This article covers everything you need to know about vibratory feeders.
Read further to learn more about:
- What is a vibratory feeder?
- Overview of bulk material handling
- Working principles of vibratory feeders
- Feeder trough design
- And much more…
Chapter 1: What is a Vibratory Feeder?
Vibratory feeders are short conveyors used to 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. Gravity counters some of the acceleration from the vibration and helps move the materials in a certain direction.
A basic vibratory feeder consists of a trough supported by springs, hinged links, or other force-dampening mechanical components. These isolate the vibratory feeder from the structural members of the building which can cause unwanted reaction forces. Attached to the trough is a drive unit that produces high frequency, low amplitude oscillations. These oscillations are tuned to create the desired movement of the material.
A vibratory feeder is one of the many pieces of equipment designed for bulk handling. Bulk handling materials have certain properties that separate them from fluids (liquid and gas). Other equipment used for transporting bulk materials are screw conveyors, belt conveyors, apron conveyors, flight and drag conveyors, pneumatic conveyors, reciprocating plates, and so on.
Chapter 2: Overview of Bulk Material Handling
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. These materials have varied behaviors depending on temperature, humidity, time, and so on. They do not flow as easily and as predictable as liquids and gases. They can also easily degrade any equipment for conveying and handling by erosion and impingement.
In handling bulk materials, it is important to know their properties as summarized below. These properties must be determined to properly design bulk handling equipment.
- Adhesion: This is the property of a material to stick or cling to another material. When being gravimetrically discharged, they 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 is the ability of the material to attract or stick onto materials with the same chemical composition. Highly cohesive material does not flow readily as 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 is the difference between the angle of repose and the angle of fall. The greater is the angle of difference, the greater is the free flow characteristic 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 taking a spatula into a heap of sample material and lifting it with maximum material coverage. The angle of spatula is the average of the angles made by the lateral sides of the material with the horizontal.
- Compressibility: This is the percentage difference of packed density with aerated density. Compressibility describes the 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 is the amount of water dispersed throughout the bulk. Materials with high moisture content are more difficult to handle due to the more pronounced effects of adhesion and cohesion. Moisture also contributes to the variation of weight of the material.
- Hygroscopicity: This is the tendency of the material to absorb moisture. The design of the equipment that handles materials with high hygroscopicity must prevent the entry of air containing high moisture.
Static Charge: Because of the continuous contact of particles with each other and the walls of the container, the particle tends to build up static charge. This phenomenon becomes a problem since the cohesive and adhesive forces become stronger making the flow more difficult.
- 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.
Chapter 3: Working Principle of Vibratory Feeders
The general design of a vibratory feeder consists of a drive unit that generates the vibratory action, and a deep channel or trough which contains the bulk material. The drive unit causes vibrations with both horizontal and vertical force components. The vibration causes a straight-line motion, provided that the vibration is sinusoidal, and the force components are in-phase. Besides the drive unit and trough, a vibratory feeder is made up of the following parts:
- Feed End: This is the part of the trough that is 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 the weight attached to the shaft or flywheel with a slight offset from the axis of rotation. Rotating the shaft produces an unbalanced moment creating oscillations.
- Reactor Springs: These are the primary springs in the vibrating system that continuously store and release energy during operation.
- Isolation Springs: These springs are used to 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: Material added to cover the surface of the trough design to resist wear, to heat or cool, to reduce noise and friction, or to 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 have operating frequencies that range from 200 to 3600 vibrations per minute with an amplitude of 1 to 40 mm. The vertical acceleration component is usually near gravitational acceleration (9.81 m/s2). This is enough to transport materials with a gentle shuffling motion producing minimal impact and noise. Because of this, the material moves across the trough by sliding action. The material does not actually leave the surface of the trough when the pressure between the surface and the material is at a minimum. In applications where the material has to lift from the trough and then impact again as it falls, special considerations must be made to counter the impact force and the increased noise levels.
Vibratory feeders are distinct from other bulk material handling equipment because the material moves independently from the conveying medium. This contrasts equipment such as conveyor belts and aprons where the material is static relative to the conveying medium. This enables additional processes to be integrated while the material is in transit. Below are some of the processes that can be performed while transporting using vibratory feeders.
