Smoother materials handling today relies on an ever evolving suite of vibratory feeders and conveying equipment. Rob Yandrick highlights the customised and advanced designs available to extractive operators that offer precise handling, uninterrupted flow and improved safety.
The need to move, convey and feed materials exists in nearly every processing facility handling dry materials. Whether a sophisticated processing plant or a packaging line, raw and unfinished goods need to move from one area to the next.
Vibratory feeding and conveying equipment has been used in the processing and packaging industries for several decades as a means to efficiently handle a broad range of dry bulk solid materials. Vibratory solutions are available to handle nearly any product from granular powders such as titanium dioxide or saw dust to bulky, leafy and tacky materials such as tobacco or gummy confectionery.
In addition, vibratory feeder and conveyor models are available to handle high temperature materials and operate in ambient temperatures up to 150oC as well as hazardous environments.
There are four areas where vibratory equipment has advanced appreciably:
- Meter material at a controlled rate. In a processing plant, vibratory feeders are commonly used to meter material from bulk supply hoppers, supersacks or totes into downstream processing equipment. The feeder is the control point to meter material at a controllable, easily adjusted rate.
- Screening for fines and oversize material removal. Vibratory equipment designs are well suited and readily adapted for many types of screening applications. Scalping or oversized product removal and de-dusting or fines removal are common applications.
- Automation. Solid state controls allow vibratory feeders or conveyors to be readily integrated into automated processing or packaging applications. Remote on/off, adjustment of feed rates with 4-20mA DC signal or 0-10 VDC and Ethernet are all readily available.
- Cleanliness and sanitation. A primary benefit of vibratory feeding and conveying is the clean nature of the conveyor or feeder tray. With no screws or other complex geometries in the conveyor or feeder tray, they can be quickly wiped down or washed out for product changeover or sanitation procedures. If screens or tray covers are incorporated in the conveyor or feeder, quick release (toolless) clamps can be incorporated for easy removal.
DEFINING EQUIPMENT TERMS
In broadest terms, to convey is “to take or carry from one place to another or to transport”. Conveyors can be used to move raw materials from a rail car to a storage tank, and then again to move that material from the storage tank into the plant. In other process applications, material must be conveyed repeatedly throughout the plant. In many instances, that material must first be fed onto the conveyor.
Feeding means “to supply or maintain a flow of material”. Feeders are placed throughout a plant to maintain the flow of product coming into the next stage of the process. Feeders often control the flow of the process and are often required to turn off and on frequently, based on demand.
Vibrating means “to move back and forth rapidly”. On a vibratory feeder, material is thrown up and forward so that it drops to the surface at a point further down the tray. This is referred to as the feeder’s amplitude. The number of times per minute this cycle repeats is the frequency. A third variable is the angle of deflection, meaning how high the product is thrown, as compared to its horizontal movement.
Each vibratory feeder or conveyor is designed with a different amplitude, frequency and angle of deflection to move different materials at specific rates. The design is based on many factors, including the material being processed, the flow rate of the process, nature of the environment, need to start and stop (cycle) the process, cost to operate the equipment and likelihood of repairs.
Feeding and conveying equipment is typically selected with the help of the equipment manufacturer. Sales representatives, technical representatives or application specialists are available to ensure the best conveyor or feeder designs are selected for specific applications.
There are various feeder and conveyor designs to be considered:
- Standard design vibratory feeders are ideal for denser materials greater than 100 mesh (150µm) in size and heavier than 160kg/m3 and as high as 4000kg/m3 or applications where significant material load may be applied to the feeder. Standard models provide lower amplitude and high frequency operating characteristics.
- High speed feeders are an excellent choice for applications where fast travel speeds are necessary. These units are ideally suited for packaging applications and offer high stroke and high frequency operating characteristics. • High stroke/low frequency feeders and conveyors are the typical choice for handling loose or powdery materials and are a good choice for screening applications.
High stroke mechanical conveyors are well suited for high capacity applications where longer lengths or intermediate discharge gates are required.
HIGH DEFLECTION FEATURES
Vibratory feeders and conveyors have undergone numerous design changes and upgrades that enhance their role in processing applications. The latest equipment offers increased energy savings, more precise control over material flow, easier maintenance and a greater variety of options.
Electromagnetic feeders have long been a popular and hassle-free way to meter and convey bulk materials and powders. However, they have never been the most effective way to feed fine powders, or leafy, tacky and fluffy materials. High deflection electromagnetic feeders solve this problem.
These newer, high deflection (HD) feeders feature faster travel speeds and the ability to handle the most difficult materials.
Materials from -50 mesh (-300µm) to -400 mesh (-37µm) are used to fluidise and flush on traditional electromagnetic feeders. After years of research, HD feeders now offer high deflection of up to 4.8mm and lower frequency (30 cycles per minute) to handle finer product such as long-stranded chopped fibreglass, talc or flour. Even tacky materials such as sticky lollies respond well to the feed characteristics of the HD feeders. The HD feeders have throughputs ranging from 4.25m3 per hour to 20m3 per hour for greater flexibility in packaging and other difficult applications.
