ore dressing humboldt vibrating screens

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.

rubber spring for vibrating screen - rubber spring for vibrating screen

Rubber spring for vibrating screen is a kind of polymeric elastomer with efficient anti-vibration, small resonance region, long service life, low cost and good cold tolerance, air tightness, waterproof, electrical insulativity, and it is the best choice for reducing vibration.

Specifications D*H*d(mm) Outer Diameter (mm) Inside Diameter (mm) FreeHeight (mm) Deformation (cm) Rigidity (kg/cm) Maxload (Kg) 300*245*80 300 80 245 1 480 2800 250*250*50 250 50 250 2.5 370 2000 220*220*50 220 50 220 2.2 320 1500 200*200*50 200 50 200 2 280 1000 180*180*40 180 40 180 1.8 260 800 160*160*30 160 30 160 1.6 240 750 140*140*30 140 30 140 1.4 210 700 140*160*30 127 30 160 1.4 180 700 127*127*30 120 30 127 1.2 180 700 120*120*30 100 30 120 1.2 170 700 100*100*30 100 30 100 1 140 600 100*130*30 100 30 130 1 100 500 80*80*20 80 20 80 0.8 100 400 60*60*18 60 18 60 0.8 60 200 50*50*18 50 18 50 0.8 40 100

humboldt vibrating ball mill

For each project scheme design, we will use professional knowledge to help you, carefully listen to your demands, respect your opinions, and use our professional teams and exert our greatest efforts to create a more suitable project scheme for you and realize the project investment value and profit more quickly.

The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter ( Figure 8.11 ). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight.

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vibrating screens archives - international mining

These trends hold great potential for the mining sector, and Kwatani has been at the forefront of technologies driving this direction, Annelize van der Walt, Kwatanis Business Development Manager for Mining and Minerals, says.

Larger, engineered-for-tonnage screens are growing in popularity, as they reduce the number of processing modules and hence the level of infrastructure required, especially on mega-projects, van der Walt says. Higher capacity is becoming the new design standard for greenfields projects.

There is also an ever-greater demand for reliability and uptime in these mission-critical machines, as well as an expectation of longer lifespans. All this requires bespoke solutions that address site-specific conditions, van der Walt says, while leveraging digital technology for real-time monitoring and control.

Kwatanis metallurgists and engineers use their extensive on-site experience and in-house laboratory facilities to innovate from our proven technologies, she says. A cornerstone of our philosophy is close collaboration with engineering, procurement and construction management contractors and end-customers to customise solutions, from concept to construction, commissioning and operation.

Specific conditions include waterless beneficiation in arid Mauritania, where Kwatanis screens operate completely dry in an iron ore plant. In South Africa and Botswana, meanwhile, the company has retrofitted dewatering screens to reduce water consumption, while increasing output by 40% with the same footprint.

We also recently designed screens for exceptional ore characteristics in a precious metal beneficiation facility in Canada, she said. This required a high level of customisation, not only in the screening media but in the mechanical design.

Remote mine locations which are difficult to access for maintenance and replacement purposes also guide the design parameters. In a recent project, Kwatani innovated by selecting special hard-wearing materials for the construction of the screening equipment. The design included components that would provide early warning of wear.

Embracing a more holistic plant design approach, customers often invite Kwatani to participate in optimising the screening side of their chosen beneficiation technology, van der Walt says. A different screening approach would be taken, for instance, in a dry pre-concentration application than in wet dense medium separation.

This holistic approach is also facilitating greater synergy between original equipment manufacturers, she says. This is a very positive trend, allowing us to consider the impact of different equipment on the performance of each from mineral processing apparatus to transfer chutes.

Our R&D unit is currently working on projects to suit our designs to novel crushing and grinding technologies, which are changing the whole approach to the process flow of future plants, van der Walt says. These are significant innovations for the mining sector, and we are excited to be at the forefront with our evolving screen designs.

