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vibrating feeder design - stockpile & reclaim | general kinematics

vibrating feeder design - stockpile & reclaim | general kinematics

The expanding applications of vibratory feeders for controlling the flow of bulk materials, and their adaptation for processing requirements, have developed a considerable interest in stockpiling and reclaim systems. The general design of these units consists of a material transporting trough (or platform) driven by a vibratory force system. The flexibility and variety of designs are limited only by the ingenuity of design engineers. The basic motion of the vibratory trough, or work member, is a controlled directional linear vibration which produces a tossing or hopping action of the material. Material travel speeds vary from 0 to approximately 100 ft. per minute, depending on the combination of frequency, amplitude, and slope vibration angle.

The installation of vibrating feeders in over 300 power plants has proven the reliability and economical construction for these feeder units. System designers must apply improved designs for controlling the flow of coal or other bulk materials from storage including full consideration for dust control and pollution. Automated coal handling systems should include manpower and equipment maintenance requirements in the evaluation of any layout. Overall operating costs in a material handling system are passed on to the consumer in the price of energy. Minimizing the use of dozers and mobile equipment reduces the fugitive dust problems and improves the reliability of the system. The efficient and economical storage, movement, and control of large tonnage material handling installations unit train loading and unloading, storage, blending, and reclaim systems depend on the proper application and design of vibrating feeders.

Vibratory feeders are basically applied to a control function to meter or control the flow of material from a hopper, bin, or stockpile, much the sameas an orifice or valve control flow in a hydraulic system. In a similar sense, feeders can be utilized as fixed rate, such as an orifice, or adjustable rate, as a valve. Feeders are supported by a structure or hung from hoppers by cables with soft springs to isolate the vibration of the deck from the supporting structure. Capacities range from a few pounds to 5000 tons per hour or more.

Vibratory feeders are basically applied to a control function to meter or control the flow of material from a hopper, bin, or stockpile, much the same as an orifice or valve control flow in a hydraulic system. In a similar sense, feeders can be utilized as fixed rate, such as an orifice, or adjustable rate, as a valve. Feeders are supported by astructure or hung from hoppers by cables with soft springs to isolate the vibration of the deck from the supporting structure. Capacities range from a few pounds to 5,000 tons per hour or more.

Some of the principal advantages of vibratory feeders over other types of bulk feeding devices are the opportunity for utilizing full sized hopper openings to reduce bridging and assure the free flow of material. This free flow comes via vibrating material in the hopper throat and eliminating the requirement for bin vibrators. In most cases, the vibratory feeder pan eliminates the requirements for rack and pinion gates and other shut-off devices above feeders since the feeder pan functions as a shut-off plate. The design of the unit permits replacement of the drive mechanism without removing the feeder trough. There is a reduction in headroom requirements and considerable savings in pit or tunnel construction and elimination of gates. Eliminating gates also promotes the free unobstructed flow of material. In process requirements, the ability to vary the feed control from absolute zero to maximum in response to instrumentation signals meets the design requirements for automated blending and reclaim systems. No return run such as belt feeders eliminates scrapers and spillage. They can be designed for dust-tight applications.

1. Direct-force type in which 100 percent of the vibratory forces are produced by heavy centrifugal counterweights.The forces developed are transmitted directly to the deck through heavy-duty bearings. Linear motion can be generated by the use of counter-rotating shafts with timing gears operating in an oil-bath housing and driven through a V-belt. Other designs utilize two synchronizing motors, with counterweights mounted on the motor shaft.In general, the direct-force type is applied as a constant-rate feeder. The feed rate can be adjusted by changing the slope of the pan, size of the hopper opening, or changing the amount of counterweight, and stroke. In some cases, mechanical or electrical variable-speed drives are applied to vary the frequency and feed rate, but the regulation and control range is limited.The stroke and capacity are affected by the hopper opening and the amount of material on the feeder pan.

2. Indirect-force types, better known as resonant or natural frequency units, generate the vibratory forces from a relatively small exciting force which is amplified through the application of a secondary spring-mass system.In most designs, natural frequency feeders are tuned at a mechanical natural frequency above the operating frequency of the drive in order to prevent excess dampening effect of the material head load, particularly in larger units with large hopper openings or high capabilities. The term sub resonant is used to describe these units.

