Vibratory Feeders

Chapter 1: What is a Vibratory Feeder?

A vibratory feeder is a conveying system designed to deliver components or materials into an assembly process through controlled vibratory forces, gravity, and guiding mechanisms that ensure proper positioning and orientation. The system features accumulation tracks of various widths, lengths, and depths, which are specifically selected to match the requirements of the application, material, component, or part.

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The goal of vibratory feeders is to move, feed, and convey bulk materials using various forms of vibrations to ensure proper orientation for integration into a production line. They are highly efficient for accelerating assembly operations and gently separating bulk materials. The guided movement produced by a vibratory feeder relies on horizontal and vertical accelerations, which generate the precise amount of force needed to position materials accurately.

The accumulation track of a vibratory feeder, whether linear or gravity-based, helps slow the vibrations and aids in directing the movement of materials. Drive units, which can be piezoelectric, electromagnetic, or pneumatic motors, provide the vibrations, rotation, and necessary force to ensure the feeder operates efficiently.

The design of a vibratory feeder starts with a transporting trough or platform, where materials are moved by controlled linear vibrations. These vibrations create jumping, hopping, and tossing motions of the materials. The travel speeds of the materials can range from a few feet per minute to over 100 feet (30 meters) per minute, depending on design features such as frequency, amplitude, and the slope angle of the trough or platform.

Vibratory feeders control material flow in a manner similar to how orifices or valves control fluid flow. They can be adjusted to feed bulk materials at a fixed rate. The structure of a vibratory feeder typically includes soft springs that manage vibrations and capacities, allowing for the handling of bulk materials ranging from a few pounds per hour to several tons per hour.

One advantage of vibratory feeders is their ability to prevent bridging, a problem that can slow down processes and hinder efficient material flow. The free-flow design in the throat of a vibratory feeder minimizes bridging caused by friction. The forces that ensure smooth and even material flow are categorized into direct force and indirect force. Direct force applies energy directly to the feeder's deck, while indirect force relies on resonant or natural frequencies to achieve the desired material movement.

Recent designs of vibratory feeders often feature enclosed, box-shaped constructions with flanged inlets and outlets, enhancing their ability to contain dust and prevent water ingress. This design modification helps in eliminating spillage and streamlining installation processes. Additionally, some enclosed models integrate a vibrating bin bottom activator with the vibratory feeder to further control material flow and improve efficiency.

Chapter 2: Overview of Bulk Material Handling

Bulk materials are dry solids that come in powder, granular, or particle forms and are often grouped randomly to form a bulk. These materials exhibit diverse behaviors depending on factors such as temperature, humidity, and time, which can affect their flow properties. Unlike liquids and gases, bulk materials do not flow as easily or predictably. Additionally, their handling can pose challenges, as they can cause erosion and impingement that may degrade conveying and handling equipment.

In handling bulk materials, it is essential to understand their properties, as outlined below. These properties are critical for the proper design of bulk handling equipment.

• Adhesion: This is the property of a material to stick or cling to another material. When being gravimetrically discharged, materials tend to arc, bridge, cake, etc. while clinging onto the surface of the container. This behavior can interrupt the material flow. A debridging mechanism is needed to break this formation.

• Cohesion: This refers to the material's ability to attract or adhere to other materials with the same chemical composition. Materials with high cohesion do not flow easily because they tend to clump together.

  
  
• Angle of Repose: This is the maximum angle made by the lateral side of a cone-shaped pile of falling material with the horizontal. This indicates how free-flowing a material will be. The angle of repose is particularly useful in designing feeders and conveyors relying on gravity.
• Angle of Fall: This is the angle made by the slope of the cone with the horizontal after getting the angle of repose and applying an external force to collapse the cone.

• Angle of Difference: This represents the difference between the angle of repose and the angle of fall. A larger angle of difference indicates better free flow characteristics of the material.

  
  
• Angle of Slide: This is the angle made by a flat surface containing a certain amount of material with the horizontal. This indicates the material's flow characteristics inside hoppers, pipes, chutes, etc.

• Angle of Spatula: This is measured by inserting a spatula into a heap of sample material and lifting it to achieve maximum material coverage. The angle of spatula is the average of the angles formed by the lateral sides of the material with the horizontal.

