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.
large vibrating screen design & maintenance
Large vibrating screens represent a unique challenge for Manufacturers, Plant Designers, and Plant Operators. The inherent mode of operation for vibrating screens is self-destructive. More often than Manufacturers admit, Designers plan for, or Operators staff for, a vibrating screen succeeds and self-destructs. This is a problem. It can magnify with larger vibrating screens.
Vibrating screen structures are subjected to nearly 250 million fatigue cycles in an operating year. The design and construction of these structures are critical in achieving reliable screen performance. Regardless of screen size, the maxims for design continue to be:
A screen design meeting these criteria yields the lowest cost per ton performance. Large screen technology is evolving more scientifically than did the development of small screen technology. As vibrating screen designs increase beyond six foot widths, reliable designs result from sophisticated engineering methods and manufacturing techniques. In addition, large screen technology amplifies the direct relationship of production cost and reliability.
Static Stresses: At rest, motionless, a vibrating screen structure is subjected to the force of gravity, at a minimum. A vibrating screen must first support its own weight. Other motionless stresses are present in the structure as a result of cutting, bending, welding, burning, drilling, assembly, tolerancing, and manufacturing variances. Quite simply, these stresses exist whether or not the screen is operating.
The second step in FEA can be considered the construction of structural loads. These include the imposition of static, dynamic, material, and fatigue conditions on the mathematical model, which approximates the load conditions. An example would be to describe a structural misalignment and the forces input co bolt up this structure through the misalignment.
Reliable vibrating screen designs are dependent upon the proper marriage of a firms manufacturing capabilities and the requirements of the design. It is not reasonable to expect that closely toleranced airframes will be successfully produced in a metal-bending job shop. As design safety factors narrow on larger screens, manufacturing techniques evolve which minimize production variables. Design tolerancing is necessarily compatible with manufacturing accuracy.
Residual metal working stress is the left-over stress in metal when melted or formed into a shape. It is a result of a materials resistance to change shape. Stress concentration sites are more commonly termed notches or stress risers. These areas are not stresses, but sharp geometric transitions or reversals in a structure. Stress loads focus their effect on a structure at these sites. Experience has proven that the methods and procedures of structural assembly can result in preloading screen bodies with excessive static stresses. The scope of this discussion is limited to the discussion of welding, forming, and bolting as they relate to conditions described above.
The side plate of a vibrating screen literally bristles with fasteners. Multi-shift production facilities, as well as maintenance crews, quickly realize the merits of this system. Unlike conventional threaded fasteners, swaged bolts exhibit a distinctly different physical appearance when installed versus loosely installed. The guess-work and wasted efforts to repeatedly insure all bolts are properly torqued are eliminated. A second-shift assembler need not consult with his first-shift counter-part regarding loose or torqued bolts . Sound maintenance practice precludes the reuse of major structural fasteners. A huck-type fastener is destroyed during removal. Normal threaded fasteners depend on proper installation torques to achieve the optimum clamping force. Registered torque wrench values may not be indicative of the true values due to the effects of thread lubrication and frictional force of the fastener face on the bolting surface. Swaged fasteners are installed strictly in tension at an optimum preset tensile load. The positive clamping values are reliably consistent. Installation error is minimal. Replaceable, non-structural components may be installed with conventional fasteners.
Anticipated operating and maintenance costs over the productive life of a processing plant design significantly influence the go or no-go decision to build the plant. Large vibrating screens can both add to and reduce the magnitude of these costs. Plant designers must examine the serviceability of these large units. This includes the complexity of installation, start-up, routine maintenance, major repairs, and operating instrumentation. In assessing these costs, the likely condition exists somewhere between the extreme of a screen leaping momentarily out of position long enough to repair itself and swarms of mechanics covering the unit like bees on honey over several production-robbing shifts.
As larger vibrating screens are used, their size will exceed cost-effective shipping limits fully assembled. Screen manufacturers will join the ranks of other major equipment suppliers in on-site assembly and testing of these units. The incremental costs associated with these efforts must be considered in evaluating the plant construction and start-up costs.