The resonant or natural frequency vibratory feeder is designed to control the flow of bulk materials using the amplification principle of a two-mass spring system with a constant exciting force.The prime mover is a standard squirrel cage ac motor. Small eccentric counterweights mounted on the double-extended shaft of the squirrel-cage motor in the exciter assembly produce a constant rotating exciting force.This drive design completely eliminates the requirements for heavy bearings, V-belt drives, guards, electric plugging circuits, pressure switches, gears and lubrication problems. Other designs use an unbalanced eccentric shaft driven by belts from a separately supported motor designed for vibratory service.The component of the rotating exciting force, in line with the desired feeder stroke, is amplified by coil or polymer springs to produce a powerful straight line conveying action on the deck. The squirrel-cage motor speed varies less than 1-1/2% with +/- 10 percent fluctuation. The constant rotating exciting force results in accurate feed control regardless of normal voltage fluctuations.

The total spring system of the vibratory feeder is designed so that the amplitude-frequency response of the two-mass system is such that the greater the material effect, the greater the amplification of the spring-weight system. This results in an automatic increase of the amplified exciter force which naturally compensates for material head load and weight effect. This anti-dampening characteristic results in accurate volumetric feed-rate control regardless of material head load variations.

Electromagnetic feeders have been used extensively. These units are designed as Two-Mass spring systems in which the pan or deck is mounted on a bank of leaf springs which is rigidly attached to a relatively larger impulse mass. Alternating or pulsating direct current creates an exciting magnetic force between an armature and the field coils which are usually mounted on the impulse mass. Variable amplitude is obtained through a rheostat and rectifying equipment or variable-voltage transformers.Electromagnetic units are usually sensitive to material head loads and voltage fluctuations. In some applications electronic circuits and voltage-regulation equipment are employed.

Maximum feed rate can be fixed or set by adjusting the small eccentric weights located on the motor or vibrating shaft. Stroke can also be adjusted by the use of tuning springs to vary the resonance effect. Some designs attempt to control the feed rate by varying the RPM of a squirrel cage motor with SCR controls or variable voltage transformers. This method of adjusting the control is satisfactory for relatively limited ranges. Vibrating feeders, like those at General Kinematics, are suspended on coil springs to isolate the motion from the supporting structure. The natural frequency of the suspension system is generally 50% of the operating speed of the feeder motor. Reducing the RPM of the feeder motor approaches the natural frequency of the suspension system so that at some point the feeding becomes erratic or causes problems in the suspension system. Other designs may have internal drive constructions which also respond in an erratic fashion to variable speed drives. For applications requiring maximum adjustable control of feed rate, an infinitely variable, stepless feed rate is obtained by the use of a Variable Force counterweight wheel on each of the extended motor shafts.

This vibrating feeder design provides linear control from zero to maximum feed rate. Variable Force counterweight control alters the exciting force by varying only the counterweight effect rather than the motor speed. As air or hydraulic pressure signal varies from zero to maximum, the unbalanced forces vary proportionally. Motor speed remains constant. Since the NEMA design squirrel cage motor operates with full torque at all times, it can stop and resume feed at any capacity, even 5000 TPH. The control responds accurately and smoothly to any manual, pneumatic, hydraulic or electronic input signal-load cell, belt scale, computer for fully automated operation.

Material characteristics and size distribution generally dictate the hopper or bin slopes as well as the hopper opening. In determining the size of hopper opening it is important to consider the largest size particles as well as the bridging effect of the material. The projected vertical opening should be two or three times the largest size pieces. Materials with high bridging characteristics require adequate openings to assure flowability. Larger openings save headroom but require feeders with the ability to operate under headloads. Another feature of large hopper openings is the transmission of feeder-pan vibration directly to the material to reduce bridging, eliminating the requirement for bin vibrators, and promoting smooth uniform flow of materials. These design factors require feeders that are able to operate under a material head-load with minimum damping or muffling effect. Para-Mount II Feeders are ideal as they are tuned to increase vibratory forces to compensate for the material mass effect.

