What Type of Mass Flow Will Prevent or Limit Segregation of Powders – Calculation of Custom Design Curves for a Particular Powder in Preselected Process Geometry.
By Kerry Johanson
Material Flow Solutions Inc.
Controlling segregation of direct compression formulations in the surge hopper above the feed frame is critical to robust production of good tablets. Likewise, filling bottles with a known quantity and quality of pharmaceutical mixture is critical to assure that each dose meets product specifications prior to reconstitution and use. In a similar fashion, each unit dose of consumer product such as detergent or a food product must have the right ingredients and amount in each unit dose. All of these production goals have three things in common. They use powders that segregate with a distinctive pattern and magnitude. The feed systems consist of devices that have inherent velocity profiles that can induce segregation or enhance segregation patterns causing quality issues during filling. The mode of filling packing machines, combined with the mode of emptying them, often governs the expected segregation present in the packing line and as material leaves the system.
Funnel flow designs are usually poor choices to prevent segregation. Current literature claims that segregation is solved by simply using a mass flow device in the packing lines so as to prevent segregation after the mixing step. However, simply using a mass flow design may not be sufficient to eliminate the segregation of active ingredient in drug mixtures during a filling and discharge cycle of tableting operation. This is far too simplistic. It is completely possible to create a perfectly mixed product only to place it into a tableting, capsuling, bottle filling, or unit dose packaging device, and find that segregation between doses is a serious issue. Segregation is solved by matching the segregation pattern, the filling profile in the equipment, and the velocity profile during flow to generate a product that does not segregate in a particular packing system.
This paper presents a general approach to solving segregation issues. The method measures a segregation pattern and magnitude with a segregation test device called the SPECTester® and combines that with flow properties of the mixture and the specific geometry of key packing systems to generate velocity profiles in the process – then uses those velocity profiles and segregation patterns to determine the quality of material leaving the system as a function of discharge. The segregation tester measures the segregation pattern. The flow properties allow the calculation of velocity profiles in the process equipment using radial stress theory. The filling pattern (side fill, center fill, or distributed fill) determines the placement of key ingredients in the feed system. Knowing the characteristic segregation pattern for a particular material, the velocity in the feed system, and the initial placement of key ingredients in the packing system, one can compute the expected segregation leaving that system. In fact, the goal of this work is to relate key parameters such as hopper slope, fill position, and initial feed distribution pattern to the expected segregation and then generate general design curves similar to the mass flow design curves developed by Jerry Johanson and Andrew Jenike. A surrogate material was chosen as the drug mixture using ibuprofen as the API. Three feed geometries were considered (a funnel flow cone, a cone-in-cone, and a series of mass flow cones). Three initial fill positions were considered (a side fill, a central fill and a distributed fill). The expected segregation profiles leaving these geometries was computed and design curves similar to traditional mass flow / funnel flow curves were generated for these conditions – outlining good and bad segregation operation zones unique to this material.
Dr. Kerry Johanson began his career in powder flow and material handling as a summer lab technician with Jenike & Johanson in Billerica, Massachusetts during his high school and undergraduate years. After receiving his BS in 1985, he spent 14 years with JR Johanson, Inc. in San Luis Obispo California, finally serving as their Chief Technical Officer. He received his Ph.D. in chemical engineering from Brigham Young University in 1994 and in 2000, he branched out and moved to Florida, where he divides his time researching at the University of Florida Particle Engineering Research Center and serving as the Chief Operations Officer for Material Flow Solutions, Inc., the consulting firm he founded in 2001. He has authored 40+ technical papers which have been published in numerous technical journals internationally. He has developed a course for teaching powder flow and technology to graduate students and mentored five recent doctoral graduates at the University of Florida. Dr. Johanson has presented numerous industry seminars on the topic of powder flow in industrial applications. Married for 38 years, he is the father of six children, and a grandfather to 15. He holds the rank of Eagle Scout with the Boy Scouts of America, and continues to serve as a Scout leader in his community. Dr. Johanson holds PE licenses in both Florida and Utah and is an active member of AAPS, AIChE, ASME, ASTM, and IChemE.