The use of larger vibrating screens results in the dependence of a larger percentage of total plant production on each unit. It is imperative that plant operators maximize the production availability of large screens. This effort is enhanced by carefully planned operating and maintenance procedures. Since volumes have been published on efficient and successful preventative maintenance programs, this discussion will not deal with that topic. There are several suggestions that can be made to help potential big screen users better position themselves to react to the service requirements of these units.
As trite as it sounds, talk to potential screen suppliers specifically about the service requirements of their screens. Determine how recently a manufacturer has entered the wide screen market. Was this entry preceded by years of research and testing? There are generally two major shortfalls in a hastily planned new product introduction. Invariably, replacement parts availability is a problem. Second is the frustrating response to a frantic maintenance question, The only guy who knows that unit is on an island in Indonesia. Solidly planned programs will have organizational depth.
The labor pains, which have normally accompanied the birth of new vibrating screen designs, have been no less severe with the gradual introduction of large, high-capacity screens. More difficulty would have been encountered without the aid of advanced engineering and manufacturing techniques.
The development of vibrating screens over the last century has seen many variations to suit the exacting requirements of industry. Indeed, as each year passes, industry has presented the challenge to screen manufacturers of supplying larger machines than those used in the past and the question is often posed what is the maximum limit?
Innovations introduced such as bouncing ball decks, heated decks, tri-sloped and bi-sloped decks and pool washing features have all sought to achieve improved anti-blinding results and improved capacity for a given screening efficiency. Although the benefits achieved by the inclusion of these features were shown in some cases to be beneficial, the application of good throw in conjunction with the required G force in the operation of the screen has proven in screen performance today, to provide maximum screening efficiency and capacity. The importance of good throw is often overlooked and should be the first consideration when wishing to maximize screen capacity.
For a straight line motion screen the throw is the distance between the extremities of motion. For a circular motion screen, the throw is measured across the diameter of motion but if the screen has an oval motion, throw is measured by taking the mean of the major and minor axes.
The throw which is specified for a particular application is determined on a screen body eccentric weight basis and normally does not take into allowance the load of material which will be handled by the vibrating screen.
Therefore it is imperative that the live weight of the vibrating screen is sufficient to maintain, within reason, the throw which has been originally specified so as to effectively handle the loads being fed to the screen.
The above comments relate essentially to a dry screening application but in wet applications where metalliferous pulp is received on the screen, the benefits of a large throw in terms of increased screen capacity have been demonstrated in commercial practice. The ideal machine for receiving pulp for wet screening or desliming, dewatering etc. is a horizontal screen. Among other reasons, the horizontal screen provides the benefit of long retention time for handling the pulp. Also the straight line motion provided with good throw imparts a positive breaking of surface tension present between the pulp and the screen deck within the apertures.
The inclusion of large vibrating screens in the design of new plants by planning engineers and metallurgists responsible for such work, particularly where large associated equipment is available, is inevitable and is in fact a progression of size we have witnessed over the years.
We should remind ourselves that size progression could not proceed without the accumulation of experience in screen body design, in application knowledge, improved quality of manufacture and refinements of mechanism design with regard to achieving improved bearing life which allows the use of a good G force.
As referenced previously G force and throw are interrelated and therefore with the good G forces available today in the modern vibrating screens, the way is clear to taking full opportunity of increasing throw to handle the high tonnages which can be expected and are currently experienced on large vibrating screens.
Where abrasion of the screen deck surface is severe as in most metalliferous mining applications, and the separation sizes are in the order of mm to 50 mm aperture sizes, polyurethane screen panels are now in common use because of their excellent resistance to wear. The trend in the use of polyurethane panels in the metalliferous mining industry is quite definite and in fact in the major mining operations in Australia at least, the use of polyurethane screening panels is firmly established.
With reference to metalliferous tailings the need for dewatering presents a new dimension. The amount of tailings produced is very much greater since some 98-99% of mined ore is rejected in tailings form compared with varying amount of 3 to 5% rejected in a coal washing operation. Furthermore with dewatering of metalliferous tailings, using equipment as mostly used in coal washing would present maintenance problems because of the more abrasive nature of the tailings and therefore for that reason it is customary to discharge all metalliferous tailings slurry to a dam.