The projected horizontal opening is determined by the particle size and capacity requirements. The minimum opening should be approximately 1-1/2 times the largest lump size.The maximum size opening is determined by the volumetric capacity consistent with feeder length. It is desirable to include a slide plate or gate to permit field adjustment.

The projected horizontal area is a function of the projected horizontal opening and feeder-pan width. The average material velocity will vary with material flow characteristics, the coefficient of friction, feeder pan slope, length, and vibration intensity.

Material velocities will range from 30 to 60 fpm with pan slopes from 0 to 20 deg. Feeder-pan trough length is determined by the material angle of repose and pan slope. The feeder pan must be of sufficient length to assure complete material shutoff when the feeder is at rest. A line drawn from the maximum opening at the material angle of repose should intersect the pan trough, leaving a margin of cutoff length to allow for variations in material characteristics.

Selection capacities shown in the table are guides for selecting the feeder size. Feed rates may vary widely with material characteristics such as density, particle size distribution, moisture content and angle of repose. Maximum feed rates are obtained by declining feeder pan consistent with hopper opening and feeder length. Minimum length of feeder may be determined by hopper opening, feeder slope and angle of repose. Select feeder with adequate length to prevent flushing. Hopper opening required to minimize hopper bridging effect may determine width and length of the feeder. In some cases, headroom or minimum tunnel depth consideration justify a size selection larger than required for volumetric flow.

Feeder troughs can be ruggedly built for heavy-duty service. Frames are heavily reinforced. Deck plates are bolted to husky channel side members and are readily replaceable. Decks are available in mild steel, abrasion-resistant steel, stainless steel or special alloys, thus providing a wide range of materials to suit application requirements. Thicknesses from 10 ga. to 1 widths from 18 to 144. Liners are also available in the above materials, as well as rubber, plastics or ceramics. Dust-tight covers can be furnished where required.

As you think about the design of your vibrating feeder, the lining materials should be selected with consideration to the material being handled as well as the economic factors. For extremely abrasive materials, ceramic liners in the form of high-density aluminum oxide tiles can be installed on a flat deck with epoxy resins with a high degree of success. This has been very successful in applications involving coke, for example in the steel mills. Another type of material is a UHMW Polymer (ultra-high molecular weight) polyethylene plastic, used as a liner for abrasive, wet fine, material. This in many cases prevents the buildup encountered with metal decks.

A very common material as a liner is Type 304 stainless steel. This is particularly adaptable to materials which have a corrosive effect as well as wear. The stainless steel material is excellent for this application as the general action of the material on the feeder is a sliding action, which polishes the stainless to a very smooth finish preventing buildup and also resulting in longer life. Experience has shown that feeders in power plants have been operating for over 15 years with no appreciable wear on the 304 stainless steel material. Many alloy decks such as T-1 and Jalloy can also be used for abrasive service.

The conventional feeders that have been available consist of a flat pan trough with relatively low sides. This requires that stationary skirts be installed between the hopper or storage opening and the inside of the feeder trough to contain the material being conveyed by the vibrating feeder pan. Also, there has been a difficult design problem to provide dust or mud seals between the stationary skirts and the vibrating feeder pan. Another problem has been to provide a satisfactory seal between the feeder pan and any dust housing over the conveyor belt or receiving chute. A newer vibrating feeder design incorporates the side skirts as part of the feeder forming a totally-enclosed design. The feeder is shaped like a box structure with a flanged inlet and bottom flanged outlet cooperating with the inlet-chute and receiving chute or hopper. In this case, the seals are never in contact with the material and are much simpler to install and maintain. The feeding unit can now be made completely dust-tight (or watertight) and eliminates any spillage encountered with conventional feeders. Installation is simplified. This design also eliminates the problem encountered in trapping material between stationary skirts and the vibrating pan, which may cause reduced capacity or complete locking of the pan to the stationary skirts in the case of material that has a tendency to cake or cement when inactive.

