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What is a banana screen The banana screen is a vibration grading with a box vibrator and a plurality of different inclined screen faces. The shape of the main box is similar to that of a banana. It is mainly used for the classification of large and medium-sized materials with high fine content, and can also be used for dehydration, de-intermediation, and de-sludge operations. (The fine particles refer to particles with a particle size of less than half the size of the mesh.) The banana screen is designed by injecting a banana-shaped multi-stage working surface on the basis of a linear classifier. There is a larger slope screen at the feed end, followed by a stepwise decrease at a certain number of angles until the discharge opening, the overall screen surface is concave curved. The sloped screen at the feed end allows for more material to pass through the screen surface with higher screening speeds and thinner material delamination. Because the bulk material passes through the steep slope faster, this earlier stratification allows the fine particles to move closer to the screen surface and pass through the gap relatively unhindered, so the banana sieve has a very high screening efficiency and It is the most advanced and most popular screening machinery product, which is 1.5-2 times higher than traditional grading screen. working principle The banana vibrating screen has a sloped surface at the feed end, starting with 34 and then descending to a discharge end of about 10 at a certain number of angles. The screen surface is in the form of a fold line with different inclination angles, and the thickness of the material layer from the feed end to the discharge end is constant. The ratio of material volume to flow rate on each screen surface is stable, the material layer is higher, and the screening efficiency is uniform, which is 1-2 times higher than that of the same effective area screening machine. For high fine content, especially materials The banana vibratory screening machine has a very high screening efficiency when the medium content is larger than the material having a classification size of less than 1/2. Advantages and features of LZZG banana screen 1. Low power consumption, high vibration intensity (9-12mm), high screening efficiency (>95%); 2. The domestic brand patented screen surface configuration is adopted, and the material handling capacity is large; 3, light weight, low working noise, stable operation; 4. The operation and maintenance of the sieve machine is simple, safe to use and cost-effective. Operation rules 1. Before the sieve is started, all the protective covers should be installed in place and all personnel should be evacuated from the sieve; 2. It is forbidden to start the sieve machine until the various protective covers are not fixed; 3. Do not stand within one meter of the screen machine during the start and stop of the screen machine; 4. When the sieve machine is in operation, do not stand on the vibrating parts; 5. The screen motor must be de-energized and the screen machine stopped before any work can be started on the screen.
The banana screen is a vibration grading with a box vibrator and a plurality of different inclined screen faces. The shape of the main box is similar to that of a banana. It is mainly used for the classification of large and medium-sized materials with high fine content, and can also be used for dehydration, de-intermediation, and de-sludge operations. (The fine particles refer to particles with a particle size of less than half the size of the mesh.)
The banana screen is designed by injecting a banana-shaped multi-stage working surface on the basis of a linear classifier. There is a larger slope screen at the feed end, followed by a stepwise decrease at a certain number of angles until the discharge opening, the overall screen surface is concave curved. The sloped screen at the feed end allows for more material to pass through the screen surface with higher screening speeds and thinner material delamination. Because the bulk material passes through the steep slope faster, this earlier stratification allows the fine particles to move closer to the screen surface and pass through the gap relatively unhindered, so the banana sieve has a very high screening efficiency and It is the most advanced and most popular screening machinery product, which is 1.5-2 times higher than traditional grading screen.
The banana vibrating screen has a sloped surface at the feed end, starting with 34 and then descending to a discharge end of about 10 at a certain number of angles. The screen surface is in the form of a fold line with different inclination angles, and the thickness of the material layer from the feed end to the discharge end is constant. The ratio of material volume to flow rate on each screen surface is stable, the material layer is higher, and the screening efficiency is uniform, which is 1-2 times higher than that of the same effective area screening machine. For high fine content, especially materials The banana vibratory screening machine has a very high screening efficiency when the medium content is larger than the material having a classification size of less than 1/2.
1. Low power consumption, high vibration intensity (9-12mm), high screening efficiency (>95%); 2. The domestic brand patented screen surface configuration is adopted, and the material handling capacity is large; 3, light weight, low working noise, stable operation; 4. The operation and maintenance of the sieve machine is simple, safe to use and cost-effective.
1. Before the sieve is started, all the protective covers should be installed in place and all personnel should be evacuated from the sieve; 2. It is forbidden to start the sieve machine until the various protective covers are not fixed; 3. Do not stand within one meter of the screen machine during the start and stop of the screen machine; 4. When the sieve machine is in operation, do not stand on the vibrating parts; 5. The screen motor must be de-energized and the screen machine stopped before any work can be started on the screen.
