In simple terms, the coil (a magnet wound in copper wire to create an electromagnet) is attached to the base unit, and the magnet is attached to the feeder tray. The coil attracts and releases the magnet, generating the relative movement between the base unit and the feeder tray.
Drive systems are available that incorporate all the components of the electromagnetic drive (i.e. the coil, magnet, and springs) into a complete drive unit. A mounting plate is provided at the top end of the springs to add a feeder tray suitable for the application.
The magnet (attached to the feeder tray) is held a few millimetres away from the coil by the flat springs. As the current moves in one direction, the coil attracts the magnet and adds tension to the springs.
When the current switches direction the magnet is released, and the potential energy stored as tension in the springs is used to move the tray. This action throws any product in the tray forward creating the hop.
It is important to try and set up the system so that the natural frequency with which the tray would oscillate on the springs matches the frequency of the electromagnetic drive. This will reduce stresses in the feeder tray and encourage product to flow as quickly and efficiently as possible.
The natural frequency of the oscillation is determined by the relationship between the combined total stiffness of the springs in the system and the mass of the feeder tray plus any product in the tray.
As the feeder tray and mass of product is largely determined by the application, and the electromagnetic drive (minus variable controls) will operate at the frequency of the alternating input (e.g. mains supply at 50Hz), the design variable is the springs.
A tray which is not rigid will lead to areas of the tray vibrating at different frequencies, called secondary vibrations. These areas create anomalies in the flow of product, meaning product can slow, stop, or even run backwards.
The mass of the base counteracts the movement of the feeder tray, and prevents vibration from the system transferring into supporting structures, which over time could lead to serious structural damage.
To keep the base secured to a supporting structure, it is connected to the structure using flexible rubber blocks. These blocks, while being stable enough to guarantee safety and stability during operation, do allow some movement of the base relative to the supports.
Typically the feeder will be designed to keep the movement of the base to below 0.5mm in any direction (although different blocks will be designed to allow greater ranges of movement), so for a high frequency feeder with a tray amplitude of 1.5mm, the base would be 3 times as heavy as the tray plus any product. The calculation is:
It is rare that a variable speed control function will be used during a production process. Product throughputs are usually much more dependent on actual processing equipment within the overall process, with feeder usually only moving product from one process to another.
Under these circumstances, a feeder may be set to deliver the majority of an ingredient into the mixer at maximum speed, with the final few percent of product added at a reduced rate to prevent overfilling the system.
Vibration is a is a mechanical phenomenon that is used in the manufacturing field to orient and select various types of pieces. For this reason, vibratory feeders are part of numerous processes such as transport, dosing and packaging of different industry: pharma, automotive and food just to name a few.
No matter the size, all these systems, including electromagnetic feeder, work on the same principle: they moves product by making the feeder vibrate.The pieces in the feeder, when it start to vibrate, move in a series of small hops. This series of hops create a flow, a constant motion of pieces.The most common devices used in this niche are vibratory bowl feeder, design to orient the parts to a specific orientation, and linear feeder, horizontal conveying of components.
For example, in a linear vibrating feeder we have a system composed of a base unit, coil, elastic springs, magnet, and a tray.The tray is connected to the base unit by elastic springs, they allow the movement between the two, and thanks to this movements the pieces move.The coil attracts and releases the magnet connected to the tray, generating the relative movement between the base unit and the feeder tray.
The vibration of an electromagnetic feeder is generated as the alternating electrical current moves back and forward through the wires of the coil.As the current moves in one direction, the coil attracts the magnet and adds tension to the springs. When the current switches direction the magnet is released, and the potential energy stored as tension in the springs is used to move the tray.When this process is repeated at high frequency, a continuous flow of pieces is created.
MP Elettronica was established more than 30 years ago in Italy and since 1998 the quality management system of the Company is certified ISO 9001:2015. The company is based in Milan and has a local branch in Varese (Italy). Since its establishment MP Elettronica designs, engineers and manufactures controllers for electromagnetic vibrators and nowadays the company has affirmed its market leader position due to its innovative solutions and products.
