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A volumetric screw feeder is a type of bulk powder feeder for metering powder products. Different designs are suitable for specific processes, and here are some common types:
Single-screw feeder
A single-screw volumetric feeder has a hopper that feeds material into a rotating auger/screw inside a casing. The auger then conveys the material to a discharge opening, where a constant volume is released per unit of time. Material flow is directly related to the screw's rotational speed, which can be adjusted to change the feed rate. Single-screw feeders work well for granular materials that can flow freely. They are also one of the most affordable options.
Rotary paddle feeder
A rotary paddle feeder uses the paddles mounted on a horizontal shaft to meter the bulk material. The paddles are enclosed in a rectangular feeder body. As the shaft rotates, the paddles sweep across the bulk material, which is pushed toward the discharge opening. The feed rate can be changed by altering the rotational speed of the shaft. Rotary feeders work for bulk materials that are more cohesive and can not be easily fed with screw feeders.
Double screw feeder
Double screw feeders have two parallel screws. Cohesive materials can be accommodated with this design, as it prevents material jacketing in the hopper. This type of feeder works better in high-temperature and high-pressure environments when needing to feed bulk materials. Increasing feed rate and changing feed direction is also more efficient.
Liquid volumetric feeder
Liquids are also fed volumetrically using the combination of a pump and flow meter. A pump with a known displacement is used to transfer the liquid to the feeder section, which may include a flow meter or measuring cylinder for volume confirmation. The system is usually auto-controlled based on data from the flow meter.
Loss-in-weight feeder
A loss-in-weight feeder differs from other feeders in that it meters material based on weight loss over time instead of volumetric flow. The material is pre-weighed in a hopper, and material falling from the hopper is weighed using load cells. Since it relies on weight instead of volume, this design is more precise. However, it also has a complex design and higher cost compared to volumetric feeders.
Capacity:
Generally, the capacity of volumetric screw feeders can range from small feeder screws that handle a few grams per minute to larger systems that can handle tons per day; the setting is usually dependent on the speed of the auger and the material being dispensed.
Feed Rate:
With volumetric feeding, the feed rate is usually based on the speed of the rotating screw. It can usually range from a few revolutions per minute (RPM) to several hundred RPMs, depending on the size of the screw, the material's properties, and the desired feeding rate.
hopper size
Hopper size is usually measured in cubic feet or liters, and it can range from small hoppers with a capacity of a few liters to large hoppers with a capacity of several cubic feet or meters.
Feed Accuracy:
When it comes to presenting materials accurately, volumetric screw feeders can achieve an accuracy level of ±5% to ±10% of the target feeding rate. This is generally dependent on factors such as the design of the dispenser, calibration, and installation.
Power Source
Generally, screw feeders are driven by electric motors. It can range from small motors with a capacity of a few watts to large industrial motors with several kilowatts capacity.
Materials of Construction:
Volumetric screw feeders are commonly made with stainless steel, carbon steel, or high-density polyethylene (HDPE). This will depend largely on the application and material being dispensed.
Mounting Options:
Volumetric screw feeders are usually mounted on brackets, flanged connections, or quick-release clamps, allowing easy installation and removal for maintenance purposes.
It goes without saying that proper maintenance of screw feeder hoppers is very important to ensure they perform their best, accurate, and smooth feeding operations. Hence, here are some key maintenance tips for volumetric screw feeders:
Regular Cleaning:
Users should ensure they clean the feeder regularly to get rid of any material buildup or residue. This is likely to ensure accurate feed rates and prevent contamination of materials being dispensed.
Lubrication:
Depending on the design of the screw feeder, it may have a few movable parts or components. Hence, it is advisable to lubricate them consistently so as to reduce wear and tear and ensure a smooth feeding operation. Lubrication can be done as per the manufacturer's guidelines.
Calibration:
Users should consider calibrating the volumetric screw feeder periodically so as to maintain its accuracy. This will involve adjusting the speed of the motor, screw feeder, and hopper discharge setting until the desired feeding rate is attained. Calibration may be necessary when there is a change in material characteristics or feeding requirements.
Inspection:
It is advisable to regularly inspect the screw feeder for signs of material accumulation, wear and tear, or damage to parts and components. Any irregularities should be addressed promptly to maintain the proper functioning of the feeder.
The volumetric screw feeder is a piece of equipment that is useful in many industries. It can work as a stand-alone device or as part of a bigger system. Here are some common uses of a screw feeder in different industries to know its importance.