  
  
• Compressibility: This is the percentage difference between packed density and aerated density. Compressibility describes the material's size, uniformity, deformability, surface area, cohesion, and moisture content of the material.
• Bulk Density: This is defined as the mass of the material per unit volume. Bulk density is important for finding the equipment capacity and the compressive strength of the material that can occur within the container.
• Particle Size: This is the average dimension across a single particle. This is commonly determined by getting the equivalent diameter of the particle. Typical particle sizes of common bulk materials are shown in the table below. Bulk Material Typical Size Range Coarse Solid 5 ' 500 mm Granular Solid 0.3 ' 5 mm Coarse Powder 100 ' 300 µm Fine Powder 10 ' 100 µm Superfine Powder 1 ' 10 µm Ultrafine Powder < 1 µm

• Moisture Content: Moisture content refers to the amount of water distributed throughout the bulk material. Materials with high moisture content are more challenging to handle due to increased adhesion and cohesion effects. Additionally, moisture contributes to variations in the material's weight.

  
  
• Hygroscopicity: This is the tendency of the material to absorb moisture. The design of the equipment that handles materials with high hygroscopicity must prevent air containing high moisture from entering.

• Static Charge: Continuous contact between particles and the walls of the container can cause the particles to build up a static charge. This buildup of static electricity strengthens cohesive and adhesive forces, making material flow more challenging.

  
  
• Abrasion: Abrasion is the ability of the material to scrape or wear the surface of the handling equipment. This is a problem when handling materials such as coke and sand. To counter abrasion, steels with high hardness or plastics with high abrasion resistance are used.

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Chapter 3: Working Principles of Vibratory Feeders

The general design of a vibratory feeder includes a drive unit that generates the vibratory action and a deep channel, or trough, that holds the bulk material. The drive unit produces vibrations with both horizontal and vertical force components. When the vibration is sinusoidal and the force components are in-phase, the resulting motion is straight-line. In addition to the drive unit and trough, a vibratory feeder comprises the following parts:

• Feed End: This is the part of the trough located at the most upstream end where the material is fed.
• Discharge End: Opposite the feed end is the discharge end, located at the most downstream part of the trough. This is where the material is ejected off of the unit.

• Eccentric Weight: This is a weight attached to the shaft or flywheel, slightly offset from the axis of rotation. As the shaft rotates, the unbalanced moment produced creates oscillations.

  
  
• Reactor Springs: These are the primary springs in the vibrating system that continuously store and release energy during operation.
• Isolation Springs: These springs support the feeder while protecting the supporting structure from the generated vibrations.
• Tuning Springs: These springs are used to tune the frequency of a natural frequency feeder. This is done by adding or subtracting springs or by modifying the spring rate. Other feeder designs tune the frequency by adding or subtracting weights.
• Dynamic Balancer: Balanced vibratory feeders use a dynamic balancer that reduces the transmitted dynamic forces to the supporting structure. This is achieved by reacting to the reversing forces of the drive unit.

• Liner: This is material added to the surface of the trough to resist wear, manage heat or cooling, reduce noise and friction, or prevent material buildup.

  
  
• Screen: An additional part that is used to separate fine particles from coarser materials.
• Grizzly: This is a heavy-duty screen consisting of bars, rails, or tubes running in the direction of material flow. This is used for screening coarser materials.

Vibratory feeders and conveyors typically operate at frequencies ranging from 200 to vibrations per minute and have amplitudes of 1 to 40 mm. The vertical acceleration component is usually close to gravitational acceleration (9.81 m/s²). This setup provides a gentle shuffling motion that minimizes impact and noise, allowing materials to move across the trough through sliding action. The material generally remains in contact with the trough's surface, with minimal pressure between the surface and the material. In cases where the material must lift from the trough and fall back down, additional measures may be needed to manage impact forces and reduce noise levels.

Vibratory feeders differ from other bulk material handling equipment because the material moves independently of the conveying medium. This is unlike equipment such as conveyor belts and aprons, where the material remains static relative to the conveying medium. This unique feature allows for additional processes to be integrated while the material is in transit. Below are some processes that can be performed during transport with vibratory feeders.

• Scalping
• Screening
• Sorting
• Spreading or Distributing

• Cooling
• Drying
• Dewatering
• Water Quenching

Besides the integration of additional processes, vibratory feeders are preferred for the following reasons:

Low Headroom Requirement: Vibratory feeders are ideal for installations with limited vertical clearance, providing an effective solution for gravimetric feeding. They are well-suited for the horizontal movement of bulk products.