The screen-cyclone system relies on the blinding tendency of the screen deck apertures for its success, using either stainless steel wedgewire or polyurethane deck panels in conjunction with the use of cross dams spaced every 120 cm along the deck surface. When considering the screen-cyclone system it is important to appreciate that the screen function is not one of separation at a given aperture size but bleeding of water through the restricted deck apertures caused by the semi blinding condition. That is, if the deck apertures were to remain completely free of blinding, which is not the case, practically all of the tailings would pass through the apertures in the first pass and would not allow the system to function.
The underflow from the primary cyclones should be deposited on the horizontal section of the screen deck at the feed end where the maximum of water should be removed with the assistance of an additional section of wedgewire located on a 45 inclined back plate to remove free water that has accumulated on top of the bed of slurry most solids having stratified to the deck surface. The underflow should be evenly distributed across the width of the screen at minimum velocity, so as to allow the full benefit of stratification provided by the screen.
The actual results from the initial test run taken on the pilot plant installed at Philex Mining Corporation, Philippines in March, 1980 are as follows using a gravitated flow of tailing slurry from the concentrator.
The problems involved in installing, maintaining, and operating large vibrating screens have been summarized and discussed, based on a survey of current use of such screens in selected North American mineral processing applications. Practical, effective solutions for the more serious common problems are described, along with some recommendations on design practice for specifying, selecting, and installing large screens.
In order to properly assess the information gathered through the survey questionnaire, the results pertaining to each group of applications will be presented and discussed separately in the following section. The small number of installations actually surveyed makes any rigorous statistical interpretation of the data difficult, therefore the information is presented in a generalized fashion. Notwithstanding the small sample of operations as compared to the total number of such large screen installations around the world, the results are felt to fairly represent typical operating, maintenance and installation problems and practices in the sectors of the mineral processing industry the survey covered.
The results reported in this section refer to inclined vibrating screens used in conventional crushing and screening plants. Four operations replied to the survey questionnaire, all four are medium sized producers, primarily of copper concentrate, some with significant by-product production of Mo or Ag. Daily throughputs range from 5,300 tons to 38,000 tons.
The major problem areas reported by the users of these screens were bearing failure and replacement and side plate cracking. The minor problems reported were loose bolts, seals and routine wear items such as cloth and liner changes. Reported availability of the screens ranged from 92-96%. At one operation, the crushing and screening plant is oversized and operates only one shift per day, therefore downtime for maintenance is readily available and actual availability was not reported.
The maintenance of large vibrating screens in conventional crushing applications would normally consist of the regular replacement of wear parts, such as liners and screen cloths, as well as regular lubrication of the bearings and other moving parts as recommended by the manufacturer of the particular screens in use.
The operations with large horizontal vibrating screen installations replying to the survey questionnaire were Syncrude Canada Ltd., Climax Molybdenun (Henderson Operations), Quintana Minerals and Fording Coal Ltd. As previously noted, the screen applications at these operations are all basically very similar, involving wet screening of relatively large tonnages of slurry feed.
The major problem areas with these screen installations once again include bearing failure and side plate cracking in three out of the four installations. The fourth installation, Henderson, reported major problems with the mounting springs and feed lip both of which have presently been rectified to the point where only minimal unscheduled downtime occurs.
The major problems associated with the horizontal screens were with bearings and side plate cracking, and were evident soon after commissioning. Major efforts were undertaken at all the operations to correct the serious problems.
Large vibrating screens are normally selected for applications where multiple screens would be more costly to purchase and install. There have been a considerable number of large screen installations in a variety of mineral processing applications, therefore a considerable amount of operating data with respect to the screen components and performance has been gathered. From the plant designers viewpoint the design of a screen installation should consider the following areas:
The design of a large vibrating screen installation requires close attention to not only the screen itself, but also to the ancillary structures, maintenance procedures and personnel comfort and protection.