Insulation mortar is a kind of ready-mixed dry powder mortar made of various lightweight materials as aggregate, cement as cement, mixed with some modified additives, and stirred by the production enterprise. It is mainly used for thermal insulation of external walls of buildings, and has the advantages of convenient construction and good durability. Insulation sand production line process Insulation sand
The size of the screen of the carbon dewatering screen and the size of the screen hole affect the screening efficiency, which can be customized according to user needs. The working principle of carbon linear vibrating screen The linear vibrating screen uses the vibration motor as the vibration source. When two vibration motors perform synchronous and reverse operation, the excitation
Through years of development and introduction of absorption, the level of coal washing technology and technical equipment has been continuously improved, and the heavy media, jigging, vibrating screen technology and composite dry coal washing technology have developed rapidly, forming a variety of types and series of washing equipment. Coal washing equipment is important equipment for industrial raw materials and energy
Recently, Vietnamese colleagues received good news, and the Vietnam crushed stone production line has made new progress. Now that the Vietnamese production line has officially started production, and it has achieved the desired results, the stone particles produced are highly valued by Vietnamese customers. The installation site of the production line: the production line is still being installed at a
The vibrating screen produced by our company adopts advanced design concepts and finite element analysis and calculation methods, and is equipped with advanced numerical control processing, technology and testing equipment to ensure the quality and performance of the product and the safety of the screen.
The side plates of the screen and the reinforcing ribs (angle steel) are all riveted with HUCK bolts without any welds. This ensures that the side plate has no stress concentration and cracking, improves the strength and rigidity of the side plate, thereby improving the reliability of the equipment.
The vibrating screen exciter beam and the screen frame beam adopt a box-shaped beam structure with reinforcing ribs inside to improve the rigidity and strength of the screen machine and reduce the weight of the whole machine. Thereby improving the efficiency of the whole machine and reducing power consumption.
All the mating surfaces of beams and vibrating screen exciter beams are processed by automatic CNC machine tools before assembly. The non-processed surfaces of all components are sandblasted and painted with epoxy resin. All gaps will be filled with waterproof glue. Make sure it does not rust.
The overall weight of the screen body can be reduced to the greatest extent under the conditions that meet the requirements of all aspects of the vibrating screen. Make the whole vibrating screen have high strength, light weight, large processing capacity, low power consumption, high vibration intensity and high screening efficiency;
The connecting parts of the equipment are assembled with noise reduction technology, so that the noise of the whole screen is low when working, and the noise within 1m from the equipment is less than 80db;
Each vibrating screen is fully assembled before leaving the factory and undergoes an idling test run for 8 hours. The amplitude and frequency are tested with a VB instrument, and the operating curve is drawn with the coordinate method to verify the reliability;
the frequency analyzer is tested for 72 hours During the period, the natural frequency is detected, and the collected data is uploaded to the computer for finite element analysis to ensure that each vibrating screen can achieve efficient and safe production.
The motor is powered on and starts, and the driving force is transmitted to the main drive shaft through the belt drive mechanism and the secondary shaft system. The main drive shaft drives the vibrating screen exciter to generate linear vibration force. The direction of the excitation force is at an angle of 45 to the horizontal. The linear vibration force cyclically acts on the screen body continuously to make the screen body vibrate on the buffer spring. At the same time, the buffer spring reduces the dynamic load of the screen body on the support foundation of the screen machine and reduces the noise of the screen machine. The screen body drives the screen surface to vibrate synchronously. The force is transmitted to the material on the screen, and the impact material is stratified before being thrown up on the screen surface and classified according to the specified particle size. The material is continuously buffered from the feeding chute to the receiving plate, and is screened through the screen surface. The bottom material is discharged into the under-screen chute, and the over-screen material is discharged into the discharge chute.
Two vibrating motors with the same parameters installed symmetrically on the excitation beam rotate synchronously and reversely when connected to electricity, and each generates centrifugal force of equal magnitude. The components of the two forces in the vertical vibration direction are opposite to cancel each other, and the components in the parallel vibration direction are consistent with each other. The linear vibration force is superimposed to form a linear vibration force. The linear vibration force cyclically and continuously acts on the screen body to make the screen body vibrate on the buffer spring. At the same time, the buffer spring reduces the dynamic load of the screen body on the support foundation of the screen machine. The screen body drives the screen surface to vibrate synchronously. , The force is transmitted to the material on the screen, the impact material is thrown up on the screen surface for dehydration, the material is continuously input from the feeding chute, and the dehydration treatment is carried out through the screen surface. Material chute.