Food Processing Industry
The volumetric screw feeder finds lots of uses in this industry because of its hygienic designs. It can handle greasy, sticky, and damp materials with ease. Many feeder hoppers have stainless steel as a main construction material. This makes them compatible with frequent cleaning and antiseptic processes. Therefore, feeders can handle dry and bulk-y food items like flour, cereals, sugar, rice, and snacks like candies and chocolates.
Chemistry and Petrochemicals
This screw feeder works well with powders and bulk solids like fumes and fillers. In chemical plants, it can evenly and accurately feed catalysts, additives, and gases into reactors and mixers. It can also feed solid fuels such as coal, biofuels, and natural fibers in power plants to boilers. Therefore, chemical plants can use it to handle solids, liquids, and powders.
Construction Industry
Use a volumetric screw feeder to handle solid building materials. It can feed items such as cement, plaster, lime, fly ash, sand, and gypsum into mixers or storage silos. The feeder is part of a brick-moulding machine that helps make concrete bricks at low costs. Screw feeders increase the accuracy and efficiency of mixing construction materials. As a result, it improves the quality of building projects in the end.
Plastic Recycling Industry
In this industry, it can feed plastic granules, flakes, and reprocessed materials into extruders and injection molds. A volumetric screw feeder becomes part of a sorting and shredding system that plays a role in upstream material handling. It also helps in precise and continuous feeding of plastic raw materials into processing machines.
Metals and Mining Industries
This apparatus can accurately feed additives, fluxes, and mineral powders in metallurgical furnaces and mining separation units. It can handle abrasive and corrosive materials. Therefore, skip feeders improve operational efficiency in mining and metallurgy processes.
Industries that deal with bulk material should select the right screw feeder for their application to avoid issues with supply consistency, budget, and feeder floor space. Here are some of the key parameters to consider when choosing a volumetric screw feeder:
Product flow rate and volume
Consider the quantity of material to be supplied per unit time. This includes knowing the material's bulk density and whether it will change when it's stored. The feeder's capacity should be high enough to supply the required quantity without interruption.
Feeder design
Apart from the standard screw conveyor, it is important to consider other designs like variable pitch, shaggy, or segmented feeders. Select a design that provides the required flow rate while avoiding excessive degradation of the material to be conveyed.
Compatible drive mechanisms
The volumetric feeder drive mechanism determines how accurately it will supply material. Some feeder drives are better suited to certain materials than others. While a belt drive can be used to convey many types of material, a DC motor works well with cohesive powder. A stepper motor suits precision feeding of free-flowing granules. B considering the material's properties and choosing a drive that suits the application will help ensure accurate feeding.
Accessibility for maintenance
The volumetric screw feeder should provide access for maintenance and cleaning. Maintainability will improve the overall productivity of the industrial process. It will also help prevent the screw conveyor feeder from becoming a source of cross-contamination between different materials.
Integration with other systems
A feeder that can be integrated into the material handling process will help achieve a smooth operation. Consider how the screw feeder can be integrated with sensors, PLCs and other automated systems. For instance, PLCs can be used to control the motor feeder's speed based on the quantity of material required in a specific production line.
Economical options
The required screw feeder type can be found within the budget by analyzing the total cost of ownership. This includes feeder construction, installation and operation costs. Comparing the upfront purchase and long-term operating costs of different models helps choose the most economical option.
Q1: How is the volumetric screw feeder different from other types of feeders?
A1: The volumetric screw feeder is different from gravimetric feeders in that it does not depend on the weight of the material being conveyed. A volumetric feeder conveys a specific volume of material by adjusting the feeder's rate and material flow configuration.
Q2: What are the limitations of a volumetric screw feeder?
A2: While volumetric feeders are useful in many applications, they may not be suitable for all situations. One of the limitations is that they are affected by the material's bulk density, flow characteristics, and friction coefficients. Also, in cases where high precision is required, a gravimetric feeder may be more appropriate.
Q3: Can a volumetric screw feeder be used for all types of materials?
A3: Volumetric screw feeders are more applicable for materials with consistent flow characteristics. Nonetheless, they can also be used for powders with different densities and granular materials with some modifications.
Q4: How accurate are volumetric screw feeders?
A4: The typical accuracy of volumetric screw feeders is +/- 5% to 10% of the setting. However, this may depend on factors like the operator's skill and the feeder's calibration. For improved accuracy, it's better to use feeders with automatic flow control and feedback systems.