Large vibrating screens represent a considerable investment in equipment alone. In addition the loss due to interrupted production should one of these units go out of service can be economically much more severe. As plant tonnages have risen and larger equipment has been utilized in single trains or a small number of multiple trains, the risk of having a single large screen down for any length of time has become too great to ignore.
dewatering vibrating screen henan victory machinery co., ltd
Dewatering screen is mainly used for dewatering, desliming and demineralization. It can be used for washing sand in sand and stone plant, recovering slime in coal preparation plant, dry discharging of tailings in ore dressing plant, etc. Therefore, it is also called sand dewatering screen, mining dewatering screen, slime dewatering screen, tailings dewatering screen, high frequency dewatering screen, etc. Although they belong to the same dewatering equipment, the structure of the dewatering screen is different when it acts on different materials, such as the sand dewatering screen on the water washing sand production line and the tailings dewatering screen commonly used in the concentrator. The vibrating dewatering screen is mainly used in the wet sand production line, which can be used with the sand washing machine or alone.
Why should they be used together? We should know that the sand washed by the sand washing machine is not very clean in fact. The sand not only contains a certain amount of mud and is too wet (with large water content), but also does not meet the production needs of low standard and high standard of sand mud content. Therefore, it is necessary to configure a vibrating dewatering screen for dewatering and desliming! After the sand is cleaned by the sand washing machine, the desliming and dehydration screening treatment of the dehydration screen can achieve a reasonable particle size ratio and reduce the mud content to less than 0.7%.
The dewatering screen can also be used alone when it acts on some materials with low mud content, without the need of a sand washing machine, such as quartz sand. Because of the low mud content of quartz sand, washing sand with water by sand washing machine not only consumes energy but also has poor effect. More importantly, the investment cost of dewatering screen is lower than that of sand washing machine.
The dewatering screen adopts double motor self synchronization technology, universal eccentric block and adjustable amplitude vibrator. It is mainly composed of screen box, exciter, supporting system and motor. Two unrelated vibrators operate synchronously and reversely. The centrifugal force generated by two groups of eccentric mass is superposed along the component force in the direction of vibration, and the reverse centrifugal force is counteracted, thus forming a single exciting vibration along the direction of vibration, making the screen box move in a reciprocating straight line. Through the exciting force provided by the vibrating motor to the screen machine, the material can jump on the screen surface in a straight line, so as to achieve the purpose of dehydration, classification, demineralization and desliming of the material.
1. The material of dehydrating screen is high polymer polyurethane (UHMW - PE), with hardness of 95 and opening rate of 100%. It has the characteristics of impact resistance, low temperature resistance, wear resistance, chemical corrosion resistance, self lubrication and impact energy absorption, with long service life.
2. The vibration motor of the dewatering screen is easy to replace, and the rubber spring of the base is used for shock absorption, so that the vibration amplitude is small and the vibration is slow, and can be removed cleanly. The screen frame is made of special material, laser cutting for the whole plate, laser cutting for screw hole, no welding, high precision.
3. The dewatering screen can be customized according to the output and water content. The side plate of the machine body has a reinforcing plate, the bottom is equipped with a support, the bottom is equipped with a horizontal bar, and the outlet is supported by a triangular steel plate, which is thick.
4. The equipment adopts high-strength torsional shear type fastening bolts. The high-strength torsional shear type bolt is initially screwed, and the connection of each component is closely coordinated, so as to reach the design standard strength.
5. The motor beam is made of special material with 24-26mm steel plate thickness, which can effectively eliminate the stress and has the characteristics of strong durability, good support performance, large bearing capacity and strong stability.
We provide sand making solutions all over the world. With over 20 years of experience well ensure that youre always getting the best results from Henan Victory Machinery Co., Ltd. focused on quality.
basic concepts of vibrating screens: what they are, what they are for and how they work. - rollier
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.
vibrating screen types & working principle [how to choose] | m&c
According to different structure and use, vibrating screens usually be devided into many types by the vibrating screen manufacturers. Below wil introduce the top 10 vibrating screens, and how to choose the right vibratory screen?
linear vibrating screen is driven by double vibrating motors. When the two vibrating motors are rotating synchronously and reversely, the excitation force generated by the eccentric block offsets each other in the direction parallel to the axis of the motor, and overlaps into a resultant force in the direction perpendicular to the axis of the motor, so the motion track of the linear vibrating screen machine is a straight line.