Handling of Hot Materials Without Excessive Heating: Vibratory feeders can be adjusted to produce minimal lift during the upward phases of the oscillation cycle. This configuration allows air to circulate and cool the material while reducing contact and heat buildup.

Handling Abrasive Materials: By tuning the vibratory feeder to minimize contact with the material, vibration is reduced. Additionally, vibratory feeders can be lined with abrasion-resistant materials to enhance durability.

Inherent Self-Cleaning Properties: Because the material is not static on the surface of the machine, it does not easily adhere. This prevents material from accumulating on the trough's surface.

Adherence to Strict Sanitation Requirements: In addition to its self-cleaning properties, the trough or pan of a vibratory feeder is a continuous surface without cavities or holes where contaminants could accumulate. The pan can be made of stainless steel, making it suitable for food applications.

Water and Dust-Tight: Vibratory feeders can be designed with IP or NEMA-rated covers and sealing to prevent the ingress of water and dust.

No Moving Parts Where Material Can Impinge and Interrupt Operation: The trough of a vibratory feeder is a continuous channel without hinges, joints, or deformable members, unlike belt and apron conveyors. This design minimizes interruptions and enhances reliability. As a result, vibratory feeders are extensively used in various industries, including mining, smelting, metal casting, recycling, glass batch processing, furnace charging, wood processing, food processing, pharmaceuticals, and packaging.

Chapter 4: Types of Vibratory Feeders

Vibratory feeders can be classified based on their drive unit, vibration application method, and the reactions generated by the supporting structures. When selecting a vibratory feeder, understanding these distinctions is crucial. For instance, specifying only brute force vibratory feeders is insufficient, as they come with various drive units, such as electromagnetic or electromechanical. This chapter explores the working principles of each type and their recommended applications.

Below are vibratory feeders classified according to their drive unit:

Vibratory Feeders by Drive Unit

Electromechanical Vibratory Feeders

These feeders generate vibrations by rotating eccentric weights with electric motors and are also known as eccentric-mass mechanical feeders. A basic design features a single rotating eccentric mass, but the more common approach uses two counter-rotating masses. These masses rotate in the same plane with synchronized axes, creating the desired oscillation.

Electromagnetic Vibratory Feeders

Electromagnetic feeders use the cyclic energization of one or more electromagnets to operate. Compared to electromechanical drives, electromagnetic drive units have fewer moving parts. The electromagnets provide magnetic force impulses that cause the trough to vibrate. Electromagnetic feeders are more cost-effective for low-volume applications, particularly at rates below 5 tons per hour.

Hydraulic and Pneumatic Vibratory Feeders

These feeders use pneumatic or hydraulic oscillating pistons for operation. They are particularly advantageous in hazardous areas because the motors driving the pumping units can be situated in remote locations, reducing the need for costly explosion-proof specifications.

Direct Vibratory Feeders

Direct or positive mechanical vibratory feeders employ a crank and connecting rod to create oscillations with low frequency and high amplitude. These feeders are infrequently used because they transmit significant vibration to the supporting structures. To mitigate this, counterweights or counter-vibrating double troughs can be used to balance the vibrations.

Next are the types of vibratory feeders classified by the method of applying vibration to the trough. They vary based on their spring configurations and the frequency and amplitude of their drive units.

Brute Force Feeders

This type of feeder is known as single-mass systems because the vibratory drive is directly connected to the trough assembly. They are typically used for heavy-duty applications. While the drive system can be electromagnetic, electromechanical drives are more commonly used. Brute force feeders generate oscillating forces by rotating a heavy centrifugal counterweight.

Brute force feeders have the simplest design among vibratory feeders. However, they offer limited feed rate regulation and range, as they are designed as constant rate feeders. Feed rate adjustments can be made by changing the slope of the trough, the opening size, the amount of counterweight, or the length of the stroke. Variable speed drives are rarely used because the trough stroke is only slightly dependent on the motor's operating speed. Tuning the motor speed is generally unnecessary for brute force feeders.

Centrifugal Feeders

Centrifugal feeders, also known as rotary feeders, use a spinning bowl to move parts towards its outer edge. The feeder features a centrally driven conical rotor surrounded by the bowl walls. As the feeder spins, rotary force separates the parts and components, pushing them towards the outer circumference of the bowl.