- Spreading or Distributing
- Water Quenching
Besides the integration of additional processes, vibratory feeders are desired due to these reasons,
Low Headroom Requirement: Vibratory feeders are a solution to gravimetric feeding in installations where there is limited vertical clearance. Conveying using vibratory feeders is suited for the horizontal movement of bulk products.
Handling of Hot Materials Without Excessive Heating of the Equipment: Vibratory feeders can be tuned so there is a little lift produced from the upward phases of the oscillation cycle. This allows some air to pass and cool the material while at the same time minimizing contact.
Handling of Abrasive Materials: Tuning the vibratory feeder to minimize contact with the material also reduces vibration. Also, vibratory feeders can be lined with abrasion-resistant materials.
Inherent Self-Cleaning Properties: Since the material is not static on the surface of the machine, the material does not easily adhere. There is no chance for the material to accumulate on the surface of the trough.
Able to Meet Strict Sanitation Requirements: Aside from its self-cleaning properties, the trough or pan of a vibratory feeder is a continuous surface. There are no cavities or holes where contaminants can accumulate. The pan can be made of stainless steel suited for food applications.
Can Be Made Water and Dust-Tight: Vibratory feeders can be designed with IP or NEMA-rated covers and sealing.
No Moving Parts in Contact Where the Material Can Impinge and Interrupt Operation: The trough is a continuous channel with no hinges, joints, or deformable members, unlike belt and apron conveyors. Because of these benefits, vibratory feeders are widely used in 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 according to their drive unit, method of applying vibration to the trough, and the generated reaction to the supporting structures. In selecting a vibratory feeder, it is important to know the distinction between these categories. For example, it is not enough to specify only brute force vibratory feeders. Brute force feeders are available with electromagnetic or electromechanical drive units. This chapter tackles the working principle of each type and their recommended applications.
Below are vibratory feeders classified according to their drive unit:
Electromechanical Vibratory Feeders: These types of feeders create vibration by rotating eccentric weights using electric motors. They are also referred to as eccentric-mass mechanical feeders. A simple design consists of a single rotating eccentric mass. However, the more common is the use of two counter-rotating masses. The axes of rotation of these two masses lie within the same plane and their rotation is synchronized to produce the right oscillation.
Electromagnetic Vibratory Feeders: Electromagnetic feeders operate using the cyclic energization of one or more electromagnets. In comparison with electromechanical drives, electromagnetic drive units contain lesser moving parts. The trough is caused to vibrate using the magnetic force impulses supplied by the electromagnet. In terms of cost, electromagnetic feeders are cheaper for low-volume applications. This is true at rates less than 5 tons per hour.
Hydraulic and Pneumatic Vibratory Feeders: These types of feeders operate using pneumatic or hydraulic oscillating pistons. The main advantage of using these types is their suitability for hazardous areas. The motors for driving the pumping units can be located in remote areas. This eliminates the need for expensive explosion-proof specifications.
Direct Vibratory Feeders: Direct or positive mechanical vibratory feeders use a crank and connecting rod that generate oscillation with a low frequency and high amplitude. Positive conveyors are rarely used due to the high vibration transmitted to the supporting structures. A way to counter the high vibration transmitted is to use a counterweight or counter-vibrating double troughs.
Next are the types of vibratory feeders according to the method of applying vibration to the trough. They differ on the configurations of their springs and the frequency and amplitude of their drive unit.
Brute Force Feeders: This type of feeder is called single-mass systems because the vibratory drive is directly connected to the trough assembly. They are generally used for heavy-duty applications. The drive system can also be electromagnetic, but the electromechanical drive is mostly used. Brute force feeders create oscillating forces by rotating a heavy centrifugal counterweight.
Brute force feeders have the simplest design among the vibratory feeders. However, they have limited feed rate regulation and range since they are designed as constant rate feeders. The feed rate can be adjusted by changing the slope of the trough, opening, amount of counterweight, and length of stroke. Variable speed drives are rarely installed since the trough stroke is slightly independent of the operating speed of the motor. Tuning the motor speed is not necessary for brute force feeders.
