Gravimetric Screw Feeders
Precision and quality combined
AT A GLANCE..
Self-calibrating system – The weighing controller constantly adjusts the discharge speed to minimise overfeeding and underfeeding, reducing material waste and associated costs. This is particularly beneficial in industries where raw materials are expensive.
Precise and consistent feed rate – Gravimetric screw feeders provide precise control over the feed rate by continuously weighing the material and adjusting the screw speed accordingly to accuracies of 1% or better.
Easy-clean model available – Our easy-clean screw feeder range is designed to minimise downtime to mere minutes while also improving hygiene standards. This innovative feature allows for tool-less, rapid removal of components, ensuring easy maintenance and cleaning procedures.
Longevity and reliability – Manufactured from corrosion-resistant materials like stainless steel 316 which is not only hygienic but also durable, resisting wear and tear from both the materials being processed and cleaning agents.
Flexible in their application – These feeders can be used in both continuous and batch processes, popular across different manufacturing setups.
Sanitary versions available – Can be designed with a crevice-free design with a (0.2Ra) polish for sanitary material with a (0.2Ra) polish for sanitary material handling, ensures that all surfaces are easy to clean, reduces the risk of contamination.
Models – True-flow screw feeder (efficient & cost-effective), QR Tec (easy-clean), Pharmaceutical (Pharma Grade), Micro Feeder (Low Dosing applications)
GRAVIMETRIC FEEDING PROCESS
Gravimetric feeders, often called ‘loss in weight’ feeders, have the same key parts as a volumetric feeder, including the hopper, also known as the conditioning section, auger screw and agitator. If the material is free-flowing, the metering feeder can be designed without the agitator.
Gravimetric feeders deliver material at a weight-based rate using an advanced load cell and digital controller combination. Whether in continuous or intermitted operation, loss in weight feeders achieves a constant weight per unit of time at high accuracies of ± 1 to 2%. Gravimetric feeders are particularly suitable for materials that fluctuate in density. As the material is released, the system weight decreases, and the weighing controller constantly adjusts the feeder’s discharge rate speed, correcting any errors, regardless of material characteristics.
Our feeders are constructed from materials that meet all EC and FDA food contact regulations for food and pharmaceutical applications. They can be manufactured with a standard finish or crack and crevice-free with a high polish (0.2Ra) suitable for sanitary material handling.
If you are looking for a user-friendly, simple design, our True Flow Screw Feeder is designed with a focus on functionality, offering a no-frills solution that gets the job done efficiently. With its bolted, low-maintenance design, it provides reliable performance without unnecessary extras. This straightforward approach ensures ease of operation and minimal upkeep, making it an ideal choice for businesses that prioritise practicality and cost-effectiveness over unnecessary features.
However, for applications that demand precision, reliability, and sanitary material handling, our QR TEC screw feeder would be better suited. Featuring quick-release handwheels, it allows for tool-free dismantling and enables the entire machine to be stripped down in under three minutes. After disassembly, all components can be conveniently cleaned in a dishwasher or processed in an autoclave for thorough sterilisation. With a commitment to innovation, we continuously adapt our products to stay at the cutting edge of the industry, ensuring we meet the ever-evolving needs of our clients.
GRAVIMETIC CONTROLS IN DETAIL
Gravimetric control is aimed at applications requiring a continuous, exact, and monitored product flow from the metering feeder. Also known as PID control (proportional integral derivative), Gravimetric controls use software algorithms to continuously sample the amount of weight lost or gained and then correct the feed rate of the Screw feeder to maintain a pre-programmed target flow.
Typically, the screw feeder will be mounted on load cells to measure the weight of the complete machine and its contents. This can be as simple as a platform scale or a dedicated weighing support frame for larger feeders. The selection of the correct weight system is essential. The weighing capacity must be sufficient to carry the weight of the screw feeder, a full complement of bulk solid and have some spare capacity for dynamic “shock” loads or overloads. Too greater a weighing capacity produces poor resolution, whilst too small a capacity risks damage to the weighing transducers. Resolution is particularly important at very low feed rates. Parking a grain tanker on a weighbridge and emptying it with a thimble is an extreme analogy. How long before the weighbridge can take a meaningful reading? Gravimetric controls share the same restrictions.
During continuous operation, the metering feeder will eventually run out of product and need refilling. During a refill cycle, gravimetric monitoring must be suspended, and the screw feeder goes into volumetric mode. The refilling process should be as fast as possible to minimise the period without monitored control. This is best achieved using a “surge hopper” to discharge its entire contents into the metering feeder hopper in one event. This surge hopper can then be refilled whilst the feeder is in normal “monitored” running. Where a surge hopper cannot be used, for example, in limited space, a fast-filling screw conveyor can be employed.
Unsure which metering feeder fits your business needs? Click here for the differences between Trantec’s gravimetric and volumetric feeders.
Even with the most advanced gravimetric controls, the design of the feeding machine should be optimised. The gravimetric controls work best, acting as a policeman, adjusting the feeder operation to correct for errors. An error must have occurred for the controller to apply a correction. Trantec’s approach is to design a metering screw feeder which doesn’t have the errors in the first place. Where this can’t be achieved due to the characteristics of the material being dosed, the continuous monitoring and control provided by a gravimetric system boosts the overall performance and maintains continual accuracy.
Trantec partners with process control specialists to offer a range of gravimetric modules that can match your process requirements. From cost-effective single-line display units to complete recipe and factory automation systems.
SUGGESTED PRODUCTS
Micro Screw Feeders
QR Tec Feeder Range
True-Flow Screw Feeder
