consult the aggregate screen manufacturer and make adjustments within the tolerance of the motor.
The damper spring is the part that connects the base of the screen machine with the screen frame. Another function is to act as a buffer. If the spring hardness is too large to play the buffer effect, the device will run out of the problem. The user may choose to replace the high-quality spring to solve this kind of problem.
If the ground is installed horizontally which appears abnormal vibration. We can check if the anchor bolts are loose. Under the action of the vibrating motor, the screen machine itself will produce certain mechanical vibration, and the fixed anchor bolt will loosen after a long time operation. The vibration wave is transmitted to the ground through the base, and the vibration is regenerated. The solution to this problem is that the user can tighten the anchor bolt.
Some aggregate screens use a double vibration motor, and the factory will adjust the motor steering. But when the motor wear, damage and other phenomena, the users replace and the motor steering, power inconsistency, it also cause the screen machine violent beating. We can consult technical personnel to vibration motor steering, eccentric block and other to re-installation.
Jiangxi Shicheng stone crusher manufacturer is a new and high-tech factory specialized in R&D and manufacturing crushing lines, beneficial equipment,sand-making machinery and grinding plants.
the latest in screening equipment - pit & quarry : pit & quarry
Simplicity has provided vibrating equipment to virtually every industry requiring the separation of materials into various sizes since 1921. According to Terex MPS, Simplicitys DM Series incline screens are uncompromised workhorses designed for virtually any application. The screen is designed for heavy-duty scalping, intermediate sizing or finished screening of virtually any material. The DM Series twin-shafted dual mechanism delivers the rugged reliability for large, heavy production demands with a variety of configurations to meet specific applications, the company adds. The dual mechanism is optimized to provide maximum bearing life, superb reliability and can be custom engineered to fit existing envelopes, Terex MPS says.
According to Major, its smartphone app provides customers with up-to-date information and access to advanced digital tools. The app is free and available for Apple and Android phones, and the tool is available for aggregate producers and Major dealers, with customizations for each. Depending on the type of user, the app includes marketing materials, expert documents and Majors newsletter. The app also integrates with the new Flex-Mat Sensor screen box vibration analysis tool, giving users the ability to operate the sensor and view vibration analysis reports. The Flex-Mat Sensor enables readings of screen box vibrations within seconds and generates a report that can be sent or reviewed. The sensor allows users to review results and fine-tune their screen machine without shutting down the equipment, according to Major.
Want to make changeouts easier? Pull everything from one pallet. Unified Screening & Crushing stocks screen rails in rubber, steel and urethane. According to Unified, it offers the largest inventory of screen media in the U.S., with hundreds of different square opening screen sizes. Producers, however, can turn to Unified for all of their screen installation needs, including rails, channel rubber, bolts and fasteners. Single sourcing means less work for producers, Unified says, and greater efficiency for frontline teams.
Aggregate producers can easily test and track screen performance and ensure maximum screening productivity with Deister Machine Co.s Orbit+ mobile app and wireless accelerometer. The portable Orbit+ wireless accelerometer is small enough to fit in a pocket, utilizing powerful magnets to securely attach to the screening unit to provide accurate, high-precision measurements, Deister says. Turn Orbit+ on, connect to the mobile app and its ready to conduct multi- and single-point tests, as well as log and share results. Producers can quickly and easily conduct vibration tests and monitor machine speed, stroke, amplitude, angle of throw and side motion. They can also view orbit, waveform and spectrum data, and log test records and maintenance schedules.
Monitoring vibrating screening equipment and issuing a warning before a catastrophic failure can save tens of thousands of dollars in unscheduled outages, Syntron Material Handling says. Using smart technology, Syntron generates warning messages through a phone or iPad app about a customers screening equipment by integrating devices such as temperature and stroke measuring sensors, vibration monitoring devices, and oil level indicators to predict oncoming conditions. These messages are immediately distributed to maintenance and operations personnel to schedule repairs to prevent downtime.
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optimised vibrating screens boost family business - quarry
A third-generation family quarrying business is maintaining its commitment to quality across changing seasons through its decades-long preference for sophisticated and optimised vibrating screens and their screen media.
The Peace River region of northeastern British Columbia, in Canada, is often associated with rich soils and moderate temperatures, making it an ideal agricultural environment. But there is also plenty of income to be made just below the surface. An aggregates producer recognised this in the mid-1960s and decided to take action.
