Improving Continuous Loss-in-weight Feeding Accuracy by a Novel Hopper Design

Powder feeding is a vital unit operation in the continuous manufacturing of pharmaceutical products. Loss-in-weight twin-screw feeders are commonly used in continuous manufacturing lines. The feeding performance, i.e., the accuracy and consistency of feeding, influences the content uniformity of the final drug product. In this study, a redesigned hopper for K-Tron KT20 twin-screw feeder was designed, implemented, and investigated to improve feeding performance. The basic idea was to design the hopper in such a way that the stresses on top of the screw entrance are independent of the fill level.

Our study compared the novel system to that of the original cylindrical hopper. The effect of the redesigned hopper on the start-up, the process’ sensitivity to refill level, and the refill portion size were studied. A free-flowing, barely compressible powder and a compressible blend were used in this study to evaluate the feeding performance and the refill effects.

When using compressible powders, the results showed a larger process window for refilling in the redesigned hopper and a lower refill-level sensitivity compared to the original hopper.

The homogenization of stresses in the redesigned hopper allowed operating at lower refill levels, and variability, especially due to refilling, was reduced. This study demonstrates novel design approaches for successfully implementing hard-to-feed materials in continuous manufacturing.