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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.
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Vibration sieving machine structure and working principle Henan Pingyuan Mining Machinery is one of the best professional manufacturers in Belt Conveyor, Bucket Elevator, Vibrating Screen, Screw Conveyor and Tripper.The Introduction Company is the production of the screen structure and working principle. Sieving machine with crank and connecting rod mechanism is used as a transmission part. The motor through a belt and a belt wheel drives the eccentric shaft rotation, so that the body along a certain direction through the connecting rod for reciprocating motion. Body movement in a direction perpendicular to the supporting rods or the suspension rod center line, because the body swing motion, so that the screen material in a certain speed to the discharging end of mobile, and screening material. Screening machine structure and working principles of the following categories: ( 1) fixed screen work part fixed on the material, sliding along the working surface and the material sieving. Fixed screen in mineral processing plant a more applicable, are generally used for crushing or breaking prior screening. It has the advantages of simple structure, convenient manufacture. No consumption of power, to unload the ores to the sieve surface. The main disadvantage is the productivity is low, the screening efficiency is low, only 50 - 60%. ( 2) roller screen working face is arranged transversely to the root of a rolling shaft, shaft plates, fine material from the roller or plates through the apertures. Bulk material from the roller belt at one end and discharged from the end of mobile. Ore dressing plant rarely use this sieve. ( 3) cylinder screen work part is cylindrical, the entire screen around the cylinder axis, axis in general under the conditions of small dip into. Material from one end of the cylinder is entered, fine level of material from the cylindrical working surface of the passing, coarse material from the other end of the cylinder is discharged. Cylinder screen rotational speed is very low, stable work, dynamic balance. But the pore blockage, low screening efficiency, small working area, low productivity. Ore dressing plant rarely use it as a screening device. ( 4) plane motion sieve body is a plane of swing or vibration. According to the planar motion trajectory is divided into linear motion, circular motion, elliptical motion and complex motion. Shaking sieve vibration sieve belongs in this category.
Now, Vibrating screens are widely used in industrial sectors such as mining, metallurgy, coal, hydropower, transportation, and chemical sectors to perform a variety of processes. such as screening, grading, washing, decontamination, and dewatering of materials. Mineral processing is an intermediate link in mining and smelting. It efficiency not only directly affects the beneficiation productivity but also has a profound impact on the rational use of national resources.
Although the vibrating screening machine has achieved unprecedented development. The theoretical framework of the vibratory screens has been stabilized and matured in recent years. But the high screening efficiency and large output is a new direction in the development of screening research all the time.
The coal or ore mined at the mining site, or the broken material, needs to be divided into several grades with similar particle size or dehydrated, de-mediated, de-sludged, sometimes several items before the material are used or further processed. And there is. When performing the above work, there is always a problem of grading of the through-holes of the material passing through the screen surface. And the grading of the material through the sieve surface is called sieving.
It is necessary to satisfy the condition that relative motion between the material and the screen surface, in order to smoothly complete the screening process of the material. Therefore, the screen box should have suitable motion characteristics. On the one hand, the material on the screen surface can be loosened; On the other hand, the coarse grain material plugged in the sieve hole will jump aside to the road is smooth.
In the actual production process, the actual screening process is: After a large number of different sizes and coarse and fine mixed materials enter the screen surface. Only a part of the material is in contact with the screen surface. In this part of the material contacting the screen surface, the fine particulate material is not completely smaller than the mesh size. And the remaining fine particulate material which is mostly smaller than the mesh size is distributed throughout the entire layer.
Through the movement of the screen box, the material layer on the screen surface is loosened. So that the existing gap between the large particle materials is further enlarged. And the small particle material is taken through the gap and transferred to the lower layer. At the same time, the bulk material site reaching higher during the movement, because the gap is small between the granular material. So the original disordered material particle group was separated. the layer was stratified according to the particle size. And the arrangement rule of the small particle material under the coarse particle material was formed.
The fine-grained material reaching the sieve surface can be smoothly shifted due to its smaller size than the mesh size. And finally, the separation of the coarse and fine-grained materials is completed, and the screening process is completed. However, sufficient separation cannot be achieved in the sieve. In time-sharing, generally, some of the fine particulate material remains in the coarse particulate material on the sieve and cannot be permeable. The research shows that although the size of the fine particulate material is smaller than the sieve hole, the ease of screening is not the same. Compared with the sieve holes, the smaller the particle size, the easier the sieve is, and the more difficult it is.