In 1966, Nels Ostero established a sand and gravel operation in the Peace River Region Nels Ostero Ltd. Since then, the company has grown significantly but has always remained humble and family-orientated. Nels Osteros son Tom Ostero took over the plant in 1982, and in 2007, his grandson Nilson Ostero assumed the manager position where he remains today.
The plant, which resides on 130 hectares of land, supplies sand and gravel for residential and commercial needs in the Peace River regional district. The companys products are used in concrete applications, asphalt plants, oil fields and highways. With a capacity of more than one million tonnes per year, the equipment on-site plays a huge role in the plants success.
To keep up with the demand of sand and gravel products, the quarry requires top level machinery. There are 11 vibrating screens, two crushers and dozens of loaders, trucks and excavators on-site, all of which need to be performing efficiently.
Haver & Boecker Niagara has been delivering dependable equipment to Nels Ostero for decades. In fact, the Canadian-based screen manufacturer has been Nels Osteros go-to since the quarrys first years of establishment, back when the manufacturer was known asWSTyler.
The first piece of Haver & Boecker Niagara equipment the company purchased was a Ty-Rock (today known as an F-class vibrating screen) installed in 1966. Since then, they have added a number of technologies from themanufacturer.
My father chose the company because of the reliability of the equipment, Nilson Ostero said. I have tried some different equipment and screen media brands over the years, but nothing compares to Haver & Boecker Niagara.
Most recently, Nilson Ostero replaced his two 4.8m x 2.1m machines, which were situated at the finishing end of the operation. They were supplied by another manufacturer and had been running since the 1980s. The equipment was outdated, inefficient and required more maintenance than the value they offered. He turned to Haver & Boecker Niagara which evaluated his operation and recommended implementing two Niagara T-class machines. The new screens have proven themselves a good fit, increasing capacity and requiring little to no maintenance.
The T-class machines are on their third season with us, and we havent had a single issue, Nilson Ostero said. They allow us 20 per cent more capacity than our old screens, but more importantly they are stronger andmore reliable.
Haver & Boecker Niagara characterises the T-class machines as highly efficient and durable, which is important to the success of any screening business. This is especially true for this particular operation, which runs year-round and sees the effects of cold weather on material and screening equipment.
The British Columbia winter weather averages about four degrees Celsius but can dip down as low as -40oC. While some screen plants shut down their whole operation in the winter, Nilson Osteros high performing equipment allows him to performcrushing and screening year-round. When temperatures remain steadily below -3o C, they pause aggregate washing. However, even with a portion of the operations process shut down, they are still able to produce more than an operation that has to completely shut down for several months.
The colder it gets outside, the stickier the material becomes, Nilson Ostero said. The extra moisture can lead to blinding and pegging, resulting in downtime for maintenance to clear out the material. That doesnt happen with the T-class machines.
At the end of the day, if the guys are working with good equipment, they are happier and perform better, Nilson Ostero said. Safety is obviously a big deal, but another thing is providing efficient, top-notch machines that dont require unnecessary maintenance.
Maintenance is required on all jobsites, but unexpected maintenance and subsequent shutdowns can equate to a significant loss of money for any company. Scheduled maintenance activities are only possible with thorough analysis and planning as well as quality equipment and screen media. Nilson Ostero consistently found that any attempt to cut corners only resulted in lost profits. Each time he experimented with lower-cost screen media, he would watch as unexpected downtime and lost revenue skyrocketed.
Until the operation implemented the Haver & Boecker PROdeck method, the standard screen media required attention after every eight shifts, and a complete change-out every two weeks. PROdeck evaluates the screening process to effectively blend screen media for the highest production with the least amount of unscheduled downtime. Markus Kopper, general manager of Haver & Boecker Niagara Rocky Mountains, and Dave Warden, Haver & Boecker Niagara sales manager, worked with the company to determine the optimal screen media combination for the operation. This included a combination of Ty-Max, Ty-Wire and traditional woven wire, as well as Majors Flex-Mat.
Haver & Boecker Niagara partners with each customer and thoroughly evaluates an operation before making recommendations, Kopper said. For Nels Ostero, they were able to achieve a 70 per deck increase in wear life with our PROdeck approach.
Nilson Ostero also consulted with Haver & Boecker Niagara to determine if any additional upgrades for his vibrating screens could reduce the time required for maintenance and screen change-outs. Hefound a time saver in the companys Ty-Rail quick-tensioning system. The new T-class machines are equipped with this system, which combines the tension rail and all hardware together in one assembly. Ty-Rail has simplified the process and saves his team at least three hours each time a change-out is needed, as well as helping to eliminate losing nuts and bolts into the hoppers below.
