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Gravimetric or Volumetric screw feeder?

Making the right choice

In the world of manufacturing, choosing the right type of screw feeder is critical to ensuring process efficiency, accuracy, and overall productivity. As energy costs rise and manufacturing expenses increase, staying competitive in regional and global markets has become increasingly challenging. Manufacturers are constantly seeking ways to improve their processes and enhance their competitiveness. Here’s a detailed comparison of the two most common types of screw feeders to help you understand the differences and make an informed decision. Screw feeders are particularly popular in the food, pharmaceutical, chemical, environmental, and plastic industries due to their ability to provide precise dosing of materials in various forms, including grains, granules, pellets, and powders. They play a critical role in the solids handling sector, maintaining process consistency, product quality, and operational efficiency. 

Both volumetric and gravimetric screw feeders use a combination of mechanical and electronic components to control and regulate the amount of material fed into a process or other equipment and are manufactured with one or two critical moving components, the stainless-steel auger screw and the (optional) agitator, this helps keep maintenance low. The agitator is required for use with materials prone to sticking, bridging, or ratholing, as it helps prevent blockages from forming, ensuring a consistent material flow. Agitation mechanisms range from simple steel bars on a rotating shaft to complex paddles and hammers designed for effective agitation and lump breaking. One of the most efficient designs employs the geometry of ribbon blenders, featuring opposite hands on the same shaft. These left- and right-handed scrolls move material from the feeder’s sides and ends to the centre, pushing it into the pockets between the auger screw and trough. This ensures a continuous even flow and material density, which are essential for an optimal metering screw feeder.

The main difference between Volumetric and Gravimetric screw feeders lies in their operation principles. Gravimetric feeders, also known as loss-in-weight feeders, dose materials based on weight over time and incorporate weighing cells for self-calibration. These feeders continuously measure the material’s weight and adjust the dosing speed to maintain accuracy, ensuring that fluctuations in material density do not affect the outcome. In contrast, volumetric screw feeders dispense materials based on volume over time, without the use of weighing cells. They require manual calibration when introducing a new material or batch to ensure the correct mass is dosed over a set period. Despite this, volumetric feeders are highly accurate, reliable, and can be easily modified to suit various applications.

Both screw feeder types also offer long-lasting, flexible, and reliable dosing solutions. Built robustly, they are available in mild steel, stainless steel 316, or 304, with various finishes such as bead blasted, polished, or mirror (0.2Ra) finish to meet customer requirements. Crevice-free and mirror finishes ensure a contamination-free process, which is ideal for handling food and pharmaceutical sanitary material. They can also be tailored to meet the specific requirements of various materials and processing environments. By assessing factors such as material flow characteristics, required dosing accuracy, budget constraints, and long-term operational goals, you can determine the most appropriate feeder for your application.

In conclusion, integrating a volumetric feeder into your processing lines is a practical choice for both free-flowing and poor-flowing materials. However, due to their superior precision, gravimetric feeders are the preferred option for handling problematic materials. When purchasing, the investment cost is a crucial factor when selecting a suitable screw feeder. While gravimetric feeders come with a higher initial cost, they offer a quicker return on investment (ROI) and are recommended for applications requiring high accuracy. On the other hand, volumetric screw feeders have a lower initial investment cost due to their more straightforward design and fewer features, making them a cost-effective and reliable solution for many processing needs. When choosing between these two types of feeders, it is essential to consider your specific application requirements and the configuration options available. Volumetric feeders provide an economical and dependable solution for many standard dosing applications. In contrast, gravimetric feeders offer enhanced control and precision, making them ideal for processes where material density varies or where exact dosing is critical.

Trantec’s engineers are ready to provide expert advice in selecting the most suitable dosing equipment for your application requirements. We offer a comprehensive testing and evaluation service to ensure our screw feeders meet your application requirements. Our packages are customisable and upgradeable, guaranteeing that our solutions can adapt as your business evolves. To discuss your requirements or to learn more about Trantec’s range of screw feeders and other dosing equipment, please get in touch with our sales team at or call us at 01282 777566. Our team is committed to helping you find the perfect solution for your material handling challenges.

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