How Much Flow Aid Does My Powder Need?

By Vinnie Hebert, Product Manager - Powder Flow Tester, Brookfield Engineering

Powder handling and processing in gravity feed systems have one basic requirement: Knowledge of your powder's flow properties. Too often, this simple requirement is lacking, thereby causing manufacturing downtime due to jamming of feeder systems, arching, and rat-holing. To solve or minimize these types of issues, flow aids are often used. However, a determination of how much (or how little) to use is the challenge. A tablet machine is one such example of a gravity feed discharge system.

This type of equipment will produce large volumes of tablets. Downtime for this piece of equipment is not an option. Flow aids can be used to ensure proper flow through the feeder system, but use of these flow aids needs to be characterized and tested to ensure the proper amount is used every time. To define how much flow aid should be mixed with a material, consider characterizing the product using a test method called "flow function" along with an annular shear cell. Through the use of this method, characterization of flow aid electiveness can be done quickly, easily and cost effectively. We will consider this example for this discussion.

Flow function is an easy to interpret metric that will quickly define powder flow in a gravity feed discharge system. The flow function characterizes a powder's flow behavior into one or more of "ve distinct regions: free flowing, easy flowing, cohesive, very cohesive and non-flowing. This method applies increasing amounts of consolidating pressure to the powder sample to simulate the self-weight of the powder in the bin as a function of fill level. It then measures the powder failure strength (resistance to flow) with the annular shear cell to produce the flow function graph.