A good vibrating screen must be reliable. Minimize wear and maintenance, and have a strong vibration as any vibrating machine that boasts. The more it vibrates the better it goes, that is, it gives more production and efficiency.
On the other hand, most of the bad screens are not really bad but inappropriate to use. If the product is wet and sticky, it will stick to a metal screening element rather than a polyurethane screening element. If it is dry and fine, the screen should be dust-tight. In case it is a matter of screening large and heavy particles, the screen should be very robust. And if it is very robust and used with fine products, it will consume more than necessary in electricity and maintenance costs.
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. Read More
Journal of Vibroengineering, Vol. 21, Issue 1, 2019, p. 28-39. https://doi.org/10.21595/jve.2018.19543 Received 18 December 2017; received in revised form 16 August 2018; accepted 23 August 2018; published 15 February 2019
Li Zhanfu, Li Kunyuan, Ge Xiaole, Tong Xin Performance optimization of banana vibrating screens based on PSO-SVR under DEM simulations. Journal of Vibroengineering, Vol. 21, Issue 1, 2019, p. 28-39. https://doi.org/10.21595/jve.2018.19543
This paper carried out the numerical simulation about the movement of non-spherical particles on banana vibrating screen using direct element method (DEM) considering the complexity of particle collision and avoiding obtaining motion information with difficulty. Experimental prototype of banana vibrating screen under variable parameters was manufactured to verify the feasibility of simulations. Because the complex non-linear mathematical model is the basis of optimization. Based on the simulation data this paper applied the least squares support vector machines (LS-SVM) to establish relationships between vibrating parameters of banana screen and screening performance. LS-SVM based on statistical theory can effectively solve the mapping problem of small sample. At same time, in order to improving the quality of modeling, the kernel parameters of SVM were optimized by particle swarm optimization (PSO). Considering multi-extremum, large-scale, and non-differentiable of this computational model, the artificial fish-swarm algorithm (AFSA) with strong robustness and global convergence was applied to vibration parameters optimization. Finally, the optimal vibration parameters were: vibration amplitude 2.4mm, vibration frequency 21Hz, vibration direction angle 40 degrees.
Sieving is a technique for separating particles of different sizes. It is widely used in many granular media industries such as the construction, mineral separation, medicine and food fields [1-3]. When small particles penetrate the plate under suitable vibration source, other particles run to outlet indicating that the screening process finished. As an important screen machine in industrial screening, banana screens which named by the curved screening plate have better performance and throughput. The curved plate can make the same material layer thickness. With large inclined angle in the feeding end, it is helpful for small particles rapid movement and layering to penetrate sieve mesh. Then with the small particles and the inclined angles gradually decreasing, the time of screening process gets longer, and the thickness of material keeps stable. That makes the lager particles have more opportunities to pass though screening aperture. The research on the design and mechanism of banana screen has gradually attracted the attention of scholars [4-6].
Due to the complex collisions between particle-particle and particle-machine, plenty of time from traditional screen experiment including the statistics of particles motion information and size, DEM has been proved to be an effective method for dealing with granular systems. In 2002, Cleary simulated the separation process of 8000 3D-spherical particles in vibrating screen with inclined plate using DEM . In 2007, Jiao and Zhao studied the penetrate motion of particle with 2D Sieve-DEM developed by VC++.NET . Based on DEM considering the collision property and simulation condition, Liu and Tong analysed the relationships between parameter and screening efficiency . Recent years, on the basis of DEM on screening simulation, the research of banana screen has become a hot spot. K. J. Dong do the deeply investigate in the effect of the equal inclination angle on the sieving performance of three-plate banana screen by DEM  in 2009. In 2013, J.W. Fernandez used SPH-DEM to simulate the movement of moist particles over the plate of banana screen . Liu presented the mathematical study of particle flow on a banana screen deck using DEM . In 2017, Li studied the sieving process of banana screen with the inclinations improved by Fibonacci sequence based on DEM . But due to the lack of the mapping between vibration parameters and screening performance, it is hard to optimize reasonable parameters without the valid mathematic model of banana screen.