Working Principle:The two motor axes of the linear vibrating screen have an angle of inclination in the vertical direction relative to the screen panel. Under the combined force of the exciting force and the self gravity of the material, the material is thrown on the screen surface to jump or move forward in a straight line. Through the multi-layer screen panels, a variety of specifications of materials are generated, and discharged from their respective outlets, so as to achieve screening and classification. linear vibrating screen is suitable for screening various dry powder or granular materials with particle size of 0.074-5mm, moisture content <7%, and no viscosity. The feed particle size is not more than 10 mm.
Circular vibrating screen is a new type of vibrating screen with multi-layer screen and high efficiency. According to the type of materials and the requirements of users, the high manganese steel woven screen, punched screen plate and rubber screen plate can be used. The circular vibrating screen is installed in the seat type. The adjustment of the screen surface angle can be realized by changing the position and height of the spring support.
Working Principle: The motion track of the screen box of the circular vibrating screen is circular. The circular vibrating screen uses the inertia exciter to produce vibration. The main shaft fixed on the screen box is driven by the motor to rotate at high speed, and the eccentric body installed on the main shaft rotates with it, generating centrifugal inertia force, so that the screen box that can freely vibrate will produce vibration similar to the circular track.
Circular vibrating screen is widely used in the materials classification of mining, building materials, transportation, energy, chemical industry and other industries because of its long flowing line and many screening specifications.
Elliptical vibrating screen is a vibrating screen with elliptical motion track (Elliptical Shale Shaker), which has the advantages of high efficiency, high screening accuracy and wide range of application. Compared with the ordinary sieve machine of the same specification, it has larger processing capacity and higher screening efficiency.
Triaxial elliptical vibrating screen is widely used for the screening operation of sand and stone materials in sand plant. It is the ideal screening equipment for all kinds of mines, quarries and mobile screening stations.
Working Principle: The power is transmitted from the motor to the main shaft of the exciter and the gear vibrator (speed ratio is 1) through the V-belt, so that the three shafts can rotate at the same speed and generate the exciting force. The exciter is connected with the high-strength bolts of the screen box, resulting in elliptical movement.
Materials on the screens do high-speed elliptical movement along with the screen machine, so as to achieve uickly separate, sift and move forward, and ultimately complete the classification of materials.
The working surface of the roller screen is composed of a series of rolling shafts that arranged horizontally, on which there are many screen plates. When working, the fine material passes through the gap between the roller or screen plate, large blocks of materials are driven by rollers, moving to the ends and discharging from the outlets. Roller screens are mostly used in the traditional coal industry.
Working Principle: For the rolling shafts are arranged according to different working angles, the speed of the material is faster when it runs in the position with higher working angle; the speed of the material is slower when it runs in the position with lower working angle.
When two kinds of materials running at different speeds converge at a certain position on the screen surface, they start to move axially, so that the materials are evenly distributed on the screen surface, and the screening efficiency is improved.
Rotary vibrating screen is mainly used for the classification of materials with high screening efficiency and fine screening accuracy. Fully closed structure, no flying powder, no leakage of liquid, no blocking of mesh, automatic discharge, no material storage in the machine, no dead angle of grid structure, increased screen area.
Any particle, powder and mucus can be screened within a certain range. Sieve to 500 mesh or 0.028mm, filter to 5 microns minimum. It can be used for classification, classification and filtration in food, chemical, metal, mining and other industries.
With the help of the heavy hammer installed at the upper and lower ends of the motor shaft, the rotary motion of the motor is transformed into a horizontal, vertical and inclined three-dimensional motion, which is then transmitted to the screen surface to make the material do an outward involute motion on the screen surface. Working Principle: After the rotary screen is started, the eccentric blocks of different phases at the upper and lower ends of the vibrating motor generate a composite inertia force, which forces the vibrating body of the rotary screen machine to rotate again and again, and the screen frame continuously moves to and fro under the action of the vibration force, and then drives the screen surface to vibrate periodically, so that the materials on the screen surface move in a positive and directional manner together with the screen box. Materials smaller than the screen meshes fall to the lower layer, and the materials larger than the screen meshes discharged from the discharge port.
