Optimization of Powders for Flowability

Greg Mehos, Ph.D., P.E

Course description

There are several metrics that formulators use to quantify the flowability of powder blends, including angle of repose, Carr and Hausner ratios, FFC, and flow energies. They all have one thing in common: none will predict whether or not a powder will flow in a hopper. Frequently, powders that are deemed easy flowing exhibit flow problems such as bridging, ratholing, or erratic discharge.

Many laboratories are equipped with shear cell testers, which measure the fundamental flow properties of powders, i.e., cohesive strength, internal friction, compressibility, and wall friction. Together with permeability test results, a formulator can determine if a hopper has an outlet large enough to ensure unobstructed flow and allow the desired discharge rate and the hopper angle required to prevent a rathole from developing. Alternatively, an investigator can use the test results to design or choose a bin or hopper that will provide reliable flow.

This accredited course will cover fundamental powder flow properties, testers that measure them, and what inputs should be used to obtain the most valuable test results. Anyone who owns a shear cell and permeability tester should never have a powder flow problem.

Upon completion of this course, you will be able to:

• Identify the fundamental flow properties of powders
• Select inputs on shear cell testers that will provide the most useful results
• Utilize the test results to determine if a bin or hopper is appropriate for your formulation or if it will likely arch or develop a stable
  rathole
• Determine if the size of your hopper outlet will allow the required solids discharge rate