What Is Dwell Time?
Dwell time is the brief interval, measured in milliseconds, during which the punch head remains fully engaged under the compression roller, with no vertical movement. This period directly influences powder consolidation and tablet strength. Unlike turret RPM, tangential velocity (TV)—measured in mm/sec—provides a more accurate assessment of press speed relative to turret circumference, affecting dwell time inversely unless compensated by tooling design.
Impact of Turret and Tooling Design
Different tooling standards, such as TSM and European ISO types, define punch geometries including body diameter and head flat length. For example, D-type punches with larger diameters typically have longer head flats, increasing dwell time, while B-type punches are designed for higher throughput but shorter dwell times. Additionally, turret pitch circle diameter (PCD) influences dwell time; larger turrets allow slower RPMs for effective compression, whereas smaller turrets require higher speeds that can challenge powder flow and tablet uniformity.
Why Head Flat Design Matters
Modifying the punch head flat is an effective way to control dwell time without reducing press speed. A longer head flat provides extended compression duration, benefitting formulations sensitive to compression speed or those requiring plastic deformation for cohesion. Adjusting this parameter during scale-up aligns compression profiles across different machines and tooling types, improving process reproducibility and product quality.
Summary
Compaction dwell time is a critical process parameter influencing tablet robustness and consistency. Understanding how turret dynamics and punch head geometry affect dwell time enables manufacturers to minimize scale-up variability, optimize tooling design, and maintain product integrity across equipment platforms.
For optimal scale-up and tooling selection, consulting with tooling experts on head flat customization and turret compatibility is highly recommended to enhance compaction efficiency and tablet quality.