Kwatani is incorporating digital technologies to facilitate remote monitoring and control of its vibrating screens. It is also piloting a service app for mobile phones, which helps operations predict their maintenance needs more accurately. The app also helps to drive down the total cost of ownership by gathering data that can be used in future design improvements.

Sales Manager, Graham Standers, says the company has recently supplied 15 new screens to mining customers in coal, diamonds, iron ore and manganese. These operations are based in South Africa, Botswana and Australia. MBE Minerals has also fully refurbished a further four screens to as new condition as they approached the end of their planned lifecycle, the company said.

We place high priority on design capacity, to ensure that every screen suits the application and material it must screen, Standers said. Five of the screens supplied were newly designed to suit changing customer needs and processes.

Each screen is designed by the companys design office, and the design is then confirmed by finite element analysis through highly specialised software using data from the drawing model, according to the company.

We have also introduced a range of screens designed specifically for fine coal dewatering, using a design which has proven to be cost effective, efficient and reliable, Standers says. Focus was placed on the design of the screen deck support system and screen drive, with a view to reducing downtime by minimising maintenance and enhancing reliability.

Our unique T-Lock pinless panel fastening system for polyurethane screen panels also significantly reduces the need to hold spares in stock, while reducing the changeout time for screen panels, he says.

Technical and sales staff conduct regular on-site visits to customers to carry out inspections of equipment in operation. The teams report on equipment condition and performance, and provide customers with value-adding feedback and advice.

Weir Minerals Africa, having over the last 40 years proven the credentials of its Enduron range of vibrating screens, is now locally designing and manufacturing new-generation linear motion vibrating screens.

One of these new, modern screen designs is part of a recent Weir Minerals Africa complete comminution plant contract for a South Africa mining project. The scope included two crushing stations, a screening station and all the related feed chutes, bins and conveyors.

According to Christian Stehle, Head of Engineering at Weir Minerals Africa, the companys design capability provides the flexibility to produce vibrating screens to suit each customers plant layout. At the same time, the designs will optimise cost, efficiency and performance. South Africa also hosts Weir Minerals global screening and separation technology group.

This expertise ensures that our robust Enduron vibrating screens provide exceptional classification and dewatering screening performance, Stehle said. The screens are deployed in a wide range of minerals processing applications.

The final design must address key criteria like screening efficiency, throughput and loading, while still operating within the acceptable fatigue life limits of the materials of construction, he said.

Stehle highlighted that the use of finite element analysis (FEA) tools allow engineers to optimise screen life by obtaining the stress and deflection levels in the equipment and applying the appropriate structural design and utilisation of materials in the areas experiencing high stresses.

Traditionally, screen designs used to be heavier in an effort to extend the life of the equipment, he said. Using FEA tools during the design stage allows us to retain structural integrity while actually reducing the overall weight of the machine.

While there are areas of high stress on the equipment that need more strength, technology tools indicate where lower stresses occur. In these areas, less steel can be used to make the structure lighter, according to Weir Minerals Africa. Leveraging this technology, the weight of some new-generation screens has been cut by up to 15%, the company said.

Stehle noted that Weirs Synertrex IoT platform can also be applied to monitor and improve the performance of the companys vibrating screens. Synertrex technology is an industrial internet of things system that allows operators to monitor every aspect of their equipments operation, to prevent problems and increase throughput.

Specialist vibrating equipment manufacturer, Kwatani, says it leveraging a recent multi-year service contract with a large mining customer in the Northern Cape of South Africa to further boost the areas local economy.

Kim Schoepflin, CEO of Kwatani, said: Our branch near the customers mining operation has for many years employed and developed local expertise. Our latest initiative takes this further, by upskilling a local sub-contractor to conduct certain maintenance work on our behalf.

A lengthy selection process was conducted by Kwatani to find a suitable sub-contractor, followed by ongoing training to empower artisans and other workers with specialised skills. Schoepflin says it was also important to involve the mine itself, so that it remained confident in the strength of its supply chain.