Centrifugal feeder systems are commonly used in industries such as food processing, pharmaceuticals, and medical supplies, where rapid handling of small or unusually shaped components is necessary. These systems can sort and properly orient components at rates of up to 3,000 per minute, regardless of their size or shape. With a simple design, centrifugal feeders are cost-effective, highly reliable, and require low maintenance.

Natural Frequency Feeder

Natural frequency feeders, also known as tuned or resonant feeders, utilize two or more spring-connected masses. The most common configuration involves a two-mass system: one mass for the trough and the other for the reaction or excitation mass. These feeders take advantage of the natural magnification of oscillations when the system operates near its natural frequency or resonance condition. This design allows a relatively small force to generate the necessary vibratory forces. Vibratory force can be produced by rotating eccentric weights or electromagnets.

The main design factor to consider is not the weight of the material or load but the damping capacity of the bulk. Damping effect refers to the energy absorption of the material. Granular and powdered materials tend to dissipate energy through intergranular friction and deformation when vibrated.

Vibratory feeders are also classified based on their reactions to their foundations and supporting structures. The choice of type depends on the rigidity and allowable stresses of the supporting structure.

Vibratory Feeders by Supporting Structures

Unbalanced Vibratory Feeders

These feeders generate oscillating forces that subject the supporting structures to reversing load conditions. This means the structures experience continuous and alternating tensile and compressive forces with a mean stress of zero. While the structure can handle the static load of the feeder, it can become easily fatigued during operation. Unbalanced vibratory feeders should only be installed on structures with very large allowable deflections relative to the amplitude of the vibrations. Additionally, the structure must have a natural frequency that significantly exceeds the operating frequency of the feeder.

Balanced Vibratory Feeders

A balanced vibratory feeder features a dynamic balancing system with counterbalancing weights mounted on the conveyor base. Some designs use secondary weights attached to the reactor springs. These feeders are designed to minimize the unbalanced reaction force transmitted to the supporting structure by vibrating the secondary weights 180° out of phase with the trough's oscillation. Balanced vibratory feeders are recommended for installation on structures with questionable rigidity.

Horizontal Motion Conveyors

Horizontal motion conveyors, also known as horizontal differential conveyors, differential motion conveyors, or differential conveyors, use a two-cycle motion to transport free-flowing bulk materials horizontally. This motion involves a slow forward advance followed by a quick return. The conveying surface can be an open pan or a closed conduit with a seamless one-piece construction. During the forward movement, components remain stationary, while in the return cycle, the pan or conduit moves rapidly backward, depositing the components.

A horizontal motion conveyor operates with a continuous forward and backward motion, allowing materials to be conveyed smoothly at speeds of up to 40 feet (12 m) per minute over distances of up to 200 feet (61 m). With no moving parts other than the drive unit, these conveyors minimize safety risks, simplify cleaning, and reduce maintenance. Their smooth, even motion makes them particularly suited for handling fragile materials that require careful handling.

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Horizontal motion conveyors are capable of moving components either backward or forward one direction at a time. They can be configured for slight inclines or declines to handle flat rectangular or square parts. Additionally, these conveyors can be set up to deliver parts at their midsection. The design ensures that components move along the open pan or conduit without experiencing vertical acceleration or bouncing action.

Chapter 5: Feeder Trough Design

The capacity of a vibrating feeder is determined by several factors including the width of the trough, the depth of material flow, the bulk density of the material, and the linear feed rate. This can be expressed using the formula:

C = WdR /

In this formula, C represents the capacity in tons per hour (metric tons per hour), W denotes the trough width in inches (millimeters), d is the depth of material in inches (millimeters), γ stands for the bulk density in pounds per cubic foot (grams per cubic centimeter), and R indicates the linear feed rate in feet per minute (meters per minute). When using metric units, replace the constant 4,800 with 16,700.

Typically, the required capacity is determined by the needs of upstream or downstream processes. Given this required capacity, you can derive possible combinations of trough width and linear feed rate, factoring in the material's bulk density and the anticipated feed depth. Manufacturers usually offer charts, tables, and graphs that outline the feeder's specifications and performance characteristics.