Particle morphology is another important impact on the particle micromechanical behavior. Cleary  have carried out three-dimensional simulations about screening process of spherical particles and non-spherical particles. The results showed that screening rate of spherical particles is larger than that of non-spherical particles. Li explored a simple two-dimensional crop seed DEM model, and discussed their effects on screening efficiency, the physical mechanism of separation . Spherical, conical, cylindrical particles respectively in different vibration parameters and structure parameters, transmission speed and screening rate were studied by Frederik and Elskamp . In this paper, non-spherical particles which match sands sphericity and a banana vibrating screen with a curved sieving surface were established by using DEM modeling. In order to study the relationship between vibration parameters and screening performance, Brereton and Dymott based on particle penetrating probability theory of Gaudin established the mathematical model of two-layer thickness screening stage [14, 15]. Chen established a comprehensive screening model about vibration and structure parameters . Li presented A novel application of non-linear regression modeling based on Support Vector Machines (SVMs) is used for mapping the sample space of operating parameters and vibrating screen configuration . In this paper, Simulation data which can be verified by the adjustable parameters are used, and the optimization model of banana is established by using the optimized support vector machine. At last, the overall parameters of banana screen were optimized by intelligent optimization algorithm.
DEM is a means to study the mechanical behavior of granular media systems. A soft ball model considering the surface deformation of particles is used as the basis of contact theory. According to the calculation of the intergranular contact force between the normal and tangential displacement, calculation strength is small which is beneficial to engineering problem. Particles in the initial position (the inlet) with a certain initial velocity under the influence of gravity fell down screening surface. After that the collision occurred between particles.
Using the theory of contact mechanics and elastic mechanics to determine the force and the material displacement, the speeds and positions of all particles in banana screen are constantly updated along with time by applying Newtons second law [18,19]. When the particles movements of whole system stop, that is system balance, iteration process ends. All the particles in the working surface conform to Newton's second law. These equations are:
where mi is particle-I mass; ri is position vector; Fcn,ij and Fct,ij are respectively Normal and tangential contact forces which are caused by intergranular collisions; Fdn,ij and Fdt,ij are respectively normal and tangential damping; g is gravity; Ii is rotational inertia; Tij is the torque generated by rolling friction; Mij is contact torque. After the time step t, the new velocity and location of the granules are obtained:
DEM has been successfully used in non-spherical shaped particles interactions and has provided useful qualitative information of particles [20-22] (Cleary, 2009; Zhu et al., 2008; Elskamp et al., 2015). Gabriel et al. (2013) conducted a multi-sphere pellet model of iron ore to perform DEM simulations in both the slipping and the mill tumbling, and the results showed a good agreement with experiments . In 2006 Cho, G. C.  mentioned that the sphericity of the crushed sand is generally 0.7-0.8, and the sphericity of natural sand is generally 0.5-0.9. The sphericity of the sand model selected in this paper is consistent with the sphericity of the sand.
As can be seen from the Fig. 2 and Fig. 3, the 3D-DEM modeling of banana screen was established to simulate the screening process of non-spherical particles using software-EDEM. Length, width and height of banana screen were arranged as 160 mm, 28 mm and 80 mm. The simplified banana screen model is composed of screen factory, the curved screening surface and screening box. Meanwhile the curved screening plate has 5 decks, and the angle difference of neighboring decks is 5.5 degrees. In addition, the inclination of the third deck was invariably 14degrees when banana surface was in a straight-line oscillation. Vibration parameters including frequency, amplitude and vibration direction angle were mainly set by single factor experiment. The detailed parameters and simulation conditions were listed in Table 1. In order to provide more data to complete the mathematical mapping, orthogonal tests were conducted. Each of the three predominant factors was segmented into four levels whose values were chosen based on the single factor experiment above, which were listed in Table 2. All screening efficiency data were calculated, the mathematical model was established to optimize the parameters and the optimal combination of vibration parameters under the highest screening efficiency in later chapters.
Assessment criteria of screening performance can not only effectively express the quality of screening performance, but also be the foundation of mathematical modeling. We choose as Unit-time Screening Efficiency to stand for screening capacity and screening efficiency:
where is the screening efficiency in unit interval, mS1 and mK1 are the mass of particles whose diameters smaller than the aperture size in the undersized material respectively, mS2 and mK2 are total mass of particles whose diameters smaller than the aperture size respectively. tis the duration of the sieving process.