Simple design and flexible control account for the efficient, economical performance of Syntron volumetric feeder machines, and the growing industrial preference for them. These units can feed most dry bulk materials and can be supplied to conform to FDA and USDA specifications. Six Syntron volumetric feeder machine models are available.
Syntron volumetric feeder machine designs include four basic components: a supply hopper, a hopper vibrator, a vibrating feeder, and the supporting frame. Supply hoppers are usually fabricated from mild steel but are available in stainless steel. Most supply hoppers are conical; however, rectangular hoppers are an option. Adjusting the gate height between the hopper and feeder trough regulates material depth for most models. Material depth for model FM-T0 is regulated by hopper tilt.
Arching, plugging, or bridging of materials in the hopper is prevented through incorporation of a Syntron electromagnetic vibrator. The hopper vibrator features a variable power control, assuring free flow of material to the feeder trough. Vibrating feeders on the Syntron volumetric feeder machines operate at 3,600 vpm (at 60 Hz) and trough options include flat pan (standard), V-shaped, tubular, or screening troughs of mild or stainless steel.
Because of their simple design, Syntron volumetric feeder machines are dependable and have an exceptionally long service life. There are no moving parts such as motors, belts, gears, valves, connecting arms, or sliding rods to wear or lubricate.
Drives on Syntron vibrating feeders are available with dust-proof, dust-tight, and waterproof construction. For dust-tight sealing, special covered or tubular troughs feature flexible seals on the discharge end of the supply hopper. In addition, flexible seals that seal the top of the supply hopper to an overhead chute, as well as removable dust covers for the supply hopper are available. These units are virtually noiseless, meeting applicable OSHA specifications. Even at maximum feed, a hum is the only indication that the machine is operating.
Syntron volumetric feeder machines are supplied with electric controls that can be mounted separately at any desired location. Standard controls contain operating switches, rectifiers, and rheostats. The electric control regulates the feed rate by varying the vibrating intensity of the electromagnetic feeder. A graduated dial on the control panel permits variation of the flow speeds. Timers are also available to provide intermittent feed.
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Vibratory feeders have been used in the manufacturing industry for several decades to efficiently move fine and coarse materials which tend to pack, cake, smear, break apart, or fluidize. Because they can control material flow, vibratory feeders handle bulk materials across all industries, including pharmaceuticals, automotive, electronic, food, and packaging. These feeders also advance materials like glass, foundry steel, and plastics at construction and manufacturing facilities.
Feeders can range from small base-mounted, pneumatic-powered models moving small quantities of dry bulk material to much larger electro-mechanical feeders that convey tons of material an hour. Users turn to vibratory feeders when they want to move delicate or sticky materials without damaging or liquefying them.
Vibratory feeders handle a wide assortment of materials including but not limited to: almonds, crushed limestone, shelled corn, powdered metal, metal billets, various pipe fittings, scrap brass and bronze, crushed and shredded automobiles, hot dross, and much more. Because they emit precise vibrations, vibratory feeders are also used to process small parts, like coins, washers, or O-rings, as they move along a belt conveyor.
* Controlled flow of ingredients to mixing tanks * Sprinkling toppings or coatings on food and dairy products * Adding binders and carbons to foundry sand reprocessing systems * Chemical additive feeding in the pulp and paper bleaching or chip handling processes * Feeding metal parts to heat treating furnaces * Feeding scrap or glass cullet to furnaces
Manufacturers have upgraded and modified vibratory feeders and conveyors over the years to enhance their role in multiple processing applications. The latest equipment offers increased energy savings, more precise control over material flow, easier maintenance, and a broader variety of options. Leading suppliers also now provide better technical support, and, in some cases, faster delivery of product to your plant.
Virtually all vibratory equipmentregardless of type or sizeis built with materials that can withstand the harsh environment of the manufacturing industry. Vibratory feeder trays can be made from stainless steel which is far less susceptible to corrosive materials. The internal motors fully enclosed construction offers protection from environmental elements to ensure maximum uptime.
