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Pharmaceutical Manufacturing Handbook: Production and

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Powder flow rate<br />

FIGURE 6<br />

No flow below 50 μm<br />

(a) Core flow<br />

(b) Massflow<br />

POWDER CHARACTERISTICS 907<br />

Powder fl ow patterns in hoppers.<br />

Particle size<br />

No flow above 1200 μm<br />

FIGURE 7 Effect of particle size on rate of powder fl ow through orifi ce.<br />

the rate decreases due to mechanical blocking or obstruction of the orifi ce. Flow<br />

will stop completely when the orifi ce – particle ratio falls below 6 <strong>and</strong> if the size is<br />

above 1200 μ m.<br />

There are several different methods available for determining the fl ow properties<br />

of powders. Shear cell methods provide an assessment of powder fl ow properties as<br />

a function of consolidation load <strong>and</strong> time. There are a number of types of shear cells<br />

available, the most common being the Jenike shear cell [21] .

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