To verify the reliability of the simulation, the characteristics of experimental prototype are simple structure, short period, easy installation and maintained. Above all many parameters of banana screen such as incline angle, vibrating direction angle and so on can be adjusted and the structure is widely used in bolt fixing type. The vibrating screen was presented in Fig. 4, and Fig.5 showed that the vibrating motor is installed on the mounting rack to provide exciting force. The purpose of adjusting vibration direction angle is achieved through fixing the shaft at one end of the mounting bracket and adjusting the mounting hole at the other end to the different positions. As shown in Fig. 5, the specific scope of the adjustable are: 15, 25, 35, 45, 55, 65, 75 and 85.
In this part, the paper carries out the comparison between physical experiment and simulation experiment. The result was listed in Fig. 7. In order to improve the reliability of contrast as far as possible, the material selected as sands with the shock type-based vibrating screen (Fig. 6) tried to meet size distribution of granules in the EDEM model. Meanwhile the main conditions of physical experiment are as follows: capacity 0.5 ton/h, vibrating amplitude 2.2 mm, vibrating frequency 22 Hz, the aperture 0.7 mm and the diameter of mesh 0.4mm. Under different vibrating direction angles, statistical regularity of Unit-time Screening Efficiency was conducted. But physics experiment and the simulation experiment cannot completely consistent. Because the process of numerical simulation cannot fully meet the conditions of physical experiments, such as the property of particle, the particle size distributions, the complex random particle shape and so on. Unit-time Screening Efficiency has a certain gap in physical experiment and simulation experiment. More important, the effect of vibration direction angle on Unit-time Screening Efficiency is consistent (same crest value and variation tendency). Fig. 7 showed that numerical simulation can reflect the law of screening, and screening mechanism research can be carried out by using DEM-numerical simulation method.
In this paper, the vibration parameters (vibration amplitude, vibration frequency, vibrating direction angle) are the mainly optimized parameters of vibrating screen. In industrial production, with the fixed equipment structure and craft parameters, the vibration parameters (that is operation parameters) are the most direct optimization parameters in production site. The purpose of building mathematical modeling is to optimize the parameters of banana screen. The optimized parameters are effective way to improve screening performance. High-dimension, non-linear and complex mathematical mapping between vibrating parameters and Unit-time screening efficiency was solved by support vector regression (SVR) which can deal with small sample problems and has good generalization ability using the principles of structural risk minimization. Kernel function directly affects the quality of SVR. In this paper, in order to improving the leaning ability and the predicting ability of the SVR modeling, the intelligent algorithm-particle swarm optimization was used to optimize the parameters including penalty parameter C and Kernel function parameter in Radial Basis Function-RBF .
Linear regression which is basis of explaining the nonlinear regression is an important part of SVR . All training data sets xi,yii= 1, 2, 3, n, xiRn, yiR, under the fitting precision , are fit by the linear function as possible f(x)=wx+b. The corresponding function as follow:
At the same time, in order to control the complexity of functions, according to the optimization theory, this paper optimized w2 and minimized the VC dimension to control the expected risk of the whole sample.
Optimal parameters C, in RBF which depends on SVR generalization performance are further complicated due to SVM model complexity. As an intelligent algorithm in computing, PSO algorithm was inspired by the behavior of birds. Each group of particles (similar to birds in nature) in algorithm are the optimization goal of a set of potential solutions, and each group of particles have a N-dimensional search space on behalf of the number of parameters to be optimized in combinations . The fitness of each group of particles can get the corresponding value. Within the search space, particle swarm with a certain flight direction and initial velocity varies with the individual and group flight experience for dynamic adjustment, so as to realize the globe optimization solution.
where x1 is vibrating amplitude, (mm), x2 is vibrating direction angle, (), x3 is vibrating frequency, (HZ)The function relation is difficult to express using a simple function because of its highly nonlinear. The data of DEM solutions were used as input and output sample data listed in Table 3 for training and testing. Of the 44 groups of data, 35 groups were chosen randomly as training data and the remaining 9 groups of data were selected as testing data. The data which were listed in Table 3 consisted of two parts: single factor experiments and orthogonal test. The total sample size meets the need of regression modeling. In this paper the lower limit and upper limit of SVR parameters (C, 2) in PSO optimal process were set in Table 4. At last the optimal results also listed in Table 4.
Fig. 8 shows PSO-SVR ability of learning about simulation data of 35 samples. From Fig.9, we can see that the 9 sets of testing data results obtained by DEM-solution and the predicting outcomes established by PSO-SVR are compared. The two do have errors, but the overall trend and output errors are within acceptable limits. At the same time, two graphs show that the model established by PSO-SVR has good learning ability of samples, and the generalization prediction ability of fresh data is also better. In conclusion, vibration parameters of the sieving banana screen can be optimized by using the model described above.