Vibratory feeders save users time and money on maintenance as well, because they have no moving parts, aside from the vibrating drive unit. This means they break down less frequently and vibratory feeder parts are easy to replace. Other advantages of vibratory feeders include: ergonomic design, adaptability and versatility, effectiveness and accuracy.
How to Select the Proper Vibrating Feeder Design There are two basic designs available when selecting a vibrating feeder: electromagnetic and electromechanical. A third optionair-powered vibrating feedersare basically an alternate to electromechanical feeders since they have the same simple brute force design conceptthe vibratory drive is directly attached to the tray.
Electromagnetic feeders provide variable intensity with typically fixed frequency of 3600 vibrations per minute (VPM). They only require single phase power, offer quick stopping, and are ideal for cold weather. However, they are sensitive to line voltage fluctuations and temperature swings are not suitable for hazardous areas. They also need constant tuning if there are rate or load changes.
These units work well with dry, free-flowing, pelletized or granulated material. They can control material flow from a few pounds to several tons per hours and can be custom designed to accommodate material flow from a few feet (with a single drive) to up to 20 feet (with multiple drives).
Electromechanical feeders are powered by twin rotary electric vibrators which provide a broader range of stroke/frequency combinations. Their flexibility is further enhanced with a variable frequency drive (VFD), which provides quick and easy adjustment without having to manually adjust the eccentric weights.
A VFD with dynamic braking or a starter with a dynamic brake will end the vibration faster to limit the erratic motion a shut down. This design provides the quietest operation and is less susceptible to head loads. These feeders work well in hazardous conditions when explosion proof vibrators are installed.
Air-powered feeders work best under hazardous conditions because they are driven by an air-cushioned piston vibrator, which produces smoother linear force and can work safely in high temperatures. Its the simplest of the three feeders to maintain and the controls are the most economical.
While an air-powered feeder doesnt require tuning, there are limitations to the physical size of the tray and feed rates. These units are also less suitable for outdoor operation because the air lines can freeze up. These feeders are also susceptible to head load.
Tray Designs Are Limitless The shape, length, and width of modern feeder trays are almost limitless. Customers can order custom feeder trays to suit their unique process applications. Every configuration of flat, curved, vee, and tubular designs are available.
Units can be furnished with special coatings, such as neoprene, UHMW, urethane, non-stick polymer, non-stick textured surfaces, or removable abrasive-resistant steel plate. Liners made from either neoprene, UHMW, or urethane protect the feed tray while processing harsh materials. The trough can be furnished in steel or polished stainless steel to meet the most demanding requirements.
Trays can be designed for fast removal and cleanout to avoid cross contamination of materials and decreased production line downtime. Custom trays can have quick release clamps to enable removal of the tray and cover without tools. The tray is simply lifted and disconnected from the frame for easier cleaning.
Spring Systems from Steel to Fiberglass Springs are an integral part of the feeding system process because they convert the vibration from the drive to the tray, thus causing the material to move. Like trays, springs today come in a variety of materials, sizes, and configurations depending upon the application.
Fiberglass springs are the most popular configuration for light- and medium-duty applications. Small electromagnetic feeders, light- to medium-duty conveyors, and most high-precision vibratory equipment use fiberglass or multiple pieces of fiberglass as their primary spring action material.
Dense rubber springs are typically used on heavy-duty feeders and conveyors to provide stability and motion control between the drive and tray. However, rubber springs are limited to use in environments below 120F.
Air mount springs are designed to handle tough industries such as construction and mining, which present dirty, dusty, and wet environments. They withstand common issues such as rust and corrosion that typically lead to broken parts. They also reduce structural noise and are versatile.
Factors to Determine a Vibratory Feeder Typically, a feeder application will require the movement of some given material with a known bulk density over a desired distance. Parameters that influence the sizing and design of a vibratory feeder include:
* The inlet and discharge conditions for that piece of equipment * How the material is being placed on the feeding surface * The dimensions of the incoming material stream * Batch dumping vs. continuous flow * Feeding another piece of equipment, such as a belt conveyor, bucket elevator or furnace * Feed rate * Material properties, including bulk density and particle or part size.
