This article covers everything you need to know about vibratory feeders.
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A vibratory feeder is a transportation mechanism engineered to supply components or materials into an assembly process using controlled vibratory forces, gravity, and guiding systems to ensure accurate positioning and alignment. The system incorporates accumulation tracks of varying widths, lengths, and depths, carefully chosen to suit the specific requirements of the application, material, or component.
The principal function of vibratory feeders is the movement, transfer, and conveyance of bulk materials utilizing various forms of vibrations that secure proper alignment for seamless integration into a production sequence. They are exceptionally effective for enhancing assembly operations and gently segregating bulk materials. The guided movement created by a vibratory feeder depends on horizontal and vertical accelerations, delivering the precise force needed for accurate material positioning.
The accumulation track of a vibratory feeder, whether it employs a linear or gravity-based approach, contributes to reducing vibrations and assists in guiding the material flow. Vibrations, rotation, and the necessary force for optimal operation are supplied by drive units, which may include piezoelectric, electromagnetic, or pneumatic motors.
The construction of a vibratory feeder begins with a transportation trough or platform, where materials are moved through controlled linear vibrations. These vibrations induce motions like jumping, hopping, and tossing of the materials. Depending on design features such as frequency, amplitude, and trough or platform slope angle, material travel speeds can vary from a few feet per minute to over 100 feet (approximately 30 meters) per minute.
Vibratory feeders regulate material flow akin to the control exerted by orifices or valves over fluid flow. They can be modified to deliver bulk materials at a consistent rate. Typically, a vibratory feeder comprises soft springs that manage vibrations and capacities, allowing it to handle bulk materials ranging from a few pounds per hour to several tons per hour.
A notable benefit of vibratory feeders is their capability to prevent bridging, an issue that can decelerate processes and obstruct effective material flow. The free-flow design within the throat of the vibratory feeder minimizes friction-induced bridging. The forces that facilitate smooth and even material flow are categorized into direct and indirect forces. Direct force applies energy straight to the feeder's deck, while indirect force utilizes resonant or natural frequencies to accomplish the desired material motion.
Contemporary designs of vibratory feeders often incorporate enclosed, box-shaped structures with flanged inlets and outlets, enhancing their ability to contain dust and stave off water intrusion. This design evolution assists in reducing spillage and simplifying installation procedures. Additionally, some enclosed designs combine a vibrating bin bottom activator with the vibratory feeder for enhanced material flow control and effectiveness.
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.
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 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 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.
| 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.
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.
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:
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.
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.
Vibratory feeders and conveyors typically operate at frequencies ranging from 200 to 3600 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.
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.
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:
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 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.
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 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.
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, 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 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.
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.
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, 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.
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.
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 / 4800
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:
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.
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