Endpoint Accuracy in High-Shear Mixer Granulation: Methods and Insights
In tablet and capsule production, high-shear mixer (HSM) granulation remains the most widely used wet granulation technique. Although it consistently produces well-formed granules, identifying the exact endpoint of the process poses ongoing challenges. Manufacturers rely on various detection methods, each with its own advantages and limitations. This article reviews these methods and spotlights a leading approach.
Why the Endpoint Matters
More than 70% of global granulation processes use wet granulation, with HSM preferred for its control and efficiency. Determining the endpoint accurately is vital to achieving target granule attributes like strength, density, particle size uniformity, and flowability — all of which influence final tablet performance.
Even with technological progress, empirical observation remains common, leading to variable outcomes. Manual inspections are still prevalent but can lack consistency. Any reliable method must also consider factors such as mixer dimensions, rotational speed, production scale, and binder application technique.
HSM granulation involves three stages: dry mixing, binder application, and wet mixing. While wet mixing plays the dominant role in shaping the endpoint, binder addition significantly influences particle nucleation and densification. Accurate determination must account for both.
Monitoring impeller load via motor current is a widely used practice, but with HSM’s broad particle size distribution, precision in this step is critical.
Common Endpoint Detection Methods
Wet mixing time: Based on duration after binder addition; prone to variation from raw materials and operator handling.
Motor current monitoring: Tracks resistance during mixing; influenced by multiple factors.
Calculated torque: Derived from motor current; susceptible to AC motor inconsistencies.
Reaction torque sensing: Measures force on stationary motor base; accuracy affected by mixing fluctuations.
Torque rheometry: Offline method for granule rheology; no real-time capability.
Acoustic monitoring: Detects particle property shifts; effective but expensive.
NIR spectroscopy: Assesses moisture content; not always precise for endpoint.
Focused beam reflectance measurement: Measures particle size changes; accurate but costly.
Direct torque measurement: Provides real-time torque readings directly from the impeller shaft, minimizing error.
Key Components for Direct Torque Measurement
Integrated torque sensor on impeller shaft
Contactless transmission
Pre-calibrated device
HMI with live readings
Programmable endpoint thresholds
Takeaway
For consistent tablet quality, endpoint determination in HSM granulation must be both accurate and reproducible. Direct torque measurement stands out as the optimal approach, enabling real-time control and reducing variability in production.