The distance the material must travel drives the length of the unit and may include some additional length to properly interface with the receiving equipment. The volume of material moved per hour plus the materials bulk density helps determine the width and depth of the vibratory tray. The size of equipment that passes material onto the vibratory feeder also factors into the feeders width.
Proper Location of Vibrators on Feeders There are several options when deciding where to install the vibrators on a particular feeder model. With vibratory feeders, there is a concern about the product discharge height, as the equipment is often feeding material downstream to other devices.
Typically, on vibratory feeders the default location is below deck where the vibrators are attached on the underside of the unit. With below deck vibrators, the feeder will need a higher discharge height compared to a similarly-sized unit where the vibrators are side mounted or even in some applications where the vibrators are attached above the deck.
Functionally, there is no benefit to locating the vibrators above, on the side or below the unit. Provided the structure is appropriately designed for the force output of the vibrators and they sense each other, either vibrator location can provide satisfactory results.
Controlling Material Flow from a Feeder Precise metering of material flow (whether moist or dry) onto trays or other receptacles is critical to the operation of any vibratory feeder, particularly those equipped with a hopper. Several factors below influence the material flow, but when all three are combined, it is possible to vary the flow rate and provide very repeatable results as the material cascades off the feeder end.
Bed depth of material on the tray. The material must be free flowing and always available in the hopper to charge the feeder. Not enough material will starve the feeder, reduce the bed depth and cause inconsistent discharge rates.
A hopper slide gate helps adjust material depth. Opening the gate allows for a higher volume of material to be removed from the hopper, resulting in a deeper material flow and higher volume off the feeder end. Likewise, reducing the opening restricts the volume of flow out of the hopper, resulting in more shallow material flow as well as lower volume.
* Two-pole vibrators that operate at 3600 vibrations per minute (VPM) have the highest frequency and smallest amplitude * Four-pole vibrators that operate at 1800 VPM * Six-pole vibrators that operate at 1200 VPM * Eight-pole vibrators that operate at 900 VPM
Necessary adjustments to the eccentric weights of the vibrators can be made to reduce the force output from the units rated maximum. For a given frequency, more force output will result in a larger amplitude or stroke of the finished equipment.
Technical Support is Key Purchasing and installing a vibratory feeder poses fewer risks today because of increased technical assistance before and after the sale. Material samples of various densities and configurations can be tested beforehand to determine the optimum piece of vibratory and conveying equipment. This pre-testing virtually eliminates the potential problem of installing an under or oversized piece of equipment for the job at hand.
Jack Steinbuch is equipment sales engineer, Cleveland Vibrator Co. (Cleveland, OH). Cleveland Vibrators in-house testing lab allows engineers to determine optimal vibration conditions for any material and prediction of feed rates and process outcomes. Customers can visit the facility or view the testing online in real-time or request a video of their product test. For more information, call 800-221-3298 or visit www.clevelandvibrator.com.
Vibratory feeders are used in gravimetric feeding systems to handle solids with particles that are loo large to be handled by screw, rotary-vane, or vertical-gate feeders, or in operations where the physical characteristics of the solid particles would be adversely affected by passage through these volumetric feeding devices. The discharge flow pattern of a vibrating feeder is extremely smooth and thus is ideal for continuous weighing in solids flow metering applications.
The vibratory feeder consists of a feed chute (which may be an open pan or closed tube) that is moved back and forth by the oscillating armature of an electromagnetic driver. The flow rate of the solids can be controlled by adjusting the current input into the electromagnetic driver of the feeder.
The vibratory feed chute can be jacketed for heating or cooling, and the tubular chutes can be made dust-tight by flexible connections at both ends. The vibratory feeders can resist flooding (liquid-like flow) and are available for capacity ranges from ounces to tons per hour.