Promoting local employment, skills and sustainability cannot be a tick-box exercise, Schoepflin says. It has to be based on proper engagement, hands-on training and the sub-contractors own commitment.

Mining legislation and regulatory pressure can tempt stakeholders to rush such a process, she warned. This would be a mistake; rather, it should be treated as an opportunity to strengthen the capability of all stakeholders.

Kwatanis 35 years of experience in heavy duty minerals applications means the OEM now has around 800 vibrating screens and feeders in the Northern Cape. The maintenance contract is an ideal opportunity to involve and foster the technical capability of local players, Schoepflin says.

As a South Africa OEM with our own technologies and intellectual property, we are able to certify the sub-contractor and their quality of work, Schoepflin says. Phase 1 of our initiative will see them conducting basic service and maintenance functions.

Kwatani retains responsibility for all work conducted, and continues with services such as detailed technical inspections, engineering support, on-site testing and diagnosis. It also supplies OEM spare parts, ensuring quality control, increased lifecycle time and reduced downtime, the company said.

Schoepflin noted that communities countrywide are eager to see more benefits from economic activity, and the countrys Mining Charter provides clear guidance on how mining companies can contribute to this process. Kwatanis mining customer is therefore also eager and incentivised to promote local businesses, both directly and through the supply chains of its main local contractors, Kwatani said.

Schoepflin highlights the importance of supporting local firms to build sustainability in the local economy. This also strengthens the skills base for this economy to diversify, making it less dependent on mining and more resilient to commodity cycles and eventual mine closure.

Our own business is local from the ground up, sourcing 99% of direct purchases from inside South Africa, she says. So, we understand the positive role that local procurement and skills development can play.

Working collaboratively with our mining customers and businesses close to their operations, we can help spread local economic benefits, she says. In turn, we can continue to develop our focus on leading-edge technology and quality manufacture.

The companys custom engineered products are now in some of the worlds largest mines, and many customers have standardised on their screens to ensure lowest cost of ownership and high performance, according to General Manager, Sales and Service, Jan Schoepflin.

While our base and core market are in Africa, the global demand for Kwatani products has grown rapidly. A leading diamond mining company in Russia is very pleased with Kwatani screens at their newest operation and specified Kwatani for future projects, Schoepflin says.

In another order from a large diamond operation, this time in South Africa, the customer replaced the last of its competitor screens with a Kwatani unit. Schoepflin says this is because it has enjoyed years without unplanned stoppages by using Kwatani screens.

At a local brownfield diamond expansion project, the companys multi-slope banana screens were matched to the available plant footprint, raising throughput from 250 t/h to 500 t/h and, later, breaking the mines tonnage record.

While screening in heavy minerals is Kwatanis stronghold, the company has moved extensively into coal, supplying the countrys (South Africas) leading coal producer with no fewer than 45 items of large screening equipment, including out-sized 4.3-m-wide units, the company said.

Other recent coal-related orders included run-of-mine screens for a medium-sized coal mine in Mpumalanga, South Africa. Again, competitor equipment was replaced by custom designed screens with optimised deck angles, which significantly increased tonnage, according to the company.

For world largest zinc mine, Kwatani was contracted to supply all the screens, while, at Africas largest iron ore mine, the company recently completed two projects, renewing existing equipment with updated solutions and replacing 24 items of competitor equipment.

The platinum sector is also keeping Kwatani busy, not just in South Africa but over the border in Zimbabwe too, Kwatani says. A recent turnkey solution focused on platinum by-product chromite, where the company supplied a complete solution which included feeder, dryer and screen to treat chromite of 45 micron size at 15 t/h.

Schoepflin said: Our screens have been a popular choice for modular gold plants going to West Africa as well as Central and South America. We also supplied to two of Africas largest copper producers in Zambia, to a tanzanite producer in Tanzania, and repeat orders to a manganese mine in Ghana.