Vibratory feeders feature a drive system with AC-powered drive unit(s), mounted either from above or below to produce a consistent vibratory force. The latest feeder and conveyor equipment features electromagnetic drive designs that utilise full-wave AC rather than half-wave. This allows the same vibratory force to be generated with less power consumption.
The full-wave AC electromagnetic drive systems typically consume up to 65 per cent less energy than their half-wave AC counterparts. These units have no sliding or rotating parts to wear out and require very little power to operate.
Conversely, half-wave operated electromagnetic drives produce the same vibratory action as AC units but are not as energy-efficient. Half-wave drives use a less efficient “attract and release” system where half of the sine wave is eliminated with a rectifier and turned into heat, and the half-wave-pulsed power delivery is much less linear. Alternatively, an AC-operated drive using the full sine wave delivers power to the unit proportionately to the voltage increase.
Still popular are mechanical drives used in a variety of feeding and conveying applications. Mechanical drives utilise traditional motors with eccentric weights or motor vibrators to create the vibratory force required to excite the feeder or conveyor.
Mechanical feeders and conveyors typically operate at a low frequency and high tray displacement. While mechanical feeders do not offer the same level of feed rate control as an electromagnetic design, they are effective for handling high capacities. Mechanical conveyors can be a cost-effective means to move material distances over three metres.
LIMITLESS TRAY DESIGNS
The shape, length and width of feeder trays are almost limitless. Feeder trays can be ordered with custom designs to satisfy the process application and material being conveyed, including flat, curved, vee-channel and tubular designs. Intermediate discharge slide gates can be incorporated in some designs to allow for multiple discharge points along the tray length.
Trays are typically fabricated from mild steel or stainless steel. The latter is often used in food and pharmaceutical applications, while the former is for general purpose processing. Trays can be lined with abrasion-resistant steel, stainless, urethane, rubber, Teflon and other coatings. Polishing the tray to various specified levels is another option to help keep material from adhering to the tray.
Generally, trays are easy to access and clean, making it simpler to avoid cross-contamination of materials and decrease production downtime. Many trays have quick release clamps that allow the tray covers or screens to be removed without tools.
There are various equipment options on the market that intelligently track the operation of feeders and conveyors and verify the equipment is responding appropriately. They prevent equipment damage in upset situations. An over-deflection monitor is one such piece of equipment.
The monitor detects changes in tray deflection, due to material sticking on the tray surface. As material accumulates on the tray surface, it adds weight to the tray, affecting performance and possibly damaging the feeder. The monitor alerts, warns or shuts down the feeder so the tray can be cleaned to improve performance and reduce costly downtime.
Vibration sensors are also available that generate a 4-20mA DC signal based upon the vibration level the feeder is operating. As the vibration changes, the analog signal will also change and send this information to the customer’s PLC.
Electromagnetic feeder controls are available that operate in a “closed loop” mode and make automatic feeder adjustment to maintain tray vibration under varying conditions. For example, if material builds up on the feeder tray surface, the tray deflection will typically be affected. If a closed loop control is utilised, the vibration level is constantly being monitored and the control will automatically adjust the power to the feeder so the tray vibration level does not change.
Springs are an integral part of the feeding system design because they transfer 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 to suit the application.
Fibreglass and carbon fibre springs are the most typical configurations for light and medium duty applications. Small and compact electromagnetic feeders, light to medium duty conveyors and most high precision vibratory equipment use multiple fibreglass or carbon fibre springs as the means to tune the unit and create the appropriate vibration.
Steel leaf springs are commonly used on heavy-duty feeders. These springs provide the higher spring rates required for these larger and heavier designs.
Dense rubber springs are often used on heavy-duty mechanical feeders and conveyors to provide stability and motion control between the drive and tray. However, rubber springs are limited to environments below 50°C.
SOLID STATE CONTROL UNITS
Solid state control units available today operate feeders with impressive precision and can easily adjust the flow of material with a manually adjusted potentiometer or automatically through a customer’s analog signal from a PLC.
Feed rates can vary from zero to 100 per cent thanks to control potentiometers or digital keypads that precisely lock in control settings. A “smart” transducer mounted on the tray and wired to the control gives constant feedback of the tray’s amplitude.
The constant feed rate system allows plant operators to set the feed rate and the control system automatically compensates for the changes in head load and any voltage fluctuations during the production run.
Purchasing and installing a vibratory feeder poses fewer risks today because of increased technical assistance before and after the sale. Material samples of various density and configuration 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 undersized or oversized piece of equipment for the job at hand.
On-site diagnostic testing or virtual testing via webinars can prevent significant downtime for vibratory feeders and conveyors.
Advancements in technology make vibratory feeding and conveying solutions more applicable than ever. Vibratory solutions have long been a preferred means to meter and convey materials. The sanitary construction, ease of cleaning, low maintenance and latest design features make them ideal for many applications in processing plants where greater product purity, energy costs savings, decreased equipment maintenance expenses and streamlined manufacturing operations are desired.
Rob Yandrick is Eriez Magnetics’ vibratory/screening product manager.