The Electric Vibratory Feeder is a vibratorthat provides an extremely efficient, simple and economical solution to the problem of making the most stubborn material flow freely. No longer need there be a sticking together of wet ore in the ore bin, or the arching over and hanging up of materials in hoppers and chutes with resulting lowered operating efficiency.
The powerful vibration of the simple, electro-magnetic vibrator is controlled by a separate, wall-mounted Controller, which is furnished with each vibrator. The dial rheostat in the controller varies the power of vibration. By merely turning the manual dial rheostat the power of vibration can be turned down to provide the most effective vibration required for the purpose. The controller is in a separate, dust-proof housing, arranged for wall-mounting at any desirable distance away from the vibrating mechanism attached to the bin, hopper, or chute.
These vibrators are furnished in many different sizes. Units are available that range from those equipped to handle large tonnages in ore bins down to the small noiseless model best suited to be attached to a dry reagent feeder. Reagent feeder applications are numerous, but a well-known use is where the vibrator is utilized to keep moist lime or soda-ash stirred up and flowing evenly.
In an ore bin with a flat bottom and a center discharge, the material, especially when wet, will build up in the corners and form a dead storage space just inside the walls of the bin. One or two vibrators mounted on the outside of the ore bin (opposite to each other, when two are used), will eliminate the work that otherwise frequently has to be done by hand with a pick and shovel. Another, and possibly more important aspect, is that maximum treatment efficiency is assured by an even feed to crushers or ball mills.
These vibrators are also available at extra cost with totally-enclosed explosion-proof, or water and dust-proof cases. Also, for special jobs where danger of explosion or fire exists, a water or air-pressure vibrator can be furnished. A major advantage of these hydraulic vibrators over electricvibrators is that they can be made to run at a slow speed as well as at a high speed (2400 to 4800 vibrations per minute).
The flow velocity depends on the method for loading the feederis it fed through a hopper? The velocity is also dependent on the material characteristics, size distribution and moisture content, as well as the slope of the feeder. The only way to determine the value for v is by actual observation and then the feeding rate may vary considerably.
Feeders are used to provide and control the flow of bulk solids to the process from storage units, such as bins, bunkers, silos, and hoppers. In to-days fully instrumented process plants, it is mandatory that feeders maintain a uniform flow of material at the rate set by signals from process equipment farther downstream in the flow. Large variations in feed, due to feeder blocking, arching or ratholing in the bin, may completely defeat the purpose of such a sophisticated control system with all its planned advantages to the process.
Most of the bins used in the mining and metallurgical industry to-day are of the plug flow type, as they are suited for the storage of hard, abrasive or coarse materials. Exceptions are the ore concentrate or fine powder bins which usually are of the mass flow type.
Plug flow occurs in bins or hoppers with flat sloping walls and is characterized by the flow of solids in a vertical channel extending upward from the bin outlet. Plug-flow bins are suited for solids which are free flowing, do not deteriorate with time and in which segregation is of no importance. As flow does not occur at the bin walls, this type of bin is useful for the storage of hard and abrasive materials. The drawbacks of this type of flow, however, are as follows:-
a) The live bin capacity of the bin is drastically reduced. b) The bin is not self-cleaning and usually cannot be emptied by gravity flow. c) Materials which deteriorate with time cannot be stored in this type of bin. d) The flow is erratic and non-uniform, as solids flowing through a vertical channel with a constant cross section tend to form arches which collapse and compact the material below, thus causing arching again. e) This type of flow pattern in the bin aggravates the segregation of particle sizes.
In many instances, hopper openings are large enough to prevent arching: however if the hopper is not designed for mass flow, piping or ratholing may occur. In plug flow bins, the material flows in the centre of the bin, into which the sides slough as the material is drawn from the bin. Reaching a certain level in the bin where the material has time to consolidate, sloughing will cease and a steady channel or rathole (limited flow) will form, drastically reducing the bins live capacity. In mass flow bins, channelling can also occur if the feeder does not draw the material uniformly across the whole area of the feed opening.