Some installations use a combination of a vibrating bin bottom or pile activator with a vibrating feeder to control flow.The UN-COALER combines the flow control characteristics of a totally enclosed vibrating feeder with the material activating action of a vibrating bin bottom to assure maximum material drawdown without the attendant problems of flushing or compacting. Until now, it has been necessary to select a circular bin activator sized to provide maximum material flow and the use a vibrating feeder to control the flow and prevent flushing. A single unit can do the job effectively and economically.

The construction consists of a square or rectangular box structure with two symmetrical feeder pans in combination with a center dome.The geometry of the material flow path is similar to the requirements for open pan feeders. The center dome is part of the box structure and functions as a pile activator or vibrating hopper bottom.

The entire assembly is vibrated horizontally by the natural frequency drive mechanism identical in design to a coil spring feeder drive. The bottom slot opening feeds the material to the belt to deposit the coal symmetrically and centrally to develop an ideal belt loading.The center dome produces a vibratory action on the material to reduce the arching and induce the flow in the storage pile.Sealing is simple and complete with installation of seals as shown in the diagrams.

When applied to any type of bulk material storage unit, the UN-COALER activator / feeder will increase the amount of reclaimable live storage. It is especially advantageous when used with sluggish, hard to handle ores, lignite coal, and other materials with high particle friction or a poor natural angle of repose. Units are available up to 12 x 12 or larger openings, depending on your application.Large openings mean fewer units are required to achieve the same amount of live reclaim. Compact low profile reduces tunnel depth. Rectangular shape allows simple hopper design without the need for expensive circular transition piece between hopper and activator. The UN-COALER mounts on a separate support.A curved arch breaker mounted above the material feeding troughs is designed to transmit vibrating forces into the storage pile without compacting the material. Its leading edges are provided with adjustable baffles which are set in accordance with the materials angle of repose the same as a cut-off gate on feeder hoppers.

Each UN-COALER is foot mounted on steel coil isolation springs, thus the tunnel roof does not have to be designed to withstand the weight of the unit or any dynamic forces. Automated control systems arranged to respond to belt scale, load cell or computer signals, allow individual or multiple unit control of the UN-COALER for selective reclaiming from virtually any point or combination of points along the tunnel.The low profile design of the UN-COALER reduces the cost of foundation excavation since the tunnel does not have to be as deep. Straight-line surfaces eliminate elaborate concrete forming. The few moving mechanical parts of the UN-COALER are easily accessible from the tunnel to minimize maintenance procedures.

As unit trains deposit enormous quantities of material into large hoppers, a series of feeders can be called upon to uniformly distribute the material onto reclaim belt conveyors. The large, rectangular outlet opening of the feeders mounted directly over the conveyor assures maximum draw-down. Adjustable rate units equipped with the counterweight control respond accurately to belt scale, load cell or computer signals to allow precise proportioning or blending. UN-COALERS can be applied with considerable savings in pit depth.

Vibrating feeders can be supplied to match the crusher openings to provide an ideal curtain feed with a uniform distribution to assure maximum crusher efficiency and uniform wear life on the hammer elements. Foot-mounted directly above a crusher, the UN-COALERs low profile, compact straight-line design simplifies hopper and dust seal installation. 100% linear feed rate adjustment can be controlled by the crusher amphere draw or feed hopper load cells.The long, narrow shape of the UN-COALER discharge opening provides the perfect configuration for evenly distributing material across the crusher inlet.

The basic aim of any reclaim system is to activate the larges volume of stored material without resorting to manual manipulation to eliminate rat-holing or segregation. Feeders can be applied to obtain maximum live storage in either windrow or silo storage. the design of systems to reduce the use of dozers has proven to be advantageous in operating costs and eliminating much of the fugitive dust problem generated by the moving equipment.

The illustration below shows an arrangement of feeders which provides 100 percent reclaim of material and at the same time reduces the required storage area. In this system, the material is reclaimed from what are essentially live storage piles through a series of below-grade hoppers. These feeder hoppers are contiguous and arranged to permit pairs of opposed vibrating feeders to feed to a central belt conveyor. The feeder troughs are enclosed and the drive can be provided with explosion-proof motors thus reducing dust problems and the risk of fire. This arrangement makes it convenient to blend materials of various compositions or content by operating appropriate pairs of feeders along the pile. Material is 100% reclaimed from live storage area through a series of UN-COALERs that are foot mounted directly below grade. The contiguous hoppers are arranged to permit the UN-COALERS to feed to a central conveyor belt. Simple straight-line dust seals at the inlet and discharge openings, eliminate dust problems and reduce the risk of explosion. The UN-COALER is mounted completely below grade, reducing hazards during dozing operations. Low profile reduces tunnel depth and concrete cost is cut even further since units are supported from tunnel floor and not suspended from overhead.

