(189i) Agitator Impact on the Net Weight Signal of a Loss-in-Weight Feeder Operating at Low Mass Flow Rates

O'Mahony, M., Vertex Pharmaceuticals
Dale, S., Vertex Pharmaceuticals
Dinarello, E., Vertex Pharmaceuticals
Connelly, G., Vertex Pharmaceuticals
Kinney, I., Vertex Pharmaceuticals
Gloria, H., Vertex Pharmaceuticals
Continuous manufacturing is being adopted at an accelerated rate as a platform to produce new drug products and has been described as one of the most important tools modernizing the pharmaceutical industry.1 Continuous loss-in-weight screw feeders are the key dispensing units for enabling the mass flow driven requirements of continuous drug product manufacture. These feeders most often operate in gravimetric mode where feedback from the net weight signal is used to update and control the screw speed. Continuous feeding performance evaluation methodologies 2,3 as well as the impact of raw material properties 4 on continuous feeding performance have been well identified and studied in the literature. It is recognized that the interaction of the feeder agitator and feeder screws has an impact on the mass flow feed rate during continuous feeding.3 Understanding the impact of the agitator on the net weight signal (and hence screw speed control) is necessary for optimizing feeding performance.

In this work, the impact of agitator movement on the net weight signal during loss-in-weight feeding is studied. Specifically, the position of the agitator is monitored in real time to observe the impact of agitator motion on the net weight loss signal at low mass flow rates. It is identified that the agitator has a significant impact on the net weight signal. The frequency of the agitator speed co-varies with the frequency in the change of the net weight loss signal. The operating net weight of the feeder is a key factor determining the magnitude of variation in the changing net weight signal. This study provides direction for improving the net weight mass loss signal and reducing potential impact to mass flow feed rate variation at low mass flow rates by optimizing the operating net weight range of the feeder. Directions are also provided on modified agitator configurations for the raw material being fed and material mass flow rate requirements.


1 Gottlieb, S. & Woodcock, J. Statement from FDA Commissioner Scott Gottlieb, M.D., and Janet Woodcock, M.D., director of the Center for Drug Evaluation and Research on FDA’s modern approach to advanced pharmaceutical manufacturing, https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm632043.htm (2019).

2 Engisch, W. E. & Muzzio, F. J. Feedrate deviations caused by hopper refill of loss-in-weight feeders. Powder Technology 283, 389-400, doi:https://doi.org/10.1016/j.powtec.2015.06.001 (2015).

3 Engisch, W. E. & Muzzio, F. J. Method for characterization of loss-in-weight feeder equipment. Powder Technology 228, 395-403, doi:https://doi.org/10.1016/j.powtec.2012.05.058 (2012).

4 Wang, Y., Li, T., Muzzio, F. J. & Glasser, B. J. Predicting feeder performance based on material flow properties. Powder Technology 308, 135-148, doi:https://doi.org/10.1016/j.powtec.2016.12.010 (2017).