To overcome flow problems, flow-promoting devices such as external vibrators, pneumatic air panels, air jets and vibrating internal structures are usually installed. These relatively inexpensive devices can solve the problem in marginal cases. However, where the costly complete re-design of bins or hoppers is indicated by bulk solids flow calculations, other apparently less costly ways for improvement are usually sought.
The extension of the mine workings under adjacent lakes for the reach of the recently found copper ore body, and the introduction of sand fill underground in the past years using the mill tailings, led to build-up of the moisture content of the fine ore. In the meantime, the 50% increase of daily mill output from the original 2000 to 3000 tons necessitated finer fourth stage crushing and the addition of an extra grinding mill. The fine ore actual handled to-day is a roll-crusher product of -5/32 in size with a moisture content of 2% to 3%.
The fine ore bin, as originally conceived with its wear angles on the sloped walls, is of the plug-flow type. It performed satisfactorily in the earlier stages of operation of the plant when the material handled was coarser and lower in moisture content. With increasing ore moisture and material fineness, however, the live capacity of the fine ore bin was gradually reduced to a point where, in some instances, only channelling or ratholing occurred over the feed openings.
After visiting installations using long belt feeders, consideration was given to the use of the existing gathering conveyors as belt feeders. This scheme involved the cutting of long slots into the bin bottom above the entire length of the existing belts.
The flow pattern in a flat bottom bin with single or multiple openings is usually of the plug-flow type. The drawbacks of this type of flow have been explained previously. It was felt, however, by the author that improvements could be made by the appropriate location of feed openings and by the use of suitable feeders. The basic idea for this improvement was initiated by the review of the results of model tests performed on flat bottom bins, which indicate a mass flow type of pattern at the beginning of the bin discharge. This pattern switches gradually to plug flow as the material level drops below a certain point. This partial mass flow situation can prevail only if the material handled is reasonably free-flowing, the feed openings are sufficiently closely spaced, and the material is drawn uniformly from each opening.
The example illustrated is taken from an iron ore concentrator, and shows the arrangement in which the mill feed conveyor is receiving material from the gathering belt located underneath the two silos. The fine ore handled is taconite, -5/8 in size, and a tertiary cone crusher product with 1 to 2% moisture.
When drawn empty, the dead material left in the bin generally takes the form of a wedge-shaped hopper. However, the slope of the material should not be mistaken for the angle of repose , as it is really the included half angle e of the flow channel, which is usually much steeper due to material consolidation. Approximate expected values of e can be calculated knowing the flow properties of the material handled.
Along with our other vibratory equipment, vibratory feedersare also great problem solvers. Well-known for their ability to effectively move material from point A to point B, a well-designed vibratory feeder offers flexibility to the end-user and increased safety and efficiency in the process.
Feeders can range from small base mounted CF-A, pneumatic powered feeders moving small quantities of dry bulk material in a controlled manner to a much larger base, to a cable-supported EMF, electromechanical feederconveyingliterally tons of material an hour. We have incorporated vibratory feeders into the processes of these materials and more: almonds, crushed limestone, shelled corn, powdered metal, metal billets, various pipe fittings, scrap brass and bronze, crushed and shredded automobiles, hot dross and much more. We work with a variety of industries feeding an endless variety of materials!
How far to move obviously drives the length of the unit and may include some additional length to properly interface with the receiving equipment. The volume of material moved per hour plus the materials bulk density will drive the width and depth of the vibratory tray. If the equipment that passes the material onto the vibratory feeder doesnt restrict the specification of the feeders width, we then look at the volume and density of the material.
Using past experience and product testing, an estimated linear velocity for the material is used to calculate a cross-sectional area for the material flow based on the rate per hour and bulk density. Once weve calculated that cross-sectional flow area, we factor in the tray width and see what happens to our depth of material on the vibratory tray. If everything looks good and makes sense for the specifics of theapplicationweve arrived at the final size and specifications for the vibratory feeder.
