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Tablets & Capsules July 2020 33 I N D U S T R Y a p p l i c a t i o n Gravimetric feeders support Eli Lilly's advancements in continuous direct-compression tableting weight of the feeder and its contents. The system immediately detects any changes in the feedrate—whether caused by a change in the material's bulk density or other factors—and automatically adjusts the feed screw speed to almost instantly restore the correct feedrate. Pharmaceutical applications, such as CDC tableting, require consistent and highly accurate feeding of ingre- dients that commonly have extremely poor flowability and require very low feedrates. The gravimetric feeder's closed-loop mode of operation makes it ideal for such applications. In addi- material per unit time, and gravimet- ric feeders—also called loss-in-weight (LIW) feeders—which discharge a specified weight of material per unit time. Volumetric feeders are simple and inexpensive and can be useful in non-critical applications, but they have no way of detecting or respond- ing to changes in the bulk density of the material they are handling. On a gravimetric feeder, the hop- per and feed screw are mounted on a scale or load cells. During oper- ation, as material discharges from the feed screw, the feeder's control system continuously monitors the Continuous direct compression (CDC) tableting offers several key technical and process advantages over traditional batch tableting pro- cesses. First and foremost, it allows the manufacturer to develop a drug product on the same equipment drivetrain that will be used for the product's final manufacture, elimi- nating process scale-up. CDC tablet- ing also allows for increased quality assurance and requires less produc- tion space, which lowers utility and labor costs. In continuous processing systems, active pharmaceutical ingredients (APIs) and excipients must be deliv- ered continuously at the proper pro- portions to ensure the quality and efficacy of the final drug product. As a result, feeding accuracy and consis- tent refill of the feeders are critical. A CDC line typically includes individ- ual feeders for the API and excipients feeding directly into a blender, with the blended formulation discharg- ing directly to the tablet press. Each feeder can be continuously refilled via an automated system to ensure consistent material flow during the continuous process. Gravimetric versus volumetric feeders In principle, process designers have a choice between volumetric feeders, which discharge a specified volume of Photo 1: The continuous direct compression suite including gravimetric feeders is mounted on a custom lift assembly to ease access, cleaning, and product changeover.