High frequency vibrating screen is also called high frequency screen for short. High frequency vibrating screen (high frequency screen) is composed of exciter, pulp distributor, screen frame, supporting, suspension spring and screen, etc. High frequency vibrating screen is the most important screening machine in mineral processing industry, which is suitable for completely wet or dry raw materials.
Working Principle: Different from ordinary screening equipments, high frequency screen adopts high frequency, which destroys the tension on the pulp surface and makes the fine materials vibrate at high speed on the screen, accelerates the separation of useful minerals with large density (specific gravity), and increases the probability of contact between the materials with smaller than the separated particle size and the screen holes.
As a result, high frequency screen results in a better separation conditions, which makes the materials that smaller than the separation size (especially with larger specific gravity), and pulp pass through the screen holes together to complete the screening. High-frequency vibrating screen is usually operated at an inclined angle 0-25, up to 45, and the operating frequency range is 1500-7200r/m.
Grizzly screen has simple and solid structure, no power consumption, no moving parts, low equipment cost and convenient maintenance, but the productivity is low, the screening efficiency is not high, generally 50% 60%, and the mesh is easy to be blocked.
Working Principle: Generally, the grizzly screen is placed in an inclined position, and the materials are dumped at the high end. Under the action of its own weight, it slides down the screen surface, and the particles smaller than the gap or hole on the screen surface pass through the screen to achieve classification.
Banana screen is mainly suitable for the classification of large and medium-sized materials with high content of fine particles, and it can also be used for dehydration, demineralization and desliming.
Working Principle: During operation, the motor is connected with the vibration exciter through the V-belt or soft connection. The motor drives the eccentric shaft to rotate to generate centrifugal inertia force, which forces the screen box to vibrate. After the materials fall into the screen from the feeding inlet, they move forward rapidly under the action of the vibration force, loosely and pass through the screen.The thickness of the material layer of banana screen from the feeding inlet to the discharging outlet is constant. The ratio of the material quantity to the flow speed on the screen of each section is stable, the material layer is high and uniform. The screening efficiency of banana screen is higher, which is 1-2 times higher than that of other screening machines with the same effective area.
Heavy inclined screen can be applied to the treatment of debris from quarry, mine and building demolition, the treatment of topsoil, the recycling of construction materials, the screening of gravel, and the screening of gravel and aggregates.
Working Principle: The screen box shaft is driven by the motor installed on the auxiliary frame through three V-belts, the auxiliary frame is rigidly connected with the machine underframe, and the screen box spring is used to support the screen box.Inclined screen usually adopts 2-4-layer screen panels, and is fixed on the inclined frame at an angle between 15 and 30. The material can be screened into 3-5 grades at the same time.
Horizontal screen has the advantages of both inclined screen and linear vibrating screen. horizontal screen has the features of good screen permeability, large processing capacity and small installation height.
The installation angle of common vibrating screen is 15-30, while the installation of horizontal screen is parallel to the ground, or slightly inclined 0-5. Horizontal screen is an ideal equipment for all kinds of mines, quarries and mobile screening stations.
Working Principle: Horizontal screen is designed with oval stroke. The advantage of this design is that it can change the oval big diameter length and angle of throwing material stroke to meet the best needs of vibrating screen. The oval stroke is easy to adjust by center gear, counterweight wheel and motor speed.
Different types of vibrating screens can be used for the same material to get different screening effects. The reasonable selection of vibrating screen is an effective way to improve vibration efficiency and maximize economic benefits. Generally, you need to consider the following 5 tips:
When choosing vibratory screen, the material characteristics should be taken into account, including the content of material particles under the screen, the content of difficult screen particles, material moisture, the shape and specific gravity of the material, and the content of clay.
Tips: Heavy vibrating screen is used for materials above 200mm; circular vibrating screen is used for materials above 10mm; linear vibrating screen and high frequency vibrating screen are used for desliming, dewatering and grading.