Computation model is a highly non-linear, multiple maximum and non-differentiable large computational problem. Although the traditional regression algorithms such as Powell method and gradient decent method have their merits, its hard to solve the PSO-SVR modeling which doesnt possess strict mathematical conditions for example differential and continuous. As an intelligence algorithm, Artificial Fish Swarm Algorithm (ASFA) has the advantages of global optimality, robustness and high convergent speed [27, 28]. The algorithm simulates fish foraging, tailgating and clustering behavior, and the local optimization of each fish can achieve global optimization, which has been used to solve various combinatorial optimization problems.
In the actual process of banana vibrating screen, vibration strength needs to keep within the reasonable limit avoiding particles to attach screen and to excessive fly. So, the feasible region range of each design variable is the constraint condition of parameter combination optimization. According to the mathematical model established above, the relationship between parameters and Unit-time Screening Efficiency needs to be optimized and optimization objectives can be expressed as:
Suppose the artificial fish (X=x1, x2, x3,, xn), individual fish xi stands for optimal variables such as vibrating frequency. In this algorithm, Distance Perception suggested scope of individual fish activities; individual fish moving step length value and the other main parameters was listed on Table 5. Fig. 10 presented the flowchart of AFSA-PSO-SVR for optimization.
The change of 20 iterations is shown in Fig. 11. By the whole algorithm of AFSA-PSO-SVR, the optimal combination is as follow: vibration amplitude 2.36018 mm, the optimization results of vibration frequency 20.61352 Hz, vibrating direction angle 40.339 screening efficiency 55.0654 %. The round numbers of combination parameters (amplitude of 2.4 mm, vibration frequency of 21 Hz, vibration direction Angle of 40) were used to simulate the sieving process of banana screen. DEM-solutions result is about Unit-time Screening Efficiency of 56.1 %. The non-parametric model established using the integration of DEM and SVR, combined with ASFA algorithm in subsequent parameter optimization offered insights to the design and manufacture of vibrating banana screens.
1.DEM-solutions which instead of a time-consuming physical experiment can effectively simulate the irregular particles movements considering the collisions and material properties in banana screen. The variation tendency of screening efficiency under the different vibration parameters between simulations and physical experiments is consistent.
2.Mathematical modeling of highly nonlinear screening process is performed using SVR that was optimized by PSO. The mapping which provides the basis for parameter combination demonstrates good learning and generalization ability.
3.Non-differentiable and highly non-linear SVR modeling of banana screen was optimized by AFSA. The optimal combination is as follow: vibration amplitude 2.36018 mm, the optimization results of vibration frequency 20.61 Hz, vibrating direction angle 40.339 screening efficiency 55.07 %.
The authors gratefully acknowledged the support from the Program for scientific and technological innovation flats of Fujian Province (2014H2002). Fujian Natural Science Foundation (2017J01675). Key projects of Fujian provincial youth natural fund (JZ160460). 51st scientific research fund program of Fujian University of Technology (GY-Z160139). No part of this paper has published or submitted elsewhere. The authors declared that they have no conflicts of interest to this work. All authors have seen the manuscript and approved to submit to your journal.
The screens serve to classify the different particles by size, starting from a bulk product in a continuous process. The inlet material (the raw product) advances from the part where the screen is fed to the opposite end in which the particles come out separately according to their size, shape or density. There are also vibrating screens that are loaded by the center and the product moves radially to the outputs that are on the periphery.
For the correct advancement of the product it is necessary that the process is continuous, and it is due to the vibration if the screening surface is horizontal. Most of the screens have a certain inclination in such a way that the advance movement of the product is due to a combination between gravity and vibration.
The screening elements are flat or slightly curved surfaces having perforations of a certain size such that when a product is poured in bulk on the element it only passes those particles whose size is smaller than the size of the perforations.
The screening elements can be a metallic or nylon wire mesh, bars that pass material between them, metal sheet with circular, square or hexagonal perforations, more or less rigid sheets of rubber or polyurethane with perforations.
A screen can have several screening elements on top of each other forming different floors. In this case, the floor with the larger perforations is placed in the upper part and successively in lower floors the elements with smaller and smaller perforations are mounted. In this way each particle is trapped between the floor that has cut points (openings) greater than the particle and the floor that has smaller cut points.
