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cones is much less steep. One might think that the more uniform the velocity, the better the segregation preven- tion. However, as shown in Figure 13, the 15-degree hop- per creates more variation in API concentration than the 20-degree hopper. This suggests that, for a given material, there exists a mass-flow design with just the right velocity profile to minimize segregation as the blend discharges. Conical hoppers are not the only option for creating mass flow to solve a segregation problem. Cone-in-cone devices and plane-flow Diamondback hoppers can also achieve the right velocity profile for many materials (Figure 15). In fact, the cone-in-cone device is the most flexible mass-flow device because its inner-cone geome- try relative to its outer cone can create many more veloc- ity profiles to resolve segregation issues. Summary To resolve a segregation problem, it is critical to char- acterize the material, assess its flow properties, and mea- sure its segregation tendencies relative to the expected stimuli in the process. This segregation measurement should account for, in detail, all the ingredients in the blend and reveal the segregation pattern, magnitude, and root cause(s). Ranking the types of segregation active in the material and feed system is helpful. This requires measuring key particle- or ingredient-scale properties. Any resolution of a segregation problem must also include a review of the entire process following the blending step. The review should account for the blend's flow properties and segregation tendencies to identify regions where ingredients may concentrate. The assess- ment should also account for how the blender discharges material, which is often ignored. In addition, any design proposed to decrease segregation should either 1) attack the cause of segregation and reduce the segregation dur- ing filling and operation or 2) include velocity profiles compatible with the type and magnitude of segregation present in the blend. Mass flow is often important, but may not be the optimal method to prevent segregation. Rather, segregation prevention from a process point of view must center on controlling the velocity profile in the handling equipment. This will often require custom designs. Segregation prevention may also require modify- ing one or more process steps after blending. T&C Reference 1. SpecTester from Material Flow Solutions, Gainesville, FL. Kerry Johanson, PhD, is president of Material Flow Solutions, 5921 North County Road 225, Gainesville, FL 32609. Tel. 352 379 8879. Website: www.matflowsol.com. 26 May 2017 Tablets & Capsules Figure 15 Mass flow hoppers that can reduce segregation effects Cone-in-cone Plane flow (Diamondback) Conical hopper