When selecting the vibratory screen, the screen areas, layer numbers, shape, size and area ratio of the screen holes, as well as the motion mode, vibration frequency and amplitude of the vibrating screen should also be considered.
Tips: In order to keep the screens under good working conditions, the ratio of screen length to width should be in the range of 2-3; when there is much viscous mud and high moisture in the material, double deck screens should be avoided as far as possible.
Vibratory screens need to be selected according to different screening purposes. If it is necessary to pre screen materials, circular vibrating screens are generally used; for the classification and screening of crushed materials, large vibrating screens and probability screens are selected; for the deionization and dehydration of materials, linear vibrating screens are better; if it is necessary to desliminate and clean up materials, probability screens are used.
When selecting the shale shakers, it also needs to be considered according to the processing capacity of the production line, screening method, screening efficiency and the tilt angle of the shale shakers.
Professional vibrating screen manufacturers could provide competitive vibrating screen price, diversity customized vibrating screen models, timely after-sales service, spare parts and can continue to provide services for customers whole production circle.
5 vibrating screen common problems and how to solve? | m&c
There are many kinds of vibration screens, such as electromagnetic vibration screens, circular vibration screens, linear vibration screens, etc. The latter two belong to inertial vibration screens, which are commonly referred to as vibration screens. In daily production, vibration screen will encounter a variety of problems, such as poor screening quality, bearing overheating, abnormal sound, wrong technical indicators and so on.
Table of Contents 1. Poor screening quality1) Screen hole blockage2) serious wear of screen hole3) Non-uniform feeding of sieve4) too thick material on screen5) insufficient inclination of screen surface6) The motion direction of eccentric block is not in the same phase2. Bearing overheating1) too small radial clearance of bearing2) too tight top of bearing cover3) Bearing oil shortage or excessive, oil pollution or inconsistency3. Abnormal sound when the sieve is running1) Spring damage2) Bearing wear3) Bolt loosening of fixed bearings4) Untightened screen4. Technical indicators do not meet the requirements1) The sieve cannot start or its amplitude is too small.2) Insufficient rotational speed of sieve3) The Vibration Force of the Screen is Weak4) The amplitude of four points of the sieve is inconsistent5. Severe or damaged parts of sieve1) Pipe Beam Fracture2) Beam fracture3) Fracture of screen frame
There are many factors affecting the screening effect, including the nature of feeding, equipment factors, operation factors and so on. The reasons for poor screening quality include blocking of sieve hole, serious wear of sieve hole, uneven feeding of sieve, too thick material on sieve and insufficient inclination of sieve surface.
When the mud content and water content in the feed are high, the material will stick to the sieve hole and block the sieve hole. At this time, the sieve hole should be cleaned first, and then the spray amount and the inclination angle of the sieve surface should be adjusted appropriately.
When the screen is used for a long time, the wear of the screen hole will be serious and the screening effect will be seriously affected. At this time, the wear screen hole should be repaired. When the wear situation is very serious, the replacement of screen mesh should be considered.
When the feeding trough of the sieve is too narrow, the material can not be uniformly distributed along the whole sieve surface, which makes the sieve surface inefficient to use, and will affect the screening effect. At this time, the width of feeding trough should be adjusted to make the feeding of sieve uniform.
The excessive thickness of material on screen may be caused by the increase of feeding quantity, blocking of screen hole and small inclination angle of screen surface. At this time, it should be adjusted according to the specific situation.
For the circular vibrating screen, the most common reason for the poor screening effect is the inadequate inclination of the screen surface, so it is necessary to pad the back support. In practical application, the inclination angle of screen surface is more suitable when it is 20 degrees. The inclination angle of circular vibrating screen is generally 16-20 degrees. If the inclination angle is lower than 16 degrees, the phenomenon that the material on the screen is not moving smoothly or rolling upward will occur.