Natural Frequency Feeder: Natural frequency feeders, also known as tuned or resonant feeders, use two or more spring-connected masses. The most common is the two-mass, spring-connected vibratory system. One mass is for the trough, while the other is for the reaction or excitation mass. The natural frequency feeder takes advantage of the natural magnification of the oscillations which occurs when the system operates at a speed near its natural frequency or resonance condition. Because of this, a relatively small force is required to generate the necessary vibratory forces. The vibratory force can be generated by rotating eccentric weights or electromagnets.
The main design factor that needs to be considered is not the weight of the material or load, but the damping capacity of the bulk. The damping effect is the result of the energy absorption of the material. Granular and powdered materials tend to dissipate energy intergranular friction and deformation when vibrated through.
Vibratory feeders are also classified according to their reactions to their foundations and supporting structures. Selecting which type depends on the rigidity and allowable stresses of the structure.
- Unbalanced Vibratory Feeders: These types of feeders have oscillating forces that subject the supporting structures to reversing load conditions. A reversing load condition means continuous, alternating tensile, and compressive forces while the mean stress is zero. Though the supporting structure can easily carry the static load of the feeder, it becomes easily fatigued during operation. Unbalanced vibratory feeders can only be installed on structures that have very large allowable deflections compared to the amplitude of the vibrations. Moreover, the structure must have a natural frequency that excessively exceeds the operating frequency of the feeder.
- Balanced Vibratory Feeders: A balanced vibratory feeder is equipped with a dynamic balancing system composed of counterbalancing weights installed to the conveyor base. Other designs employ secondary weights attached to the reactor springs. These types of feeders are designed to reduce the unbalanced reaction force transmitted to the supporting structure. This is achieved by vibrating the secondary weights 180° out of phase with the oscillation of the trough. Balanced vibratory feeders are recommended to be installed on structures with questionable rigidity.
Chapter 5: Feeder Trough Design
The capacity of the vibrating feeder depends on the width of the trough, depth of material flow, bulk density of the material, and the linear feed rate. This is expressed by the formula,
C = WdR / 4800
Where C is the capacity in tons per hour (metric tons per hour), W is the trough width in inches (millimeter), d is the depth of material in inches (millimeter), γ is the bulk density in pounds per cubic feet (grams per cubic centimeter), and R is the linear feed rate in feet per minute (meter per minute). For metric units, change the 4,800 constant to 16,700.
Usually, the required capacity is already given by the rate requirement of upstream or downstream processes. From the required capacity, combinations of trough width and linear feed rate can be obtained along with the bulk density of the material and expected feed depth. Manufacturers typically provide charts, tables, and graphs that describe the characteristics of the feeder.
Feeder troughs are usually made from mild steel, stainless steel (particularly grade 304), and special alloys with higher abrasion resistance. Other constructions feature ordinary steels that are lined with replaceable materials such as rubber, plastic, or ceramics. Troughs are formed into different shapes depending on the type and properties of the materials and the integrated processes. Common trough shapes and features are:
- Flat Bottom
- Half Round Bottom
- Radius Bottom
- V Shape
- Grizzly Section
- Dust and water-tight sealing and cover
- Belt-centering Discharge
- Diagonal Discharge
- Screen Decks
Chapter 6: Vibratory Bowl Feeders
Vibratory feeders discussed in the previous chapters have a linear trough. Vibratory bowl feeders, on the other hand, are special types of vibratory feeders that have troughs wound helically. These machines use vibration to toss and shuffle the materials along the slightly slanted surface of the helical trough. Because of the tossing and shuffling action, parts with asymmetrical shape tend to be oriented as it moves through the bowl feeder. This is the main benefit of vibratory bowl feeder; it is not only used for conveying, but also for orienting items. Its trough is not flat but has a specific profile that only accepts materials with the correct orientation. Screening devices are sometimes attached to the bowl to remove parts that are not positioned or oriented properly. Vibratory bowl feeders are used in assembly and packaging lines in industries such as electronics, automotive, and pharmaceutical.
- Vibratory feeders are short conveyors used to 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 as predictable as liquids and gases.
- The general design of a vibratory feeder consists of a drive unit that generates the vibratory action and a deep channel or trough which contains the bulk material.
- Vibratory feeders can be classified according to their drive unit, method of applying vibration to the trough, and the generated reaction to the supporting structures.
- Vibratory bowl feeders, on the other hand, are special types of vibratory feeders which 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.