A well-designed and properly installed vibratory feeder is a thing of beauty! Simple and effective, it lives to move material from point A to point B. These feeders are mechanically very clean and virtually maintenance-free. Small air-powered CF-A units are driven by a variety of appropriately sized robust and quiet air-cushioned pneumatic piston vibrators. Supply clean and lubricated air to these units and theyll provide dependable service for a very long time. If the feeder is powered by a pair of Cleveland Vibrators rotary electric vibrators, some of which are permanently lubricated, the equipment will perform its task of effectively moving material for years to come.
Without a doubt, the most common use for a vibratory feeder is to move material as described above, but a number of our customers also use vibratory feeders to add or spread dry material onto the surface of their products.
We have a number of customers who use our EMF units to apply a layer of dry product onto the surface of a moving product as it passes under the feeder. By adjusting the operating speed of the vibratory motors and/or the eccentric weights, operators can dial in the right combination of frequency and force to apply a consistent and repeatable volume of material onto the surface of their product to successfully meet their rate requirements.
We visited a potential customers facility to review such an application. The company is looking to improve on their current method of applying a granular product onto the surface of their raw product as it moves down a conveyor belt. Currently, they have a hopper mounted above the conveyor and a rotating knurled cylinder on the bottom opening of the hopper. Rotating the cylinder is intended to permit the material to drop onto the moving product. Unfortunately, the material size varies a bit and that different sized material is important to the process, but it also creates a problem for the current process. Jams and inconsistent spreading of the product have a negative impact on the finished product.
After looking at their current process, we suggested the use of a cable suspended vibratory feeder. Due to the open nature of the feeder, different sized particles can be easily conveyed without concerns about jamming. By adjusting the operating speed and force output of the vibrators, the feeder can spread a consistent layer of the secondary product edge to edge on to the material below. Coupling the feeder with a small storage hopper would ensure that the feeder has a plentiful supply of material, critical in making sure the feeder maintains a consistent and repeatable thickness of material on the vibratory feeding surface, resulting in a well-controlled and regulated volume of product conveyed by the feeder.
Its worth keeping in mind that a properly sized, designed and installed vibratory feeder is a real problem-solver. Feeders can successfully move a very wide variety of products from point A to B and can be used to meter or spread one product onto another.
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.
Vibratory feeders vibrate in a controlled fashion to feed dry materials such as powders, flour, sand, or coal at a consistent speed and volume in bulk conveying applications. They are typically used under hoppers or similar storage vessels to control the flow of materials moving from the vessel into other processes or conveying systems.
The bullfrog froglets receiving food in a vibrating feeder present better productive performance (weight gain, feed conversion and specific growth rate) than animals fed ration and housefly larvae in a linear feeder.A production system with vibratory feeders avoids the housefly larvae production in bullfrogs creating, thus avoiding an increase in production costs.This response can be related to the greater visual stimulus of the food by bullfrogs fed in the vibrating feeders, in which food had greater movement.
The bullfrog froglets receiving food in a vibrating feeder present better productive performance (weight gain, feed conversion and specific growth rate) than animals fed ration and housefly larvae in a linear feeder.
Studies have developed techniques for bullfrog feeding in which movement of the food stimulates food intake in the absence of housefly larvae. We analyze a completely randomized design with two treatments (vibrating tray and linear feeder) in triplicate. A total of 1800 bullfrog froglets (Lithobates catesbeianus) (7.600.59g) were divided in six pens of 12m2 and density 25/m2. Three fattening pens contained linear cement feeders (3.00.50m) with a V-shaped bottom that crossed the pen longitudinally at each side of the pool containing commercial diet (40% crude protein) with added 5% housefly larvae. In the other three pens, six vibrating feeders trays (8034cm) per pen were arranged linearly, three at each side of the pool with commercial ration without housefly larvae. The productive performance of frogs was assessed by weight gain, feed intake, feed conversion, specific growth rate and survival by 90 days. We observed that bullfrog froglets receiving food in a vibrating feeder tray present better productive performance (weight gain, feed conversion and specific growth rate) than animals fed ration and housefly larvae in a linear feeder. This response can be related to the greater visual stimulus of the food by frogs fed in vibrating feeder trays, in which food had greater movement.