Feeder troughs are typically constructed from mild steel, grade 304 stainless steel, or abrasion-resistant alloys. In some designs, ordinary steels are lined with replaceable materials like rubber, plastic, or ceramics. The shape of the troughs varies based on the type and properties of the materials being handled and the specific processes they are integrated into. Common trough shapes and features include:

• Flat Bottom
• Half Round Bottom
• Radius Bottom
• V Shape
• Tubular

• Grizzly Section
• Dust and water-tight sealing and cover
• Belt-centering Discharge
• Diagonal Discharge
• Screen Decks
• Water-jacketed

Chapter 6: Vibratory Bowl Feeders

Vibratory bowl feeders feature troughs that are wound in a helical pattern and utilize vibrations to move and shuffle materials along the gently inclined surface of the trough. This tossing and shuffling action helps to orient parts with irregular shapes as they progress through the feeder.

Vibratory bowl feeders offer several advantages, including efficient conveying and proper positioning of parts. The troughs are designed with specific profiles to ensure materials are oriented correctly. Screening devices attached to the bowl help remove parts that are not properly positioned or oriented. These feeders are commonly used in assembly and packaging lines across industries such as electronics, automotive, and pharmaceuticals.

Conclusion

• Vibratory feeders are short conveyors that transport bulk materials utilizing a controlled vibratory force system and gravity. The vibrations impart a combination of horizontal and vertical acceleration through tossing, hopping, or sliding-type of action to the materials being handled.
• Bulk materials are dry solids that can be in powder, granular, or particle form with different sizes and densities randomly grouped to form a bulk. They do not flow as easily and predictably as liquids and gasses.
• The general design of a vibratory feeder consists of a drive unit that generates the vibratory action and a deep channel, or trough, that contains the bulk material.
• Vibratory feeders can be classified according to their drive unit, method of applying vibration to the trough, and generated reaction to the supporting structures.
• Vibratory bowl feeders are special types of vibratory feeders that have troughs wound helically with special profiles and attachments. They are used in part or item feeding applications where the items are required to be in a specific orientation.

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.

What are Vibratory 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 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 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 tons per hour or more.

Advantages 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 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 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 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.

Vibrating Feeder Design Types:

The mechanism for producing the vibratory forces can be classified as follows:

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 Principal of Natural Frequency Operation:

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.

Control in Vibrating Feeder Design

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 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.

Hopper Bottom and Feed Opening Geometry

Since most applications involve bulk materials, a typical layout consists of a hopper with a vibrating feeder mounted below to feed the material to a conveyor, scale, or processing unit.

Projected Vertical Hopper Opening

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.

Projected Horizontal Opening

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.

Feeder Size, Slope, and Trough Length

Capacity requirements determine the feeder-pan dimensions and slope. The volumetric capacity of a feeder may be determined by the formula:

A x V = Q Q= cu. fpm A= projected horizontal area V= average velocity of material through opening

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.

Feeder Size Selection

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.

Trough Material Selection

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.

New Developments in Feeders

Totally Enclosed Feeders

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.

Activator / Feeder (UN-COALER®)

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 material's 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.

Advantages of this feeder design:

• Large vibrating opening, up to 12' x 12', permits large hopper discharge openings for greater drawdown volume.
• Compact, low profile design reduces tunnel depth for substantial savings in foundation costs.
• Fixed or variable feed rate designs permit continuous operation to assure uniform feed to reclaim conveyor.
• Unit mounts directly above belt conveyor and evenly distributes material to eliminate belt tracking problems.
• Few moving mechanical parts are easily maintained from the tunnel.
• The entire UN-COALER®  is mounted below grade.
• Rectangular shape with straight line surfaces greatly simplify hopper design, dust and connections and concrete work.

APPLICATIONS

Track Hopper Reclaim:

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-COALER®S  can be applied with considerable savings in pit depth.

Crusher Feeder:

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-COALER®'s 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.

RECLAIM SYSTEMS

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.

Windrow Reclaim:

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-COALER®s that are foot mounted directly below grade. The contiguous hoppers are arranged to permit the UN-COALER®S  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.

Barn-Type Storage

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 reclaimed simultaneously 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.

Silo Reclaim

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 savings occurs because of fewer pieces of equipment, simpler and less costly concrete work and installation procedures.

For more information, please visit PE Jaw Crusher Supplier.