This type of bulk storage facility is a V-shaped slot with a bathtub shape having 55 degrees sloped concrete walls in some cases completely covered by a metal building. The upper-most portion of the structure houses a tripper conveyor which will deliver the incoming material to any point along the bunker. A series of UN-COALER activator / feeders, with sizes up to 12 x 12 or larger, are housed in a rectangular concrete reclaim tunnel extending along the entire bottom of the bunker and are positioned to provide 100 percent reclaim. This is an ideal layout for reliable and controlled blending. Any percentage of material can be reclaimedsimultaneously from any portion of the pile. The low profile design of the UN-COALER reduces the cost of foundation excavation since the tunnel does not have to be as deep. Straight-line surfaces eliminate elaborate concrete forming and eliminate the requirement for tepee housing used with plow systems. The few moving mechanical parts of the UN-COALER are easily accessible from the tunnel to minimize maintenance procedures. Discharge is directly on the belt thus eliminating belt tracking problems. Square or rectangular outline simplifies feed opening design, concrete work, and dust sealing.

The fast efficient, high-tonnage method of reclaiming coal from concrete storage silos is to use a series of feeders to extract uniformly across the entire bottom of the silo. For example, a 70 ft. diameter silo would use seven feeders located beneath 10 ft. square openings, three directly over a belt and two on either side, to provide mass-flow unloading while minimizing segregation problems. Two or more silos in tandem facilitate blending.

Several UN-COALER units installed across the bottom of the silo, a 70 diameter silo, for example, would require only four UN-COALER units mounted in-line between the 60 degree inclined discharge chutes compared to at least seven conventional activators and feeders. A significant cost savingsoccurs because of fewer pieces of equipment, simpler and less costly concrete work and installation procedures.

cu-pb-zn, copper-lead-zinc ores, copper lead zinc flotation

cu-pb-zn, copper-lead-zinc ores, copper lead zinc flotation

It is reported that more than 90% of non-ferrous metal ores (copper, lead, zinc, etc.) adopt flotation process, especially for those with fine grain and complex symbiosis. Flotation process can achieve ideal separation effect, and separately recover low-grade ore then enrich multiple high-grade concentrates. Different ore properties means different flotation process. According to the dissemination characteristics of metal minerals, Xinhai has determined four kinds of flotation processes:

Xinhai separates two useful minerals that with similar floatability into the mixed concentrate, and then floats each concentrate. That is, copper sulphide and lead ore with similar floatability are selected as mixed concentrate, and copper and lead is separated. Then the tailings were reactivated to separate the zinc concentrate.

With the principle of " easiness to hardness ", Xinhai divides the recovered minerals into two parts: easy-to-float and difficult-to-float according to the difference of natural floatability, and then separate the copper, lead and zinc concentrate from the mixed concentrate.

In general, the most difficulty of the polymetallic sulfide ores separation is the separation among several kinds of ores, especially those low-graded ores with complex embedded features. Therefore, its a significant step for separating lead-zinc, copper-zinc, copper-lead to choose right flotation reagents. Xinhai strictly implements the reagent system, controls the dosage of reagent, reduces multiple circulation and loss, then strengthens the flotation effect.

froth flotation process used in the lead zinc sulfide ore - xinhai

froth flotation process used in the lead zinc sulfide ore - xinhai

In nature, the lead-zinc ore can be divided into sulfide ore, oxidized ore and mixed ore according to the degree of oxidation. The single lead sulfide ore or zinc sulfide ore is very rare in nature. The most common lead-zinc sulfide ore is lead-zinc sulfide polymetallic ore.