For linear vibrating screen and high frequency vibrating screen, the poor screening quality may be related to the movement direction of eccentric block, because two groups of eccentric blocks with the same mass need to rotate in self-synchronization and reverse direction to produce a single exciting force along the vibration direction at each instant, which has a fixed angle with the horizontal direction, so that the screen box can move in a reciprocating straight line. If not in the same phase, the direction of excitation force and direction of vibration will not overlap, and the effect of efficient screening will not be achieved.
Because the bearing on the vibrating screen bears a large load, a high frequency, and the load is always changing, the bearing must adopt a large clearance. If the bearing with ordinary clearance is used, the outer ring of the bearing must be grinded again to make it a large clearance.
There must be a clearance between the cover and the outer ring of the bearing to ensure the normal heat dissipation and certain axial movement of the bearing. The clearance can be adjusted by a gasket between the end cap and the bearing seat.
The technical indicators of the operation of the sieve include the rotational speed, vibration force, amplitude and frequency of the sieve, etc. Common fault types are: the screen can not start or the amplitude is too small, the speed is not enough, the vibration force is weak, the four-point amplitude is inconsistent, and so on.
When the vibration screen can not start or the amplitude is too small, the first consideration should be whether there is an electrical fault. Damage of motor and insufficient voltage can lead to faults. When there are no problems in the above aspects, we should start with the mechanical aspects. Whether the material on the screen surface is heavily accumulated or not, if so, it should be removed in time; whether the bolts on the coupling of the exciter fall off or not, whether the grease is caked; if so, the bolts should be tightened in time and the grease should be replaced.
Insufficient rotational speed may be the electrical reason. At this time, we should find out the reason and deal with it in time. It may also be that the transmission tape is too loose. At this time, we should tighten the transmission tape.
The inconsistency of four-point amplitude of sieve may be caused by the asynchronism of two exciters on the same axis or material segregation. At this time, adjustments should be made to make the two exciters work synchronously and eliminate material segregation in time.
(a) The thin wall of pipe girder may lead to fracture. At this time, the same type of thick wall pipe or the first type of pipe girder should be selected, but it should not be too large or too thick, because this will increase the vibration quality of the sieve and bring many problems;
B) There must be horizontal and vertical pressure strips at the joints of the sieve plates of dehydration and de-mediation screens. If there is no longitudinal pressure strip, water will leak from the gap between the sieve screens and wash down the pipe girders, which are easy to break at the scouring point.
D) If the fracture of the pipe beam is not serious, in order not to affect production, the pipe beam can be repaired to continue to use. When repairing, the weld should be along the longitudinal direction of the pipe beam, and no transverse weld must be allowed, otherwise the pipe beam is more likely to fracture from the transverse weld.
Cross beam fracture is mostly due to the long working time at critical frequency, a large number of high-strength bolts to tighten the side plate are relaxed, serious deformation of the spring makes a great difference between left and right, or it may be that the weight error of eccentric block is too large, causing structural damage and cross beam fracture. At this time, the damaged structural parts and beams should be replaced, bolts should be tightened, and the quality of eccentric blocks should be adjusted.
The sieve frame is liable to break because of tremor. The best way to solve this problem is to thicken the side plate or add additional plate to the local area of the side plate near the exciter to enhance the rigidity of the whole sieve frame.
Thanks for explaining that you should replace screen mesh if it has been used for a long time. This makes sense, because that way you can save money by getting more efficient results. Ill have to look for a wire mesh screen.
dynamics and screening characteristics of a vibrating screen with variable elliptical trace - sciencedirect
The ideal motion characteristics for the vibrating screen was presented according to the principle of screening process with constant bed thickness. A new vibrating screen with variable elliptical trace was proposed. An accurate mechanical model was constructed according to the required structural motion features. Applying multi-degree-of-freedom vibration theory, characteristics of the vibrating screen was analyzed. Kinematics parameters of the vibrating screen which motion traces were linear, circular or elliptical were obtained. The stable solutions of the dynamic equations gave the motions of the vibrating screen by means of computer simulations. Technological parameters, including amplitude, movement velocity and throwing index, of five specific points along the screen surface were gained by theoretical calculation. The results show that the traces of the new designed vibrating screen follow the ideal screening motion. The screening efficiency and processing capacity may thus be effectively improved.