A complete screen change-out, on one screen, would have normally taken us five or six hours, Ostero said. But with Ty-Rail, we can do it in as few as three hours. And guys arent dropping bolts every 15 seconds, so thats anadded bonus.
The three-hour time savings, coupled with increased throughput, resulted in an overall production increase over the first year. On top of that, it saved an estimated eight to 10 days of downtime per season, which equates to an increase of thousands of dollars.
However, Ty-Rail wasnt the only time-saving option Nilson Ostero discovered. After years of frequently replacing worn out cross-beams, he opted to add Zip-Guard to his T-class machines. The 13mm-thick polyurethane liner is designed to reduce the impact of passing material by protecting the cross beams from wear. This results in increased equipment longevity and minimised downtime formaintenance.
All of the technologies on-site are supported by an ongoing service program, which gives Nels Ostero an added level of confidence in the products. Haver & Boecker Niagara begins every service visit with its signature Pulse vibration analysis. The advanced vibration analysis technology is designed to help customers, like Nilson Ostero, examine the health of their vibrating screen. Haver & Boecker Niagara technicians use the technology and analysis to help detect irregularities that could translate into diminished performance, decreased efficiency, increased operating costs and imminent breakdowns.
Markus and his team used Pulse to help me spot issues that our team wouldnt have normally been able to find, Nilson Ostero said. Haver & Boecker Niagara first ran it on my machines right after they installed them, and now they run it once a year. It has caught problems that may have cost me money down the road, including a twisted frame on one of my screens. We knew there was a problem with the unit, but with Pulse, Haver & Boecker Niagarasservice technician determined exactlywhat was wrong.
Since the companys inception, Nels Ostero has grown to become one of the largest sand and gravel producers in the area employing more than 30 people, several of whom have been with the company for more than 15 years. With a constant focus on relationships and quality, the Ostero family built a longstanding business on enduring whatever the economy throws at them, all while maintaining their reputation for consistently providing quality product that meets the demands of theircustomers.
Looking toward the future, Nilson Ostero hopes to continue to grow the business by increasing output year over year, continue retaining and adding employees, and perhaps most importantly keep the businessin the family and one day pass it on to his children tocontinue the family tradition.
vibrating screen | crushing & mining screen - jxsc mine
Vibrating screen is a rectangular single-, double-, and multi-layer, high-efficiency new screening equipment. It does circular trajectory, so also known as the circular vibratory screen. The screen machine is ideal equipment in rock crushing and screening plant.
JXSC vibrator screens adopt the cylindrical eccentric shaft exciter and the partial block to adjust the amplitude. The long material sieve line and the screen specifications are many. Specifical design for the quarry plant, stone crusher plant and also appropriate for mining, coal and mineral preparation. Our screening installation has advantages of reliable structure, strong excitation force, durability, and low vibration noise.
The vibratory screening machine is to utilize reciprocating vibration of the vibration generator produced. The processing of the screen separates the different size material by a single- or triple-deck screen. That is, according to the size of particles to separate. The underlayer is a small material, and the upper layer is coarse particle material. In the end, the coarse and fine particles are separated and the screening process is completed.
Types of vibrating screens
According to motion theory, screening machines can divide into linear, circular, horizontal, eccentric shaft vibratory screens and inclined screen. The single deck, double deck, and multilayer vibrating screen is the basis of the numbers of the layers. Because of the different screening materials, we also call it gravel screen, sand screen machine, aggregate screening, wet vibratory screens.
1. The material screen drip line is long and has many screening specifications.
2. The eccentric block as an exciting force, a strong exciting force.
3. Sieve beams and sieve box connected by high strength bolts, no welding.
4. Sieve machine has the advantages of simple structure and convenient repair.
5. The small amplitude, high frequency, high dip structure, so this machine is of high efficiency, maximum, long life, low power consumption, low noise.
1. The shape of the particle and screen size
Most screening material is cylinder or anomaly, and the screen size has both circular and rectangle. The shape of the material granule touch screen for particle whether passed has a big effect. The rectangle screen is good for the circular particle, and the circular screen for irregularity.
5. The peculiarity of the material
All the size, humidity, friction and flowability of material will affect the screen. The humidity higher, friction bigger, flowability too bad, so the passing rate lower.
Jiangxi Shicheng stone crusher manufacturer is a new and high-tech factory specialized in R&D and manufacturing crushing lines, beneficial equipment,sand-making machinery and grinding plants.