The lead-zinc sulfide is often associated with a variety of valuable components, such as lead, zinc, copper, sulfur and other useful minerals, whose floatability is obviously different, which determines the different froth flotation process of lead and zinc sulfide ores. The common froth flotation process of sulfide ore mainly includes priority froth flotation process, mixed froth flotation process, iso-flotation process, differential branching flotation process and potential-controlled flotation process.

The flow of lead and zinc priority froth flotation process is mainly to suppress zinc first and float lead, then activate zinc to get lead concentrate and zinc concentrate. According to the buoyancy degree of lead zinc ore, the valuable minerals, such as lead and zinc, can be recovered successively by the froth flotation process.

The priority froth flotation process is suitable for rich ores with simple mineral composition, high lead and zinc content, and coarse disseminated ores. It is also suitable for dense massive sulfide ores with a large number of sulfide ores. It has the advantages of easy to control, high concentrate quality, small fluctuation of the flotation index.

The mixed froth flotation process lead and zinc sulfide ore are to float the mixed concentrate of lead and zinc sulfide first, and then separate the mixed concentrate of lead and zinc sulfide. That is, all lead sulfide and zinc sulfide minerals are first separated into the mixed concentrate, and then the mixed concentrate is separated individually after the reagent removal, and the single flotation concentrate is obtained.

The mixed froth flotation process can discard a large number of gangue minerals after rough grinding, which reduces the processing capacity of subsequent operations, saves the reagents dosage used in the separation stage, reduces the energy consumption. It is suitable for treating the lead-zinc ores with little difference in floatability, low grade, and the useful minerals are the aggregation or dense coexistence.

The iso-flotation process used in lead-zinc sulfide ore is to divide the lead and zinc sulfide ore with similar floatability into two parts: easy-to-float part and difficult-to-float part. Then the mixed concentrate is obtained by the mixed froth flotation process, which is separated as the single concentrates of various useful minerals successively. In some ore dressing processes, some sphalerite has a close flotability with galena, a few parts of galena have and a close flotability with most sphalerite. Therefore, make full use of different flotability between lead and zinc ore, and make a part of zinc ore with good flotability floated in the lead flotation process, and the rest of lead ore is floated along with the zinc flotation process. Finally, the mixed concentrate of lead and zinc is separated, which can be separated again by the froth flotation process to obtain the lead concentrate and zinc concentrate respectively.

The iso-flotation process is suitable for the lead-zinc sulfide ore whose useful minerals containing easy-to-float and difficult-to-float ore. This process has the advantage of a mixed froth flotation process and priority flotation process. It can reduce the reagent dosage, eliminate the drug adverse impacts on the flotation separation, improve the quality and recovery rate of concentrate. But the iso-flotation process has relatively complex flow, takes long flotation time and much flotation cell.

The differential branching flotation process used in lead-zinc sulfide ore is to quickly float the lead zinc ore which can be floated fast and easily, and then float the lead zinc ore which is floated slowly and difficultly. This froth flotation process is applicable to lead and zinc sulfide minerals with different flotation behaviors due to different inset components, which can obtain the better flotation indexes while reducing the configuration volume of the flotation machine, reduce metal circulation and loss, decrease the flotation reagent consumption and simplify the process flow.

Potential-controlled flotation process used in the lead-zinc processing is to change the electrochemical conditions of flotation system to control the process and direction of oxidation-reduction reaction on the surface of the sulfide minerals in the slurry system, thus affecting the surface state of sulfide ore, the product form and stability of collector on the surface of sulfide ore, increasing the hydrophilic and hydrophobic properties of sulfide ore surface, so as to achieve the flotation separation of sulfide mineral.

The potential-controlled flotation process is characterized by low reagent dosage, simple formulation, little environmental pollution and high selectivity, especially suitable for the separation of low-grade lead-zinc sulfide ore.

The material composition of lead zinc ore is particularly complex. The different material composition of the ore has different impregnation and mosaic characteristics, which determines the froth flotation process of the ore. The selection of the froth flotation process will affect the flotation effect. It is suggested that each mine owner should adopt the scientific and reasonable froth flotation process according to the report of the mineral processing test report, avoiding the unnecessary economic loss.

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