Traditionally there have been non-vibrating screens consisting of a fixed mesh with a lot of inclination. When introducing the vibration, the product shakes and the particles jump without sliding on the screening surface. Each jump is an attempt of the particle to pass through a hole and the probability of this happening is much greater if the machine vibrates. In other words, the effectiveness is much greater.
When a particle jumps and falls again it can do so in a hole or an area where there is no hole. If the screening element is a wire mesh, the particle can fall on the wire or on another particle and not squeeze through the hole it should. This is why no screen has an efficiency of 100% because it would require an infinite number of jumps so that all the smaller particles that the holes actually leak.
The more quantity of product you intend to classify, the more surface you need for screening. The most immediate symptom that a screen has become too small is that it decreases its effectiveness because it simply does not fit so many particles through the holes.
As a general rule for large classifications, low frequencies and large vibration amplitudes are preferable and for fine classifications high frequencies and small amplitudes. In other words, if the particle is large, a slow and wide movement is better in which the particle gives few jumps but large and if it is small it is better than many jumps but smaller. It is a question of the particle not passing several single jump holes.
In the screens, as in any sorting machine, it is necessary to take advantage of the entire width of the work surface from the beginning of it. If the product falls piled on the screening surface, the particles of the top of the pile will not touch the mesh or the screening element until the pile disappears by the vibration. By the time this happens, it will already have traveled half way of the surface. In other words, we waste surface with a very important loss of production and also the area where the pile is made will receive severe wear with the consequent extra maintenance expenses. It also increases, especially with products of low density, the risk of jams if the pile takes a lot of height. This makes no sense and it is not acceptable for correct screening.
A good vibrating screen must be reliable, minimize wear and maintenance and have a strong vibration as any vibrating machine that boasts: the more it vibrates the better it goes, that is, it gives more production and efficiency.
On the other hand, most of the bad screens are not really bad but inappropriate to use: If the product is wet and sticky, it will stick to a metal screening element rather than a polyurethane screening element. If it is dry and fine, the screen should be dust-tight. If it is a matter of screening large and heavy particles, the screen should be very robust. If it is very robust and used with fine products, it will consume more than necessary in electricity and maintenance costs (but that shouldnt pose as a problem because business energy suppliers can be compared at Utility Saving Expert).
The combinations are endless, and a good selection, suitable for use at first, will make the user does not have to remember this machine again in life, or at least until he needs to install another screen.
A new concept of banana vibrating screen which has the same effect as traditional banana vibrating screen in a new way was put forward. The dynamic model of vibrating screen was established and its working principle was analyzed when the action line of the exciting force did not act through the centroid of screen box. Moreover, the dynamic differential equations of centroid and screen surface were obtained. The motions of centroid and screen surface were simulated with actual parameters of the design example in Matlab/Simulink. The results show that not only the amplitude has a significant decrease from 9.38 to 4.10 mm, but also the throwing index and vibrating direction angle have a significant decrease from 10.49 to 4.59, and from 58.10 to 33.29, respectively, along the screen surface, which indicates that motion characteristics of vibrating screen are consistent with those of traditional banana vibrating screen only by means of a single angle of screen surface. Whats more, such banana vibrating screen of variable linear trajectory with greater processing capacity could be obtained by adjusting the relative position of force center and the centroid of screen box properly.
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HE Xiao-mei, LIU Chu-sheng, ZHANG Cheng-yong. Optimal design of large vibrating screen based on multiple frequencies constraints and analytical sensitivity methods [J]. Journal of Central South University: Science and Technology, 2011, 42(3): 664670. (in Chinese)
ZHAO Yue-min, LIU Chu-sheng, HE Xiao-mei, ZHANG Cheng-yong, WANG Yi-bin, REN Zi-ting. Dynamic design theory and application of large vibrating screen [J]. Procedia Earth and Planetary Science, 2009, 1(1): 776784.
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Foundation item: Projects(50574091, 50774084) supported by the National Natural Science Foundation of China; Project(50921001) supported by the Innovative Research Group Science Foundation, China; Project supported by Jiangsu Scientific Researching Fund Project (333 Project), China
Liu, Cs., Zhang, Sm., Zhou, Hp. et al. Dynamic analysis and simulation of four-axis forced synchronizing banana vibrating screen of variable linear trajectory. J. Cent. South Univ. Technol. 19, 15301536 (2012). https://doi.org/10.1007/s11771-012-1172-5Get in Touch with Mechanic